X-Git-Url: http://git.silcnet.org/gitweb/?a=blobdiff_plain;f=doc%2Fdraft-riikonen-silc-spec-07.nroff;fp=doc%2Fdraft-riikonen-silc-spec-07.nroff;h=0000000000000000000000000000000000000000;hb=f9d9c92fcc179ff82ae7aa5f724440215f194827;hp=6dcbc302cdca1b116e3d7313a3e4df275453f35c;hpb=e7b6c157b80152bf9fb9266e6bdd93f9fb0db776;p=crypto.git diff --git a/doc/draft-riikonen-silc-spec-07.nroff b/doc/draft-riikonen-silc-spec-07.nroff deleted file mode 100644 index 6dcbc302..00000000 --- a/doc/draft-riikonen-silc-spec-07.nroff +++ /dev/null @@ -1,2579 +0,0 @@ -.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 - - -.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- AES in mode, 192 bit key (OPTIONAL) -aes-128- AES in mode, 128 bit key (RECOMMENDED) -twofish-256- Twofish in mode, 256 bit key (OPTIONAL) -twofish-192- Twofish in mode, 192 bit key (OPTIONAL) -twofish-128- Twofish in mode, 128 bit key (OPTIONAL) -cast-256- CAST-256 in mode, 256 bit key (OPTIONAL) -cast-192- CAST-256 in mode, 192 bit key (OPTIONAL) -cast-128- CAST-256 in mode, 128 bit key (OPTIONAL) -serpent-- Serpent in mode, bit key (OPTIONAL) -rc6-- RC6 in mode, bit key (OPTIONAL) -mars-- MARS in mode, bit key (OPTIONAL) -none No encryption (OPTIONAL) - -The is either "cbc", "ctr" or "rcbc". Other encryption modes MAY -be defined to be used in SILC using the same name format. The 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-- -.in 3 - -The version strings are of the following format: - -.in 6 -protocol version = . -software version = [.[.]] -.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-. If new protocol version -causes incompatibilities with older version the version number -MUST be incremented. The 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.