8 .ds RF FORMFEED[Page %]
12 .ds CH SILC Packet Protocol
17 Network Working Group P. Riikonen
19 draft-riikonen-silc-pp-00.txt 27 June 2000
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53 This memo describes a Packet Protocol used in the Secure Internet Live
54 Conferencing (SILC) protocol specified in the Secure Internet Live
55 Conferencing, Protocol Specification Internet Draft [SILC1]. This
56 protocol describes the packet types and packet payloads which defines
57 the contents of the packets. The protocol provides secure binary packet
58 protocol that assures that the contents of the packets are secured and
73 1 Introduction .................................................. 3
74 2 SILC Packet Protocol .......................................... 4
75 2.1 SILC Packet ............................................... 4
76 2.2 SILC Packet Header ........................................ 5
77 2.3 SILC Packet Types ......................................... 7
78 2.3.1 SILC Packet Payloads ................................ 15
79 2.3.2 Disconnect Payload .................................. 15
80 2.3.3 Success Payload ..................................... 16
81 2.3.4 Failure Payload ..................................... 16
82 2.3.5 Reject Payload ...................................... 17
83 2.3.6 Notify Payload ...................................... 17
84 2.3.7 Error Payload ....................................... 18
85 2.3.8 Channel Message Payload ............................. 19
86 2.3.9 Channel Key Payload ................................. 20
87 2.3.10 Private Message Payload ............................ 23
88 2.3.11 Private Message Key Payload ........................ 24
89 2.3.12 Command Payload .................................... 25
90 2.3.12.1 Command Argument Payload .................. 25
91 2.3.13 Command Reply Payload .............................. 26
92 2.3.14 Connection Auth Request Payload .................... 27
93 2.3.15 New ID Payload ..................................... 28
94 2.3.16 New ID List Payload ................................ 29
95 2.3.17 New Client Payload ................................. 29
96 2.3.18 New Server Payload ................................. 31
97 2.3.19 New Channel Payload ................................ 31
98 2.3.20 New Channel User Payload ........................... 32
99 2.3.21 New Channel List Payload ........................... 33
100 2.3.22 New Channel User List Payload ...................... 34
101 2.3.23 Replace ID Payload ................................. 34
102 2.3.24 Remove ID Payload .................................. 35
103 2.4 SILC ID Types ............................................. 36
104 2.5 Packet Encryption And Decryption .......................... 37
105 2.5.1 Normal Packet Encryption And Decryption ............. 37
106 2.5.2 Channel Message Encryption And Decryption ........... 37
107 2.5.3 Private Message Encryption And Decryption ........... 38
108 2.6 Packet MAC Generation ..................................... 39
109 2.7 Packet Padding Generation ................................. 39
110 2.8 Packet Compression ........................................ 40
111 2.9 Packet Sending ............................................ 40
112 2.10 Packet Reception ......................................... 41
113 2.11 Packet Broadcasting ...................................... 41
114 2.12 Packet Routing ........................................... 42
115 2.13 Packet Tunneling ......................................... 42
116 3 Security Considerations ....................................... 43
117 4 References .................................................... 43
118 5 Author's Address .............................................. 44
124 Figure 1: Typical SILC Packet
125 Figure 2: SILC Packet Header
126 Figure 3: Disconnect Payload
127 Figure 4: Success Payload
128 Figure 5: Failure Payload
129 Figure 6: Reject Payload
130 Figure 7: Notify Payload
131 Figure 8: Error Payload
132 Figure 9: Channel Message Payload
133 Figure 10: Channel Key Payload
134 Figure 11: Private Message Payload
135 Figure 12: Private Message Key Payload
136 Figure 13: Command Payload
137 Figure 14: Command Argument Payload
138 Figure 15: Connection Auth Request Payload
139 Figure 16: New ID Payload
140 Figure 17: New Client Payload
141 Figure 18: New Server Payload
142 Figure 19: New Channel Payload
143 Figure 20: New Channel User Payload
144 Figure 21: Replace ID Payload
145 Figure 22: Remove ID Payload
151 This document describes a Packet Protocol used in the Secure Internet
152 Live Conferencing (SILC) protocol specified in the Secure Internet Live
153 Conferencing, Protocol Specification Internet Draft [SILC1]. This
154 protocol describes the packet types and packet payloads which defines
155 the contents of the packets. The protocol provides secure binary packet
156 protocol that assures that the contents of the packets are secured and
159 The basis of SILC protocol relies in the SILC packets and it is with
160 out a doubt the most important part of the protocol. It is also probably
161 the most complicated part of the protocol. Packets are used all the
162 time in the SILC network to send messages, commands and other information.
163 All packets in SILC network are always encrypted and their integrity
164 is assured by computed MACs. The protocol defines several packet types
165 and packet payloads. Each packet type usually has a specific packet
166 payload that actually defines the contents of the packet. Each packet
167 also includes a default SILC Packet Header that provides sufficient
168 information about the origin of the packet and destination of the
173 2 SILC Packet Protocol
178 SILC packets deliver messages from sender to receiver securely by
179 encrypting important fields of the packet. The packet consists of
180 default SILC Packet Header, Padding, Packet Payload data, and, packet
183 The following diagram illustrates typical SILC packet.
188 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
189 | n bytes | 1 - n bytes | n bytes | n bytes
190 | SILC Header | Padding | Data Payload | MAC
191 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
195 Figure 1: Typical SILC Packet
198 SILC Header is always the first part of the packet and its purpose
199 is to provide information about the packet. It provides for example
200 the packet type, origin of the packet and the destination of the packet.
201 The header is variable in length and first two (2) bytes of the
202 header (thus first two bytes of the packet) are not encrypted. The
203 first two (2) bytes are the length of the packet which is not encrypted.
204 See following section for description of SILC Packet header. Packets
205 without SILC header or with malformed SILC header must be dropped.
207 Padding follows the packet header. The purpose of the padding is to
208 make the packet multiple by eight (8) or by the block size of the
209 cipher used in the encryption, which ever is larger. The maximum
210 length of padding is currently 16 bytes. The padding is always
213 Data payload area follows padding and it is the actual data of the
214 packet. The packet data is the packet payloads defined in this
215 protocol. The data payload area is always encrypted.
217 The last part of SILC packet is the packet MAC that assures the
218 integrity of the packet. The MAC is always computed from the packet
219 before the encryption is applied to the packet. If compression is used
220 in the packet the MAC is computed after the compression has been
221 applied. The compression, on the other hand, is always applied before
224 All fields in all packet payloads are always in MSB (most significant
229 2.2 SILC Packet Header
231 The default SILC packet header is applied to all SILC packets and it is
232 variable in length. The purpose of SILC Packet header is to provide
233 detailed information about the packet. The receiver of the packet uses
234 the packet header to parse the packet and gain other relevant parameters
237 Following diagram represents the default SILC header format.
238 (*) indicates that this field is never encrypted. Other fields are
245 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
246 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
247 | Payload Length * | Flags | Packet Type |
248 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
249 | Source ID Length | Destination ID Length |
250 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
256 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
262 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
266 Figure 2: SILC Packet Header
270 o Payload Length (2 bytes) - Is the length of the packet
271 not including the padding of the packet. This field must
272 not be encrypted but must always be authenticated.
274 o Flags (1 byte) - Indicates flags to be used in packet
275 processing. Several flags may be set by ORing the flags
278 Following flags are reserved for this field:
285 In this case the field is ignored.
288 Private Message Key 0x01
290 Indicates that the packet must include private
291 message that is encrypted using private key set by
292 client. Servers does not know anything about this
293 key and this causes that the private message is
294 not handled by the server at all, it is just
295 passed along. See section 2.5.3 Private Message
296 Encryption And Decryption for more information.
301 Marks the packet to be broadcasted. Client cannot
302 send broadcast packet and normal server cannot send
303 broadcast packet. Only router server may send broadcast
304 packet. The router receiving of packet with this flag
305 set must send (broadcast) the packet to its primary
306 route. If router has several router connections the
307 packet may be sent only to the primary route. See
308 section 2.11 Packet Broadcasting for description of
314 Marks that the packet is tunneled. Tunneling means
315 that extra SILC Packet Header has been applied to the
316 original packet. The outer header has this flag
317 set. See section 2.13 Packet Tunneling for more
323 o Packet Type (1 byte) - Is the type of the packet. Receiver
324 uses this field to parse the packet. See section 2.3
325 SILC Packets for list of defined packet types.
327 o Source ID Length (2 bytes) - Indicates the length of the
328 Source ID field in the header, not including this or any
333 o Destination ID Length (2 bytes) - Indicates the length of the
334 Destination ID field in the header, not including this or
337 o Src ID Type (1 byte) - Indicates the type of ID in the
338 Source ID field. See section 2.4 SILC ID Types for
341 o Source ID (variable length) - The actual source ID that
342 indicates who is the original sender of the packet.
344 o Dst ID Type (1 byte) - Indicates the type of ID in the
345 Destination ID field. See section 2.4 SILC ID Types for
348 o Destination ID (variable length) - The actual source ID that
349 indicates who is the end receiver of the packet.
353 2.3 SILC Packet Types
355 SILC packet types defines the contents of the packet and it is used by
356 the receiver to parse the packet. The packet type is 8 bits, as a one
357 byte, in length. The range for the packet types are from 0 - 255,
358 where 0 is never sent and 255 is currently reserved for future
359 extensions and must not be defined to any other purpose. Every SILC
360 specification compliant implementation should support all of these packet
363 The below list of the SILC Packet types includes reference to the packet
364 payload as well. Packet payloads are the actual packet, that is, the data
365 that the packet consists of. Each packet type defines packet payload
366 which usually may only be sent with the specific packet type.
368 Most of the packets are packets that must be destined directly to entity
369 that is connected to the sender. It is not allowed, for example, for
370 router to send disconnect packet to client that is not directly connected
371 to the router. However, there are some special packet types that may
372 be destined to some entity that the sender has not direct connection
373 with. These packets are for example private message packets, channel
374 message packets, command packets and some other packets that may be
375 broadcasted in the SILC network. If the packet is allowed to be sent to
376 indirectly connected entity it is mentioned separately in the packet
377 description (unless it is obvious as in private and channel message
378 packets). Other packets must not be sent or accepted, if sent, to
379 indirectly connected entities.
381 List of SILC Packet types are defined as follows.
386 This type is reserved and it is never sent.
389 1 SILC_PACKET_DISCONNECT
391 This packet is sent to disconnect the remote end. Reason of
392 the disconnection is sent inside the packet payload. Client
393 usually does not send this packet.
395 Payload of the packet: See section 2.3.2 Disconnect Payload
398 2 SILC_PACKET_SUCCESS
400 This packet is sent upon successful execution of some protocol.
401 The status of the success is sent in the packet.
403 Payload of the packet: See section 2.3.3 Success Payload
406 3 SILC_PACKET_FAILURE
408 This packet is sent upon failure of some protocol. The status
409 of the failure is sent in the packet.
411 Payload of the packet: See section 2.3.4 Failure Payload
416 This packet may be sent upon rejection of some protocol.
417 The status of the rejection is sent in the packet.
419 Payload of the packet: See section 2.3.5 Reject Payload
424 This packet is used to send notify message, usually from
425 server to client, although it may be sent from server to another
426 server as well. Client never sends this packet. Server may
427 send this packet to channel as well when the packet is
428 distributed to all clients on the channel. Receiver of this
429 packet may ignore the packet if it chooses so. However, it
430 should not be ignored.
432 Payload of the packet: See section 2.3.6 Notify Payload.
437 This packet is sent when an error occurs. Server may
438 send this packet. Client never sends this packet. The
439 client may entirely ignore the packet, however, server is
440 most likely to take action anyway.
442 Payload of the packet: See section 2.3.7 Error Payload.
445 7 SILC_PACKET_CHANNEL_MESSAGE
447 This packet is used to send messages to channels. The packet
448 includes Channel ID of the channel and the actual message to
449 the channel. Messages sent to the channel are always protected
450 by channel specific keys. Channel Keys are distributed by
451 SILC_PACKET_CHANNEL_KEY packet.
453 When client sends this packet the destination ID in the SILC
454 header must be the Channel ID of the channel the message is
455 destined to. If server sends this packet to a client the
456 destination ID in the SILC header must be the Client ID of
457 the client receiving the packet.
459 If server sends this packet to router or if router sends this
460 packet to server or another router the destination ID in the
461 SILC header must be the Channel ID of the channel. Server
462 (including router) distributes this packet only to its local
463 clients who are joined to the channel. Servers and routers
464 also determines who are on the channel and when this packet
465 needs to be sent, as described in section Client To Client
468 Payload of the packet: See section 2.3.8 Channel Message
472 8 SILC_PACKET_CHANNEL_KEY
474 This packet is used to distribute new key for particular
475 channel. Each channel has their own independent keys that
476 is used to protect the traffic on the channel. Only server
477 may send this packet. This packet may be sent to entity
478 that is indirectly connected to the sender.
480 Payload of the packet: See section 2.3.9 Channel Key Payload
483 9 SILC_PACKET_PRIVATE_MESSAGE
485 This packet is used to send private messages from client
486 to another client. By default, private messages are protected
487 by session keys established by normal key exchange protocol.
488 However, it is possible to use specific key to protect private
489 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
490 agree the key with the remote client. Pre-shared key may be
491 used as well if both of the client knows it, however, it needs
492 to be agreed outside SILC. See more of this in [SILC1].
494 Payload of the packet: See section 2.3.10 Private Message
498 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
500 This packet is used to agree about a key to be used to protect
501 the private messages between two clients. If this is not sent
502 the normal session key is used to protect the private messages
503 inside SILC network. Agreeing to use specific key to protect
504 private messages adds security, as no server between the two
505 clients will be able to decrypt the private message. However,
506 servers inside SILC network are considered to be trusted, thus
507 using normal session key to protect private messages does not
508 degree security. Whether to agree to use specific keys by
509 default or to use normal session keys by default, is
510 implementation specific issue. See more of this in [SILC1].
512 Payload of the packet: See section 2.3.11 Private Message
516 11 SILC_PACKET_COMMAND
518 This packet is used to send commands from client to server.
519 Server may send this packet to other servers as well. All
520 commands are listed in their own section SILC Command Types
521 in [SILC1]. The contents of this packet is command specific.
522 This packet may be sent to entity that is indirectly connected
525 Payload of the packet: See section 2.3.12 Command Payload
528 12 SILC_PACKET_COMMAND_REPLY
530 This packet is send as reply to the SILC_PACKET_COMMAND packet.
531 The contents of this packet is command specific. This packet
532 maybe sent to entity that is indirectly connected to the sender.
534 Payload of the packet: See section 2.3.13 Command Reply
535 Payload and section 2.3.12 Command
539 13 SILC_PACKET_KEY_EXCHANGE
541 This packet is used to start SILC Key Exchange Protocol,
542 described in detail in [SILC3].
544 Payload of the packet: Payload of this packet is described
545 in the section SILC Key Exchange
546 Protocol and its sub sections in
550 14 SILC_PACKET_KEY_EXCHANGE_1
552 This packet is used as part of the SILC Key Exchange Protocol.
554 Payload of the packet: Payload of this packet is described
555 in the section SILC Key Exchange
556 Protocol and its sub sections in
560 15 SILC_PACKET_KEY_EXCHANGE_2
562 This packet is used as part of the SILC Key Exchange Protocol.
564 Payload of the packet: Payload of this packet is described
565 in the section SILC Key Exchange
566 Protocol and its sub sections in
570 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
572 This packet is used to request the authentication method to
573 be used in the SILC Connection Authentication Protocol. If
574 initiator of the protocol does not know the mandatory
575 authentication method this packet is used to determine it.
577 The party receiving this payload must respond with the same
578 packet including the mandatory authentication method.
580 Payload of the packet: See section 2.3.14 Connection Auth
584 17 SILC_PACKET_CONNECTION_AUTH
586 This packet is used to start and perform the SILC Connection
587 Authentication Protocol. This protocol is used to authenticate
588 the connecting party. The protocol is described in detail in
591 Payload of the packet: Payload of this packet is described
592 in the section SILC Authentication
593 Protocol and it sub sections in [SILC].
596 18 SILC_PACKET_NEW_ID
598 This packet is used to distribute new ID's from server to
599 router and from router to all routers in the SILC network.
600 This is used when for example new client is registered to
601 SILC network. The newly created ID's of these operations are
602 distributed by this packet. Only server may send this packet,
603 however, client must be able to receive this packet.
605 Payload of the packet: See section 2.3.15 New ID Payload
608 19 SILC_PACKET_NEW_ID_LIST
610 This packet is used to distribute list of new ID's from
611 server to routers. This is equivalent to previous packet
612 type except that it may include several ID's. Client must
613 not send this packet.
615 Payload of the packet: See section 2.3.16 New ID List
619 20 SILC_PACKET_NEW_CLIENT
621 This packet is used by client to register itself to the
622 SILC network. This is sent after key exchange and
623 authentication protocols has been completed. Client sends
624 various information about itself in this packet.
626 Payload of the packet: See section 2.3.17 New Client Payload
629 21 SILC_PACKET_NEW_SERVER
631 This packet is used by server to register itself to the
632 SILC network. This is sent after key exchange and
633 authentication protocols has been completed. Server sends
634 this to the router it connected to, or, if router was
635 connecting, to the connected router. Server sends
636 its Server ID and other information in this packet.
637 Client must not send or receive this packet.
639 Payload of the packet: See section 2.3.18 New Server Payload
642 22 SILC_PACKET_NEW_CHANNEL
644 This packet is used to notify routers about newly created
645 channel. Channels are always created by the router and it must
646 notify other routers about the created channel. Router sends
647 this packet to its primary route. Client must not send this
648 packet. This packet maybe sent to entity that is indirectly
649 connected to the sender.
651 Payload of the packet: See section 2.3.19 New Channel Payload
654 23 SILC_PACKET_NEW_CHANNEL_USER
656 This packet is used to notify routers about new user on channel.
657 The packet is sent after user has joined to the channel. Server
658 may send this packet to its router and router may send this to
659 its primary router. Client must not send this packet. This
660 packet maybe sent to entity that is indirectly connected to the
663 Payload of the packet: See section 2.3.20 New Channel User
667 24 SILC_PACKET_NEW_CHANNEL_LIST
669 This packet is used to distribute list of created channels
670 from server to routers. This is equivalent to the packet
671 SILC_PACKET_NEW_CHANNEL except that it may include several
672 payloads. Client must not send this packet.
674 Payload of the packet: See section 2.3.21 New Channel List
678 25 SILC_PACKET_NEW_CHANNEL_USER_LIST
680 This packet is used to distribute list of users on specific
681 channel from server to routers. This is equivalent to the
682 packet SILC_PACKET_NEW_CHANNEL_USER except that it may
683 include several payloads. Client must not send this packet.
685 Payload of the packet: See section 2.3.22 New Channel User
689 26 SILC_PACKET_REPLACE_ID
691 This packet is used to replace old ID with new ID sent in
692 the packet payload. For example, when client changes its
693 nickname new ID is created and this packet can be used to
694 distribute the new ID and the old ID is removed when it is
695 send in the packet. Client cannot send or receive this
696 packet. This packet maybe sent to entity that is indirectly
697 connected to the sender.
699 Payload of the packet: See section 2.3.23 Replace ID Payload
702 27 SILC_PACKET_REMOVE_ID
704 This packet is used to removed ID. For example, when client
705 exits SILC network its ID is removed. Client must not send
706 this packet. This packet maybe sent to entity that is
707 indirectly connected to the sender.
709 Payload of the packet: See section 2.3.24 Remove ID Payload
714 This packet is used to indicate that re-key must be performed
715 for session keys. See section Session Key Regeneration in
716 [SILC1] for more information. This packet does not have
722 29 SILC_PACKET_REKEY_DONE
724 This packet is used to indicate that re-key is performed and
725 new keys must be used hereafter. This is sent only if re-key
726 was done without PFS option. If PFS is set, this is not sent
727 as SILC Key Exchange protocol is executed. This packet does
733 Currently undefined commands.
738 This type is reserved for future extensions and currently it
744 2.3.1 SILC Packet Payloads
746 All payloads resides in the main data area of the SILC packet. However
747 all payloads must be at the start of the data area after the default
748 SILC packet header and padding. All fields in the packet payload are
749 always encrypted, as, they reside in the data area of the packet which
752 Payloads described in this section are common payloads that must be
753 accepted anytime during SILC session. Most of the payloads may only
754 be sent with specific packet type which is defined in the description
757 There are a lot of other payloads in the SILC as well. However, they
758 are not common in the sense that they could be sent at any time.
759 These payloads are not described in this section. These are payloads
760 such as SILC Key Exchange payloads and so on. These are described
761 in [SILC1] and [SILC3].
765 2.3.2 Disconnect Payload
767 Disconnect payload is sent upon disconnection. The payload is simple;
768 reason of disconnection is sent to the disconnected party.
770 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
771 must not be sent in any other packet type. Following diagram represents
772 the Disconnect Payload.
778 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
779 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
781 ~ Disconnect Message ~
783 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
787 Figure 3: Disconnect Payload
793 o Disconnect Message (variable length) - Human readable
794 reason of the disconnection.
799 2.3.3 Success Payload
801 Success payload is sent when some protocol execution is successfully
802 completed. The payload is simple; indication of the success is sent.
803 This maybe any data, including binary or human readable data.
808 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
809 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
811 ~ Success Indication ~
813 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
817 Figure 4: Success Payload
821 o Success Indication (variable length) - Indication of
822 the success. This maybe for example some flag that
823 indicates the protocol and the success status or human
824 readable success message. The true length of this
825 payload is available by calculating it from the SILC
831 2.3.4 Failure Payload
833 This is opposite of Success Payload. Indication of failure of
834 some protocol is sent in the payload.
839 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
840 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
842 ~ Failure Indication ~
844 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
848 Figure 5: Failure Payload
852 o Failure Indication (variable length) - Indication of
853 the failure. This maybe for example some flag that
854 indicates the protocol and the failure status or human
855 readable failure message. The true length of this
856 payload is available by calculating it from the SILC
864 This payload is sent when some protocol is rejected to be executed.
865 Other operations may send this as well that was rejected. The
866 indication of the rejection is sent in the payload. The indication
867 may be binary or human readable data.
873 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
874 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
876 ~ Reject Indication ~
878 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
882 Figure 6: Reject Payload
886 o Reject Indication (variable length) - Indication of
887 the rejection. This maybe for example some flag that
888 indicates the protocol and the rejection status or human
889 readable rejection message. The true length of this
890 payload is available by calculating it from the SILC
898 Notify payload is used to send notify messages. The payload is usually
899 sent from server to client, however, server may send it to another
900 server as well. Client must not send this payload. The receiver of
901 this payload may totally ignore the contents of the payload, however,
902 notify message should be noted and possibly logged.
904 The payload may only be sent with SILC_PACKET_NOTIFY packet. It must
905 not be sent in any other packet type. Following diagram represents the
915 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
916 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
920 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
924 Figure 7: Notify Payload
928 o Notify Message (variable length) - Human readable notify
936 Error payload is sent upon error. Error may occur in various
937 conditions when server sends this packet. Client may not send this
938 payload but must be able to accept it. However, client may
939 totally ignore the contents of the packet as server is going to
940 take action on the error anyway. However, it is recommended
941 that the client takes error packet seriously.
947 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
948 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
952 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
956 Figure 8: Error Payload
960 o Error Message (variable length) - Human readable error
966 2.3.8 Channel Message Payload
968 Channel messages are the most common messages sent in the SILC.
969 Channel Message Payload is used to send message to channels. These
970 messages can only be sent if client has joined to some channel.
971 Even though this packet is the most common in SILC it is still
972 special packet. Some special handling on sending and reception
973 of channel message is required.
975 Padding must be applied into this payload since the payload is
976 encrypted separately from other parts of the packet with the
977 channel specific key. Hence the requirement of the padding.
978 The padding should be random data. The packet must be made
979 multiple by eight (8) or by the block size of the cipher, which
982 The SILC header in this packet is encrypted with the session key
983 of the next receiver of the packet. Nothing else is encrypted
984 with that key. Hence, the actual packet and padding to be
985 encrypted with the session key is SILC Header plus padding to it
986 to make it multiple by eight (8) or multiple by the block size
987 of the cipher, which ever is larger.
989 Receiver of the the channel message packet is able to determine
990 the channel the message is destined to by checking the destination
991 ID from the SILC Packet header which tells the destination channel.
992 The original sender of the packet is also determined by checking
993 the source ID from the header which tells the who client sent
996 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
997 It must not be sent in any other packet type. Following diagram
998 represents the Notify Payload.
1000 (*) indicates that the field is not encrypted.
1026 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
1027 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1028 | Nickname Length | |
1029 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1033 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1034 | Message Length | |
1035 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1039 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1040 | Padding Length | |
1041 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1045 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1047 ~ Initial Vector * ~
1049 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1053 Figure 9: Channel Message Payload
1057 o Nickname Length (2 bytes) - Indicates the length of the
1058 Nickname field, not including any other field.
1060 o Nickname (variable length) - Nickname of the sender of the
1061 channel message. This should not be trusted as a definite
1062 sender of the channel message. The SILC Packet Header in
1063 the packet indicates the true sender of the packet and
1064 client should verify that the nickname sent here belongs
1065 to the Client ID in the SILC Packet Header. This nickname
1066 is merely provided to be displayed by the client.
1068 If server is sending this packet this field is not included
1069 and zero (0) length must be set to the Nickname Length field.
1071 o Message Length (2 bytes) - Indicates the length of the
1072 the Message Data field in the payload, not including any
1076 o Message Data (variable length) - The actual message to
1079 o Padding Length (2 bytes) - Indicates the length of the
1080 Padding field in the payload, not including any other
1083 o Padding (variable length) - The padding that must be
1084 applied because this payload is encrypted separately from
1085 other parts of the packet.
1087 o Initial Vector (variable length) - The initial vector
1088 that has been used in packet encryption. It needs to be
1089 used in the packet decryption as well. What this field
1090 includes is implementation issue. However, it is
1091 recommended that it would be random data or, perhaps,
1092 a timestamp. It is not recommended to use zero (0) as
1093 initial vector. This field is not encrypted. This field
1094 is not included into the padding calculation. Length
1095 of this field equals the cipher's block size. This field
1096 is, however, authenticated.
1101 2.3.9 Channel Key Payload
1103 All traffic in channels are protected by channel specific keys.
1104 Channel Key Payload is used to distribute channel keys to all
1105 clients on the particular channel. Channel keys are sent when
1106 the channel is created, when new user joins to the channel and
1107 whenever a user leaves a channel. Server creates the new
1108 channel key and distributes it to the clients by encrypting this
1109 payload with the session key shared between the server and
1110 the client. After that, client starts using the key received
1111 in this payload to protect the traffic on the channel.
1113 Channel keys are cell specific thus every router in cell have
1114 to create a channel key and distribute it if any client in the
1115 cell has joined to a channel. Channel traffic between cell's
1116 are not encrypted using channel keys, they are encrypted using
1117 normal session keys between two routers. Inside a cell, all
1118 channel traffic is encrypted with the specified channel key.
1119 Channel key should expire peridiocally, say, in one hour, in
1120 which case new channel key is created and distributed.
1122 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1123 It must not be sent in any other packet type. Following diagram
1124 represents the Channel Key Payload.
1130 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
1131 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1132 | Channel ID Length | |
1133 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1137 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1138 | Cipher Name Length | |
1139 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1144 | Channel Key Length | |
1145 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1153 Figure 10: Channel Key Payload
1158 o Channel ID Length (2 bytes) - Indicates the length of the
1159 Channel ID field in the payload, not including any other
1162 o Channel ID (variable length) - The Channel ID of the
1163 channel this key is meant for.
1165 o Cipher Name Length (2 bytes) - Indicates the length of the
1166 Cipher name field in the payload, not including any other
1169 o Cipher Name (variable length) - Name of the cipher used
1170 in the protection of channel traffic. This name is
1171 initially decided by the creator of the channel but it
1172 may change during the life time of the channel as well.
1174 o Channel Key Length (2 bytes) - Indicates the length of the
1175 Channel Key field in the payload, not including any other
1178 o Channel Key (variable length) - The actual channel key
1179 material. This key is used as such as key material for
1180 encryption function.
1185 2.3.10 Private Message Payload
1187 Private Message Payload is used to send private message between
1188 two clients (or users for that matter). The messages are sent only
1189 to the specified user and no other user inside SILC network is
1190 able to see the message. The message is protected by the session
1191 key established by the SILC Key Exchange Protocol. However,
1192 it is also possible to agree to use specific keys to protect
1193 just the private messages. See section 2.3.11 Private Message
1194 Key Payload for detailed description of how to agree to use
1197 If normal session key is used to protect the message, every
1198 server between the sender client and the receiving client needs
1199 to decrypt the packet and always re-encrypt it with the session
1200 key of the next receiver of the packet. See section Client
1201 To Client in [SILC1].
1203 When specific key is used to protect the message, servers between
1204 the sender and the receiver needs not to decrypt/re-encrypt the
1205 packet. Section 4.8.2 Client To Client in [SILC1] gives example of
1206 this scheme as well.
1208 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1209 packet. It must not be sent in any other packet type. Following
1210 diagram represents the Private Message Payload.
1216 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
1217 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1218 | Nickname Length | |
1219 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1223 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1231 Figure 11: Private Message Payload
1235 o Nickname Length (2 bytes) - Indicates the length of the
1236 Nickname field, not including any other field.
1238 o Nickname (variable length) - Nickname of the sender of the
1239 private message. This should not be trusted as a definite
1240 sender of the private message. The SILC Packet Header in
1241 the packet indicates the true sender of the packet and
1242 client should verify that the nickname sent here belongs
1243 to the Client ID in the SILC Packet Header. This nickname
1244 is merely provided to be displayed by the client.
1246 o Message Data (variable length) - The actual message to
1247 the client. Rest of the packet is reserved for the message
1253 2.3.11 Private Message Key Payload
1255 This payload is used to send key from client to another client that
1256 is going to be used to protect the private messages between these
1257 two clients. If this payload is not sent normal session key
1258 established by the SILC Key Exchange Protocol is used to protect
1259 the private messages.
1261 This payload may only be sent by client to another client. Server
1262 must not send this payload at any time. After sending this payload
1263 the sender of private messages must set the Private Message Key
1264 flag into SILC Packet Header.
1266 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1267 packet. It must not be sent in any other packet type. Following
1268 diagram represents the Private Message Payload.
1274 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
1275 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1276 | Private Message Key Length | |
1277 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1279 ~ Private Message Key ~
1281 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1285 Figure 12: Private Message Key Payload
1291 o Private Message Key Length (2 bytes) - Indicates the length
1292 of the Private Message Key field in the payload, not including
1295 o Private Message Key (variable length) - The actual private
1296 message key material. This key is used as such as key material
1297 for encryption function.
1302 2.3.12 Command Payload
1304 Command Payload is used to send SILC commands from client to server.
1305 Following diagram represents the Command Payload.
1311 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
1312 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1313 | SILC Command | Arguments Num | Payload Length |
1314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1318 Figure 13: Command Payload
1322 o SILC Command (1 byte) - SILC Command identifier. This must
1323 be set to non-zero value. If zero (0) value is found in this
1324 field the packet must be discarded.
1326 o Arguments Num (1 byte) - Indicates the number of arguments
1327 associated with the command. If there are no arguments this
1328 field is set to zero (0). The arguments must follow the
1331 o Payload Length (2 bytes) - Length of the entire command
1332 payload including any command argument payloads associated
1336 See [SILC1] for detailed description of different SILC commands,
1337 their arguments and their reply messages.
1341 2.3.12.1 Command Argument Payload
1343 Command Argument Payload is used to set arguments for SILC commands.
1344 Number of arguments associated with a command are indicated by the
1345 Command Payload in the Arguments Num field. Command argument
1346 payloads may only be used with a command payload and they must
1347 always reside right after the command payload. Incorrect amount of
1348 argument payloads must cause rejection of the packet. Following
1349 diagram represents the Command Argument Payload.
1355 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
1356 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1357 | Argument Num | Argument Type | Payload Length |
1358 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1366 Figure 14: Command Argument Payload
1370 o Argument Num (1 byte) - Indicates the number of this argument.
1371 For first argument this is set to 1, for second argument this
1372 is set to 2, and so forth. If incorrect value is found
1373 in this field the packet must be discarded. Value is
1374 incorrect if it is zero (0) or, for example, a third argument
1375 does not include value 3.
1377 o Argument Type (1 byte) - Indicates the type of the argument.
1378 Every command specify a number for each argument that maybe
1379 associated with the command. By using this number the receiver
1380 of the packet knows what type of argument this is. The numbers
1381 are command specific and has been defined in section SILC
1382 Commands in [SILC1]. This field makes it possible to send
1383 arguments in free order as this field is used to identify
1384 the specific type of the argument.
1386 o Payload Length (2 bytes) - Length of the argument payload data
1387 area not including the length of any other fields in the
1390 o Argument Data (variable length) - Argument data.
1395 2.3.13 Command Reply Payload
1397 Command Reply Payload is used to send replies to the commands sent
1398 by the client. The Command Reply Payload is identical to the
1399 Command Payload hence see the upper sections for Command Payload
1400 and for Command Argument Payload specifications. Command Reply
1401 message uses the Command Argument Payload as well.
1403 See SILC Commands in [SILC1] for detailed description of different
1404 SILC commands, their arguments and their reply messages.
1408 2.3.14 Connection Auth Request Payload
1410 Client may send this payload to server to request the authentication
1411 method that must be used in authentication protocol. If client knows
1412 this information beforehand this payload is not necessary to be sent.
1413 Server performing authentication with another server may also send
1414 this payload to request the authentication method. If the connecting
1415 server already knows this information this payload is not necessary
1418 Server receiving this request must reply with same payload sending
1419 the mandatory authentication method. Algorithms that may be required
1420 to be used by the authentication method are the ones already
1421 established by the SILC Key Exchange protocol. See section Key
1422 Exchange Start Payload in [SILC3] for detailed information.
1424 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1425 packet. It must not be sent in any other packet type. Following
1426 diagram represents the Connection Auth Request Payload.
1432 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
1433 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1434 | Connection Type | Authentication Method |
1435 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1439 Figure 15: Connection Auth Request Payload
1443 o Connection Type (2 bytes) - Indicates the type of the ID.
1444 Following connection types are defined:
1450 If any other type is found in this field the packet must be
1451 discarded and the authentication must be failed.
1453 o Authentication Method (2 bytes) - Indicates the authentication
1454 method to be used in the authentication protocol. Following
1455 authentication methods are defined:
1460 1 password (mandatory)
1461 2 public key (mandatory)
1463 If any other type is found in this field the packet must be
1464 discarded and the authentication must be failed. If this
1465 payload is sent as request to receive the mandatory
1466 authentication method this field must be set to zero (0),
1467 indicating that receiver should send the mandatory
1468 authentication method. The receiver sending this payload
1469 to the requesting party, may also set this field to zero (0)
1470 to indicate that authentication is not required. In this
1471 case authentication protocol still must be started but
1472 server is most likely to respond with SILC_PACKET_SUCCESS
1478 2.3.15 New ID Payload
1480 New ID Payload is a multipurpose payload. It is used to send newly
1481 created ID's from clients and servers. When client connects to server
1482 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
1483 packet, server replies with this packet by sending the created ID for
1484 the client. Server always creates the ID for the client.
1486 This payload is also used when server tells its router that new client
1487 has registered to the SILC network. In this case the server sends
1488 the Client ID of the client to the router. Similiary when router
1489 distributes information to other routers about the client in the SILC
1490 network this payload is used.
1492 Also, when server connects to router, router uses this payload to inform
1493 other routers about new server in the SILC network. However, every
1494 server (or router) creates their own ID's thus the ID distributed by
1495 this payload is not created by the distributor in this case. Servers
1496 create their own ID's. Server registers itself to the network by sending
1497 SILC_PACKET_NEW_SERVER to the router it connected to. The case is same
1498 when router connects to another router.
1500 Hence, this payload is very important and used every time when some
1501 new entity is registered to the SILC network. Client never sends this
1502 payload. Both client and server (and router) may receive this payload.
1504 The payload may only be sent with SILC_PACKET_NEW_ID packet. It must
1505 not be sent in any other packet type. Following diagram represents the
1512 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
1513 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1514 | ID Type | ID Length |
1515 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1519 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1523 Figure 16: New ID Payload
1527 o ID Type (2 bytes) - Indicates the type of the ID. See
1528 section 2.4 SILC ID Types for list of defined ID types.
1530 o ID Length (2 bytes) - Length of the ID Data area not
1531 including the length of any other fields in the payload.
1533 o ID Data (variable length) - The actual ID data.
1539 2.3.16 New ID List Payload
1541 New ID List Payload is used to distribute list of ID's usually from
1542 server to router but also from router to other routers in the network.
1543 This payload is used, for example, when server is connected to router
1544 and the server wants to distribute all of its locally connected clients
1545 and locally created channels to the router. It is convenient in this
1546 case to use this payload instead of sending all the information one
1547 by one using New ID Payload.
1549 There is no specific payload for this packet type. The packet type
1550 uses same payload as described in previous section. To form a list
1551 several payloads is put in the packet each after each. The payload
1552 is variable in length but can be calculated by calculating the ID
1553 Type field, Length field and the ID Data fields together. This forms
1554 one New ID Payload in the list.
1556 The list of payloads may only be sent with SILC_PACKET_NEW_ID_LIST
1557 packet. They must not be sent in any other packet type.
1561 2.3.17 New Client Payload
1563 When client is connected to the server, keys has been exchanged and
1564 connection has been authenticated client must register itself to the
1565 server. Clients first packet after key exchange and authentication
1566 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
1567 the relevant information about the connected user. Server creates a new
1568 client ID for the client when received this payload and sends it to the
1569 client in New ID Payload.
1571 This payload sends username and real name of the user on the remote host
1572 which is connected to the SILC server with SILC client. The server
1573 creates the client ID according the information sent in this payload.
1574 The nickname of the user becomes the username sent in this payload.
1575 However, client should call NICK command after sending this payload to
1576 set the real nickname of the user which is then used to create new
1579 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
1580 must not be sent in any other packet type. Following diagram represents
1581 the New Client Payload.
1587 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
1588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1589 | Username Length | |
1590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1594 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1595 | Real Name Length | |
1596 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1600 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1604 Figure 17: New Client Payload
1608 o Username Length (2 bytes) - Length of the username.
1610 o Username (variable length) - The username of the user on
1611 the host where connecting to the SILC server.
1613 o Real Name Length (2 bytes) - Length of the Real Name.
1615 o Real Name (variable length) - The real name of the user
1616 on the host where connecting to the SILC server.
1621 2.3.18 New Server Payload
1623 This payload is sent by server when it has completed successfully both
1624 key exchange and connection authentication protocols. The server
1625 uses this payload to register itself to the SILC network. The
1626 first packet after these key exchange and authentication protocols
1627 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
1628 of the server that it has created by itself. It also includes a
1629 name of the server that is associated to the Server ID.
1631 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
1632 must not be sent in any other packet type. Following diagram represents
1633 the New Server Payload.
1639 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
1640 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1641 | Server ID Length | |
1642 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1646 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1647 | Server Name Length | |
1648 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1652 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1656 Figure 18: New Server Payload
1660 o Server ID Length (2 bytes) - Length of the ID Data area not
1661 including the length of any other fields in the payload.
1663 o Server ID Data (variable length) - The actual Server ID
1666 o Server Name Length (2 bytes) - Length of the server name.
1668 o Server Name (variable length) - The server name.
1673 2.3.19 New Channel Payload
1675 Information about newly created channel is broadcasted to all routers
1676 in the SILC network by sending this packet payload. Channels are
1677 created by router of the cell. Server never creates channels unless
1678 it is a standalone server and it does not have router connection,
1679 in this case server acts as router. Normal server sends JOIN command
1680 to the router (after it has received JOIN command from client) which
1681 then processes the command and creates the channel. Client never sends
1684 The payload may only be sent with SILC_PACKET_NEW_CHANNEL packet.
1685 It must not be sent in any other packet type. Following diagram
1686 represents the New Channel Payload.
1692 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
1693 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1694 | Channel Name Length | |
1695 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1699 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1700 | Channel ID Length | |
1701 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1705 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1709 Figure 19: New Channel Payload
1714 o Channel Name Length (2 bytes) - Length of the channel name.
1716 o Channel Name (variable length) - The name of the created
1719 o Channel ID Length (2 bytes) - Length of the Channel ID.
1721 o Channel ID (variable length) - The created Channel ID.
1726 2.3.20 New Channel User Payload
1728 When client (user) joins to a channel, server must notify routers
1729 about the new user on the channel. Normal server sends this packet
1730 payload to its router which then broadcasts the packet further.
1731 Router sends this packet always to its primary router. Client must
1732 not send this packet payload. The mode of the user is NONE after
1733 user has joined to the channel.
1735 The payload may only be sent with SILC_PACKET_NEW_CHANNEL_USER
1736 packet. It must not be sent in any other packet type. Following
1737 diagram represents the New Channel User Payload.
1743 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
1744 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1745 | Channel ID Length | |
1746 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1750 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1751 | Client ID Length | |
1752 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1756 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1760 Figure 20: New Channel User Payload
1764 o Channel ID Length (2 bytes) - Length of the Channel ID.
1766 o Channel ID (variable length) - The Channel ID of the channel
1767 to which the client has joined.
1769 o Client ID Length (2 bytes) - Length of the Client ID.
1771 o Client ID (variable length) - The Client ID of the client
1772 who has joined the channel.
1777 2.3.21 New Channel List Payload
1779 This payload is used to distribute list of new channels from server
1780 to routers. It might convenient to send list of new channels when
1781 existing server connects to router, instead of sending them one
1784 There is no specific payload for this packet type. The packet type
1785 uses same payload as described in 2.3.19 New Channel Payload. To form
1786 a list several payloads is put in the packet each after each. The
1787 payload is variable in length but can be calculated by calculating
1788 the length of the fields together. This forms one New Channel Payload
1791 The list of payloads may only be sent with SILC_PACKET_NEW_CHANNEL_LIST
1792 packet. They must not be sent in any other packet type.
1796 2.3.22 New Channel User List Payload
1798 This payload is used to distribute list of channel users on specific
1799 channel from server to routers. It might convenient to send list of
1800 channel users when existing server connects to router, instead of
1801 sending them one by one.
1803 There is no specific payload for this packet type. The packet type
1804 uses same payload as described in 2.3.20 New Channel User Payload.
1805 To form a list several payloads is put in the packet each after each.
1806 The payload is variable in length but can be calculated by calculating
1807 the length of the fields together. This forms one New Channel User
1808 Payload in the list.
1810 The list of payloads may only be sent with packet
1811 SILC_PACKET_NEW_CHANNEL_USER_LIST. They must not be sent in any other
1816 2.3.23 Replace ID Payload
1818 This payload is used to replace old ID with new ID sent in the payload.
1819 When ID changes for some entity and the new ID is wanted to replace the
1820 old one this payload must be used. Client cannot send or receive this
1821 payload. Normal server and router server may send and receive this
1822 payload. After this packet has been sent the old ID must not be used
1825 The payload may only be sent with SILC_PACKET_REPLACE_ID packet. It must
1826 not be sent in any other packet type. Following diagram represents the
1827 Replace Payload Payload.
1840 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
1841 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1842 | Old ID Type | Old ID Length |
1843 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1847 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1848 | New ID Type | New ID Length |
1849 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1853 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1857 Figure 21: Replace ID Payload
1861 o Old ID Type (2 bytes) - Indicates the type of the old ID. See
1862 section 2.4 SILC ID Types for list of defined ID types.
1864 o Old ID Length (2 bytes) - Length of the old ID Data area not
1865 including the length of any other fields in the payload.
1867 o Old ID Data (variable length) - The actual old ID data.
1869 o New ID Type (2 bytes) - Indicates the type of the new ID. See
1870 section 2.4 SILC ID Types for list of defined ID types.
1872 o New ID Length (2 bytes) - Length of the new ID Data area not
1873 including the length of any other fields in the payload.
1875 o New ID Data (variable length) - The actual new ID data.
1880 2.3.24 Remove ID Payload
1882 Remove ID payload is used to remove ID from SILC network. This is used
1883 for example when client exits SILC network. The server must in this
1884 case send this payload to notify that this ID is not valid anymore.
1885 After this has been send the old ID must not be used anymore. Client
1886 must not send this payload.
1888 The payload may only be sent with SILC_PACKET_REMOVE_ID packet. It must
1889 not be sent in any other packet type. Following diagram represents the
1890 Remove Payload Payload.
1896 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
1897 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1898 | ID Type | ID Length |
1899 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1903 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1907 Figure 22: Remove ID Payload
1911 o ID Type (2 bytes) - Indicates the type of the ID to be
1912 removed. See section 2.4 SILC ID Types for list of defined
1915 o ID Length (2 bytes) - Length of the D Data area not including
1916 the length of any other fields in the payload.
1918 o ID Data (variable length) - The actual ID data to be removed.
1925 ID's are extensively used in the SILC network to associate different
1926 entities. Following ID's has been defined to be used in the SILC
1932 When ever specific ID cannot be used this is used.
1936 Server ID to associate servers. See the format of
1941 Client ID to associate clients. See the format of
1946 Channel ID to associate channels. See the format of
1952 2.5 Packet Encryption And Decryption
1954 SILC packets are encrypted almost entirely. Only small part of SILC
1955 header is not encrypted as described in section 5.2 SILC Packet Header.
1956 The SILC Packet header is the first part of a packet to be encrypted
1957 and it is always encrypted with the key of the next receiver of the
1958 packet. The data payload area of the packet is always entirely
1959 encrypted and it is usually encrypted with the next receiver's key.
1960 However, there are some special packet types and packet payloads
1961 that require special encryption process. These special cases are
1962 described in the next sections. First is described the normal packet
1967 2.5.1 Normal Packet Encryption And Decryption
1969 Normal SILC packets are encrypted with the session key of the next
1970 receiver of the packet. The entire SILC Packet header and the packet
1971 data payload is is also encrypted with the same key. Padding of the
1972 packet is also encrypted always with the session key, also in special
1973 cases. Computed MAC of the packet must not be encrypted.
1975 Decryption process in these cases are straightforward. The receiver
1976 of the packet must first decrypt the SILC Packet header, or some parts
1977 of it, usually first 16 bytes of it. Then the receiver checks the
1978 packet type from the decrypted part of the header and can determine
1979 how the rest of the packet must be decrypted. If the packet type is
1980 any of the special cases described in following sections the packet
1981 decryption is special. If the packet type is not among those special
1982 packet types rest of the packet may be decrypted with the same key.
1984 Also, note that two bytes of the SILC Packet header are not encrypted
1985 thus it must be noticed in the decryption process by starting the
1986 decryption from the second byte of the header. This sets some rules
1987 to padding generation as well, see the section 2.7 Packet Padding
1990 With out a doubt, this sort of decryption processing causes some
1991 overhead to packet decryption, but never the less, is required.
1995 2.5.2 Channel Message Encryption And Decryption
1997 Channel Messages (Channel Message Payload) are always encrypted with
1998 the channel specific key. However, the SILC Packet header is not
1999 encrypted with that key. As in normal case, the header is encrypted
2000 with the key of the next receiver of the packet, who ever that might
2001 be. Note that in this case the encrypted data area is not touched
2002 at all; it must not be re-encrypted with the session key.
2004 Receiver of a channel message, who ever that is, is required to decrypt
2005 the SILC Packet header to be able to even recognize the packet to be as
2006 channel message. This is same procedure as for normal SILC packets.
2007 As the receiver founds the packet to be channel message, rest of the
2008 packet processing is special. Rest of the SILC Packet header is
2009 decrypted with the same session key along with the padding of the
2010 packet. After that the packet is protected with the channel specific
2011 key and hence can be decrypted only if the receiver is the client on
2012 the channel. See section 2.7 Packet Padding Generation for more
2013 information about padding on special packets.
2015 If the receiver of the channel message is router who is routing the
2016 message to another router then it must decrypt the Channel Message
2017 payload. Between routers (that is, between cells) channel messages
2018 are protected with session keys shared between the routers. This
2019 causes another special packet processing for channel messages. If
2020 the channel message is received from another router then the entire
2021 packet, including Channel Message payload, is encrypted with the
2022 session key shared between the routers. In this case the packet
2023 decryption process is as with normal SILC packets. Hence, if the
2024 router is sending channel message to another router the Channel
2025 Message payload must have been decrypted and must be re-encrypted
2026 with the session key shared between the another router. In this
2027 case the packet encryption is as with any normal SILC packet.
2029 It must be noted that this is only when the channel messages are sent
2030 from router to another router. In all other cases the channel
2031 message encryption and decryption is as described above. This
2032 different processing of channel messages with router to router
2033 connection is because channel keys are cell specific. All cells has
2034 their own channel keys thus the channel message traveling from one
2035 cell to another must be protected as it would be any normal SILC
2040 2.5.3 Private Message Encryption And Decryption
2042 By default, private message in SILC are protected by session keys.
2043 In this case the private message encryption and decryption process is
2044 equivalent to normal packet encryption and decryption.
2046 However, private messages can be protected with private message key
2047 which causes the packet to be special packet. The procedure in this
2048 case is very much alike to channel packets. The actual private message
2049 is encrypted with the private message key and other parts of the
2050 packet is encrypted with the session key. See 2.7 Packet Padding
2051 Generation for more information about padding on special packets.
2053 The difference from channel message processing is that server or router
2054 en route never decrypts the actual private message, as it does not
2055 have the key to do that. Thus, when sending packets between router
2056 the processing is same as in any other case as well; the packet's header
2057 and padding is protected by the session key and the data area is not
2060 The true receiver of the private message, client, that is, is able
2061 to decrypt the private message as it shares the key with the sender
2066 2.6 Packet MAC Generation
2068 Data integrity of a packet is protected by including a message
2069 authentication code (MAC) at the end of the packet. The MAC is computed
2070 from shared secret MAC key, that is established by the SILC Key Exchange
2071 protocol, and from the original contents of the packet. The MAC is
2072 always computed before the packet is encrypted, although after it is
2073 compressed if compression is used.
2075 The MAC is computed from entire packet. Every bit of data in the packet,
2076 including SILC Packet Header is used in the MAC computing. This way
2077 the entire packet becomes authenticated.
2079 If the packet is special packet MAC is computed from the entire packet
2080 but part of the packet may be encrypted before the MAC is computed.
2081 This is case, for example, with channel messages where the message data
2082 is encrypted with key that server may not now. In this case the MAC
2083 has been computed from the encrypted data.
2085 See [SILC1] for defined and allowed MAC algorithms.
2089 2.7 Packet Padding Generation
2091 Padding is needed in the packet because the packet is encrypted. It
2092 must always be multiple by eight (8) or multiple by the size of the
2093 cipher's block size, which ever is larger. The padding is always
2096 For normal packets the padding is added after the SILC Packet Header
2097 and between the Data Payload area. The padding for normal packets
2098 are calculated as follows:
2101 padding length = 16 - ((packet length - 2) % 16)
2104 The 16 is the maximum padding allowed in SILC packet. Two (2) is
2105 subtracted from the true length of the packet because two (2) bytes
2106 is not encrypted in SILC Packet Header, see section 2.2 SILC Packet
2107 Header. Those two bytes that are not encrypted must not be calculated
2108 to the padding length.
2110 For special packets the padding calculation may be different as special
2111 packets may be encrypted differently. In these cases the encrypted
2112 data area must already be multiple by the block size thus in this case
2113 the padding is calculated only for SILC Packet Header, not for any
2114 other area of the packet. The same algorithm works in this case as
2115 well, except that the `packet length' is now the SILC Packet Header
2116 length. In this case, as well, two (2) is subtracted from the
2119 The padding must be random data, preferably, generated by
2120 cryptographically strong random number generator.
2124 2.8 Packet Compression
2126 SILC Packets may be compressed. In this case the data payload area
2127 is compressed and all other areas of the packet must remain as they
2128 are. After compression is performed for the data area, the length
2129 field of Packet Header must be set to the compressed length of the
2132 The compression must always be applied before encryption. When
2133 the packet is received and decrypted the data area must be decompressed.
2134 Note that the true sender of the packet must apply the compression and
2135 the true receiver of the packet must apply the decompression. Any
2136 server or router en route must not decompress the packet.
2142 The sender of the packet must assemble the SILC Packet Header with
2143 correct values. It must set the Source ID of the header as its own
2144 ID. It must also set the Destination ID of the header to the true
2145 destination. If the destination is client it will be Client ID, if
2146 it is server it will be Server ID and if it is channel it will be
2149 If the sender wants to compress the packet it must apply the
2150 compression now. Sender must also compute the padding as described
2151 in above sections. Then sender must compute the MAC of the packet.
2153 Then sender encrypts the packet as has been described in above
2154 sections according whether the packet is normal packet or special
2155 packet. The computed MAC must not be encrypted.
2159 2.10 Packet Reception
2161 On packet reception the receiver must check that all fields in the
2162 SILC Packet Header are valid sain. It must check the flags of the
2163 header and act accordingly. It must also check the MAC of the packet
2164 and if it is to be failed the packet must be discarded. Also if the
2165 header of the packet includes any bad fields the packet must be
2168 See above sections on the decryption process of the received packet.
2170 The receiver must also check that the ID's in the header are valid
2171 ID's. Unsupported ID types or malformed ID's must cause packet
2172 rejection. The padding on the reception is always ignored.
2174 The receiver must also check the packet type and start parsing the
2175 packet according to the type. However, note the above sections on
2176 special packet types and their parsing.
2180 2.11 Packet Broadcasting
2182 SILC packets may be broadcasted in SILC network. However, only router
2183 server may send or receive broadcast packets. Client and normal server
2184 must not send broadcast packets and they must ignore broadcast packets
2185 if they receive them. Broadcast packets are sent by setting Broadcast
2186 flag to the SILC packet header.
2188 Broadcasting packets means that the packet is sent to all routers in
2189 the SILC network, except to the router that sent the packet. The router
2190 receiving broadcast packet must send the packet to its primary route.
2191 The fact that SILC routers may have several router connections may
2192 cause problems, such as race conditions inside the SILC network, if
2193 care is not taken when broadcasting packets. Router must not send
2194 the broadcast packet to any other route except to its primary route.
2196 If the primary route of the router is the original sender of the packet
2197 the packet must not be sent to the primary route. This may happen
2198 if router has several router connections and some other router uses
2199 the router as its primary route.
2201 Routers use broadcast packets to broadcast for example information
2202 about newly registered clients, servers, channels etc. so that all the
2203 routers may keep these informations up to date.
2209 Routers are the primary entities in the SILC network that takes care
2210 of packet routing. However, normal servers routes packets as well, for
2211 example, when they are routing channel message to the local clients.
2212 Routing is quite simple as every packet tells the true origin and the
2213 true destination of the packet.
2215 It is still recommended for routers that has several routing connections
2216 to create route cache for those destinations that has faster route than
2217 the router's primary route. This information is available for the router
2218 when other router connects to the router. The connecting party then
2219 sends all of its locally connected clients, server and channels. These
2220 informations helps to create the route cache. Also, when new channels
2221 are created to a cell its information is broadcasted to all routers
2222 in the network. Channel ID's are based on router's ID thus it is easy
2223 to create route cache based on these informations. If faster route for
2224 destination does not exist in router's route cache the packet must be
2225 routed to the primary route (default route).
2227 For server who receives a packet to be routed to its locally connected
2228 client the server must check whether the particular packet type is
2229 allowed to be routed to the client. Not all packets may be sent by
2230 some odd entity to client that is indirectly connected to the sender.
2231 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2232 entities and sending packets to them. The section mentions the packets
2233 that may be sent to indirectly connected entities. It is clear that some
2234 server cannot send, for example, disconnect packet to client that is not
2235 directly connected to the server.
2239 2.13 Packet Tunneling
2241 Tunneling is a feature that is available in SILC protocol. Tunneling
2242 means that extra SILC Packet Header is applied to the original packet
2243 and thus hiding the original packet entirely. There can be some
2244 interesting applications using tunneling, such as, using ID's based on
2245 private network IP addresses inside in the tunneled packet. This can
2246 open many interesting features relating to connecting to private network
2247 from the Internet with SILC and many more. However, this feature is
2248 optional currently in SILC as there does not exist thorough analysis of
2249 this feature. It is with out a doubt that there will be many more
2250 applications that has not yet been discovered. Thus, it is left
2251 to Internet Community to investigate the use of tunneling in SILC
2252 protocol. This document is updated according those investigations
2253 and additional documents on the issue may be written.
2257 3 Security Considerations
2259 Security is central to the design of this protocol, and these security
2260 considerations permeate the specification.
2266 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2267 Protocol Specification", Internet Draft, June 2000.
2269 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2270 Protocols", Internet Draft, June 2000.
2272 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2275 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2278 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2281 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2284 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2285 Infrastructure, Certificate and CRL Profile", RFC 2459,
2288 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2289 John Wiley & Sons, New York, NY, 1996.
2291 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2294 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2295 RFC 2412, November 1998.
2297 [ISAKMP] Maughan D., et al, "Internet Security Association and
2298 Key Management Protocol (ISAKMP)", RFC 2408, November
2301 [IKE] Harkins D., and Carrel D., "The Internet Key Exhange
2302 (IKE)", RFC 2409, November 1998.
2304 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2305 Authentication", RFC 2104, February 1997.
2317 EMail: priikone@poseidon.pspt.fi