+++ /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 29 July 2003
-.ds CH
-.na
-.hy 0
-.in 0
-.nf
-Network Working Group P. Riikonen
-Internet-Draft
-draft-riikonen-silc-spec-07.txt 29 July 2003
-Expires: 29 January 2004
-
-.in 3
-
-.ce 3
-Secure Internet Live Conferencing (SILC),
-Protocol Specification
-<draft-riikonen-silc-spec-07.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 provides advanced and feature rich conferencing
-services with security as main design principal. Strong cryptographic
-methods are used to protect SILC packets inside the SILC network.
-Three other specifications 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 ............................... 6
- 2.3 Communication in the Network .............................. 7
- 2.4 Channel Communication ..................................... 7
- 2.5 Router Connections ........................................ 8
-3 SILC Specification ............................................ 9
- 3.1 Client .................................................... 9
- 3.1.1 Client ID ........................................... 9
- 3.2 Server .................................................... 10
- 3.2.1 Server's Local ID List .............................. 11
- 3.2.2 Server ID ........................................... 12
- 3.2.3 SILC Server Ports ................................... 12
- 3.3 Router .................................................... 13
- 3.3.1 Router's Local ID List .............................. 13
- 3.3.2 Router's Global ID List ............................. 14
- 3.3.3 Router's Server ID .................................. 14
- 3.4 Channels .................................................. 14
- 3.4.1 Channel ID .......................................... 16
- 3.5 Operators ................................................. 16
- 3.6 SILC Commands ............................................. 17
- 3.7 SILC Packets .............................................. 17
- 3.8 Packet Encryption ......................................... 17
- 3.8.1 Determination of the Source and the Destination ..... 18
- 3.8.2 Client To Client .................................... 19
- 3.8.3 Client To Channel ................................... 20
- 3.8.4 Server To Server .................................... 21
- 3.9 Key Exchange And Authentication ........................... 21
- 3.9.1 Authentication Payload .............................. 21
- 3.10 Algorithms ............................................... 23
- 3.10.1 Ciphers ............................................ 23
- 3.10.1.1 CBC Mode .................................. 24
- 3.10.1.2 CTR Mode .................................. 24
- 3.10.1.3 Randomized CBC Mode ....................... 26
- 3.10.2 Public Key Algorithms .............................. 26
- 3.10.2.1 Multi-Precision Integers .................. 27
- 3.10.3 Hash Functions ..................................... 27
- 3.10.4 MAC Algorithms ..................................... 27
- 3.10.5 Compression Algorithms ............................. 28
- 3.11 SILC Public Key .......................................... 29
- 3.12 SILC Version Detection ................................... 31
- 3.13 Backup Routers ........................................... 31
- 3.13.1 Switching to Backup Router ......................... 33
- 3.13.2 Resuming Primary Router ............................ 34
-4 SILC Procedures ............................................... 36
- 4.1 Creating Client Connection ................................ 37
- 4.2 Creating Server Connection ................................ 38
- 4.2.1 Announcing Clients, Channels and Servers ............ 39
- 4.3 Joining to a Channel ...................................... 40
- 4.4 Channel Key Generation .................................... 41
- 4.5 Private Message Sending and Reception ..................... 42
- 4.6 Private Message Key Generation ............................ 42
- 4.7 Channel Message Sending and Reception ..................... 43
- 4.8 Session Key Regeneration .................................. 44
- 4.9 Command Sending and Reception ............................. 44
- 4.10 Closing Connection ....................................... 45
- 4.11 Detaching and Resuming a Session ......................... 46
-5 Security Considerations ....................................... 47
-6 References .................................................... 48
-7 Author's Address .............................................. 50
-8 Full Copyright Statement ...................................... 50
-
-.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
-Figure 6: Counter Block
-
-
-.ti 0
-1. Introduction
-
-This document describes a Secure Internet Live Conferencing (SILC)
-protocol which provides secure conferencing services over insecure
-network channel. SILC can be used as a secure conferencing service
-that provides rich conferencing features. Some of the SILC features
-are found in traditional chat protocols such as IRC [IRC] but many
-of the SILC features can also be found in Instant Message (IM) style
-protocols. SILC combines features from both of these chat protocol
-styles, and can be implemented as either IRC-like system or IM-like
-system. Some of the more advanced and secure features of the
-protocol are new to all conferencing protocols. SILC also supports
-multimedia messages and can also be implemented as a video and audio
-conferencing system.
-
-Strong cryptographic methods are used to protect SILC packets inside
-the SILC network. Three other specifications 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 SILC Packet Protocol provides secured
-and authenticated packets, and the protocol is designed to be compact.
-This makes SILC also suitable in environment of low bandwidth
-requirements such as mobile networks. All packet payloads in SILC
-can be also compressed.
-
-The security of SILC protocol sessions are 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 forms a ring as opposed to tree style network topology that
-conferencing protocols usually have. The network has a cells which are
-constructed from a router and zero or more servers. The servers are
-connected to the router in a star like network topology. Routers in the
-network are connected to each other forming a ring. 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 router servers.
-
-A difference between normal server and router server is that routers
-knows all global information and keep the global network state up to date.
-They also do the actual routing of the messages to the correct receiver
-between other cells. Normal servers knows only local information and
-receive global information only when it is needed. They do not need to
-keep the global network state up to date. This makes the network faster
-and scalable as there are less servers that needs to maintain global
-network state.
-
-This, on the other hand, leads into a 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 able to act
-as 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. Other direct routes between
-other routers is also possible in addition of the mandatory ring
-connections. This leads into a hybrid ring-mesh network topology.
-
-There are many issues in this network topology that needs to be careful
-about. Issues like routing, 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 client that does not belong to local cell
-the message is routed to the router server to which the destination
-client 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 ring.
-
-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. This sort of ring network, with
-ability to have other direct routes in the network can cause interesting
-routing problems. The [SILC2] discusses the routing of packets in this
-sort of network in more detail.
-
-
-.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 user's IP address and nickname. User use logical nicknames
-in communication which are then mapped to the corresponding Client ID.
-Client IDs are low level identifications and should 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 typically causes the server names or client's
-host names to be used along with the nicknames on user interface 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. Also, any kind
-of nickname registering service becomes obsolete. The maximum length of
-nickname is 128 bytes.
-
-
-.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 IDs,
-and IDs based on IPv6 addresses extends this to 2^224 different Client
-IDs. 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 the client is 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 lowercase 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. Note that the nickname MUST be in
- lowercase format.
-
-.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 serious 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.
-
-
-.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 IDs, 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 do not have to worry about global clients. Server is also responsible
-of creating the Client IDs for their clients.
-
-Normal server also keeps information about locally created channels and
-their Channel IDs.
-
-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 IDs 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 IDs also provide
-information for Client IDs, 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 and keeps the global state.
-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.
-
-
-.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 IDs 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. Router MAY also cache same detailed information for other clients
-if needed.
-
-
-.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 IDs, all created channels
-and their Channel IDs and all servers and routers on SILC and their
-Server IDs. 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 IDs on channel
- o Client ID modes on channel
-.in 3
-
-
-
-.ti 0
-3.3.3 Router's Server ID
-
-Router's Server ID is equivalent to normal Server ID. As routers are
-normal servers same types of IDs applies for routers as well. 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 Channel ID of the channel. If the channel has
-a founder mode set and last client leaves the channel the channel does
-not cease to exist. The founder mode can be used to make permanent
-channels in the network. The founder of the channel can regain the
-channel founder privileges on the channel later when he joins 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 bytes. Channel names MUST NOT contain any
-whitespaces (` '), 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 to 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 or counter
-
-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 or counter
-
-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 or counter - To further randomize the Channel ID.
- Another choice is to use a counter starting from zero (0).
- This makes sure that there are no collisions. This also means
- that in a cell there can be 2^16 different 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
-channels, to gain access to the contents of 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 any normal user 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. Usually server cannot send commands to
-clients, however there MAY be commands that allow the server to send
-commands to client. By default servers MAY send commands only to other
-servers and routers.
-
-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 misused 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 misuse 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. It is not possible to send a packet in SILC network without
-encryption. 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
-gives generic description of 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 have a channel 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 have 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 beforehand to be able to talk on the
-channel. In this case, no server or router knows the key for the 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 router. However, every packet passed
-from router to other router, including packets for channels, are
-encrypted with the shared session key. Every router connection MUST
-have 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 of whom is the 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 IDs attached to the header. The IDs 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 however, that some
-packets such as commands may be resent by a server to serve the client's
-original command. In this case the command packet sent by the server
-includes the server's IDs as it is a different packet. When server
-or router receives a packet it MUST verify that the Source ID is
-valid and correct ID for that sender.
-
-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 have established a 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 header
- is encrypted with the session key shared between the client and
- server, and the private message 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. Header is encrypted with the session key.
-
-o Router determines the destination of the packet and sends the
- packet to the server. Header is encrypted with the session key.
-
-o Server determines the client to which the packet is destined
- to and sends the packet to the client. Header is encrypted with
- the session key.
-
-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 entire packet.
-The packet header however is always encrypted with session key and
-is decrypted and re-encrypted with the session key of next recipient.
-
-The process for clients on same server is much simpler as there is
-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.
- Packet header is encrypted with the session key, message
- data is encrypted with channel key.
-
-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 it.
-
-
-.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 another router connect
-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, clients MAY be accepted
-to connect to server without explicit authentication. Servers are
-REQUIRED to use authentication protocol when connecting. The
-authentication may be based on passphrase (pre-shared secret) or public
-key based on digital signatures. All passphrases sent in SILC protocol
-MUST be UTF-8 [RFC2279] encoded. 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 protocols. It can be used during the session to
-authenticate with a remote. For example, a client can authenticate
-itself to a 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 bytes) - 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 MAY include random data for padding purposes.
- However, in this case the field MUST be ignored by the
- receiver.
-
- 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. If zero (0)
- value is found in this field the payload MUST be
- discarded.
-
-o Authentication Data (variable length) - Authentication
- method dependent authentication data.
-.in 3
-
-
-If the authentication method is passphrase-based, the Authentication
-Data field includes the plaintext UTF-8 encoded passphrase. It is safe
-to send plaintext passphrase since the entire payload is encrypted. In
-this case the Public Data Length is set to zero (0), but MAY also include
-random data for padding purposes. It is also RECOMMENDED that maximum
-amount of padding is applied to SILC packet when using passphrase-based
-authentication. This way it is not possible to approximate the length
-of the passphrase from the encrypted packet.
-
-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, unless otherwise
-stated in the context where this payload is used. 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 encoding is described in [SILC2]. 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. Also in case of public key
-authentication this 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] for 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:
-
-aes-256-cbc AES in CBC mode, 256 bit key (REQUIRED)
-aes-256-ctr AES in CTR mode, 256 bit key (RECOMMENDED)
-aes-256-rcbc AES in randomized CBC mode, 256 bit key (OPTIONAL)
-aes-192-<mode> AES in <mode> mode, 192 bit key (OPTIONAL)
-aes-128-<mode> AES in <mode> mode, 128 bit key (RECOMMENDED)
-twofish-256-<mode> Twofish in <mode> mode, 256 bit key (OPTIONAL)
-twofish-192-<mode> Twofish in <mode> mode, 192 bit key (OPTIONAL)
-twofish-128-<mode> Twofish in <mode> mode, 128 bit key (OPTIONAL)
-cast-256-<mode> CAST-256 in <mode> mode, 256 bit key (OPTIONAL)
-cast-192-<mode> CAST-256 in <mode> mode, 192 bit key (OPTIONAL)
-cast-128-<mode> CAST-256 in <mode> mode, 128 bit key (OPTIONAL)
-serpent-<len>-<mode> Serpent in <mode> mode, <len> bit key (OPTIONAL)
-rc6-<len>-<mode> RC6 in <mode> mode, <len> bit key (OPTIONAL)
-mars-<len>-<mode> MARS in <mode> mode, <len> bit key (OPTIONAL)
-none No encryption (OPTIONAL)
-
-The <mode> is either "cbc", "ctr" or "rcbc". Other encryption modes MAY
-be defined to be used in SILC using the same name format. The <len> is
-either 256, 192 or 128 bit key length. Also, additional ciphers MAY be
-defined to be used in SILC by using the same name format as above.
-
-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 algorithm except in special
-debugging mode.
-
-
-.ti 0
-3.10.1.1 CBC Mode
-
-The "cbc" encryption mode is CBC mode with inter-packet chaining. This
-means that the Initialization Vector (IV) for the next encryption block
-is the previous ciphertext block. The very first IV MUST be random and
-is generated as described in [SILC3].
-
-
-.ti 0
-3.10.1.2 CTR Mode
-
-The "ctr" encryption mode is Counter Mode (CTR). The CTR mode in SILC is
-stateful in encryption and decryption. Both sender and receiver maintain
-the counter for the CTR mode and thus can precompute the key stream for
-encryption and decryption. By default, CTR mode does not require
-plaintext padding, however implementations MAY apply padding to the
-packets. If the last key block is larger than the last plaintext block
-the resulted value is truncated to the size of the plaintext block and
-the most significant bits are used. When sending authentication data
-inside packets the maximum amount of padding SHOULD be applied with
-CTR mode as well.
-
-In CTR mode only the encryption operation of the cipher is used. The
-decryption operation is not needed since both encryption and decryption
-process is simple XOR with the plaintext block and the key stream block.
-
-The counter block is used to create the key for the CTR mode. When
-SILC specifications refer to Initialization Vector (IV) in general cases,
-in case of CTR mode it refers to the counter block. The format of the
-128 bit counter block 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
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-| Truncated HASH from SKE |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-| Sending/Receiving IV from SKE |
-| |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-| Block Counter |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-.in 3
-
-.ce
-Figure 6: Counter Block
-
-.in 6
-o Truncated HASH from SKE (4 bytes) - This value is the first 4
- bytes from the HASH value that was computed as a result of SKE
- protocol. This acts as session identifier and each rekey MUST
- produce a new HASH value.
-
-o Sending/Receiving IV from SKE (8 bytes) - This value is the
- first 8 bytes from the Sending IV or Receiving IV generated in
- the SKE protocol. When this mode is used to encrypt sending
- traffic the Sending IV is used, when used to decrypt receiving
- traffic the Receiving IV is used. This assures that two parties
- of the protocol use different IV for sending traffic. Each rekey
- MUST produce a new value.
-
-o Block Counter (4 bytes) - This is the counter value for the
- counter block and is MSB ordered number starting from one (1)
- value for first block and incrementing for subsequent blocks.
- The same value MUST NOT be used twice. The rekey MUST be
- performed before this counter value wraps.
-.in 3
-
-CTR mode MUST NOT be used with "none" MAC. Implementations also MUST
-assure that the same counter block is not used to encrypt more than
-one block. Also, the key material used with CTR mode MUST be fresh
-key material. Static keys (pre-shared keys) MUST NOT be used with
-CTR mode. For this reason using CTR mode to encrypt for example
-channel messages or private messages with a pre-shared key is
-inappropriate. For private messages, the Key Agreement could be
-performed to produce fresh key material.
-
-If the IV Included flag was negotiated in SKE, implementations SHOULD
-still use the same counter block format as defined above. However,
-implementations are RECOMMENDED to replace the Truncated HASH field
-with a 32 bit random value for each IV (counter block) per encrypted
-SILC packet. Also note, that in this case the decryption process is
-not stateful and receiver cannot precompute the key stream.
-
-
-.ti 0
-3.10.1.3 Randomized CBC Mode
-
-The "rcbc" encryption mode is CBC mode with randomized IV. This means
-that each IV for each packet MUST be chosen randomly. When encrypting
-more than one block the normal inter-packet chaining is used, but for
-the first block new random IV is selected in each packet. In this mode
-the IV is appended at the end of the last ciphertext block and thus
-delivered to the recipient. This mode increases the ciphertext size by
-one ciphertext block. Note also that some data payloads in SILC are
-capable of delivering the IV to the recipient. When explicitly
-encrypting these payloads with randomized CBC the IV MUST NOT be appended
-at the end of the ciphertext, but is placed at the specified location
-in the payload. However, Message Payload for example has the IV at
-the location which is equivalent to placing it after the last ciphertext
-block. When using CBC mode with such payloads it is actually equivalent
-to using randomized CBC since the IV is selected in random and included
-in the ciphertext.
-
-
-.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.
-
-When signatures are computed in SILC the computing of the signature is
-represented as sign(). The signature computing procedure is dependent
-of the public key algorithm, and the public key or certificate encoding.
-When using SILC public key the signature is computed as described in
-previous paragraph for RSA and DSS keys. If the hash function is not
-specified separately for signing process SHA-1 MUST be used. When using
-SSH2 public keys the signature is computed as described in [SSH-TRANS].
-When using X.509 version 3 certificates the signature is computed as
-described in [PKCS7]. When using OpenPGP certificates the signature is
-computed as described in [PGP].
-
-
-.ti 0
-3.10.2.1 Multi-Precision Integers
-
-Multi-Precision (MP) integers in SILC are encoded and decoded as defined
-in PKCS #1 [PKCS1]. MP integers are unsigned, encoded with desired octet
-length. This means that if the octet length is more than the actual
-length of the integer one or more leading zero octets will appear at the
-start of the encoding. The actual length of the integer is the bit size
-of the integer not counting any leading zero bits.
-
-
-.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 (RECOMMENDED)
-.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 for a packet.
-
-The following MAC algorithms are defined in SILC protocol:
-
-.in 6
-hmac-sha1-96 HMAC-SHA1, length = 12 bytes (REQUIRED)
-hmac-md5-96 HMAC-MD5, length = 12 bytes (OPTIONAL)
-hmac-sha1 HMAC-SHA1, length = 20 bytes (OPTIONAL)
-hmac-md5 HMAC-MD5, length = 16 bytes (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]. The hash algorithms used
-in HMACs, the SHA-1 is described in [RFC3174] and MD5 is described
-in [RFC1321].
-
-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 SILC 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 escaped as `\\,',
- for example, `O=Company XYZ\\, Inc.'. Other characters that
- require escaping are listed in [RFC2253] and are to be escaped
- as defined therein.
-
-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. All strings in the public key MUST be UTF-8 encoded.
-
-If an external protocol needs to refer to SILC Public Key by name, the
-names "silc-rsa" and "silc-dss" for SILC Public Key based on RSA algorithm
-and SILC Public Key based on DSS algorithm, respectively, are to be used.
-However, this SILC specification does not use these names directly, and
-they are defined here for external protocols (protocols that may like
-to use SILC Public Key).
-
-
-.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 or vendor string>]]
-.in 3
-
-Protocol version MUST provide both major and minor version. Currently
-implementations MUST set the protocol version and accept at least the
-protocol version as SILC-1.2-<software version>. If new protocol version
-causes incompatibilities with older version the <minor> version number
-MUST be incremented. The <major> is incremented if new protocol version
-is fully incompatible.
-
-Software version MAY provide major, minor and build (vendor) version.
-The software version MAY be freely set and accepted. The version string
-MUST consist of printable US-ASCII characters.
-
-Thus, the version strings could be, for example:
-
-.in 6
-SILC-1.1-2.0.2
-SILC-1.0-1.2
-SILC-1.2-1.0.VendorXYZ
-SILC-1.2-2.4.5 Vendor Limited
-.in 3
-
-
-.ti 0
-3.13 Backup Routers
-
-Backup routers may exist in the cell in addition to the primary router.
-However, they must not be active routers or 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 one of the backup routers becomes 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. When the backup router connects to the primary router
-of the cell it MUST present itself as router server in the Connection
-Authentication protocol, even though it is normal server as long as the
-primary router is available. Reason for this is that the configuration
-needed in the responder end requires usually router connection level
-configuration. The responder, however must understand and treat the
-connection as normal server (except when feeding router level data 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 an actual router server when it feeds the data
-to it.
-
-In addition to having direct connection to the primary router of the
-cell, the backup router must also have connection to the same router
-to which the primary router of the cell is connected. However, it must
-not be the 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 to as being a passive connection. Some keepalive actions may
-be needed by the router to keep the connection alive.
-
-It is required that other normal servers have 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.
-
-Also, if any other router in the network is using the cell's primary
-router as its own primary router, it must also have passive connection
-to the cell's backup router. It too is prepared to switch to use the
-backup router as its new primary router as soon as the original primary
-router becomes unresponsive.
-
-All of the parties of this protocol know which one is the backup router
-of the cell from their local configuration. Each of the entities must
-be configured accordingly and care must be taken when configuring the
-backup routers, servers and other routers in the network.
-
-It must be noted that some of the channel messages and private messages
-may be lost during the switch to the backup router. The announcements
-assure that the state of the network is not lost during the switch.
-
-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 local configuration
-phase. All the parties of this protocol must be configured accordingly to
-understand the order of the backup routers. It is not required that the
-backup server is actually an active server in the cell. The backup router
-may be a redundant server in the cell that does not accept normal client
-connections at all. It may be reserved purely for the backup purposes.
-
-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
-3.13.1 Switching to Backup Router
-
-When the primary router of the cell becomes unresponsive, for example
-by sending EOF to the connection, all the parties of this protocol MUST
-replace the old connection to the primary router with first configured
-backup router. The backup router usually needs to do local modifications
-to its database in order to update all the information needed to maintain
-working routes. The backup router must understand that clients that
-were originated from the primary router are now originated from some of
-the existing server connections and must update them accordingly. It
-must also remove those clients that were owned by the primary router
-since those connections were lost when the primary router became
-unresponsive.
-
-All the other parties of the protocol must also update their local
-database to understand that the route to the primary router will now go
-to the backup router.
-
-Servers connected to the backup router MUST send SILC_PACKET_RESUME_ROUTER
-packet with type value 21, to indicate that the server will start using
-the backup router as primary router. The backup router MUST NOT allow
-this action if it detects that primary is still up and running. If
-backup router knows that primary is up and running it MUST send
-SILC_PACKET_FAILURE with type value 21 (4 bytes, MSB first order) back
-to the server. The server then MUST NOT use the backup as primary
-router, but must try to establish connection back to the primary router.
-If the action is allowed type value 21 is sent back to the server from
-the backup router. It is RECOMMENDED that implementations use the
-SILC_COMMAND_PING command to detect whether primary router is responsive.
-
-The servers connected to the backup router must then announce their
-clients, channels, channel users, channel user modes, channel modes,
-topics and other information to the backup router. This is to assure
-that none of the important notify packets were lost during the switch
-to the backup router. The backup router must check which of these
-announced entities it already has and distribute the new ones to the
-primary router.
-
-The backup router too must announce its servers, clients, channels
-and other information to the new primary router. The primary router
-of the backup router too must announce its information to the backup
-router. Both must process only the ones they do not know about. If
-any of the announced modes do not match then they are enforced in
-normal manner as defined in section 4.2.1 Announcing Clients, Channels
-and Servers.
-
-
-.ti 0
-3.13.2 Resuming Primary Router
-
-Usually the primary router is unresponsive only a short period of time
-and it is intended that the original router of the cell will resume
-its position as primary router when it comes back online. The backup
-router that is now acting as primary router of the cell must constantly
-try to connect to the original primary router of the cell. It is
-RECOMMENDED that it would try to reconnect in 30 second intervals to
-the primary router.
-
-When the connection is established to the primary router the backup
-resuming protocol is executed. The protocol is advanced as follows:
-
- 1. Backup router sends SILC_PACKET_RESUME_ROUTER packet with type
- value 1 to the primary router that came back online. The packet
- will indicate the primary router has been replaced by the backup
- router. After sending the packet the backup router will announce
- all of its channels, channel users, modes etc. to the primary
- router.
-
- If the primary knows that it has not been replaced (for example
- the backup itself disconnected from the primary router and thinks
- that it is now primary in the cell) the primary router send
- SILC_PACKET_FAILURE with the type value 1 (4 bytes, MSB first
- order) back to the backup router. If backup receives this it
- MUST NOT continue with the backup resuming protocol.
-
- 2. Backup router sends SILC_PACKET_RESUME_ROUTER packet with type
- value 1 to its current primary router to indicate that it will
- resign as being primary router. Then, backup router sends the
- SILC_PACKET_RESUME_ROUTER packet with type value 1 to all
- connected servers to also indicate that it will resign as being
- primary router.
-
- 3. Backup router also send SILC_PACKET_RESUME_ROUTER packet with
- type value 1 to the router that is using the backup router
- currently as its primary router.
-
- 4. Any server and router that receives the SILC_PACKET_RESUME_ROUTER
- with type value 1 must reconnect immediately to the primary
- router of the cell that came back online. After they have created
- the connection they MUST NOT use that connection as active primary
- route but still route all packets to the backup router. After
- the connection is created they MUST send SILC_PACKET_RESUME_ROUTER
- with type value 2 back to the backup router. The session ID value
- found in the first packet MUST be set in this packet.
-
- 5. Backup router MUST wait for all packets with type value 2 before
- it continues with the protocol. It knows from the session ID values
- set in the packet when it has received all packets. The session
- value should be different in all packets it has sent earlier.
- After the packets are received the backup router sends the
- SILC_PACKET_RESUME_ROUTER packet with type value 3 to the
- primary router that came back online. This packet will indicate
- that the backup router is now ready to resign as being primary
- router. The session ID value in this packet MUST be the same as
- in the first packet sent to the primary router. During this time
- the backup router must still route all packets it is receiving
- from server connections.
-
- 6. The primary router receives the packet and send the packet
- SILC_PACKET_RESUME_ROUTER with type value 4 to all connected servers
- including the backup router. It also sends the packet with type
- value 4 to its primary router, and to the router that is using
- it as its primary router. The Session ID value in this packet
- SHOULD be zero (0).
-
- 7. Any server and router that receives the SILC_PACKET_RESUME_ROUTER
- packet with type value 4 must switch their primary route to the new
- primary router and remove the route for the backup router, since
- it is no longer the primary router of the cell. They must also
- update their local database to understand that the clients are
- not originated from the backup router but from the locally connected
- servers. After that they MUST announce their channels, channel
- users, modes etc. to the primary router. They MUST NOT use the
- backup router connection after this and the connection is considered
- to be a passive connection. The implementation SHOULD be able
- to disable the connection without closing the actual link.
-
-After this protocol is executed the backup router is now again a normal
-server in the cell that has the backup link to the primary router. The
-primary router feeds the router specific data again to the backup router.
-All server connections to the backup router are considered passive
-connections.
-
-When the primary router of the cell comes back online and connects
-to its remote primary router, the remote primary router MUST send the
-SILC_PACKET_RESUME_ROUTER packet with type value 20 indicating that the
-connection is not allowed since the router has been replaced by an
-backup router in the cell. The session ID value in this packet SHOULD be
-zero (0). When the primary router receives this packet it MUST NOT use
-the connection as active connection but must understand that it cannot
-act as primary router in the cell, until the backup resuming protocol has
-been executed.
-
-The following type values has been defined for SILC_PACKET_RESUME_ROUTER
-packet:
-
- 1 SILC_SERVER_BACKUP_START
- 2 SILC_SERVER_BACKUP_START_CONNECTED
- 3 SILC_SERVER_BACKUP_START_ENDING
- 4 SILC_SERVER_BACKUP_START_RESUMED
- 20 SILC_SERVER_BACKUP_START_REPLACED
- 21 SILC_SERVER_BACKUP_START_USE
-
-If any other value is found in the type field the packet MUST be
-discarded. The SILC_PACKET_RESUME_ROUTER packet and its payload
-is defined in [SILC2].
-
-
-.ti 0
-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 references [SILC2], [SILC3] and [SILC4] permeate this
-section's definitions.
-
-
-
-
-.ti 0
-4.1 Creating Client Connection
-
-This section describes the procedure when a 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, a 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. The 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 perform
-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
-MUST register itself by sending SILC_PACKET_NEW_CLIENT packet to the
-server. This packet includes various information about the client
-that the server uses to register the client. Server registers 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 that
-information rather than what it received from client. This is a 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 may set the nickname to something
-more desirable 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].
-
-Router server MUST also check whether some client in the local cell
-is watching for the nickname this new client has, and send the
-SILC_NOTIFY_TYPE_WATCH to the watcher.
-
-
-.ti 0
-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 to when a 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 authentication or public key authentication based on
-digital signatures.
-
-After server and router have successfully performed the key exchange
-and connection authentication protocol, the server MUST 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. The router receiving the
-ID MUST verify that the IP address in the Server ID is same as the
-server's real IP address.
-
-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 is in [SILC2].
-
-As the 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.
-
-
-.ti 0
-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.
-Channels' mode and founder public key and other channel mode specific
-data is announced by sending SILC_NOTIFY_TYPE_CMODE_CHANGE notify list.
-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.
-
-Also, clients' modes (user modes in SILC) MUST be announced. This is
-done by compiling a list of Notify Payloads with SILC_NOTIFY_UMODE_CHANGE
-notify type into the SILC_PACKET_NOTIFY packet. Also, channels' topics
-MUST be announced by compiling a list of Notify Payloads with the
-SILC_NOTIFY_TOPIC_SET notify type into the SILC_PACKET_NOTIFY packet.
-
-The router which receives these lists MUST process them and broadcast
-the packets to its primary router. 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 already 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.
-
-
-.ti 0
-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 the 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 have 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 have 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 are set for the client.
-
-If the router created the channel in the process, information about the
-new channel MUST be broadcast 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 or distributed if the SILC_CMODE_PRIVKEY mode is set.
-
-
-.ti 0
-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 client MUST start
-using the new key. If server creates the new key the server MUST also
-send the new key to its router. See [SILC2] for more information about
-how channel messages must be encrypted and decrypted when router is
-processing them.
-
-If the key changes very often due to joining traffic on the channel it
-is RECOMMENDED that client implementation would cache some of the old
-channel keys for short period of time so that it is able to decrypt all
-channel messages it receives. It is possible that on a heavy traffic
-channel a message encrypted with channel key that was just changed
-is received by client after the new key was set into use. This is
-possible because not all clients may receive the new key at the same
-time, and may still be sending messages encrypted with the old key.
-
-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 also MUST save the channel key.
-
-
-.ti 0
-4.5 Private Message Sending and Reception
-
-Private messages are sent point to point. Client explicitly destine
-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 in any
-other packet as well. The Source ID in the SILC Packet Header MUST be
-the ID of the sender of the message.
-
-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.
-
-If server receives a private message packet which includes invalid
-destination Client ID the server MUST send SILC_NOTIFY_TYPE_ERROR
-notify to the client with error status indicating that such Client ID
-does not exist.
-
-See [SILC2] for description of private message encryption and decryption
-process.
-
-
-.ti 0
-4.6 Private Message Key Generation
-
-Private message MAY be protected with a 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.
-The key sent inside the payload SHOULD be randomly generated. This
-packet MUST NOT be used to send pre-shared keys.
-
-Another choice is to entirely use keys that are not sent through
-the SILC network at all. This significantly adds security. This key
-could be a pre-shared key that is known by both of the clients. Both
-agree about using the key and start sending packets that indicate
-that the private message is secured using private message key. In
-case of pre-shared keys (static keys) the IV used in encryption SHOULD
-be chosen randomly.
-
-It is also possible to negotiate fresh key material by performing
-Key Agreement. The SILC_PACKET_KEY_AGREEMENT packet MAY be used to
-negotiate the fresh key material. In this case the resulting key
-material is used to secure the private messages. Also, the IV used
-in encryption is used as defined in [SILC3], unless otherwise stated
-by the encryption mode used. By performing Key Agreement the clients
-may negotiate the cipher and HMAC to be used in the private message
-encryption and to negotiate additional security parameters.
-
-If the key is pre-shared key or other key material not generated by
-Key Agreement, then the key material SHOULD be processed as defined
-in [SILC3]. The hash function to be used SHOULD be SHA1. 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].
-In this case also, implementations SHOULD use the SILC protocol's
-mandatory cipher and HMAC in private message encryption.
-
-
-.ti 0
-4.7 Channel Message Sending and Reception
-
-Channel messages are delivered to a group of users. The group forms a
-channel and all clients on the channel receives messages sent to the
-channel. The Source ID in the SILC Packet Header MUST be the ID
-of the sender of the message.
-
-Channel messages are destined to a 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. However,
-the Destination ID MUST still remain as the Channel ID.
-
-If server receives a channel message packet which includes invalid
-destination Channel ID the server MUST send SILC_NOTIFY_TYPE_ERROR
-notify to the sender with error status indicating that such Channel ID
-does not exist.
-
-See the [SILC2] for description of channel message routing for router
-servers, and channel message encryption and decryption process.
-
-
-.ti 0
-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 have 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.
-
-
-.ti 0
-4.9 Command Sending and Reception
-
-Client usually sends the commands in the SILC network. In this case
-the client simply sends the command packet to server and the server
-processes it and replies with command reply packet. See the [SILC4]
-for detailed description of all commands.
-
-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 [SILC4]. 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 servers. Client
-MUST NOT accept command reply packet originated from anyone else but
-from its own server.
-
-
-.ti 0
-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.
-
-Router server MUST also check whether some client in the local cell
-is watching for the nickname this client has, and send the
-SILC_NOTIFY_TYPE_WATCH to the watcher, unless the client which left
-the network has the SILC_UMODE_REJECT_WATCHING user mode set.
-
-
-
-
-.ti 0
-4.11 Detaching and Resuming a Session
-
-SILC protocol provides a possibility for a client to detach itself from
-the network without actually signing off from the network. The client
-connection to the server is closed but the client remains as valid client
-in the network. The client may then later resume its session back from
-any server in the network.
-
-When client wishes to detach from the network it MUST send the
-SILC_COMMAND_DETACH command to its server. The server then MUST set
-SILC_UMODE_DETACHED mode to the client and send SILC_NOTIFY_UMODE_CHANGE
-notify to its primary router, which then MUST broadcast it further
-to other routers in the network. This user mode indicates that the
-client is detached from the network. Implementations MUST NOT use
-the SILC_UMODE_DETACHED flag to determine whether a packet can be sent
-to the client. All packets MUST still be sent to the client even if
-client is detached from the network. Only the server that originally
-had the active client connection is able to make the decision after it
-notices that the network connection is not active. In this case the
-default case is to discard the packet.
-
-The SILC_UMODE_DETACHED flag cannot be set by client itself directly
-with SILC_COMMAND_UMODE command, but only implicitly by sending the
-SILC_COMMAND_DETACH command. The flag also cannot be unset by the
-client, server or router with SILC_COMMAND_UMODE command, but only
-implicitly by sending and receiving the SILC_PACKET_RESUME_CLIENT
-packet.
-
-When the client wishes to resume its session in the SILC Network it
-connects to a server in the network, which MAY also be a different
-from the original server, and performs normal procedures regarding
-creating a connection as described in section 4.1. After the SKE
-and the Connection Authentication protocols has been successfully
-completed the client MUST NOT send SILC_PACKET_NEW_CLIENT packet, but
-MUST send SILC_PACKET_RESUME_CLIENT packet. This packet is used to
-perform the resuming procedure. The packet MUST include the detached
-client's Client ID, which the client must know. It also includes
-Authentication Payload which includes signature computed with the
-client's private key. The signature is computed as defined in the
-section 3.9.1. Thus, the authentication method MUST be based in
-public key authentication.
-
-When server receive the SILC_PACKET_RESUME_CLIENT packet it MUST
-do the following: Server checks that the Client ID is valid client
-and that it has the SILC_UMODE_DETACHED mode set. Then it verifies
-the Authentication Payload with the detached client's public key.
-If it does not have the public key it retrieves it by sending
-SILC_COMMAND_GETKEY command to the server that has the public key from
-the original client connection. The server MUST NOT use the public
-key received in the SKE protocol for this connection. If the
-signature is valid the server unsets the SILC_UMODE_DETACHED flag,
-and sends the SILC_PACKET_RESUME_CLIENT packet to its primary router.
-The routers MUST broadcast the packet and unset the SILC_UMODE_DETACHED
-flag when the packet is received. If the server is router server it
-also MUST send the SILC_PACKET_RESUME_CLIENT packet to the original
-server whom owned the detached client.
-
-The servers and routers that receives the SILC_PACKET_RESUME_CLIENT
-packet MUST know whether the packet already has been received for
-the client. It is a protocol error to attempt to resume the client
-session from more than one server. The implementations could set
-internal flag that indicates that the client is resumed. If router
-receive SILC_PACKET_RESUME_CLIENT packet for client that is already
-resumed the client MUST be killed from the network. This would
-indicate that the client is attempting to resume the session more
-than once which is a protocol error. In this case the router sends
-SILC_NOTIFY_TYPE_KILLED to the client. All routers that detect
-the same situation MUST also send the notify for the client.
-
-The servers and routers that receive the SILC_PACKET_RESUME_CLIENT
-must also understand that the client may not be found behind the
-same server that it originally came from. They must update their
-caches according to this. The server that now owns the client session
-MUST check whether the Client ID of the resumed client is based
-on the server's Server ID. If it is not it creates a new Client
-ID and send SILC_NOTIFY_TYPE_NICK_CHANGE to the network. It MUST
-also send the channel keys of all channels that the client has
-joined to the client since it does not have them. Whether the
-Client ID was changed or not the server MUST send SILC_PACKET_NEW_ID
-packet to the client. Only after this is the client resumed back
-to the network and may start sending packets and messages.
-
-It is also possible that the server did not know about the global
-channels before the client resumed. In this case it joins the client
-to the channels, generates new channel keys and distributes the keys
-to the channels as described in section 4.4.
-
-It is an implementation issue for how long servers keep detached client
-sessions. It is RECOMMENDED that the detached sessions would be
-persistent as long as the server is running.
-
-
-.ti 0
-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 to 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 to acceptance to
-the SILC Network. Even though the SILC protocol is secure in a network
-of mutual distrust between clients, servers, routers and administrators
-of the servers, the client should be able to trust the servers they are
-using if they wish to do so.
-
-It however must be noted that if the client requires absolute security
-by not trusting any of the servers or routers in the SILC Network, it can
-be accomplished by negotiating private keys outside the SILC Network,
-either using SKE or some other key exchange 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 a foolproof system; the SILC servers and routers could very well be
-compromised. However, to provide an acceptable level of security and
-usability for end users, the protocol uses many times session keys or
-other keys generated by the servers to secure the messages. This is an
-intentional design feature to allow ease of use for end users. This way
-the network is still usable, and remains encrypted even if the external
-means of distributing the keys is not working. The implementation,
-however, may like to not follow this design feature, and may always
-negotiate the keys outside SILC network. This is an acceptable solution
-and many times recommended. The implementation still must be able to
-work with the server generated keys.
-
-If this is unacceptable for the client or end user, the private keys
-negotiated outside the SILC Network should always be used. In the end
-it is the 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,
- May 2002.
-
-[SILC3] Riikonen, P., "SILC Key Exchange and Authentication
- Protocols", Internet Draft, May 2002.
-
-[SILC4] Riikonen, P., "SILC Commands", Internet Draft, May 2002.
-
-[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.
-
-[RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO
- 10646", RFC 2279, January 1998.
-
-[RFC1321] Rivest R., "The MD5 Message-Digest Algorithm", RFC 1321,
- April 1992.
-
-[RFC3174] Eastlake, F., et al., "US Secure Hash Algorithm 1 (SHA1)",
- RFC 3174, September 2001.
-
-[PKCS7] Kalinski, B., "PKCS #7: Cryptographic Message Syntax,
- Version 1.5", RFC 2315, March 1998.
-
-[RFC2253] Wahl, M., et al., "Lightweight Directory Access Protocol
- (v3): UTF-8 String Representation of Distinguished Names",
- RFC 2253, December 1997.
-
-
-.ti 0
-7 Author's Address
-
-.nf
-Pekka Riikonen
-Snellmaninkatu 34 A 15
-70100 Kuopio
-Finland
-
-EMail: priikone@iki.fi
-
-
-.ti 0
-8 Full Copyright Statement
-
-Copyright (C) The Internet Society (2003). All Rights Reserved.
-
-This document and translations of it may be copied and furnished to
-others, and derivative works that comment on or otherwise explain it
-or assist in its implementation may be prepared, copied, published
-and distributed, in whole or in part, without restriction of any
-kind, provided that the above copyright notice and this paragraph are
-included on all such copies and derivative works. However, this
-document itself may not be modified in any way, such as by removing
-the copyright notice or references to the Internet Society or other
-Internet organizations, except as needed for the purpose of
-developing Internet standards in which case the procedures for
-copyrights defined in the Internet Standards process must be
-followed, or as required to translate it into languages other than
-English.
-
-The limited permissions granted above are perpetual and will not be
-revoked by the Internet Society or its successors or assigns.
-
-This document and the information contained herein is provided on an
-"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
-TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
-BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
-HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
-MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
projects / runtime.git / blobdiff