[silc.git] / doc / draft-riikonen-silc-spec-01.nroff

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Network Working Group                                      P. Riikonen
Internet-Draft
draft-riikonen-silc-spec-01.txt                         6 October 2000
Expires: 6 Jun 2001

.in 3

.ce 3
Secure Internet Live Conferencing (SILC),
Protocol Specification
<draft-riikonen-silc-spec-01.txt>

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Status of this Memo

This document is an Internet-Draft and is in full conformance with   
all provisions of Section 10 of RFC 2026.  Internet-Drafts are   
working documents of the Internet Engineering Task Force (IETF), its   
areas, and its working groups.  Note that other groups may also   
distribute working documents as Internet-Drafts.   

Internet-Drafts are draft documents valid for a maximum of six months   
and may be updated, replaced, or obsoleted by other documents at any   
time.  It is inappropriate to use Internet-Drafts as reference   
material or to cite them other than as "work in progress."   

The list of current Internet-Drafts can be accessed at   
http://www.ietf.org/ietf/1id-abstracts.txt   

The list of Internet-Draft Shadow Directories can be accessed at   
http://www.ietf.org/shadow.html   

The distribution of this memo is unlimited.  


.ti 0
Abstract

This memo describes a Secure Internet Live Conferencing (SILC)
protocol which provides secure conferencing services over insecure
network channel.  SILC is IRC [IRC] like protocol, however, it is 
not equivalent to IRC and does not support IRC.  Strong cryptographic
methods are used to protect SILC packets inside SILC network.  Two
other Internet Drafts relates very closely to this memo;  SILC Packet
Protocol [SILC2] and SILC Key Exchange and Authentication Protocols
[SILC3].








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Table of Contents

.nf
1 Introduction ..................................................  3
2 SILC Concepts .................................................  3
  2.1 SILC Network Topology .....................................  4
  2.2 Communication Inside a Cell ...............................  5
  2.3 Communication in the Network ..............................  6
  2.4 Channel Communication .....................................  7
  2.5 Router Connections ........................................  7
3 SILC Specification ............................................  8
  3.1 Client ....................................................  8
      3.1.1 Client ID ...........................................  9
  3.2 Server .................................................... 10
      3.2.1 Server's Local ID List .............................. 10
      3.2.2 Server ID ........................................... 11 
      3.2.3 SILC Server Ports ................................... 11
  3.3 Router .................................................... 12
      3.3.1 Router's Local ID List .............................. 12
      3.3.2 Router's Global ID List ............................. 13
      3.3.3 Router's Server ID .................................. 13
  3.4 Channels .................................................. 14
      3.4.1 Channel ID .......................................... 15
  3.5 Operators ................................................. 15
  3.6 SILC Commands ............................................. 15
  3.7 SILC Packets .............................................. 16
  3.8 Packet Encryption ......................................... 16
      3.8.1 Determination of the Source and the Destination ..... 17
      3.8.2 Client To Client .................................... 17
      3.8.3 Client To Channel ................................... 19
      3.8.4 Server To Server .................................... 19
  3.9 Key Exchange And Authentication ........................... 20
  3.10 Algorithms ............................................... 20
      3.10.1 Ciphers ............................................ 20
      3.10.2 Public Key Algorithms .............................. 21
      3.10.3 MAC Algorithms ..................................... 21
      3.10.4 Compression Algorithms ............................. 22
  3.11 SILC Public Key .......................................... 22
  3.12 SILC Version Detection ................................... 24
4 SILC Procedures ............................................... 25
  4.1 Creating Client Connection ................................ 25
  4.2 Creating Server Connection ................................ 26
  4.3 Joining to a Channel ...................................... 27
  4.4 Channel Key Generation .................................... 28
  4.5 Private Message Sending and Reception ..................... 29
  4.6 Private Message Key Generation ............................ 29
  4.7 Channel Message Sending and Reception ..................... 30
  4.8 Session Key Regeneration .................................. 30
  4.9 Command Sending and Reception ............................. 30
5 SILC Commands ................................................. 31
  5.1 SILC Commands Syntax ...................................... 31
  5.2 SILC Commands List ........................................ 33
  5.3 SILC Command Status Types ................................. 56
      5.3.1 SILC Command Status Payload ......................... 56
      5.3.2 SILC Command Status List ............................ 57
6 Security Considerations ....................................... 61
7 References .................................................... 61
8 Author's Address .............................................. 62


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List of Figures

.nf
Figure 1:  SILC Network Topology
Figure 2:  Communication Inside cell
Figure 3:  Communication Between Cells
Figure 4:  Router Connections
Figure 5:  SILC Public Key
Figure 6:  SILC Command Status Payload


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1. Introduction

This document describes a Secure Internet Live Conferencing (SILC)
protocol which provides secure conferencing services over insecure
network channel.  SILC is IRC [IRC] like protocol, however, it is 
not equivalent to IRC and does not support IRC.

Strong cryptographic methods are used to protect SILC packets inside
SILC network.  Two other Internet Drafts relates very closely to this
memo; SILC Packet Protocol [SILC2] and SILC Key Exchange and
Authentication Protocols [SILC3].

The protocol uses extensively packets as conferencing protocol 
requires message and command sending.  The SILC Packet Protocol is
described in [SILC2] and should be read to fully comprehend this
document and protocol.  [SILC2] also describes the packet encryption
and decryption in detail.

The security of SILC protocol and for any security protocol for that
matter is based on strong and secure key exchange protocol.  The SILC
Key Exchange protocol is described in [SILC3] along with connection
authentication protocol and should be read to fully comprehend this
document and protocol.

The SILC protocol has been developed to work on TCP/IP network
protocol, although it could be made to work on other network protocols
with only minor changes.  However, it is recommended that TCP/IP
protocol is used under SILC protocol.  Typical implementation would
be made in client-server model.


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2. SILC Concepts

This section describes various SILC protocol concepts that forms the 
actual protocol, and in the end, the actual SILC network.  The mission
of the protocol is to deliver messages from clients to other clients 
through routers and servers in secure manner.  The messages may also 
be delivered from one client to many clients forming a group, also 
known as a channel.

This section does not focus to security issues, instead basic network 
concepts are introduced to make the topology of the SILC network 
clear.


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2.1 SILC Network Topology

SILC network is a cellular network as opposed to tree style network 
topology.  The rationale for this is to have servers that can perform 
specific kind of tasks what other servers cannot perform.  This leads 
to two kinds of servers; normal SILC servers and SILC routers.

A difference between normal server and router server is that routers 
knows everything about everything in the network.  They also do the 
actual routing of the messages to the correct receiver.  Normal servers 
knows only about local information and nothing about global information.
This makes the network faster as there are less servers that needs to 
keep global information up to date at all time.

This, on the other hand, leads to cellular like network, where routers 
are in the center of the cell and servers are connected to the router.

Following diagram represents SILC network topology.

















.in 8
.nf
  ---- ---- ----         ---- ---- ----
 | S8 | S5 | S4 |       | S7 | S5 | S6 |
 ----- ---- -----       ----- ---- -----
| S7 | S/R1 | S2 | --- | S8 | S/R2 | S4 |
 ---- ------ ----       ---- ------ ----
 | S6 | S3 | S1 |       | S1 | S3 | S2 |         ---- ----
  ---- ---- ----         ---- ---- ----         | S3 | S1 |
     Cell 1.   \\             Cell 2.  | \\____  ----- -----
                |                     |        | S4 | S/R4 |
    ---- ---- ----         ---- ---- ----       ---- ------
   | S7 | S4 | S2 |       | S1 | S3 | S2 |      | S2 | S5 |
   ----- ---- -----       ----- ---- -----       ---- ----
  | S6 | S/R3 | S1 | --- | S4 | S/R5 | S5 | ____/ Cell 4.
   ---- ------ ----       ---- ------ ----
   | S8 | S5 | S3 |       | S6 | S7 | S8 |     ... etc ...
    ---- ---- ----         ---- ---- ----
       Cell 3.                Cell 5.
.in 3

.ce
Figure 1:  SILC Network Topology


A cell is formed when a server or servers connect to one router.  In
SILC network normal server cannot directly connect to other normal
server.  Normal server may only connect to SILC router which then
routes the messages to the other servers in the cell.  Router servers
on the other hand may connect to other routers to form the actual SILC 
network, as seen in above figure.  However, router is also normal SILC 
server; clients may connect to it the same way as to normal SILC 
servers.  Normal server also cannot have active connections to more 
than one router.  Normal server cannot be connected to two different 
cells.  Router servers, on the other hand, may have as many router to 
router connections as needed.

There are many issues in this network topology that needs to be careful
about.  Issues like the size of the cells, the number of the routers in 
the SILC network and the capacity requirements of the routers.  These
issues should be discussed in the Internet Community and additional
documents on the issue will be written.


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2.2 Communication Inside a Cell

It is always guaranteed that inside a cell message is delivered to the 
recipient with at most two server hops.  Client who is connected to
server in the cell and is talking on channel to other client connected 
to other server in the same cell, will have its messages delivered from 
its local server first to the router of the cell, and from the router 
to the other server in the cell.

Following diagram represents this scenario:


.in 25
.nf
1 --- S1     S4 --- 5
         S/R
 2 -- S2     S3
     /        |
    4         3
.in 3


.ce
Figure 2:  Communication Inside cell


Example:  Client 1. connected to Server 1. message sent to
          Client 4. connected to Server 2. travels from Server 1.
          first to Router which routes the message to Server 2.
          which then sends it to the Client 4.  All the other
          servers in the cell will not see the routed message.


If client is connected directly to the router, as router is also normal 
SILC server, the messages inside the cell are always delivered only with 
one server hop.  If clients communicating with each other are connected 
to the same server, no router interaction is needed.  This is the optimal
situation of message delivery in the SILC network.


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2.3 Communication in the Network

If the message is destined to server that does not belong to local cell 
the message is routed to the router server to which the destination 
server belongs, if the local router is connected to destination router.
If there is no direct connection to the destination router, the local
router routes the message to its primary route.  Following diagram
represents message sending between cells.


.in 16
.nf
1 --- S1     S4 --- 5            S2 --- 1
         S/R - - - - - - - - S/R
 2 -- S2     S3           S1
     /        |             \\
    4         3              2

   Cell 1.               Cell 2.
.in 3


.ce
Figure 3:  Communication Between Cells


Example:  Client 5. connected to Server 4. in Cell 1. message sent
          to Client 2. connected to Server 1. in Cell 2. travels
          from Server 4. to Router which routes the message to
          Router in Cell 2, which then routes the message to 
          Server 1.  All the other servers and routers in the
          network will not see the routed message.


The optimal case of message delivery from client point of view is
when clients are connected directly to the routers and the messages
are delivered from one router to the other router.


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2.4 Channel Communication

Messages may be sent to group of clients as well.  Sending messages to
many clients works the same way as sending messages point to point, from
message delivery point of view.  Security issues are another matter
which are not discussed in this section.

Router server handles the message routing to multiple recipients.  If 
any recipient is not in the same cell as the sender the messages are 
routed further.

Server distributes the channel message to its local clients who are 
joined to the channel.  Also, router distributes the message to its 
local clients on the channel.


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2.5 Router Connections

Router connections play very important role in making the SILC like
network topology to work.  For example, sending broadcast packets in
SILC network require special connections between routers; routers must
be connected in specific way.

Every router has their primary route which is a connection to another
router in the network.  Unless there is only two routers in the network
must not routers use each other as their primary routes.  The router
connections in the network must form a circular.

Example with three routers in the network:







.in 16
.nf
    S/R1 - > - > - > - > - > - > - S/R2
     \\                               /
      ^                             v
       \\ - < -  < - S/R3 - < - < - /
.in 3


.ce
Figure 4:  Router Connections


Example:  Network with three routers.  Router 1. uses Router 2. as its
          primary router.  Router 2. uses Router 3. as its primary router,
          and Router 3. uses Router 1. as its primary router.  There may
          be other direct connections between the routers but they must
          not be used as primary routes.

The above example is applicable to any amount of routers in the network
except for two routers.  If there are only two routers in the network both
routers must be able to handle situation where they use each other as their
primary routes.

The issue of router connections are very important especially with SILC
broadcast packets.  Usually all router wide information in the network is
distributed by SILC broadcast packets.


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3. SILC Specification

This section describes the SILC protocol.  However, [SILC2] and
[SILC3] describes other important protocols that are part of this SILC
specification and must be read.


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3.1 Client

A client is a piece of software connecting to SILC server.  SILC client 
cannot be SILC server.  Purpose of clients is to provide the user 
interface of the SILC services for end user.  Clients are distinguished
from other clients by unique Client ID.  Client ID is a 128 bit ID that
is used in the communication in the SILC network.  The client ID is 
based on the nickname selected by the user.  User uses logical nicknames
in communication which are then mapped to the corresponding Client ID.
Client ID's are low level identifications and must not be seen by the
end user.

Clients provide other information about the end user as well. Information
such as the nickname of the user, username and the hostname of the end 
user and user's real name.  See section 3.2 Server for information of 
the requirements of keeping this information.

The nickname selected by the user is not unique in the SILC network.
There can be 2^8 same nicknames for one IP address.  As for comparison
to IRC [IRC] where nicknames are unique this is a fundamental difference
between SILC and IRC.  This causes the server names to be used along
with the nicknames to identify specific users when sending messages.
This feature of SILC makes IRC style nickname-wars obsolete as no one
owns their nickname; there can always be someone else with the same
nickname.  The maximum length of nickname is 128 characters.


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3.1.1 Client ID

Client ID is used to identify users in the SILC network.  The Client ID
is unique to the extent that there can be 2^128 different Client ID's,
and ID's based on IPv6 addresses extends this to 2^224 different Client
ID's.  Collisions are not expected to happen.  The Client ID is defined
as follows.

.in 6
128 bit Client ID based on IPv4 addresses:

32 bit  Server ID IP address (bits 1-32)
 8 bit  Random number or counter
88 bit  Truncated MD5 hash value of the nickname

224 bit Client ID based on IPv6 addresses:

128 bit  Server ID IP address (bits 1-128)
  8 bit  Random number or counter
 88 bit  Truncated MD5 hash value of the nickname

o Server ID IP address - Indicates the server where this
  client is coming from.  The IP address hence equals the
  server IP address where to the client has connected.

o Random number or counter - Random number to further 
  randomize the Client ID.  Another choice is to use
  a counter starting from the zero (0).  This makes it
  possible to have 2^8 same nicknames from the same
  server IP address.

o MD5 hash - MD5 hash value of the nickname is truncated
  taking 88 bits from the start of the hash value.  This
  hash value is used to search the user's Client ID from
  the ID lists.

.in 3
Collisions could occur when more than 2^8 clients using same nickname
from the same server IP address is connected to the SILC network.  
Server must be able to handle this situation by refusing to accept 
anymore of that nickname.

Another possible collision may happen with the truncated hash value of
the nickname.  It could be possible to have same truncated hash value for
two different nicknames.  However, this is not expected to happen nor
cause any problems if it would occur.  Nicknames are usually logical and
it is unlikely to have two distinct logical nicknames produce same
truncated hash value.


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3.2 Server

Servers are the most important parts of the SILC network.  They form the
basis of the SILC, providing a point to which clients may connect to.
There are two kinds of servers in SILC; normal servers and router servers.
This section focus on the normal server and router server is described
in the section 3.3 Router.

Normal servers may not directly connect to other normal server.  Normal
servers may only directly connect to router server.  If the message sent
by the client is destined outside the local server it is always sent to
the router server for further routing.  Server may only have one active
connection to router on same port.  Normal server may not connect to other
cell's router except in situations where its cell's router is unavailable.

Servers and routers in the SILC network are considered to be trusted.
With out a doubt, servers that are set to work on ports above 1023 are
not considered to be trusted.  Also, the service provider acts important
role in the server's trustworthy.


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3.2.1 Server's Local ID List

Normal server keeps various information about the clients and their end
users connected to it.  Every normal server must keep list of all locally
connected clients, Client ID's, nicknames, usernames and hostnames and
user's real name.  Normal servers only keeps local information and it
does not keep any global information.  Hence, normal servers knows only
about their locally connected clients.  This makes servers efficient as
they don't have to worry about global clients.  Server is also responsible
of creating the Client ID's for their clients.

Normal server also keeps information about locally created channels and
their Channel ID's.


Hence, local list for normal server includes:

.in 6
server list        - Router connection
   o Server name
   o Server IP address
   o Server ID
   o Sending key
   o Receiving key
   o Public key




client list        - All clients in server
   o Nickname
   o Username@host
   o Real name
   o Client ID
   o Sending key
   o Receiving key

channel list       - All channels in server
   o Channel name
   o Channel ID
   o Client ID's on channel
   o Client ID modes on channel
   o Channel key
.in 3



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3.2.2 Server ID

Servers are distinguished from other servers by unique 64 bit Server ID 
(for IPv4) or 160 bit Server ID (for IPv6).  The Server ID is used in
the SILC to route messages to correct servers.  Server ID's also provide
information for Client ID's, see section 3.1.1 Client ID.  Server ID is
defined as follows.

.in 6
64 bit Server ID based on IPv4 addresses:

32 bit  IP address of the server
16 bit  Port
16 bit  Random number

160 bit Server ID based on IPv6 addresses:

128 bit  IP address of the server
 16 bit  Port
 16 bit  Random number

o IP address of the server - This is the real IP address of
  the server.

o Port - This is the port the server is bound to.

o Random number - This is used to further randomize the Server ID.

.in 3
Collisions are not expected to happen in any conditions.  The Server ID
is always created by the server itself and server is responsible of
distributing it to the router.


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3.2.3 SILC Server Ports

Following ports has been assigned by IANA for the SILC protocol:

.in 10
silc            706/tcp    SILC
silc            706/udp    SILC
.in 3

If there are needs to create new SILC networks in the future the port
numbers must be officially assigned by the IANA.

Server on network above privileged ports (>1023) should not be trusted
as they could have been set up by untrusted party.


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3.3 Router

Router server in SILC network is responsible for keeping the cell together
and routing messages to other servers and to other routers.  Router server
is also a normal server thus clients may connect to it as it would be
just normal SILC server.

However, router servers has a lot of important tasks that normal servers
do not have.  Router server knows everything about everything in the SILC.
They know all clients currently on SILC, all servers and routers and all
channels in SILC.  Routers are the only servers in SILC that care about
global information and keeping them up to date at all time.  And, this
is what they must do.


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3.3.1 Router's Local ID List

Router server as well must keep local list of connected clients and
locally created channels.  However, this list is extended to include all
the informations of the entire cell, not just the server itself as for
normal servers.

However, on router this list is a lot smaller since routers do not keep
information about user's nickname, username and hostname and real name
since these are not needed by the router.  Router keeps only information
that it needs.


Hence, local list for router includes:

.in 6
server list        - All servers in the cell
   o Server name
   o Server ID
   o Router's Server ID
   o Sending key
   o Receiving key

client list        - All clients in the cell
   o Client ID


channel list       - All channels in the cell
   o Channel ID
   o Client ID's on channel
   o Client ID modes on channel
   o Channel key
.in 3


Note that locally connected clients and other information include all the
same information as defined in section section 3.2.1 Server's Local ID
List.


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3.3.2 Router's Global ID List

Router server must also keep global list.  Normal servers do not have
global list as they know only about local information.  Global list
includes all the clients on SILC, their Client ID's, all created channels
and their Channel ID's and all servers and routers on SILC and their
Server ID's.  That is said, global list is for global information and the
list must not include the local information already on the router's local
list.

Note that the global list does not include information like nicknames,
usernames and hostnames or user's real names.  Router does not keep
these informations as they are not needed by the router.  This 
information is available from the client's server which maybe queried
when needed.

Hence, global list includes:

.in 6
server list        - All servers in SILC
   o Server name
   o Server ID
   o Router's Server ID


client list        - All clients in SILC
   o Client ID

channel list       - All channels in SILC
   o Channel ID
   o Client ID's on channel
   o Client ID modes on channel
.in 3


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3.3.3 Router's Server ID

Router's Server ID's are equivalent to normal Server ID's.  As routers
are normal servers as well same types of ID's applies for routers as well.
Thus, see section 3.2.2 Server ID.  Server ID's for routers are always
created by the remote router where the router is connected to.


.ti 0
3.4 Channels

A channel is a named group of one or more clients which will all receive
messages addressed to that channel.  The channel is created when first
client requests JOIN command to the channel, and the channel ceases to
exist when the last client has left it.  When channel exists, any client
can reference it using the name of the channel.

Channel names are unique although the real uniqueness comes from 64 bit
Channel ID that unifies each channel.  However, channel names are still
unique and no two global channels with same name may exist.  The Channel
name is a string of maximum length of 256 characters.  Channel names may
not contain any spaces (`  '), any non-printable ASCII characters,
commas (`,') and wildcard characters.

Channels can have operators that can administrate the channel and
operate all of its modes.  Following operators on channel exist on SILC
network.

.in 6
o Channel founder - When channel is created the joining client becomes
  channel founder.  Channel founder is channel operator with some more
  privileges.  Basically, channel founder can fully operate the channel
  and all of its modes.  The privileges are limited only to the particular
  channel.  There can be only one channel founder per channel.  Channel
  founder supersedes channel operator's privileges.

  Channel founder privileges cannot be removed by any other operator on
  channel.  When channel founder leaves the channel there is no channel
  founder on the channel.  Channel founder also cannot be removed by
  force from the channel.

o Channel operator - When client joins to channel that has not existed
  previously it will become automatically channel operator (and channel
  founder discussed above).  Channel operator is able administrate the
  channel, set some modes on channel, remove a badly behaving client from
  the channel and promote other clients to become channel operator.
  The privileges are limited only to the particular channel.

  Normal channel user may be promoted (opped) to channel operator
  gaining channel operator privileges.  Channel founder or other channel
  operator may also demote (deop) channel operator to normal channel
  user.
.in 3


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3.4.1 Channel ID

Channels are distinguished from other channels by unique Channel ID.
The Channel ID is a 64 bit ID (for IPv4) or 160 bit ID (for IPv6), and
collisions are not expected to happen in any conditions.  Channel names
are just for logical use of channels.  The Channel ID is created by the
server where the channel is created.  The Channel ID is defined as
follows.

.in 6
64 bit Channel ID based on IPv4 addresses:

32 bit  Router's Server ID IP address (bits 1-32)
16 bit  Router's Server ID port (bits 33-48)
16 bit  Random number

160 bit Channel ID based on IPv6 addresses:

128 bit  Router's Server ID IP address (bits 1-128)
 16 bit  Router's Server ID port (bits 129-144)
 16 bit  Random number

o Router's Server ID IP address - Indicates the IP address of 
  the router of the cell where this channel is created.  This is 
  taken from the router's Server ID.  This way SILC router knows 
  where this channel resides in the SILC network.

o Router's Server ID port - Indicates the port of the channel on 
  the server.  This is taken from the router's Server ID.

o Random number - To further randomize the Channel ID.  This makes
  sure that there are no collisions.  This also means that
  in a cell there can be 2^16 channels.
.in 3


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3.5 Operators

Operators are normal users with extra privileges to their server or
router.  Usually these people are SILC server and router administrators
that take care of their own server and clients on them.  The purpose of
operators is to administrate the SILC server or router.  However, even
an operator with highest privileges is not able to enter invite-only
channel, to gain access to the contents of a encrypted and authenticated
packets traveling in the SILC network or to gain channel operator
privileges on public channels without being promoted.  They have the
same privileges as everyone else except they are able to administrate
their server or router.


.ti 0
3.6 SILC Commands

Commands are very important part on SILC network especially for client
which uses commands to operate on the SILC network.  Commands are used
to set nickname, join to channel, change modes and many other things.

Client usually sends the commands and server replies by sending a reply
packet to the command.  Server may also send commands usually to serve
the original client's request.  However, server may not send command
to client and there are some commands that server must not send.

Note that the command reply is usually sent only after client has sent
the command request but server is allowed to send command reply packet
to client even if client has not requested the command.  Client may,
however, choose ignore the command reply, but should not.

It is expected that some of the commands may be miss-used by clients
resulting various problems on the server side.  Every implementation
should assure that commands may not be executed more than once, say,
in two (2) seconds.  This should be sufficient to prevent the miss-use
of commands.

SILC commands are described in section 5 SILC Commands.


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3.7 SILC Packets

Packets are naturally the most important part of the protocol and the
packets are what actually makes the protocol.  Packets in SILC network
are always encrypted using, usually, the shared secret session key
or some other key, for example, channel key, when encrypting channel
messages.  The SILC Packet Protocol is a wide protocol and is described
in [SILC2].  This document does not define or describe details of
SILC packets.



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3.8 Packet Encryption

All packets passed in SILC network must be encrypted.  This section
defines how packets must be encrypted in the SILC network.  The detailed
description of the actual encryption process of the packets are
described in [SILC2].

Client and its server shares secret symmetric session key which is
established by the SILC Key Exchange Protocol, described in [SILC3]. 
Every packet sent from client to server, with exception of packets for
channels, are encrypted with this session key.

Channels has their own key that are shared by every client on the channel.
However, the channel keys are cell specific thus one cell does not know
the channel key of the other cell, even if that key is for same channel.
Channel key is also known by the routers and all servers that has clients
on the channel.  However, channels may have channel private keys that
are entirely local setting for client.  All clients on the channel must
know the channel private key before hand to be able to talk on the
channel.  In this case, no server or router knows the key for channel.

Server shares secret symmetric session key with router which is
established by the SILC Key Exchange Protocol.  Every packet passed from
server to router, with exception of packets for channels, are encrypted
with the shared session key.  Same way, router server shares secret
symmetric key with its primary route.  However, every packet passed
from router to other router, including packets for channels, are
encrypted with the shared session key.  Every router connection has
their own session keys.


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3.8.1 Determination of the Source and the Destination

The source and the destination of the packet needs to be determined
to be able to route the packets to correct receiver.  This information
is available in the SILC Packet Header which is included in all packets
sent in SILC network.  The SILC Packet Header is described in [SILC2].

The header is always encrypted with the session key who is next receiver
of the packet along the route.  The receiver of the packet, for example
a router along the route, is able to determine the sender and the
destination of the packet by decrypting the SILC Packet Header and
checking the ID's attached to the header.  The ID's in the header will
tell to where the packet needs to be sent and where it is coming from.

The header in the packet does not change during the routing of the
packet.  The original sender, for example client, assembles the packet
and the packet header and server or router between the sender and the
receiver must not change the packet header.

Note that the packet and the packet header may be encrypted with
different keys.  For example, packets to channels are encrypted with
the channel key, however, the header is encrypted with the session key
as described above.  However, the header and the packet may be encrypted
with same key.  This is case, for example, with command packets.


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3.8.2 Client To Client

Process of message delivery and encryption from client to another
client is as follows.

Example:  Private message from client to another client on different
          servers.  Clients do not share private message delivery
          keys; normal session keys are used.

o Client 1. sends encrypted packet to its server.  The packet is
  encrypted with the session key shared between client and its
  server.

o Server determines the destination of the packet and decrypts
  the packet.  Server encrypts the packet with session key shared
  between the server and its router, and sends the packet to the
  router.

o Router determines the destination of the packet and decrypts
  the packet.  Router encrypts the packet with session key 
  shared between the router and the destination server, and sends
  the packet to the server.

o Server determines the client to which the packet is destined
  to and decrypts the packet.  Server encrypts the packet with
  session key shared between the server and the destination client,
  and sends the packet to the client.

o Client 2. decrypts the packet.


Example:  Private message from client to another client on different
          servers.  Clients has established secret shared private
          message delivery key with each other and that is used in 
          the message encryption.

o Client 1. sends encrypted packet to its server.  The packet is
  encrypted with the private message delivery key shared between
  clients.

o Server determines the destination of the packet and sends the 
  packet to the router.

o Router determines the destination of the packet and sends the
  packet to the server.

o Server determines the client to which the packet is destined
  to and sends the packet to the client.

o Client 2. decrypts the packet with the secret shared key.


If clients share secret key with each other the private message
delivery is much simpler since servers and routers between the
clients do not need to decrypt and re-encrypt the packet.

The process for clients on same server is much simpler as there are
no need to send the packet to the router.  The process for clients 
on different cells is same as above except that the packet is routed 
outside the cell.  The router of the destination cell routes the 
packet to the destination same way as described above.


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3.8.3 Client To Channel

Process of message delivery from client on channel to all the clients
on the channel.

Example:  Channel of four users; two on same server, other two on
          different cells.  Client sends message to the channel.

o Client 1. encrypts the packet with channel key and sends the
  packet to its server.

o Server determines local clients on the channel and sends the
  packet to the Client on the same server.  Server then sends
  the packet to its router for further routing.

o Router determines local clients on the channel, if found
  sends packet to the local clients.  Router determines global
  clients on the channel and sends the packet to its primary
  router or fastest route.

o (Other router(s) do the same thing and sends the packet to
   the server(s))

o Server determines local clients on the channel and sends the
  packet to the client.

o All clients receiving the packet decrypts the packet.


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3.8.4 Server To Server

Server to server packet delivery and encryption is described in above
examples. Router to router packet delivery is analogous to server to
server.  However, some packets, such as channel packets, are processed
differently.  These cases are described later in this document and
more in detail in [SILC2].


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3.9 Key Exchange And Authentication

Key exchange is done always when for example client connects to server
but also when server and router and router and router connects to each
other.  The purpose of key exchange protocol is to provide secure key
material to be used in the communication.  The key material is used to
derive various security parameters used to secure SILC packets.  The
SILC Key Exchange protocol is described in detail in [SILC3].

Authentication is done after key exchange protocol has been successfully
completed.  The purpose of authentication is to authenticate for example
client connecting to the server.  However, Usually clients are accepted
to connect to server without explicit authentication.  Servers are
required use authentication protocol when connecting.  The authentication
may be based on passphrase (pre-shared-secret) or public key.  The
connection authentication protocol is described in detail in [SILC3].


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3.9.1 Authentication Payload

Authentication payload is used separately from the SKE and the Connection
authentication protocol.  It is used during the session to authenticate
with the remote.  For example, the client can authenticate itself to the
server to be server operator.  In this case, Authentication Payload is
used.

The format of the Authentication Payload is as follows:


.in 5
.nf
                     1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Payload Length         |     Authentication Method     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      Public Data Length       |                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
|                                                               |
~                           Public Data                         ~
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Authentication Data Length  |                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
|                                                               |
~                       Authentication Data                     ~
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+|
.in 3
 
.ce
Figure 5:  Authentication Payload


.in 6
o Payload Length (2 bytes) - Length of the entire payload.

o Authentication Type (2) - The method of the authentication.
  The authentication methods are defined in [SILC2] in the
  Connection Auth Request Payload.  The NONE authentication
  method is not recommended.

o Public Data Length (2 bytes) - Indicates the length of
  the Public Data field.

o Public Data (variable length) - This is defined only if
  the authentication method is public key.  If it is any other
  this field does not exist and the Public Data Length field
  is set to zero (0).

  When the authentication method is public key this includes
  128 to 4096 bytes of non-zero random data that is used in
  the signature process, described subsequently.

o Authentication Data Length (2 bytes) - Indicates the
  length of the Authentication Data field.

o Authentication Data (variable length) - Authentication 
  method dependent authentication data.
.in 3


If the authentication method is password based, the Authentication
Data field includes the plaintext password.  It is safe to send
plaintext password since the entire payload is encrypted.

If the authentication method is public key based (or certificate)
the Authentication Data is computed as follows:

  HASH = hash(random bytes | ID | public key (or certificate));
  Authentication Data = sign(HASH);

The hash() and the sign() are the hash funtion and the public key
cryptography function selected in the SKE protocol.  The public key
is SILC style public key unless certificates are used.  The ID is the
entity's ID (Client or Server ID) who is authenticating itself.  The ID
is raw ID data.  The random bytes are non-zero random bytes of length
between 128 and 4096 bytes, and will be included into the Public Data
field as is.

The receiver will compute the signature using the random data received
in the payload, the ID associated to the connection and the public key
(or certificate) received in the SKE protocol.  After computing the
receiver must verify the signature.  In this case also, the entire
payload is encrypted.


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3.10 Algorithms

This section defines all the allowed algorithms that can be used in
the SILC protocol.  This includes mandatory cipher, mandatory public
key algorithm and MAC algorithms.


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3.10.1 Ciphers

Cipher is the encryption algorithm that is used to protect the data
in the SILC packets.  See [SILC2] of the actual encryption process and
definition of how it must be done.  SILC has a mandatory algorithm that
must be supported in order to be compliant with this protocol.

Following ciphers are defined in SILC protocol:

.in 6
aes-256-cbc         AES in CBC mode, 256 bit key       (mandatory)
aes-192-cbc         AES in CBC mode, 192 bit key       (optional)
aes-128-cbc         AES in CBC mode, 128 bit key       (optional)
twofish-256-cbc     Twofish in CBC mode, 256 bit key   (optional)
twofish-192-cbc     Twofish in CBC mode, 192 bit key   (optional)
twofish-128-cbc     Twofish in CBC mode, 128 bit key   (optional)
blowfish-128-cbc    Blowfish in CBC mode, 128 bit key  (optional)
cast-256-cbc        CAST-256 in CBC mode, 256 bit key  (optional)
cast-192-cbc        CAST-256 in CBC mode, 192 bit key  (optional)
cast-128-cbc        CAST-256 in CBC mode, 128 bit key  (optional)
rc6-256-cbc         RC6 in CBC mode, 256 bit key       (optional)
rc6-192-cbc         RC6 in CBC mode, 192 bit key       (optional)
rc6-128-cbc         RC6 in CBC mode, 128 bit key       (optional)
mars-256-cbc        Mars in CBC mode, 256 bit key      (optional)
mars-192-cbc        Mars in CBC mode, 192 bit key      (optional)
mars-128-cbc        Mars in CBC mode, 128 bit key      (optional)
none                No encryption         (optional)
.in 3


Algorithm none does not perform any encryption process at all and 
thus is not recommended to be used.  It is recommended that no client
or server implementation would accept none algorithms except in special
debugging mode.

Additional ciphers may be defined to be used in SILC by using the
same name format as above.


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3.10.2 Public Key Algorithms

Public keys are used in SILC to authenticate entities in SILC network
and to perform other tasks related to public key cryptography.  The 
public keys are also used in the SILC Key Exchange protocol [SILC3].

Following public key algorithms are defined in SILC protocol:

.in 6
rsa        RSA  (mandatory)
dss        DSS  (optional)
.in 3

DSS is described in [Menezes].  The RSA must be implemented according
PKCS #1 [PKCS1].  The mandatory PKCS #1 implementation in SILC must be
compliant to either PKCS #1 version 1.5 or newer with the following
notes: The signature encoding is always in same format as the encryption
encoding regardles of the PKCS #1 version.  The signature with appendix
(with hash algorithm OID in the data) must not be used in the SILC.  The
rationale for this is that there is no binding between the PKCS #1 OIDs
and the hash algorithms used in the SILC protocol.  Hence, the encoding
is always in PKCS #1 version 1.5 format.

Additional public key algorithms may be defined to be used in SILC.


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3.10.3 MAC Algorithms

Data integrity is protected by computing a message authentication code
(MAC) of the packet data.  See [SILC2] for details how to compute the
MAC.

Following MAC algorithms are defined in SILC protocol:

.in 6
hmac-sha1        HMAC-SHA1, length = 20  (mandatory)
hmac-md5         HMAC-MD5, length = 16   (optional)
none             No MAC                  (optional)
.in 3

The none MAC is not recommended to be used as the packet is not
authenticated when MAC is not computed.  It is recommended that no
client or server would accept none MAC except in special debugging
mode.

The HMAC algorithm is described in [HMAC] and hash algorithms that
are used as part of the HMACs are described in [Scheneir] and in
[Menezes]

Additional MAC algorithms may be defined to be used in SILC.


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3.10.4 Compression Algorithms

SILC protocol supports compression that may be applied to unencrypted
data.  It is recommended to use compression on slow links as it may
significantly speed up the data transmission.  By default, SILC does not
use compression which is the mode that must be supported by all SILC
implementations.

Following compression algorithms are defined:

.in 6
none        No compression               (mandatory)
zlib        GNU ZLIB (LZ77) compression  (optional)
.in 3

Additional compression algorithms may be defined to be used in SILC.


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3.11 SILC Public Key

This section defines the type and format of the SILC public key.  All
implementations must support this public key type.  See [SILC3] for
other optional public key and certificate types allowed in SILC
protocol.  Public keys in SILC may be used to authenticate entities
and to perform other tasks related to public key cryptography.

The format of the SILC Public Key is as follows:


.in 5
.nf
                     1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Public Key Length                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Algorithm Name Length     |                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
|                                                               |
~                         Algorithm Name                        ~
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|       Identifier Length       |                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
|                                                               |
~                           Identifier                          ~
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
~                           Public Data                         ~
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.in 3

.ce
Figure 5:  SILC Public Key


.in 6
o Public Key Length (4 bytes) - Indicates the full length
  of the public key, not including this field.

o Algorithm Name Length (2 bytes) - Indicates the length
  of the Algorithm Length field, not including this field.

o Algorithm name (variable length) - Indicates the name
  of the public key algorithm that the key is.  See the
  section 3.10.2 Public Key Algorithms for defined names.

o Identifier Length (2 bytes) - Indicates the length of
  the Identifier field, not including this field.

o Identifier (variable length) - Indicates the identifier
  of the public key.  This data can be used to identify
  the owner of the key.  The identifier is of following
  format:

     UN   User name
     HN   Host name or IP address
     RN   Real name
     E    EMail address
     O    Organization
     C    Country


  Examples of an identifier:

    `UN=priikone, HN=poseidon.pspt.fi, E=priikone@poseidon.pspt.fi'

    `UN=sam, HN=dummy.fi, RN=Sammy Sam, O=Company XYZ, C=Finland'

  At least user name (UN) and host name (HN) must be provided as
  identifier.  The fields are separated by commas (`,').  If
  comma is in the identifier string it must be written as `\\,',
  for example, `O=Company XYZ\\, Inc.'.

o Public Data (variable length) - Includes the actual
  public data of the public key.

  The format of this field for RSA algorithm is
  as follows:

     4 bytes            Length of e
     variable length    e
     4 bytes            Length of n
     variable length    n


  The format of this field for DSS algorithm is
  as follows:

     4 bytes            Length of p
     variable length    p
     4 bytes            Length of q
     variable length    q
     4 bytes            Length of g
     variable length    g
     4 bytes            Length of y
     variable length    y

  The variable length fields are multiple precession
  integers encoded as strings in both examples.

  Other algorithms must define their own type of this
  field if they are used.
.in 3

All fields in the public key are in MSB (most significant byte first)
order.


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3.12 SILC Version Detection

The version detection of both client and server is performed at the
connection phase while executing the SILC Key Exchange protocol.  The
version identifier is exchanged between initiator and responder.  The
version identifier is of following format:

.in 6
SILC-<protocol version>-<software version>
.in 3

The version strings are of following format:

.in 6
protocol version = <major>.<minor>
software version = <major>[.<minor>[.<build>]]
.in 3

Protocol version may provide both major and minor version.  Currently
implementations must set the protocol version and accept the protocol
version as SILC-1.0-<sotware version>. 

Software version may provide major, minor and build version.  The
software version may be freely set and accepted.


Thus, the version string could be, for example:

.in 6
SILC-1.0-1.2
.in 3


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4 SILC Procedures

This section describes various SILC procedures such as how the 
connections are created and registered, how channels are created and
so on.  The section describes the procedures only generally as details
are described in [SILC2] and [SILC3].


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4.1 Creating Client Connection

This section describes the procedure when client connects to SILC server.
When client connects to server the server must perform IP address lookup
and reverse IP address lookup to assure that the origin host really is
who it claims to be.  Client, host, connecting to server must have 
both valid IP address and fully qualified domain name (FQDN).

After that the client and server performs SILC Key Exchange protocol
which will provide the key material used later in the communication.
The key exchange protocol must be completed successfully before the
connection registration may continue.  The SILC Key Exchange protocol
is described in [SILC3].

Typical server implementation would keep a list of connections that it
allows to connect to the server.  The implementation would check, for
example, the connecting client's IP address from the connection list
before the SILC Key Exchange protocol has been started.  Reason for
this is that if the host is not allowed to connect to the server there
is no reason to perform a key exchange protocol.

After successful key exchange protocol the client and server performs
connection authentication protocol.  The purpose of the protocol is to
authenticate the client connecting to the server.  Flexible
implementation could also accept the client to connect to the server
without explicit authentication.  However, if authentication is
desired for a specific client it may be based on passphrase or
public key authentication.  If authentication fails the connection
must be terminated.  The connection authentication protocol is described
in [SILC3].

After successful key exchange and authentication protocol the client
registers itself by sending SILC_PACKET_NEW_CLIENT packet to the
server.  This packet includes various information about the client
that the server uses to create the client.  Server creates the client
and sends SILC_PACKET_NEW_ID to the client which includes the created
Client ID that the client must start using after that.  After that
all SILC packets from the client must have the Client ID as the
Source ID in the SILC Packet Header, described in [SILC2].

Client must also get the server's Server ID that is to be used as
Destination ID in the SILC Packet Header when communicating with
the server (for example when sending commands to the server).  The
ID may be resolved in two ways.  Client can take the ID from an
previously received packet from server that must include the ID,
or to send SILC_COMMAND_INFO command and receive the Server ID as
command reply.

Server may choose not to use the information received in the
SILC_PACKET_NEW_CLIENT packet.  For example, if public key or 
certificate were used in the authentication, server may use those
informations rather than what it received from client.  This is suitable
way to get the true information about client if it is available.

The nickname of client is initially set to the username sent in the
SILC_PACKET_NEW_CLIENT packet.  User should set the nickname to more
suitable by sending SILC_COMMAND_NICK command.  However, this is not
required as part of registration process.

Server must also distribute the information about newly registered
client to its router (or if the server is router, to all routers in
the SILC network).  More information about this in [SILC2].


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4.2 Creating Server Connection

This section descibres the procedure when server connects to its
router (or when router connects to other router, the cases are
equivalent).  The procedure is very much alike when client connects
to the server thus it is not repeated here.

One difference is that server must perform connection authentication
protocol with proper authentication.  Proper authentication is based
on passphrase or public key authentication.

After server and router has successfully performed the key exchange
and connection authentication protocol, the server register itself
to the router by sending SILC_PACKET_NEW_SERVER packet.  This packet
includes the server's Server ID that it has created by itself and
other relevant information about the server.

After router has received the SILC_PACKET_NEW_SERVER packet it
distributes the information about newly registered server to all routers
in the SILC network.  More information about this in [SILC2].

As client needed to resolve the destination ID this must be done by the
server that connected to the router, as well.  The way to resolve it is
to get the ID from previously received packet.  Server must also start
using its own Server ID as Source ID in SILC Packet Header and the
router's Server ID as Destination when communicating with the router.

If the server has already connected clients and locally created
channels the server must distribute these informations to the router.
The distribution is done by sending packet SILC_PACKET_NEW_CHANNEL.
See [SILC2] for more information on this.


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4.3 Joining to a Channel

This section describes the procedure when client joins to a channel.
Client may join to channel by sending command SILC_COMMAND_JOIN to the
server.  If the receiver receiving join command is normal server the
server must check its local list whether this channel already exists
locally.  This would indicate that some client connected to the server
has already joined to the channel.  If this is case the client is
joined to the client, new channel key is created and information about
newly joined channel is sent to the router.  The router is informed
by sending SILC_NOTIFY_TYPE_JOIN notify type.  The notify type must
also be sent to the local clients on the channel.  The new channel key
is also sent to the router and to local clients on the channel.

If the channel does not exist in the local list the client's command
must be sent to the router which will then perform the actual joining
procedure.  When server receives the reply to the command from the
router it must be sent to the client who sent the command originally.
Server will also receive the channel key from the server that it must
send to the client who originally requested the join command.  The server
must also save the channel key.

If the receiver of the join command is router it must first check its
local list whether anyone in the cell has already joined to the channel.
If this is the case the client is joined to the channel and reply is
sent to the client.  If the command was sent by server the command reply
is sent to the server who sent it.  Then the router must also create
new channel key and distribute it to all clients on the channel and
all servers that has clients on the channel.  Router must also send
the SILC_NOTIFY_TYPE_JOIN notify type to local clients on the channel
and to local servers that has clients on the channel.

If the channel does not exist on the router's local list it must
check the global list whether the channel exists at all.  If it does
the client is joined to the channel as described previously.  If
the channel does not exist the channel is created and the client
is joined to the channel.  The channel key is also created and
distributed as previously described.  The client joining to the created
channel is made automatically channel founder and both channel founder
and channel operator privileges is set for the client.

If the router created the channel in the process, information about the
new channel must be broadcasted to all routers.  This is done by 
broadcasting SILC_PACKET_NEW_CHANNEL packet to the router's primary
route.  When the router joins the client to the channel it must also
send information about newly joined client to all routers in the SILC
network.  This is done by broadcasting the SILC_NOTIFY_TYPE_JOIN notify
type to the router's primary route. 

After joining the client to the channel server or router must send
command reply packet for SILC_COMMAND_USERS command.  This way the
client gets the list of users on the channel.  If the router joined
the client to the channel then the router sends this command reply
to the server which must send it further to the original client.

It is important to note that new channel key is created always when
new client joins to channel, whether the channel has existed previously
or not.  This way the new client on the channel is not able to decrypt
any of the old traffic on the channel.  Client who receives the reply to
the join command must start using the received Channel ID in the channel
message communication thereafter.  Client also receives the key for the
channel in the command reply.


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4.4 Channel Key Generation

Channel keys are created by router who creates the channel by taking
enough randomness from cryptographically strong random number generator.
The key is generated always when channel is created, when new client
joins a channel and after the key has expired.  Key could expire for
example in an hour.

The key must also be re-generated whenever some client leaves a channel.
In this case the key is created from scratch by taking enough randomness
from the random number generator.  After that the key is distributed to
all clients on the channel.  However, channel keys are cell specific thus
the key is created only on the cell where the client, who left the
channel, exists.  While the server or router is creating the new channel
key, no other client may join to the channel.  Messages that are sent
while creating the new key are still processed with the old key.  After
server has sent the SILC_PACKET_CHANNEL_KEY packet must client start
using the new key.  If server creates the new key the server must also
send the new key to its router.  See [SILC2] on more information about
how channel messages must be encrypted and decrypted when router is
processing them.


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4.5 Private Message Sending and Reception

Private messages are sent point to point.  Client explicitly destines
a private message to specific client that is delivered to only to that
client.  No other client may receive the private message.  The receiver
of the private message is destined in the SILC Packet Header as any
other packet as well.

If the sender of a private message does not know the receiver's Client
ID, it must resolve it from server.  There are two ways to resolve the
client ID from server; it is recommended that client implementations
send SILC_COMMAND_IDENTIFY command to receive the Client ID.  Client
may also send SILC_COMMAND_WHOIS command to receive the Client ID.
If the sender has received earlier a private message from the receiver
it should have cached the Client ID from the SILC Packet Header.

Receiver of a private message should not explicitly trust the nickname
that it receives in the Private Message Payload, described in [SILC2].
Implementations could resolve the nickname from server, as described
previously, and compare the received Client ID and the SILC Packet
Header's Client ID.  The nickname in the payload is merely provided
to be displayed for end user.

See [SILC2] for description of private message encryption and decryption
process.


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4.6 Private Message Key Generation

Private message may be protected by key generated by client.  The key
may be generated and sent to the other client by sending packet
SILC_PACKET_PRIVATE_MESSAGE_KEY which travels through the network
and is secured by session keys.  After that the private message key
is used in the private message communication between those clients.

Other choice is to entirely use keys that are not sent through
the SILC network at all.  This significantly adds security.  This key
would be pre-shared-key that is known by both of the clients.  Both
agree about using the key and starts sending packets that indicate
that the private message is secured using private message key.

The key material used as private message key is implementation issue.
However, SILC_PACKET_KEY_AGREEMENT packet may be used to negotiate
the key material.  If the key is normal pre-shared-key or randomly
generated key, and the SILC_PACKET_KEY_AGREEMENT was not used, then
the key material should be processed as defined in the [SILC3].  After
processing the key material it is employed as defined in [SILC3],
however, the HMAC key material must be discarded.


.ti 0
4.7 Channel Message Sending and Reception

Channel messages are delivered to group of users.  The group forms a
channel and all clients on the channel receives messages sent to the
channel.

Channel messages are destined to channel by specifying the Channel ID
as Destination ID in the SILC Packet Header.  The server must then
distribute the message to all clients on the channel by sending the
channel message destined explicitly to a client on the channel.

See [SILC2] for description of channel message encryption and decryption
process.


.ti 0
4.8 Session Key Regeneration

Session keys should be regenerated periodically, say, once in an hour.
The re-key process is started by sending SILC_PACKET_REKEY packet to
other end, to indicate that re-key must be performed.

If perfect forward secrecy (PFS) flag was selected in the SILC Key
Exchange protocol [SILC3] the re-key must cause new key exchange with
SKE protocol.  In this case the protocol is secured with the old key
and the protocol results to new key material.  See [SILC3] for more
information.  After the SILC_PACKET_REKEY packet is sent the sender
will perform the SKE protocol.

If PFS flag was not set, which is the default case, then re-key is done
without executing SKE protocol.  In this case, the new key is created by
hashing the old key with hash function selected earlier in the SKE
protocol.  If the digest length of the hash function is too short for the
key, then the key is distributed as described in section Processing the
Key Material in [SILC3].  After both parties has regenerated the session
key, both send SILC_PACKET_REKEY_DONE packet to each other.  These packets
are still secured with the old key.  After these packets, following
packets must be protected with the new key.


.ti 0
4.9 Command Sending and Reception

Client usually sends the commands in the SILC network.  In this case
the client simply sends the command packet to server and the server
processes it and replies with command reply packet.

However, if the server is not able to process the command, it is sent 
to the server's router.  This is case for example with commands such
as, SILC_COMMAND_JOIN and SILC_COMMAND_WHOIS commands.  However, there
are other commands as well.  For example, if client sends the WHOIS
command requesting specific information about some client the server must
send the WHOIS command to router so that all clients in SILC network
are searched.  The router, on the other hand, sends the WHOIS command
further to receive the exact information about the requested client.
The WHOIS command travels all the way to the server who owns the client
and it replies with command reply packet.  Finally, the server who
sent the command receives the command reply and it must be able to
determine which client sent the original command.  The server then
sends command reply to the client.  Implementations should have some
kind of cache to handle, for example, WHOIS information.  Servers
and routers along the route could all cache the information for faster
referencing in the future.

The commands sent by server may be sent hop by hop until someone is able
to process the command.  However, it is preferred to destine the command
as precisely as it is possible.  In this case, other routers en route
must route the command packet by checking the true sender and true
destination of the packet.  However, servers and routers must not route
command reply packets to clients coming from other server.  Client
must not accept command reply packet originated from anyone else but
from its own server.


.ti 0
5 SILC Commands

.ti 0
5.1 SILC Commands Syntax

This section briefly describes the syntax of the command notions
in this document.  Every field in command is separated from each
other by whitespaces (` ') indicating that each field is independent
argument and each argument must have own Command Argument Payload.
The number of maximum arguments are defined with each command
separately.  The Command Argument Payload is described in [SILC2].

Every command defines specific number for each argument.  Currently,
they are defined in ascending order; first argument has number one 
(1), second has number two (2) and so on.  This number is set into the
Argument Type field in the Command Argument Payload.  This makes it
possible to send the arguments in free order as the number must be
used to identify the type of the argument.  This makes is it also
possible to have multiple optional arguments in commands and in
command replies.  The number of argument is marked in parentheses
before the actual argument.



.in 6
Example:  Arguments:  (1) <nickname> (2) <username@host>
.in 3
   

Every command replies with Status Payload.  This payload tells the
sender of the command whether the command was completed successfully or
whether there was an error.  If error occured the payload includes the
error type.  In the next section the Status Payload is not described 
as it is common to all commands and has been described here.  Commands 
may reply with other arguments as well.  These arguments are command 
specific and are described in the next section.

Example command:
.in 6

EXAMPLE_COMMAND

.in 8
Max Arguments:  3
    Arguments:  (1) <nickname>[@<server>]  (2) <message>
                (3) [<count>]

The command has maximum of 3 arguments.  However, only first
and second arguments are mandatory.

First argument <nickname> is mandatory but may have optional
<nickname@server> format as well.  Second argument is mandatory
<message> argument.  Third argument is optional <count> argument.

The numbers in parentheses are the argument specific numbers
that specify the type of the argument in Command Argument Payload.
The receiver always knows that, say, argument number two (2) is
<message> argument, regardless of the ordering of the arguments in
the Command Payload.

Reply messages to the command:

Max Arguments:  4
    Arguments:  (1) <Status Payload>  (2) [<channel list>]
                (3) <idle time>       (4) [<away message>]

This command may reply with maximum of 4 arguments.  However,
only the first and third arguments are mandatory.  The numbers
in the parentheses have the same meaning as in the upper
command sending specification.

Every command reply with <Status Payload>, it is mandatory 
argument for all command replies and for this reason it is not
described in the command reply descriptions.



Status messages:

    SILC_STATUS_OK
    SILC_STATUS_ERR_TOO_MANY_TARGETS
    SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
    SILC_STATUS_ERR_NO_SUCH_NICK

Every command reply also defines set of status message that it
may return inside the <Status Payload>.  All status messages
are defined in the section 5.3 SILC Command Status Types.

.in 3
Every command that has some kind of ID as argument (for example
<Client ID>) are actually ID Payloads, defined in [SILC2] that includes
the type of the ID, length of the ID and the actual ID data.  This
way variable length ID's can be sent as arguments.


.ti 0
5.2 SILC Commands List

This section lists all SILC commands, however, it is expected that a
implementation and especially client implementation has many more
commands that has only local affect.  These commands are official
SILC commands that has both client and server sides and cannot be
characterized as local commands.

List of all defined commands in SILC follows.

.in 0
   0    SILC_COMMAND_NONE

        None.  This is reserved command and must not be sent.


   1    SILC_COMMAND_WHOIS

        Max Arguments:  3328
            Arguments:  (1) [<nickname>[@<server>]]  (2) [<count>]
                        (3) [<Client ID>]            (n) [...]

        Whois command is used to query various information about specific
        user.  The user maybe requested by their nickname and server name.
        The query may find multiple matching users as there are no unique
        nicknames in the SILC.  The <count> option maybe given to narrow
        down the number of accepted results.  If this is not defined there
        are no limit of accepted results.  The query may also be narrowed
        down by defining the server name of the nickname.

        It is also possible to search the user by Client ID.  If <Client ID>
        is provided server must use it as the search value instead of
        the <nickname>.  One of the arguments must be given.  It is also
        possible to define multiple Client ID's to search multiple users
        sending only one WHOIS command.  In this case the Client ID's are
        appended as normal arguments.  The server replies in this case
        with only one reply message for all requested users.

        To prevent miss-use of this service wildcards in the nickname
        or in the servername are not permitted.  It is not allowed
        to request all users on some server.  The WHOIS requests must 
        be based on specific nickname request.

        The WHOIS request must be always sent to the router by server
        so that all users are searched.  However, the server still must
        search its locally connected clients.  The router must send
        this command to the server who owns the requested client.  That
        server must reply to the command.  Server should not send whois
        replies to the client until it has received the reply from its
        router.

        Reply messages to the command:

        Max Arguments:  7
            Arguments:  (1) <Status Payload>       (2) <Client ID> 
                        (3) <nickname>[@<server>]  (4) <username@host> 
                        (5) <real name>            (6) [<channel list>] 
                        (7) [<idle time>]

        This command may reply with several command reply messages to
        form a list of results.  In this case the status payload will
        include STATUS_LIST_START status in the first reply and
        STATUS_LIST_END in the last reply to indicate the end of the
        list.  If there are only one reply the status is set to normal
        STATUS_OK.

        The command replies include the Client ID of the nickname,
        nickname and servername, username and hostname and users real
        name.  Client should process these replies only after the last
        reply has been received with the STATUS_LIST_END status.  If the
        <count> option were defined in the query there will be only
        <count> many replies from the server.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_LIST_START
            SILC_STATUS_LIST_END
            SILC_STATUS_ERR_NO_SUCH_NICK
            SILC_STATUS_ERR_NO_SUCH_CLIENT_ID
            SILC_STATUS_ERR_WILDCARDS
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS




   2    SILC_COMMAND_WHOWAS

        Max Arguments:  2
            Arguments:  (1) <nickname>[@<server>]  (2) [<count>]

        Whowas.  This command is used to query history information about
        specific user.  The user maybe requested by their nickname and 
        server name.  The query may find multiple matching users as there
        are no unique nicknames in the SILC.  The <count> option maybe
        given to narrow down the number of accepted results.  If this
        is not defined there are no limit of accepted results.  The query
        may also be narrowed down by defining the server name of the 
        nickname.

        To prevent miss-use of this service wildcards in the nickname
        or in the servername are not permitted.  The WHOWAS requests must 
        be based on specific nickname request.

        The WHOWAS request must be always sent to the router by server
        so that all users are searched.  However, the server still must
        search its locally connected clients.

        Reply messages to the command:

        Max Arguments:  3
            Arguments:  (1) <Status Payload>  (2) <nickname>[@<server>]
                        (3) <username@host>

        This command may reply with several command reply messages to form
        a list of results.  In this case the status payload will include
        STATUS_LIST_START status in the first reply and STATUS_LIST_END in 
        the last reply to indicate the end of the list.  If there are only 
        one reply the status is set to normal STATUS_OK.

        The command replies with nickname and username and hostname.
        Every server must keep history for some period of time of its
        locally connected clients.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_LIST_START
            SILC_STATUS_LIST_END
            SILC_STATUS_ERR_NO_SUCH_NICK
            SILC_STATUS_ERR_WILDCARDS
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS


   3    SILC_COMMAND_IDENTIFY

        Max Arguments:  3328
            Arguments:  (1) [<nickname>[@<server>]]  (2) [<count>]
                        (3) [<Client ID>]            (n) [...]

        Identify.  Identify command is almost analogous to WHOIS command,
        except that it does not return as much information.  Only relevant
        information such as Client ID is returned.  This is usually used
        to get the Client ID of a client used in the communication with
        the client.

        The query may find multiple matching users as there are no unique 
        nicknames in the SILC.  The <count> option maybe given to narrow 
        down the number of accepted results.  If this is not defined there 
        are no limit of accepted results.  The query may also be narrowed 
        down by defining the server name of the nickname.

        It is also possible to search the user by Client ID.  If <Client ID>
        is provided server must use it as the search value instead of
        the <nickname>.  One of the arguments must be given.  It is also
        possible to define multiple Client ID's to search multiple users
        sending only one IDENTIFY command.  In this case the Client ID's are
        appended as normal arguments.  The server replies in this case
        with only one reply message for all requested users.

        To prevent miss-use of this service wildcards in the nickname
        or in the servername are not permitted.  It is not allowed
        to request all users on some server.  The IDENTIFY requests must 
        be based on specific nickname request.

        Implementations may not want to give interface access to this
        command as it is hardly a command that would be used by an end user.
        However, it must be implemented as it is used with private message
        sending.

        The IDENTIFY must be always sent to the router by server so that
        all users are searched.  However, server must still search its
        locally connected clients.

        Reply messages to the command:

        Max Arguments:  4
            Arguments:  (1) <Status Payload>         (2) <Client ID>
                        (3) [<nickname>[@<server>]]  (4) [<username@host>]

        This command may reply with several command reply messages to form
        a list of results.  In this case the status payload will include
        STATUS_LIST_START status in the first reply and STATUS_LIST_END in 
        the last reply to indicate the end of the list.  If there are only 
        one reply the status is set to normal STATUS_OK.

        The command replies with Client ID of the nickname and if more
        information is available it may reply with nickname and username
        and hostname.  If the <count> option were defined in the query
        there will be only <count> many replies from the server.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_LIST_START
            SILC_STATUS_LIST_END
            SILC_STATUS_ERR_NO_SUCH_NICK
            SILC_STATUS_ERR_NO_SUCH_CLIENT_ID
            SILC_STATUS_ERR_WILDCARDS
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS


   4    SILC_COMMAND_NICK

        Max Arguments:  1
            Arguments:  (1) <nickname>

        Set/change nickname.  This command is used to set nickname for
        user.  There is no limit of the length of the nickname in SILC.
        Nickname must not include any spaces (` '), non-printable
        characters, commas (`,') and any wildcard characters.  Note:
        nicknames in SILC are case-sensitive which must be taken into
        account when searching clients by nickname.

        When nickname is changed new Client ID is generated.  Server must
        distribute SILC_NOTIFY_TYPE_NICK_CHANGE to local clients on the
        channels (if any) the client is joined on.  Then it must send
        SILC_PACKET_REPLACE_ID to its primary route to replace the old
        Client ID with the new one.

        Reply messages to the command:

        Max Arguments:  2
            Arguments:  (1) <Status Payload>  (2) <New ID Payload>

        This command is replied always with New ID Payload that is
        generated by the server every time user changes their nickname.
        Client receiving this payload must start using the received
        Client ID as its current valid Client ID.  The New ID Payload
        is described in [SILC2].

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_WILDCARDS
            SILC_STATUS_ERR_NICKNAME_IN_USE
            SILC_STATUS_ERR_BAD_NICKNAME
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS


   5    SILC_COMMAND_LIST

        Max Arguments:  2
            Arguments:  (1) [<Channel ID>] [<server>]

        The list command is used to list channels and their topics on
        current server.  If the <Channel ID> parameter is used, only the
        status of that channel is displayed.  Secret channels are not
        listed at all.  Private channels are listed with status indicating
        that the channel is private.

        If the <server> argument is specified the specified server's
        channels are listed.  In this case the command must be sent to
        the server who owns the channel that was requested.

        Reply messages to the command:

        Max Arguments:  4
            Arguments:  (1) <Status Payload>  (2) <Channel ID>
                        (3) <channel>         (4) <topic>

        This command may reply with several command reply messages to form
        a list of results.  In this case the status payload will include
        STATUS_LIST_START status in the first reply and STATUS_LIST_END in 
        the last reply to indicate the end of the list.  If there are only 
        one reply the status is set to normal STATUS_OK.

        This command replies with Channel ID, name and the topic of the
        channel.  If the channel is private channel the <topic> includes
        "*private*" string.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_LIST_START
            SILC_STATUS_LIST_END
            SILC_STATUS_ERR_WILDCARDS
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NO_SUCH_CHANNEL
            SILC_STATUS_ERR_NO_SUCH_CHANNEL_ID
            SILC_STATUS_ERR_NO_SUCH_SERVER


   6    SILC_COMMAND_TOPIC

        Max Arguments:  2
            Arguments:  (1) <Channel ID>  (2) [<topic>]]

        This command is used to change or view the topic of a channel.
        The topic for channel <Channel ID> is returned if there is no
        <topic> given.  If the <topic> parameter is present, the topic
        for that channel will be changed, if the channel modes permit
        this action.

        Reply messages to the command:

        Max Arguments:  2
            Arguments:  (1) <Status Payload>  (2) <Channel ID> 
                        (3) [<topic>]

        The command may reply with the topic of the channel if it is
        set.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_ON_CHANNEL
            SILC_STATUS_ERR_WILDCARDS
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_NO_SUCH_CHANNEL
            SILC_STATUS_ERR_NO_SUCH_CHANNEL_ID
            SILC_STATUS_ERR_NO_CHANNEL_ID
            SILC_STATUS_ERR_BAD_CHANNEL_ID
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NO_CHANNEL_PRIV


   7    SILC_COMMAND_INVITE

        Max Arguments:  2
            Arguments:  (1) <Client ID>  (2) <Channel ID>

        This command is used to invite other clients to join to the
        channel.  The <Client ID> argument is the target client's ID that
        is being invited.  The <Channel ID> is the Channel ID of the
        requested channel.  The sender of this command must be on the
        channel.  This command must fail if the requested channel does
        not exist, the requested client is already on the channel or if
        the channel is invite only channel and the caller of this command
        does not have at least channel operator privileges.

        Reply messages to the command:

        Max Arguments:  2
            Arguments:  (1) <Status Payload>

        This command replies only with Status Payload.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NO_SUCH_CLIENT_ID
            SILC_STATUS_ERR_NO_CLIENT_ID
            SILC_STATUS_ERR_NO_SUCH_CHANNEL_ID
            SILC_STATUS_ERR_NO_CHANNEL_ID
            SILC_STATUS_ERR_NOT_ON_CHANNEL
            SILC_STATUS_ERR_USER_ON_CHANNEL


   8    SILC_COMMAND_QUIT

        Max Arguments:  1
            Arguments:  (1) [<quit message>]

        This command is used by client to end SILC session.  The server
        must close the connection to a client which sends this command.
        if <quit message> is given it will be sent to other clients on
        channel if the client is on channel when quitting.

        Reply messages to the command:

        This command does not reply anything.


    9   SILC_COMMAND_KILL

        Max Arguments:  2
            Arguments:  (1) <Client ID>  (2) [<comment>]

        This command is used by SILC operators to remove a client from
        SILC network.  The removing has temporary effects and client may
        reconnect to SILC network.  The <Client ID> is the client to be
        removed from SILC.  The <comment> argument may be provided to 
        give to the removed client some information why it was removed
        from the network.

        Reply messages to the command:

        Max Arguments:  1
            Arguments:  (1) <Status Payload>

        This command replies only with Status Payload.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_WILDCARDS
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NO_SUCH_CLIENT_ID
            SILC_STATUS_ERR_NO_CLIENT_ID
            SILC_STATUS_ERR_NO_ROUTER_PRIV


   10   SILC_COMMAND_INFO

        Max Arguments:  1
            Arguments:  (1) [<server>]

        This command is used to fetch various information about a server.
        If <server> argument is specified the command must be sent to
        the requested server.

        Reply messages to the command:

        Max Arguments:  3
            Arguments:  (1) <Status Payload>  (2) <Server ID>
                        (3) <string>

        This command replies with the Server ID of the server and a
        string which tells the information about the server.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_WILDCARDS
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NO_SUCH_SERVER


   11   SILC_COMMAND_CONNECT

        Max Arguments:  2
            Arguments:  (1) <remote server/router>  (2) [<port>]

        This command is used by operators to force a server to try to
        establish a new connection to remote server or router. The
        Operator must specify the server/router to be connected by
        setting <remote server> argument.  The port is 32 bit MSB value.

        Reply messages to the command:

        Max Arguments:  1
            Arguments:  (1) <Status Payload>

        This command replies only with Status Payload.



        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_WILDCARDS
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NO_SERVER_PRIV
            SILC_STATUS_ERR_NO_ROUTER_PRIV


   12   SILC_COMMAND_PING

        Max Arguments:  1
            Arguments:  (1) <Server ID>

        This command is used by client and server to test the communication
        channel to its server if one suspects that the communication is not
        working correctly.  The <Server ID> is the ID of the server the
        sender is connected to.

        Reply messages to the command:

        Max Arguments:  1
            Arguments:  (1) <Status Payload>

        This command replies only with Status Payload.  Server returns
        SILC_STATUS_OK in Status Payload if pinging was successful.



        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NO_SERVER_ID
            SILC_STATUS_ERR_NO_SUCH_SERVER
            SILC_STATUS_ERR_NOT_REGISTERED


   13   SILC_COMMAND_OPER

        Max Arguments:  2
            Arguments:  (1) <username>  (2) <authentication data>

        This command is used by normal client to obtain server operator
        privileges on some server or router.  Note that router operator
        has router privileges that supersedes the server operator
        privileges and this does not obtain those privileges.  Client
        must use SILCOPER command to obtain router level privileges.

        The <username> is the username set in the server configurations
        as operator.  The <authentication data> is the data that the
        client is authenticated against.  It may be passphrase prompted
        for user on client's screen or it may be public key
        authentication data (data signed with private key), or 
        certificate.

        Reply messages to the command:

        Max Arguments:  1
            Arguments:  (1) <Status Payload>

        This command replies only with Status Payload.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_BAD_PASSWORD
            SILC_STATUS_ERR_AUTH_FAILED


   14   SILC_COMMAND_JOIN

        Max Arguments:  4
            Arguments:  (1) <channel>       (2) <Client ID>
                        (3) [<passphrase>]  (4) [<cipher>]

        Join to channel/create new channel.  This command is used to
        join to a channel.  If the channel does not exist the channel is
        created.  If server is normal server this command must be sent
        to router who will create the channel.  The channel may be
        protected with passphrase.  If this is the case the passphrase
        must be sent along the join command.

        The name of the <channel> must not include any spaces (` '),
        non-printable characters, commas (`,') or any wildcard characters.

        The second argument <Client ID> is the Client ID of the client who
        is joining to the client.  When client sends this command to the
        server the <Client ID> must be the client's own ID.

        Cipher to be used to secure the traffic on the channel may be
        requested by sending the name of the requested <cipher>.  This
        is used only if the channel does not exist and is created.  If
        the channel already exists the cipher set previously for the
        channel will be used to secure the traffic.

        The server must check whether the user is allowed to join to
        the requested channel.  Various modes set to the channel affect
        the ability of the user to join the channel.  These conditions
        are:

            o  The user must be invited to the channel if the channel
               is invite-only channel.

            o  The Client ID/nickname/username/hostname must not match
               any active bans.

            o  The correct passphrase must be provided if passphrase 
               is set to the channel.

            o  The user count limit, if set, must not be reached.

        Reply messages to the command:

        Max Arguments:  9
            Arguments:  (1) <Status Payload>  (2) <channel> 
                        (3) <Channel ID>      (4) <channel mode mask>
                        (5) <created>         (6) <Channel Key Payload>
                        (7) [<ban mask>]      (8) [<invite list>]
                        (9) [<topic>]

        This command replies with the channel name requested by the
        client, channel ID of the channel and topic of the channel
        if it exists.  It also replies with the channel mode mask
        which tells all the modes set on the channel.  If the
        channel is created the mode mask is zero (0).  If ban mask
        and/or invite list is set they are sent as well.

        Client receives the channel key in the reply message as well
        inside <Channel Key Payload>.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_WILDCARDS
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_BAD_PASSWORD
            SILC_STATUS_ERR_CHANNEL_IS_FULL
            SILC_STATUS_ERR_NOT_INVITED
            SILC_STATUS_ERR_BANNED_FROM_CHANNEL
            SILC_STATUS_ERR_BAD_CHANNEL
            SILC_STATUS_ERR_USER_ON_CHANNEL


   15   SILC_COMMAND_MOTD

        Max Arguments:  1
            Arguments:  (1) <server>

        This command is used to query the Message of the Day of the server.

        Reply messages to the command:

        Max Arguments:  2
            Arguments:  (1) <Status Payload>  (2) [<motd>]

        This command replies with the motd message if it exists.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NO_SUCH_SERVER


   16   SILC_COMMAND_UMODE

        Max Arguments:  2
            Arguments:  (1) <Client ID>  (2) <client mode mask>

        This command is used by client to set/unset modes for itself.
        However, there are some modes that the client may not set itself,
        but they will be set by server.  However, client may unset any
        mode.  Modes may be masked together ORing them thus having
        several modes set.  Client must keep its client mode mask
        locally so that the mode setting/unsetting would work without
        problems.  Client may change only its own modes.

        Following client modes are defined:

           0x0000    SILC_UMODE_NONE

              No specific mode for client.  This is the initial
              setting when new client is created.  The client is
              normal client now.


           0x0001    SILC_UMODE_SERVER_OPERATOR

              Marks the user as server operator.  Client cannot
              set this mode itself.  Server sets this mode to the
              client when client attains the server operator
              privileges by SILC_COMMAND_OPER command.  Client
              may unset the mode itself.


           0x0002    SILC_UMODE_ROUTER_OPERATOR

              Marks the user as router (SILC) operator.  Client
              cannot this mode itself.  Router sets this mode to
              the client when client attains the router operator
              privileges by SILC_COMMAND_SILCOPER command.  Client
              may unset the mode itself.

        Reply messages to the command:

        Max Arguments:  2
            Arguments:  (1) <Status Payload>  (2) <client mode mask>

        This command replies with the changed client mode mask that
        the client is required to keep locally.


        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NO_SUCH_CLIENT_ID
            SILC_STATUS_ERR_BAD_CLIENT_ID
            SILC_STATUS_ERR_NOT_YOU
            SILC_STATUS_ERR_UNKNOWN_MODE
            SILC_STATUS_ERR_NO_RECIPIENT
            SILC_STATUS_ERR_NO_CLIENT_ID


   17   SILC_COMMAND_CMODE

        Max Arguments:  7
            Arguments:  (1) <Channel ID>    (2) <channel mode mask>
                        (3) [<user limit>]  (4) [<passphrase>]
                        (5) [<ban mask>]    (6) [<invite list>]
                        (7) [<cipher>[:<key len>]]

        This command is used by client to set or change channel flags on
        a channel.  Channel has several modes that set various properties
        of a channel.  Modes may be masked together by ORing them thus
        having several modes set.  The <Channel ID> is the ID of the
        target channel.  The client changing channel mode must be on
        the same channel and poses sufficient privileges to be able to
        change the mode.

        When the mode is changed SILC_NOTIFY_TYPE_CMODE_CHANGE notify
        type is distributed to the channel.

        Following channel modes are defined:

           0x0000    SILC_CMODE_NONE

              No specific mode on channel.  This is the default when
              channel is created.  This means that channel is just plain
              normal channel.


           0x0001    SILC_CMODE_PRIVATE

              Channel is private channel.  Private channels are shown
              in the channel list listed with SILC_COMMAND_LIST command
              with indication that the channel is private.  Also,
              client on private channel will no be detected to be on
              the channel as the channel is not shown in the client's
              currently joined channel list.  Channel founder and 
              channel operator may set/unset this mode.

              Typical implementation would use [+|-]p on user interface
              to set/unset this mode.


           0x0002    SILC_CMODE_SECRET

              Channel is secret channel.  Secret channels are not shown
              in the list listed with SILC_COMMAND_LIST command.  Secret
              channels can be considered to be invisible channels.
              Channel founder and channel operator may set/unset this
              mode.

              Typical implementation would use [+|-]s on user interface
              to set/unset this mode.


           0x0004    SILC_CMODE_PRIVKEY

              Channel uses private channel key to protect the traffic
              on the channel.  When this mode is set the client will be
              responsible to set the key it wants to use to encrypt and
              decrypt the traffic on channel.  Server generated channel
              keys are not used at all.  This mode provides additional
              security as clients on channel may agree to use private
              channel key that even servers do not know.  Naturally,
              this requires that every client on the channel knows
              the key before hand (it is considered to be pre-shared-
              key).  This specification does not define how the private
              channel key is set as it is entirely local setting on
              the client end.

              As it is local setting it is possible to have several
              private channel keys on one channel.  In this case several
              clients can talk on same channel but only those clients
              that share the key with the message sender will be able
              to hear the talking.  Client should not display those
              message for the end user that it is not able to decrypt
              when this mode is set.

              Only channel founder may set/unset this mode.  If this
              mode is unset the server will distribute new channel
              key to all clients on the channel which will be used
              thereafter.

              Typical implementation would use [+|-]k on user interface
              to set/unset this mode.


           0x0008    SILC_CMODE_INVITE

              Channel is invite only channel.  Client may join to this
              channel only if it is invited to the channel.  Channel
              founder and channel operator may set/unset this mode.

              Typical implementation would use [+|-]i on user interface
              to set/unset this mode.


           0x0010    SILC_CMODE_TOPIC

              The topic of the channel may only be set by client that
              is channel founder or channel operator.  Normal clients
              on channel will not be able to set topic when this mode
              is set.  Channel founder and channel operator may set/
              unset this mode.

              Typical implementation would use [+|-]t on user interface
              to set/unset this mode.


           0x0020    SILC_CMODE_ULIMIT

              User limit has been set to the channel.  New clients
              may not join to the channel when the limit set is
              reached.  Channel founder and channel operator may set/
              unset the limit.  The <user limit> argument is the
              number of limited users.

              Typical implementation would use [+|-]l on user interface
              to set/unset this mode.


           0x0040    SILC_CMODE_PASSPHRASE

              Passphrase has been set to the channel.  Client may
              join to the channel only if it is able to provide the
              correct passphrase.  Setting passphrases to channel
              is entirely safe as all commands are protected in the
              SILC network.  Only channel founder may set/unset
              the passphrase.  The <passphrase> argument is the
              set passphrase.

              Typical implementation would use [+|-]a on user interface
              to set/unset this mode.


           0x0080    SILC_CMODE_BAN

              Ban mask has been set to the channel.  The ban mask
              may be used to ban specific clients to join the channel.
              The <ban mask> argument is the set ban mask.  When
              unsetting a ban mask the mask must be provided as
              argument.  Channel founder and channel operator may
              set/unset this mode.  Channel founder may not be
              added to the ban list.  <ban mask> is an comma (`,')
              separated list of banned clients in the following format:

                [<nickname>[@<server>]!][<username>]@[<hostname>]

              Wildcards maybe used when banning clients.

              Typical implementation would use [+|-]b on user interface
              to set/unset this mode.


           0x0100    SILC_CMODE_INVITE_LIST

              Invite list has been set to the channel.  The invite list
              can be used to mark the clients that is able to join
              channel without being invited when the channel is set to
              be invite-only channel.  The <invite list> argument is the
              set invite mask.  When unsetting entry from the invite list
              the entry must be provided as argument.  Channel founder and
              channel operator may set/unset this mode.  The <invite list>
              is command (`,') separated list of invited clients in the
              following format:

                [<nickname>[@<server>]!][<username>]@[<hostname>]

              Wildcards maybe used when setting the invite list.

              Typical implementation would use [+|-]I on user interface
              to set/unset this mode.

        
           0x0200    SILC_CMODE_CIPHER

              Sets specific cipher to be used to protect channel
              traffic.  The <cipher> argument is the requested cipher.
              When set or unset the server must re-generate new
              channel key.  If <key len> argument is specified with
              <cipher> argument the new key is generated of <key len>
              length in bits.  Only channel founder may set the cipher of 
              the channel.  When unset the new key is generated using
              default cipher for the channel.

              Typical implementation would use [+|-]c on user interface
              to set/unset this mode.


        To make the mode system work, client must keep the channel mode
        mask locally so that the mode setting and unsetting would work
        without problems.  The client receives the initial channel mode
        mask when it joins to the channel.  When the mode changes on
        channel the servers distributes the changed channel mode mask to
        all clients on the channel by sending SILC_NOTIFY_TYPE_CMODE_CHANGE
        notify type.


        Reply messages to the command:

        Max Arguments:  2
            Arguments:  (1) <Status Payload>  (2) <channel mode mask>

        This command replies with the changed channel mode mask that
        client is required to keep locally.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NOT_ON_CHANNEL
            SILC_STATUS_ERR_NO_SUCH_CHANNEL_ID
            SILC_STATUS_ERR_BAD_CHANNEL_ID
            SILC_STATUS_ERR_NO_CHANNEL_ID
            SILC_STATUS_ERR_NO_CHANNEL_PRIV
            SILC_STATUS_ERR_UNKNOWN_MODE
            SILC_STATUS_ERR_NO_SUCH_CLIENT_ID


   19   SILC_COMMAND_CUMODE

        Max Arguments:  3
            Arguments:  (1) <Channel ID>  (2) <mode mask>
                        (3) <Client ID>

        This command is used by client to change channel user modes on
        channel.  Users on channel may have some special modes and this
        command is used by channel operators to set or change these modes.
        The <Channel ID> is the ID of the target channel.  The <mode mask>
        is OR'ed mask of modes.  The <Client ID> is the target client.
        The client changing channel user modes must be on the same channel
        as the target client and poses sufficient privileges to be able to
        change the mode.

        When the mode is changed SILC_NOTIFY_TYPE_CUMODE_CHANGE notify
        type is distributed to the channel.

        Following channel modes are defined:

           0x0000    SILC_CUMODE_NONE

              No specific mode.  This is the normal situation for client.
              Also, this is the mode set when removing all modes from client.


           0x0001    SILC_CUMODE_FOUNDER

              The client is channel founder of the channel.  This mode
              cannot be set by other client, it is set by the server when
              the channel was founded (created).  The mode is provided 
              because client may remove the founder rights from itself.


           0x0002    SILC_CUMODE_OPERATOR

              Sets channel operator privileges on the channel for a
              client on the channel.  Channel founder and channel operator
              may set/unset (promote/demote) this mode.


        Reply messages to the command:

        Max Arguments:  3
            Arguments:  (1) <Status Payload>  (2) <channel user mode mask>
                        (3) <Client ID>

        This command replies with the changed channel user mode mask that
        client is required to keep locally.  The <Client ID> is the target
        client.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NOT_ON_CHANNEL
            SILC_STATUS_ERR_NO_SUCH_CHANNEL_ID
            SILC_STATUS_ERR_BAD_CHANNEL_ID
            SILC_STATUS_ERR_NO_CHANNEL_ID
            SILC_STATUS_ERR_NO_CHANNEL_PRIV
            SILC_STATUS_ERR_UNKNOWN_MODE
            SILC_STATUS_ERR_NO_SUCH_CLIENT_ID


   19   SILC_COMMAND_KICK

        Max Arguments:  3
            Arguments:  (1) <Channel ID>  (2) <Client ID>  
                        (3) [<comment>]

        This command is used by channel operators to remove a client from
        channel.  The <channel> argument is the channel the client to be
        removed is on currently.  Note that the "kicker" must be on the same
        channel.  If <comment> is provided it will be sent to the removed
        client.

        Reply messages to the command:

        Max Arguments:  1
            Arguments:  (1) <Status Payload>

        This command replies only with Status Payload.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NO_SUCH_CHANNEL
            SILC_STATUS_ERR_NO_SUCH_CLIENT_ID
            SILC_STATUS_ERR_NO_CHANNEL_PRIV
            SILC_STATUS_ERR_NO_CLIENT_ID


   20   SILC_COMMAND_RESTART

        Max Arguments:  0
            Arguments:  None

        This command may only be used by server operator to force a
        server to restart itself.

        Reply messages to the command:

        Max Arguments:  1
            Arguments:  (1) <Status Payload>

        This command replies only with Status Payload.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NO_SERVER_PRIV





   21   SILC_COMMAND_CLOSE

        Max Arguments:  2
            Arguments:  (1) <remote server/router>  (2) [<port>]

        This command is used only by operator to close connection to a
        remote site.

        Reply messages to the command:

        Max Arguments:  1
            Arguments:  (1) <Status Payload>

        This command replies only with Status Payload.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NO_SUCH_SERVER
            SILC_STATUS_ERR_NO_SERVER_PRIV
            SILC_STATUS_ERR_NO_SUCH_SERVER_ID


   22   SILC_COMMAND_SHUTDOWN

        Max Arguments:  0
            Arguments:  None

        This command is used only by operator to shutdown the server.
        All connections to the server will be closed and the server is
        shutdown.

        Reply messages to the command:



        Max Arguments:  1
            Arguments:  (1) <Status Payload>

        This command replies only with Status Payload.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NO_SERVER_PRIV


   23   SILC_COMMAND_SILCOPER

        Max Arguments:  2
            Arguments:  (1) <username>  (2) <authentication data>

        This command is used by normal client to obtain router operator
        privileges (also known as SILC operator) on some router.  Note
        that router operator has router privileges that supersedes the
        server operator privileges.

        The <username> is the username set in the server configurations
        as operator.  The <authentication data> is the data that the
        client is authenticated against.  It may be passphrase prompted
        for user on client's screen or it may be public key
        authentication data (data signed with private key), or 
        certificate.

        Difference between router operator and server operator is that
        router operator is able to handle cell level properties while
        server operator (even on router server) is able to handle only
        local properties, such as, local connections and normal server
        administration.

        Reply messages to the command:

        Max Arguments:  1
            Arguments:  (1) <Status Payload>

        This command replies only with Status Payload.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_BAD_PASSWORD
            SILC_STATUS_ERR_AUTH_FAILED


   24   SILC_COMMAND_LEAVE

        Max Arguments:  1
            Arguments:  (1) <Channel ID>

        This command is used by client to leave a channel the client is
        joined to.  After a client has leaved the channel the server
        must create new key for the channel and distribute to all clients
        still currently on the channel.

        Reply messages to the command:

        Max Arguments:  1
            Arguments:  (1) <Status Payload>

        This command replies only with Status Payload.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NO_SUCH_CHANNEL_ID
            SILC_STATUS_ERR_BAD_CHANNEL_ID
            SILC_STATUS_ERR_NO_CHANNEL_ID


   25   SILC_COMMAND_USERS

        Max Arguments:  1
            Arguments:  (1) <Channel ID>

        This command is used to list user names currently on the requested
        channel; argument <Channel ID>.  The server must resolve the
        user names and send a comma (`,') separated list of user names
        on the channel.  Server or router may resolve the names by sending
        SILC_COMMAND_WHOIS commands.

        If the requested channel is a private or secret channel, this
        command must not send the list of users, as private and secret
        channels cannot be seen by outside.  In this case the returned
        name list may include a indication that the server could not 
        resolve the names of the users on the channel.  Also, in this case
        Client ID's or client modes are not sent either.

        Reply messages to the command:

        Max Arguments:  5
            Arguments:  (1) <Status Payload>  (2) <Channel ID>
                        (3) <list count>      (4) <Client ID list>
                        (5) <client mode list>

        This command replies with the Channel ID of the requested channel
        Client ID list of the users on the channel and list of their modes.
        The Client ID list has Client ID's of all users in the list.  The 
        <Client ID list> is formed by adding Client ID's one after another.
        The <client mode list> is formed by adding client's user modes on
        the channel one after another (4 bytes (32 bits) each).  The <list 
        count> of length of 4 bytes (32 bits), tells the number of entries
        in the lists.  Both lists must have equal number of entries.

        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_REGISTERED
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NO_SUCH_CHANNEL_ID
            SILC_STATUS_ERR_BAD_CHANNEL_ID
            SILC_STATUS_ERR_NO_CHANNEL_ID
            SILC_STATUS_ERR_NOT_ON_CHANNEL


   26 - 199

        Currently undefined commands.


   200 - 254

        These commands are reserved for private use and will not be defined
        in this document.


   255  SILC_COMMAND_MAX   

        Reserved command.  This must not be sent.
.in 3


.ti 0
5.3 SILC Command Status Types

.ti 0
5.3.1 SILC Command Status Payload

Command Status Payload is sent in command reply messages to indicate
the status of the command.  The payload is one of argument in the
command thus this is the data area in Command Argument Payload described
in [SILC2].  The payload is only 2 bytes of length.  Following diagram
represents the Command Status Payload (field is always in MSB order).





.in 21
.nf
                     1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Status Message         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.in 3

.ce
Figure 6:  SILC Command Status Payload


.in 6
o Status Message (2 bytes) - Indicates the status message.
  All Status messages are described in the next section.
.in 3


.ti 0
5.3.2 SILC Command Status List

Command Status messages are returned in the command reply messages
to indicate whether the command were executed without errors.  If error
has occured the status tells which error occured.  Status payload only
sends numeric reply about the status.  Receiver of the payload must
convert the numeric values into human readable error messages.  The
list of status messages below has an example human readable error
messages that client may display for the user.

List of all defined command status messages following.

.in 0
   Generic status messages:

   0    SILC_STATUS_OK

        Ok status.  Everything went Ok.  The status payload maybe
        safely ignored in this case.

   1    SILC_STATUS_LIST_START

        Start of the list.  There will be several command replies and
        this reply is the start of the list.

   2    SILC_STATUS_LIST_ITEM

        Item in the list.  This is one of the item in the list but not the
        first or last one.

   3    SILC_STATUS_LIST_END

        End of the list.  There were several command replies and this
        reply is the last of the list.  There won't be other replies
        belonging to this list after this one.

   4 - 9

        Currently undefined and has been reserved for the future.


   Error status message:

   10   SILC_STATUS_ERR_NO_SUCH_NICK

        "No such nickname".  Requested nickname does not exist.

   11   SILC_STATUS_ERR_NO_SUCH_CHANNEL

        "No such channel".  Requested channel name does not exist.

   12   SILC_STATUS_ERR_NO_SUCH_SERVER

        "No such server".  Requested server name does not exist.

   13   SILC_STATUS_ERR_TOO_MANY_TARGETS

        "Duplicate recipients. No message delivered".  Message were
        tried to be sent to recipient which has several occurrences in 
        the recipient list.

   14   SILC_STATUS_ERR_NO_RECIPIENT

        "No recipient given".  Command required recipient which was
        not provided.

   15   SILC_STATUS_ERR_UNKNOWN_COMMAND

        "Unknown command".  Command sent to server is unknown by the
        server.

   16   SILC_STATUS_ERR_WILDCARDS

        "Wildcards cannot be used".  Wildcards were provided but they
        weren't permitted.

   17   SILC_STATUS_ERR_NO_CLIENT_ID

        "No Client ID given".  Client ID were expected as command
        parameter but were not found.

   18   SILC_STATUS_ERR_NO_CHANNEL_ID

        "No Channel ID given".  Channel ID were expected as command
        parameter but were not found.

   19   SILC_STATUS_ERR_NO_SERVER_ID

        "No Serve ID given".  Server ID were expected as command
        parameter but were not found.

   20   SILC_STATUS_ERR_BAD_CLIENT_ID

        "Bad Client ID".  Client ID provided were erroneous.

   21   SILC_STATUS_ERR_BAD_CHANNEL_ID

        "Bad Channel ID".  Channel ID provided were erroneous.

   22   SILC_STATUS_ERR_NO_SUCH_CLIENT_ID

        "No such Client ID".  Client ID provided does not exist.

   23   SILC_STATUS_ERR_NO_SUCH_CHANNEL_ID

        "No such Channel ID".  Channel ID provided does not exist.

   24   SILC_STATUS_ERR_NICKNAME_IN_USE

        "Nickname already exists".  Nickname created could not be 
        registered because number of same nicknames were already set to
        maximum.  This is not expected to happen in real life but is
        possible to occur.

   25   SILC_STATUS_ERR_NOT_ON_CHANNEL

        "You are not on that channel".  The command were specified for
        channel user is not currently on.

   26   SILC_STATUS_ERR_USER_NOT_ON_CHANNEL

        "They are not on channel".  The requested target client is not
        on requested channel.

   27   SILC_STATUS_ERR_USER_ON_CHANNEL

        "User already on channel".  User were invited on channel they
        already are on.

   28   SILC_STATUS_ERR_NOT_REGISTERED

        "You have not registered".  User executed command that requires
        the client to be registered on the server before it may be
        executed.

   29   SILC_STATUS_ERR_NOT_ENOUGH_PARAMS

        "Not enough parameters".  Command requires more parameters
        than provided.

   30   SILC_STATUS_ERR_TOO_MANY_PARAMS

        "Too many parameters".  Too many parameters were provided
        for the command.

   31   SILC_STATUS_ERR_PERM_DENIED

        "Your host is not among the privileged".  The client tried to
        register on server that does not allow this host to connect.

   32   SILC_STATUS_ERR_BANNED_FROM_SERVER

        "You are banned from this server".  The client tried to register
        on server that has explicitly denied this host to connect.

   33   SILC_STATUS_ERR_BAD_PASSWORD

        "Cannot join channel. Incorrect password".  Password provided for 
        channel were not accepted.

   34   SILC_STATUS_ERR_CHANNEL_IS_FULL

        "Cannot join channel. Channel is full".  The channel is full
        and client cannot be joined to it.

   35   SILC_STATUS_ERR_NOT_INVITED

        "Cannot join channel. You have not been invited".  The channel
        is invite only channel and client has not been invited.

   36   SILC_STATUS_ERR_BANNED_FROM_CHANNEL

        "Cannot join channel. You have been banned".  The client has
        been banned from the channel.

   37   SILC_STATUS_ERR_UNKNOWN_MODE

        "Unknown mode".  Mode provided by the client were unknown to
        the server.

   38   SILC_STATUS_ERR_NOT_YOU

        "Cannot change mode for other users".  User tried to change
        someone else's mode.

   39   SILC_STATUS_ERR_NO_CHANNEL_PRIV

        "Permission denied. You are not channel operator".  Command may 
        be executed only by channel operator.

   40   SILC_STATUS_ERR_NO_CHANNEL_FOPRIV

        "Permission denied. You are not channel founder".  Command may 
        be executed only by channel operator.

   41   SILC_STATUS_ERR_NO_SERVER_PRIV

        "Permission denied. You are not server operator".  Command may
        be executed only by server operator.

   42   SILC_STATUS_ERR_NO_ROUTER_PRIV

        "Permission denied. You are not SILC operator".  Command may be
        executed only by router (SILC) operator.

   43   SILC_STATUS_ERR_BAD_NICKNAME

        "Bad nickname".  Nickname requested contained illegal characters
        or were malformed.

   44   SILC_STATUS_ERR_BAD_CHANNEL

        "Bad channel name".  Channel requested contained illegal characters
        or were malformed.

   45   SILC_STATUS_ERR_AUTH_FAILED

        "Authentication failed".  The authentication data sent as 
        argument were wrong and thus authentication failed.

   46   SILC_STATUS_ERR_UNKOWN_ALGORITHM

        "The algorithm was not supported."  The server does not support the
        requested algorithm.
.in 3


.ti 0
6 Security Considerations

Security is central to the design of this protocol, and these security
considerations permeate the specification.  Common security considerations
such as keeping private keys truly private and using adequate lengths for
symmetric and asymmetric keys must be followed in order to maintain the
security of this protocol.


.ti 0
7 References

[SILC2]      Riikonen, P., "SILC Packet Protocol", Internet Draft,
             June 2000.

[SILC3]      Riikonen, P., "SILC Key Exchange and Authentication 
             Protocols", Internet Draft, June 2000.

[IRC]        Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
             RFC 1459, May 1993.

[IRC-ARCH]   Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
             April 2000.

[IRC-CHAN]   Kalt, C., "Internet Relay Chat: Channel Management", RFC
             2811, April 2000.

[IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
             2812, April 2000.

[IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
             2813, April 2000.

[SSH-TRANS]  Ylonen, T., et al, "SSH Transport Layer Protocol", 
             Internet Draft.

[PGP]        Callas, J., et al, "OpenPGP Message Format", RFC 2440,
             November 1998.

[SPKI]       Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
             September 1999.

[PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key 
             Infrastructure, Certificate and CRL Profile", RFC 2459,
             January 1999.

[Schneier]   Schneier, B., "Applied Cryptography Second Edition",
             John Wiley & Sons, New York, NY, 1996.

[Menezes]    Menezes, A., et al, "Handbook of Applied Cryptography",
             CRC Press 1997.

[OAKLEY]     Orman, H., "The OAKLEY Key Determination Protocol",
             RFC 2412, November 1998.

[ISAKMP]     Maughan D., et al, "Internet Security Association and
             Key Management Protocol (ISAKMP)", RFC 2408, November
             1998.

[IKE]        Harkins D., and Carrel D., "The Internet Key Exchange
             (IKE)", RFC 2409, November 1998.

[HMAC]       Krawczyk, H., "HMAC: Keyed-Hashing for Message
             Authentication", RFC 2104, February 1997.

[PKCS1]      Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
             Specifications, Version 2.0", RFC 2437, October 1998.


.ti 0
8 Author's Address

.nf
Pekka Riikonen
Kasarmikatu 11 A4
70110 Kuopio
Finland

EMail: priikone@poseidon.pspt.fi

This Internet-Draft expires 6 Jun 2001