8 .ds RF FORMFEED[Page %]
17 Network Working Group P. Riikonen
19 draft-riikonen-silc-pp-01.txt 6 October 2000
26 <draft-riikonen-silc-pp-01.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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35 distribute working documents as Internet-Drafts.
37 Internet-Drafts are draft documents valid for a maximum of six months
38 and may be updated, replaced, or obsoleted by other documents at any
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
43 http://www.ietf.org/ietf/1id-abstracts.txt
45 The list of Internet-Draft Shadow Directories can be accessed at
46 http://www.ietf.org/shadow.html
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 Generic payloads .................................... 16
81 2.3.2.1 ID Payload .................................. 16
82 2.3.2.2 Argument Payload ............................ 16
83 2.3.3 Disconnect Payload .................................. 17
84 2.3.4 Success Payload ..................................... 18
85 2.3.5 Failure Payload ..................................... 18
86 2.3.6 Reject Payload ...................................... 19
87 2.3.7 Notify Payload ...................................... 20
88 2.3.8 Error Payload ....................................... 21
89 2.3.9 Channel Message Payload ............................. 22
90 2.3.10 Channel Key Payload ................................ 24
91 2.3.11 Private Message Payload ............................ 26
92 2.3.12 Private Message Key Payload ........................ 27
93 2.3.13 Command Payload .................................... 28
94 2.3.14 Command Reply Payload .............................. 29
95 2.3.15 Connection Auth Request Payload .................... 29
96 2.3.16 New ID Payload ..................................... 30
97 2.3.17 New Client Payload ................................. 31
98 2.3.18 New Server Payload ................................. 32
99 2.3.19 New Channel Payload ................................ 33
100 2.4 SILC ID Types ............................................. 39
101 2.5 Packet Encryption And Decryption .......................... 39
102 2.5.1 Normal Packet Encryption And Decryption ............. 39
103 2.5.2 Channel Message Encryption And Decryption ........... 40
104 2.5.3 Private Message Encryption And Decryption ........... 41
105 2.6 Packet MAC Generation ..................................... 41
106 2.7 Packet Padding Generation ................................. 42
107 2.8 Packet Compression ........................................ 42
108 2.9 Packet Sending ............................................ 43
109 2.10 Packet Reception ......................................... 43
110 2.11 Packet Routing ........................................... 44
111 2.12 Packet Broadcasting ...................................... 45
112 2.13 Packet Tunneling ......................................... 45
113 3 Security Considerations ....................................... 46
114 4 References .................................................... 46
115 5 Author's Address .............................................. 47
121 Figure 1: Typical SILC Packet
122 Figure 2: SILC Packet Header
124 Figure 4: Argument Payload
125 Figure 5: Disconnect Payload
126 Figure 6: Success Payload
127 Figure 7: Failure Payload
128 Figure 8: Reject Payload
129 Figure 9: Notify Payload
130 Figure 10: Error Payload
131 Figure 11: Channel Message Payload
132 Figure 12: Channel Key Payload
133 Figure 13: Private Message Payload
134 Figure 14: Private Message Key Payload
135 Figure 15: Command Payload
136 Figure 16: Connection Auth Request Payload
137 Figure 17: New Client Payload
138 Figure 18: New Server Payload
139 Figure 19: New Channel Payload
145 This document describes a Packet Protocol used in the Secure Internet
146 Live Conferencing (SILC) protocol specified in the Secure Internet Live
147 Conferencing, Protocol Specification Internet Draft [SILC1]. This
148 protocol describes the packet types and packet payloads which defines
149 the contents of the packets. The protocol provides secure binary packet
150 protocol that assures that the contents of the packets are secured and
153 The basis of SILC protocol relies in the SILC packets and it is with
154 out a doubt the most important part of the protocol. It is also probably
155 the most complicated part of the protocol. Packets are used all the
156 time in the SILC network to send messages, commands and other information.
157 All packets in SILC network are always encrypted and their integrity
158 is assured by computed MACs. The protocol defines several packet types
159 and packet payloads. Each packet type usually has a specific packet
160 payload that actually defines the contents of the packet. Each packet
161 also includes a default SILC Packet Header that provides sufficient
162 information about the origin of the packet and destination of the
167 2 SILC Packet Protocol
172 SILC packets deliver messages from sender to receiver securely by
173 encrypting important fields of the packet. The packet consists of
174 default SILC Packet Header, Padding, Packet Payload data, and, packet
177 The following diagram illustrates typical SILC packet.
182 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
183 | n bytes | 1 - n bytes | n bytes | n bytes
184 | SILC Header | Padding | Data Payload | MAC
185 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
189 Figure 1: Typical SILC Packet
192 SILC Header is always the first part of the packet and its purpose
193 is to provide information about the packet. It provides for example
194 the packet type, origin of the packet and the destination of the packet.
195 The header is variable in length and first two (2) bytes of the
196 header (thus first two bytes of the packet) are not encrypted. The
197 first two (2) bytes are the length of the packet which is not encrypted.
198 See following section for description of SILC Packet header. Packets
199 without SILC header or with malformed SILC header must be dropped.
201 Padding follows the packet header. The purpose of the padding is to
202 make the packet multiple by eight (8) or by the block size of the
203 cipher used in the encryption, which ever is larger. The maximum
204 length of padding is currently 16 bytes. The padding is always
207 Data payload area follows padding and it is the actual data of the
208 packet. The packet data is the packet payloads defined in this
209 protocol. The data payload area is always encrypted.
211 The last part of SILC packet is the packet MAC that assures the
212 integrity of the packet. The MAC is always computed from the packet
213 before the encryption is applied to the packet. If compression is used
214 in the packet the MAC is computed after the compression has been
215 applied. The compression, on the other hand, is always applied before
218 All fields in all packet payloads are always in MSB (most significant
223 2.2 SILC Packet Header
225 The default SILC packet header is applied to all SILC packets and it is
226 variable in length. The purpose of SILC Packet header is to provide
227 detailed information about the packet. The receiver of the packet uses
228 the packet header to parse the packet and gain other relevant parameters
231 Following diagram represents the default SILC header format.
232 (*) indicates that this field is never encrypted. Other fields are
239 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
240 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
241 | Payload Length * | Flags | Packet Type |
242 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
243 | Source ID Length | Destination ID Length |
244 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
250 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
256 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
260 Figure 2: SILC Packet Header
264 o Payload Length (2 bytes) - Is the length of the packet
265 not including the padding of the packet. This field must
266 not be encrypted but must always be authenticated.
268 o Flags (1 byte) - Indicates flags to be used in packet
269 processing. Several flags may be set by ORing the flags
272 Following flags are reserved for this field:
277 In this case the field is ignored.
280 Private Message Key 0x01
282 Indicates that the packet must include private
283 message that is encrypted using private key set by
284 client. Servers does not know anything about this
285 key and this causes that the private message is
286 not handled by the server at all, it is just
287 passed along. See section 2.5.3 Private Message
288 Encryption And Decryption for more information.
293 Indicates that the packet consists of list of
294 packet payloads indicated by the Packet Type field.
295 The payloads are added one after the other. Note that
296 there are packet types that must not be used as
297 list. Parsing of list packet is done by calculating
298 the length of each payload and parsing them one by
304 Marks the packet to be broadcasted. Client cannot
305 send broadcast packet and normal server cannot send
306 broadcast packet. Only router server may send broadcast
307 packet. The router receiving of packet with this flag
308 set must send (broadcast) the packet to its primary
309 route. If router has several router connections the
310 packet may be sent only to the primary route. See
311 section 2.13 Packet Broadcasting for description of
317 Marks that the packet is tunneled. Tunneling means
318 that extra SILC Packet Header has been applied to the
319 original packet. The outer header has this flag
320 set. See section 2.14 Packet Tunneling for more
326 o Packet Type (1 byte) - Is the type of the packet. Receiver
327 uses this field to parse the packet. See section 2.3
328 SILC Packets for list of defined packet types.
330 o Source ID Length (2 bytes) - Indicates the length of the
331 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 This packet must not be sent as list and the List flag must
399 Payload of the packet: See section 2.3.3 Disconnect Payload
402 2 SILC_PACKET_SUCCESS
404 This packet is sent upon successful execution of some protocol.
405 The status of the success is sent in the packet.
407 This packet must not be sent as list and the List flag must
410 Payload of the packet: See section 2.3.4 Success Payload
413 3 SILC_PACKET_FAILURE
415 This packet is sent upon failure of some protocol. The status
416 of the failure is sent in the packet.
418 This packet must not be sent as list and the List flag must
421 Payload of the packet: See section 2.3.5 Failure Payload
426 This packet may be sent upon rejection of some protocol.
427 The status of the rejection is sent in the packet.
429 This packet must not be sent as list and the List flag must
432 Payload of the packet: See section 2.3.6 Reject Payload
437 This packet is used to send notify message, usually from
438 server to client, although it may be sent from server to another
439 server as well. Client never sends this packet. Server may
440 send this packet to channel as well when the packet is
441 distributed to all clients on the channel.
443 Payload of the packet: See section 2.3.7 Notify Payload.
448 This packet is sent when an error occurs. Server may
449 send this packet. Client never sends this packet. The
450 client may entirely ignore the packet, however, server is
451 most likely to take action anyway. This packet may be sent
452 to entity that is indirectly connected to the sender.
454 This packet must not be sent as list and the List flag must
457 Payload of the packet: See section 2.3.8 Error Payload.
460 7 SILC_PACKET_CHANNEL_MESSAGE
462 This packet is used to send messages to channels. The packet
463 includes Channel ID of the channel and the actual message to
464 the channel. Messages sent to the channel are always protected
465 by channel specific keys. Channel Keys are distributed by
466 SILC_PACKET_CHANNEL_KEY packet.
468 This packet must not be sent as list and the List flag must
471 Payload of the packet: See section 2.3.9 Channel Message
475 8 SILC_PACKET_CHANNEL_KEY
477 This packet is used to distribute new key for particular
478 channel. Each channel has their own independent keys that
479 is used to protect the traffic on the channel. Only server
480 may send this packet. This packet may be sent to entity
481 that is indirectly connected to the sender.
483 This packet must not be sent as list and the List flag must
486 Payload of the packet: See section 2.3.10 Channel Key Payload
489 9 SILC_PACKET_PRIVATE_MESSAGE
491 This packet is used to send private messages from client
492 to another client. By default, private messages are protected
493 by session keys established by normal key exchange protocol.
494 However, it is possible to use specific key to protect private
495 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
496 agree the key with the remote client. Pre-shared key may be
497 used as well if both of the client knows it, however, it needs
498 to be agreed outside SILC. See more of this in [SILC1].
500 This packet must not be sent as list and the List flag must
503 Payload of the packet: See section 2.3.11 Private Message
507 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
509 This packet is used to agree about a key to be used to protect
510 the private messages between two clients. If this is not sent
511 the normal session key is used to protect the private messages
512 inside SILC network. Agreeing to use specific key to protect
513 private messages adds security, as no server between the two
514 clients will be able to decrypt the private message. However,
515 servers inside SILC network are considered to be trusted, thus
516 using normal session key to protect private messages does not
517 degree security. Whether to agree to use specific keys by
518 default or to use normal session keys by default, is
519 implementation specific issue. See more of this in [SILC1].
521 This packet must not be sent as list and the List flag must
524 Payload of the packet: See section 2.3.12 Private Message
528 11 SILC_PACKET_COMMAND
530 This packet is used to send commands from client to server.
531 Server may send this packet to other servers as well. All
532 commands are listed in their own section SILC Command Types
533 in [SILC1]. The contents of this packet is command specific.
534 This packet may be sent to entity that is indirectly connected
537 This packet must not be sent as list and the List flag must
540 Payload of the packet: See section 2.3.13 Command Payload
543 12 SILC_PACKET_COMMAND_REPLY
545 This packet is send as reply to the SILC_PACKET_COMMAND packet.
546 The contents of this packet is command specific. This packet
547 maybe sent to entity that is indirectly connected to the sender.
549 This packet must not be sent as list and the List flag must
552 Payload of the packet: See section 2.3.14 Command Reply
553 Payload and section 2.3.13 Command
557 13 SILC_PACKET_KEY_EXCHANGE
559 This packet is used to start SILC Key Exchange Protocol,
560 described in detail in [SILC3].
562 This packet must not be sent as list and the List flag must
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 14 SILC_PACKET_KEY_EXCHANGE_1
573 This packet is used as part of the SILC Key Exchange Protocol.
575 This packet must not be sent as list and the List flag must
578 Payload of the packet: Payload of this packet is described
579 in the section SILC Key Exchange
580 Protocol and its sub sections in
584 15 SILC_PACKET_KEY_EXCHANGE_2
586 This packet is used as part of the SILC Key Exchange Protocol.
588 This packet must not be sent as list and the List flag must
591 Payload of the packet: Payload of this packet is described
592 in the section SILC Key Exchange
593 Protocol and its sub sections in
597 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
599 This packet is used to request the authentication method to
600 be used in the SILC Connection Authentication Protocol. If
601 initiator of the protocol does not know the mandatory
602 authentication method this packet is used to determine it.
604 The party receiving this payload must respond with the same
605 packet including the mandatory authentication method.
607 This packet must not be sent as list and the List flag must
610 Payload of the packet: See section 2.3.15 Connection Auth
614 17 SILC_PACKET_CONNECTION_AUTH
616 This packet is used to start and perform the SILC Connection
617 Authentication Protocol. This protocol is used to authenticate
618 the connecting party. The protocol is described in detail in
621 This packet must not be sent as list and the List flag must
624 Payload of the packet: Payload of this packet is described
625 in the section SILC Authentication
626 Protocol and it sub sections in [SILC].
629 18 SILC_PACKET_NEW_ID
631 This packet is used to distribute new ID's from server to
632 router and from router to all routers in the SILC network.
633 This is used when for example new client is registered to
634 SILC network. The newly created ID's of these operations are
635 distributed by this packet. Only server may send this packet,
636 however, client must be able to receive this packet.
638 Payload of the packet: See section 2.3.16 New ID Payload
641 19 SILC_PACKET_NEW_CLIENT
643 This packet is used by client to register itself to the
644 SILC network. This is sent after key exchange and
645 authentication protocols has been completed. Client sends
646 various information about itself in this packet.
648 This packet must not be sent as list and the List flag must
651 Payload of the packet: See section 2.3.19 New Client Payload
654 20 SILC_PACKET_NEW_SERVER
656 This packet is used by server to register itself to the
657 SILC network. This is sent after key exchange and
658 authentication protocols has been completed. Server sends
659 this to the router it connected to, or, if router was
660 connecting, to the connected router. Server sends
661 its Server ID and other information in this packet.
662 Client must not send or receive this packet.
664 This packet must not be sent as list and the List flag must
667 Payload of the packet: See section 2.3.20 New Server Payload
670 21 SILC_PACKET_NEW_CHANNEL
672 This packet is used to notify routers about newly created
673 channel. Channels are always created by the router and it must
674 notify other routers about the created channel. Router sends
675 this packet to its primary route. Client must not send this
676 packet. This packet maybe sent to entity that is indirectly
677 connected to the sender.
679 Payload of the packet: See section 2.3.21 New Channel Payload
684 This packet is used to indicate that re-key must be performed
685 for session keys. See section Session Key Regeneration in
686 [SILC1] for more information. This packet does not have
689 This packet must not be sent as list and the List flag must
693 23 SILC_PACKET_REKEY_DONE
695 This packet is used to indicate that re-key is performed and
696 new keys must be used hereafter. This is sent only if re-key
697 was done without PFS option. If PFS is set, this is not sent
698 as SILC Key Exchange protocol is executed. This packet does
701 This packet must not be sent as list and the List flag must
705 24 SILC_PACKET_HEARTBEAT
707 This packet is used by clients, servers and routers to keep the
708 connection alive. It is recommended that all servers implement
709 keepalive actions and perform it to both direction in a link.
710 This packet does not have a payload.
712 This packet must not be sent as list and the List flag must
718 Currently undefined commands.
723 These packet types are reserved for private use and they will not
724 be defined by this document.
729 This type is reserved for future extensions and currently it
735 2.3.1 SILC Packet Payloads
737 All payloads resides in the main data area of the SILC packet. However
738 all payloads must be at the start of the data area after the default
739 SILC packet header and padding. All fields in the packet payload are
740 always encrypted, as, they reside in the data area of the packet which
743 Payloads described in this section are common payloads that must be
744 accepted anytime during SILC session. Most of the payloads may only
745 be sent with specific packet type which is defined in the description
748 There are a lot of other payloads in the SILC as well. However, they
749 are not common in the sense that they could be sent at any time.
750 These payloads are not described in this section. These are payloads
751 such as SILC Key Exchange payloads and so on. These are described
752 in [SILC1] and [SILC3].
756 2.3.2 Generic payloads
758 This section describes generic payloads that are not associated to any
759 specific packet type. They can be used for example inside some other
766 This payload can be used to send an ID. ID's are variable length thus
767 this payload provides a way to send variable length ID's.
769 Following diagram represents the ID Payload.
774 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
775 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
776 | ID Type | ID Length |
777 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
781 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
789 o ID Type (2 bytes) - Indicates the type of the ID. See
790 section 2.4 SILC ID Types for list of defined ID types.
792 o ID Length (2 bytes) - Length of the ID Data area not
793 including the length of any other fields in the payload.
795 o ID Data (variable length) - The actual ID data.
800 2.3.2.2 Argument Payload
802 Argument Payload is used to set arguments for any packet payload that
803 needs and supports arguments, such as commands. Number of arguments
804 associated with a packet must be indicated by the packet payload who
805 needs the arguments. Argument Payloads must always reside right after
806 the packet payload needing the arguments. Incorrect amount of argument
807 payloads must cause rejection of the packet. Following diagram represents
808 the Argument Payload.
814 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
815 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
816 | Payload Length | Argument Type | |
817 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
821 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
825 Figure 4: Argument Payload
829 o Payload Length (2 bytes) - Length of the argument payload data
830 area not including the length of any other fields in the
833 o Argument Type (1 byte) - Indicates the type of the argument.
834 Every argument may have a specific type that must be defined
835 by the packet payload needing the argument. For example
836 every command specify a number for each argument that maybe
837 associated with the command. By using this number the receiver
838 of the packet knows what type of argument this is. If there is
839 no specific argument type this field is set to zero (0).
841 o Argument Data (variable length) - Argument data.
846 2.3.3 Disconnect Payload
848 Disconnect payload is sent upon disconnection. The payload is simple;
849 reason of disconnection is sent to the disconnected party.
851 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
852 must not be sent in any other packet type. Following diagram represents
853 the Disconnect Payload.
864 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
865 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
867 ~ Disconnect Message ~
869 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
873 Figure 5: Disconnect Payload
879 o Disconnect Message (variable length) - Human readable
880 reason of the disconnection.
885 2.3.4 Success Payload
887 Success payload is sent when some protocol execution is successfully
888 completed. The payload is simple; indication of the success is sent.
889 This maybe any data, including binary or human readable data.
894 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
895 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
897 ~ Success Indication ~
899 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
903 Figure 6: Success Payload
907 o Success Indication (variable length) - Indication of
908 the success. This maybe for example some flag that
909 indicates the protocol and the success status or human
910 readable success message. The true length of this
911 payload is available by calculating it from the SILC
917 2.3.5 Failure Payload
919 This is opposite of Success Payload. Indication of failure of
920 some protocol is sent in the payload.
926 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
927 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
929 ~ Failure Indication ~
931 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
935 Figure 7: Failure Payload
939 o Failure Indication (variable length) - Indication of
940 the failure. This maybe for example some flag that
941 indicates the protocol and the failure status or human
942 readable failure message. The true length of this
943 payload is available by calculating it from the SILC
951 This payload is sent when some protocol is rejected to be executed.
952 Other operations may send this as well that was rejected. The
953 indication of the rejection is sent in the payload. The indication
954 may be binary or human readable data.
960 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
961 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
963 ~ Reject Indication ~
965 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
969 Figure 8: Reject Payload
973 o Reject Indication (variable length) - Indication of
974 the rejection. This maybe for example some flag that
975 indicates the protocol and the rejection status or human
976 readable rejection message. The true length of this
977 payload is available by calculating it from the SILC
988 Notify payload is used to send notify messages. The payload is usually
989 sent from server to client, however, server may send it to another
990 server as well. This payload may also be sent to a channel. Client must
991 not send this payload. The receiver of this payload may totally ignore the
992 contents of the payload, however, notify message should be audited.
994 The payload may only be sent with SILC_PACKET_NOTIFY packet. It must
995 not be sent in any other packet type. Following diagram represents the
1001 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
1002 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1003 | Notify Type | Payload Length |
1004 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1010 Figure 9: Notify Payload
1014 o Notify Type (2 bytes) - Indicates the type of the notify
1017 o Payload Length (2 bytes) - Length of the entire Notify Payload
1018 including any associated Argument Payloads.
1020 o Argument Nums (2 bytes) - Indicates the number of Argument
1021 Payloads associated to this payload. Notify types may define
1022 arguments to be send along the notify message.
1025 Following list of currently defined notify types. The format for notify
1026 arguments is same as in SILC commands described in [SILC1]. Also, all
1027 ID's sent in arguments are sent inside ID Payload.
1030 0 SILC_NOTIFY_TYPE_NONE
1032 If no specific notify type apply for the notify message this type
1036 Arguments: (1) <message>
1038 The <message> is implementation specific free text string. Receiver
1039 may ignore this message.
1042 1 SILC_NOTIFY_TYPE_INVITE
1044 Sent when receiver has been invited to a channel. This type must be
1045 sent directly to the invited client.
1048 Arguments: (1) <Client ID> (2) <Channel ID>
1050 The <Client ID> is the client who invites the receiver of this type
1051 to channel indicated by <Channel ID>.
1054 2 SILC_NOTIFY_TYPE_JOIN
1056 Sent when client has joined to a channel. The server must distribute
1057 this type only to the local clients on the channel and then send
1058 it to its primary router. The router or server receiving the packet
1059 distributes this type to the local clients on the channel and
1060 broadcast it to the network.
1063 Arguments: (1) <Client ID> (2) <Channel ID>
1065 The <Client ID> is the client that joined to the channel indicated
1066 by the <Channel ID>.
1069 3 SILC_NOTIFY_TYPE_LEAVE
1071 Sent when client has left a channel. The server must distribute
1072 this type only to the local clients on the channel and then send
1073 it to its primary router. The router or server receiving the packet
1074 distributes this type to the local clients on the channel and
1075 broadcast it to the network.
1078 Arguments: (1) <Client ID>
1080 The <Client ID> is the client who left the channel.
1083 4 SILC_NOTIFY_TYPE_SIGNOFF
1085 Sent when client signoffs from SILC network. The server must
1086 distribute this type only to the local clients on the channel and
1087 then send it to its primary router. The router or server receiving
1088 the packet distributes this type to the local clients on the channel
1089 and broadcast it to the network.
1092 Arguments: (1) <Client ID> (2) <message>
1094 The <Client ID> is the client who left SILC network. The <message>
1095 is free text string indicating the reason of signoff.
1098 5 SILC_NOTIFY_TYPE_TOPIC_SET
1100 Sent when topic is set/changed on a channel. This type must be sent
1101 only to the clients who is joined on the channel whose topic was
1105 Arguments: (1) <Client ID> (2) <topic>
1107 The <Client ID> is the client who set or changed the <topic>.
1110 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1112 Sent when client changes nick on a channel. The server must
1113 distribute this type only to the local clients on the channel and
1114 then send it to its primary router. The router or server receiving
1115 the packet distributes this type to the local clients on the channel
1116 and broadcast it to the network.
1119 Arguments: (1) <Old Client ID> (2) <New Client ID>
1121 The <Old Client ID> is the old ID of the client who changed the
1122 nickname. The <New Client ID> is the new ID generated by the change
1126 7 SILC_NOTIFY_TYPE_CMODE_CHANGE
1128 Sent when channel mode has changed. This type must be sent only to
1129 the clients who is joined on the channel whose mode was changed.
1132 Arguments: (1) <Client ID> (2) <mode mask>
1134 The <Client ID> is the client who changed the mode. The <mode mask>
1135 is the new mode mask of the channel.
1138 8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
1140 Sent when user mode on channel has changed. This type must be sent
1141 only to the clients who is joined on the channel where the target
1145 Arguments: (1) <Client ID> (2) <mode mask>
1146 (3) <Target Client ID>
1148 The <Client ID> is the client who changed the mode. The <mode mask>
1149 is the new mode mask of the channel. The <Target Client ID> is the
1150 client which mode was changed.
1153 9 SILC_NOTIFY_TYPE_MOTD
1155 Sent when Message of the Day (motd) is sent to client.
1158 Arguments: (1) <motd>
1160 The <motd> is the Message of the Day.
1163 10 SILC_NOTIFY_TYPE_CHANNEL_CHANGE
1165 Sent when channel's ID has changed for a reason or another. This
1166 is sent by noral server to the client. Client must change the
1167 old Channel ID to the new one. This type must be sent only to the
1168 clients who is joined on the channel.
1171 Arguments: (1) <Old Channel ID> (2) <New Channel ID>
1173 The <Old Channel ID> is the channel's old ID and the <New Channel ID>
1174 is the new one that must replace the old one.
1177 11 SILC_NOTIFY_TYPE_SERVER_SIGNOFF
1179 Sent when server quits SILC network. Those clients from this server
1180 that are on channels must be removed from the channel.
1183 Arguments: (1) <Server ID>
1185 The <Server ID> is the server's ID.
1189 Notify types starting from 16384 are reserved for private notify
1196 Error payload is sent upon error. Error may occur in various
1197 conditions when server sends this packet. Client may not send this
1198 payload but must be able to accept it. However, client may
1199 totally ignore the contents of the packet as server is going to
1200 take action on the error anyway. However, it is recommended
1201 that the client takes error packet seriously.
1207 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
1208 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1212 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1216 Figure 10: Error Payload
1220 o Error Message (variable length) - Human readable error
1226 2.3.9 Channel Message Payload
1228 Channel messages are the most common messages sent in the SILC.
1229 Channel Message Payload is used to send message to channels. These
1230 messages can only be sent if client has joined to some channel.
1231 Even though this packet is the most common in SILC it is still
1232 special packet. Some special handling on sending and reception
1233 of channel message is required.
1235 Padding must be applied into this payload since the payload is
1236 encrypted separately from other parts of the packet with the
1237 channel specific key. Hence the requirement of the padding.
1238 The padding should be random data. The packet must be made
1239 multiple by eight (8) or by the block size of the cipher, which
1242 The SILC header in this packet is encrypted with the session key
1243 of the next receiver of the packet. Nothing else is encrypted
1244 with that key. Thus, the actual packet and padding to be
1245 encrypted with the session key is SILC Header plus padding to it
1246 to make it multiple by eight (8) or multiple by the block size
1247 of the cipher, which ever is larger.
1249 Receiver of the the channel message packet is able to determine
1250 the channel the message is destined to by checking the destination
1251 ID from the SILC Packet header which tells the destination channel.
1252 The original sender of the packet is also determined by checking
1253 the source ID from the header which tells the client who sent
1256 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1257 It must not be sent in any other packet type. Following diagram
1258 represents the Channel Message Payload.
1260 (*) indicates that the field is not encrypted.
1266 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
1267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1268 | Message Length | |
1269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1273 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1274 | Padding Length | |
1275 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1279 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1281 ~ Initial Vector * ~
1283 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1287 Figure 11: Channel Message Payload
1291 o Message Length (2 bytes) - Indicates the length of the
1292 the Message Data field in the payload, not including any
1295 o Message Data (variable length) - The actual message to
1298 o Padding Length (2 bytes) - Indicates the length of the
1299 Padding field in the payload, not including any other
1302 o Padding (variable length) - The padding that must be
1303 applied because this payload is encrypted separately from
1304 other parts of the packet.
1306 o Initial Vector (variable length) - The initial vector
1307 that has been used in packet encryption. It needs to be
1308 used in the packet decryption as well. What this field
1309 includes is implementation issue. However, it is
1310 recommended that it would be random data or, perhaps,
1311 a timestamp. It is not recommended to use zero (0) as
1312 initial vector. This field is not encrypted. This field
1313 is not included into the padding calculation. Length
1314 of this field equals the cipher's block size. This field
1315 is, however, authenticated.
1320 2.3.10 Channel Key Payload
1322 All traffic in channels are protected by channel specific keys.
1323 Channel Key Payload is used to distribute channel keys to all
1324 clients on the particular channel. Channel keys are sent when
1325 the channel is created, when new user joins to the channel and
1326 whenever a user has left a channel. Server creates the new
1327 channel key and distributes it to the clients by encrypting this
1328 payload with the session key shared between the server and
1329 the client. After that, client starts using the key received
1330 in this payload to protect the traffic on the channel.
1332 The client who is joining to the channel receives its key in the
1333 SILC_COMMAND_JOIN command reply message thus it is not necessary to
1334 send this payload to the entity who sent the SILC_COMMAND_JOIN command.
1336 Channel keys are cell specific thus every router in cell have
1337 to create a channel key and distribute it if any client in the
1338 cell has joined to a channel. Channel traffic between cell's
1339 are not encrypted using channel keys, they are encrypted using
1340 normal session keys between two routers. Inside a cell, all
1341 channel traffic is encrypted with the specified channel key.
1342 Channel key should expire periodically, say, in one hour, in
1343 which case new channel key is created and distributed.
1345 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1346 It must not be sent in any other packet type. Following diagram
1347 represents the Channel Key Payload.
1364 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
1365 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1366 | Channel ID Length | |
1367 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1372 | Cipher Name Length | |
1373 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1377 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1378 | Channel Key Length | |
1379 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1383 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1387 Figure 12: Channel Key Payload
1392 o Channel ID Length (2 bytes) - Indicates the length of the
1393 Channel ID field in the payload, not including any other
1396 o Channel ID (variable length) - The Channel ID of the
1397 channel this key is meant for.
1399 o Cipher Name Length (2 bytes) - Indicates the length of the
1400 Cipher name field in the payload, not including any other
1403 o Cipher Name (variable length) - Name of the cipher used
1404 in the protection of channel traffic. This name is
1405 initially decided by the creator of the channel but it
1406 may change during the life time of the channel as well.
1408 o Channel Key Length (2 bytes) - Indicates the length of the
1409 Channel Key field in the payload, not including any other
1412 o Channel Key (variable length) - The actual channel key
1413 material. This key is used as such as key material for
1414 encryption function.
1419 2.3.11 Private Message Payload
1421 Private Message Payload is used to send private message between
1422 two clients (or users for that matter). The messages are sent only
1423 to the specified user and no other user inside SILC network is
1424 able to see the message. The message is protected by the session
1425 key established by the SILC Key Exchange Protocol. However,
1426 it is also possible to agree to use specific keys to protect
1427 just the private messages. See section 2.3.11 Private Message
1428 Key Payload for detailed description of how to agree to use
1431 If normal session key is used to protect the message, every
1432 server between the sender client and the receiving client needs
1433 to decrypt the packet and always re-encrypt it with the session
1434 key of the next receiver of the packet. See section Client
1435 To Client in [SILC1].
1437 When specific key is used to protect the message, servers between
1438 the sender and the receiver needs not to decrypt/re-encrypt the
1439 packet. Section 4.8.2 Client To Client in [SILC1] gives example of
1440 this scheme as well.
1442 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1443 packet. It must not be sent in any other packet type. Following
1444 diagram represents the Private Message Payload.
1450 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
1451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1452 | Nickname Length | |
1453 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1457 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1461 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1465 Figure 13: Private Message Payload
1469 o Nickname Length (2 bytes) - Indicates the length of the
1470 Nickname field, not including any other field.
1472 o Nickname (variable length) - Nickname of the sender of the
1473 private message. This should not be trusted as a definite
1474 sender of the private message. The SILC Packet Header in
1475 the packet indicates the true sender of the packet and
1476 client should verify that the nickname sent here belongs
1477 to the Client ID in the SILC Packet Header. This nickname
1478 is merely provided to be displayed by the client.
1480 o Message Data (variable length) - The actual message to
1481 the client. Rest of the packet is reserved for the message
1487 2.3.12 Private Message Key Payload
1489 This payload is used to send key from client to another client that
1490 is going to be used to protect the private messages between these
1491 two clients. If this payload is not sent normal session key
1492 established by the SILC Key Exchange Protocol is used to protect
1493 the private messages.
1495 This payload may only be sent by client to another client. Server
1496 must not send this payload at any time. After sending this payload
1497 the sender of private messages must set the Private Message Key
1498 flag into SILC Packet Header.
1500 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1501 packet. It must not be sent in any other packet type. Following
1502 diagram represents the Private Message Key Payload.
1508 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
1509 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1510 | Private Message Key Length | |
1511 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1513 ~ Private Message Key ~
1515 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1519 Figure 14: Private Message Key Payload
1525 o Private Message Key Length (2 bytes) - Indicates the length
1526 of the Private Message Key field in the payload, not including
1529 o Private Message Key (variable length) - The actual private
1530 message key material. This key is used as such as key material
1531 for encryption function.
1536 2.3.13 Command Payload
1538 Command Payload is used to send SILC commands from client to server.
1539 Also server may send commands to other servers. Following diagram
1540 represents the Command Payload.
1546 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
1547 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1548 | Payload Length | SILC Command | Arguments Num |
1549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1550 | Command Identifier |
1551 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1555 Figure 15: Command Payload
1559 o Payload Length (2 bytes) - Length of the entire command
1560 payload including any command argument payloads associated
1563 o SILC Command (1 byte) - Indicates the SILC command. This must
1564 be set to non-zero value. If zero (0) value is found in this
1565 field the packet must be discarded.
1567 o Arguments Num (1 byte) - Indicates the number of arguments
1568 associated with the command. If there are no arguments this
1569 field is set to zero (0). The arguments must follow the
1570 command payload. See section 2.3.2.2 for definition of the
1573 o Command Identifier (2 bytes) - Identifies this command at the
1574 sender's end. The entity who replies to this command must
1575 set the value found from this field into the Command Payload
1576 used to send the reply to the sender. This way the sender
1577 can identify which command reply belongs to which originally
1578 sent command. What this field includes is implementation
1579 issue but it is recommended that wrapping counter value is
1580 used in the field. Value zero (0) in this field means that
1581 no specific value is set.
1584 See [SILC1] for detailed description of different SILC commands,
1585 their arguments and their reply messages.
1589 2.3.14 Command Reply Payload
1591 Command Reply Payload is used to send replies to the commands. The
1592 Command Reply Payload is identical to the Command Payload thus see the
1593 upper sections for Command Payload and for Command Argument Payload
1594 specifications. Command Reply message uses the Command Argument Payload
1597 The entity who sends the reply packet must set the Command Unifier
1598 field in the reply packet's Command Payload to the value it received
1599 in the original command packet.
1601 See SILC Commands in [SILC1] for detailed description of different
1602 SILC commands, their arguments and their reply messages.
1606 2.3.15 Connection Auth Request Payload
1608 Client may send this payload to server to request the authentication
1609 method that must be used in authentication protocol. If client knows
1610 this information beforehand this payload is not necessary to be sent.
1611 Server performing authentication with another server may also send
1612 this payload to request the authentication method. If the connecting
1613 server already knows this information this payload is not necessary
1616 Server receiving this request must reply with same payload sending
1617 the mandatory authentication method. Algorithms that may be required
1618 to be used by the authentication method are the ones already
1619 established by the SILC Key Exchange protocol. See section Key
1620 Exchange Start Payload in [SILC3] for detailed information.
1622 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1623 packet. It must not be sent in any other packet type. Following
1624 diagram represents the Connection Auth Request Payload.
1630 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
1631 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1632 | Connection Type | Authentication Method |
1633 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1637 Figure 16: Connection Auth Request Payload
1641 o Connection Type (2 bytes) - Indicates the type of the ID.
1642 Following connection types are defined:
1648 If any other type is found in this field the packet must be
1649 discarded and the authentication must be failed.
1651 o Authentication Method (2 bytes) - Indicates the authentication
1652 method to be used in the authentication protocol. Following
1653 authentication methods are defined:
1658 1 password (mandatory)
1659 2 public key (mandatory)
1661 If any other type is found in this field the packet must be
1662 discarded and the authentication must be failed. If this
1663 payload is sent as request to receive the mandatory
1664 authentication method this field must be set to zero (0),
1665 indicating that receiver should send the mandatory
1666 authentication method. The receiver sending this payload
1667 to the requesting party, may also set this field to zero (0)
1668 to indicate that authentication is not required. In this
1669 case authentication protocol still must be started but
1670 server is most likely to respond with SILC_PACKET_SUCCESS
1676 2.3.16 New ID Payload
1678 New ID Payload is a multipurpose payload. It is used to send newly
1679 created ID's from clients and servers. When client connects to server
1680 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
1681 packet, server replies with this packet by sending the created ID for
1682 the client. Server always creates the ID for the client.
1684 This payload is also used when server tells its router that new client
1685 has registered to the SILC network. In this case the server sends
1686 the Client ID of the client to the router. Similary when router
1687 distributes information to other routers about the client in the SILC
1688 network this payload is used.
1690 Also, when server connects to router, router uses this payload to inform
1691 other routers about new server in the SILC network. However, every
1692 server (or router) creates their own ID's thus the ID distributed by
1693 this payload is not created by the distributor in this case. Servers
1694 create their own ID's. Server registers itself to the network by sending
1695 SILC_PACKET_NEW_SERVER to the router it connected to. The case is same
1696 when router connects to another router.
1698 However, this payload is not and must not be used to send information
1699 about new channels. New channels are always distributed by sending the
1700 dedicated SILC_PACKET_NEW_CHANNEL packet.
1702 Hence, this payload is very important and used every time when some
1703 new entity is registered to the SILC network. Client never sends this
1704 payload. Both client and server (and router) may receive this payload.
1706 The packet uses generic ID Payload as New ID Payload. See section
1707 2.3.2.1 for generic ID Payload.
1711 2.3.18 New Client Payload
1713 When client is connected to the server, keys has been exchanged and
1714 connection has been authenticated client must register itself to the
1715 server. Clients first packet after key exchange and authentication
1716 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
1717 the relevant information about the connected user. Server creates a new
1718 client ID for the client when received this payload and sends it to the
1719 client in New ID Payload.
1721 This payload sends username and real name of the user on the remote host
1722 which is connected to the SILC server with SILC client. The server
1723 creates the client ID according the information sent in this payload.
1724 The nickname of the user becomes the username sent in this payload.
1725 However, client should call NICK command after sending this payload to
1726 set the real nickname of the user which is then used to create new
1729 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
1730 must not be sent in any other packet type. Following diagram represents
1731 the New Client Payload.
1738 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
1739 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1740 | Username Length | |
1741 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1745 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1746 | Real Name Length | |
1747 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1751 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1755 Figure 17: New Client Payload
1759 o Username Length (2 bytes) - Length of the username.
1761 o Username (variable length) - The username of the user on
1762 the host where connecting to the SILC server.
1764 o Real Name Length (2 bytes) - Length of the Real Name.
1766 o Real Name (variable length) - The real name of the user
1767 on the host where connecting to the SILC server.
1772 2.3.19 New Server Payload
1774 This payload is sent by server when it has completed successfully both
1775 key exchange and connection authentication protocols. The server
1776 uses this payload to register itself to the SILC network. The
1777 first packet after these key exchange and authentication protocols
1778 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
1779 of the server that it has created by itself. It also includes a
1780 name of the server that is associated to the Server ID.
1782 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
1783 must not be sent in any other packet type. Following diagram represents
1784 the New Server Payload.
1793 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
1794 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1795 | Server ID Length | |
1796 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1800 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1801 | Server Name Length | |
1802 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1806 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1810 Figure 18: New Server Payload
1814 o Server ID Length (2 bytes) - Length of the ID Data area not
1815 including the length of any other fields in the payload.
1817 o Server ID Data (variable length) - The actual Server ID
1820 o Server Name Length (2 bytes) - Length of the server name.
1822 o Server Name (variable length) - The server name.
1827 2.3.20 New Channel Payload
1829 Information about newly created channel is broadcasted to all routers
1830 in the SILC network by sending this packet payload. Channels are
1831 created by router of the cell. Server never creates channels unless
1832 it is a standalone server and it does not have router connection,
1833 in this case server acts as router. Normal server send JOIN command
1834 to the router (after it has received JOIN command from client) which
1835 then processes the command and creates the channel. Client never sends
1838 The payload may only be sent with SILC_PACKET_NEW_CHANNEL packet.
1839 It must not be sent in any other packet type. Following diagram
1840 represents the New Channel Payload.
1848 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
1849 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1850 | Channel Name Length | |
1851 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1855 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1856 | Channel ID Length | |
1857 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1861 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1865 Figure 19: New Channel Payload
1870 o Channel Name Length (2 bytes) - Length of the channel name.
1872 o Channel Name (variable length) - The name of the created
1875 o Channel ID Length (2 bytes) - Length of the Channel ID.
1877 o Channel ID (variable length) - The created Channel ID.
1884 ID's are extensively used in the SILC network to associate different
1885 entities. Following ID's has been defined to be used in the SILC
1891 When ever specific ID cannot be used this is used.
1895 Server ID to associate servers. See the format of
1900 Client ID to associate clients. See the format of
1905 Channel ID to associate channels. See the format of
1911 2.5 Packet Encryption And Decryption
1913 SILC packets are encrypted almost entirely. Only small part of SILC
1914 header is not encrypted as described in section 5.2 SILC Packet Header.
1915 The SILC Packet header is the first part of a packet to be encrypted
1916 and it is always encrypted with the key of the next receiver of the
1917 packet. The data payload area of the packet is always entirely
1918 encrypted and it is usually encrypted with the next receiver's key.
1919 However, there are some special packet types and packet payloads
1920 that require special encryption process. These special cases are
1921 described in the next sections. First is described the normal packet
1926 2.5.1 Normal Packet Encryption And Decryption
1928 Normal SILC packets are encrypted with the session key of the next
1929 receiver of the packet. The entire SILC Packet header and the packet
1930 data payload is is also encrypted with the same key. Padding of the
1931 packet is also encrypted always with the session key, also in special
1932 cases. Computed MAC of the packet must not be encrypted.
1934 Decryption process in these cases are straightforward. The receiver
1935 of the packet must first decrypt the SILC Packet header, or some parts
1936 of it, usually first 16 bytes of it. Then the receiver checks the
1937 packet type from the decrypted part of the header and can determine
1938 how the rest of the packet must be decrypted. If the packet type is
1939 any of the special cases described in following sections the packet
1940 decryption is special. If the packet type is not among those special
1941 packet types rest of the packet may be decrypted with the same key.
1943 Also, note that two bytes of the SILC Packet header are not encrypted
1944 thus it must be noticed in the decryption process by starting the
1945 decryption from the second byte of the header. This sets some rules
1946 to padding generation as well, see the section 2.7 Packet Padding
1949 With out a doubt, this sort of decryption processing causes some
1950 overhead to packet decryption, but never the less, is required.
1954 2.5.2 Channel Message Encryption And Decryption
1956 Channel Messages (Channel Message Payload) are always encrypted with
1957 the channel specific key. However, the SILC Packet header is not
1958 encrypted with that key. As in normal case, the header is encrypted
1959 with the key of the next receiver of the packet, who ever that might
1960 be. Note that in this case the encrypted data area is not touched
1961 at all; it must not be re-encrypted with the session key.
1963 Receiver of a channel message, who ever that is, is required to decrypt
1964 the SILC Packet header to be able to even recognize the packet to be as
1965 channel message. This is same procedure as for normal SILC packets.
1966 As the receiver founds the packet to be channel message, rest of the
1967 packet processing is special. Rest of the SILC Packet header is
1968 decrypted with the same session key along with the padding of the
1969 packet. After that the packet is protected with the channel specific
1970 key and hence can be decrypted only if the receiver is the client on
1971 the channel. See section 2.7 Packet Padding Generation for more
1972 information about padding on special packets.
1974 If the receiver of the channel message is router who is routing the
1975 message to another router then it must decrypt the Channel Message
1976 payload. Between routers (that is, between cells) channel messages
1977 are protected with session keys shared between the routers. This
1978 causes another special packet processing for channel messages. If
1979 the channel message is received from another router then the entire
1980 packet, including Channel Message payload, is encrypted with the
1981 session key shared between the routers. In this case the packet
1982 decryption process is as with normal SILC packets. Hence, if the
1983 router is sending channel message to another router the Channel
1984 Message payload must have been decrypted and must be re-encrypted
1985 with the session key shared between the another router. In this
1986 case the packet encryption is as with any normal SILC packet.
1988 It must be noted that this is only when the channel messages are sent
1989 from router to another router. In all other cases the channel
1990 message encryption and decryption is as described above. This
1991 different processing of channel messages with router to router
1992 connection is because channel keys are cell specific. All cells has
1993 their own channel keys thus the channel message traveling from one
1994 cell to another must be protected as it would be any normal SILC
1999 2.5.3 Private Message Encryption And Decryption
2001 By default, private message in SILC are protected by session keys.
2002 In this case the private message encryption and decryption process is
2003 equivalent to normal packet encryption and decryption.
2005 However, private messages can be protected with private message key
2006 which causes the packet to be special packet. The procedure in this
2007 case is very much alike to channel packets. The actual private message
2008 is encrypted with the private message key and other parts of the
2009 packet is encrypted with the session key. See 2.7 Packet Padding
2010 Generation for more information about padding on special packets.
2012 The difference from channel message processing is that server or router
2013 en route never decrypts the actual private message, as it does not
2014 have the key to do that. Thus, when sending packets between router
2015 the processing is same as in any other case as well; the packet's header
2016 and padding is protected by the session key and the data area is not
2019 The true receiver of the private message, client, that is, is able
2020 to decrypt the private message as it shares the key with the sender
2025 2.6 Packet MAC Generation
2027 Data integrity of a packet is protected by including a message
2028 authentication code (MAC) at the end of the packet. The MAC is computed
2029 from shared secret MAC key, that is established by the SILC Key Exchange
2030 protocol, and from the original contents of the packet. The MAC is
2031 always computed before the packet is encrypted, although after it is
2032 compressed if compression is used.
2034 The MAC is computed from entire packet. Every bit of data in the packet,
2035 including SILC Packet Header is used in the MAC computing. This way
2036 the entire packet becomes authenticated.
2038 If the packet is special packet MAC is computed from the entire packet
2039 but part of the packet may be encrypted before the MAC is computed.
2040 This is case, for example, with channel messages where the message data
2041 is encrypted with key that server may not now. In this case the MAC
2042 has been computed from the encrypted data.
2044 See [SILC1] for defined and allowed MAC algorithms.
2048 2.7 Packet Padding Generation
2050 Padding is needed in the packet because the packet is encrypted. It
2051 must always be multiple by eight (8) or multiple by the size of the
2052 cipher's block size, which ever is larger. The padding is always
2055 For normal packets the padding is added after the SILC Packet Header
2056 and between the Data Payload area. The padding for normal packets
2057 are calculated as follows:
2060 padding length = 16 - ((packet length - 2) % 16)
2063 The 16 is the maximum padding allowed in SILC packet. Two (2) is
2064 subtracted from the true length of the packet because two (2) bytes
2065 is not encrypted in SILC Packet Header, see section 2.2 SILC Packet
2066 Header. Those two bytes that are not encrypted must not be calculated
2067 to the padding length.
2069 For special packets the padding calculation may be different as special
2070 packets may be encrypted differently. In these cases the encrypted
2071 data area must already be multiple by the block size thus in this case
2072 the padding is calculated only for SILC Packet Header, not for any
2073 other area of the packet. The same algorithm works in this case as
2074 well, except that the `packet length' is now the SILC Packet Header
2075 length. In this case, as well, two (2) is subtracted from the
2078 The padding must be random data, preferably, generated by
2079 cryptographically strong random number generator.
2083 2.8 Packet Compression
2085 SILC Packets may be compressed. In this case the data payload area
2086 is compressed and all other areas of the packet must remain as they
2087 are. After compression is performed for the data area, the length
2088 field of Packet Header must be set to the compressed length of the
2091 The compression must always be applied before encryption. When
2092 the packet is received and decrypted the data area must be decompressed.
2093 Note that the true sender of the packet must apply the compression and
2094 the true receiver of the packet must apply the decompression. Any
2095 server or router en route must not decompress the packet.
2102 The sender of the packet must assemble the SILC Packet Header with
2103 correct values. It must set the Source ID of the header as its own
2104 ID, unless it is forwarding the packet. It must also set the Destination
2105 ID of the header to the true destination. If the destination is client
2106 it will be Client ID, if it is server it will be Server ID and if it is
2107 channel it will be Channel ID.
2109 If the sender wants to compress the packet it must apply the
2110 compression now. Sender must also compute the padding as described
2111 in above sections. Then sender must compute the MAC of the packet.
2113 Then sender encrypts the packet as has been described in above
2114 sections according whether the packet is normal packet or special
2115 packet. The computed MAC must not be encrypted.
2119 2.10 Packet Reception
2121 On packet reception the receiver must check that all fields in the
2122 SILC Packet Header are valid. It must check the flags of the
2123 header and act accordingly. It must also check the MAC of the packet
2124 and if it is to be failed the packet must be discarded. Also if the
2125 header of the packet includes any bad fields the packet must be
2128 See above sections on the decryption process of the received packet.
2130 The receiver must also check that the ID's in the header are valid
2131 ID's. Unsupported ID types or malformed ID's must cause packet
2132 rejection. The padding on the reception is always ignored.
2134 The receiver must also check the packet type and start parsing the
2135 packet according to the type. However, note the above sections on
2136 special packet types and their parsing.
2142 Routers are the primary entities in the SILC network that takes care
2143 of packet routing. However, normal servers routes packets as well, for
2144 example, when they are routing channel message to the local clients.
2145 Routing is quite simple as every packet tells the true origin and the
2146 true destination of the packet.
2148 It is still recommended for routers that has several routing connections
2149 to create route cache for those destinations that has faster route than
2150 the router's primary route. This information is available for the router
2151 when other router connects to the router. The connecting party then
2152 sends all of its locally connected clients, server and channels. These
2153 informations helps to create the route cache. Also, when new channels
2154 are created to a cell its information is broadcasted to all routers
2155 in the network. Channel ID's are based on router's ID thus it is easy
2156 to create route cache based on these informations. If faster route for
2157 destination does not exist in router's route cache the packet must be
2158 routed to the primary route (default route).
2160 For server who receives a packet to be routed to its locally connected
2161 client the server must check whether the particular packet type is
2162 allowed to be routed to the client. Not all packets may be sent by
2163 some odd entity to client that is indirectly connected to the sender.
2164 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2165 entities and sending packets to them. The section mentions the packets
2166 that may be sent to indirectly connected entities. It is clear that some
2167 server cannot send, for example, disconnect packet to client that is not
2168 directly connected to the server.
2172 2.12 Packet Broadcasting
2174 SILC packets may be broadcasted in SILC network. However, only router
2175 server may send or receive broadcast packets. Client and normal server
2176 must not send broadcast packets and they must ignore broadcast packets
2177 if they receive them. Broadcast packets are sent by setting Broadcast
2178 flag to the SILC packet header.
2180 Broadcasting packets means that the packet is sent to all routers in
2181 the SILC network, except to the router that sent the packet. The router
2182 receiving broadcast packet must send the packet to its primary route.
2183 The fact that SILC routers may have several router connections may
2184 cause problems, such as race conditions inside the SILC network, if
2185 care is not taken when broadcasting packets. Router must not send
2186 the broadcast packet to any other route except to its primary route.
2188 If the primary route of the router is the original sender of the packet
2189 the packet must not be sent to the primary route. This may happen
2190 if router has several router connections and some other router uses
2191 the router as its primary route.
2193 Routers use broadcast packets to broadcast for example information
2194 about newly registered clients, servers, channels etc. so that all the
2195 routers may keep these informations up to date.
2199 2.13 Packet Tunneling
2201 Tunneling is a feature that is available in SILC protocol. Tunneling
2202 means that extra SILC Packet Header is applied to the original packet
2203 and thus hiding the original packet entirely. There can be some
2204 interesting applications using tunneling, such as, using ID's based on
2205 private network IP addresses inside in the tunneled packet. This can
2206 open many interesting features relating to connecting to private network
2207 from the Internet with SILC and many more. However, this feature is
2208 optional currently in SILC as there does not exist thorough analysis of
2209 this feature. It is with out a doubt that there will be many more
2210 applications that has not yet been discovered. Thus, it is left
2211 to Internet Community to investigate the use of tunneling in SILC
2212 protocol. This document is updated according those investigations
2213 and additional documents on the issue may be written.
2217 3 Security Considerations
2219 Security is central to the design of this protocol, and these security
2220 considerations permeate the specification. Common security considerations
2221 such as keeping private keys truly private and using adequate lengths for
2222 symmetric and asymmetric keys must be followed in order to maintain the
2223 security of this protocol.
2229 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2230 Protocol Specification", Internet Draft, June 2000.
2232 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2233 Protocols", Internet Draft, June 2000.
2235 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2238 [IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
2241 [IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
2244 [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
2247 [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
2250 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2253 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2256 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2259 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2260 Infrastructure, Certificate and CRL Profile", RFC 2459,
2263 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2264 John Wiley & Sons, New York, NY, 1996.
2266 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2269 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2270 RFC 2412, November 1998.
2272 [ISAKMP] Maughan D., et al, "Internet Security Association and
2273 Key Management Protocol (ISAKMP)", RFC 2408, November
2276 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2277 (IKE)", RFC 2409, November 1998.
2279 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2280 Authentication", RFC 2104, February 1997.
2282 [PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
2283 Specifications, Version 2.0", RFC 2437, October 1998.
2295 EMail: priikone@poseidon.pspt.fi
2297 This Internet-Draft expires 6 Jun 2001