8 .ds RF FORMFEED[Page %]
17 Network Working Group P. Riikonen
19 draft-riikonen-silc-spec-05.txt XXX
25 Secure Internet Live Conferencing (SILC),
26 Protocol Specification
27 <draft-riikonen-silc-spec-05.txt>
32 This document is an Internet-Draft and is in full conformance with
33 all provisions of Section 10 of RFC 2026. Internet-Drafts are
34 working documents of the Internet Engineering Task Force (IETF), its
35 areas, and its working groups. Note that other groups may also
36 distribute working documents as Internet-Drafts.
38 Internet-Drafts are draft documents valid for a maximum of six months
39 and may be updated, replaced, or obsoleted by other documents at any
40 time. It is inappropriate to use Internet-Drafts as reference
41 material or to cite them other than as "work in progress."
43 The list of current Internet-Drafts can be accessed at
44 http://www.ietf.org/ietf/1id-abstracts.txt
46 The list of Internet-Draft Shadow Directories can be accessed at
47 http://www.ietf.org/shadow.html
49 The distribution of this memo is unlimited.
55 This memo describes a Secure Internet Live Conferencing (SILC)
56 protocol which provides secure conferencing services over insecure
57 network channel. SILC is IRC [IRC] like protocol, however, it is
58 not equivalent to IRC and does not support IRC. Strong cryptographic
59 methods are used to protect SILC packets inside the SILC network.
60 Three other Internet Drafts relates very closely to this memo;
61 SILC Packet Protocol [SILC2], SILC Key Exchange and Authentication
62 Protocols [SILC3] and SILC Commands [SILC4].
73 1 Introduction .................................................. 3
74 1.1 Requirements Terminology .................................. 4
75 2 SILC Concepts ................................................. 4
76 2.1 SILC Network Topology ..................................... 4
77 2.2 Communication Inside a Cell ............................... 5
78 2.3 Communication in the Network .............................. 6
79 2.4 Channel Communication ..................................... 7
80 2.5 Router Connections ........................................ 7
81 3 SILC Specification ............................................ 8
82 3.1 Client .................................................... 8
83 3.1.1 Client ID ........................................... 9
84 3.2 Server .................................................... 10
85 3.2.1 Server's Local ID List .............................. 10
86 3.2.2 Server ID ........................................... 11
87 3.2.3 SILC Server Ports ................................... 12
88 3.3 Router .................................................... 12
89 3.3.1 Router's Local ID List .............................. 12
90 3.3.2 Router's Global ID List ............................. 13
91 3.3.3 Router's Server ID .................................. 14
92 3.4 Channels .................................................. 14
93 3.4.1 Channel ID .......................................... 16
94 3.5 Operators ................................................. 16
95 3.6 SILC Commands ............................................. 16
96 3.7 SILC Packets .............................................. 17
97 3.8 Packet Encryption ......................................... 17
98 3.8.1 Determination of the Source and the Destination ..... 17
99 3.8.2 Client To Client .................................... 18
100 3.8.3 Client To Channel ................................... 19
101 3.8.4 Server To Server .................................... 20
102 3.9 Key Exchange And Authentication ........................... 20
103 3.9.1 Authentication Payload .............................. 20
104 3.10 Algorithms ............................................... 22
105 3.10.1 Ciphers ............................................ 22
106 3.10.2 Public Key Algorithms .............................. 23
107 3.10.3 Hash Functions ..................................... 24
108 3.10.4 MAC Algorithms ..................................... 24
109 3.10.5 Compression Algorithms ............................. 25
110 3.11 SILC Public Key .......................................... 25
111 3.12 SILC Version Detection ................................... 27
112 3.13 Backup Routers ........................................... 28
113 3.13.1 Switching to Backup Router ......................... 29
114 3.13.2 Resuming Primary Router ............................ 30
115 3.13.3 Discussion on Backup Router Scheme ................. 32
116 4 SILC Procedures ............................................... 33
117 4.1 Creating Client Connection ................................ 33
118 4.2 Creating Server Connection ................................ 34
119 4.2.1 Announcing Clients, Channels and Servers ............ 35
120 4.3 Joining to a Channel ...................................... 36
121 4.4 Channel Key Generation .................................... 37
122 4.5 Private Message Sending and Reception ..................... 38
123 4.6 Private Message Key Generation ............................ 38
124 4.7 Channel Message Sending and Reception ..................... 39
125 4.8 Session Key Regeneration .................................. 39
126 4.9 Command Sending and Reception ............................. 40
127 4.10 Closing Connection ....................................... 41
128 5 Security Considerations ....................................... 41
129 6 References .................................................... 42
130 7 Author's Address .............................................. 44
138 Figure 1: SILC Network Topology
139 Figure 2: Communication Inside cell
140 Figure 3: Communication Between Cells
141 Figure 4: Router Connections
142 Figure 5: SILC Public Key
148 This document describes a Secure Internet Live Conferencing (SILC)
149 protocol which provides secure conferencing services over insecure
150 network channel. SILC is IRC [IRC] like protocol, however, it is
151 not equivalent to IRC and does not support IRC.
153 Strong cryptographic methods are used to protect SILC packets inside
154 the SILC network. Three other Internet Drafts relates very closely
155 to this memo; SILC Packet Protocol [SILC2], SILC Key Exchange and
156 Authentication Protocols [SILC3] and SILC Commands [SILC4].
158 The protocol uses extensively packets as conferencing protocol
159 requires message and command sending. The SILC Packet Protocol is
160 described in [SILC2] and should be read to fully comprehend this
161 document and protocol. [SILC2] also describes the packet encryption
162 and decryption in detail.
164 The security of SILC protocol, and for any security protocol for that
165 matter, is based on strong and secure key exchange protocol. The SILC
166 Key Exchange protocol is described in [SILC3] along with connection
167 authentication protocol and should be read to fully comprehend this
168 document and protocol.
170 The SILC protocol has been developed to work on TCP/IP network
171 protocol, although it could be made to work on other network protocols
172 with only minor changes. However, it is recommended that TCP/IP
173 protocol is used under SILC protocol. Typical implementation would
174 be made in client-server model.
178 1.1 Requirements Terminology
180 The keywords MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED,
181 MAY, and OPTIONAL, when they appear in this document, are to be
182 interpreted as described in [RFC2119].
188 This section describes various SILC protocol concepts that forms the
189 actual protocol, and in the end, the actual SILC network. The mission
190 of the protocol is to deliver messages from clients to other clients
191 through routers and servers in secure manner. The messages may also
192 be delivered from one client to many clients forming a group, also
195 This section does not focus to security issues. Instead, basic network
196 concepts are introduced to make the topology of the SILC network
201 2.1 SILC Network Topology
203 SILC network is a cellular network as opposed to tree style network
204 topology. The rationale for this is to have servers that can perform
205 specific kind of tasks what other servers cannot perform. This leads
206 to two kinds of servers; normal SILC servers and SILC routers.
208 A difference between normal server and router server is that routers
209 knows everything about everything in the network. They also do the
210 actual routing of the messages to the correct receiver. Normal servers
211 knows only about local information and nothing about global information.
212 This makes the network faster as there are less servers that needs to
213 keep global information up to date at all time.
215 This, on the other hand, leads to cellular like network, where routers
216 are in the center of the cell and servers are connected to the router.
224 The following diagram represents SILC network topology.
228 ---- ---- ---- ---- ---- ----
229 | S8 | S5 | S4 | | S7 | S5 | S6 |
230 ----- ---- ----- ----- ---- -----
231 | S7 | S/R1 | S2 | --- | S8 | S/R2 | S4 |
232 ---- ------ ---- ---- ------ ----
233 | S6 | S3 | S1 | | S1 | S3 | S2 | ---- ----
234 ---- ---- ---- ---- ---- ---- | S3 | S1 |
235 Cell 1. \\ Cell 2. | \\____ ----- -----
237 ---- ---- ---- ---- ---- ---- ---- ------
238 | S7 | S4 | S2 | | S1 | S3 | S2 | | S2 | S5 |
239 ----- ---- ----- ----- ---- ----- ---- ----
240 | S6 | S/R3 | S1 | --- | S4 | S/R5 | S5 | ____/ Cell 4.
241 ---- ------ ---- ---- ------ ----
242 | S8 | S5 | S3 | | S6 | S7 | S8 | ... etc ...
243 ---- ---- ---- ---- ---- ----
248 Figure 1: SILC Network Topology
251 A cell is formed when a server or servers connect to one router. In
252 SILC network normal server cannot directly connect to other normal
253 server. Normal server may only connect to SILC router which then
254 routes the messages to the other servers in the cell. Router servers
255 on the other hand may connect to other routers to form the actual SILC
256 network, as seen in above figure. However, router is also normal SILC
257 server; clients may connect to it the same way as to normal SILC
258 server. Normal server also cannot have active connections to more
259 than one router. Normal server cannot be connected to two different
260 cells. Router servers, on the other hand, may have as many router to
261 router connections as needed.
263 There are many issues in this network topology that needs to be careful
264 about. Issues like the size of the cells, the number of the routers in
265 the SILC network and the capacity requirements of the routers. These
266 issues should be discussed in the Internet Community and additional
267 documents on the issue may be written.
271 2.2 Communication Inside a Cell
273 It is always guaranteed that inside a cell message is delivered to the
274 recipient with at most two server hops. A client which is connected to
275 server in the cell and is talking on channel to other client connected
276 to other server in the same cell, will have its messages delivered from
277 its local server first to the router of the cell, and from the router
278 to the other server in the cell.
280 The following diagram represents this scenario:
294 Figure 2: Communication Inside cell
297 Example: Client 1. connected to Server 1. send message to
298 Client 4. connected to Server 2. travels from Server 1.
299 first to Router which routes the message to Server 2.
300 which then sends it to the Client 4. All the other
301 servers in the cell will not see the routed message.
304 If the client is connected directly to the router, as router is also normal
305 SILC server, the messages inside the cell are always delivered only with
306 one server hop. If clients communicating with each other are connected
307 to the same server, no router interaction is needed. This is the optimal
308 situation of message delivery in the SILC network.
312 2.3 Communication in the Network
314 If the message is destined to server that does not belong to local cell
315 the message is routed to the router server to which the destination
316 server belongs, if the local router is connected to destination router.
317 If there is no direct connection to the destination router, the local
318 router routes the message to its primary route. The following diagram
319 represents message sending between cells.
324 1 --- S1 S4 --- 5 S2 --- 1
325 S/R - - - - - - - - S/R
335 Figure 3: Communication Between Cells
338 Example: Client 5. connected to Server 4. in Cell 1. sends message
339 to Client 2. connected to Server 1. in Cell 2. travels
340 from Server 4. to Router which routes the message to
341 Router in Cell 2, which then routes the message to
342 Server 1. All the other servers and routers in the
343 network will not see the routed message.
346 The optimal case of message delivery from the client point of view is
347 when clients are connected directly to the routers and the messages
348 are delivered from one router to the other.
352 2.4 Channel Communication
354 Messages may be sent to group of clients as well. Sending messages to
355 many clients works the same way as sending messages point to point, from
356 message delivery point of view. Security issues are another matter
357 which are not discussed in this section.
359 Router server handles the message routing to multiple recipients. If
360 any recipient is not in the same cell as the sender the messages are
363 Server distributes the channel message to its local clients which are
364 joined to the channel. Router also distributes the message to its
365 local clients on the channel.
369 2.5 Router Connections
371 Router connections play very important role in making the SILC like
372 network topology to work. For example, sending broadcast packets in
373 SILC network require special connections between routers; routers must
374 be connected in a specific way.
376 Every router has their primary route which is a connection to another
377 router in the network. Unless there is only two routers in the network
378 must not routers use each other as their primary routes. The router
379 connections in the network must form a ring.
387 Example with three routers in the network:
392 S/R1 - < - < - < - < - < - < - S/R2
395 \\ - > - > - S/R3 - > - > - /
400 Figure 4: Router Connections
403 Example: Network with three routers. Router 1. uses Router 2. as its
404 primary router. Router 2. uses Router 3. as its primary router,
405 and Router 3. uses Router 1. as its primary router. There may
406 be other direct connections between the routers but they must
407 not be used as primary routes.
409 The above example is applicable to any amount of routers in the network
410 except for two routers. If there are only two routers in the network both
411 routers must be able to handle situation where they use each other as their
414 The issue of router connections are very important especially with SILC
415 broadcast packets. Usually all router wide information in the network is
416 distributed by SILC broadcast packets. This sort of ring network, with
417 ability to have other direct routes in the network cause interesting
418 routing problems. The [SILC2] discusses the routing of packets in this
419 sort of network in more detail.
423 3. SILC Specification
425 This section describes the SILC protocol. However, [SILC2] and
426 [SILC3] describes other important protocols that are part of this SILC
427 specification and must be read.
433 A client is a piece of software connecting to SILC server. SILC client
434 cannot be SILC server. Purpose of clients is to provide the user
435 interface of the SILC services for end user. Clients are distinguished
436 from other clients by unique Client ID. Client ID is a 128 bit ID that
437 is used in the communication in the SILC network. The client ID is
438 based on the nickname selected by the user. User uses logical nicknames
439 in communication which are then mapped to the corresponding Client ID.
440 Client ID's are low level identifications and must not be seen by the
443 Clients provide other information about the end user as well. Information
444 such as the nickname of the user, username and the host name of the end
445 user and user's real name. See section 3.2 Server for information of
446 the requirements of keeping this information.
448 The nickname selected by the user is not unique in the SILC network.
449 There can be 2^8 same nicknames for one IP address. As for comparison
450 to IRC [IRC] where nicknames are unique this is a fundamental difference
451 between SILC and IRC. This causes the server names or client's host names
452 to be used along with the nicknames to identify specific users when sending
453 messages. This feature of SILC makes IRC style nickname-wars obsolete as
454 no one owns their nickname; there can always be someone else with the same
455 nickname. The maximum length of nickname is 128 bytes.
461 Client ID is used to identify users in the SILC network. The Client ID
462 is unique to the extent that there can be 2^128 different Client ID's,
463 and ID's based on IPv6 addresses extends this to 2^224 different Client
464 ID's. Collisions are not expected to happen. The Client ID is defined
470 128 bit Client ID based on IPv4 addresses:
472 32 bit Server ID IP address (bits 1-32)
473 8 bit Random number or counter
474 88 bit Truncated MD5 hash value of the nickname
476 224 bit Client ID based on IPv6 addresses:
478 128 bit Server ID IP address (bits 1-128)
479 8 bit Random number or counter
480 88 bit Truncated MD5 hash value of the nickname
482 o Server ID IP address - Indicates the server where this
483 client is coming from. The IP address hence equals the
484 server IP address where to the client has connected.
486 o Random number or counter - Random number to further
487 randomize the Client ID. Another choice is to use
488 a counter starting from the zero (0). This makes it
489 possible to have 2^8 same nicknames from the same
492 o MD5 hash - MD5 hash value of the nickname is truncated
493 taking 88 bits from the start of the hash value. This
494 hash value is used to search the user's Client ID from
498 Collisions could occur when more than 2^8 clients using same nickname
499 from the same server IP address is connected to the SILC network.
500 Server MUST be able to handle this situation by refusing to accept
501 anymore of that nickname.
503 Another possible collision may happen with the truncated hash value of
504 the nickname. It could be possible to have same truncated hash value for
505 two different nicknames. However, this is not expected to happen nor
506 cause any problems if it would occur. Nicknames are usually logical and
507 it is unlikely to have two distinct logical nicknames produce same
508 truncated hash value.
514 Servers are the most important parts of the SILC network. They form the
515 basis of the SILC, providing a point to which clients may connect to.
516 There are two kinds of servers in SILC; normal servers and router servers.
517 This section focus on the normal server and router server is described
518 in the section 3.3 Router.
520 Normal servers MUST NOT directly connect to other normal server. Normal
521 servers may only directly connect to router server. If the message sent
522 by the client is destined outside the local server it is always sent to
523 the router server for further routing. Server may only have one active
524 connection to router on same port. Normal server MUST NOT connect to other
525 cell's router except in situations where its cell's router is unavailable.
529 3.2.1 Server's Local ID List
531 Normal server keeps various information about the clients and their end
532 users connected to it. Every normal server MUST keep list of all locally
533 connected clients, Client ID's, nicknames, usernames and host names and
534 user's real name. Normal servers only keeps local information and it
535 does not keep any global information. Hence, normal servers knows only
536 about their locally connected clients. This makes servers efficient as
537 they don't have to worry about global clients. Server is also responsible
538 of creating the Client ID's for their clients.
540 Normal server also keeps information about locally created channels and
544 Hence, local list for normal server includes:
547 server list - Router connection
555 client list - All clients in server
565 channel list - All channels in server
568 o Client ID's on channel
569 o Client ID modes on channel
577 Servers are distinguished from other servers by unique 64 bit Server ID
578 (for IPv4) or 160 bit Server ID (for IPv6). The Server ID is used in
579 the SILC to route messages to correct servers. Server ID's also provide
580 information for Client ID's, see section 3.1.1 Client ID. Server ID is
584 64 bit Server ID based on IPv4 addresses:
586 32 bit IP address of the server
590 160 bit Server ID based on IPv6 addresses:
592 128 bit IP address of the server
596 o IP address of the server - This is the real IP address of
599 o Port - This is the port the server is bound to.
601 o Random number - This is used to further randomize the Server ID.
604 Collisions are not expected to happen in any conditions. The Server ID
605 is always created by the server itself and server is responsible of
606 distributing it to the router.
610 3.2.3 SILC Server Ports
612 The following ports has been assigned by IANA for the SILC protocol:
620 If there are needs to create new SILC networks in the future the port
621 numbers must be officially assigned by the IANA.
623 Server on network above privileged ports (>1023) SHOULD NOT be trusted
624 as they could have been set up by untrusted party.
630 Router server in SILC network is responsible for keeping the cell together
631 and routing messages to other servers and to other routers. Router server
632 is also a normal server thus clients may connect to it as it would be
633 just normal SILC server.
635 However, router servers has a lot of important tasks that normal servers
636 do not have. Router server knows everything about everything in the SILC.
637 They know all clients currently on SILC, all servers and routers and all
638 channels in SILC. Routers are the only servers in SILC that care about
639 global information and keeping them up to date at all time. And, this
640 is what they must do.
644 3.3.1 Router's Local ID List
646 Router server as well MUST keep local list of connected clients and
647 locally created channels. However, this list is extended to include all
648 the informations of the entire cell, not just the server itself as for
651 However, on router this list is a lot smaller since routers do not need
652 to keep information about user's nickname, username and host name and real
653 name since these are not needed by the router. The router keeps only
654 information that it needs.
657 Hence, local list for router includes:
660 server list - All servers in the cell
667 client list - All clients in the cell
671 channel list - All channels in the cell
673 o Client ID's on channel
674 o Client ID modes on channel
679 Note that locally connected clients and other information include all the
680 same information as defined in section section 3.2.1 Server's Local ID
685 3.3.2 Router's Global ID List
687 Router server MUST also keep global list. Normal servers do not have
688 global list as they know only about local information. Global list
689 includes all the clients on SILC, their Client ID's, all created channels
690 and their Channel ID's and all servers and routers on SILC and their
691 Server ID's. That is said, global list is for global information and the
692 list must not include the local information already on the router's local
695 Note that the global list does not include information like nicknames,
696 usernames and host names or user's real names. Router does not need to
697 keep these informations as they are not needed by the router. This
698 information is available from the client's server which maybe queried
701 Hence, global list includes:
704 server list - All servers in SILC
709 client list - All clients in SILC
712 channel list - All channels in SILC
714 o Client ID's on channel
715 o Client ID modes on channel
721 3.3.3 Router's Server ID
723 Router's Server ID's are equivalent to normal Server ID's. As routers
724 are normal servers as well same types of ID's applies for routers as well.
725 Thus, see section 3.2.2 Server ID.
731 A channel is a named group of one or more clients which will all receive
732 messages addressed to that channel. The channel is created when first
733 client requests JOIN command to the channel, and the channel ceases to
734 exist when the last client has left it. When channel exists, any client
735 can reference it using the name of the channel.
737 Channel names are unique although the real uniqueness comes from 64 bit
738 Channel ID. However, channel names are still unique and no two global
739 channels with same name may exist. The Channel name is a string of
740 maximum length of 256 bytes. Channel names MUST NOT contain any
741 spaces (` '), any non-printable ASCII characters, commas (`,') and
744 Channels can have operators that can administrate the channel and
745 operate all of its modes. The following operators on channel exist on
749 o Channel founder - When channel is created the joining client becomes
750 channel founder. Channel founder is channel operator with some more
751 privileges. Basically, channel founder can fully operate the channel
752 and all of its modes. The privileges are limited only to the
753 particular channel. There can be only one channel founder per
754 channel. Channel founder supersedes channel operator's privileges.
756 Channel founder privileges cannot be removed by any other operator on
757 channel. When channel founder leaves the channel there is no channel
758 founder on the channel. However, it is possible to set a mode for
759 the channel which allows the original channel founder to regain the
760 founder privileges even after leaving the channel. Channel founder
761 also cannot be removed by force from the channel.
763 o Channel operator - When client joins to channel that has not existed
764 previously it will become automatically channel operator (and channel
765 founder discussed above). Channel operator is able administrate the
766 channel, set some modes on channel, remove a badly behaving client
767 from the channel and promote other clients to become channel
768 operator. The privileges are limited only to the particular channel.
770 Normal channel user may be promoted (opped) to channel operator
771 gaining channel operator privileges. Channel founder or other
772 channel operator may also demote (deop) channel operator to normal
780 Channels are distinguished from other channels by unique Channel ID.
781 The Channel ID is a 64 bit ID (for IPv4) or 160 bit ID (for IPv6), and
782 collisions are not expected to happen in any conditions. Channel names
783 are just for logical use of channels. The Channel ID is created by the
784 server where the channel is created. The Channel ID is defined as
788 64 bit Channel ID based on IPv4 addresses:
790 32 bit Router's Server ID IP address (bits 1-32)
791 16 bit Router's Server ID port (bits 33-48)
794 160 bit Channel ID based on IPv6 addresses:
796 128 bit Router's Server ID IP address (bits 1-128)
797 16 bit Router's Server ID port (bits 129-144)
800 o Router's Server ID IP address - Indicates the IP address of
801 the router of the cell where this channel is created. This is
802 taken from the router's Server ID. This way SILC router knows
803 where this channel resides in the SILC network.
805 o Router's Server ID port - Indicates the port of the channel on
806 the server. This is taken from the router's Server ID.
808 o Random number - To further randomize the Channel ID. This makes
809 sure that there are no collisions. This also means that
810 in a cell there can be 2^16 channels.
817 Operators are normal users with extra privileges to their server or
818 router. Usually these people are SILC server and router administrators
819 that take care of their own server and clients on them. The purpose of
820 operators is to administrate the SILC server or router. However, even
821 an operator with highest privileges is not able to enter invite-only
822 channel, to gain access to the contents of a encrypted and authenticated
823 packets traveling in the SILC network or to gain channel operator
824 privileges on public channels without being promoted. They have the
825 same privileges as everyone else except they are able to administrate
826 their server or router.
832 Commands are very important part on SILC network especially for client
833 which uses commands to operate on the SILC network. Commands are used
834 to set nickname, join to channel, change modes and many other things.
836 Client usually sends the commands and server replies by sending a reply
837 packet to the command. Server MAY also send commands usually to serve
838 the original client's request. However, server MUST NOT send commands
839 to client and there are some commands that server must not send.
841 Note that the command reply is usually sent only after client has sent
842 the command request but server is allowed to send command reply packet
843 to client even if client has not requested the command. Client MAY,
844 choose to ignore the command reply.
846 It is expected that some of the commands may be miss-used by clients
847 resulting various problems on the server side. Every implementation
848 SHOULD assure that commands may not be executed more than once, say,
849 in two (2) seconds. However, to keep response rate up, allowing for
850 example five (5) commands before limiting is allowed. It is RECOMMENDED
851 that commands such as SILC_COMMAND_NICK, SILC_COMMAND_JOIN,
852 SILC_COMMAND_LEAVE and SILC_COMMAND_KILL SHOULD be limited in all cases
853 as they require heavy operations. This should be sufficient to prevent
854 the miss-use of commands.
856 SILC commands are described in [SILC4].
862 Packets are naturally the most important part of the protocol and the
863 packets are what actually makes the protocol. Packets in SILC network
864 are always encrypted using, usually the shared secret session key
865 or some other key, for example, channel key, when encrypting channel
866 messages. It is not possible to send packet in SILC network without
867 encryption. The SILC Packet Protocol is a wide protocol and is described
868 in [SILC2]. This document does not define or describe details of
873 3.8 Packet Encryption
875 All packets passed in SILC network MUST be encrypted. This section
876 defines how packets must be encrypted in the SILC network. The detailed
877 description of the actual encryption process of the packets are
878 described in [SILC2].
880 Client and its server shares secret symmetric session key which is
881 established by the SILC Key Exchange Protocol, described in [SILC3].
882 Every packet sent from client to server, with exception of packets for
883 channels, are encrypted with this session key.
885 Channels has their own key that are shared by every client on the channel.
886 However, the channel keys are cell specific thus one cell does not know
887 the channel key of the other cell, even if that key is for same channel.
888 Channel key is also known by the routers and all servers that has clients
889 on the channel. However, channels MAY have channel private keys that
890 are entirely local setting for the client. All clients on the channel
891 MUST know the channel private key before hand to be able to talk on the
892 channel. In this case, no server or router know the key for channel.
894 Server shares secret symmetric session key with router which is
895 established by the SILC Key Exchange Protocol. Every packet passed from
896 server to router, with exception of packets for channels, are encrypted
897 with the shared session key. Same way, router server shares secret
898 symmetric key with its primary route. However, every packet passed
899 from router to other router, including packets for channels, are
900 encrypted with the shared session key. Every router connection has
901 their own session keys.
905 3.8.1 Determination of the Source and the Destination
907 The source and the destination of the packet needs to be determined
908 to be able to route the packets to correct receiver. This information
909 is available in the SILC Packet Header which is included in all packets
910 sent in SILC network. The SILC Packet Header is described in [SILC2].
912 The header MUST be encrypted with the session key who is next receiver
913 of the packet along the route. The receiver of the packet, for example
914 a router along the route, is able to determine the sender and the
915 destination of the packet by decrypting the SILC Packet Header and
916 checking the ID's attached to the header. The ID's in the header will
917 tell to where the packet needs to be sent and where it is coming from.
919 The header in the packet MUST NOT change during the routing of the
920 packet. The original sender, for example client, assembles the packet
921 and the packet header and server or router between the sender and the
922 receiver MUST NOT change the packet header.
924 Note that the packet and the packet header may be encrypted with
925 different keys. For example, packets to channels are encrypted with
926 the channel key, however, the header is encrypted with the session key
927 as described above. However, the header and the packet may be encrypted
928 with same key. This is the case, for example, with command packets.
932 3.8.2 Client To Client
934 The process of message delivery and encryption from client to another
935 client is as follows.
937 Example: Private message from client to another client on different
938 servers. Clients do not share private message delivery
939 keys; normal session keys are used.
941 o Client 1. sends encrypted packet to its server. The packet is
942 encrypted with the session key shared between client and its
945 o Server determines the destination of the packet and decrypts
946 the packet. Server encrypts the packet with session key shared
947 between the server and its router, and sends the packet to the
950 o Router determines the destination of the packet and decrypts
951 the packet. Router encrypts the packet with session key
952 shared between the router and the destination server, and sends
953 the packet to the server.
955 o Server determines the client to which the packet is destined
956 to and decrypts the packet. Server encrypts the packet with
957 session key shared between the server and the destination client,
958 and sends the packet to the client.
960 o Client 2. decrypts the packet.
963 Example: Private message from client to another client on different
964 servers. Clients has established secret shared private
965 message delivery key with each other and that is used in
966 the message encryption.
968 o Client 1. sends encrypted packet to its server. The packet is
969 encrypted with the private message delivery key shared between
972 o Server determines the destination of the packet and sends the
973 packet to the router.
975 o Router determines the destination of the packet and sends the
976 packet to the server.
978 o Server determines the client to which the packet is destined
979 to and sends the packet to the client.
981 o Client 2. decrypts the packet with the secret shared key.
984 If clients share secret key with each other the private message
985 delivery is much simpler since servers and routers between the
986 clients do not need to decrypt and re-encrypt the packet.
988 The process for clients on same server is much simpler as there are
989 no need to send the packet to the router. The process for clients
990 on different cells is same as above except that the packet is routed
991 outside the cell. The router of the destination cell routes the
992 packet to the destination same way as described above.
996 3.8.3 Client To Channel
998 Process of message delivery from client on channel to all the clients
1001 Example: Channel of four users; two on same server, other two on
1002 different cells. Client sends message to the channel.
1004 o Client 1. encrypts the packet with channel key and sends the
1005 packet to its server.
1007 o Server determines local clients on the channel and sends the
1008 packet to the Client on the same server. Server then sends
1009 the packet to its router for further routing.
1011 o Router determines local clients on the channel, if found
1012 sends packet to the local clients. Router determines global
1013 clients on the channel and sends the packet to its primary
1014 router or fastest route.
1016 o (Other router(s) do the same thing and sends the packet to
1019 o Server determines local clients on the channel and sends the
1020 packet to the client.
1022 o All clients receiving the packet decrypts the packet.
1026 3.8.4 Server To Server
1028 Server to server packet delivery and encryption is described in above
1029 examples. Router to router packet delivery is analogous to server to
1030 server. However, some packets, such as channel packets, are processed
1031 differently. These cases are described later in this document and
1032 more in detail in [SILC2].
1036 3.9 Key Exchange And Authentication
1038 Key exchange is done always when for example client connects to server
1039 but also when server and router, and router and router connects to each
1040 other. The purpose of key exchange protocol is to provide secure key
1041 material to be used in the communication. The key material is used to
1042 derive various security parameters used to secure SILC packets. The
1043 SILC Key Exchange protocol is described in detail in [SILC3].
1045 Authentication is done after key exchange protocol has been successfully
1046 completed. The purpose of authentication is to authenticate for example
1047 client connecting to the server. However, usually clients are accepted
1048 to connect to server without explicit authentication. Servers are
1049 required use authentication protocol when connecting. The authentication
1050 may be based on passphrase (pre-shared-secret) or public key. All
1051 passphrases sent in SILC protocol MUST be UTF-8 [RFC2279] encoded.
1052 The connection authentication protocol is described in detail in [SILC3].
1056 3.9.1 Authentication Payload
1058 Authentication payload is used separately from the SKE and the Connection
1059 Authentication protocol. It is used during the session to authenticate
1060 with the remote. For example, the client can authenticate itself to the
1061 server to become server operator. In this case, Authentication Payload is
1064 The format of the Authentication Payload is as follows:
1070 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
1071 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1072 | Payload Length | Authentication Method |
1073 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1074 | Public Data Length | |
1075 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1079 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1080 | Authentication Data Length | |
1081 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1083 ~ Authentication Data ~
1085 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1089 Figure 5: Authentication Payload
1093 o Payload Length (2 bytes) - Length of the entire payload.
1095 o Authentication Method (2) - The method of the authentication.
1096 The authentication methods are defined in [SILC2] in the
1097 Connection Auth Request Payload. The NONE authentication
1098 method SHOULD NOT be used.
1100 o Public Data Length (2 bytes) - Indicates the length of
1101 the Public Data field.
1103 o Public Data (variable length) - This is defined only if
1104 the authentication method is public key. If it is any other
1105 this field MAY include a random data for padding purposes.
1106 However, in this case the field MUST be ignored by the
1109 When the authentication method is public key this includes
1110 128 to 4096 bytes of non-zero random data that is used in
1111 the signature process, described subsequently.
1113 o Authentication Data Length (2 bytes) - Indicates the
1114 length of the Authentication Data field.
1116 o Authentication Data (variable length) - Authentication
1117 method dependent authentication data.
1121 If the authentication method is password based, the Authentication
1122 Data field includes the plaintext UTF-8 encoded password. It is safe
1123 to send plaintext password since the entire payload is encrypted. In
1124 this case the Public Data Length is set to zero (0), but MAY also include
1125 random data for padding purposes. It is also RECOMMENDED that maximum
1126 amount of padding is applied to SILC packet when using password based
1127 authentication. This way it is not possible to approximate the length
1128 of the password from the encrypted packet.
1130 If the authentication method is public key based (or certificate)
1131 the Authentication Data is computed as follows:
1133 HASH = hash(random bytes | ID | public key (or certificate));
1134 Authentication Data = sign(HASH);
1136 The hash() and the sign() are the hash function and the public key
1137 cryptography function selected in the SKE protocol. The public key
1138 is SILC style public key unless certificates are used. The ID is the
1139 entity's ID (Client or Server ID) which is authenticating itself. The
1140 ID is raw ID data. The random bytes are non-zero random bytes of
1141 length between 128 and 4096 bytes, and will be included into the
1142 Public Data field as is.
1144 The receiver will compute the signature using the random data received
1145 in the payload, the ID associated to the connection and the public key
1146 (or certificate) received in the SKE protocol. After computing the
1147 receiver MUST verify the signature. In this case also, the entire
1148 payload is encrypted.
1154 This section defines all the allowed algorithms that can be used in
1155 the SILC protocol. This includes mandatory cipher, mandatory public
1156 key algorithm and MAC algorithms.
1162 Cipher is the encryption algorithm that is used to protect the data
1163 in the SILC packets. See [SILC2] of the actual encryption process and
1164 definition of how it must be done. SILC has a mandatory algorithm that
1165 must be supported in order to be compliant with this protocol.
1167 The following ciphers are defined in SILC protocol:
1170 aes-256-cbc AES in CBC mode, 256 bit key (REQUIRED)
1171 aes-192-cbc AES in CBC mode, 192 bit key (OPTIONAL)
1172 aes-128-cbc AES in CBC mode, 128 bit key (OPTIONAL)
1173 twofish-256-cbc Twofish in CBC mode, 256 bit key (OPTIONAL)
1174 twofish-192-cbc Twofish in CBC mode, 192 bit key (OPTIONAL)
1175 twofish-128-cbc Twofish in CBC mode, 128 bit key (OPTIONAL)
1176 blowfish-128-cbc Blowfish in CBC mode, 128 bit key (OPTIONAL)
1177 cast-256-cbc CAST-256 in CBC mode, 256 bit key (OPTIONAL)
1178 cast-192-cbc CAST-256 in CBC mode, 192 bit key (OPTIONAL)
1179 cast-128-cbc CAST-256 in CBC mode, 128 bit key (OPTIONAL)
1180 rc6-256-cbc RC6 in CBC mode, 256 bit key (OPTIONAL)
1181 rc6-192-cbc RC6 in CBC mode, 192 bit key (OPTIONAL)
1182 rc6-128-cbc RC6 in CBC mode, 128 bit key (OPTIONAL)
1183 mars-256-cbc Mars in CBC mode, 256 bit key (OPTIONAL)
1184 mars-192-cbc Mars in CBC mode, 192 bit key (OPTIONAL)
1185 mars-128-cbc Mars in CBC mode, 128 bit key (OPTIONAL)
1186 none No encryption (OPTIONAL)
1190 Algorithm none does not perform any encryption process at all and
1191 thus is not recommended to be used. It is recommended that no client
1192 or server implementation would accept none algorithms except in special
1195 Additional ciphers MAY be defined to be used in SILC by using the
1196 same name format as above.
1200 3.10.2 Public Key Algorithms
1202 Public keys are used in SILC to authenticate entities in SILC network
1203 and to perform other tasks related to public key cryptography. The
1204 public keys are also used in the SILC Key Exchange protocol [SILC3].
1206 The following public key algorithms are defined in SILC protocol:
1213 DSS is described in [Menezes]. The RSA MUST be implemented according
1214 PKCS #1 [PKCS1]. The mandatory PKCS #1 implementation in SILC MUST be
1215 compliant to either PKCS #1 version 1.5 or newer with the following
1216 notes: The signature encoding is always in same format as the encryption
1217 encoding regardless of the PKCS #1 version. The signature with appendix
1218 (with hash algorithm OID in the data) MUST NOT be used in the SILC. The
1219 rationale for this is that there is no binding between the PKCS #1 OIDs
1220 and the hash algorithms used in the SILC protocol. Hence, the encoding
1221 is always in PKCS #1 version 1.5 format.
1223 Additional public key algorithms MAY be defined to be used in SILC.
1227 3.10.3 Hash Functions
1229 Hash functions are used as part of MAC algorithms defined in the next
1230 section. They are also used in the SILC Key Exchange protocol defined
1233 The following Hash algorithm are defined in SILC protocol:
1236 sha1 SHA-1, length = 20 (REQUIRED)
1237 md5 MD5, length = 16 (OPTIONAL)
1242 3.10.4 MAC Algorithms
1244 Data integrity is protected by computing a message authentication code
1245 (MAC) of the packet data. See [SILC2] for details how to compute the
1248 The following MAC algorithms are defined in SILC protocol:
1251 hmac-sha1-96 HMAC-SHA1, length = 12 (REQUIRED)
1252 hmac-md5-96 HMAC-MD5, length = 12 (OPTIONAL)
1253 hmac-sha1 HMAC-SHA1, length = 20 (OPTIONAL)
1254 hmac-md5 HMAC-MD5, length = 16 (OPTIONAL)
1255 none No MAC (OPTIONAL)
1258 The none MAC is not recommended to be used as the packet is not
1259 authenticated when MAC is not computed. It is recommended that no
1260 client or server would accept none MAC except in special debugging
1263 The HMAC algorithm is described in [HMAC] and hash algorithms that
1264 are used as part of the HMACs are described in [Scheneir] and in
1267 Additional MAC algorithms MAY be defined to be used in SILC.
1273 3.10.5 Compression Algorithms
1275 SILC protocol supports compression that may be applied to unencrypted
1276 data. It is recommended to use compression on slow links as it may
1277 significantly speed up the data transmission. By default, SILC does not
1278 use compression which is the mode that must be supported by all SILC
1281 The following compression algorithms are defined:
1284 none No compression (REQUIRED)
1285 zlib GNU ZLIB (LZ77) compression (OPTIONAL)
1288 Additional compression algorithms MAY be defined to be used in SILC.
1292 3.11 SILC Public Key
1294 This section defines the type and format of the SILC public key. All
1295 implementations MUST support this public key type. See [SILC3] for
1296 other optional public key and certificate types allowed in the SILC
1297 protocol. Public keys in SILC may be used to authenticate entities
1298 and to perform other tasks related to public key cryptography.
1300 The format of the SILC Public Key is as follows:
1306 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
1307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1308 | Public Key Length |
1309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1310 | Algorithm Name Length | |
1311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1316 | Identifier Length | |
1317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1325 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1329 Figure 5: SILC Public Key
1333 o Public Key Length (4 bytes) - Indicates the full length
1334 of the public key, not including this field.
1336 o Algorithm Name Length (2 bytes) - Indicates the length
1337 of the Algorithm Length field, not including this field.
1339 o Algorithm name (variable length) - Indicates the name
1340 of the public key algorithm that the key is. See the
1341 section 3.10.2 Public Key Algorithms for defined names.
1343 o Identifier Length (2 bytes) - Indicates the length of
1344 the Identifier field, not including this field.
1346 o Identifier (variable length) - Indicates the identifier
1347 of the public key. This data can be used to identify
1348 the owner of the key. The identifier is of the following
1352 HN Host name or IP address
1359 Examples of an identifier:
1361 `UN=priikone, HN=poseidon.pspt.fi, E=priikone@poseidon.pspt.fi'
1363 `UN=sam, HN=dummy.fi, RN=Sammy Sam, O=Company XYZ, C=Finland'
1365 At least user name (UN) and host name (HN) MUST be provided as
1366 identifier. The fields are separated by commas (`,'). If
1367 comma is in the identifier string it must be written as `\\,',
1368 for example, `O=Company XYZ\\, Inc.'.
1370 o Public Data (variable length) - Includes the actual
1371 public data of the public key.
1373 The format of this field for RSA algorithm is
1382 The format of this field for DSS algorithm is
1394 The variable length fields are multiple precession
1395 integers encoded as strings in both examples.
1397 Other algorithms must define their own type of this
1398 field if they are used.
1401 All fields in the public key are in MSB (most significant byte first)
1406 3.12 SILC Version Detection
1408 The version detection of both client and server is performed at the
1409 connection phase while executing the SILC Key Exchange protocol. The
1410 version identifier is exchanged between initiator and responder. The
1411 version identifier is of the following format:
1414 SILC-<protocol version>-<software version>
1417 The version strings are of the following format:
1420 protocol version = <major>.<minor>
1421 software version = <major>[.<minor>[.<build or vendor string>]]
1424 Protocol version MAY provide both major and minor version. Currently
1425 implementations MUST set the protocol version and accept at least the
1426 protocol version as SILC-1.1-<software version>. If new protocol version
1427 causes in compatibilities with older version the the <minor> versio number
1428 MUST be incremented. The <major> is incremented if new protocol version
1429 is fully incompatible.
1431 Software version MAY provide major, minor and build (vendor) version.
1432 The software version MAY be freely set and accepted. The version string
1433 MUST consist of printable US-ASCII characters.
1436 Thus, the version strings could be, for example:
1441 SILC-1.1-1.0.VendorXYZ
1442 SILC-1.1-2.4.5 Vendor Limited
1449 Backup routers may exist in the cell in addition of the primary router.
1450 However, they must not be active routers and act as routers in the cell.
1451 Only one router may be acting as primary router in the cell. In the case
1452 of failure of the primary router may one of the backup routers become
1453 active. The purpose of backup routers are in case of failure of the
1454 primary router to maintain working connections inside the cell and outside
1455 the cell and to avoid netsplits.
1457 Backup routers are normal servers in the cell that are prepared to take
1458 over the tasks of the primary router if needed. They need to have at
1459 least one direct and active connection to the primary router of the cell.
1460 This communication channel is used to send the router information to
1461 the backup router. When the backup router connects to the primary router
1462 of the cell it MUST present itself as router server in the Connection
1463 Authentication protocol, even though it is normal server as long as the
1464 primary router is available. Reason for this is that the configuration
1465 needed in the responder end requires usually router connection level
1466 configuration. The responder, however must understand and treat the
1467 connection as normal server (except when feeding router level data to
1470 Backup router must know everything that the primary router knows to be
1471 able to take over the tasks of the primary router. It is the primary
1472 router's responsibility to feed the data to the backup router. If the
1473 backup router does not know all the data in the case of failure some
1474 connections may be lost. The primary router of the cell must consider
1475 the backup router being actual router server when it feeds the data to
1478 In addition of having direct connection to the primary router of the
1479 cell, the backup router must also have connection to the same router
1480 the primary router of the cell is connected. However, it must not be
1481 active router connection meaning that the backup router must not use
1482 that channel as its primary route and it must not notify the router
1483 about having connected servers, channels and clients behind it. It
1484 merely connects to the router. This sort of connection is later
1485 referred as being passive connection. Some keepalive actions may be
1486 needed by the router to keep the connection alive.
1488 It is required that other normal servers have passive connections to
1489 the backup router(s) in the cell. Some keepalive actions may be needed
1490 by the server to keep the connection alive. After they notice the
1491 failure of the primary router they must start using the connection to
1492 the first backup router as their primary route.
1494 Also, if any other router in the network is using the cell's primary
1495 router as its own primary router, it must also have passive connection
1496 to the cell's backup router. It too is prepared to switch to use the
1497 backup router as its new primary router as soon as the orignal primary
1498 router becomes unresponsive.
1500 All of the parties of this protocol knows which one is the backup router
1501 of the cell from their local configuration. Each of the entity must
1502 be configured accordingly and care must be taken when configuring the
1503 backup routers, servers and other routers in the network.
1505 It must be noted that some of the channel messages and private messages
1506 may be lost during the switch to the backup router. The announcements
1507 assures that the state of the network is not lost during the switch.
1509 It is RECOMMENDED that there would be at least one backup router in
1510 the cell. It is NOT RECOMMENDED to have all servers in the cell acting
1511 as backup routers as it requires establishing several connections to
1512 several servers in the cell. Large cells can easily have several
1513 backup routers in the cell.
1515 The order of the backup routers are decided at the configuration phase.
1516 All the parties of this protocol must be configured accordingly to
1517 understand the order of the backup routers. It is not required that
1518 the backup server is actually active server in the cell. Backup router
1519 may be a spare server in the cell that does not accept normal client
1520 connections at all. It may be reserved purely for the backup purposes.
1521 These, however, are cell management issues.
1523 If also the first backup router is down as well and there is another
1524 backup router in the cell then it will start acting as the primary
1525 router as described above.
1529 3.13.1 Switching to Backup Router
1531 When the primary router of the cell becomes unresponsive, for example
1532 by sending EOF to the connection, all the parties of this protocol MUST
1533 replace the old connection to the primary router with first configured
1534 backup router. The backup router usually needs to do local modifications
1535 to its database in order to update all the information needed to maintain
1536 working routes. The backup router must understand that clients that
1537 were orignated from the primary router are now originated from some of
1538 the existing server connections and must update them accordingly. It
1539 must also remove those clients that were owned by the primary router
1540 since those connections were lost when the primary router became
1543 All the other parties of the protocol must also update their local
1544 database to understand that the route to the primary router will now go
1545 to the backup router.
1547 The servers connected to the backup router must announce their clients,
1548 channels, channel users, channel user modes and channel modes to the
1549 backup router. This is to assure that none of the important notify
1550 packets were lost during the switch to the backup router. The backup
1551 router must check which of these announced entities it already have
1552 and distribute the new ones to the primary route.
1554 The backup router too must announce its servers, clients, channels
1555 and other information to the new primary router. The primary router
1556 of the backup router too must announce its informations to the backup
1557 router. Both must process only the ones they do not know about. If
1558 any of the announced modes does not match then they are enforced in
1559 normal manner defined later in this specification.
1563 3.13.2 Resuming Primary Router
1565 Usually the primary router is unresponsive only a short period of time
1566 and it is intended that the original router of the cell will reassume
1567 its position as primary router when it comes back online. The backup
1568 router that is now acting as primary router of the cell must constantly
1569 try to connect to the original primary router of the cell. It is
1570 RECOMMENDED that it would try to reconnect in 30 second intervals to
1573 When the connection is established to the primary router the backup
1574 resuming protocol is executed. The protocol is advanced as follows:
1576 1. Backup router sends SILC_PACKET_RESUME_ROUTER packet with type
1577 value 1 the primary router that came back online. The packet
1578 will indicate the primary router has been replaced by the backup
1579 router. After sending the packet the backup router will announce
1580 all of its channels, channel users, modes etc. to the primary
1583 2. Backup router sends SILC_PACKET_RESUME_ROUTER packet with type
1584 value 2 to its current primary router to indicate that it will
1585 resign as being primary router. Then, backup router sends the
1586 SILC_PACKET_RESUME_ROUTER packet with type value 1 to all
1587 connected servers to also indicate that it will resign as being
1590 3. Backup router also send SILC_PACKET_RESUME_ROUTER packet with
1591 type value 2 to the router that is using the backup router
1592 currently as its primary router.
1594 4. Any server and router that receives the SILC_PACKET_RESUME_ROUTER
1595 with type value 1 or 2 must reconnect immediately to the
1596 primary router of the cell that came back online. After they
1597 have created the connection they MUST NOT use that connection
1598 as active primary route but still route all packets to the
1599 backup router. After the connection is created they MUST send
1600 SILC_PACKET_RESUME_ROUTER with type value 3 back to the
1601 backup router. The session ID value found in the first packet
1602 MUST be set in this packet.
1604 5. Backup router MUST wait for all packets with type value 3 before
1605 it continues with the protocol. It knows from the session ID values
1606 set in the packet when it have received all packets. The session
1607 value should be different in all packets it have send earlier.
1608 After the packets is received the backup router sends the
1609 SILC_PACKET_RESUME_ROUTER packet with type value 4 to the
1610 primary router that came back online. This packet will indicate
1611 that the backup router is now ready to resign as being primary
1612 router. The session ID value in this packet MUST be the same as
1613 in first packet sent to the primary router. During this time
1614 the backup router should still route all packets it is receiving
1615 from server connections.
1617 6. The primary router receives the packet and send the
1618 SILC_PACKET_RESUME_ROUTER with type value 5 to all connected servers
1619 including the backup router. It also sends the packet with type
1620 value 6 to its primary router, and to the router that is using
1621 it as its primary router. The Session ID value in this packet
1624 7. Any server and router that receives the SILC_PACKET_RESUME_ROUTER
1625 with type value 5 or 6 must switch their primary route to the
1626 new primary router and remove the route for the backup router, since
1627 it is not anymore the primary router of the cell. They must also
1628 update their local database to understand that the clients are
1629 not originated from the backup router but from the locally connected
1630 servers. After that they MUST announce their channels, channel
1631 users, modes etc. to the primary router. They must not use the
1632 backup router connection after this and the connection is considered
1633 to be passive connection. The implementations SHOULD be able
1634 to disable the connection without closing the actual link.
1636 After this protocol is executed the backup router is now again normal
1637 server in the cell that has the backup link to the primary router. The
1638 primary router feeds the router specific data again to the backup router.
1639 All server connections in the backup router are considered passive
1642 When the primary router of the cell comes back online and connects
1643 to its primary router, the remote primary router must send the
1644 SILC_PACKET_RESUME_ROUTER with type value 20 indicating that the
1645 connection is not allowed since the router has been replaced by an
1646 backup router. The session ID value in this packet SHOULD be zero (0).
1647 When the router receives this packet it must not use the connection
1648 as active connection but to understand that it cannot act as primary
1649 router in the cell. It must wait that the backup router connects to
1650 it, and the backup resuming protocol is executed.
1652 The following type values has been defined for SILC_PACKET_RESUME_ROUTER
1655 1 SILC_SERVER_BACKUP_START
1656 2 SILC_SERVER_BACKUP_START_GLOBAL
1657 3 SILC_SERVER_BACKUP_START_CONNECTED
1658 4 SILC_SERVER_BACKUP_START_ENDING
1659 5 SILC_SERVER_BACKUP_START_RESUMED
1660 6 SILC_SERVER_BACKUP_START_GLOBAL
1661 20 SILC_SERVER_BACKUP_START_REPLACED
1663 If any other value is found in the type field the packet must be
1664 discarded. The SILC_PACKET_RESUME_ROUTER packet and its payload
1665 is defined in [SILC2].
1669 3.13.3 Discussion on Backup Router Scheme
1671 It is clear that this backup router support is not able to handle all
1672 possible situations arrising in unreliable network environment. This
1673 scheme for example does not handle situation when the router actually
1674 does not go offline but the network link goes down temporarily. It would
1675 require some intelligence to figure out when it is best time to switch
1676 to the backup router. To make it even more complicated it is possible
1677 that the backup router may have not lost the network link to the primary
1680 Other possible situation is when the network link is lost temporarily
1681 between two primary routers in the SILC network. Unless the routers
1682 notice the link going down they cannot perhaps find alternative routes.
1683 Worst situation is when the link goes down only for a short period of
1684 time, thus causing lag. Should the routers or servers find alternative
1685 routes if they cannot get response from the router during the lag?
1686 When alternative routes are being found it must be careful not to
1687 mess up existing primary routes between routers in the network.
1689 It is suggested that the current backup router scheme is only temporary
1690 solution and existing backup router protocols are studied further. It
1691 is also suggested that the backup router specification will be separated
1692 from this SILC specification Internet-Draft and additional specification
1693 is written on the subject.
1699 This section describes various SILC procedures such as how the
1700 connections are created and registered, how channels are created and
1701 so on. The section describes the procedures only generally as details
1702 are described in [SILC2] and [SILC3].
1706 4.1 Creating Client Connection
1708 This section describes the procedure when client connects to SILC server.
1709 When client connects to server the server MUST perform IP address lookup
1710 and reverse IP address lookup to assure that the origin host really is
1711 who it claims to be. Client, host, connecting to server SHOULD have
1712 both valid IP address and fully qualified domain name (FQDN).
1714 After that the client and server performs SILC Key Exchange protocol
1715 which will provide the key material used later in the communication.
1716 The key exchange protocol MUST be completed successfully before the
1717 connection registration may continue. The SILC Key Exchange protocol
1718 is described in [SILC3].
1720 Typical server implementation would keep a list of connections that it
1721 allows to connect to the server. The implementation would check, for
1722 example, the connecting client's IP address from the connection list
1723 before the SILC Key Exchange protocol has been started. Reason for
1724 this is that if the host is not allowed to connect to the server there
1725 is no reason to perform the key exchange protocol.
1727 After successful key exchange protocol the client and server performs
1728 connection authentication protocol. The purpose of the protocol is to
1729 authenticate the client connecting to the server. Flexible
1730 implementation could also accept the client to connect to the server
1731 without explicit authentication. However, if authentication is
1732 desired for a specific client it may be based on passphrase or
1733 public key authentication. If authentication fails the connection
1734 MUST be terminated. The connection authentication protocol is described
1737 After successful key exchange and authentication protocol the client
1738 registers itself by sending SILC_PACKET_NEW_CLIENT packet to the
1739 server. This packet includes various information about the client
1740 that the server uses to create the client. Server creates the client
1741 and sends SILC_PACKET_NEW_ID to the client which includes the created
1742 Client ID that the client MUST start using after that. After that
1743 all SILC packets from the client MUST have the Client ID as the
1744 Source ID in the SILC Packet Header, described in [SILC2].
1746 Client MUST also get the server's Server ID that is to be used as
1747 Destination ID in the SILC Packet Header when communicating with
1748 the server (for example when sending commands to the server). The
1749 ID may be resolved in two ways. Client can take the ID from an
1750 previously received packet from server that MUST include the ID,
1751 or to send SILC_COMMAND_INFO command and receive the Server ID as
1754 Server MAY choose not to use the information received in the
1755 SILC_PACKET_NEW_CLIENT packet. For example, if public key or
1756 certificate were used in the authentication, server MAY use those
1757 informations rather than what it received from client. This is suitable
1758 way to get the true information about client if it is available.
1760 The nickname of client is initially set to the username sent in the
1761 SILC_PACKET_NEW_CLIENT packet. User should set the nickname to more
1762 suitable by sending SILC_COMMAND_NICK command. However, this is not
1763 required as part of registration process.
1765 Server MUST also distribute the information about newly registered
1766 client to its router (or if the server is router, to all routers in
1767 the SILC network). More information about this in [SILC2].
1771 4.2 Creating Server Connection
1773 This section describes the procedure when server connects to its
1774 router (or when router connects to other router, the cases are
1775 equivalent). The procedure is very much alike when client connects
1776 to the server thus it is not repeated here.
1778 One difference is that server MUST perform connection authentication
1779 protocol with proper authentication. A proper authentication is based
1780 on passphrase or public key authentication.
1782 After server and router has successfully performed the key exchange
1783 and connection authentication protocol, the server register itself
1784 to the router by sending SILC_PACKET_NEW_SERVER packet. This packet
1785 includes the server's Server ID that it has created by itself and
1786 other relevant information about the server.
1788 After router has received the SILC_PACKET_NEW_SERVER packet it
1789 distributes the information about newly registered server to all routers
1790 in the SILC network. More information about this in [SILC2].
1792 As client needed to resolve the destination ID this MUST be done by the
1793 server that connected to the router, as well. The way to resolve it is
1794 to get the ID from previously received packet. The server MAY also
1795 use SILC_COMMAND_INFO command to resolve the ID. Server MUST also start
1796 using its own Server ID as Source ID in SILC Packet Header and the
1797 router's Server ID as Destination when communicating with the router.
1801 4.2.1 Announcing Clients, Channels and Servers
1803 After server or router has connected to the remote router, and it already
1804 has connected clients and channels it MUST announce them to the router.
1805 If the server is router server, also all the local servers in the cell
1808 All clients are announced by compiling a list of ID Payloads into the
1809 SILC_PACKET_NEW_ID packet. All channels are announced by compiling a
1810 list of Channel Payloads into the SILC_PACKET_NEW_CHANNEL packet. Also,
1811 the channel users on the channels must be announced by compiling a
1812 list of Notify Payloads with the SILC_NOTIFY_TYPE_JOIN notify type into
1813 the SILC_PACKET_NOTIFY packet. The users' modes on the channel must
1814 also be announced by compiling list of Notify Payloads with the
1815 SILC_NOTIFY_TYPE_CUMODE_CHANGE notify type into the SILC_PACKET_NOTIFY
1818 The router MUST also announce the local servers by compiling list of
1819 ID Payloads into the SILC_PACKET_NEW_ID packet.
1821 Also, clients' modes (user modes in SILC) MUST be announced. This is
1822 done by compiling a list of Notify Payloads with the
1823 SILC_NOTIFY_UMODE_CHANGE nofity type into the SILC_PACKET_NOTIFY packet.
1825 Also, channel's topics MUST be announced by compiling a list of Notify
1826 Payloads with the SILC_NOTIFY_TOPIC_SET notify type into the
1827 SILC_PACKET_NOTIFY packet.
1829 The router which receives these lists MUST process them and broadcast
1830 the packets to its primary route.
1832 When processing the announced channels and channel users the router MUST
1833 check whether a channel exists already with the same name. If channel
1834 exists with the same name it MUST check whether the Channel ID is
1835 different. If the Channel ID is different the router MUST send the notify
1836 type SILC_NOTIFY_TYPE_CHANNEL_CHANGE to the server to force the channel ID
1837 change to the ID the router has. If the mode of the channel is different
1838 the router MUST send the notify type SILC_NOTIFY_TYPE_CMODE_CHANGE to the
1839 server to force the mode change to the mode that the router has.
1841 The router MUST also generate new channel key and distribute it to the
1842 channel. The key MUST NOT be generated if the SILC_CMODE_PRIVKEY mode
1845 If the channel has channel founder on the router the router MUST send
1846 the notify type SILC_NOTIFY_TYPE_CUMODE_CHANGE to the server to force
1847 the mode change for the channel founder on the server. The channel
1848 founder privileges MUST be removed.
1850 The router processing the channels MUST also compile a list of
1851 Notify Payloads with the SILC_NOTIFY_TYPE_JOIN notify type into the
1852 SILC_PACKET_NOTIFY and send the packet to the server. This way the
1853 server (or router) will receive the clients on the channel that
1858 4.3 Joining to a Channel
1860 This section describes the procedure when client joins to a channel.
1861 Client joins to channel by sending command SILC_COMMAND_JOIN to the
1862 server. If the receiver receiving join command is normal server the
1863 server MUST check its local list whether this channel already exists
1864 locally. This would indicate that some client connected to the server
1865 has already joined to the channel. If this is case the client is
1866 joined to the channel, new channel key is created and information about
1867 newly joined channel is sent to the router. The router is informed
1868 by sending SILC_NOTIFY_TYPE_JOIN notify type. The notify type MUST
1869 also be sent to the local clients on the channel. The new channel key
1870 is also sent to the router and to local clients on the channel.
1872 If the channel does not exist in the local list the client's command
1873 MUST be sent to the router which will then perform the actual joining
1874 procedure. When server receives the reply to the command from the
1875 router it MUST be sent to the client which sent the command originally.
1876 Server will also receive the channel key from the server that it MUST
1877 send to the client which originally requested the join command. The
1878 server MUST also save the channel key.
1880 If the receiver of the join command is router it MUST first check its
1881 local list whether anyone in the cell has already joined to the channel.
1882 If this is the case the client is joined to the channel and reply is
1883 sent to the client. If the command was sent by server the command reply
1884 is sent to the server which sent it. Then the router MUST also create
1885 new channel key and distribute it to all clients on the channel and
1886 all servers that has clients on the channel. Router MUST also send
1887 the SILC_NOTIFY_TYPE_JOIN notify type to local clients on the channel
1888 and to local servers that has clients on the channel.
1890 If the channel does not exist on the router's local list it MUST
1891 check the global list whether the channel exists at all. If it does
1892 the client is joined to the channel as described previously. If
1893 the channel does not exist the channel is created and the client
1894 is joined to the channel. The channel key is also created and
1895 distributed as previously described. The client joining to the created
1896 channel is made automatically channel founder and both channel founder
1897 and channel operator privileges is set for the client.
1899 If the router created the channel in the process, information about the
1900 new channel MUST be broadcasted to all routers. This is done by
1901 broadcasting SILC_PACKET_NEW_CHANNEL packet to the router's primary
1902 route. When the router joins the client to the channel it MUST also
1903 send information about newly joined client to all routers in the SILC
1904 network. This is done by broadcasting the SILC_NOTIFY_TYPE_JOIN notify
1905 type to the router's primary route.
1907 It is important to note that new channel key is created always when
1908 new client joins to channel, whether the channel has existed previously
1909 or not. This way the new client on the channel is not able to decrypt
1910 any of the old traffic on the channel. Client which receives the reply to
1911 the join command MUST start using the received Channel ID in the channel
1912 message communication thereafter. Client also receives the key for the
1913 channel in the command reply. Note that the channel key is never
1914 generated if the SILC_CMODE_PRIVKEY mode is set.
1918 4.4 Channel Key Generation
1920 Channel keys are created by router which creates the channel by taking
1921 enough randomness from cryptographically strong random number generator.
1922 The key is generated always when channel is created, when new client
1923 joins a channel and after the key has expired. Key could expire for
1926 The key MUST also be re-generated whenever some client leaves a channel.
1927 In this case the key is created from scratch by taking enough randomness
1928 from the random number generator. After that the key is distributed to
1929 all clients on the channel. However, channel keys are cell specific thus
1930 the key is created only on the cell where the client, which left the
1931 channel, exists. While the server or router is creating the new channel
1932 key, no other client may join to the channel. Messages that are sent
1933 while creating the new key are still processed with the old key. After
1934 server has sent the SILC_PACKET_CHANNEL_KEY packet MUST client start
1935 using the new key. If server creates the new key the server MUST also
1936 send the new key to its router. See [SILC2] on more information about
1937 how channel messages must be encrypted and decrypted when router is
1940 When client receives the SILC_PACKET_CHANNEL_KEY packet with the
1941 Channel Key Payload it MUST process the key data to create encryption
1942 and decryption key, and to create the HMAC key that is used to compute
1943 the MACs of the channel messages. The processing is as follows:
1945 channel_key = raw key data
1946 HMAC key = hash(raw key data)
1948 The raw key data is the key data received in the Channel Key Payload.
1949 The hash() function is the hash function used in the HMAC of the channel.
1950 Note that the server MUST also save the channel key.
1954 4.5 Private Message Sending and Reception
1956 Private messages are sent point to point. Client explicitly destines
1957 a private message to specific client that is delivered to only to that
1958 client. No other client may receive the private message. The receiver
1959 of the private message is destined in the SILC Packet Header as any
1960 other packet as well.
1962 If the sender of a private message does not know the receiver's Client
1963 ID, it MUST resolve it from server. There are two ways to resolve the
1964 client ID from server; it is RECOMMENDED that client implementations
1965 send SILC_COMMAND_IDENTIFY command to receive the Client ID. Client
1966 MAY also send SILC_COMMAND_WHOIS command to receive the Client ID.
1967 If the sender has received earlier a private message from the receiver
1968 it should have cached the Client ID from the SILC Packet Header.
1970 If server receives a private message packet which includes invalid
1971 destionation Client ID the server MUST send SILC_COMMAND_IDENTIFY
1972 command reply packet destined to the client with error status.
1974 See [SILC2] for description of private message encryption and decryption
1979 4.6 Private Message Key Generation
1981 Private message MAY be protected by the key generated by the client.
1982 The key may be generated and sent to the other client by sending packet
1983 SILC_PACKET_PRIVATE_MESSAGE_KEY which travels through the network
1984 and is secured by session keys. After that the private message key
1985 is used in the private message communication between those clients.
1987 Other choice is to entirely use keys that are not sent through
1988 the SILC network at all. This significantly adds security. This key
1989 would be pre-shared-key that is known by both of the clients. Both
1990 agree about using the key and starts sending packets that indicate
1991 that the private message is secured using private message key.
1993 The key material used as private message key is implementation issue.
1994 However, SILC_PACKET_KEY_AGREEMENT packet MAY be used to negotiate
1995 the key material. If the key is normal pre-shared-key or randomly
1996 generated key, and the SILC_PACKET_KEY_AGREEMENT was not used, then
1997 the key material SHOULD be processed as defined in the [SILC3]. In
1998 the processing, however, the HASH, as defined in [SILC3] MUST be
1999 ignored. After processing the key material it is employed as defined
2000 in [SILC3], however, the HMAC key material MUST be discarded.
2002 If the key is pre-shared-key or randomly generated the implementations
2003 should use the SILC protocol's mandatory cipher as the cipher. If the
2004 SKE was used to negotiate key material the cipher was negotiated as well.
2007 4.7 Channel Message Sending and Reception
2009 Channel messages are delivered to group of users. The group forms a
2010 channel and all clients on the channel receives messages sent to the
2013 Channel messages are destined to channel by specifying the Channel ID
2014 as Destination ID in the SILC Packet Header. The server MUST then
2015 distribute the message to all clients on the channel by sending the
2016 channel message destined explicitly to a client on the channel.
2018 See the [SILC2] for description of channel messege routing for router
2021 See [SILC2] for description of channel message encryption and decryption
2026 4.8 Session Key Regeneration
2028 Session keys MUST be regenerated periodically, say, once in an hour.
2029 The re-key process is started by sending SILC_PACKET_REKEY packet to
2030 other end, to indicate that re-key must be performed. The initiator
2031 of the connection SHOULD initiate the re-key.
2033 If perfect forward secrecy (PFS) flag was selected in the SILC Key
2034 Exchange protocol [SILC3] the re-key MUST cause new key exchange with
2035 SKE protocol. In this case the protocol is secured with the old key
2036 and the protocol results to new key material. See [SILC3] for more
2037 information. After the SILC_PACKET_REKEY packet is sent the sender
2038 will perform the SKE protocol.
2040 If PFS flag was set the resulted key material is processed as described
2041 in the section Processing the Key Material in [SILC3]. The difference
2042 with re-key in the processing is that the initial data for the hash
2043 function is just the resulted key material and not the HASH as it
2044 is not computed at all with re-key. Other than that, the key processing
2045 it equivalent to normal SKE negotiation.
2047 If PFS flag was not set, which is the default case, then re-key is done
2048 without executing SKE protocol. In this case, the new key is created by
2049 providing the current sending encryption key to the SKE protocol's key
2050 processing function. The process is described in the section Processing
2051 the Key Material in [SILC3]. The difference in the processing is that
2052 the initial data for the hash function is the current sending encryption
2053 key and not the SKE's KEY and HASH values. Other than that, the key
2054 processing is equivalent to normal SKE negotiation.
2056 After both parties has regenerated the session key, both MUST send
2057 SILC_PACKET_REKEY_DONE packet to each other. These packets are still
2058 secured with the old key. After these packets, the subsequent packets
2059 MUST be protected with the new key.
2063 4.9 Command Sending and Reception
2065 Client usually sends the commands in the SILC network. In this case
2066 the client simply sends the command packet to server and the server
2067 processes it and replies with command reply packet.
2069 However, if the server is not able to process the command, it is sent
2070 to the server's router. This is case for example with commands such
2071 as, SILC_COMMAND_JOIN and SILC_COMMAND_WHOIS commands. However, there
2072 are other commands as well. For example, if client sends the WHOIS
2073 command requesting specific information about some client the server must
2074 send the WHOIS command to router so that all clients in SILC network
2075 are searched. The router, on the other hand, sends the WHOIS command
2076 further to receive the exact information about the requested client.
2077 The WHOIS command travels all the way to the server which owns the client
2078 and it replies with command reply packet. Finally, the server which
2079 sent the command receives the command reply and it must be able to
2080 determine which client sent the original command. The server then
2081 sends command reply to the client. Implementations should have some
2082 kind of cache to handle, for example, WHOIS information. Servers
2083 and routers along the route could all cache the information for faster
2084 referencing in the future.
2086 The commands sent by server may be sent hop by hop until someone is able
2087 to process the command. However, it is preferred to destine the command
2088 as precisely as it is possible. In this case, other routers en route
2089 MUST route the command packet by checking the true sender and true
2090 destination of the packet. However, servers and routers MUST NOT route
2091 command reply packets to clients coming from other server. Client
2092 MUST NOT accept command reply packet originated from anyone else but
2093 from its own server.
2097 4.10 Closing Connection
2099 When remote client connection is closed the server MUST send the notify
2100 type SILC_NOTIFY_TYPE_SIGNOFF to its primary router and to all channels
2101 the client was joined. The server MUST also save the client's information
2102 for a period of time for history purposes.
2104 When remote server or router connection is closed the server or router
2105 MUST also remove all the clients that was behind the server or router
2106 from the SILC Network. The server or router MUST also send the notify
2107 type SILC_NOTIFY_TYPE_SERVER_SIGNOFF to its primary router and to all
2108 local clients that are joined on the same channels with the remote
2109 server's or router's clients.
2113 5 Security Considerations
2115 Security is central to the design of this protocol, and these security
2116 considerations permeate the specification. Common security considerations
2117 such as keeping private keys truly private and using adequate lengths for
2118 symmetric and asymmetric keys must be followed in order to maintain the
2119 security of this protocol.
2121 Special attention must also be paid on the servers and routers that are
2122 running the SILC service. The SILC protocol's security depends greatly
2123 on the security and the integrity of the servers and administrators that
2124 are running the service. It is recommended that some form of registration
2125 is required by the server and router administrator prior acceptance to
2126 the SILC Network. Even though, the SILC protocol is secure in a network
2127 of mutual distrust between clients, servers, routers and adminstrators
2128 of the servers, the client should be able to trust the servers they are
2129 using if they whish to do so.
2131 It however must be noted that if the client requires absolute security
2132 by not trusting any of the servers or routers in the SILC Network, it can
2133 be accomplished by negotiating private keys outside the SILC Network,
2134 either using SKE or some other key exchange protocol, or to use some
2135 other external means for distributing the keys. This applies for all
2136 messages, private messages and channel messages.
2138 It is important to note that SILC, like any other security protocol is
2139 not full proof system and cannot secure from insecure environment; the
2140 SILC servers and routers could very well be compromised. However, to
2141 provide acceptable level of security and usability for end user the
2142 protocol use many times session keys or other keys generated by the
2143 servers to secure the messages. This is intentional design feature to
2144 allow ease of use for end user. This way the network is still usable,
2145 and remains encrypted even if the external means of distributing the
2146 keys is not working. The implementation, however, may like to not
2147 follow this design feature, and always negotiate the keys outside SILC
2148 network. This is acceptable solution and many times recommended. The
2149 implementation still must be able to work with the server generated keys.
2151 If this is unacceptable for the client or end user, the private keys
2152 negotiatied outside the SILC Network should always be used. In the end
2153 it is always implementor's choice whether to negotiate private keys by
2154 default or whether to use the keys generated by the servers.
2156 It is also recommended that router operators in the SILC Network would
2157 form a joint forum to discuss the router and SILC Network management
2158 issues. Also, router operators along with the cell's server operators
2159 should have a forum to discuss the cell management issues.
2165 [SILC2] Riikonen, P., "SILC Packet Protocol", Internet Draft,
2168 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2169 Protocols", Internet Draft, April 2001.
2171 [SILC4] Riikonen, P., "SILC Commands", Internet Draft, April 2001.
2173 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2176 [IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
2179 [IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
2182 [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
2185 [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
2188 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2191 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2194 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2197 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2198 Infrastructure, Certificate and CRL Profile", RFC 2459,
2201 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2202 John Wiley & Sons, New York, NY, 1996.
2204 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2207 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2208 RFC 2412, November 1998.
2210 [ISAKMP] Maughan D., et al, "Internet Security Association and
2211 Key Management Protocol (ISAKMP)", RFC 2408, November
2214 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2215 (IKE)", RFC 2409, November 1998.
2217 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2218 Authentication", RFC 2104, February 1997.
2220 [PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
2221 Specifications, Version 2.0", RFC 2437, October 1998.
2223 [RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate
2224 Requirement Levels", BCP 14, RFC 2119, March 1997.
2226 [RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO
2227 10646", RFC 2279, January 1998.
2236 Snellmanninkatu 34 A 15
2240 EMail: priikone@iki.fi
2242 This Internet-Draft expires XXX