8 .ds RF FORMFEED[Page %]
17 Network Working Group P. Riikonen
19 draft-riikonen-silc-pp-04.txt XXX
26 <draft-riikonen-silc-pp-04.txt>
31 This document is an Internet-Draft and is in full conformance with
32 all provisions of Section 10 of RFC 2026. Internet-Drafts are
33 working documents of the Internet Engineering Task Force (IETF), its
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37 Internet-Drafts are draft documents valid for a maximum of six months
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39 time. It is inappropriate to use Internet-Drafts as reference
40 material or to cite them other than as "work in progress."
42 The list of current Internet-Drafts can be accessed at
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45 The list of Internet-Draft Shadow Directories can be accessed at
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48 The distribution of this memo is unlimited.
54 This memo describes a Packet Protocol used in the Secure Internet Live
55 Conferencing (SILC) protocol, specified in the Secure Internet Live
56 Conferencing, Protocol Specification Internet Draft [SILC1]. This
57 protocol describes the packet types and packet payloads which defines
58 the contents of the packets. The protocol provides secure binary packet
59 protocol that assures that the contents of the packets are secured and
74 1 Introduction .................................................. 3
75 1.1 Requirements Terminology .................................. 4
76 2 SILC Packet Protocol .......................................... 4
77 2.1 SILC Packet ............................................... 4
78 2.2 SILC Packet Header ........................................ 5
79 2.3 SILC Packet Types ......................................... 7
80 2.3.1 SILC Packet Payloads ................................ 16
81 2.3.2 Generic payloads .................................... 16
82 2.3.2.1 ID Payload .................................. 16
83 2.3.2.2 Argument Payload ............................ 17
84 2.3.2.3 Channel Payload ............................. 18
85 2.3.2.4 Public Key Payload .......................... 19
86 2.3.3 Disconnect Payload .................................. 19
87 2.3.4 Success Payload ..................................... 19
88 2.3.5 Failure Payload ..................................... 20
89 2.3.6 Reject Payload ...................................... 21
90 2.3.7 Notify Payload ...................................... 22
91 2.3.8 Error Payload ....................................... 21
92 2.3.9 Channel Message Payload ............................. 28
93 2.3.10 Channel Key Payload ................................ 31
94 2.3.11 Private Message Payload ............................ 33
95 2.3.12 Private Message Key Payload ........................ 34
96 2.3.13 Command Payload .................................... 36
97 2.3.14 Command Reply Payload .............................. 37
98 2.3.15 Connection Auth Request Payload .................... 37
99 2.3.16 New ID Payload ..................................... 38
100 2.3.17 New Client Payload ................................. 39
101 2.3.18 New Server Payload ................................. 40
102 2.3.19 New Channel Payload ................................ 41
103 2.3.20 Key Agreement Payload .............................. 42
104 2.3.21 Resume Router Payload .............................. 43
105 2.3.22 File Transfer Payload .............................. 43
106 2.4 SILC ID Types ............................................. 44
107 2.5 Packet Encryption And Decryption .......................... 44
108 2.5.1 Normal Packet Encryption And Decryption ............. 45
109 2.5.2 Channel Message Encryption And Decryption ........... 45
110 2.5.3 Private Message Encryption And Decryption ........... 46
111 2.6 Packet MAC Generation ..................................... 47
112 2.7 Packet Padding Generation ................................. 47
113 2.8 Packet Compression ........................................ 48
114 2.9 Packet Sending ............................................ 48
115 2.10 Packet Reception ......................................... 49
116 2.11 Packet Routing ........................................... 49
117 2.12 Packet Broadcasting ...................................... 50
118 3 Security Considerations ....................................... 50
119 4 References .................................................... 50
120 5 Author's Address .............................................. 52
126 Figure 1: Typical SILC Packet
127 Figure 2: SILC Packet Header
129 Figure 4: Argument Payload
130 Figure 5: Channel Payload
131 Figure 6: Public Key Payload
132 Figure 7: Disconnect Payload
133 Figure 8: Success Payload
134 Figure 9: Failure Payload
135 Figure 10: Reject Payload
136 Figure 11: Notify Payload
137 Figure 12: Error Payload
138 Figure 13: Channel Message Payload
139 Figure 14: Channel Key Payload
140 Figure 15: Private Message Payload
141 Figure 16: Private Message Key Payload
142 Figure 17: Command Payload
143 Figure 18: Connection Auth Request Payload
144 Figure 19: New Client Payload
145 Figure 20: New Server Payload
146 Figure 21: Key Agreement Payload
147 Figure 22: Resume Router Payload
148 Figure 23: File Transfer Payload
154 This document describes a Packet Protocol used in the Secure Internet
155 Live Conferencing (SILC) protocol specified in the Secure Internet Live
156 Conferencing, Protocol Specification Internet Draft [SILC1]. This
157 protocol describes the packet types and packet payloads which defines
158 the contents of the packets. The protocol provides secure binary packet
159 protocol that assures that the contents of the packets are secured and
162 The basis of SILC protocol relies in the SILC packets and it is with
163 out a doubt the most important part of the protocol. It is also probably
164 the most complicated part of the protocol. Packets are used all the
165 time in the SILC network to send messages, commands and other information.
166 All packets in SILC network are always encrypted and their integrity
167 is assured by computed MACs. The protocol defines several packet types
168 and packet payloads. Each packet type usually has a specific packet
169 payload that actually defines the contents of the packet. Each packet
170 also includes a default SILC Packet Header that provides sufficient
171 information about the origin of the packet and destination of the
176 1.1 Requirements Terminology
178 The keywords MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED,
179 MAY, and OPTIONAL, when they appear in this document, are to be
180 interpreted as described in [RFC2119].
184 2 SILC Packet Protocol
189 SILC packets deliver messages from sender to receiver securely by
190 encrypting important fields of the packet. The packet consists of
191 default SILC Packet Header, Padding, Packet Payload data, and, packet
194 The following diagram illustrates typical SILC packet.
199 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
200 | n bytes | 1 - n bytes | n bytes | n bytes
201 | SILC Header | Padding | Data Payload | MAC
202 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
206 Figure 1: Typical SILC Packet
209 SILC Header is always the first part of the packet and its purpose
210 is to provide information about the packet. It provides for example
211 the packet type, origin of the packet and the destination of the packet.
212 The header is variable in length. See the following section for
213 description of SILC Packet header. Packets without SILC header or
214 with malformed SILC header MUST be dropped.
216 Padding follows the packet header. The purpose of the padding is to
217 make the packet multiple by eight (8) or by the block size of the
218 cipher used in the encryption, which ever is larger. The maximum
219 length of padding is currently 128 bytes. The padding is always
220 encrypted. The padding is applied always, even if the packet is
221 not encrypted. See the section 2.7 Padding Generation for more
222 detailed information.
224 Data payload area follows padding and it is the actual data of the
225 packet. The packet data is the packet payloads defined in this
226 protocol. The data payload area is always encrypted.
228 The last part of SILC packet is the packet MAC that assures the
229 integrity of the packet. The MAC is always computed from the packet
230 before the encryption is applied to the packet. If compression is used
231 in the packet the MAC is computed after the compression has been
232 applied. The compression, on the other hand, is always applied before
233 encryption. See more details in the section 2.6 Packet MAC Generation.
235 All fields in all packet payloads are always in MSB (most significant
240 2.2 SILC Packet Header
242 The SILC packet header is applied to all SILC packets and it is
243 variable in length. The purpose of SILC Packet header is to provide
244 detailed information about the packet. The receiver of the packet
245 uses the packet header to parse the packet and gain other relevant
246 parameters of the packet.
248 The following diagram represents the SILC packet header.
253 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
254 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
255 | Payload Length | Flags | Packet Type |
256 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
257 | Pad Length | RESERVED | Source ID Len | Dest ID Len |
258 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
270 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
274 Figure 2: SILC Packet Header
278 o Payload Length (2 bytes) - Is the length of the packet
279 not including the padding of the packet.
281 o Flags (1 byte) - Indicates flags to be used in packet
282 processing. Several flags may be set by ORing the flags
285 The following flags are reserved for this field:
290 In this case the field is ignored.
293 Private Message Key 0x01
295 Indicates that the packet must include private
296 message that is encrypted using private key set by
297 client. Servers does not know anything about this
298 key and this causes that the private message is
299 not handled by the server at all, it is just
300 passed along. See section 2.5.3 Private Message
301 Encryption And Decryption for more information.
306 Indicates that the packet consists of list of
307 packet payloads indicated by the Packet Type field.
308 The payloads are added one after the other. Note that
309 there are packet types that must not be used as
310 list. Parsing of list packet is done by calculating
311 the length of each payload and parsing them one by
317 Marks the packet to be broadcasted. Client cannot
318 send broadcast packet and normal server cannot send
319 broadcast packet. Only router server may send broadcast
320 packet. The router receiving of packet with this flag
321 set MUST send (broadcast) the packet to its primary
322 route. If router has several router connections the
323 packet may be sent only to the primary route. See
324 section 2.12 Packet Broadcasting for description of
332 o Packet Type (1 byte) - Is the type of the packet. Receiver
333 uses this field to parse the packet. See section 2.3
334 SILC Packets for list of defined packet types.
336 o Pad Length (1 byte) - Indicates the length of the padding
337 applied after the SILC Packet header. Maximum length for
338 padding is 128 bytes.
340 o RESERVED (1 byte) - Reserved field and must include a
343 o Source ID Length (1 byte) - Indicates the length of the
344 Source ID field in the header, not including this or any
347 o Destination ID Length (1 byte) - Indicates the length of the
348 Destination ID field in the header, not including this or
351 o Src ID Type (1 byte) - Indicates the type of ID in the
352 Source ID field. See section 2.4 SILC ID Types for
355 o Source ID (variable length) - The actual source ID that
356 indicates which is the original sender of the packet.
358 o Dst ID Type (1 byte) - Indicates the type of ID in the
359 Destination ID field. See section 2.4 SILC ID Types for
362 o Destination ID (variable length) - The actual destination
363 ID that indicates which is the end receiver of the packet.
368 2.3 SILC Packet Types
370 SILC packet types defines the contents of the packet and it is used by
371 the receiver to parse the packet. The packet type is 8 bits, as a one
372 byte, in length. The range for the packet types are from 0 - 255,
373 where 0 is never sent and 255 is currently reserved for future
374 extensions and MUST NOT be defined to any other purpose. Every SILC
375 specification compliant implementation SHOULD support all of these packet
378 The below list of the SILC Packet types includes reference to the packet
379 payload as well. Packet payloads are the actual packet, that is, the data
380 that the packet consists of. Each packet type defines packet payload
381 which usually may only be sent with the specific packet type.
383 Most of the packets are packets that must be destined directly to entity
384 that is connected to the sender. It is not allowed, for example, for
385 router to send disconnect packet to client that is not directly connected
386 to the router. However, there are some special packet types that may
387 be destined to some entity that the sender has not direct connection
388 with. These packets are for example private message packets, channel
389 message packets, command packets and some other packets that may be
390 broadcasted in the SILC network. If the packet is allowed to be sent to
391 indirectly connected entity it is mentioned separately in the packet
392 description (unless it is obvious as in private and channel message
393 packets). Other packets MUST NOT be sent or accepted, if sent, to
394 indirectly connected entities.
396 List of SILC Packet types are defined as follows.
401 This type is reserved and it is never sent.
404 1 SILC_PACKET_DISCONNECT
406 This packet is sent to disconnect the remote end. Reason of
407 the disconnection is sent inside the packet payload. Client
408 usually does not send this packet.
410 This packet MUST NOT be sent as list and the List flag MUST
413 Payload of the packet: See section 2.3.3 Disconnect Payload
416 2 SILC_PACKET_SUCCESS
418 This packet is sent upon successful execution of some protocol.
419 The status of the success is sent in the packet.
421 This packet MUST NOT be sent as list and the List flag MUST
424 Payload of the packet: See section 2.3.4 Success Payload
427 3 SILC_PACKET_FAILURE
429 This packet is sent upon failure of some protocol. The status
430 of the failure is sent in the packet.
432 This packet MUST NOT be sent as list and the List flag MUST
435 Payload of the packet: See section 2.3.5 Failure Payload
440 This packet MAY be sent upon rejection of some protocol.
441 The status of the rejection is sent in the packet.
443 This packet MUST NOT be sent as list and the List flag MUST
446 Payload of the packet: See section 2.3.6 Reject Payload
451 This packet is used to send notify message, usually from
452 server to client, although it MAY be sent from server to another
453 server as well. Client MUST NOT send this packet. Server MAY
454 send this packet to channel as well when the packet is
455 distributed to all clients on the channel.
457 Payload of the packet: See section 2.3.7 Notify Payload.
462 This packet is sent when an error occurs. Server MAY
463 send this packet. Client MUST NOT send this packet. The
464 client MAY entirely ignore the packet, however, server is
465 most likely to take action anyway. This packet MAY be sent
466 to entity that is indirectly connected to the sender.
468 This packet MUST NOT be sent as list and the List flag MUST
471 Payload of the packet: See section 2.3.8 Error Payload.
474 7 SILC_PACKET_CHANNEL_MESSAGE
476 This packet is used to send messages to channels. The packet
477 includes Channel ID of the channel and the actual message to
478 the channel. Messages sent to the channel are always protected
479 by channel specific keys. Channel Keys are distributed by
480 SILC_PACKET_CHANNEL_KEY packet.
482 This packet MUST NOT be sent as list and the List flag MUST
485 Payload of the packet: See section 2.3.9 Channel Message
489 8 SILC_PACKET_CHANNEL_KEY
491 This packet is used to distribute new key for particular
492 channel. Each channel has their own independent keys that
493 is used to protect the traffic on the channel. Only server
494 may send this packet. This packet MAY be sent to entity
495 that is indirectly connected to the sender.
497 This packet MUST NOT be sent as list and the List flag MUST
500 Payload of the packet: See section 2.3.10 Channel Key Payload
503 9 SILC_PACKET_PRIVATE_MESSAGE
505 This packet is used to send private messages from client
506 to another client. By default, private messages are protected
507 by session keys established by normal key exchange protocol.
508 However, it is possible to use specific key to protect private
509 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
510 agree the key with the remote client. Pre-shared key MAY be
511 used as well if both of the client knows it, however, it needs
512 to be agreed outside SILC. See more of this in [SILC1].
514 This packet MUST NOT be sent as list and the List flag MUST
517 Payload of the packet: See section 2.3.11 Private Message
521 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
523 This packet is used to agree about a key to be used to protect
524 the private messages between two clients. If this is not sent
525 the normal session key is used to protect the private messages
526 inside SILC network. Agreeing to use specific key to protect
527 private messages adds security, as no server between the two
528 clients will be able to decrypt the private message. However,
529 servers inside SILC network are considered to be trusted, thus
530 using normal session key to protect private messages does not
531 degrade security. Whether to agree to use specific keys by
532 default or to use normal session keys by default, is
533 implementation specific issue. See more of this in [SILC1].
535 This packet MUST NOT be sent as list and the List flag MUST
538 Payload of the packet: See section 2.3.12 Private Message
542 11 SILC_PACKET_COMMAND
544 This packet is used to send commands from client to server.
545 Server MAY send this packet to other servers as well. All
546 commands are listed in their own section SILC Command Types
547 in [SILC4]. The contents of this packet is command specific.
548 This packet MAY be sent to entity that is indirectly connected
551 This packet MUST NOT be sent as list and the List flag MUST
554 Payload of the packet: See section 2.3.13 Command Payload
557 12 SILC_PACKET_COMMAND_REPLY
559 This packet is sent as reply to the SILC_PACKET_COMMAND packet.
560 The contents of this packet is command specific. This packet
561 MAY be sent to entity that is indirectly connected to the
564 This packet MUST NOT be sent as list and the List flag MUST
567 Payload of the packet: See section 2.3.14 Command Reply
568 Payload and section 2.3.13 Command
572 13 SILC_PACKET_KEY_EXCHANGE
574 This packet is used to start SILC Key Exchange Protocol,
575 described in detail in [SILC3].
577 This packet MUST NOT be sent as list and the List flag MUST
580 Payload of the packet: Payload of this packet is described
581 in the section SILC Key Exchange
582 Protocol and its sub sections in
586 14 SILC_PACKET_KEY_EXCHANGE_1
588 This packet is used as part of the SILC Key Exchange Protocol.
590 This packet MUST NOT be sent as list and the List flag MUST
593 Payload of the packet: Payload of this packet is described
594 in the section SILC Key Exchange
595 Protocol and its sub sections in
599 15 SILC_PACKET_KEY_EXCHANGE_2
601 This packet is used as part of the SILC Key Exchange Protocol.
603 This packet MUST NOT be sent as list and the List flag MUST
606 Payload of the packet: Payload of this packet is described
607 in the section SILC Key Exchange
608 Protocol and its sub sections in
612 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
614 This packet is used to request the authentication method to
615 be used in the SILC Connection Authentication Protocol. If
616 initiator of the protocol does not know the mandatory
617 authentication method this packet MAY be used to determine it.
619 The party receiving this payload MUST respond with the same
620 packet including the mandatory authentication method.
622 This packet MUST NOT be sent as list and the List flag MUST
625 Payload of the packet: See section 2.3.15 Connection Auth
631 17 SILC_PACKET_CONNECTION_AUTH
633 This packet is used to start and perform the SILC Connection
634 Authentication Protocol. This protocol is used to authenticate
635 the connecting party. The protocol is described in detail in
638 This packet MUST NOT be sent as list and the List flag MUST
641 Payload of the packet: Payload of this packet is described
642 in the section SILC Authentication
643 Protocol and it sub sections in [SILC].
646 18 SILC_PACKET_NEW_ID
648 This packet is used to distribute new ID's from server to
649 router and from router to all routers in the SILC network.
650 This is used when for example new client is registered to
651 SILC network. The newly created ID's of these operations are
652 distributed by this packet. Only server may send this packet,
653 however, client MUST be able to receive this packet. This
654 packet MAY be sent to entity that is indirectly connected
657 Payload of the packet: See section 2.3.16 New ID Payload
660 19 SILC_PACKET_NEW_CLIENT
662 This packet is used by client to register itself to the
663 SILC network. This is sent after key exchange and
664 authentication protocols has been completed. Client sends
665 various information about itself in this packet.
667 This packet MUST NOT be sent as list and the List flag MUST
670 Payload of the packet: See section 2.3.17 New Client Payload
673 20 SILC_PACKET_NEW_SERVER
675 This packet is used by server to register itself to the
676 SILC network. This is sent after key exchange and
677 authentication protocols has been completed. Server sends
678 this to the router it connected to, or, if router was
679 connecting, to the connected router. Server sends its
680 Server ID and other information in this packet. The client
681 MUST NOT send or receive this packet.
683 This packet MUST NOT be sent as list and the List flag MUST
686 Payload of the packet: See section 2.3.18 New Server Payload
689 21 SILC_PACKET_NEW_CHANNEL
691 This packet is used to notify routers about newly created
692 channel. Channels are always created by the router and it MUST
693 notify other routers about the created channel. Router sends
694 this packet to its primary route. Client MUST NOT send this
695 packet. This packet MAY be sent to entity that is indirectly
696 connected to the sender.
698 Payload of the packet: See section 2.3.19 New Channel Payload
703 This packet is used to indicate that re-key must be performed
704 for session keys. See section Session Key Regeneration in
705 [SILC1] for more information. This packet does not have
708 This packet MUST NOT be sent as list and the List flag MUST
712 23 SILC_PACKET_REKEY_DONE
714 This packet is used to indicate that re-key is performed and
715 new keys must be used hereafter.
717 This packet MUST NOT be sent as list and the List flag MUST
721 24 SILC_PACKET_HEARTBEAT
723 This packet is used by clients, servers and routers to keep the
724 connection alive. It is recommended that all servers implement
725 keepalive actions and perform it to both direction in a link.
726 This packet does not have a payload.
728 This packet MUST NOT be sent as list and the List flag MUST
732 25 SILC_PACKET_KEY_AGREEMENT
734 This packet is used by clients to request key negotiation
735 between another client in the SILC network. If the negotiation
736 is started it is performed using the SKE protocol. The result of
737 the negotiation, the secret key material, can be used for
738 example as private message key. The server and router MUST NOT
741 This packet MUST NOT be sent as list and the List flag MUST
744 Payload of the packet: See section 2.3.20 Key Agreement Payload
747 26 SILC_PACKET_RESUME_ROUTER
749 This packet is used during backup router protocol when the
750 original primary router of the cell comes back online and wishes
751 to resume the position as being the primary router of the cell.
753 Payload of the packet: See section 2.3.21 Resume Router Payload
758 This packet is used to perform an file transfer protocol in the
759 SILC session with some entity in the network. The packet is
760 multi purpose. The packet is used to tell other entity in the
761 network that the sender wishes to perform an file transfer
762 protocol. The packet is also used to actually tunnel the
763 file transfer protocol stream. The file transfer protocol
764 stream is always protected with the SILC packet.
766 This packet MUST NOT be sent as list and the List flag MUST
769 Payload of the packet: See section 2.3.22 File Transfer Payload
774 Currently undefined commands.
779 These packet types are reserved for private use and they will
780 not be defined by this document.
787 This type is reserved for future extensions and currently it
793 2.3.1 SILC Packet Payloads
795 All payloads resides in the main data area of the SILC packet. However
796 all payloads MUST be at the start of the data area after the SILC
797 packet header and padding. All fields in the packet payload are always
798 encrypted, as they reside in the data area of the packet which is
801 Payloads described in this section are common payloads that MUST be
802 accepted anytime during SILC session. Most of the payloads may only
803 be sent with specific packet type which is defined in the description
806 There are a lot of other payloads in the SILC as well. However, they
807 are not common in the sense that they could be sent at any time.
808 These payloads are not described in this section. These are payloads
809 such as SILC Key Exchange payloads and so on. These are described
810 in [SILC1], [SILC3] and [SILC4].
814 2.3.2 Generic payloads
816 This section describes generic payloads that are not associated to any
817 specific packet type. They can be used for example inside some other
824 This payload can be used to send an ID. ID's are variable in length
825 thus this payload provides a way to send variable length ID's.
838 The following diagram represents the ID Payload.
843 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
844 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
845 | ID Type | ID Length |
846 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
850 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
858 o ID Type (2 bytes) - Indicates the type of the ID. See
859 section 2.4 SILC ID Types for list of defined ID types.
861 o ID Length (2 bytes) - Length of the ID Data area not
862 including the length of any other fields in the payload.
864 o ID Data (variable length) - The actual ID data.
869 2.3.2.2 Argument Payload
871 Argument Payload is used to set arguments for any packet payload that
872 needs and supports arguments, such as commands. Number of arguments
873 associated with a packet MUST be indicated by the packet payload which
874 needs the arguments. Argument Payloads MUST always reside right after
875 the packet payload needing the arguments. Incorrect amount of argument
876 payloads MUST cause rejection of the packet.
878 The following diagram represents the Argument Payload.
883 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
884 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
885 | Payload Length | Argument Type | |
886 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
890 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
894 Figure 4: Argument Payload
898 o Payload Length (2 bytes) - Length of the argument payload data
899 area not including the length of any other fields in the
902 o Argument Type (1 byte) - Indicates the type of the argument.
903 Every argument may have a specific type that MUST be defined
904 by the packet payload needing the argument. For example
905 every command specify a number for each argument that maybe
906 associated with the command. By using this number the receiver
907 of the packet knows what type of argument this is. If there is
908 no specific argument type this field is set to zero (0).
910 o Argument Data (variable length) - Argument data.
915 2.3.2.3 Channel Payload
917 Generic Channel Payload may be used to send information about channel,
918 its name, the Channel ID and a mode.
920 The following diagram represents the Channel 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
928 | Channel Name Length | |
929 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
933 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
934 | Channel ID Length | |
935 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
939 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
941 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
945 Figure 5: New Channel Payload
949 o Channel Name Length (2 bytes) - Length of the channel name
952 o Channel Name (variable length) - The name of the channel.
954 o Channel ID Length (2 bytes) - Length of the Channel ID field.
956 o Channel ID (variable length) - The Channel ID.
958 o Mode Mask (4 bytes) - A mode. This can be the mode of the
959 channel but it can also be the mode of the client on the
960 channel. The contents of this field is dependent of the
961 usage of this payload. The usage is defined separately
962 when this payload is used. This is a 32 bit MSB first value.
967 2.3.2.4 Public Key Payload
969 Generic Public Key Payload may be used to send different types of
970 public keys and certificates.
972 The following diagram represents the Public Key Payload.
978 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
979 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
980 | Public Key Length | Public Key Type |
981 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
983 ~ Public Key of the party (or certificate) ~
985 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
989 Figure 6: Public Key Payload
993 o Public Key Length (2 bytes) - The length of the Public Key
994 (or certificate) field, not including any other field.
996 o Public Key Type (2 bytes) - The public key (or certificate)
997 type. This field indicates the type of the public key in
998 the packet. See the [SILC3] for defined public key types.
1000 o Public Key (or certificate) (variable length) - The
1001 public key or certificate.
1006 2.3.3 Disconnect Payload
1008 Disconnect payload is sent upon disconnection. The payload is simple;
1009 reason of disconnection is sent to the disconnected party.
1011 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
1012 MUST NOT be sent in any other packet type. The following diagram
1013 represents the Disconnect Payload.
1019 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
1020 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1022 ~ Disconnect Message ~
1024 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1028 Figure 7: Disconnect Payload
1034 o Disconnect Message (variable length) - Human readable
1035 reason of the disconnection.
1040 2.3.4 Success Payload
1042 Success payload is sent when some protocol execution is successfully
1043 completed. The payload is simple; indication of the success is sent.
1044 This may be any data, including binary or human readable data.
1049 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
1050 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1052 ~ Success Indication ~
1054 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1058 Figure 8: Success Payload
1062 o Success Indication (variable length) - Indication of
1063 the success. This may be for example some flag that
1064 indicates the protocol and the success status or human
1065 readable success message. The true length of this
1066 payload is available by calculating it from the SILC
1073 2.3.5 Failure Payload
1075 This is opposite of Success Payload. Indication of failure of
1076 some protocol is sent in the payload.
1082 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
1083 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1085 ~ Failure Indication ~
1087 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1091 Figure 9: Failure Payload
1095 o Failure Indication (variable length) - Indication of
1096 the failure. This may be for example some flag that
1097 indicates the protocol and the failure status or human
1098 readable failure message. The true length of this
1099 payload is available by calculating it from the SILC
1105 2.3.6 Reject Payload
1107 This payload is sent when some protocol is rejected to be executed.
1108 Other operations MAY send this as well that was rejected. The
1109 indication of the rejection is sent in the payload. The indication
1110 may be binary or human readable data.
1116 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
1117 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1119 ~ Reject Indication ~
1121 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1125 Figure 10: Reject Payload
1129 o Reject Indication (variable length) - Indication of
1130 the rejection. This maybe for example some flag that
1131 indicates the protocol and the rejection status or human
1132 readable rejection message. The true length of this
1133 payload is available by calculating it from the SILC
1139 2.3.7 Notify Payload
1141 Notify payload is used to send notify messages. The payload is usually
1142 sent from server to client, however, server MAY send it to another
1143 server as well. This payload MAY also be sent to a channel. Client
1144 MUST NOT send this payload. The receiver of this payload MAY ignore
1145 the contents of the payload, however, notify message SHOULD be audited.
1147 The payload may only be sent with SILC_PACKET_NOTIFY packet. It MUST
1148 not be sent in any other packet type. The following diagram represents
1154 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
1155 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1156 | Notify Type | Payload Length |
1157 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1163 Figure 11: Notify Payload
1167 o Notify Type (2 bytes) - Indicates the type of the notify
1170 o Payload Length (2 bytes) - Length of the entire Notify Payload
1171 including any associated Argument Payloads.
1173 o Argument Nums (2 bytes) - Indicates the number of Argument
1174 Payloads associated to this payload. Notify types may define
1175 arguments to be send along the notify message.
1178 The following list of currently defined notify types. The format for
1179 notify arguments is same as in SILC commands described in [SILC4].
1180 Also, all ID's sent in arguments are sent inside ID Payload.
1183 0 SILC_NOTIFY_TYPE_NONE
1185 If no specific notify type apply for the notify message this type
1189 Arguments: (1) <message>
1191 The <message> is implementation specific free text string.
1192 Receiver MAY ignore this message.
1195 1 SILC_NOTIFY_TYPE_INVITE
1197 Sent when an client is invited to a channel. This is also sent
1198 when the invite list of the channel is changed. This notify type
1199 is sent between routers and if an client was invited, to the
1200 client as well. In this case the packet is destined to the client.
1203 Arguments: (1) <Channel ID> (2) <channel name>
1204 (3) [<sender Client ID>] (4) [<adding client>]
1205 (5) [<removing client>]
1207 The <Channel ID> is the channel. The <channel name> is the name
1208 of the channel and is provided because the client which receives
1209 this notify packet may not have a way to resolve the name of the
1210 channel from the <Channel ID>. The <sender Client ID> is the
1211 Client ID which invited the client to the channel. The <adding
1212 client> and the <removing client> indicates the added or removed
1213 client from the channel's invite list. The format of the <adding
1214 client> and the <removing client> is defined in the [SILC4] with
1215 SILC_COMMAND_INVITE command.
1217 The <adding client> and <removing client> MUST NOT be sent when
1218 the packet is destined to a client.
1221 2 SILC_NOTIFY_TYPE_JOIN
1223 Sent when client has joined to a channel. The server MUST
1224 distribute this type only to the local clients on the channel
1225 and then send it to its primary router. The router or server
1226 receiving the packet distributes this type to the local clients
1227 on the channel and broadcast it to the network.
1230 Arguments: (1) [<Client ID>] (2) <Channel ID>
1232 The <Client ID> is the client that joined to the channel indicated
1233 by the <Channel ID>.
1236 3 SILC_NOTIFY_TYPE_LEAVE
1238 Sent when client has left a channel. The server must distribute
1239 this type only to the local clients on the channel and then send
1240 it to its primary router. The router or server receiving the
1241 packet distributes this type to the local clients on the channel
1242 and broadcast it to the network.
1245 Arguments: (1) <Client ID>
1247 The <Client ID> is the client which left the channel.
1250 4 SILC_NOTIFY_TYPE_SIGNOFF
1252 Sent when client signoff from SILC network. The server MUST
1253 distribute this type only to the local clients on the channel and
1254 then send it to its primary router. The router or server receiving
1255 the packet distributes this type to the local clients on the
1256 channel and broadcast it to the network.
1259 Arguments: (1) <Client ID> (2) <message>
1261 The <Client ID> is the client which left SILC network. The
1262 <message> is free text string indicating the reason of the signoff.
1265 5 SILC_NOTIFY_TYPE_TOPIC_SET
1267 Sent when topic is set/changed on a channel. This type must be
1268 sent only to the clients which is joined on the channel which
1269 topic was set or changed.
1272 Arguments: (1) <Client ID> (2) <topic>
1274 The <Client ID> is the client which set or changed the <topic>.
1277 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1279 Sent when client changes nick on a channel. The server MUST
1280 distribute this type only to the local clients on the channel
1281 and then send it to its primary router. The router or server
1282 receiving the packet distributes this type to the local clients
1283 on the channel and broadcast it to the network.
1286 Arguments: (1) <Old Client ID> (2) <New Client ID>
1288 The <Old Client ID> is the old ID of the client which changed
1289 the nickname. The <New Client ID> is the new ID generated by
1290 the change of the nickname.
1293 7 SILC_NOTIFY_TYPE_CMODE_CHANGE
1295 Sent when channel mode has changed. This type MUST be sent only
1296 to the clients which is joined on the channel which mode was
1300 Arguments: (1) <ID Payload> (2) <mode mask>
1301 (3) [<cipher>] (4) <[hmac>]
1303 The <ID Payload> is the ID (usually Client ID but it can be
1304 Server ID as well when the router is enforcing channel mode
1305 change) of the entity which changed the mode. The <mode mask>
1306 is the new mode mask of the channel. The client can safely
1307 ignore the <cipher> argument since the SILC_PACKET_CHANNEL_KEY
1308 packet will force the new channel key change anyway. The <hmac>
1309 argument is important since the client is responsible of setting
1310 the new HMAC and the hmac key into use.
1313 8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
1315 Sent when user mode on channel has changed. This type MUST be
1316 sent only to the clients which is joined on the channel where
1317 the target client is on.
1320 Arguments: (1) <ID Payload> (2) <mode mask>
1321 (3) <Target Client ID>
1323 The <ID Payload> is the ID (usually Client ID but it can be
1324 Server ID as well when the router is enforcing user's mode
1325 change) of the entity which changed the mode. The <mode mask>
1326 is the new mode mask of the channel. The <Target Client ID>
1327 is the client which mode was changed.
1330 9 SILC_NOTIFY_TYPE_MOTD
1332 Sent when Message of the Day (motd) is sent to a client.
1335 Arguments: (1) <motd>
1337 The <motd> is the Message of the Day.
1340 10 SILC_NOTIFY_TYPE_CHANNEL_CHANGE
1342 Sent when channel's ID has changed for a reason or another.
1343 This is sent by normal server to the client. This can also be
1344 sent by router to other server to force the Channel ID change.
1345 The Channel ID MUST be changed to use the new one. When sent
1346 to clients, this type MUST be sent only to the clients which is
1347 joined on the channel.
1350 Arguments: (1) <Old Channel ID> (2) <New Channel ID>
1352 The <Old Channel ID> is the channel's old ID and the <New
1353 Channel ID> is the new one that MUST replace the old one.
1356 11 SILC_NOTIFY_TYPE_SERVER_SIGNOFF
1358 Sent when server quits SILC network. Those clients from this
1359 server that are on channels must be removed from the channel.
1362 Arguments: (1) <Server ID> (n) [<Client ID> [...]
1364 The <Server ID> is the server's ID. The rest of the arguments
1365 are the Client ID's of the client's which are coming from this
1366 server and are thus quitting the SILC network also. If the
1367 maximum number of arguments are reached another
1368 SILC_NOTIFY_TYPE_SERVER_SIGNOFF notify packet MUST be sent.
1369 When this notify packet is sent between routers the Client ID's
1373 12 SILC_NOTIFY_TYPE_KICKED
1375 Sent when a client has been kicked from a channel. This is
1376 sent also to the client which was kicked from the channel.
1377 The client which was kicked from the channel MUST be removed
1378 from the channel. This notify type is always destined to the
1379 channel. The router or server receiving the packet distributes
1380 this type to the local clients on the channel and broadcast it
1384 Arguments: (1) <Client ID> (2) [<comment>]
1386 The <Client ID> is the client which was kicked from the channel.
1387 The kicker may have set the <comment> to indicate the reason for
1391 13 SILC_NOTIFY_TYPE_KILLED
1393 Sent when a client has been killed from the network. This is sent
1394 also to the client which was killed from the network. The client
1395 which was killed from the network MUST be removed from the network.
1396 This notify type is destined directly to the client which was
1397 killed and to channel if the client is on any channel. The router
1398 or server receiving the packet distributes this type to the local
1399 clients on the channel and broadcast it to the network.
1402 Arguments: (1) <Client ID> (2) [<comment>]
1404 The <Client ID> is the client which was killed from the network.
1405 The killer may have set the <comment> to indicate the reason for
1409 14 SILC_NOTIFY_TYPE_UMODE_CHANGE
1411 Sent when user's mode in the SILC changes. This type is sent
1412 only between routers as broadcast packet.
1415 Arguments: (1) <Client ID> (2) <mode mask>
1417 The <Client ID> is the client which mode was changed. The
1418 <mode mask> is the new mode mask.
1421 15 SILC_NOTIFY_TYPE_BAN
1423 Sent when the ban list of the channel is changed. This type is
1424 sent only between routers as broadcast packet.
1427 Arguments: (1) <Channel ID> (2) [<adding client>]
1428 (3) [<removing client>]
1430 The <Channel ID> is the channel which ban list was changed. The
1431 <adding client> is used to indicate that a ban was added and the
1432 <removing client> is used to indicate that a ban was removed from
1433 the ban list. The format of the <adding client> and the
1434 <removing client> is defined in the [SILC4] with SILC_COMMAND_BAN
1439 Notify types starting from 16384 are reserved for private notify
1446 Error payload is sent upon error. Error may occur in various
1447 conditions when server sends this packet. Client MUST NOT send this
1448 payload but MUST be able to accept it. However, client MAY
1449 totally ignore the contents of the packet as server is going to
1450 take action on the error anyway. However, it is recommended
1451 that the client takes error packet seriously.
1457 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
1458 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1462 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1466 Figure 12: Error Payload
1470 o Error Message (variable length) - Human readable error
1476 2.3.9 Channel Message Payload
1478 Channel messages are the most common messages sent in the SILC.
1479 Channel Message Payload is used to send message to channels. These
1480 messages can only be sent if client has joined to some channel.
1481 Even though this packet is the most common in SILC it is still
1482 special packet. Some special handling on sending and reception
1483 of channel message is required.
1485 Padding MUST be applied into this payload since the payload is
1486 encrypted separately from other parts of the packet with the
1487 channel specific key. Hence the requirement of the padding.
1488 The padding SHOULD be random data. The packet MUST be made
1489 multiple by eight (8) or by the block size of the cipher, which
1492 The SILC header in this packet is encrypted with the session key
1493 of the next receiver of the packet. Nothing else is encrypted
1494 with that key. Thus, the actual packet and padding to be
1495 encrypted with the session key is SILC Header plus padding to it
1496 to make it multiple by eight (8) or multiple by the block size
1497 of the cipher, which ever is larger.
1499 Receiver of the the channel message packet is able to determine
1500 the channel the message is destined to by checking the destination
1501 ID from the SILC Packet header which tells the destination channel.
1502 The original sender of the packet is also determined by checking
1503 the source ID from the header which tells the client which sent
1506 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1507 It MUST NOT be sent in any other packet type. The following diagram
1508 represents the Channel Message Payload.
1510 (*) indicates that the field is not encrypted.
1516 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
1517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1518 | Flags | Message Length |
1519 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1524 | Padding Length | |
1525 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1529 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1533 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1535 ~ Initial Vector * ~
1537 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1541 Figure 13: Channel Message Payload
1545 o Flags (2 bytes) - Includes the flags of the channel
1546 messages. The flags can indicate a reason or purpose
1547 for the channel message. Note that the Private Message
1548 Payload use these same flags for the same purpose. The
1549 following flags are defined:
1551 0x0000 SILC_MESSAGE_FLAG_NONE
1553 No specific flags set.
1555 0x0001 SILC_MESSAGE_FLAG_AUTOREPLY
1557 This message is an automatic reply to an earlier
1560 0x0002 SILC_MESSAGE_FLAG_NOREPLY
1562 There should not be reply messages to this
1565 0x0004 SILC_MESSAGE_FLAG_ACTION
1567 The sender is performing an action and the message
1568 is the indication of the action.
1570 0x0008 SILC_MESSAGE_FLAG_NOTICE
1572 The message is for example an informational notice
1575 0x0010 SILC_MESSAGE_FLAG_REQUEST
1577 This is a generic request flag to send request
1578 messages. A separate document should define any
1579 payloads associated to this flag.
1581 0x0020 SILC_MESSAGE_FLAG_SIGNED
1583 This flag indicates that the message is signed
1584 with sender's private key and thus can be verified
1585 by the receiver using the sender's public key. A
1586 separate document should define the detailed procedure
1587 of the signing process and any associated payloads
1590 0x0040 - 0x0200 RESERVED
1592 Reserved for future flags
1594 0x0400 - 0x8000 PRIVATE RANGE
1596 Private range for free use.
1598 o Message Length (2 bytes) - Indicates the length of the
1599 the Message Data field in the payload, not including any
1602 o Message Data (variable length) - The actual message to
1605 o Padding Length (2 bytes) - Indicates the length of the
1606 Padding field in the payload, not including any other
1609 o Padding (variable length) - The padding that MUST be
1610 applied because this payload is encrypted separately from
1611 other parts of the packet.
1613 o MAC (variable length) - The MAC computed from the
1614 Message Length, Message Data, Padding Length and Padding
1615 fields. This protects the integrity of the plaintext
1616 channel message. The receiver can verify from the MAC
1617 whether the message decrypted correctly. Also, if more than
1618 one private key has been set for the channel, the receiver
1619 can verify which of the keys decrypted the message
1620 correctly. Note that, this field is encrypted and MUST
1621 be added to the padding calculation.
1623 o Initial Vector (variable length) - The initial vector
1624 that has been used in packet encryption. It needs to be
1625 used in the packet decryption as well. What this field
1626 includes is implementation issue. However, it is
1627 RECOMMENDED that it would be random data or, perhaps,
1628 a timestamp. It is NOT RECOMMENDED to use zero (0) as an
1629 initial vector. This field is not encrypted. This field
1630 is not included into the padding calculation. Length
1631 of this field equals the cipher's block size. This field
1632 is, however, authenticated.
1637 2.3.10 Channel Key Payload
1639 All traffic in channels are protected by channel specific keys.
1640 Channel Key Payload is used to distribute channel keys to all
1641 clients on the particular channel. Channel keys are sent when
1642 the channel is created, when new user joins to the channel and
1643 whenever a user has left a channel. Server creates the new
1644 channel key and distributes it to the clients by encrypting this
1645 payload with the session key shared between the server and
1646 the client. After that, client starts using the key received
1647 in this payload to protect the traffic on the channel.
1649 The client which is joining to the channel receives its key in the
1650 SILC_COMMAND_JOIN command reply message thus it is not necessary to
1651 send this payload to the entity which sent the SILC_COMMAND_JOIN
1654 Channel keys are cell specific thus every router in the cell have
1655 to create a channel key and distribute it if any client in the
1656 cell has joined to a channel. Channel traffic between cell's
1657 are not encrypted using channel keys, they are encrypted using
1658 normal session keys between two routers. Inside a cell, all
1659 channel traffic is encrypted with the specified channel key.
1660 Channel key should expire periodically, say, in one hour, in
1661 which case new channel key is created and distributed.
1663 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1664 It MUST NOT be sent in any other packet type. The following diagram
1665 represents the Channel Key Payload.
1671 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
1672 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1673 | Channel ID Length | |
1674 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1678 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1679 | Cipher Name Length | |
1680 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1685 | Channel Key Length | |
1686 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1694 Figure 14: Channel Key Payload
1699 o Channel ID Length (2 bytes) - Indicates the length of the
1700 Channel ID field in the payload, not including any other
1703 o Channel ID (variable length) - The Channel ID of the
1704 channel this key is meant for.
1706 o Cipher Name Length (2 bytes) - Indicates the length of the
1707 Cipher name field in the payload, not including any other
1710 o Cipher Name (variable length) - Name of the cipher used
1711 in the protection of channel traffic. This name is
1712 initially decided by the creator of the channel but it
1713 MAY change during the life time of the channel as well.
1715 o Channel Key Length (2 bytes) - Indicates the length of the
1716 Channel Key field in the payload, not including any other
1719 o Channel Key (variable length) - The actual channel key
1725 2.3.11 Private Message Payload
1727 Private Message Payload is used to send private message between
1728 two clients (or users for that matter). The messages are sent only
1729 to the specified user and no other user inside SILC network is
1730 able to see the message. The message is protected by the session
1731 key established by the SILC Key Exchange Protocol. However,
1732 it is also possible to agree to use a private key to protect
1733 just the private messages. See section 2.3.11 Private Message
1734 Key Payload for detailed description of how to agree to use
1737 If normal session key is used to protect the message, every server
1738 between the sender client and the receiving client MUST decrypt the
1739 packet and always re-encrypt it with the session key of the next
1740 receiver of the packet. See section Client To Client in [SILC1].
1742 When private key is used to protect the message, servers between
1743 the sender and the receiver needs not to decrypt/re-encrypt the
1744 packet. Section Client To Client in [SILC1] gives example of this
1747 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1748 packet. It MUST NOT be sent in any other packet type. The following
1749 diagram represents the Private Message Payload.
1755 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
1756 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1757 | Flags | Message Data Length |
1758 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1762 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1766 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1770 Figure 15: Private Message Payload
1774 o Flags (2 bytes) - This field includes the flags of the
1775 private message. They can indicate a different reason or
1776 purpose for the private message. See the section 2.3.9
1777 Channel Message Payload for defined flags. Note that
1778 the Channel Message Payload use the same flags for the
1781 o Message Data Length (2 bytes) - Indicates the length of the
1782 Message Data field, not includes any other field.
1784 o Message Data (variable length) - The actual message to
1785 the client. Rest of the packet is reserved for the message
1788 o Padding (variable length) - This field is present only
1789 when the private message payload is encrypted with private
1790 message key. In this case the padding is applied to make
1791 the payload multiple by eight (8), or by the block size of
1792 the cipher, which ever is larger. When encrypted with
1793 normal session keys, this field MUST NOT be included.
1798 2.3.12 Private Message Key Payload
1800 This payload is used to send key from client to another client that
1801 is going to be used to protect the private messages between these
1802 two clients. If this payload is not sent normal session key
1803 established by the SILC Key Exchange Protocol is used to protect
1804 the private messages.
1806 This payload may only be sent by client to another client. Server
1807 MUST NOT send this payload at any time. After sending this payload
1808 the sender of private messages must set the Private Message Key
1809 flag into SILC Packet Header.
1811 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1812 packet. It MUST NOT be sent in any other packet type. The following
1813 diagram represents the Private Message Key Payload.
1819 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
1820 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1821 | Private Message Key Length | |
1822 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1824 ~ Private Message Key ~
1826 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1827 | Cipher Name Length | |
1828 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1832 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1836 Figure 16: Private Message Key Payload
1842 o Private Message Key Length (2 bytes) - Indicates the length
1843 of the Private Message Key field in the payload, not including
1846 o Private Message Key (variable length) - The actual private
1847 message key material.
1849 o Cipher Name Length (2 bytes) - Indicates the length of the
1850 Cipher Name field in the payload, not including any other
1853 o Cipher Name (variable length) - Name of the cipher to use
1854 in the private message encryption. If this field does not
1855 exist then the default cipher of the SILC protocol is used.
1856 See the [SILC1] for defined ciphers.
1862 2.3.13 Command Payload
1864 Command Payload is used to send SILC commands from client to server.
1865 Also server MAY send commands to other servers. The following diagram
1866 represents the Command Payload.
1872 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
1873 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1874 | Payload Length | SILC Command | Arguments Num |
1875 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1876 | Command Identifier |
1877 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1881 Figure 17: Command Payload
1885 o Payload Length (2 bytes) - Length of the entire command
1886 payload including any command argument payloads associated
1889 o SILC Command (1 byte) - Indicates the SILC command. This MUST
1890 be set to non-zero value. If zero (0) value is found in this
1891 field the packet MUST be discarded.
1893 o Arguments Num (1 byte) - Indicates the number of arguments
1894 associated with the command. If there are no arguments this
1895 field is set to zero (0). The arguments MUST follow the
1896 command payload. See section 2.3.2.2 for definition of the
1899 o Command Identifier (2 bytes) - Identifies this command at the
1900 sender's end. The entity which replies to this command MUST
1901 set the value found from this field into the Command Payload
1902 used to send the reply to the sender. This way the sender
1903 can identify which command reply belongs to which originally
1904 sent command. What this field includes is implementation
1905 issue but it is RECOMMENDED that wrapping counter value is
1906 used in the field. Value zero (0) in this field means that
1907 no specific value is set.
1910 See [SILC4] for detailed description of different SILC commands,
1911 their arguments and their reply messages.
1917 2.3.14 Command Reply Payload
1919 Command Reply Payload is used to send replies to the commands. The
1920 Command Reply Payload is identical to the Command Payload thus see
1921 the upper section for the Command Payload specification.
1923 The entity which sends the reply packet MUST set the Command Identifier
1924 field in the reply packet's Command Payload to the value it received
1925 in the original command packet.
1927 See SILC Commands in [SILC4] for detailed description of different
1928 SILC commands, their arguments and their reply messages.
1932 2.3.15 Connection Auth Request Payload
1934 Client MAY send this payload to server to request the authentication
1935 method that must be used in authentication protocol. If client knows
1936 this information beforehand this payload is not necessary to be sent.
1937 Server performing authentication with another server MAY also send
1938 this payload to request the authentication method. If the connecting
1939 server already knows this information this payload is not necessary
1942 Server receiving this request MUST reply with same payload sending
1943 the mandatory authentication method. Algorithms that may be required
1944 to be used by the authentication method are the ones already
1945 established by the SILC Key Exchange protocol. See section Key
1946 Exchange Start Payload in [SILC3] for detailed information.
1948 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1949 packet. It MUST NOT be sent in any other packet type. The following
1950 diagram represents the Connection Auth Request Payload.
1956 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
1957 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1958 | Connection Type | Authentication Method |
1959 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1963 Figure 18: Connection Auth Request Payload
1967 o Connection Type (2 bytes) - Indicates the type of the
1968 connection. The following connection types are defined:
1975 If any other type is found in this field the packet MUST be
1976 discarded and the authentication MUST be failed.
1978 o Authentication Method (2 bytes) - Indicates the authentication
1979 method to be used in the authentication protocol. The following
1980 authentication methods are defined:
1983 1 password (mandatory)
1984 2 public key (mandatory)
1986 If any other type is found in this field the packet MUST be
1987 discarded and the authentication MUST be failed. If this
1988 payload is sent as request to receive the mandatory
1989 authentication method this field MUST be set to zero (0),
1990 indicating that receiver should send the mandatory
1991 authentication method. The receiver sending this payload
1992 to the requesting party, MAY also set this field to zero (0)
1993 to indicate that authentication is not required. In this
1994 case authentication protocol still MUST be started but
1995 server is most likely to respond with SILC_PACKET_SUCCESS
2001 2.3.16 New ID Payload
2003 New ID Payload is a multipurpose payload. It is used to send newly
2004 created ID's from clients and servers. When client connects to server
2005 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
2006 packet, server replies with this packet by sending the created ID for
2007 the client. Server always creates the ID for the client.
2009 This payload is also used when server tells its router that new client
2010 has registered to the SILC network. In this case the server sends
2011 the Client ID of the client to the router. Similarly when router
2012 distributes information to other routers about the client in the SILC
2013 network this payload is used.
2015 Also, when server connects to router, router uses this payload to inform
2016 other routers about new server in the SILC network. However, every
2017 server (or router) creates their own ID's thus the ID distributed by
2018 this payload is not created by the distributor in this case. Servers
2019 create their own ID's. Server registers itself to the network by
2020 sending SILC_PACKET_NEW_SERVER to the router it connected to. The case
2021 is same when router connects to another router.
2023 However, this payload MUST NOT be used to send information about new
2024 channels. New channels are always distributed by sending the dedicated
2025 SILC_PACKET_NEW_CHANNEL packet.
2027 Thus, this payload is very important and used every time when some
2028 new entity is registered to the SILC network. Client MUST NOT send this
2029 payload. Both client and server (and router) MAY receive this payload.
2031 The packet uses generic ID Payload as New ID Payload. See section
2032 2.3.2.1 for generic ID Payload.
2036 2.3.17 New Client Payload
2038 When client is connected to the server, keys has been exchanged and
2039 connection has been authenticated client MUST register itself to the
2040 server. Client's first packet after key exchange and authentication
2041 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
2042 the relevant information about the connected user. Server creates a new
2043 client ID for the client when received this payload and sends it to the
2044 client in New ID Payload.
2046 This payload sends username and real name of the user on the remote host
2047 which is connected to the SILC server with SILC client. The server
2048 creates the client ID according the information sent in this payload.
2049 The nickname of the user becomes the username sent in this payload.
2050 However, client should call NICK command after sending this payload to
2051 set the real nickname of the user which is then used to create new
2054 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
2055 MUST NOT be sent in any other packet type. The following diagram
2056 represents the New Client Payload.
2073 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
2074 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2075 | Username Length | |
2076 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2080 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2081 | Real Name Length | |
2082 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2086 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2090 Figure 19: New Client Payload
2094 o Username Length (2 bytes) - Length of the Username field.
2096 o Username (variable length) - The username of the user on
2097 the host where connecting to the SILC server.
2099 o Real Name Length (2 bytes) - Length of the Real Name field.
2101 o Real Name (variable length) - The real name of the user
2102 on the host where connecting to the SILC server.
2107 2.3.18 New Server Payload
2109 This payload is sent by server when it has completed successfully both
2110 key exchange and connection authentication protocols. The server
2111 MUST register itself to the SILC Network by sending this payload.
2112 The first packet after these key exchange and authentication protocols
2113 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
2114 of the server that it has created by itself. It also includes a
2115 name of the server that is associated to the Server ID.
2117 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
2118 MUST NOT be sent in any other packet type. The following diagram
2119 represents the New Server Payload.
2128 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
2129 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2130 | Server ID Length | |
2131 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2135 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2136 | Server Name Length | |
2137 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2141 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2145 Figure 20: New Server Payload
2149 o Server ID Length (2 bytes) - Length of the Server ID Data
2152 o Server ID Data (variable length) - The actual Server ID
2155 o Server Name Length (2 bytes) - Length of the server name
2158 o Server Name (variable length) - The server name.
2163 2.3.19 New Channel Payload
2165 Information about newly created channel is broadcasted to all routers
2166 in the SILC network by sending this packet payload. Channels are
2167 created by router of the cell. Server never creates channels unless
2168 it is a standalone server and it does not have router connection,
2169 in this case server acts as router. Normal server send JOIN command
2170 to the router (after it has received JOIN command from client) which
2171 then processes the command and creates the channel. Client MUST NOT
2172 send this packet. Server may send this packet to a router when it is
2173 announcing its existing channels to the router after it has connected
2176 The packet uses generic Channel Payload as New Channel Payload. See
2177 section 2.3.2.3 for generic Channel Payload. The Mode Mask field in the
2178 Channel Payload is the mode of the channel.
2182 2.3.20 Key Agreement Payload
2184 This payload is used by clients to request key negotiation between
2185 another client in the SILC Network. The key agreement protocol used
2186 is the SKE protocol. The result of the protocol, the secret key
2187 material, can be used for example as private message key between the
2188 two clients. This significantly adds security as the key agreement
2189 is performed outside the SILC network. The server and router MUST NOT
2192 The sender MAY tell the receiver of this payload the hostname and the
2193 port where the SKE protocol is running in the sender's end. The
2194 receiver MAY then initiate the SKE negotiation with the sender. The
2195 sender MAY also optionally not to include the hostname and the port
2196 of its SKE protocol. In this case the receiver MAY reply to the
2197 request by sending the same payload filled with the receiver's hostname
2198 and the port where the SKE protocol is running. The sender MAY then
2199 initiate the SKE negotiation with the receiver.
2201 This payload may be sent with SILC_PACKET_KEY_AGREEMENT and
2202 SILC_PACKET_FTP packet types. It MUST NOT be sent in any other packet
2203 types. The following diagram represents the Key Agreement Payload.
2209 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
2210 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2211 | Hostname Length | |
2212 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2222 Figure 21: Key Agreement Payload
2226 o Hostname Length (2 bytes) - Indicates the length of the
2229 o Hostname (variable length) - The hostname or IP address where
2230 the SKE protocol is running. The sender MAY fill this field
2231 when sending the payload. If the receiver sends this payload
2232 as reply to the request it MUST fill this field.
2234 o Port (4 bytes) - The port where the SKE protocol is bound.
2235 The sender MAY fill this field when sending the payload. If
2236 the receiver sends this payload as reply to the request it
2237 MUST fill this field. This is a 32 bit MSB first order value.
2241 After the key material has been received from the SKE protocol it is
2242 processed as the [SILC3] describes. If the key material is used as
2243 channel private key then the Sending Encryption Key, as defined in
2244 [SILC3] is used as the channel private key. Other key material must
2245 be discarded. The [SILC1] defines the way to use the key material if
2246 it is intended to be used as private message keys. Any other use for
2247 the key material is undefined.
2251 2.3.21 Resume Router Payload
2253 The payload may only be sent with SILC_PACKET_RESUME_ROUTER packet. It
2254 MUST NOT be sent in any other packet type. The Following diagram
2255 represents the Resume Router Payload.
2261 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
2262 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2263 | Type | Session ID |
2264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2268 Figure 22: Resume Router Payload
2272 o Type (1 byte) - Indicates the type of the backup resume
2273 protocol packet. The type values are defined in [SILC1].
2275 o Session ID (1 bytes) - Indicates the session ID for the
2276 backup resume protocol. The sender of the packet sets this
2277 value and the receiver MUST set the same value in subsequent
2283 2.3.22 File Transfer Payload
2285 File Transfer Payload is used to perform file transfer protocol
2286 between two entities in the network. The actual file transfer
2287 protocol is always encapsulated inside the SILC Packet. The actual
2288 data stream is also sent peer to peer outside SILC network.
2290 When an entity, usually a client wishes to perform file transfer
2291 protocol with another client in the network, they perform Key Agreement
2292 protocol as described in the section 2.3.20 Key Agreement Payload and
2293 in [SILC3], inside File Transfer Payload. After the Key Agreement
2294 protocol has been performed the subsequent packets in the data stream
2295 will be protected using the new key material. The actual file transfer
2296 protocol is also initialized in this stage. All file transfer protocol
2297 packets are always encapsulated in the File Transfer Payload and
2298 protected with the negotiated key material.
2300 The payload may only be sent with SILC_PACKET_FTP packet. It MUST NOT
2301 be sent in any other packet type. The following diagram represents the
2302 File Transfer Payload
2307 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
2308 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2318 Figure 23: File Transfer Payload
2322 o Type (1 byte) - Indicates the type of the file transfer
2323 protocol. The following file transfer protocols has been
2326 1 SSH File Transfer Protocol (SFTP) (mandatory)
2328 If zero (0) value or any unsupported file transfer protocol
2329 type is found in this field the packet must be discarded.
2330 The currently mandatory file transfer protocol is SFTP.
2331 The SFTP protocol is defined in [SFTP].
2333 o Data (variable length) - Arbitrary file transfer data. The
2334 contents and encoding of this field is dependent of the usage
2335 of this payload and the type of the file transfer protocol.
2336 When this payload is used to perform the Key Agreement
2337 protocol, this field include the Key Agreement Payload,
2338 as defined in the section 2.3.20 Key Agreement Payload.
2339 When this payload is used to send the actual file transfer
2340 protocol data, the encoding is defined in the corresponding
2341 file transfer protocol.
2348 ID's are extensively used in the SILC network to associate different
2349 entities. The following ID's has been defined to be used in the SILC
2355 When ever specific ID cannot be used this is used.
2359 Server ID to associate servers. See the format of
2364 Client ID to associate clients. See the format of
2369 Channel ID to associate channels. See the format of
2375 2.5 Packet Encryption And Decryption
2377 SILC packets are encrypted almost entirely. Only small part of SILC
2378 header is not encrypted as described in section 5.2 SILC Packet Header.
2379 The SILC Packet header is the first part of a packet to be encrypted
2380 and it is always encrypted with the key of the next receiver of the
2381 packet. The data payload area of the packet is always entirely
2382 encrypted and it is usually encrypted with the next receiver's key.
2383 However, there are some special packet types and packet payloads
2384 that require special encryption process. These special cases are
2385 described in the next sections. First is described the normal packet
2390 2.5.1 Normal Packet Encryption And Decryption
2392 Normal SILC packets are encrypted with the session key of the next
2393 receiver of the packet. The entire SILC Packet header and the packet
2394 data payload is is also encrypted with the same key. Padding of the
2395 packet is also encrypted always with the session key, also in special
2396 cases. Computed MAC of the packet must not be encrypted.
2398 Decryption process in these cases are straightforward. The receiver
2399 of the packet MUST first decrypt the SILC Packet header, or some parts
2400 of it, usually first 16 bytes of it. Then the receiver checks the
2401 packet type from the decrypted part of the header and can determine
2402 how the rest of the packet must be decrypted. If the packet type is
2403 any of the special cases described in the following sections the packet
2404 decryption is special. If the packet type is not among those special
2405 packet types rest of the packet can be decrypted with the same key.
2407 With out a doubt, this sort of decryption processing causes some
2408 overhead to packet decryption, but never the less, is required.
2412 2.5.2 Channel Message Encryption And Decryption
2414 Channel Messages (Channel Message Payload) are always encrypted with
2415 the channel specific key. However, the SILC Packet header is not
2416 encrypted with that key. As in normal case, the header is encrypted
2417 with the key of the next receiver of the packet, who ever that might
2418 be. Note that in this case the encrypted data area is not touched
2419 at all; it MUST NOT be re-encrypted with the session key.
2421 Receiver of a channel message, who ever that is, is REQUIRED to decrypt
2422 the SILC Packet header to be able to even recognize the packet to be as
2423 channel message. This is same procedure as for normal SILC packets.
2424 As the receiver founds the packet to be channel message, rest of the
2425 packet processing is special. Rest of the SILC Packet header is
2426 decrypted with the same session key along with the padding of the
2427 packet. After that the packet is protected with the channel specific
2428 key and thus can be decrypted only if the receiver is the client on
2429 the channel. See section 2.7 Packet Padding Generation for more
2430 information about padding on special packets.
2432 If the receiver of the channel message is router which is routing the
2433 message to another router then it MUST decrypt the Channel Message
2434 payload. Between routers (that is, between cells) channel messages
2435 are protected with session keys shared between the routers. This
2436 causes another special packet processing for channel messages. If
2437 the channel message is received from another router then the entire
2438 packet, including Channel Message payload, MUST be encrypted with the
2439 session key shared between the routers. In this case the packet
2440 decryption process is as with normal SILC packets. Hence, if the
2441 router is sending channel message to another router the Channel
2442 Message payload MUST have been decrypted and MUST be re-encrypted
2443 with the session key shared between the another router. In this
2444 case the packet encryption is as with any normal SILC packet.
2446 It must be noted that this is only when the channel messages are sent
2447 from router to another router. In all other cases the channel
2448 message encryption and decryption is as described above. This
2449 different processing of channel messages with router to router
2450 connection is because channel keys are cell specific. All cells have
2451 their own channel keys thus the channel message traveling from one
2452 cell to another MUST be protected as it would be any normal SILC
2455 If the SILC_CMODE_PRIVKEY channel mode has been set for the channel
2456 then the router cannot decrypt the packet as it does not know the
2457 private key. In this case the entire packet MUST be encrypted with
2458 the session key and sent to the router. The router receiving the
2459 packet MUST check the channel mode and decrypt the packet accordingly.
2463 2.5.3 Private Message Encryption And Decryption
2465 By default, private message in SILC are protected by session keys.
2466 In this case the private message encryption and decryption process is
2467 equivalent to normal packet encryption and decryption.
2469 However, private messages MAY be protected with private message key
2470 which causes the packet to be special packet. The procedure in this
2471 case is very much alike to channel packets. The actual private message
2472 is encrypted with the private message key and other parts of the
2473 packet is encrypted with the session key. See 2.7 Packet Padding
2474 Generation for more information about padding on special packets.
2476 The difference from channel message processing is that server or router
2477 en route never decrypts the actual private message, as it does not
2478 have the key to do that. Thus, when sending packets between router
2479 the processing is same as in any other case as well; the packet's header
2480 and padding is protected by the session key and the data area is not
2483 The true receiver of the private message, client, that is, is able
2484 to decrypt the private message as it shares the key with the sender
2489 2.6 Packet MAC Generation
2491 Data integrity of a packet is protected by including a message
2492 authentication code (MAC) at the end of the packet. The MAC is computed
2493 from shared secret MAC key, that is established by the SILC Key Exchange
2494 protocol, from packet sequence number, and from the original contents
2495 of the packet. The MAC is always computed before the packet is
2496 encrypted, although after it is compressed if compression is used.
2498 The MAC is computed from entire packet. Every bit of data in the packet,
2499 including SILC Packet Header is used in the MAC computing. This way
2500 the entire packet becomes authenticated.
2502 If the packet is special packet MAC is computed from the entire packet
2503 but part of the packet may be encrypted before the MAC is computed.
2504 This is case, for example, with channel messages where the message data
2505 is encrypted with key that server may not now. In this case the MAC
2506 has been computed from the encrypted data.
2508 Hence, packet's MAC generation is as follows:
2510 mac = MAC(key, sequence number | SILC packet)
2512 The MAC key is negotiated during the SKE protocol. The sequence number
2513 is a 32 bit MSB first value starting from zero for first packet and
2514 increasing for subsequent packets, finally wrapping after 2^32 packets.
2515 The value is never reset, not even after rekey has been performed. Note
2516 that the sequence number is incremented only when MAC is computed for a
2517 packet. If packet is not encrypted and MAC is not computed then the
2518 sequence number is not incremented. Hence, the sequence number is zero
2519 for first encrypted packet.
2521 See [SILC1] for defined and allowed MAC algorithms.
2525 2.7 Packet Padding Generation
2527 Padding is needed in the packet because the packet is encrypted. It
2528 MUST always be multiple by eight (8) or multiple by the block size
2529 of the cipher, which ever is larger. The padding is always encrypted.
2531 For normal packets the padding is added after the SILC Packet Header
2532 and between the Data Payload area. The padding for normal packets
2533 may be calculated as follows:
2536 padding length = 16 - (packet_length mod block_size)
2539 The `block_size' is the block size of the cipher. The maximum padding
2540 length is 128 bytes, and minimum is 1 byte. The above algorithm calculates
2541 the padding to the next block size, and always returns the padding
2542 length between 1 - 16 bytes. However, implementations may add padding
2543 up to 128 bytes. For example packets that include a passphrase or a
2544 password for authentication purposes SHOULD pad the packet up to the
2545 maximum padding length.
2547 For special packets the padding calculation is different as special
2548 packets may be encrypted differently. In these cases the encrypted
2549 data area MUST already be multiple by the block size thus in this case
2550 the padding is calculated only for SILC Packet Header, not for any
2551 other area of the packet. The same algorithm works in this case as
2552 well, except that the `packet length' is now the SILC Packet Header
2555 The padding MUST be random data, preferably, generated by
2556 cryptographically strong random number generator.
2560 2.8 Packet Compression
2562 SILC Packets MAY be compressed. In this case the data payload area
2563 is compressed and all other areas of the packet MUST remain as they
2564 are. After compression is performed for the data area, the length
2565 field of Packet Header MUST be set to the compressed length of the
2568 The compression MUST always be applied before encryption. When
2569 the packet is received and decrypted the data area MUST be decompressed.
2570 Note that the true sender of the packet MUST apply the compression and
2571 the true receiver of the packet MUST apply the decompression. Any
2572 server or router en route MUST NOT decompress the packet.
2578 The sender of the packet MUST assemble the SILC Packet Header with
2579 correct values. It MUST set the Source ID of the header as its own
2580 ID, unless it is forwarding the packet. It MUST also set the Destination
2581 ID of the header to the true destination. If the destination is client
2582 it will be Client ID, if it is server it will be Server ID and if it is
2583 channel it will be Channel ID.
2585 If the sender wants to compress the packet it MUST apply the
2586 compression now. Sender MUST also compute the padding as described
2587 in above sections. Then sender MUST compute the MAC of the packet.
2589 Then sender MUST encrypt the packet as has been described in above
2590 sections according whether the packet is normal packet or special
2591 packet. The computed MAC MUST NOT be encrypted.
2595 2.10 Packet Reception
2597 On packet reception the receiver MUST check that all fields in the
2598 SILC Packet Header are valid. It MUST check the flags of the
2599 header and act accordingly. It MUST also check the MAC of the packet
2600 and if it is to be failed the packet MUST be discarded. Also if the
2601 header of the packet includes any bad fields the packet MUST be
2604 See above sections on the decryption process of the received packet.
2606 The receiver MUST also check that the ID's in the header are valid
2607 ID's. Unsupported ID types or malformed ID's MUST cause packet
2608 rejection. The padding on the reception is always ignored.
2610 The receiver MUST also check the packet type and start parsing the
2611 packet according to the type. However, note the above sections on
2612 special packet types and their parsing.
2618 Routers are the primary entities in the SILC network that takes care
2619 of packet routing. However, normal servers routes packets as well, for
2620 example, when they are routing channel message to the local clients.
2621 Routing is quite simple as every packet tells the true origin and the
2622 true destination of the packet.
2624 It is still RECOMMENDED for routers that has several routing connections
2625 to create route cache for those destinations that has faster route than
2626 the router's primary route. This information is available for the router
2627 when other router connects to the router. The connecting party then
2628 sends all of its locally connected clients, servers and channels. These
2629 informations helps to create the route cache. Also, when new channels
2630 are created to a cell its information is broadcasted to all routers
2631 in the network. Channel ID's are based on router's ID thus it is easy
2632 to create route cache based on these informations. If faster route for
2633 destination does not exist in router's route cache the packet MUST be
2634 routed to the primary route (default route).
2636 However, there are some issues when routing channel messages to group
2637 of users. Routers are responsible of routing the channel message to
2638 other routers, local servers and local clients as well. Routers MUST
2639 send the channel message to only one router in the network, preferrably
2640 to the shortest route to reach the channel users. The message can be
2641 routed into either upstream or downstream. After the message is sent
2642 to a router in the network it MUST NOT be sent to any other router in
2643 either same route or other route. The message MUST NOT be routed to
2644 the router it came from.
2646 When routing for example private messages they should be routed to the
2647 shortest route always to reach the destination client as fast as possible.
2649 For server which receives a packet to be routed to its locally connected
2650 client the server MUST check whether the particular packet type is
2651 allowed to be routed to the client. Not all packets may be sent by
2652 some odd entity to client that is indirectly connected to the sender.
2653 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2654 entities and sending packets to them. The section mentions the packets
2655 that may be sent to indirectly connected entities. It is clear that
2656 server cannot send, for example, disconnect packet to client that is not
2657 directly connected to the server.
2659 Routers form a ring in the SILC network. However, routers may have other
2660 direct connections to other routers in the network too. This can cause
2661 interesting routing problems in the network. Since the network is a ring,
2662 the packets usually should be routed into counter clock-wise direction,
2663 or if it cannot be used then always clock-wise (primary route) direction.
2664 Problems may arise when a faster direct route exists and router is routing
2665 a channel message. Currently channel messages must be routed either
2666 in upstream or downstream, they cannot be routed to other direct routes.
2667 The SILC protocol should have a shortest path discovery protocol, and some
2668 existing routing protocol, that can handle a ring network with other
2669 direct routes inside the ring (so called hybrid ring-mesh topology),
2670 MAY be defined to be used with the SILC protocol. Additional
2671 specifications MAY be written on the subject to permeate this
2676 2.12 Packet Broadcasting
2678 SILC packets MAY be broadcasted in SILC network. However, only router
2679 server may send or receive broadcast packets. Client and normal server
2680 MUST NOT send broadcast packets and they MUST ignore broadcast packets
2681 if they receive them. Broadcast packets are sent by setting Broadcast
2682 flag to the SILC packet header.
2684 Broadcasting packets means that the packet is sent to all routers in
2685 the SILC network, except to the router that sent the packet. The router
2686 receiving broadcast packet MUST send the packet to its primary route.
2687 The fact that SILC routers may have several router connections can
2688 cause problems, such as race conditions inside the SILC network, if
2689 care is not taken when broadcasting packets. Router MUST NOT send
2690 the broadcast packet to any other route except to its primary route.
2692 If the primary route of the router is the original sender of the packet
2693 the packet MUST NOT be sent to the primary route. This may happen
2694 if router has several router connections and some other router uses
2695 the router as its primary route.
2697 Routers use broadcast packets to broadcast for example information
2698 about newly registered clients, servers, channels etc. so that all the
2699 routers may keep these informations up to date.
2703 3 Security Considerations
2705 Security is central to the design of this protocol, and these security
2706 considerations permeate the specification. Common security considerations
2707 such as keeping private keys truly private and using adequate lengths for
2708 symmetric and asymmetric keys must be followed in order to maintain the
2709 security of this protocol.
2715 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2716 Protocol Specification", Internet Draft, April 2001.
2718 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2719 Protocols", Internet Draft, April 2001.
2721 [SILC4] Riikonen, P., "SILC Commands", Internet Draft, April 2001.
2723 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2726 [IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
2729 [IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
2732 [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
2735 [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
2738 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2741 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2744 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2747 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2748 Infrastructure, Certificate and CRL Profile", RFC 2459,
2751 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2752 John Wiley & Sons, New York, NY, 1996.
2754 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2757 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2758 RFC 2412, November 1998.
2760 [ISAKMP] Maughan D., et al, "Internet Security Association and
2761 Key Management Protocol (ISAKMP)", RFC 2408, November
2764 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2765 (IKE)", RFC 2409, November 1998.
2767 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2768 Authentication", RFC 2104, February 1997.
2770 [PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
2771 Specifications, Version 2.0", RFC 2437, October 1998.
2773 [RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate
2774 Requirement Levels", BCP 14, RFC 2119, March 1997.
2782 Snellmanninkatu 34 A 15
2786 EMail: priikone@silcnet.org
2788 This Internet-Draft expires XXX
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