+++ /dev/null
-.pl 10.0i
-.po 0
-.ll 7.2i
-.lt 7.2i
-.nr LL 7.2i
-.nr LT 7.2i
-.ds LF Riikonen
-.ds RF FORMFEED[Page %]
-.ds CF
-.ds LH Internet Draft
-.ds RH 21 August 2001
-.ds CH
-.na
-.hy 0
-.in 0
-.nf
-Network Working Group P. Riikonen
-Internet-Draft
-draft-riikonen-silc-spec-03.txt 21 August 2001
-Expires: 21 February 2002
-
-.in 3
-
-.ce 3
-Secure Internet Live Conferencing (SILC),
-Protocol Specification
-<draft-riikonen-silc-spec-03.txt>
-
-.ti 0
-Status of this Memo
-
-This document is an Internet-Draft and is in full conformance with
-all provisions of Section 10 of RFC 2026. Internet-Drafts are
-working documents of the Internet Engineering Task Force (IETF), its
-areas, and its working groups. Note that other groups may also
-distribute working documents as Internet-Drafts.
-
-Internet-Drafts are draft documents valid for a maximum of six months
-and may be updated, replaced, or obsoleted by other documents at any
-time. It is inappropriate to use Internet-Drafts as reference
-material or to cite them other than as "work in progress."
-
-The list of current Internet-Drafts can be accessed at
-http://www.ietf.org/ietf/1id-abstracts.txt
-
-The list of Internet-Draft Shadow Directories can be accessed at
-http://www.ietf.org/shadow.html
-
-The distribution of this memo is unlimited.
-
-
-.ti 0
-Abstract
-
-This memo describes a Secure Internet Live Conferencing (SILC)
-protocol which provides secure conferencing services over insecure
-network channel. SILC is IRC [IRC] like protocol, however, it is
-not equivalent to IRC and does not support IRC. Strong cryptographic
-methods are used to protect SILC packets inside the SILC network.
-Three other Internet Drafts relates very closely to this memo;
-SILC Packet Protocol [SILC2], SILC Key Exchange and Authentication
-Protocols [SILC3] and SILC Commands [SILC4].
-
-
-
-
-
-
-.ti 0
-Table of Contents
-
-.nf
-1 Introduction .................................................. 3
- 1.1 Requirements Terminology .................................. 4
-2 SILC Concepts ................................................. 4
- 2.1 SILC Network Topology ..................................... 4
- 2.2 Communication Inside a Cell ............................... 5
- 2.3 Communication in the Network .............................. 6
- 2.4 Channel Communication ..................................... 7
- 2.5 Router Connections ........................................ 7
- 2.6 Backup Routers ............................................ 8
-3 SILC Specification ............................................ 10
- 3.1 Client .................................................... 10
- 3.1.1 Client ID ........................................... 10
- 3.2 Server .................................................... 11
- 3.2.1 Server's Local ID List .............................. 12
- 3.2.2 Server ID ........................................... 13
- 3.2.3 SILC Server Ports ................................... 14
- 3.3 Router .................................................... 14
- 3.3.1 Router's Local ID List .............................. 14
- 3.3.2 Router's Global ID List ............................. 15
- 3.3.3 Router's Server ID .................................. 15
- 3.4 Channels .................................................. 16
- 3.4.1 Channel ID .......................................... 17
- 3.5 Operators ................................................. 17
- 3.6 SILC Commands ............................................. 18
- 3.7 SILC Packets .............................................. 18
- 3.8 Packet Encryption ......................................... 19
- 3.8.1 Determination of the Source and the Destination ..... 19
- 3.8.2 Client To Client .................................... 20
- 3.8.3 Client To Channel ................................... 21
- 3.8.4 Server To Server .................................... 22
- 3.9 Key Exchange And Authentication ........................... 22
- 3.9.1 Authentication Payload .............................. 22
- 3.10 Algorithms ............................................... 24
- 3.10.1 Ciphers ............................................ 24
- 3.10.2 Public Key Algorithms .............................. 25
- 3.10.3 Hash Functions ..................................... 26
- 3.10.4 MAC Algorithms ..................................... 26
- 3.10.5 Compression Algorithms ............................. 26
- 3.11 SILC Public Key .......................................... 27
- 3.12 SILC Version Detection ................................... 29
-4 SILC Procedures ............................................... 30
- 4.1 Creating Client Connection ................................ 30
- 4.2 Creating Server Connection ................................ 31
- 4.2.1 Announcing Clients, Channels and Servers ............ 32
- 4.3 Joining to a Channel ...................................... 33
- 4.4 Channel Key Generation .................................... 34
- 4.5 Private Message Sending and Reception ..................... 34
- 4.6 Private Message Key Generation ............................ 35
- 4.7 Channel Message Sending and Reception ..................... 35
- 4.8 Session Key Regeneration .................................. 36
- 4.9 Command Sending and Reception ............................. 37
- 4.10 Closing Connection ....................................... 37
-5 Security Considerations ....................................... 38
-6 References .................................................... 38
-7 Author's Address .............................................. 40
-
-
-
-.ti 0
-List of Figures
-
-.nf
-Figure 1: SILC Network Topology
-Figure 2: Communication Inside cell
-Figure 3: Communication Between Cells
-Figure 4: Router Connections
-Figure 5: SILC Public Key
-
-
-.ti 0
-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
-the SILC network. Three other Internet Drafts relates very closely
-to this memo; SILC Packet Protocol [SILC2], SILC Key Exchange and
-Authentication Protocols [SILC3] and SILC Commands [SILC4].
-
-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.
-
-
-.ti 0
-1.1 Requirements Terminology
-
-The keywords MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED,
-MAY, and OPTIONAL, when they appear in this document, are to be
-interpreted as described in [RFC2119].
-
-
-.ti 0
-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.
-
-
-.ti 0
-2.1 SILC Network Topology
-
-SILC network is a cellular network as opposed to tree style network
-topology. The rationale for this is to have servers that can perform
-specific kind of tasks what other servers cannot perform. This leads
-to two kinds of servers; normal SILC servers and SILC routers.
-
-A difference between normal server and router server is that routers
-knows everything about everything in the network. They also do the
-actual routing of the messages to the correct receiver. Normal servers
-knows only about local information and nothing about global information.
-This makes the network faster as there are less servers that needs to
-keep global information up to date at all time.
-
-This, on the other hand, leads to cellular like network, where routers
-are in the center of the cell and servers are connected to the router.
-
-
-
-
-
-
-
-The following diagram represents SILC network topology.
-
-.in 8
-.nf
- ---- ---- ---- ---- ---- ----
- | S8 | S5 | S4 | | S7 | S5 | S6 |
- ----- ---- ----- ----- ---- -----
-| S7 | S/R1 | S2 | --- | S8 | S/R2 | S4 |
- ---- ------ ---- ---- ------ ----
- | S6 | S3 | S1 | | S1 | S3 | S2 | ---- ----
- ---- ---- ---- ---- ---- ---- | S3 | S1 |
- Cell 1. \\ Cell 2. | \\____ ----- -----
- | | | S4 | S/R4 |
- ---- ---- ---- ---- ---- ---- ---- ------
- | S7 | S4 | S2 | | S1 | S3 | S2 | | S2 | S5 |
- ----- ---- ----- ----- ---- ----- ---- ----
- | S6 | S/R3 | S1 | --- | S4 | S/R5 | S5 | ____/ Cell 4.
- ---- ------ ---- ---- ------ ----
- | S8 | S5 | S3 | | S6 | S7 | S8 | ... etc ...
- ---- ---- ---- ---- ---- ----
- Cell 3. Cell 5.
-.in 3
-
-.ce
-Figure 1: SILC Network Topology
-
-
-A cell is formed when a server or servers connect to one router. In
-SILC network normal server cannot directly connect to other normal
-server. Normal server may only connect to SILC router which then
-routes the messages to the other servers in the cell. Router servers
-on the other hand may connect to other routers to form the actual SILC
-network, as seen in above figure. However, router is also normal SILC
-server; clients may connect to it the same way as to normal SILC
-server. 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 may be written.
-
-
-.ti 0
-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. A client which 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.
-
-The following diagram represents this scenario:
-
-
-.in 25
-.nf
-1 --- S1 S4 --- 5
- S/R
- 2 -- S2 S3
- / |
- 4 3
-.in 3
-
-
-.ce
-Figure 2: Communication Inside cell
-
-
-Example: Client 1. connected to Server 1. send message to
- Client 4. connected to Server 2. travels from Server 1.
- first to Router which routes the message to Server 2.
- which then sends it to the Client 4. All the other
- servers in the cell will not see the routed message.
-
-
-If the 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.
-
-
-.ti 0
-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. The following diagram
-represents message sending between cells.
-
-
-.in 16
-.nf
-1 --- S1 S4 --- 5 S2 --- 1
- S/R - - - - - - - - S/R
- 2 -- S2 S3 S1
- / | \\
- 4 3 2
-
- Cell 1. Cell 2.
-.in 3
-
-
-.ce
-Figure 3: Communication Between Cells
-
-
-Example: Client 5. connected to Server 4. in Cell 1. sends message
- 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 the client point of view is
-when clients are connected directly to the routers and the messages
-are delivered from one router to the other.
-
-
-.ti 0
-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 which are
-joined to the channel. Router also distributes the message to its
-local clients on the channel.
-
-
-.ti 0
-2.5 Router Connections
-
-Router connections play very important role in making the SILC like
-network topology to work. For example, sending broadcast packets in
-SILC network require special connections between routers; routers must
-be connected in a specific way.
-
-Every router has their primary route which is a connection to another
-router in the network. Unless there is only two routers in the network
-must not routers use each other as their primary routes. The router
-connections in the network must form a circular.
-
-
-
-
-
-
-
-Example with three routers in the network:
-
-
-.in 16
-.nf
- S/R1 - > - > - > - > - > - > - S/R2
- \\ /
- ^ v
- \\ - < - < - S/R3 - < - < - /
-.in 3
-
-
-.ce
-Figure 4: Router Connections
-
-
-Example: Network with three routers. Router 1. uses Router 2. as its
- primary router. Router 2. uses Router 3. as its primary router,
- and Router 3. uses Router 1. as its primary router. There may
- be other direct connections between the routers but they must
- not be used as primary routes.
-
-The above example is applicable to any amount of routers in the network
-except for two routers. If there are only two routers in the network both
-routers must be able to handle situation where they use each other as their
-primary routes.
-
-The issue of router connections are very important especially with SILC
-broadcast packets. Usually all router wide information in the network is
-distributed by SILC broadcast packets.
-
-
-.ti 0
-2.6 Backup Routers
-
-Backup routers may exist in the cell in addition of the primary router.
-However, they must not be active routers and act as routers in the cell.
-Only one router may be acting as primary router in the cell. In the case
-of failure of the primary router may one of the backup routers become
-active. The purpose of backup routers are in case of failure of the
-primary router to maintain working connections inside the cell and outside
-the cell and to avoid netsplits.
-
-Backup routers are normal servers in the cell that are prepared to take
-over the tasks of the primary router if needed. They need to have at
-least one direct and active connection to the primary router of the cell.
-This communication channel is used to send the router information to
-the backup router.
-
-Backup router must know everything that the primary router knows to be
-able to take over the tasks of the primary router. It is the primary
-router's responsibility to feed the data to the backup router. If the
-backup router does not know all the data in the case of failure some
-connections may be lost. The primary router of the cell must consider
-the backup router being normal router server and feed the data
-accordingly.
-
-In addition of having direct connection to the primary router of the
-cell the backup router must also have connection to the same router
-the primary router of the cell is connected. However, it must not be
-active router connection meaning that the backup router must not use
-that channel as its primary route and it must not notify the router
-about having connected servers, channels and clients behind it. It
-merely connects to the router. This sort of connection is later
-referred as being passive connection. Some keepalive actions may be
-needed by the router to keep the connection alive.
-
-The primary router notifies its primary router about having backup
-routers in the cell by sending SILC_PACKET_CELL_ROUTERS packet. If
-and when the primary router of the cell becomes unresponsive, its
-primary router knows that there exists backup routers in the cell.
-After that it will start using the first backup router sent in the
-packet as router of that cell.
-
-In this case the backup router must notify its new primary router about
-the servers, channels and clients it has connected to it. The primary
-router knows that this server has become a router of the cell because
-of failure of the primary router in the cell. It must also cope with
-the fact that the servers, channels and clients that the new backup
-router announces are not really new, since they used to exist in the
-primary router of the cell.
-
-It is required that other normal servers has passive connections to
-the backup router(s) in the cell. Some keepalive actions may be needed
-by the server to keep the connection alive. After they notice the
-failure of the primary router they must start using the connection to
-the first backup router as their primary route.
-
-It is RECOMMENDED that there would be at least one backup router in
-the cell. It is NOT RECOMMENDED to have all servers in the cell acting
-as backup routers as it requires establishing several connections to
-several servers in the cell. Large cells can easily have several
-backup routers in the cell.
-
-The order of the backup routers are decided at the primary router of the
-cell and servers and backup routers in the cell must be configured
-accordingly. It is not required that the backup server is actually
-active server in the cell. Backup router may be a spare server in the
-cell that does not accept normal client connections at all. It may be
-reserved purely for the backup purposes. These, however, are cell
-management issues.
-
-If also the first backup router is down as well and there is another
-backup router in the cell then it will start acting as the primary
-router as described above.
-
-
-.ti 0
-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.
-
-
-.ti 0
-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 host name 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 or client's host names
-to be used along with the nicknames to identify specific users when sending
-messages. This feature of SILC makes IRC style nickname-wars obsolete as
-no one owns their nickname; there can always be someone else with the same
-nickname. The maximum length of nickname is 128 characters.
-
-
-.ti 0
-3.1.1 Client ID
-
-Client ID is used to identify users in the SILC network. The Client ID
-is unique to the extent that there can be 2^128 different Client ID's,
-and ID's based on IPv6 addresses extends this to 2^224 different Client
-ID's. Collisions are not expected to happen. The Client ID is defined
-as follows.
-
-
-
-.in 6
-128 bit Client ID based on IPv4 addresses:
-
-32 bit Server ID IP address (bits 1-32)
- 8 bit Random number or counter
-88 bit Truncated MD5 hash value of the nickname
-
-224 bit Client ID based on IPv6 addresses:
-
-128 bit Server ID IP address (bits 1-128)
- 8 bit Random number or counter
- 88 bit Truncated MD5 hash value of the nickname
-
-o Server ID IP address - Indicates the server where this
- client is coming from. The IP address hence equals the
- server IP address where to the client has connected.
-
-o Random number or counter - Random number to further
- randomize the Client ID. Another choice is to use
- a counter starting from the zero (0). This makes it
- possible to have 2^8 same nicknames from the same
- server IP address.
-
-o MD5 hash - MD5 hash value of the nickname is truncated
- taking 88 bits from the start of the hash value. This
- hash value is used to search the user's Client ID from
- the ID lists.
-
-.in 3
-Collisions could occur when more than 2^8 clients using same nickname
-from the same server IP address is connected to the SILC network.
-Server MUST be able to handle this situation by refusing to accept
-anymore of that nickname.
-
-Another possible collision may happen with the truncated hash value of
-the nickname. It could be possible to have same truncated hash value for
-two different nicknames. However, this is not expected to happen nor
-cause any problems if it would occur. Nicknames are usually logical and
-it is unlikely to have two distinct logical nicknames produce same
-truncated hash value.
-
-
-.ti 0
-3.2 Server
-
-Servers are the most important parts of the SILC network. They form the
-basis of the SILC, providing a point to which clients may connect to.
-There are two kinds of servers in SILC; normal servers and router servers.
-This section focus on the normal server and router server is described
-in the section 3.3 Router.
-
-Normal servers MUST 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 MUST 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.
-
-
-.ti 0
-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 host names and
-user's real name. Normal servers only keeps local information and it
-does not keep any global information. Hence, normal servers knows only
-about their locally connected clients. This makes servers efficient as
-they don't have to worry about global clients. Server is also responsible
-of creating the Client ID's for their clients.
-
-Normal server also keeps information about locally created channels and
-their Channel ID's.
-
-
-Hence, local list for normal server includes:
-
-.in 6
-server list - Router connection
- o Server name
- o Server IP address
- o Server ID
- o Sending key
- o Receiving key
- o Public key
-
-client list - All clients in server
- o Nickname
- o Username@host
- o Real name
- o Client ID
- o Sending key
- o Receiving key
- o Public key
-
-
-channel list - All channels in server
- o Channel name
- o Channel ID
- o Client ID's on channel
- o Client ID modes on channel
- o Channel key
-.in 3
-
-
-.ti 0
-3.2.2 Server ID
-
-Servers are distinguished from other servers by unique 64 bit Server ID
-(for IPv4) or 160 bit Server ID (for IPv6). The Server ID is used in
-the SILC to route messages to correct servers. Server ID's also provide
-information for Client ID's, see section 3.1.1 Client ID. Server ID is
-defined as follows.
-
-.in 6
-64 bit Server ID based on IPv4 addresses:
-
-32 bit IP address of the server
-16 bit Port
-16 bit Random number
-
-160 bit Server ID based on IPv6 addresses:
-
-128 bit IP address of the server
- 16 bit Port
- 16 bit Random number
-
-o IP address of the server - This is the real IP address of
- the server.
-
-o Port - This is the port the server is bound to.
-
-o Random number - This is used to further randomize the Server ID.
-
-.in 3
-Collisions are not expected to happen in any conditions. The Server ID
-is always created by the server itself and server is responsible of
-distributing it to the router.
-
-
-.ti 0
-3.2.3 SILC Server Ports
-
-The following ports has been assigned by IANA for the SILC protocol:
-
-.in 10
-silc 706/tcp SILC
-silc 706/udp SILC
-.in 3
-
-
-If there are needs to create new SILC networks in the future the port
-numbers must be officially assigned by the IANA.
-
-Server on network above privileged ports (>1023) SHOULD NOT be trusted
-as they could have been set up by untrusted party.
-
-
-.ti 0
-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.
-
-
-.ti 0
-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 need
-to keep information about user's nickname, username and host name and real
-name since these are not needed by the router. The router keeps only
-information that it needs.
-
-
-Hence, local list for router includes:
-
-.in 6
-server list - All servers in the cell
- o Server name
- o Server ID
- o Router's Server ID
- o Sending key
- o Receiving key
-
-client list - All clients in the cell
- o Client ID
-
-
-channel list - All channels in the cell
- o Channel ID
- o Client ID's on channel
- o Client ID modes on channel
- o Channel key
-.in 3
-
-
-Note that locally connected clients and other information include all the
-same information as defined in section section 3.2.1 Server's Local ID
-List.
-
-
-.ti 0
-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 host names or user's real names. Router does not need to
-keep these informations as they are not needed by the router. This
-information is available from the client's server which maybe queried
-when needed.
-
-Hence, global list includes:
-
-.in 6
-server list - All servers in SILC
- o Server name
- o Server ID
- o Router's Server ID
-
-client list - All clients in SILC
- o Client ID
-
-channel list - All channels in SILC
- o Channel ID
- o Client ID's on channel
- o Client ID modes on channel
-.in 3
-
-
-
-
-
-
-
-
-.ti 0
-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.
-
-
-.ti 0
-3.4 Channels
-
-A channel is a named group of one or more clients which will all receive
-messages addressed to that channel. The channel is created when first
-client requests JOIN command to the channel, and the channel ceases to
-exist when the last client has left it. When channel exists, any client
-can reference it using the name of the channel.
-
-Channel names are unique although the real uniqueness comes from 64 bit
-Channel ID. However, channel names are still unique and no two global
-channels with same name may exist. The Channel name is a string of
-maximum length of 256 characters. Channel names MUST 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. The following operators on channel exist on
-the SILC network.
-
-.in 6
-o Channel founder - When channel is created the joining client becomes
- channel founder. Channel founder is channel operator with some more
- privileges. Basically, channel founder can fully operate the channel
- and all of its modes. The privileges are limited only to the
- particular channel. There can be only one channel founder per
- channel. Channel founder supersedes channel operator's privileges.
-
- Channel founder privileges cannot be removed by any other operator on
- channel. When channel founder leaves the channel there is no channel
- founder on the channel. However, it is possible to set a mode for
- the channel which allows the original channel founder to regain the
- founder privileges even after leaving the channel. Channel founder
- also cannot be removed by force from the channel.
-
-o Channel operator - When client joins to channel that has not existed
- previously it will become automatically channel operator (and channel
- founder discussed above). Channel operator is able administrate the
- channel, set some modes on channel, remove a badly behaving client
- from the channel and promote other clients to become channel
- operator. The privileges are limited only to the particular channel.
-
- Normal channel user may be promoted (opped) to channel operator
- gaining channel operator privileges. Channel founder or other
- channel operator may also demote (deop) channel operator to normal
- channel user.
-.in 3
-
-
-.ti 0
-3.4.1 Channel ID
-
-Channels are distinguished from other channels by unique Channel ID.
-The Channel ID is a 64 bit ID (for IPv4) or 160 bit ID (for IPv6), and
-collisions are not expected to happen in any conditions. Channel names
-are just for logical use of channels. The Channel ID is created by the
-server where the channel is created. The Channel ID is defined as
-follows.
-
-.in 6
-64 bit Channel ID based on IPv4 addresses:
-
-32 bit Router's Server ID IP address (bits 1-32)
-16 bit Router's Server ID port (bits 33-48)
-16 bit Random number
-
-160 bit Channel ID based on IPv6 addresses:
-
-128 bit Router's Server ID IP address (bits 1-128)
- 16 bit Router's Server ID port (bits 129-144)
- 16 bit Random number
-
-o Router's Server ID IP address - Indicates the IP address of
- the router of the cell where this channel is created. This is
- taken from the router's Server ID. This way SILC router knows
- where this channel resides in the SILC network.
-
-o Router's Server ID port - Indicates the port of the channel on
- the server. This is taken from the router's Server ID.
-
-o Random number - To further randomize the Channel ID. This makes
- sure that there are no collisions. This also means that
- in a cell there can be 2^16 channels.
-.in 3
-
-
-.ti 0
-3.5 Operators
-
-Operators are normal users with extra privileges to their server or
-router. Usually these people are SILC server and router administrators
-that take care of their own server and clients on them. The purpose of
-operators is to administrate the SILC server or router. However, even
-an operator with highest privileges is not able to enter invite-only
-channel, to gain access to the contents of a encrypted and authenticated
-packets traveling in the SILC network or to gain channel operator
-privileges on public channels without being promoted. They have the
-same privileges as everyone else except they are able to administrate
-their server or router.
-
-
-.ti 0
-3.6 SILC Commands
-
-Commands are very important part on SILC network especially for client
-which uses commands to operate on the SILC network. Commands are used
-to set nickname, join to channel, change modes and many other things.
-
-Client usually sends the commands and server replies by sending a reply
-packet to the command. Server MAY also send commands usually to serve
-the original client's request. However, server MUST NOT send commands
-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,
-choose to ignore the command reply.
-
-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. However, to keep response rate up, allowing for
-example five (5) commands before limiting is allowed. It is RECOMMENDED
-that commands such as SILC_COMMAND_NICK, SILC_COMMAND_JOIN,
-SILC_COMMAND_LEAVE and SILC_COMMAND_KILL SHOULD be limited in all cases
-as they require heavy operations. This should be sufficient to prevent
-the miss-use of commands.
-
-SILC commands are described in [SILC4].
-
-
-.ti 0
-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.
-
-
-
-
-
-.ti 0
-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 the 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 know the key for channel.
-
-Server shares secret symmetric session key with router which is
-established by the SILC Key Exchange Protocol. Every packet passed from
-server to router, with exception of packets for channels, are encrypted
-with the shared session key. Same way, router server shares secret
-symmetric key with its primary route. However, every packet passed
-from router to other router, including packets for channels, are
-encrypted with the shared session key. Every router connection has
-their own session keys.
-
-
-.ti 0
-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 MUST be 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 MUST 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 the case, for example, with command packets.
-
-
-.ti 0
-3.8.2 Client To Client
-
-The process of message delivery and encryption from client to another
-client is as follows.
-
-Example: Private message from client to another client on different
- servers. Clients do not share private message delivery
- keys; normal session keys are used.
-
-o Client 1. sends encrypted packet to its server. The packet is
- encrypted with the session key shared between client and its
- server.
-
-o Server determines the destination of the packet and decrypts
- the packet. Server encrypts the packet with session key shared
- between the server and its router, and sends the packet to the
- router.
-
-o Router determines the destination of the packet and decrypts
- the packet. Router encrypts the packet with session key
- shared between the router and the destination server, and sends
- the packet to the server.
-
-o Server determines the client to which the packet is destined
- to and decrypts the packet. Server encrypts the packet with
- session key shared between the server and the destination client,
- and sends the packet to the client.
-
-o Client 2. decrypts the packet.
-
-
-Example: Private message from client to another client on different
- servers. Clients has established secret shared private
- message delivery key with each other and that is used in
- the message encryption.
-
-o Client 1. sends encrypted packet to its server. The packet is
- encrypted with the private message delivery key shared between
- clients.
-
-o Server determines the destination of the packet and sends the
- packet to the router.
-
-o Router determines the destination of the packet and sends the
- packet to the server.
-
-o Server determines the client to which the packet is destined
- to and sends the packet to the client.
-
-o Client 2. decrypts the packet with the secret shared key.
-
-
-If clients share secret key with each other the private message
-delivery is much simpler since servers and routers between the
-clients do not need to decrypt and re-encrypt the packet.
-
-The process for clients on same server is much simpler as there are
-no need to send the packet to the router. The process for clients
-on different cells is same as above except that the packet is routed
-outside the cell. The router of the destination cell routes the
-packet to the destination same way as described above.
-
-
-.ti 0
-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.
-
-
-.ti 0
-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].
-
-
-.ti 0
-3.9 Key Exchange And Authentication
-
-Key exchange is done always when for example client connects to server
-but also when server and router, and router and router connects to each
-other. The purpose of key exchange protocol is to provide secure key
-material to be used in the communication. The key material is used to
-derive various security parameters used to secure SILC packets. The
-SILC Key Exchange protocol is described in detail in [SILC3].
-
-Authentication is done after key exchange protocol has been successfully
-completed. The purpose of authentication is to authenticate for example
-client connecting to the server. However, usually clients are accepted
-to connect to server without explicit authentication. Servers are
-required use authentication protocol when connecting. The authentication
-may be based on passphrase (pre-shared-secret) or public key. The
-connection authentication protocol is described in detail in [SILC3].
-
-
-.ti 0
-3.9.1 Authentication Payload
-
-Authentication payload is used separately from the SKE and the Connection
-Authentication protocol. It is used during the session to authenticate
-with the remote. For example, the client can authenticate itself to the
-server to become server operator. In this case, Authentication Payload is
-used.
-
-
-
-
-
-
-
-
-
-
-
-The format of the Authentication Payload is as follows:
-
-
-.in 5
-.nf
- 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-| Payload Length | Authentication Method |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-| Public Data Length | |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
-| |
-~ Public Data ~
-| |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-| Authentication Data Length | |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
-| |
-~ Authentication Data ~
-| |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-.in 3
-
-.ce
-Figure 5: Authentication Payload
-
-
-.in 6
-o Payload Length (2 bytes) - Length of the entire payload.
-
-o Authentication Method (2) - The method of the authentication.
- The authentication methods are defined in [SILC2] in the
- Connection Auth Request Payload. The NONE authentication
- method SHOULD NOT be used.
-
-o Public Data Length (2 bytes) - Indicates the length of
- the Public Data field.
-
-o Public Data (variable length) - This is defined only if
- the authentication method is public key. If it is any other
- this field does not exist and the Public Data Length field
- is set to zero (0).
-
- When the authentication method is public key this includes
- 128 to 4096 bytes of non-zero random data that is used in
- the signature process, described subsequently.
-
-o Authentication Data Length (2 bytes) - Indicates the
- length of the Authentication Data field.
-
-o Authentication Data (variable length) - Authentication
- method dependent authentication data.
-.in 3
-
-
-If the authentication method is password based, the Authentication
-Data field includes the plaintext password. It is safe to send
-plaintext password since the entire payload is encrypted. In this
-case the Public Data Length is set to zero (0).
-
-If the authentication method is public key based (or certificate)
-the Authentication Data is computed as follows:
-
- HASH = hash(random bytes | ID | public key (or certificate));
- Authentication Data = sign(HASH);
-
-The hash() and the sign() are the hash function and the public key
-cryptography function selected in the SKE protocol. The public key
-is SILC style public key unless certificates are used. The ID is the
-entity's ID (Client or Server ID) which is authenticating itself. The
-ID is raw ID data. The random bytes are non-zero random bytes of
-length between 128 and 4096 bytes, and will be included into the
-Public Data field as is.
-
-The receiver will compute the signature using the random data received
-in the payload, the ID associated to the connection and the public key
-(or certificate) received in the SKE protocol. After computing the
-receiver MUST verify the signature. In this case also, the entire
-payload is encrypted.
-
-
-.ti 0
-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.
-
-
-.ti 0
-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.
-
-The following ciphers are defined in SILC protocol:
-
-.in 6
-aes-256-cbc AES in CBC mode, 256 bit key (REQUIRED)
-aes-192-cbc AES in CBC mode, 192 bit key (OPTIONAL)
-aes-128-cbc AES in CBC mode, 128 bit key (OPTIONAL)
-twofish-256-cbc Twofish in CBC mode, 256 bit key (OPTIONAL)
-twofish-192-cbc Twofish in CBC mode, 192 bit key (OPTIONAL)
-twofish-128-cbc Twofish in CBC mode, 128 bit key (OPTIONAL)
-blowfish-128-cbc Blowfish in CBC mode, 128 bit key (OPTIONAL)
-cast-256-cbc CAST-256 in CBC mode, 256 bit key (OPTIONAL)
-cast-192-cbc CAST-256 in CBC mode, 192 bit key (OPTIONAL)
-cast-128-cbc CAST-256 in CBC mode, 128 bit key (OPTIONAL)
-rc6-256-cbc RC6 in CBC mode, 256 bit key (OPTIONAL)
-rc6-192-cbc RC6 in CBC mode, 192 bit key (OPTIONAL)
-rc6-128-cbc RC6 in CBC mode, 128 bit key (OPTIONAL)
-mars-256-cbc Mars in CBC mode, 256 bit key (OPTIONAL)
-mars-192-cbc Mars in CBC mode, 192 bit key (OPTIONAL)
-mars-128-cbc Mars in CBC mode, 128 bit key (OPTIONAL)
-none No encryption (OPTIONAL)
-.in 3
-
-
-Algorithm none does not perform any encryption process at all and
-thus is not recommended to be used. It is recommended that no client
-or server implementation would accept none algorithms except in special
-debugging mode.
-
-Additional ciphers MAY be defined to be used in SILC by using the
-same name format as above.
-
-
-.ti 0
-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].
-
-The following public key algorithms are defined in SILC protocol:
-
-.in 6
-rsa RSA (REQUIRED)
-dss DSS (OPTIONAL)
-.in 3
-
-DSS is described in [Menezes]. The RSA MUST be implemented according
-PKCS #1 [PKCS1]. The mandatory PKCS #1 implementation in SILC MUST be
-compliant to either PKCS #1 version 1.5 or newer with the following
-notes: The signature encoding is always in same format as the encryption
-encoding regardless of the PKCS #1 version. The signature with appendix
-(with hash algorithm OID in the data) MUST NOT be used in the SILC. The
-rationale for this is that there is no binding between the PKCS #1 OIDs
-and the hash algorithms used in the SILC protocol. Hence, the encoding
-is always in PKCS #1 version 1.5 format.
-
-Additional public key algorithms MAY be defined to be used in SILC.
-
-
-
-
-.ti 0
-3.10.3 Hash Functions
-
-Hash functions are used as part of MAC algorithms defined in the next
-section. They are also used in the SILC Key Exchange protocol defined
-in the [SILC3].
-
-The following Hash algorithm are defined in SILC protocol:
-
-.in 6
-sha1 SHA-1, length = 20 (REQUIRED)
-md5 MD5, length = 16 (OPTIONAL)
-.in 3
-
-
-.ti 0
-3.10.4 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.
-
-The following MAC algorithms are defined in SILC protocol:
-
-.in 6
-hmac-sha1-96 HMAC-SHA1, length = 12 (REQUIRED)
-hmac-md5-96 HMAC-MD5, length = 12 (OPTIONAL)
-hmac-sha1 HMAC-SHA1, length = 20 (OPTIONAL)
-hmac-md5 HMAC-MD5, length = 16 (OPTIONAL)
-none No MAC (OPTIONAL)
-.in 3
-
-The none MAC is not recommended to be used as the packet is not
-authenticated when MAC is not computed. It is recommended that no
-client or server would accept none MAC except in special debugging
-mode.
-
-The HMAC algorithm is described in [HMAC] and hash algorithms that
-are used as part of the HMACs are described in [Scheneir] and in
-[Menezes]
-
-Additional MAC algorithms MAY be defined to be used in SILC.
-
-
-.ti 0
-3.10.5 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.
-
-
-
-The following compression algorithms are defined:
-
-.in 6
-none No compression (REQUIRED)
-zlib GNU ZLIB (LZ77) compression (OPTIONAL)
-.in 3
-
-Additional compression algorithms MAY be defined to be used in SILC.
-
-
-.ti 0
-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 the SILC
-protocol. Public keys in SILC may be used to authenticate entities
-and to perform other tasks related to public key cryptography.
-
-The format of the SILC Public Key is as follows:
-
-
-.in 5
-.nf
- 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-| Public Key Length |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-| Algorithm Name Length | |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
-| |
-~ Algorithm Name ~
-| |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-| Identifier Length | |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
-| |
-~ Identifier ~
-| |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-| |
-~ Public Data ~
-| |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-.in 3
-
-.ce
-Figure 5: SILC Public Key
-
-
-.in 6
-o Public Key Length (4 bytes) - Indicates the full length
- of the public key, not including this field.
-
-o Algorithm Name Length (2 bytes) - Indicates the length
- of the Algorithm Length field, not including this field.
-
-o Algorithm name (variable length) - Indicates the name
- of the public key algorithm that the key is. See the
- section 3.10.2 Public Key Algorithms for defined names.
-
-o Identifier Length (2 bytes) - Indicates the length of
- the Identifier field, not including this field.
-
-o Identifier (variable length) - Indicates the identifier
- of the public key. This data can be used to identify
- the owner of the key. The identifier is of the following
- format:
-
- UN User name
- HN Host name or IP address
- RN Real name
- E EMail address
- O Organization
- C Country
-
-
- Examples of an identifier:
-
- `UN=priikone, HN=poseidon.pspt.fi, E=priikone@poseidon.pspt.fi'
-
- `UN=sam, HN=dummy.fi, RN=Sammy Sam, O=Company XYZ, C=Finland'
-
- At least user name (UN) and host name (HN) MUST be provided as
- identifier. The fields are separated by commas (`,'). If
- comma is in the identifier string it must be written as `\\,',
- for example, `O=Company XYZ\\, Inc.'.
-
-o Public Data (variable length) - Includes the actual
- public data of the public key.
-
- The format of this field for RSA algorithm is
- as follows:
-
- 4 bytes Length of e
- variable length e
- 4 bytes Length of n
- variable length n
-
-
- The format of this field for DSS algorithm is
- as follows:
-
- 4 bytes Length of p
- variable length p
- 4 bytes Length of q
- variable length q
- 4 bytes Length of g
- variable length g
- 4 bytes Length of y
- variable length y
-
- The variable length fields are multiple precession
- integers encoded as strings in both examples.
-
- Other algorithms must define their own type of this
- field if they are used.
-.in 3
-
-All fields in the public key are in MSB (most significant byte first)
-order.
-
-
-.ti 0
-3.12 SILC Version Detection
-
-The version detection of both client and server is performed at the
-connection phase while executing the SILC Key Exchange protocol. The
-version identifier is exchanged between initiator and responder. The
-version identifier is of the following format:
-
-.in 6
-SILC-<protocol version>-<software version>
-.in 3
-
-The version strings are of the following format:
-
-.in 6
-protocol version = <major>.<minor>
-software version = <major>[.<minor>[.<build>]]
-.in 3
-
-Protocol version MAY provide both major and minor version. Currently
-implementations MUST set the protocol version and accept the protocol
-version as SILC-1.0-<software version>.
-
-Software version MAY provide major, minor and build version. The
-software version MAY be freely set and accepted.
-
-
-Thus, the version string could be, for example:
-
-.in 6
-SILC-1.0-1.2
-.in 3
-
-
-
-
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-4 SILC Procedures
-
-This section describes various SILC procedures such as how the
-connections are created and registered, how channels are created and
-so on. The section describes the procedures only generally as details
-are described in [SILC2] and [SILC3].
-
-
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-4.1 Creating Client Connection
-
-This section describes the procedure when client connects to SILC server.
-When client connects to server the server MUST perform IP address lookup
-and reverse IP address lookup to assure that the origin host really is
-who it claims to be. Client, host, connecting to server SHOULD have
-both valid IP address and fully qualified domain name (FQDN).
-
-After that the client and server performs SILC Key Exchange protocol
-which will provide the key material used later in the communication.
-The key exchange protocol MUST be completed successfully before the
-connection registration may continue. The SILC Key Exchange protocol
-is described in [SILC3].
-
-Typical server implementation would keep a list of connections that it
-allows to connect to the server. The implementation would check, for
-example, the connecting client's IP address from the connection list
-before the SILC Key Exchange protocol has been started. Reason for
-this is that if the host is not allowed to connect to the server there
-is no reason to perform the key exchange protocol.
-
-After successful key exchange protocol the client and server performs
-connection authentication protocol. The purpose of the protocol is to
-authenticate the client connecting to the server. Flexible
-implementation could also accept the client to connect to the server
-without explicit authentication. However, if authentication is
-desired for a specific client it may be based on passphrase or
-public key authentication. If authentication fails the connection
-MUST be terminated. The connection authentication protocol is described
-in [SILC3].
-
-After successful key exchange and authentication protocol the client
-registers itself by sending SILC_PACKET_NEW_CLIENT packet to the
-server. This packet includes various information about the client
-that the server uses to create the client. Server creates the client
-and sends SILC_PACKET_NEW_ID to the client which includes the created
-Client ID that the client MUST start using after that. After that
-all SILC packets from the client MUST have the Client ID as the
-Source ID in the SILC Packet Header, described in [SILC2].
-
-Client MUST also get the server's Server ID that is to be used as
-Destination ID in the SILC Packet Header when communicating with
-the server (for example when sending commands to the server). The
-ID may be resolved in two ways. Client can take the ID from an
-previously received packet from server that MUST include the ID,
-or to send SILC_COMMAND_INFO command and receive the Server ID as
-command reply.
-
-Server MAY choose not to use the information received in the
-SILC_PACKET_NEW_CLIENT packet. For example, if public key or
-certificate were used in the authentication, server MAY use those
-informations rather than what it received from client. This is suitable
-way to get the true information about client if it is available.
-
-The nickname of client is initially set to the username sent in the
-SILC_PACKET_NEW_CLIENT packet. User should set the nickname to more
-suitable by sending SILC_COMMAND_NICK command. However, this is not
-required as part of registration process.
-
-Server MUST also distribute the information about newly registered
-client to its router (or if the server is router, to all routers in
-the SILC network). More information about this in [SILC2].
-
-
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-4.2 Creating Server Connection
-
-This section describes the procedure when server connects to its
-router (or when router connects to other router, the cases are
-equivalent). The procedure is very much alike when client connects
-to the server thus it is not repeated here.
-
-One difference is that server MUST perform connection authentication
-protocol with proper authentication. A 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. The server MAY also
-use SILC_COMMAND_INFO command to resolve the ID. 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.
-
-
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-4.2.1 Announcing Clients, Channels and Servers
-
-After server or router has connected to the remote router, and it already
-has connected clients and channels it MUST announce them to the router.
-If the server is router server, also all the local servers in the cell
-MUST be announced.
-
-All clients are announced by compiling a list of ID Payloads into the
-SILC_PACKET_NEW_ID packet. All channels are announced by compiling a
-list of Channel Payloads into the SILC_PACKET_NEW_CHANNEL packet. Also,
-the channel users on the channels must be announced by compiling a
-list of Notify Payloads with the SILC_NOTIFY_TYPE_JOIN notify type into
-the SILC_PACKET_NOTIFY packet. The users' modes on the channel must
-also be announced by compiling list of Notify Payloads with the
-SILC_NOTIFY_TYPE_CUMODE_CHANGE notify type into the SILC_PACKET_NOTIFY
-packet.
-
-The router MUST also announce the local servers by compiling list of
-ID Payloads into the SILC_PACKET_NEW_ID packet.
-
-The router which receives these lists MUST process them and broadcast
-the packets to its primary route.
-
-When processing the announced channels and channel users the router MUST
-check whether a channel exists already with the same name. If channel
-exists with the same name it MUST check whether the Channel ID is
-different. If the Channel ID is different the router MUST send the notify
-type SILC_NOTIFY_TYPE_CHANNEL_CHANGE to the server to force the channel ID
-change to the ID the router has. If the mode of the channel is different
-the router MUST send the notify type SILC_NOTIFY_TYPE_CMODE_CHANGE to the
-server to force the mode change to the mode that the router has.
-
-The router MUST also generate new channel key and distribute it to the
-channel. The key MUST NOT be generated if the SILC_CMODE_PRIVKEY mode
-is set.
-
-If the channel has channel founder on the router the router MUST send
-the notify type SILC_NOTIFY_TYPE_CUMODE_CHANGE to the server to force
-the mode change for the channel founder on the server. The channel
-founder privileges MUST be removed.
-
-The router processing the channels MUST also compile a list of
-Notify Payloads with the SILC_NOTIFY_TYPE_JOIN notify type into the
-SILC_PACKET_NOTIFY and send the packet to the server. This way the
-server (or router) will receive the clients on the channel that
-the router has.
-
-
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-4.3 Joining to a Channel
-
-This section describes the procedure when client joins to a channel.
-Client joins 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 channel, new channel key is created and information about
-newly joined channel is sent to the router. The router is informed
-by sending SILC_NOTIFY_TYPE_JOIN notify type. The notify type MUST
-also be sent to the local clients on the channel. The new channel key
-is also sent to the router and to local clients on the channel.
-
-If the channel does not exist in the local list the client's command
-MUST be sent to the router which will then perform the actual joining
-procedure. When server receives the reply to the command from the
-router it MUST be sent to the client which sent the command originally.
-Server will also receive the channel key from the server that it MUST
-send to the client which originally requested the join command. The
-server MUST also save the channel key.
-
-If the receiver of the join command is router it MUST first check its
-local list whether anyone in the cell has already joined to the channel.
-If this is the case the client is joined to the channel and reply is
-sent to the client. If the command was sent by server the command reply
-is sent to the server which sent it. Then the router MUST also create
-new channel key and distribute it to all clients on the channel and
-all servers that has clients on the channel. Router MUST also send
-the SILC_NOTIFY_TYPE_JOIN notify type to local clients on the channel
-and to local servers that has clients on the channel.
-
-If the channel does not exist on the router's local list it MUST
-check the global list whether the channel exists at all. If it does
-the client is joined to the channel as described previously. If
-the channel does not exist the channel is created and the client
-is joined to the channel. The channel key is also created and
-distributed as previously described. The client joining to the created
-channel is made automatically channel founder and both channel founder
-and channel operator privileges is set for the client.
-
-If the router created the channel in the process, information about the
-new channel MUST be broadcasted to all routers. This is done by
-broadcasting SILC_PACKET_NEW_CHANNEL packet to the router's primary
-route. When the router joins the client to the channel it MUST also
-send information about newly joined client to all routers in the SILC
-network. This is done by broadcasting the SILC_NOTIFY_TYPE_JOIN notify
-type to the router's primary route.
-
-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 which receives the reply to
-the join command MUST start using the received Channel ID in the channel
-message communication thereafter. Client also receives the key for the
-channel in the command reply. Note that the channel key is never
-generated if the SILC_CMODE_PRIVKEY mode is set.
-
-
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-4.4 Channel Key Generation
-
-Channel keys are created by router which creates the channel by taking
-enough randomness from cryptographically strong random number generator.
-The key is generated always when channel is created, when new client
-joins a channel and after the key has expired. Key could expire for
-example in an hour.
-
-The key MUST also be re-generated whenever some client leaves a channel.
-In this case the key is created from scratch by taking enough randomness
-from the random number generator. After that the key is distributed to
-all clients on the channel. However, channel keys are cell specific thus
-the key is created only on the cell where the client, which left the
-channel, exists. While the server or router is creating the new channel
-key, no other client may join to the channel. Messages that are sent
-while creating the new key are still processed with the old key. After
-server has sent the SILC_PACKET_CHANNEL_KEY packet MUST client start
-using the new key. If server creates the new key the server MUST also
-send the new key to its router. See [SILC2] on more information about
-how channel messages must be encrypted and decrypted when router is
-processing them.
-
-When client receives the SILC_PACKET_CHANNEL_KEY packet with the
-Channel Key Payload it MUST process the key data to create encryption
-and decryption key, and to create the HMAC key that is used to compute
-the MACs of the channel messages. The processing is as follows:
-
- channel_key = raw key data
- HMAC key = hash(raw key data)
-
-The raw key data is the key data received in the Channel Key Payload.
-The hash() function is the hash function used in the HMAC of the channel.
-Note that the server MUST also save the channel key.
-
-
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-4.5 Private Message Sending and Reception
-
-Private messages are sent point to point. Client explicitly destines
-a private message to specific client that is delivered to only to that
-client. No other client may receive the private message. The receiver
-of the private message is destined in the SILC Packet Header as any
-other packet as well.
-
-If the sender of a private message does not know the receiver's Client
-ID, it MUST resolve it from server. There are two ways to resolve the
-client ID from server; it is RECOMMENDED that client implementations
-send SILC_COMMAND_IDENTIFY command to receive the Client ID. Client
-MAY also send SILC_COMMAND_WHOIS command to receive the Client ID.
-If the sender has received earlier a private message from the receiver
-it should have cached the Client ID from the SILC Packet Header.
-
-See [SILC2] for description of private message encryption and decryption
-process.
-
-
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-4.6 Private Message Key Generation
-
-Private message MAY be protected by the key generated by the client.
-The key may be generated and sent to the other client by sending packet
-SILC_PACKET_PRIVATE_MESSAGE_KEY which travels through the network
-and is secured by session keys. After that the private message key
-is used in the private message communication between those clients.
-
-Other choice is to entirely use keys that are not sent through
-the SILC network at all. This significantly adds security. This key
-would be pre-shared-key that is known by both of the clients. Both
-agree about using the key and starts sending packets that indicate
-that the private message is secured using private message key.
-
-The key material used as private message key is implementation issue.
-However, SILC_PACKET_KEY_AGREEMENT packet MAY be used to negotiate
-the key material. If the key is normal pre-shared-key or randomly
-generated key, and the SILC_PACKET_KEY_AGREEMENT was not used, then
-the key material SHOULD be processed as defined in the [SILC3]. In
-the processing, however, the HASH, as defined in [SILC3] MUST be
-ignored. After processing the key material it is employed as defined
-in [SILC3], however, the HMAC key material MUST be discarded.
-
-If the key is pre-shared-key or randomly generated the implementations
-should use the SILC protocol's mandatory cipher as the cipher. If the
-SKE was used to negotiate key material the cipher was negotiated as well.
-
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-4.7 Channel Message Sending and Reception
-
-Channel messages are delivered to group of users. The group forms a
-channel and all clients on the channel receives messages sent to the
-channel.
-
-Channel messages are destined to channel by specifying the Channel ID
-as Destination ID in the SILC Packet Header. The server MUST then
-distribute the message to all clients on the channel by sending the
-channel message destined explicitly to a client on the channel.
-
-See [SILC2] for description of channel message encryption and decryption
-process.
-
-
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-4.8 Session Key Regeneration
-
-Session keys MUST be regenerated periodically, say, once in an hour.
-The re-key process is started by sending SILC_PACKET_REKEY packet to
-other end, to indicate that re-key must be performed. The initiator
-of the connection SHOULD initiate the re-key.
-
-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 set the resulted key material is processed as described
-in the section Processing the Key Material in [SILC3]. The difference
-with re-key in the processing is that the initial data for the hash
-function is just the resulted key material and not the HASH as it
-is not computed at all with re-key. Other than that, the key processing
-it equivalent to normal SKE negotiation.
-
-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
-providing the current sending encryption key to the SKE protocol's key
-processing function. The process is described in the section Processing
-the Key Material in [SILC3]. The difference in the processing is that
-the initial data for the hash function is the current sending encryption
-key and not the SKE's KEY and HASH values. Other than that, the key
-processing is equivalent to normal SKE negotiation.
-
-After both parties has regenerated the session key, both MUST send
-SILC_PACKET_REKEY_DONE packet to each other. These packets are still
-secured with the old key. After these packets, the subsequent packets
-MUST be protected with the new key.
-
-
-
-
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-4.9 Command Sending and Reception
-
-Client usually sends the commands in the SILC network. In this case
-the client simply sends the command packet to server and the server
-processes it and replies with command reply packet.
-
-However, if the server is not able to process the command, it is sent
-to the server's router. This is case for example with commands such
-as, SILC_COMMAND_JOIN and SILC_COMMAND_WHOIS commands. However, there
-are other commands as well. For example, if client sends the WHOIS
-command requesting specific information about some client the server must
-send the WHOIS command to router so that all clients in SILC network
-are searched. The router, on the other hand, sends the WHOIS command
-further to receive the exact information about the requested client.
-The WHOIS command travels all the way to the server which owns the client
-and it replies with command reply packet. Finally, the server which
-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.
-
-
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-4.10 Closing Connection
-
-When remote client connection is closed the server MUST send the notify
-type SILC_NOTIFY_TYPE_SIGNOFF to its primary router and to all channels
-the client was joined. The server MUST also save the client's information
-for a period of time for history purposes.
-
-When remote server or router connection is closed the server or router
-MUST also remove all the clients that was behind the server or router
-from the SILC Network. The server or router MUST also send the notify
-type SILC_NOTIFY_TYPE_SERVER_SIGNOFF to its primary router and to all
-local clients that are joined on the same channels with the remote
-server's or router's clients.
-
-
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-5 Security Considerations
-
-Security is central to the design of this protocol, and these security
-considerations permeate the specification. Common security considerations
-such as keeping private keys truly private and using adequate lengths for
-symmetric and asymmetric keys must be followed in order to maintain the
-security of this protocol.
-
-Special attention must also be paid on the servers and routers that are
-running the SILC service. The SILC protocol's security depends greatly
-on the security and the integrity of the servers and administrators that
-are running the service. It is recommended that some form of registration
-is required by the server and router administrator prior acceptance to
-the SILC Network. The clients must be able to trust the servers they
-are using.
-
-It must also be noted that if the client requires absolute security by
-not trusting any of the servers or routers in the SILC Network, this can
-be accomplished by negotiating private keys outside the SILC Network,
-either using SKE or some other key negotiation protocol, or to use some
-other external means for distributing the keys. This applies for all
-messages, private messages and channel messages. It is important to note
-that SILC, like any other security protocol is not full proof system and
-cannot secure from insecure environment; the SILC servers and routers could
-very well be compromised. However, to provide acceptable level of security
-and usability for end user the protocol uses many times session keys or
-other keys generated by the servers to secure the messages. If this is
-unacceptable for the client or end user, the private keys negotiatied
-outside the SILC Network should always be used. In the end it is always
-implementor's choice whether to negotiate private keys by default or
-whether to use the keys generated by the servers.
-
-It is also recommended that router operators in the SILC Network would
-form a joint forum to discuss the router and SILC Network management
-issues. Also, router operators along with the cell's server operators
-should have a forum to discuss the cell management issues.
-
-
-.ti 0
-6 References
-
-[SILC2] Riikonen, P., "SILC Packet Protocol", Internet Draft,
- April 2001.
-
-[SILC3] Riikonen, P., "SILC Key Exchange and Authentication
- Protocols", Internet Draft, April 2001.
-
-[SILC4] Riikonen, P., "SILC Commands", Internet Draft, April 2001.
-
-[IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
- RFC 1459, May 1993.
-
-[IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
- April 2000.
-
-[IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
- 2811, April 2000.
-
-[IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
- 2812, April 2000.
-
-[IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
- 2813, April 2000.
-
-[SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
- Internet Draft.
-
-[PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
- November 1998.
-
-[SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
- September 1999.
-
-[PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
- Infrastructure, Certificate and CRL Profile", RFC 2459,
- January 1999.
-
-[Schneier] Schneier, B., "Applied Cryptography Second Edition",
- John Wiley & Sons, New York, NY, 1996.
-
-[Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
- CRC Press 1997.
-
-[OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
- RFC 2412, November 1998.
-
-[ISAKMP] Maughan D., et al, "Internet Security Association and
- Key Management Protocol (ISAKMP)", RFC 2408, November
- 1998.
-
-[IKE] Harkins D., and Carrel D., "The Internet Key Exchange
- (IKE)", RFC 2409, November 1998.
-
-[HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
- Authentication", RFC 2104, February 1997.
-
-[PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
- Specifications, Version 2.0", RFC 2437, October 1998.
-
-[RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate
- Requirement Levels", BCP 14, RFC 2119, March 1997.
-
-
-.ti 0
-7 Author's Address
-
-.nf
-Pekka Riikonen
-Snellmanninkatu 34 A 15
-70100 Kuopio
-Finland
-
-EMail: priikone@silcnet.org
-
-This Internet-Draft expires 21 February 2002
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