8 .ds RF FORMFEED[Page %]
17 Network Working Group P. Riikonen
19 draft-riikonen-silc-pp-00.txt 28 June 2000
26 <draft-riikonen-silc-pp-00.txt>
31 This document is an Internet-Draft and is in full conformance with
32 all provisions of Section 10 of RFC 2026. Internet-Drafts are
33 working documents of the Internet Engineering Task Force (IETF), its
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37 Internet-Drafts are draft documents valid for a maximum of six months
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39 time. It is inappropriate to use Internet-Drafts as reference
40 material or to cite them other than as "work in progress."
42 The list of current Internet-Drafts can be accessed at
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45 The list of Internet-Draft Shadow Directories can be accessed at
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48 The distribution of this memo is unlimited.
54 This memo describes a Packet Protocol used in the Secure Internet Live
55 Conferencing (SILC) protocol specified in the Secure Internet Live
56 Conferencing, Protocol Specification Internet Draft [SILC1]. This
57 protocol describes the packet types and packet payloads which defines
58 the contents of the packets. The protocol provides secure binary packet
59 protocol that assures that the contents of the packets are secured and
74 1 Introduction .................................................. 3
75 2 SILC Packet Protocol .......................................... 4
76 2.1 SILC Packet ............................................... 4
77 2.2 SILC Packet Header ........................................ 5
78 2.3 SILC Packet Types ......................................... 7
79 2.3.1 SILC Packet Payloads ................................ 15
80 2.3.2 Disconnect Payload .................................. 15
81 2.3.3 Success Payload ..................................... 16
82 2.3.4 Failure Payload ..................................... 16
83 2.3.5 Reject Payload ...................................... 17
84 2.3.6 Notify Payload ...................................... 17
85 2.3.7 Error Payload ....................................... 18
86 2.3.8 Channel Message Payload ............................. 19
87 2.3.9 Channel Key Payload ................................. 20
88 2.3.10 Private Message Payload ............................ 23
89 2.3.11 Private Message Key Payload ........................ 24
90 2.3.12 Command Payload .................................... 25
91 2.3.12.1 Command Argument Payload .................. 25
92 2.3.13 Command Reply Payload .............................. 26
93 2.3.14 Connection Auth Request Payload .................... 27
94 2.3.15 New ID Payload ..................................... 28
95 2.3.16 New ID List Payload ................................ 29
96 2.3.17 New Client Payload ................................. 29
97 2.3.18 New Server Payload ................................. 31
98 2.3.19 New Channel Payload ................................ 31
99 2.3.20 New Channel User Payload ........................... 32
100 2.3.21 New Channel List Payload ........................... 33
101 2.3.22 New Channel User List Payload ...................... 34
102 2.3.23 Replace ID Payload ................................. 34
103 2.3.24 Remove ID Payload .................................. 35
104 2.4 SILC ID Types ............................................. 36
105 2.5 Packet Encryption And Decryption .......................... 37
106 2.5.1 Normal Packet Encryption And Decryption ............. 37
107 2.5.2 Channel Message Encryption And Decryption ........... 37
108 2.5.3 Private Message Encryption And Decryption ........... 38
109 2.6 Packet MAC Generation ..................................... 39
110 2.7 Packet Padding Generation ................................. 39
111 2.8 Packet Compression ........................................ 40
112 2.9 Packet Sending ............................................ 40
113 2.10 Packet Reception ......................................... 41
114 2.11 Packet Broadcasting ...................................... 41
115 2.12 Packet Routing ........................................... 42
116 2.13 Packet Tunneling ......................................... 42
117 3 Security Considerations ....................................... 43
118 4 References .................................................... 43
119 5 Author's Address .............................................. 44
125 Figure 1: Typical SILC Packet
126 Figure 2: SILC Packet Header
127 Figure 3: Disconnect Payload
128 Figure 4: Success Payload
129 Figure 5: Failure Payload
130 Figure 6: Reject Payload
131 Figure 7: Notify Payload
132 Figure 8: Error Payload
133 Figure 9: Channel Message Payload
134 Figure 10: Channel Key Payload
135 Figure 11: Private Message Payload
136 Figure 12: Private Message Key Payload
137 Figure 13: Command Payload
138 Figure 14: Command Argument Payload
139 Figure 15: Connection Auth Request Payload
140 Figure 16: New ID Payload
141 Figure 17: New Client Payload
142 Figure 18: New Server Payload
143 Figure 19: New Channel Payload
144 Figure 20: New Channel User Payload
145 Figure 21: Replace ID Payload
146 Figure 22: Remove ID Payload
152 This document describes a Packet Protocol used in the Secure Internet
153 Live Conferencing (SILC) protocol specified in the Secure Internet Live
154 Conferencing, Protocol Specification Internet Draft [SILC1]. This
155 protocol describes the packet types and packet payloads which defines
156 the contents of the packets. The protocol provides secure binary packet
157 protocol that assures that the contents of the packets are secured and
160 The basis of SILC protocol relies in the SILC packets and it is with
161 out a doubt the most important part of the protocol. It is also probably
162 the most complicated part of the protocol. Packets are used all the
163 time in the SILC network to send messages, commands and other information.
164 All packets in SILC network are always encrypted and their integrity
165 is assured by computed MACs. The protocol defines several packet types
166 and packet payloads. Each packet type usually has a specific packet
167 payload that actually defines the contents of the packet. Each packet
168 also includes a default SILC Packet Header that provides sufficient
169 information about the origin of the packet and destination of the
174 2 SILC Packet Protocol
179 SILC packets deliver messages from sender to receiver securely by
180 encrypting important fields of the packet. The packet consists of
181 default SILC Packet Header, Padding, Packet Payload data, and, packet
184 The following diagram illustrates typical SILC packet.
189 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
190 | n bytes | 1 - n bytes | n bytes | n bytes
191 | SILC Header | Padding | Data Payload | MAC
192 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
196 Figure 1: Typical SILC Packet
199 SILC Header is always the first part of the packet and its purpose
200 is to provide information about the packet. It provides for example
201 the packet type, origin of the packet and the destination of the packet.
202 The header is variable in length and first two (2) bytes of the
203 header (thus first two bytes of the packet) are not encrypted. The
204 first two (2) bytes are the length of the packet which is not encrypted.
205 See following section for description of SILC Packet header. Packets
206 without SILC header or with malformed SILC header must be dropped.
208 Padding follows the packet header. The purpose of the padding is to
209 make the packet multiple by eight (8) or by the block size of the
210 cipher used in the encryption, which ever is larger. The maximum
211 length of padding is currently 16 bytes. The padding is always
214 Data payload area follows padding and it is the actual data of the
215 packet. The packet data is the packet payloads defined in this
216 protocol. The data payload area is always encrypted.
218 The last part of SILC packet is the packet MAC that assures the
219 integrity of the packet. The MAC is always computed from the packet
220 before the encryption is applied to the packet. If compression is used
221 in the packet the MAC is computed after the compression has been
222 applied. The compression, on the other hand, is always applied before
225 All fields in all packet payloads are always in MSB (most significant
230 2.2 SILC Packet Header
232 The default SILC packet header is applied to all SILC packets and it is
233 variable in length. The purpose of SILC Packet header is to provide
234 detailed information about the packet. The receiver of the packet uses
235 the packet header to parse the packet and gain other relevant parameters
238 Following diagram represents the default SILC header format.
239 (*) indicates that this field is never encrypted. Other fields are
246 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
247 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
248 | Payload Length * | Flags | Packet Type |
249 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
250 | Source ID Length | Destination ID Length |
251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
267 Figure 2: SILC Packet Header
271 o Payload Length (2 bytes) - Is the length of the packet
272 not including the padding of the packet. This field must
273 not be encrypted but must always be authenticated.
275 o Flags (1 byte) - Indicates flags to be used in packet
276 processing. Several flags may be set by ORing the flags
279 Following flags are reserved for this field:
286 In this case the field is ignored.
289 Private Message Key 0x01
291 Indicates that the packet must include private
292 message that is encrypted using private key set by
293 client. Servers does not know anything about this
294 key and this causes that the private message is
295 not handled by the server at all, it is just
296 passed along. See section 2.5.3 Private Message
297 Encryption And Decryption for more information.
302 Marks the packet to be broadcasted. Client cannot
303 send broadcast packet and normal server cannot send
304 broadcast packet. Only router server may send broadcast
305 packet. The router receiving of packet with this flag
306 set must send (broadcast) the packet to its primary
307 route. If router has several router connections the
308 packet may be sent only to the primary route. See
309 section 2.11 Packet Broadcasting for description of
315 Marks that the packet is tunneled. Tunneling means
316 that extra SILC Packet Header has been applied to the
317 original packet. The outer header has this flag
318 set. See section 2.13 Packet Tunneling for more
324 o Packet Type (1 byte) - Is the type of the packet. Receiver
325 uses this field to parse the packet. See section 2.3
326 SILC Packets for list of defined packet types.
328 o Source ID Length (2 bytes) - Indicates the length of the
329 Source ID field in the header, not including this or any
334 o Destination ID Length (2 bytes) - Indicates the length of the
335 Destination ID field in the header, not including this or
338 o Src ID Type (1 byte) - Indicates the type of ID in the
339 Source ID field. See section 2.4 SILC ID Types for
342 o Source ID (variable length) - The actual source ID that
343 indicates who is the original sender of the packet.
345 o Dst ID Type (1 byte) - Indicates the type of ID in the
346 Destination ID field. See section 2.4 SILC ID Types for
349 o Destination ID (variable length) - The actual source ID that
350 indicates who is the end receiver of the packet.
354 2.3 SILC Packet Types
356 SILC packet types defines the contents of the packet and it is used by
357 the receiver to parse the packet. The packet type is 8 bits, as a one
358 byte, in length. The range for the packet types are from 0 - 255,
359 where 0 is never sent and 255 is currently reserved for future
360 extensions and must not be defined to any other purpose. Every SILC
361 specification compliant implementation should support all of these packet
364 The below list of the SILC Packet types includes reference to the packet
365 payload as well. Packet payloads are the actual packet, that is, the data
366 that the packet consists of. Each packet type defines packet payload
367 which usually may only be sent with the specific packet type.
369 Most of the packets are packets that must be destined directly to entity
370 that is connected to the sender. It is not allowed, for example, for
371 router to send disconnect packet to client that is not directly connected
372 to the router. However, there are some special packet types that may
373 be destined to some entity that the sender has not direct connection
374 with. These packets are for example private message packets, channel
375 message packets, command packets and some other packets that may be
376 broadcasted in the SILC network. If the packet is allowed to be sent to
377 indirectly connected entity it is mentioned separately in the packet
378 description (unless it is obvious as in private and channel message
379 packets). Other packets must not be sent or accepted, if sent, to
380 indirectly connected entities.
382 List of SILC Packet types are defined as follows.
387 This type is reserved and it is never sent.
390 1 SILC_PACKET_DISCONNECT
392 This packet is sent to disconnect the remote end. Reason of
393 the disconnection is sent inside the packet payload. Client
394 usually does not send this packet.
396 Payload of the packet: See section 2.3.2 Disconnect Payload
399 2 SILC_PACKET_SUCCESS
401 This packet is sent upon successful execution of some protocol.
402 The status of the success is sent in the packet.
404 Payload of the packet: See section 2.3.3 Success Payload
407 3 SILC_PACKET_FAILURE
409 This packet is sent upon failure of some protocol. The status
410 of the failure is sent in the packet.
412 Payload of the packet: See section 2.3.4 Failure Payload
417 This packet may be sent upon rejection of some protocol.
418 The status of the rejection is sent in the packet.
420 Payload of the packet: See section 2.3.5 Reject Payload
425 This packet is used to send notify message, usually from
426 server to client, although it may be sent from server to another
427 server as well. Client never sends this packet. Server may
428 send this packet to channel as well when the packet is
429 distributed to all clients on the channel. Receiver of this
430 packet may ignore the packet if it chooses so. However, it
431 should not be ignored.
433 Payload of the packet: See section 2.3.6 Notify Payload.
438 This packet is sent when an error occurs. Server may
439 send this packet. Client never sends this packet. The
440 client may entirely ignore the packet, however, server is
441 most likely to take action anyway.
443 Payload of the packet: See section 2.3.7 Error Payload.
446 7 SILC_PACKET_CHANNEL_MESSAGE
448 This packet is used to send messages to channels. The packet
449 includes Channel ID of the channel and the actual message to
450 the channel. Messages sent to the channel are always protected
451 by channel specific keys. Channel Keys are distributed by
452 SILC_PACKET_CHANNEL_KEY packet.
454 When client sends this packet the destination ID in the SILC
455 header must be the Channel ID of the channel the message is
456 destined to. If server sends this packet to a client the
457 destination ID in the SILC header must be the Client ID of
458 the client receiving the packet.
460 If server sends this packet to router or if router sends this
461 packet to server or another router the destination ID in the
462 SILC header must be the Channel ID of the channel. Server
463 (including router) distributes this packet only to its local
464 clients who are joined to the channel. Servers and routers
465 also determines who are on the channel and when this packet
466 needs to be sent, as described in section Client To Client
469 Payload of the packet: See section 2.3.8 Channel Message
473 8 SILC_PACKET_CHANNEL_KEY
475 This packet is used to distribute new key for particular
476 channel. Each channel has their own independent keys that
477 is used to protect the traffic on the channel. Only server
478 may send this packet. This packet may be sent to entity
479 that is indirectly connected to the sender.
481 Payload of the packet: See section 2.3.9 Channel Key Payload
484 9 SILC_PACKET_PRIVATE_MESSAGE
486 This packet is used to send private messages from client
487 to another client. By default, private messages are protected
488 by session keys established by normal key exchange protocol.
489 However, it is possible to use specific key to protect private
490 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
491 agree the key with the remote client. Pre-shared key may be
492 used as well if both of the client knows it, however, it needs
493 to be agreed outside SILC. See more of this in [SILC1].
495 Payload of the packet: See section 2.3.10 Private Message
499 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
501 This packet is used to agree about a key to be used to protect
502 the private messages between two clients. If this is not sent
503 the normal session key is used to protect the private messages
504 inside SILC network. Agreeing to use specific key to protect
505 private messages adds security, as no server between the two
506 clients will be able to decrypt the private message. However,
507 servers inside SILC network are considered to be trusted, thus
508 using normal session key to protect private messages does not
509 degree security. Whether to agree to use specific keys by
510 default or to use normal session keys by default, is
511 implementation specific issue. See more of this in [SILC1].
513 Payload of the packet: See section 2.3.11 Private Message
517 11 SILC_PACKET_COMMAND
519 This packet is used to send commands from client to server.
520 Server may send this packet to other servers as well. All
521 commands are listed in their own section SILC Command Types
522 in [SILC1]. The contents of this packet is command specific.
523 This packet may be sent to entity that is indirectly connected
526 Payload of the packet: See section 2.3.12 Command Payload
529 12 SILC_PACKET_COMMAND_REPLY
531 This packet is send as reply to the SILC_PACKET_COMMAND packet.
532 The contents of this packet is command specific. This packet
533 maybe sent to entity that is indirectly connected to the sender.
535 Payload of the packet: See section 2.3.13 Command Reply
536 Payload and section 2.3.12 Command
540 13 SILC_PACKET_KEY_EXCHANGE
542 This packet is used to start SILC Key Exchange Protocol,
543 described in detail in [SILC3].
545 Payload of the packet: Payload of this packet is described
546 in the section SILC Key Exchange
547 Protocol and its sub sections in
551 14 SILC_PACKET_KEY_EXCHANGE_1
553 This packet is used as part of the SILC Key Exchange Protocol.
555 Payload of the packet: Payload of this packet is described
556 in the section SILC Key Exchange
557 Protocol and its sub sections in
561 15 SILC_PACKET_KEY_EXCHANGE_2
563 This packet is used as part of the SILC Key Exchange Protocol.
565 Payload of the packet: Payload of this packet is described
566 in the section SILC Key Exchange
567 Protocol and its sub sections in
571 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
573 This packet is used to request the authentication method to
574 be used in the SILC Connection Authentication Protocol. If
575 initiator of the protocol does not know the mandatory
576 authentication method this packet is used to determine it.
578 The party receiving this payload must respond with the same
579 packet including the mandatory authentication method.
581 Payload of the packet: See section 2.3.14 Connection Auth
585 17 SILC_PACKET_CONNECTION_AUTH
587 This packet is used to start and perform the SILC Connection
588 Authentication Protocol. This protocol is used to authenticate
589 the connecting party. The protocol is described in detail in
592 Payload of the packet: Payload of this packet is described
593 in the section SILC Authentication
594 Protocol and it sub sections in [SILC].
597 18 SILC_PACKET_NEW_ID
599 This packet is used to distribute new ID's from server to
600 router and from router to all routers in the SILC network.
601 This is used when for example new client is registered to
602 SILC network. The newly created ID's of these operations are
603 distributed by this packet. Only server may send this packet,
604 however, client must be able to receive this packet.
606 Payload of the packet: See section 2.3.15 New ID Payload
609 19 SILC_PACKET_NEW_ID_LIST
611 This packet is used to distribute list of new ID's from
612 server to routers. This is equivalent to previous packet
613 type except that it may include several ID's. Client must
614 not send this packet.
616 Payload of the packet: See section 2.3.16 New ID List
620 20 SILC_PACKET_NEW_CLIENT
622 This packet is used by client to register itself to the
623 SILC network. This is sent after key exchange and
624 authentication protocols has been completed. Client sends
625 various information about itself in this packet.
627 Payload of the packet: See section 2.3.17 New Client Payload
630 21 SILC_PACKET_NEW_SERVER
632 This packet is used by server to register itself to the
633 SILC network. This is sent after key exchange and
634 authentication protocols has been completed. Server sends
635 this to the router it connected to, or, if router was
636 connecting, to the connected router. Server sends
637 its Server ID and other information in this packet.
638 Client must not send or receive this packet.
640 Payload of the packet: See section 2.3.18 New Server Payload
643 22 SILC_PACKET_NEW_CHANNEL
645 This packet is used to notify routers about newly created
646 channel. Channels are always created by the router and it must
647 notify other routers about the created channel. Router sends
648 this packet to its primary route. Client must not send this
649 packet. This packet maybe sent to entity that is indirectly
650 connected to the sender.
652 Payload of the packet: See section 2.3.19 New Channel Payload
655 23 SILC_PACKET_NEW_CHANNEL_USER
657 This packet is used to notify routers about new user on channel.
658 The packet is sent after user has joined to the channel. Server
659 may send this packet to its router and router may send this to
660 its primary router. Client must not send this packet. This
661 packet maybe sent to entity that is indirectly connected to the
664 Payload of the packet: See section 2.3.20 New Channel User
668 24 SILC_PACKET_NEW_CHANNEL_LIST
670 This packet is used to distribute list of created channels
671 from server to routers. This is equivalent to the packet
672 SILC_PACKET_NEW_CHANNEL except that it may include several
673 payloads. Client must not send this packet.
675 Payload of the packet: See section 2.3.21 New Channel List
679 25 SILC_PACKET_NEW_CHANNEL_USER_LIST
681 This packet is used to distribute list of users on specific
682 channel from server to routers. This is equivalent to the
683 packet SILC_PACKET_NEW_CHANNEL_USER except that it may
684 include several payloads. Client must not send this packet.
686 Payload of the packet: See section 2.3.22 New Channel User
690 26 SILC_PACKET_REPLACE_ID
692 This packet is used to replace old ID with new ID sent in
693 the packet payload. For example, when client changes its
694 nickname new ID is created and this packet can be used to
695 distribute the new ID and the old ID is removed when it is
696 send in the packet. Client cannot send or receive this
697 packet. This packet maybe sent to entity that is indirectly
698 connected to the sender.
700 Payload of the packet: See section 2.3.23 Replace ID Payload
703 27 SILC_PACKET_REMOVE_ID
705 This packet is used to removed ID. For example, when client
706 exits SILC network its ID is removed. Client must not send
707 this packet. This packet maybe sent to entity that is
708 indirectly connected to the sender.
710 Payload of the packet: See section 2.3.24 Remove ID Payload
715 This packet is used to indicate that re-key must be performed
716 for session keys. See section Session Key Regeneration in
717 [SILC1] for more information. This packet does not have
723 29 SILC_PACKET_REKEY_DONE
725 This packet is used to indicate that re-key is performed and
726 new keys must be used hereafter. This is sent only if re-key
727 was done without PFS option. If PFS is set, this is not sent
728 as SILC Key Exchange protocol is executed. This packet does
734 Currently undefined commands.
739 This type is reserved for future extensions and currently it
745 2.3.1 SILC Packet Payloads
747 All payloads resides in the main data area of the SILC packet. However
748 all payloads must be at the start of the data area after the default
749 SILC packet header and padding. All fields in the packet payload are
750 always encrypted, as, they reside in the data area of the packet which
753 Payloads described in this section are common payloads that must be
754 accepted anytime during SILC session. Most of the payloads may only
755 be sent with specific packet type which is defined in the description
758 There are a lot of other payloads in the SILC as well. However, they
759 are not common in the sense that they could be sent at any time.
760 These payloads are not described in this section. These are payloads
761 such as SILC Key Exchange payloads and so on. These are described
762 in [SILC1] and [SILC3].
766 2.3.2 Disconnect Payload
768 Disconnect payload is sent upon disconnection. The payload is simple;
769 reason of disconnection is sent to the disconnected party.
771 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
772 must not be sent in any other packet type. Following diagram represents
773 the Disconnect Payload.
779 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
780 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
782 ~ Disconnect Message ~
784 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
788 Figure 3: Disconnect Payload
794 o Disconnect Message (variable length) - Human readable
795 reason of the disconnection.
800 2.3.3 Success Payload
802 Success payload is sent when some protocol execution is successfully
803 completed. The payload is simple; indication of the success is sent.
804 This maybe any data, including binary or human readable data.
809 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
810 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
812 ~ Success Indication ~
814 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
818 Figure 4: Success Payload
822 o Success Indication (variable length) - Indication of
823 the success. This maybe for example some flag that
824 indicates the protocol and the success status or human
825 readable success message. The true length of this
826 payload is available by calculating it from the SILC
832 2.3.4 Failure Payload
834 This is opposite of Success Payload. Indication of failure of
835 some protocol is sent in the payload.
841 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
842 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
844 ~ Failure Indication ~
846 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
850 Figure 5: Failure Payload
854 o Failure Indication (variable length) - Indication of
855 the failure. This maybe for example some flag that
856 indicates the protocol and the failure status or human
857 readable failure message. The true length of this
858 payload is available by calculating it from the SILC
866 This payload is sent when some protocol is rejected to be executed.
867 Other operations may send this as well that was rejected. The
868 indication of the rejection is sent in the payload. The indication
869 may be binary or human readable data.
875 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
876 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
878 ~ Reject Indication ~
880 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
884 Figure 6: Reject Payload
888 o Reject Indication (variable length) - Indication of
889 the rejection. This maybe for example some flag that
890 indicates the protocol and the rejection status or human
891 readable rejection message. The true length of this
892 payload is available by calculating it from the SILC
903 Notify payload is used to send notify messages. The payload is usually
904 sent from server to client, however, server may send it to another
905 server as well. Client must not send this payload. The receiver of
906 this payload may totally ignore the contents of the payload, however,
907 notify message should be noted and possibly logged.
909 The payload may only be sent with SILC_PACKET_NOTIFY packet. It must
910 not be sent in any other packet type. Following diagram represents the
916 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
917 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
921 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
925 Figure 7: Notify Payload
929 o Notify Message (variable length) - Human readable notify
937 Error payload is sent upon error. Error may occur in various
938 conditions when server sends this packet. Client may not send this
939 payload but must be able to accept it. However, client may
940 totally ignore the contents of the packet as server is going to
941 take action on the error anyway. However, it is recommended
942 that the client takes error packet seriously.
948 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
949 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
953 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
957 Figure 8: Error Payload
961 o Error Message (variable length) - Human readable error
967 2.3.8 Channel Message Payload
969 Channel messages are the most common messages sent in the SILC.
970 Channel Message Payload is used to send message to channels. These
971 messages can only be sent if client has joined to some channel.
972 Even though this packet is the most common in SILC it is still
973 special packet. Some special handling on sending and reception
974 of channel message is required.
976 Padding must be applied into this payload since the payload is
977 encrypted separately from other parts of the packet with the
978 channel specific key. Hence the requirement of the padding.
979 The padding should be random data. The packet must be made
980 multiple by eight (8) or by the block size of the cipher, which
983 The SILC header in this packet is encrypted with the session key
984 of the next receiver of the packet. Nothing else is encrypted
985 with that key. Thus, the actual packet and padding to be
986 encrypted with the session key is SILC Header plus padding to it
987 to make it multiple by eight (8) or multiple by the block size
988 of the cipher, which ever is larger.
990 Receiver of the the channel message packet is able to determine
991 the channel the message is destined to by checking the destination
992 ID from the SILC Packet header which tells the destination channel.
993 The original sender of the packet is also determined by checking
994 the source ID from the header which tells the who client sent
997 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
998 It must not be sent in any other packet type. Following diagram
999 represents the Channel Message Payload.
1001 (*) indicates that the field is not encrypted.
1027 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
1028 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1029 | Nickname Length | |
1030 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1034 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1035 | Message Length | |
1036 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1040 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1041 | Padding Length | |
1042 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1046 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1048 ~ Initial Vector * ~
1050 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1054 Figure 9: Channel Message Payload
1058 o Nickname Length (2 bytes) - Indicates the length of the
1059 Nickname field, not including any other field.
1061 o Nickname (variable length) - Nickname of the sender of the
1062 channel message. This should not be trusted as a definite
1063 sender of the channel message. The SILC Packet Header in
1064 the packet indicates the true sender of the packet and
1065 client should verify that the nickname sent here belongs
1066 to the Client ID in the SILC Packet Header. This nickname
1067 is merely provided to be displayed by the client.
1069 If server is sending this packet this field is not included
1070 and zero (0) length must be set to the Nickname Length field.
1072 o Message Length (2 bytes) - Indicates the length of the
1073 the Message Data field in the payload, not including any
1077 o Message Data (variable length) - The actual message to
1080 o Padding Length (2 bytes) - Indicates the length of the
1081 Padding field in the payload, not including any other
1084 o Padding (variable length) - The padding that must be
1085 applied because this payload is encrypted separately from
1086 other parts of the packet.
1088 o Initial Vector (variable length) - The initial vector
1089 that has been used in packet encryption. It needs to be
1090 used in the packet decryption as well. What this field
1091 includes is implementation issue. However, it is
1092 recommended that it would be random data or, perhaps,
1093 a timestamp. It is not recommended to use zero (0) as
1094 initial vector. This field is not encrypted. This field
1095 is not included into the padding calculation. Length
1096 of this field equals the cipher's block size. This field
1097 is, however, authenticated.
1102 2.3.9 Channel Key Payload
1104 All traffic in channels are protected by channel specific keys.
1105 Channel Key Payload is used to distribute channel keys to all
1106 clients on the particular channel. Channel keys are sent when
1107 the channel is created, when new user joins to the channel and
1108 whenever a user leaves a channel. Server creates the new
1109 channel key and distributes it to the clients by encrypting this
1110 payload with the session key shared between the server and
1111 the client. After that, client starts using the key received
1112 in this payload to protect the traffic on the channel.
1114 Channel keys are cell specific thus every router in cell have
1115 to create a channel key and distribute it if any client in the
1116 cell has joined to a channel. Channel traffic between cell's
1117 are not encrypted using channel keys, they are encrypted using
1118 normal session keys between two routers. Inside a cell, all
1119 channel traffic is encrypted with the specified channel key.
1120 Channel key should expire peridiocally, say, in one hour, in
1121 which case new channel key is created and distributed.
1123 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1124 It must not be sent in any other packet type. Following diagram
1125 represents the Channel Key Payload.
1131 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
1132 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1133 | Channel ID Length | |
1134 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1138 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1139 | Cipher Name Length | |
1140 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1144 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1145 | Channel Key Length | |
1146 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1150 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1154 Figure 10: Channel Key Payload
1159 o Channel ID Length (2 bytes) - Indicates the length of the
1160 Channel ID field in the payload, not including any other
1163 o Channel ID (variable length) - The Channel ID of the
1164 channel this key is meant for.
1166 o Cipher Name Length (2 bytes) - Indicates the length of the
1167 Cipher name field in the payload, not including any other
1170 o Cipher Name (variable length) - Name of the cipher used
1171 in the protection of channel traffic. This name is
1172 initially decided by the creator of the channel but it
1173 may change during the life time of the channel as well.
1175 o Channel Key Length (2 bytes) - Indicates the length of the
1176 Channel Key field in the payload, not including any other
1179 o Channel Key (variable length) - The actual channel key
1180 material. This key is used as such as key material for
1181 encryption function.
1186 2.3.10 Private Message Payload
1188 Private Message Payload is used to send private message between
1189 two clients (or users for that matter). The messages are sent only
1190 to the specified user and no other user inside SILC network is
1191 able to see the message. The message is protected by the session
1192 key established by the SILC Key Exchange Protocol. However,
1193 it is also possible to agree to use specific keys to protect
1194 just the private messages. See section 2.3.11 Private Message
1195 Key Payload for detailed description of how to agree to use
1198 If normal session key is used to protect the message, every
1199 server between the sender client and the receiving client needs
1200 to decrypt the packet and always re-encrypt it with the session
1201 key of the next receiver of the packet. See section Client
1202 To Client in [SILC1].
1204 When specific key is used to protect the message, servers between
1205 the sender and the receiver needs not to decrypt/re-encrypt the
1206 packet. Section 4.8.2 Client To Client in [SILC1] gives example of
1207 this scheme as well.
1209 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1210 packet. It must not be sent in any other packet type. Following
1211 diagram represents the Private Message Payload.
1217 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
1218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1219 | Nickname Length | |
1220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1228 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1232 Figure 11: Private Message Payload
1236 o Nickname Length (2 bytes) - Indicates the length of the
1237 Nickname field, not including any other field.
1239 o Nickname (variable length) - Nickname of the sender of the
1240 private message. This should not be trusted as a definite
1241 sender of the private message. The SILC Packet Header in
1242 the packet indicates the true sender of the packet and
1243 client should verify that the nickname sent here belongs
1244 to the Client ID in the SILC Packet Header. This nickname
1245 is merely provided to be displayed by the client.
1247 o Message Data (variable length) - The actual message to
1248 the client. Rest of the packet is reserved for the message
1254 2.3.11 Private Message Key Payload
1256 This payload is used to send key from client to another client that
1257 is going to be used to protect the private messages between these
1258 two clients. If this payload is not sent normal session key
1259 established by the SILC Key Exchange Protocol is used to protect
1260 the private messages.
1262 This payload may only be sent by client to another client. Server
1263 must not send this payload at any time. After sending this payload
1264 the sender of private messages must set the Private Message Key
1265 flag into SILC Packet Header.
1267 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1268 packet. It must not be sent in any other packet type. Following
1269 diagram represents the Private Message Key Payload.
1275 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
1276 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1277 | Private Message Key Length | |
1278 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1280 ~ Private Message Key ~
1282 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1286 Figure 12: Private Message Key Payload
1292 o Private Message Key Length (2 bytes) - Indicates the length
1293 of the Private Message Key field in the payload, not including
1296 o Private Message Key (variable length) - The actual private
1297 message key material. This key is used as such as key material
1298 for encryption function.
1303 2.3.12 Command Payload
1305 Command Payload is used to send SILC commands from client to server.
1306 Following diagram represents the Command Payload.
1312 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
1313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1314 | SILC Command | Arguments Num | Payload Length |
1315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1319 Figure 13: Command Payload
1323 o SILC Command (1 byte) - SILC Command identifier. This must
1324 be set to non-zero value. If zero (0) value is found in this
1325 field the packet must be discarded.
1327 o Arguments Num (1 byte) - Indicates the number of arguments
1328 associated with the command. If there are no arguments this
1329 field is set to zero (0). The arguments must follow the
1332 o Payload Length (2 bytes) - Length of the entire command
1333 payload including any command argument payloads associated
1337 See [SILC1] for detailed description of different SILC commands,
1338 their arguments and their reply messages.
1342 2.3.12.1 Command Argument Payload
1344 Command Argument Payload is used to set arguments for SILC commands.
1345 Number of arguments associated with a command are indicated by the
1346 Command Payload in the Arguments Num field. Command argument
1347 payloads may only be used with a command payload and they must
1348 always reside right after the command payload. Incorrect amount of
1349 argument payloads must cause rejection of the packet. Following
1350 diagram represents the Command Argument Payload.
1356 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
1357 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1358 | Argument Num | Argument Type | Payload Length |
1359 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1363 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1367 Figure 14: Command Argument Payload
1371 o Argument Num (1 byte) - Indicates the number of this argument.
1372 For first argument this is set to 1, for second argument this
1373 is set to 2, and so forth. If incorrect value is found
1374 in this field the packet must be discarded. Value is
1375 incorrect if it is zero (0) or, for example, a third argument
1376 does not include value 3.
1378 o Argument Type (1 byte) - Indicates the type of the argument.
1379 Every command specify a number for each argument that maybe
1380 associated with the command. By using this number the receiver
1381 of the packet knows what type of argument this is. The numbers
1382 are command specific and has been defined in section SILC
1383 Commands in [SILC1]. This field makes it possible to send
1384 arguments in free order as this field is used to identify
1385 the specific type of the argument.
1387 o Payload Length (2 bytes) - Length of the argument payload data
1388 area not including the length of any other fields in the
1391 o Argument Data (variable length) - Argument data.
1396 2.3.13 Command Reply Payload
1398 Command Reply Payload is used to send replies to the commands sent
1399 by the client. The Command Reply Payload is identical to the
1400 Command Payload hence see the upper sections for Command Payload
1401 and for Command Argument Payload specifications. Command Reply
1402 message uses the Command Argument Payload as well.
1404 See SILC Commands in [SILC1] for detailed description of different
1405 SILC commands, their arguments and their reply messages.
1409 2.3.14 Connection Auth Request Payload
1411 Client may send this payload to server to request the authentication
1412 method that must be used in authentication protocol. If client knows
1413 this information beforehand this payload is not necessary to be sent.
1414 Server performing authentication with another server may also send
1415 this payload to request the authentication method. If the connecting
1416 server already knows this information this payload is not necessary
1419 Server receiving this request must reply with same payload sending
1420 the mandatory authentication method. Algorithms that may be required
1421 to be used by the authentication method are the ones already
1422 established by the SILC Key Exchange protocol. See section Key
1423 Exchange Start Payload in [SILC3] for detailed information.
1425 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1426 packet. It must not be sent in any other packet type. Following
1427 diagram represents the Connection Auth Request Payload.
1433 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
1434 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1435 | Connection Type | Authentication Method |
1436 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1440 Figure 15: Connection Auth Request Payload
1444 o Connection Type (2 bytes) - Indicates the type of the ID.
1445 Following connection types are defined:
1451 If any other type is found in this field the packet must be
1452 discarded and the authentication must be failed.
1454 o Authentication Method (2 bytes) - Indicates the authentication
1455 method to be used in the authentication protocol. Following
1456 authentication methods are defined:
1461 1 password (mandatory)
1462 2 public key (mandatory)
1464 If any other type is found in this field the packet must be
1465 discarded and the authentication must be failed. If this
1466 payload is sent as request to receive the mandatory
1467 authentication method this field must be set to zero (0),
1468 indicating that receiver should send the mandatory
1469 authentication method. The receiver sending this payload
1470 to the requesting party, may also set this field to zero (0)
1471 to indicate that authentication is not required. In this
1472 case authentication protocol still must be started but
1473 server is most likely to respond with SILC_PACKET_SUCCESS
1479 2.3.15 New ID Payload
1481 New ID Payload is a multipurpose payload. It is used to send newly
1482 created ID's from clients and servers. When client connects to server
1483 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
1484 packet, server replies with this packet by sending the created ID for
1485 the client. Server always creates the ID for the client.
1487 This payload is also used when server tells its router that new client
1488 has registered to the SILC network. In this case the server sends
1489 the Client ID of the client to the router. Similiary when router
1490 distributes information to other routers about the client in the SILC
1491 network this payload is used.
1493 Also, when server connects to router, router uses this payload to inform
1494 other routers about new server in the SILC network. However, every
1495 server (or router) creates their own ID's thus the ID distributed by
1496 this payload is not created by the distributor in this case. Servers
1497 create their own ID's. Server registers itself to the network by sending
1498 SILC_PACKET_NEW_SERVER to the router it connected to. The case is same
1499 when router connects to another router.
1501 Hence, this payload is very important and used every time when some
1502 new entity is registered to the SILC network. Client never sends this
1503 payload. Both client and server (and router) may receive this payload.
1505 The payload may only be sent with SILC_PACKET_NEW_ID packet. It must
1506 not be sent in any other packet type. Following diagram represents the
1513 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
1514 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1515 | ID Type | ID Length |
1516 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1524 Figure 16: New ID Payload
1528 o ID Type (2 bytes) - Indicates the type of the ID. See
1529 section 2.4 SILC ID Types for list of defined ID types.
1531 o ID Length (2 bytes) - Length of the ID Data area not
1532 including the length of any other fields in the payload.
1534 o ID Data (variable length) - The actual ID data.
1540 2.3.16 New ID List Payload
1542 New ID List Payload is used to distribute list of ID's usually from
1543 server to router but also from router to other routers in the network.
1544 This payload is used, for example, when server is connected to router
1545 and the server wants to distribute all of its locally connected clients
1546 and locally created channels to the router. It is convenient in this
1547 case to use this payload instead of sending all the information one
1548 by one using New ID Payload.
1550 There is no specific payload for this packet type. The packet type
1551 uses same payload as described in previous section. To form a list
1552 several payloads is put in the packet each after each. The payload
1553 is variable in length but can be calculated by calculating the ID
1554 Type field, Length field and the ID Data fields together. This forms
1555 one New ID Payload in the list.
1557 The list of payloads may only be sent with SILC_PACKET_NEW_ID_LIST
1558 packet. They must not be sent in any other packet type.
1562 2.3.17 New Client Payload
1564 When client is connected to the server, keys has been exchanged and
1565 connection has been authenticated client must register itself to the
1566 server. Clients first packet after key exchange and authentication
1567 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
1568 the relevant information about the connected user. Server creates a new
1569 client ID for the client when received this payload and sends it to the
1570 client in New ID Payload.
1572 This payload sends username and real name of the user on the remote host
1573 which is connected to the SILC server with SILC client. The server
1574 creates the client ID according the information sent in this payload.
1575 The nickname of the user becomes the username sent in this payload.
1576 However, client should call NICK command after sending this payload to
1577 set the real nickname of the user which is then used to create new
1580 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
1581 must not be sent in any other packet type. Following diagram represents
1582 the New Client Payload.
1588 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
1589 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1590 | Username Length | |
1591 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1595 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1596 | Real Name Length | |
1597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1601 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1605 Figure 17: New Client Payload
1609 o Username Length (2 bytes) - Length of the username.
1611 o Username (variable length) - The username of the user on
1612 the host where connecting to the SILC server.
1614 o Real Name Length (2 bytes) - Length of the Real Name.
1616 o Real Name (variable length) - The real name of the user
1617 on the host where connecting to the SILC server.
1622 2.3.18 New Server Payload
1624 This payload is sent by server when it has completed successfully both
1625 key exchange and connection authentication protocols. The server
1626 uses this payload to register itself to the SILC network. The
1627 first packet after these key exchange and authentication protocols
1628 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
1629 of the server that it has created by itself. It also includes a
1630 name of the server that is associated to the Server ID.
1632 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
1633 must not be sent in any other packet type. Following diagram represents
1634 the New Server Payload.
1640 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
1641 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1642 | Server ID Length | |
1643 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1647 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1648 | Server Name Length | |
1649 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1653 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1657 Figure 18: New Server Payload
1661 o Server ID Length (2 bytes) - Length of the ID Data area not
1662 including the length of any other fields in the payload.
1664 o Server ID Data (variable length) - The actual Server ID
1667 o Server Name Length (2 bytes) - Length of the server name.
1669 o Server Name (variable length) - The server name.
1674 2.3.19 New Channel Payload
1676 Information about newly created channel is broadcasted to all routers
1677 in the SILC network by sending this packet payload. Channels are
1678 created by router of the cell. Server never creates channels unless
1679 it is a standalone server and it does not have router connection,
1680 in this case server acts as router. Normal server sends JOIN command
1681 to the router (after it has received JOIN command from client) which
1682 then processes the command and creates the channel. Client never sends
1685 The payload may only be sent with SILC_PACKET_NEW_CHANNEL packet.
1686 It must not be sent in any other packet type. Following diagram
1687 represents the New Channel Payload.
1693 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
1694 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1695 | Channel Name Length | |
1696 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1701 | Channel ID Length | |
1702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1706 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1710 Figure 19: New Channel Payload
1715 o Channel Name Length (2 bytes) - Length of the channel name.
1717 o Channel Name (variable length) - The name of the created
1720 o Channel ID Length (2 bytes) - Length of the Channel ID.
1722 o Channel ID (variable length) - The created Channel ID.
1727 2.3.20 New Channel User Payload
1729 When client (user) joins to a channel, server must notify routers
1730 about the new user on the channel. Normal server sends this packet
1731 payload to its router which then broadcasts the packet further.
1732 Router sends this packet always to its primary router. Client must
1733 not send this packet payload. The mode of the user is NONE after
1734 user has joined to the channel.
1736 The payload may only be sent with SILC_PACKET_NEW_CHANNEL_USER
1737 packet. It must not be sent in any other packet type. Following
1738 diagram represents the New Channel User Payload.
1744 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
1745 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1746 | Channel ID Length | |
1747 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1751 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1752 | Client ID Length | |
1753 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1757 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1761 Figure 20: New Channel User Payload
1765 o Channel ID Length (2 bytes) - Length of the Channel ID.
1767 o Channel ID (variable length) - The Channel ID of the channel
1768 to which the client has joined.
1770 o Client ID Length (2 bytes) - Length of the Client ID.
1772 o Client ID (variable length) - The Client ID of the client
1773 who has joined the channel.
1778 2.3.21 New Channel List Payload
1780 This payload is used to distribute list of new channels from server
1781 to routers. It might convenient to send list of new channels when
1782 existing server connects to router, instead of sending them one
1785 There is no specific payload for this packet type. The packet type
1786 uses same payload as described in 2.3.19 New Channel Payload. To form
1787 a list several payloads is put in the packet each after each. The
1788 payload is variable in length but can be calculated by calculating
1789 the length of the fields together. This forms one New Channel Payload
1792 The list of payloads may only be sent with SILC_PACKET_NEW_CHANNEL_LIST
1793 packet. They must not be sent in any other packet type.
1797 2.3.22 New Channel User List Payload
1799 This payload is used to distribute list of channel users on specific
1800 channel from server to routers. It might convenient to send list of
1801 channel users when existing server connects to router, instead of
1802 sending them one by one.
1804 There is no specific payload for this packet type. The packet type
1805 uses same payload as described in 2.3.20 New Channel User Payload.
1806 To form a list several payloads is put in the packet each after each.
1807 The payload is variable in length but can be calculated by calculating
1808 the length of the fields together. This forms one New Channel User
1809 Payload in the list.
1811 The list of payloads may only be sent with packet
1812 SILC_PACKET_NEW_CHANNEL_USER_LIST. They must not be sent in any other
1817 2.3.23 Replace ID Payload
1819 This payload is used to replace old ID with new ID sent in the payload.
1820 When ID changes for some entity and the new ID is wanted to replace the
1821 old one this payload must be used. Client cannot send or receive this
1822 payload. Normal server and router server may send and receive this
1823 payload. After this packet has been sent the old ID must not be used
1826 The payload may only be sent with SILC_PACKET_REPLACE_ID packet. It must
1827 not be sent in any other packet type. Following diagram represents the
1828 Replace Payload Payload.
1841 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
1842 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1843 | Old ID Type | Old ID Length |
1844 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1848 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1849 | New ID Type | New ID Length |
1850 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1854 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1858 Figure 21: Replace ID Payload
1862 o Old ID Type (2 bytes) - Indicates the type of the old ID. See
1863 section 2.4 SILC ID Types for list of defined ID types.
1865 o Old ID Length (2 bytes) - Length of the old ID Data area not
1866 including the length of any other fields in the payload.
1868 o Old ID Data (variable length) - The actual old ID data.
1870 o New ID Type (2 bytes) - Indicates the type of the new ID. See
1871 section 2.4 SILC ID Types for list of defined ID types.
1873 o New ID Length (2 bytes) - Length of the new ID Data area not
1874 including the length of any other fields in the payload.
1876 o New ID Data (variable length) - The actual new ID data.
1881 2.3.24 Remove ID Payload
1883 Remove ID payload is used to remove ID from SILC network. This is used
1884 for example when client exits SILC network. The server must in this
1885 case send this payload to notify that this ID is not valid anymore.
1886 After this has been send the old ID must not be used anymore. Client
1887 must not send this payload.
1889 The payload may only be sent with SILC_PACKET_REMOVE_ID packet. It must
1890 not be sent in any other packet type. Following diagram represents the
1891 Remove Payload Payload.
1897 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
1898 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1899 | ID Type | ID Length |
1900 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1904 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1908 Figure 22: Remove ID Payload
1912 o ID Type (2 bytes) - Indicates the type of the ID to be
1913 removed. See section 2.4 SILC ID Types for list of defined
1916 o ID Length (2 bytes) - Length of the D Data area not including
1917 the length of any other fields in the payload.
1919 o ID Data (variable length) - The actual ID data to be removed.
1926 ID's are extensively used in the SILC network to associate different
1927 entities. Following ID's has been defined to be used in the SILC
1933 When ever specific ID cannot be used this is used.
1937 Server ID to associate servers. See the format of
1942 Client ID to associate clients. See the format of
1947 Channel ID to associate channels. See the format of
1953 2.5 Packet Encryption And Decryption
1955 SILC packets are encrypted almost entirely. Only small part of SILC
1956 header is not encrypted as described in section 5.2 SILC Packet Header.
1957 The SILC Packet header is the first part of a packet to be encrypted
1958 and it is always encrypted with the key of the next receiver of the
1959 packet. The data payload area of the packet is always entirely
1960 encrypted and it is usually encrypted with the next receiver's key.
1961 However, there are some special packet types and packet payloads
1962 that require special encryption process. These special cases are
1963 described in the next sections. First is described the normal packet
1968 2.5.1 Normal Packet Encryption And Decryption
1970 Normal SILC packets are encrypted with the session key of the next
1971 receiver of the packet. The entire SILC Packet header and the packet
1972 data payload is is also encrypted with the same key. Padding of the
1973 packet is also encrypted always with the session key, also in special
1974 cases. Computed MAC of the packet must not be encrypted.
1976 Decryption process in these cases are straightforward. The receiver
1977 of the packet must first decrypt the SILC Packet header, or some parts
1978 of it, usually first 16 bytes of it. Then the receiver checks the
1979 packet type from the decrypted part of the header and can determine
1980 how the rest of the packet must be decrypted. If the packet type is
1981 any of the special cases described in following sections the packet
1982 decryption is special. If the packet type is not among those special
1983 packet types rest of the packet may be decrypted with the same key.
1985 Also, note that two bytes of the SILC Packet header are not encrypted
1986 thus it must be noticed in the decryption process by starting the
1987 decryption from the second byte of the header. This sets some rules
1988 to padding generation as well, see the section 2.7 Packet Padding
1991 With out a doubt, this sort of decryption processing causes some
1992 overhead to packet decryption, but never the less, is required.
1996 2.5.2 Channel Message Encryption And Decryption
1998 Channel Messages (Channel Message Payload) are always encrypted with
1999 the channel specific key. However, the SILC Packet header is not
2000 encrypted with that key. As in normal case, the header is encrypted
2001 with the key of the next receiver of the packet, who ever that might
2002 be. Note that in this case the encrypted data area is not touched
2003 at all; it must not be re-encrypted with the session key.
2005 Receiver of a channel message, who ever that is, is required to decrypt
2006 the SILC Packet header to be able to even recognize the packet to be as
2007 channel message. This is same procedure as for normal SILC packets.
2008 As the receiver founds the packet to be channel message, rest of the
2009 packet processing is special. Rest of the SILC Packet header is
2010 decrypted with the same session key along with the padding of the
2011 packet. After that the packet is protected with the channel specific
2012 key and hence can be decrypted only if the receiver is the client on
2013 the channel. See section 2.7 Packet Padding Generation for more
2014 information about padding on special packets.
2016 If the receiver of the channel message is router who is routing the
2017 message to another router then it must decrypt the Channel Message
2018 payload. Between routers (that is, between cells) channel messages
2019 are protected with session keys shared between the routers. This
2020 causes another special packet processing for channel messages. If
2021 the channel message is received from another router then the entire
2022 packet, including Channel Message payload, is encrypted with the
2023 session key shared between the routers. In this case the packet
2024 decryption process is as with normal SILC packets. Hence, if the
2025 router is sending channel message to another router the Channel
2026 Message payload must have been decrypted and must be re-encrypted
2027 with the session key shared between the another router. In this
2028 case the packet encryption is as with any normal SILC packet.
2030 It must be noted that this is only when the channel messages are sent
2031 from router to another router. In all other cases the channel
2032 message encryption and decryption is as described above. This
2033 different processing of channel messages with router to router
2034 connection is because channel keys are cell specific. All cells has
2035 their own channel keys thus the channel message traveling from one
2036 cell to another must be protected as it would be any normal SILC
2041 2.5.3 Private Message Encryption And Decryption
2043 By default, private message in SILC are protected by session keys.
2044 In this case the private message encryption and decryption process is
2045 equivalent to normal packet encryption and decryption.
2047 However, private messages can be protected with private message key
2048 which causes the packet to be special packet. The procedure in this
2049 case is very much alike to channel packets. The actual private message
2050 is encrypted with the private message key and other parts of the
2051 packet is encrypted with the session key. See 2.7 Packet Padding
2052 Generation for more information about padding on special packets.
2054 The difference from channel message processing is that server or router
2055 en route never decrypts the actual private message, as it does not
2056 have the key to do that. Thus, when sending packets between router
2057 the processing is same as in any other case as well; the packet's header
2058 and padding is protected by the session key and the data area is not
2061 The true receiver of the private message, client, that is, is able
2062 to decrypt the private message as it shares the key with the sender
2067 2.6 Packet MAC Generation
2069 Data integrity of a packet is protected by including a message
2070 authentication code (MAC) at the end of the packet. The MAC is computed
2071 from shared secret MAC key, that is established by the SILC Key Exchange
2072 protocol, and from the original contents of the packet. The MAC is
2073 always computed before the packet is encrypted, although after it is
2074 compressed if compression is used.
2076 The MAC is computed from entire packet. Every bit of data in the packet,
2077 including SILC Packet Header is used in the MAC computing. This way
2078 the entire packet becomes authenticated.
2080 If the packet is special packet MAC is computed from the entire packet
2081 but part of the packet may be encrypted before the MAC is computed.
2082 This is case, for example, with channel messages where the message data
2083 is encrypted with key that server may not now. In this case the MAC
2084 has been computed from the encrypted data.
2086 See [SILC1] for defined and allowed MAC algorithms.
2090 2.7 Packet Padding Generation
2092 Padding is needed in the packet because the packet is encrypted. It
2093 must always be multiple by eight (8) or multiple by the size of the
2094 cipher's block size, which ever is larger. The padding is always
2097 For normal packets the padding is added after the SILC Packet Header
2098 and between the Data Payload area. The padding for normal packets
2099 are calculated as follows:
2102 padding length = 16 - ((packet length - 2) % 16)
2105 The 16 is the maximum padding allowed in SILC packet. Two (2) is
2106 subtracted from the true length of the packet because two (2) bytes
2107 is not encrypted in SILC Packet Header, see section 2.2 SILC Packet
2108 Header. Those two bytes that are not encrypted must not be calculated
2109 to the padding length.
2111 For special packets the padding calculation may be different as special
2112 packets may be encrypted differently. In these cases the encrypted
2113 data area must already be multiple by the block size thus in this case
2114 the padding is calculated only for SILC Packet Header, not for any
2115 other area of the packet. The same algorithm works in this case as
2116 well, except that the `packet length' is now the SILC Packet Header
2117 length. In this case, as well, two (2) is subtracted from the
2120 The padding must be random data, preferably, generated by
2121 cryptographically strong random number generator.
2125 2.8 Packet Compression
2127 SILC Packets may be compressed. In this case the data payload area
2128 is compressed and all other areas of the packet must remain as they
2129 are. After compression is performed for the data area, the length
2130 field of Packet Header must be set to the compressed length of the
2133 The compression must always be applied before encryption. When
2134 the packet is received and decrypted the data area must be decompressed.
2135 Note that the true sender of the packet must apply the compression and
2136 the true receiver of the packet must apply the decompression. Any
2137 server or router en route must not decompress the packet.
2143 The sender of the packet must assemble the SILC Packet Header with
2144 correct values. It must set the Source ID of the header as its own
2145 ID. It must also set the Destination ID of the header to the true
2146 destination. If the destination is client it will be Client ID, if
2147 it is server it will be Server ID and if it is channel it will be
2150 If the sender wants to compress the packet it must apply the
2151 compression now. Sender must also compute the padding as described
2152 in above sections. Then sender must compute the MAC of the packet.
2154 Then sender encrypts the packet as has been described in above
2155 sections according whether the packet is normal packet or special
2156 packet. The computed MAC must not be encrypted.
2160 2.10 Packet Reception
2162 On packet reception the receiver must check that all fields in the
2163 SILC Packet Header are valid sain. It must check the flags of the
2164 header and act accordingly. It must also check the MAC of the packet
2165 and if it is to be failed the packet must be discarded. Also if the
2166 header of the packet includes any bad fields the packet must be
2169 See above sections on the decryption process of the received packet.
2171 The receiver must also check that the ID's in the header are valid
2172 ID's. Unsupported ID types or malformed ID's must cause packet
2173 rejection. The padding on the reception is always ignored.
2175 The receiver must also check the packet type and start parsing the
2176 packet according to the type. However, note the above sections on
2177 special packet types and their parsing.
2181 2.11 Packet Broadcasting
2183 SILC packets may be broadcasted in SILC network. However, only router
2184 server may send or receive broadcast packets. Client and normal server
2185 must not send broadcast packets and they must ignore broadcast packets
2186 if they receive them. Broadcast packets are sent by setting Broadcast
2187 flag to the SILC packet header.
2189 Broadcasting packets means that the packet is sent to all routers in
2190 the SILC network, except to the router that sent the packet. The router
2191 receiving broadcast packet must send the packet to its primary route.
2192 The fact that SILC routers may have several router connections may
2193 cause problems, such as race conditions inside the SILC network, if
2194 care is not taken when broadcasting packets. Router must not send
2195 the broadcast packet to any other route except to its primary route.
2197 If the primary route of the router is the original sender of the packet
2198 the packet must not be sent to the primary route. This may happen
2199 if router has several router connections and some other router uses
2200 the router as its primary route.
2202 Routers use broadcast packets to broadcast for example information
2203 about newly registered clients, servers, channels etc. so that all the
2204 routers may keep these informations up to date.
2210 Routers are the primary entities in the SILC network that takes care
2211 of packet routing. However, normal servers routes packets as well, for
2212 example, when they are routing channel message to the local clients.
2213 Routing is quite simple as every packet tells the true origin and the
2214 true destination of the packet.
2216 It is still recommended for routers that has several routing connections
2217 to create route cache for those destinations that has faster route than
2218 the router's primary route. This information is available for the router
2219 when other router connects to the router. The connecting party then
2220 sends all of its locally connected clients, server and channels. These
2221 informations helps to create the route cache. Also, when new channels
2222 are created to a cell its information is broadcasted to all routers
2223 in the network. Channel ID's are based on router's ID thus it is easy
2224 to create route cache based on these informations. If faster route for
2225 destination does not exist in router's route cache the packet must be
2226 routed to the primary route (default route).
2228 For server who receives a packet to be routed to its locally connected
2229 client the server must check whether the particular packet type is
2230 allowed to be routed to the client. Not all packets may be sent by
2231 some odd entity to client that is indirectly connected to the sender.
2232 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2233 entities and sending packets to them. The section mentions the packets
2234 that may be sent to indirectly connected entities. It is clear that some
2235 server cannot send, for example, disconnect packet to client that is not
2236 directly connected to the server.
2240 2.13 Packet Tunneling
2242 Tunneling is a feature that is available in SILC protocol. Tunneling
2243 means that extra SILC Packet Header is applied to the original packet
2244 and thus hiding the original packet entirely. There can be some
2245 interesting applications using tunneling, such as, using ID's based on
2246 private network IP addresses inside in the tunneled packet. This can
2247 open many interesting features relating to connecting to private network
2248 from the Internet with SILC and many more. However, this feature is
2249 optional currently in SILC as there does not exist thorough analysis of
2250 this feature. It is with out a doubt that there will be many more
2251 applications that has not yet been discovered. Thus, it is left
2252 to Internet Community to investigate the use of tunneling in SILC
2253 protocol. This document is updated according those investigations
2254 and additional documents on the issue may be written.
2258 3 Security Considerations
2260 Security is central to the design of this protocol, and these security
2261 considerations permeate the specification.
2267 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2268 Protocol Specification", Internet Draft, June 2000.
2270 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2271 Protocols", Internet Draft, June 2000.
2273 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2276 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2279 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2282 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2285 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2286 Infrastructure, Certificate and CRL Profile", RFC 2459,
2289 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2290 John Wiley & Sons, New York, NY, 1996.
2292 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2295 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2296 RFC 2412, November 1998.
2298 [ISAKMP] Maughan D., et al, "Internet Security Association and
2299 Key Management Protocol (ISAKMP)", RFC 2408, November
2302 [IKE] Harkins D., and Carrel D., "The Internet Key Exhange
2303 (IKE)", RFC 2409, November 1998.
2305 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2306 Authentication", RFC 2104, February 1997.
2318 EMail: priikone@poseidon.pspt.fi
2320 This Internet-Draft expires 28 Jan 2001