[silc.git] / public_html / docs / draft-riikonen-silc-spec-00.txt

Network Working Group                                      P. Riikonen
Internet-Draft
draft-riikonen-silc-spec-00.txt                           28 June 2000
Expires: 28 Jan 2001


                 Secure Internet Live Conferencing (SILC),
                          Protocol Specification

Status of this Memo

   This document is an Internet-Draft.  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
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   as reference material or to cite them other than as
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   ftp.isi.edu (US West Coast).

   The distribution of this memo is unlimited.


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].










Riikonen                                                        [Page 1]
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Table of Contents

   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
   3 SILC Specification ............................................  7
     3.1 Client ....................................................  7
         3.1.1 Client ID ...........................................  8
     3.2 Server ....................................................  8
         3.2.1 Server's Local ID List ..............................  9
         3.2.2 Server ID ........................................... 10
         3.2.3 SILC Server Ports ................................... 10
     3.3 Router .................................................... 11
         3.3.1 Router's Local ID List .............................. 11
         3.3.2 Router's Global ID List ............................. 12
         3.3.3 Router's Server ID .................................. 12
     3.4 Channels .................................................. 12
         3.4.1 Channel ID .......................................... 13
     3.5 Operators ................................................. 14
     3.6 SILC Commands ............................................. 14
     3.7 SILC Packets .............................................. 15
     3.8 Packet Encryption ......................................... 15
         3.8.1 Determination of the Source and the Destination ..... 16
         3.8.2 Client To Client .................................... 16
         3.8.3 Client To Channel ................................... 17
         3.8.4 Server To Server .................................... 18
     3.9 Key Exchange And Authentication ........................... 18
     3.10 Algorithms ............................................... 19
         3.10.1 Ciphers ............................................ 19
         3.10.2 Public Key Algorithms .............................. 20
         3.10.3 MAC Algorithms ..................................... 20
         3.10.4 Compression Algorithms ............................. 20
     3.11 SILC Public Key .......................................... 21
   4 SILC Procedures ............................................... 23
     4.1 Creating Client Connection ................................ 23
     4.2 Creating Server Connection ................................ 24
     4.3 Joining to a Channel ...................................... 25
     4.4 Channel Key Generation .................................... 26
     4.5 Private Message Sending and Reception ..................... 27
     4.6 Private Message Key Generation ............................ 27
     4.7 Channel Message Sending and Reception ..................... 28
     4.8 Session Key Regeneration .................................. 28
     4.9 Command Sending and Reception ............................. 29
   5 SILC Commands ................................................. 29
     5.1 SILC Commands Syntax ...................................... 29



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     5.2 SILC Commands List ........................................ 31
     5.3 SILC Command Status Types ................................. 54
         5.3.1 SILC Command Status Payload ......................... 54
         5.3.2 SILC Command Status List ............................ 54
   6 Security Considerations ....................................... 58
   7 References .................................................... 59
   8 Author's Address .............................................. 60


List of Figures

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


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.


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 centrum on the cell and servers are connected to the router.
   Following diagram represents SILC network topology.


          ---- ---- ----         ---- ---- ----
         | 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 ...
            ---- ---- ----         ---- ---- ----



Riikonen                                                        [Page 4]
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               Cell 3.                Cell 5.

                     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.


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.


                         1 --- S1     S4 --- 5
                                  S/R
                          2 -- S2     S3
                              /        |
                             4         3


                   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.



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             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.


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.


                1 --- S1     S4 --- 5            S2 --- 1
                         S/R - - - - - - - - S/R
                 2 -- S2     S3           S1
                     /        |             \
                    4         3              2

                   Cell 1.               Cell 2.


                  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.







Riikonen                                                        [Page 6]
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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.


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.


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.  Another difference is that there are no limit of the length



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   of the nickname in the SILC.


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.
   Collisions are not expected to happen.  The Client ID is defined as
   follows.

      128 bit Client ID based on IPv4 addresses:

      32 bit  ServerID IP address (bits 1-32)
       8 bit  Random number
      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 - Random number to further unify the
        Client ID.  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.

   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.


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 focuses on the normal server and router server is described



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   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.


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:

      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





Riikonen                                                        [Page 9]
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      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



3.2.2 Server ID

   Servers are distinguished from other servers by unique 64 bit Server ID.
   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.

      64 bit Server ID based on IPv4 addresses:

      32 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 binded to.

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

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


3.2.3 SILC Server Ports

   SILC uses currently TCP port 334 on SILC network.  However, this is not
   official port assigned for SILC.  Official port has been requested by
   the IANA.

   If there are needs to create new SILC networks in the future the port
   numbers must be officially assigned by the IANA.  Most convenience case
   would be to assign port numbers upwards from 334.

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





Riikonen                                                       [Page 10]
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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.


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:

      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


   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



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   List.


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:

      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


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.


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



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   exist when the last client leaves 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.  Channel name
   is a string which begins with `#' character.  There is no limit on the
   length of the channel name.  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.

      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.


3.4.1 Channel ID

   Channels are distinguished from other channels by unique Channel ID.
   The Channel ID is a 64 bit ID 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.




Riikonen                                                       [Page 13]
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      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

      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 unify the Channel ID.  This makes
        sure that there are no collisions.  This also means that
        in a cell there can be 2^16 channels.


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.


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 not to accept the command reply, but there are some



Riikonen                                                       [Page 14]
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   command replies that the client should accept.  Example of a such
   command reply is reply to SILC_COMMAND_CMODE command that the server
   uses to distribute the channel mode on all clients on the channel
   when the mode has changed.

   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.


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.


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



Riikonen                                                       [Page 15]
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   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.


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.


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



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     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.


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].


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



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   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].


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.


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:

      blowfish-cbc    Blowfish in CBC mode  (mandatory)
      twofish-cbc     Twofish in CBC mode   (optional)
      rc6-cbc         RC6 in CBC mode       (optional)
      rc5-cbc         RC5 in CBC mode       (optional)
      mars-cbc        Mars in CBC mode      (optional)
      none            No encryption         (optional)


   All algorithms must use minimum of 128 bit key, by default.  Several
   algorithms, however, supports longer keys and it is recommended to use
   longer keys if they are available.

   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.








Riikonen                                                       [Page 19]
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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:

      rsa        RSA  (mandatory)
      dss        DSS  (optional)

   Both of the algorithms are described in [Scheneir] and [Menezes].

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


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:

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

   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.


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.




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   Following compression algorithms are defined:

      none        No compression               (mandatory)
      zlib        GBU ZLIB (LZ77) compression  (optional)

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


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:


                          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                         ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 4:  SILC Public Key


      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



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        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:




Riikonen                                                       [Page 22]
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           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.

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


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].


4.1 Creating Client Connection

   This section descibres 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 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.




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   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].


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



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   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.


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 new channel key is
   also distributed to the router and to all clients on the channel.

   If the channel does not exist in the local list the 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 distributed to the client who sent the command
   originally.  Server will also receive the channel key from the server
   that it must distribute to the client who originally requested the
   join command.  The server must also save the channel key.




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   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.

   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.

   When the router joins the client to the channel it must send
   information about newly joined client to all routers in the SILC
   network.  Also, if the channel was created in the process, information
   about newly created channel must also be distributed to all routers.
   The distribution of newly created channel is done by sending packet
   SILC_PACKET_NEW_CHANNEL.

   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.
   However, client must not start communicating on the channel before
   it has received the packet SILC_PACKET_CHANNEL_KEY.

   If client wants to know the other clients currently on the channel
   the client must send SILC_COMMAND_NAMES command to receive a list of
   channel users.  Server implementation, however, may send command reply
   packet to SILC_COMMAND_NAMES command after client has joined to the
   channel even if the client has not sent the command.


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.



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   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 leaved 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.


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 ipmlementations
   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 describtion of private message encryption and decryption
   process.


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



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   is used in the private message communication between those clients.
   See more information about how this works technically in [SILC2].

   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.  This
   is the technical aspect mentioned previously that is described
   in [SILC2].

   If the private message keys are not set to be used, which is the
   case by default in SILC, the private messages are secured by using
   normal session keys established by SILC Key Exchange protocol.


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 describtion of channel message encryption and decryption
   process.


4.8 Session Key Regeneration

   Session keys should be regenerated peridiocally, 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



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   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.


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 usually
   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
   to 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.


5 SILC Commands

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.



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   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.

      Example:  Arguments:  (1) <nickname> (2) <username@host>


   Every command replies with Status Payload.  This payload tells the
   sender of the command whether the command was completed succefully 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:

      EXAMPLE_COMMAND

        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, regardles of the ordering of the arguments in
        the Command Payload.







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        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.


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.

   0    SILC_COMMAND_NONE

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


   2    SILC_COMMAND_WHOIS

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

        Whois.  Whois command is used to query various information about



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        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.  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 forwarded to router by server
        so that all users are searched.  However, the server still must
        search its locally connected clients.  The server must send
        this command to the server who owns the requested client.  That
        server must reply to the command.

        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 hostnamea 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_WILDCARDS



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            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS


   3    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 forwarded to 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



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            SILC_STATUS_ERR_WILDCARDS
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS


   4    SILC_COMMAND_IDENTIFY

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

        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.

        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
        commands as it is hardly a command that would be used a end user.
        However, it must be implemented as it is used with private message
        sending.

        The IDENTIFY must be always forwarded to 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.




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        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_WILDCARDS
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS


   5    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.

        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



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   6    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:  3
            Arguments:  (1) <Status Payload>  (2) <channel>
                        (3) <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 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









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   7    SILC_COMMAND_TOPIC

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

        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) [<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


   8    SILC_COMMAND_INVITE

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

        This command is used to invite other clients to join to the
        channel.  There is no requirement that the channel the target
        client is being invited to must exist or be a valid channel.
        The <Client ID> argument is the target client's ID that is being
        invited.

        Reply messages to the command:





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

        This command replies only with Status Payload.

        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_CLIENT_ID
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NO_RECIPIENT
            SILC_STATUS_ERR_USER_ON_CHANNEL
            SILC_STATUS_ERR_NO_CLIENT_ID


   9    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.


   10   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:




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        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


   11   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_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NO_SUCH_SERVER_ID
            SILC_STATUS_ERR_NO_SUCH_SERVER









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   12   SILC_COMMAND_CONNECT

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

        This command is used by operators to force a server to try to
        establish a new connection to another router (if the connecting
        server is normal server) or server (if the conneceting server is
        router server).  Operator may specify the server/router to be
        connected by setting <remote server> argument.

        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_SERVER_ID
            SILC_STATUS_ERR_NO_SERVER_PRIV
            SILC_STATUS_ERR_NO_ROUTER_PRIV


   13   SILC_COMMAND_PING

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

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



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        Status messages:

            SILC_STATUS_OK
            SILC_STATUS_ERR_NOT_ENOUGH_PARAMS
            SILC_STATUS_ERR_TOO_MANY_PARAMS
            SILC_STATUS_ERR_NO_SUCH_SERVER_ID
            SILC_STATUS_ERR_NOT_REGISTERED


   14   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









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   15   SILC_COMMAND_JOIN

        Max Arguments:  3
            Arguments:  (1) <channel>  (2) [<passphrase>]
                        (3) [<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 on the server receiving the join request.  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.

        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:  5
            Arguments:  (1) <Status Payload>  (2) <channel>
                        (3) <Channel ID>      (4) <channel mode mask>
                        (5) [<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



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        channel is created the mode mask is zero (0).

        Client must not start transmitting to the channel even after
        server has replied to this command.  Client is permitted to
        start transmitting on channel after server has sent packet
        SILC_PACKET_CHANNEL_KEY to the client.

        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


   16   SILC_COMMAND_MOTD

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

        This command is used to query the Message of the Day of a 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








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   17   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.





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        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


   18   SILC_COMMAND_CMODE

        Max Arguments:  6
            Arguments:  (1) <Channel ID>    (2) <channel mode mask>
                        (3) [<user limit>]  (4) [<passphrase>]
                        (5) [<Client ID>]   (6) [<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.

        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 indicatioin 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.




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              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
              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.





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           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.





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           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.

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


           0x0100    SILC_CMODE_OPERATOR

              Sets channel operator privileges on the channel for a
              client on the channel.  The <Client ID> argument is the
              target client on the channel.  Channel founder and
              channel operator may set/unset (promote/demote) this
              mode.

              Typical implementation would use [+|-]o 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.

              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 server distributes the changed channel mode mask to
        all clients on the channel by sending SILC_COMMAND_CMODE command
        reply packet.





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        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.  The same mask is also
        sent to all clients on channel by sending additional command
        reply to them.

        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_CLIENT_ID


   19   SILC_COMMAND_KICK

        Max Arguments:  3
            Arguments:  (1) <channel>  (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



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            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:  1
            Arguments:  (1) <Server ID>

        This command is used only by operator to close connection to a
        remote site.  The <Server ID> argument is the ID of the remote
        site and must be valid.

        Reply messages to the command:

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

        This command replies only with Status Payload.






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        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_DIE

        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



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        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



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            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_NAMES

        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.

        Reply messages to the command:

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

        This command replies with the comma separated list of users on
        the channel.

        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 - 254

        Currently undefined commands.





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   255  SILC_COMMAND_MAX

        Reserved command.  This must not be sent.


5.3 SILC Command Status Types

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).


                                          1
                      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     |        Status Message         |
                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 5:  SILC Command Status Payload


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


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.

   Generic status messages:

   0    SILC_STATUS_OK

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




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   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_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
        beloning to this list after this one.

   3 - 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.






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   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_BAD_CLIENT_ID

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

   20   SILC_STATUS_ERR_BAD_CHANNEL_ID

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

   21   SILC_STATUS_ERR_NO_SUCH_CLIENT_ID

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


   22   SILC_STATUS_ERR_NO_SUCH_CHANNEL_ID

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

   23   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.

   24   SILC_STATUS_ERR_NOT_ON_CHANNEL

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

   25   SILC_STATUS_ERR_USER_ON_CHANNEL

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



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   26   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.

   27   SILC_STATUS_ERR_NOT_ENOUGH_PARAMS

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

   28   SILC_STATUS_ERR_TOO_MANY_PARAMS

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

   29   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.

   30   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.

   31   SILC_STATUS_ERR_BAD_PASSWORD

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

   32   SILC_STATUS_ERR_CHANNEL_IS_FULL

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

   33   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.

   34   SILC_STATUS_ERR_BANNED_FROM_CHANNEL

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






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   35   SILC_STATUS_ERR_UNKNOWN_MODE

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

   36   SILC_STATUS_ERR_NOT_YOU

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

   37   SILC_STATUS_ERR_NO_CHANNEL_PRIV

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

   38   SILC_STATUS_ERR_NO_SERVER_PRIV

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

   39   SILC_STATUS_ERR_NO_ROUTER_PRIV

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

   40   SILC_STATUS_ERR_BAD_NICKNAME

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

   41   SILC_STATUS_ERR_BAD_CHANNEL

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

   42   SILC_STATUS_ERR_AUTH_FAILED

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


6 Security Considerations

   Security is central to the design of this protocol, and these security
   considerations permeate the specification.






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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.

   [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 Exhange
                (IKE)", RFC 2409, November 1998.

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









Riikonen                                                       [Page 59]
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8 Author's Address

   Pekka Riikonen
   Kasarmikatu 11 A4
   70110 Kuopio
   Finland

   EMail: priikone@poseidon.pspt.fi











































Riikonen                                                       [Page 60]
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