8 .ds RF FORMFEED[Page %]
17 Network Working Group P. Riikonen
19 draft-riikonen-silc-pp-05.txt XXX
26 <draft-riikonen-silc-pp-05.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
73 1 Introduction .................................................. 3
74 1.1 Requirements Terminology .................................. 4
75 2 SILC Packet Protocol .......................................... 4
76 2.1 SILC Packet ............................................... 4
77 2.2 SILC Packet Header ........................................ 5
78 2.3 SILC Packet Types ......................................... 7
79 2.3.1 SILC Packet Payloads ................................ 16
80 2.3.2 Generic payloads .................................... 16
81 2.3.2.1 ID Payload .................................. 17
82 2.3.2.2 Argument Payload ............................ 18
83 2.3.2.3 Channel Payload ............................. 18
84 2.3.2.4 Public Key Payload .......................... 19
85 2.3.3 Disconnect Payload .................................. 20
86 2.3.4 Success Payload ..................................... 21
87 2.3.5 Failure Payload ..................................... 21
88 2.3.6 Reject Payload ...................................... 22
89 2.3.7 Notify Payload ...................................... 22
90 2.3.8 Error Payload ....................................... 28
91 2.3.9 Channel Message Payload ............................. 29
92 2.3.10 Channel Key Payload ................................ 32
93 2.3.11 Private Message Payload ............................ 34
94 2.3.12 Private Message Key Payload ........................ 35
95 2.3.13 Command Payload .................................... 37
96 2.3.14 Command Reply Payload .............................. 38
97 2.3.15 Connection Auth Request Payload .................... 38
98 2.3.16 New ID Payload ..................................... 39
99 2.3.17 New Client Payload ................................. 40
100 2.3.18 New Server Payload ................................. 41
101 2.3.19 New Channel Payload ................................ 42
102 2.3.20 Key Agreement Payload .............................. 43
103 2.3.21 Resume Router Payload .............................. 44
104 2.3.22 File Transfer Payload .............................. 44
105 2.4 SILC ID Types ............................................. 46
106 2.5 Packet Encryption And Decryption .......................... 46
107 2.5.1 Normal Packet Encryption And Decryption ............. 46
108 2.5.2 Channel Message Encryption And Decryption ........... 47
109 2.5.3 Private Message Encryption And Decryption ........... 48
110 2.6 Packet MAC Generation ..................................... 48
111 2.7 Packet Padding Generation ................................. 49
112 2.8 Packet Compression ........................................ 50
113 2.9 Packet Sending ............................................ 50
114 2.10 Packet Reception ......................................... 51
115 2.11 Packet Routing ........................................... 51
116 2.12 Packet Broadcasting ...................................... 52
117 3 Security Considerations ....................................... 53
118 4 References .................................................... 53
119 5 Author's Address .............................................. 54
125 Figure 1: Typical SILC Packet
126 Figure 2: SILC Packet Header
128 Figure 4: Argument Payload
129 Figure 5: Channel Payload
130 Figure 6: Public Key Payload
131 Figure 7: Disconnect Payload
132 Figure 8: Success Payload
133 Figure 9: Failure Payload
134 Figure 10: Reject Payload
135 Figure 11: Notify Payload
136 Figure 12: Error Payload
137 Figure 13: Channel Message Payload
138 Figure 14: Channel Key Payload
139 Figure 15: Private Message Payload
140 Figure 16: Private Message Key Payload
141 Figure 17: Command Payload
142 Figure 18: Connection Auth Request Payload
143 Figure 19: New Client Payload
144 Figure 20: New Server Payload
145 Figure 21: Key Agreement Payload
146 Figure 22: Resume Router Payload
147 Figure 23: File Transfer Payload
153 This document describes a Packet Protocol used in the Secure Internet
154 Live Conferencing (SILC) protocol specified in the Secure Internet Live
155 Conferencing, Protocol Specification Internet Draft [SILC1]. This
156 protocol describes the packet types and packet payloads which defines
157 the contents of the packets. The protocol provides secure binary packet
158 protocol that assures that the contents of the packets are secured and
161 The basis of SILC protocol relies in the SILC packets and it is with
162 out a doubt the most important part of the protocol. It is also probably
163 the most complicated part of the protocol. Packets are used all the
164 time in the SILC network to send messages, commands and other information.
165 All packets in SILC network are always encrypted and their integrity
166 is assured by computed MACs. The protocol defines several packet types
167 and packet payloads. Each packet type usually has a specific packet
168 payload that actually defines the contents of the packet. Each packet
169 also includes a default SILC Packet Header that provides sufficient
170 information about the origin of the packet and destination of the
175 1.1 Requirements Terminology
177 The keywords MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED,
178 MAY, and OPTIONAL, when they appear in this document, are to be
179 interpreted as described in [RFC2119].
183 2 SILC Packet Protocol
188 SILC packets deliver messages from sender to receiver securely by
189 encrypting important fields of the packet. The packet consists of
190 default SILC Packet Header, Padding, Packet Payload data, and, packet
193 The following diagram illustrates typical SILC packet.
198 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
199 | n bytes | 1 - n bytes | n bytes | n bytes
200 | SILC Header | Padding | Data Payload | MAC
201 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
205 Figure 1: Typical SILC Packet
208 SILC Header is always the first part of the packet and its purpose
209 is to provide information about the packet. It provides for example
210 the packet type, origin of the packet and the destination of the packet.
211 The header is variable in length. See the following section for
212 description of SILC Packet header. Packets without SILC header or
213 with malformed SILC header MUST be dropped.
215 Padding follows the packet header. The purpose of the padding is to
216 make the packet multiple by eight (8) or by the block size of the
217 cipher used in the encryption, which ever is larger. The maximum
218 length of padding is currently 128 bytes. The padding is always
219 encrypted. The padding is applied always, even if the packet is
220 not encrypted. See the section 2.7 Padding Generation for more
221 detailed information.
223 Data payload area follows padding and it is the actual data of the
224 packet. The packet data is the packet payloads defined in this
225 protocol. The data payload area is always encrypted.
227 The last part of SILC packet is the packet MAC that assures the
228 integrity of the packet. The MAC is always computed from the packet
229 before the encryption is applied to the packet. If compression is used
230 in the packet the MAC is computed after the compression has been
231 applied. The compression, on the other hand, is always applied before
232 encryption. See more details in the section 2.6 Packet MAC Generation.
234 All fields in all packet payloads are always in MSB (most significant
239 2.2 SILC Packet Header
241 The SILC packet header is applied to all SILC packets and it is
242 variable in length. The purpose of SILC Packet header is to provide
243 detailed information about the packet. The receiver of the packet
244 uses the packet header to parse the packet and gain other relevant
245 parameters of the packet.
247 The following diagram represents the SILC packet header.
252 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
253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
254 | Payload Length | Flags | Packet Type |
255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
256 | Pad Length | RESERVED | Source ID Len | Dest ID Len |
257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
273 Figure 2: SILC Packet Header
277 o Payload Length (2 bytes) - Is the length of the packet
278 not including the padding of the packet.
280 o Flags (1 byte) - Indicates flags to be used in packet
281 processing. Several flags may be set by ORing the flags
284 The following flags are reserved for this field:
289 In this case the field is ignored.
292 Private Message Key 0x01
294 Indicates that the packet must include private
295 message that is encrypted using private key set by
296 client. Servers does not know anything about this
297 key and this causes that the private message is
298 not handled by the server at all, it is just
299 passed along. See section 2.5.3 Private Message
300 Encryption And Decryption for more information.
305 Indicates that the packet consists of list of
306 packet payloads indicated by the Packet Type field.
307 The payloads are added one after the other. Note that
308 there are packet types that must not be used as
309 list. Parsing of list packet is done by calculating
310 the length of each payload and parsing them one by
316 Marks the packet to be broadcasted. Client cannot
317 send broadcast packet and normal server cannot send
318 broadcast packet. Only router server may send broadcast
319 packet. The router receiving of packet with this flag
320 set MUST send (broadcast) the packet to its primary
321 route. If router has several router connections the
322 packet may be sent only to the primary route. See
323 section 2.12 Packet Broadcasting for description of
331 o Packet Type (1 byte) - Is the type of the packet. Receiver
332 uses this field to parse the packet. See section 2.3
333 SILC Packets for list of defined packet types.
335 o Pad Length (1 byte) - Indicates the length of the padding
336 applied after the SILC Packet header. Maximum length for
337 padding is 128 bytes.
339 o RESERVED (1 byte) - Reserved field and must include a
342 o Source ID Length (1 byte) - Indicates the length of the
343 Source ID field in the header, not including this or any
346 o Destination ID Length (1 byte) - Indicates the length of the
347 Destination ID field in the header, not including this or
350 o Src ID Type (1 byte) - Indicates the type of ID in the
351 Source ID field. See section 2.4 SILC ID Types for
354 o Source ID (variable length) - The actual source ID that
355 indicates which is the original sender of the packet.
357 o Dst ID Type (1 byte) - Indicates the type of ID in the
358 Destination ID field. See section 2.4 SILC ID Types for
361 o Destination ID (variable length) - The actual destination
362 ID that indicates which is the end receiver of the packet.
367 2.3 SILC Packet Types
369 SILC packet types defines the contents of the packet and it is used by
370 the receiver to parse the packet. The packet type is 8 bits, as a one
371 byte, in length. The range for the packet types are from 0 - 255,
372 where 0 is never sent and 255 is currently reserved for future
373 extensions and MUST NOT be defined to any other purpose. Every SILC
374 specification compliant implementation SHOULD support all of these packet
377 The below list of the SILC Packet types includes reference to the packet
378 payload as well. Packet payloads are the actual packet, that is, the data
379 that the packet consists of. Each packet type defines packet payload
380 which usually may only be sent with the specific packet type.
382 Most of the packets are packets that must be destined directly to entity
383 that is connected to the sender. It is not allowed, for example, for
384 router to send disconnect packet to client that is not directly connected
385 to the router. However, there are some special packet types that may
386 be destined to some entity that the sender has not direct connection
387 with. These packets are for example private message packets, channel
388 message packets, command packets and some other packets that may be
389 broadcasted in the SILC network. If the packet is allowed to be sent to
390 indirectly connected entity it is mentioned separately in the packet
391 description (unless it is obvious as in private and channel message
392 packets). Other packets MUST NOT be sent or accepted, if sent, to
393 indirectly connected entities.
395 List of SILC Packet types are defined as follows.
400 This type is reserved and it is never sent.
403 1 SILC_PACKET_DISCONNECT
405 This packet is sent to disconnect the remote end. Reason of
406 the disconnection is sent inside the packet payload. Client
407 usually does not send this packet.
409 This packet MUST NOT be sent as list and the List flag MUST
412 Payload of the packet: See section 2.3.3 Disconnect Payload
415 2 SILC_PACKET_SUCCESS
417 This packet is sent upon successful execution of some protocol.
418 The status of the success is sent in the packet.
420 This packet MUST NOT be sent as list and the List flag MUST
423 Payload of the packet: See section 2.3.4 Success Payload
426 3 SILC_PACKET_FAILURE
428 This packet is sent upon failure of some protocol. The status
429 of the failure is sent in the packet.
431 This packet MUST NOT be sent as list and the List flag MUST
434 Payload of the packet: See section 2.3.5 Failure Payload
439 This packet MAY be sent upon rejection of some protocol.
440 The status of the rejection is sent in the packet.
442 This packet MUST NOT be sent as list and the List flag MUST
445 Payload of the packet: See section 2.3.6 Reject Payload
450 This packet is used to send notify message, usually from
451 server to client, although it MAY be sent from server to another
452 server as well. Client MUST NOT send this packet. Server MAY
453 send this packet to channel as well when the packet is
454 distributed to all clients on the channel.
456 Payload of the packet: See section 2.3.7 Notify Payload.
461 This packet is sent when an error occurs. Server MAY
462 send this packet. Client MUST NOT send this packet. The
463 client MAY entirely ignore the packet, however, server is
464 most likely to take action anyway. This packet MAY be sent
465 to entity that is indirectly connected to the sender.
467 This packet MUST NOT be sent as list and the List flag MUST
470 Payload of the packet: See section 2.3.8 Error Payload.
473 7 SILC_PACKET_CHANNEL_MESSAGE
475 This packet is used to send messages to channels. The packet
476 includes Channel ID of the channel and the actual message to
477 the channel. Messages sent to the channel are always protected
478 by channel specific keys. Channel Keys are distributed by
479 SILC_PACKET_CHANNEL_KEY packet.
481 This packet MUST NOT be sent as list and the List flag MUST
484 Payload of the packet: See section 2.3.9 Channel Message
488 8 SILC_PACKET_CHANNEL_KEY
490 This packet is used to distribute new key for particular
491 channel. Each channel has their own independent keys that
492 is used to protect the traffic on the channel. Only server
493 may send this packet. This packet MAY be sent to entity
494 that is indirectly connected to the sender.
496 This packet MUST NOT be sent as list and the List flag MUST
499 Payload of the packet: See section 2.3.10 Channel Key Payload
502 9 SILC_PACKET_PRIVATE_MESSAGE
504 This packet is used to send private messages from client
505 to another client. By default, private messages are protected
506 by session keys established by normal key exchange protocol.
507 However, it is possible to use specific key to protect private
508 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
509 agree the key with the remote client. Pre-shared key MAY be
510 used as well if both of the client knows it, however, it needs
511 to be agreed outside SILC. See more of this in [SILC1].
513 This packet MUST NOT be sent as list and the List flag MUST
516 Payload of the packet: See section 2.3.11 Private Message
520 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
522 This packet is used to agree about a key to be used to protect
523 the private messages between two clients. If this is not sent
524 the normal session key is used to protect the private messages
525 inside SILC network. Agreeing to use specific key to protect
526 private messages adds security, as no server between the two
527 clients will be able to decrypt the private message. However,
528 servers inside SILC network are considered to be trusted, thus
529 using normal session key to protect private messages does not
530 degrade security. Whether to agree to use specific keys by
531 default or to use normal session keys by default, is
532 implementation specific issue. See more of this in [SILC1].
534 This packet MUST NOT be sent as list and the List flag MUST
537 Payload of the packet: See section 2.3.12 Private Message
541 11 SILC_PACKET_COMMAND
543 This packet is used to send commands from client to server.
544 Server MAY send this packet to other servers as well. All
545 commands are listed in their own section SILC Command Types
546 in [SILC4]. The contents of this packet is command specific.
547 This packet MAY be sent to entity that is indirectly connected
550 This packet MUST NOT be sent as list and the List flag MUST
553 Payload of the packet: See section 2.3.13 Command Payload
556 12 SILC_PACKET_COMMAND_REPLY
558 This packet is sent as reply to the SILC_PACKET_COMMAND packet.
559 The contents of this packet is command specific. This packet
560 MAY be sent to entity that is indirectly connected to the
563 This packet MUST NOT be sent as list and the List flag MUST
566 Payload of the packet: See section 2.3.14 Command Reply
567 Payload and section 2.3.13 Command
573 13 SILC_PACKET_KEY_EXCHANGE
575 This packet is used to start SILC Key Exchange Protocol,
576 described in detail in [SILC3].
578 This packet MUST NOT be sent as list and the List flag MUST
581 Payload of the packet: Payload of this packet is described
582 in the section SILC Key Exchange
583 Protocol and its sub sections in
587 14 SILC_PACKET_KEY_EXCHANGE_1
589 This packet is used as part of the SILC Key Exchange Protocol.
591 This packet MUST NOT be sent as list and the List flag MUST
594 Payload of the packet: Payload of this packet is described
595 in the section SILC Key Exchange
596 Protocol and its sub sections in
600 15 SILC_PACKET_KEY_EXCHANGE_2
602 This packet is used as part of the SILC Key Exchange Protocol.
604 This packet MUST NOT be sent as list and the List flag MUST
607 Payload of the packet: Payload of this packet is described
608 in the section SILC Key Exchange
609 Protocol and its sub sections in
613 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
615 This packet is used to request the authentication method to
616 be used in the SILC Connection Authentication Protocol. If
617 initiator of the protocol does not know the mandatory
618 authentication method this packet MAY be used to determine it.
620 The party receiving this payload MUST respond with the same
621 packet including the mandatory authentication method.
623 This packet MUST NOT be sent as list and the List flag MUST
626 Payload of the packet: See section 2.3.15 Connection Auth
632 17 SILC_PACKET_CONNECTION_AUTH
634 This packet is used to start and perform the SILC Connection
635 Authentication Protocol. This protocol is used to authenticate
636 the connecting party. The protocol is described in detail in
639 This packet MUST NOT be sent as list and the List flag MUST
642 Payload of the packet: Payload of this packet is described
643 in the section SILC Authentication
644 Protocol and it sub sections in [SILC].
647 18 SILC_PACKET_NEW_ID
649 This packet is used to distribute new ID's from server to
650 router and from router to all routers in the SILC network.
651 This is used when for example new client is registered to
652 SILC network. The newly created ID's of these operations are
653 distributed by this packet. Only server may send this packet,
654 however, client MUST be able to receive this packet. This
655 packet MAY be sent to entity that is indirectly connected
658 Payload of the packet: See section 2.3.16 New ID Payload
661 19 SILC_PACKET_NEW_CLIENT
663 This packet is used by client to register itself to the
664 SILC network. This is sent after key exchange and
665 authentication protocols has been completed. Client sends
666 various information about itself in this packet.
668 This packet MUST NOT be sent as list and the List flag MUST
671 Payload of the packet: See section 2.3.17 New Client Payload
674 20 SILC_PACKET_NEW_SERVER
676 This packet is used by server to register itself to the
677 SILC network. This is sent after key exchange and
678 authentication protocols has been completed. Server sends
679 this to the router it connected to, or, if router was
680 connecting, to the connected router. Server sends its
681 Server ID and other information in this packet. The client
682 MUST NOT send or receive this packet.
684 This packet MUST NOT be sent as list and the List flag MUST
687 Payload of the packet: See section 2.3.18 New Server Payload
690 21 SILC_PACKET_NEW_CHANNEL
692 This packet is used to notify routers about newly created
693 channel. Channels are always created by the router and it MUST
694 notify other routers about the created channel. Router sends
695 this packet to its primary route. Client MUST NOT send this
696 packet. This packet MAY be sent to entity that is indirectly
697 connected to the sender.
699 Payload of the packet: See section 2.3.19 New Channel Payload
704 This packet is used to indicate that re-key must be performed
705 for session keys. See section Session Key Regeneration in
706 [SILC1] for more information. This packet does not have
709 This packet MUST NOT be sent as list and the List flag MUST
713 23 SILC_PACKET_REKEY_DONE
715 This packet is used to indicate that re-key is performed and
716 new keys must be used hereafter.
718 This packet MUST NOT be sent as list and the List flag MUST
722 24 SILC_PACKET_HEARTBEAT
724 This packet is used by clients, servers and routers to keep the
725 connection alive. It is recommended that all servers implement
726 keepalive actions and perform it to both direction in a link.
727 This packet does not have a payload.
729 This packet MUST NOT be sent as list and the List flag MUST
733 25 SILC_PACKET_KEY_AGREEMENT
735 This packet is used by clients to request key negotiation
736 between another client in the SILC network. If the negotiation
737 is started it is performed using the SKE protocol. The result of
738 the negotiation, the secret key material, can be used for
739 example as private message key. The server and router MUST NOT
742 This packet MUST NOT be sent as list and the List flag MUST
745 Payload of the packet: See section 2.3.20 Key Agreement Payload
748 26 SILC_PACKET_RESUME_ROUTER
750 This packet is used during backup router protocol when the
751 original primary router of the cell comes back online and wishes
752 to resume the position as being the primary router of the cell.
754 Payload of the packet: See section 2.3.21 Resume Router Payload
759 This packet is used to perform an file transfer protocol in the
760 SILC session with some entity in the network. The packet is
761 multi purpose. The packet is used to tell other entity in the
762 network that the sender wishes to perform an file transfer
763 protocol. The packet is also used to actually tunnel the
764 file transfer protocol stream. The file transfer protocol
765 stream is always protected with the SILC packet.
767 This packet MUST NOT be sent as list and the List flag MUST
770 Payload of the packet: See section 2.3.22 File Transfer Payload
775 Currently undefined commands.
780 These packet types are reserved for private use and they will
781 not be defined by this document.
788 This type is reserved for future extensions and currently it
794 2.3.1 SILC Packet Payloads
796 All payloads resides in the main data area of the SILC packet. However
797 all payloads MUST be at the start of the data area after the SILC
798 packet header and padding. All fields in the packet payload are always
799 encrypted, as they reside in the data area of the packet which is
802 Payloads described in this section are common payloads that MUST be
803 accepted anytime during SILC session. Most of the payloads may only
804 be sent with specific packet type which is defined in the description
807 There are a lot of other payloads in the SILC as well. However, they
808 are not common in the sense that they could be sent at any time.
809 These payloads are not described in this section. These are payloads
810 such as SILC Key Exchange payloads and so on. These are described
811 in [SILC1], [SILC3] and [SILC4].
815 2.3.2 Generic payloads
817 This section describes generic payloads that are not associated to any
818 specific packet type. They can be used for example inside some other
825 This payload can be used to send an ID. ID's are variable in length
826 thus this payload provides a way to send variable length ID's.
828 The following diagram represents the ID Payload.
833 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
834 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
835 | ID Type | ID Length |
836 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
840 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
848 o ID Type (2 bytes) - Indicates the type of the ID. See
849 section 2.4 SILC ID Types for list of defined ID types.
851 o ID Length (2 bytes) - Length of the ID Data area not
852 including the length of any other fields in the payload.
854 o ID Data (variable length) - The actual ID data.
859 2.3.2.2 Argument Payload
861 Argument Payload is used to set arguments for any packet payload that
862 needs and supports arguments, such as commands. Number of arguments
863 associated with a packet MUST be indicated by the packet payload which
864 needs the arguments. Argument Payloads MUST always reside right after
865 the packet payload needing the arguments. Incorrect amount of argument
866 payloads MUST cause rejection of the packet.
874 The following diagram represents the Argument Payload.
879 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
880 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
881 | Payload Length | Argument Type | |
882 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
886 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
890 Figure 4: Argument Payload
894 o Payload Length (2 bytes) - Length of the argument payload data
895 area not including the length of any other fields in the
898 o Argument Type (1 byte) - Indicates the type of the argument.
899 Every argument may have a specific type that MUST be defined
900 by the packet payload needing the argument. For example
901 every command specify a number for each argument that maybe
902 associated with the command. By using this number the receiver
903 of the packet knows what type of argument this is. If there is
904 no specific argument type this field is set to zero (0).
906 o Argument Data (variable length) - Argument data.
911 2.3.2.3 Channel Payload
913 Generic Channel Payload may be used to send information about channel,
914 its name, the Channel ID and a mode.
916 The following diagram represents the Channel Payload.
932 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
933 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
934 | Channel Name Length | |
935 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
939 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
940 | Channel ID Length | |
941 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
945 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
947 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
951 Figure 5: New Channel Payload
955 o Channel Name Length (2 bytes) - Length of the channel name
958 o Channel Name (variable length) - The name of the channel.
960 o Channel ID Length (2 bytes) - Length of the Channel ID field.
962 o Channel ID (variable length) - The Channel ID.
964 o Mode Mask (4 bytes) - A mode. This can be the mode of the
965 channel but it can also be the mode of the client on the
966 channel. The contents of this field is dependent of the
967 usage of this payload. The usage is defined separately
968 when this payload is used. This is a 32 bit MSB first value.
973 2.3.2.4 Public Key Payload
975 Generic Public Key Payload may be used to send different types of
976 public keys and certificates.
978 The following diagram represents the Public Key Payload.
987 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
988 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
989 | Public Key Length | Public Key Type |
990 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
992 ~ Public Key of the party (or certificate) ~
994 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
998 Figure 6: Public Key Payload
1002 o Public Key Length (2 bytes) - The length of the Public Key
1003 (or certificate) field, not including any other field.
1005 o Public Key Type (2 bytes) - The public key (or certificate)
1006 type. This field indicates the type of the public key in
1007 the packet. See the [SILC3] for defined public key types.
1009 o Public Key (or certificate) (variable length) - The
1010 public key or certificate.
1015 2.3.3 Disconnect Payload
1017 Disconnect payload is sent upon disconnection. The payload is simple;
1018 reason of disconnection is sent to the disconnected party.
1020 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
1021 MUST NOT be sent in any other packet type. The following diagram
1022 represents the Disconnect Payload.
1028 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
1029 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1031 ~ Disconnect Message ~
1033 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1037 Figure 7: Disconnect Payload
1043 o Disconnect Message (variable length) - Human readable
1044 reason of the disconnection.
1049 2.3.4 Success Payload
1051 Success payload is sent when some protocol execution is successfully
1052 completed. The payload is simple; indication of the success is sent.
1053 This may be any data, including binary or human readable data.
1058 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
1059 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1061 ~ Success Indication ~
1063 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1067 Figure 8: Success Payload
1071 o Success Indication (variable length) - Indication of
1072 the success. This may be for example some flag that
1073 indicates the protocol and the success status or human
1074 readable success message. The true length of this
1075 payload is available by calculating it from the SILC
1082 2.3.5 Failure Payload
1084 This is opposite of Success Payload. Indication of failure of
1085 some protocol is sent in the payload.
1091 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
1092 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1094 ~ Failure Indication ~
1096 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1100 Figure 9: Failure Payload
1104 o Failure Indication (variable length) - Indication of
1105 the failure. This may be for example some flag that
1106 indicates the protocol and the failure status or human
1107 readable failure message. The true length of this
1108 payload is available by calculating it from the SILC
1114 2.3.6 Reject Payload
1116 This payload is sent when some protocol is rejected to be executed.
1117 Other operations MAY send this as well that was rejected. The
1118 indication of the rejection is sent in the payload. The indication
1119 may be binary or human readable data.
1125 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
1126 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1128 ~ Reject Indication ~
1130 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1134 Figure 10: Reject Payload
1138 o Reject Indication (variable length) - Indication of
1139 the rejection. This maybe for example some flag that
1140 indicates the protocol and the rejection status or human
1141 readable rejection message. The true length of this
1142 payload is available by calculating it from the SILC
1148 2.3.7 Notify Payload
1150 Notify payload is used to send notify messages. The payload is usually
1151 sent from server to client, however, server MAY send it to another
1152 server as well. This payload MAY also be sent to a channel. Client
1153 MUST NOT send this payload. The receiver of this payload MAY ignore
1154 the contents of the payload, however, notify message SHOULD be audited.
1156 The payload may only be sent with SILC_PACKET_NOTIFY packet. It MUST
1157 not be sent in any other packet type. The following diagram represents
1166 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
1167 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1168 | Notify Type | Payload Length |
1169 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1175 Figure 11: Notify Payload
1179 o Notify Type (2 bytes) - Indicates the type of the notify
1182 o Payload Length (2 bytes) - Length of the entire Notify Payload
1183 including any associated Argument Payloads.
1185 o Argument Nums (2 bytes) - Indicates the number of Argument
1186 Payloads associated to this payload. Notify types may define
1187 arguments to be send along the notify message.
1190 The following list of currently defined notify types. The format for
1191 notify arguments is same as in SILC commands described in [SILC4].
1192 Also, all ID's sent in arguments are sent inside ID Payload.
1195 0 SILC_NOTIFY_TYPE_NONE
1197 If no specific notify type apply for the notify message this type
1201 Arguments: (1) <message>
1203 The <message> is implementation specific free text string.
1204 Receiver MAY ignore this message.
1207 1 SILC_NOTIFY_TYPE_INVITE
1209 Sent when an client is invited to a channel. This is also sent
1210 when the invite list of the channel is changed. This notify type
1211 is sent between routers and if an client was invited, to the
1212 client as well. In this case the packet is destined to the client.
1215 Arguments: (1) <Channel ID> (2) <channel name>
1216 (3) [<sender Client ID>] (4) [<adding client>]
1217 (5) [<removing client>]
1219 The <Channel ID> is the channel. The <channel name> is the name
1220 of the channel and is provided because the client which receives
1221 this notify packet may not have a way to resolve the name of the
1222 channel from the <Channel ID>. The <sender Client ID> is the
1223 Client ID which invited the client to the channel. The <adding
1224 client> and the <removing client> indicates the added or removed
1225 client from the channel's invite list. The format of the <adding
1226 client> and the <removing client> is defined in the [SILC4] with
1227 SILC_COMMAND_INVITE command.
1229 The <adding client> and <removing client> MUST NOT be sent when
1230 the packet is destined to a client.
1233 2 SILC_NOTIFY_TYPE_JOIN
1235 Sent when client has joined to a channel. The server MUST
1236 distribute this type only to the local clients on the channel
1237 and then send it to its primary router. The router or server
1238 receiving the packet distributes this type to the local clients
1239 on the channel and broadcast it to the network.
1242 Arguments: (1) [<Client ID>] (2) <Channel ID>
1244 The <Client ID> is the client that joined to the channel indicated
1245 by the <Channel ID>.
1248 3 SILC_NOTIFY_TYPE_LEAVE
1250 Sent when client has left a channel. The server must distribute
1251 this type only to the local clients on the channel and then send
1252 it to its primary router. The router or server receiving the
1253 packet distributes this type to the local clients on the channel
1254 and broadcast it to the network.
1257 Arguments: (1) <Client ID>
1259 The <Client ID> is the client which left the channel.
1262 4 SILC_NOTIFY_TYPE_SIGNOFF
1264 Sent when client signoff from SILC network. The server MUST
1265 distribute this type only to the local clients on the channel and
1266 then send it to its primary router. The router or server receiving
1267 the packet distributes this type to the local clients on the
1268 channel and broadcast it to the network.
1271 Arguments: (1) <Client ID> (2) <message>
1273 The <Client ID> is the client which left SILC network. The
1274 <message> is free text string indicating the reason of the signoff.
1277 5 SILC_NOTIFY_TYPE_TOPIC_SET
1279 Sent when topic is set/changed on a channel. This type must be
1280 sent only to the clients which is joined on the channel which
1281 topic was set or changed.
1284 Arguments: (1) <ID Payload> (2) <topic>
1286 The <ID Payload> is the ID of the entity who set the topic. It
1287 usually is Client ID but it can be Server ID and Channel ID as well.
1290 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1292 Sent when client changes nick on a channel. The server MUST
1293 distribute this type only to the local clients on the channel
1294 and then send it to its primary router. The router or server
1295 receiving the packet distributes this type to the local clients
1296 on the channel and broadcast it to the network.
1299 Arguments: (1) <Old Client ID> (2) <New Client ID>
1302 The <Old Client ID> is the old ID of the client which changed
1303 the nickname. The <New Client ID> is the new ID generated by
1304 the change of the nickname. The <nickname> is the new nickname.
1307 7 SILC_NOTIFY_TYPE_CMODE_CHANGE
1309 Sent when channel mode has changed. This type MUST be sent only
1310 to the clients which is joined on the channel which mode was
1314 Arguments: (1) <ID Payload> (2) <mode mask>
1315 (3) [<cipher>] (4) <[hmac>]
1318 The <ID Payload> is the ID (usually Client ID but it can be
1319 Server ID as well when the router is enforcing channel mode
1320 change) of the entity which changed the mode. The <mode mask>
1321 is the new mode mask of the channel. The client can safely
1322 ignore the <cipher> argument since the SILC_PACKET_CHANNEL_KEY
1323 packet will force the new channel key change anyway. The <hmac>
1324 argument is important since the client is responsible of setting
1325 the new HMAC and the hmac key into use. The <passphrase> is
1326 the passphrase of the channel, if it was now set.
1329 8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
1331 Sent when user mode on channel has changed. This type MUST be
1332 sent only to the clients which is joined on the channel where
1333 the target client is on.
1336 Arguments: (1) <ID Payload> (2) <mode mask>
1337 (3) <Target Client ID>
1339 The <ID Payload> is the ID (usually Client ID but it can be
1340 Server ID as well when the router is enforcing user's mode
1341 change) of the entity which changed the mode. The <mode mask>
1342 is the new mode mask of the channel. The <Target Client ID>
1343 is the client which mode was changed.
1346 9 SILC_NOTIFY_TYPE_MOTD
1348 Sent when Message of the Day (motd) is sent to a client.
1351 Arguments: (1) <motd>
1353 The <motd> is the Message of the Day.
1356 10 SILC_NOTIFY_TYPE_CHANNEL_CHANGE
1358 Sent when channel's ID has changed for a reason or another.
1359 This is sent by normal server to the client. This can also be
1360 sent by router to other server to force the Channel ID change.
1361 The Channel ID MUST be changed to use the new one. When sent
1362 to clients, this type MUST be sent only to the clients which is
1363 joined on the channel.
1366 Arguments: (1) <Old Channel ID> (2) <New Channel ID>
1368 The <Old Channel ID> is the channel's old ID and the <New
1369 Channel ID> is the new one that MUST replace the old one.
1372 11 SILC_NOTIFY_TYPE_SERVER_SIGNOFF
1374 Sent when server quits SILC network. Those clients from this
1375 server that are on channels must be removed from the channel.
1378 Arguments: (1) <Server ID> (n) [<Client ID>] [...]
1380 The <Server ID> is the server's ID. The rest of the arguments
1381 are the Client ID's of the client's which are coming from this
1382 server and are thus quitting the SILC network also. If the
1383 maximum number of arguments are reached another
1384 SILC_NOTIFY_TYPE_SERVER_SIGNOFF notify packet MUST be sent.
1385 When this notify packet is sent between routers the Client ID's
1386 MAY be omitted. Server receiving the Client ID's in the payload
1387 may use them directly to remove the client.
1390 12 SILC_NOTIFY_TYPE_KICKED
1392 Sent when a client has been kicked from a channel. This is
1393 sent also to the client which was kicked from the channel.
1394 The client which was kicked from the channel MUST be removed
1395 from the channel. This notify type is always destined to the
1396 channel. The router or server receiving the packet distributes
1397 this type to the local clients on the channel and broadcast it
1401 Arguments: (1) <Client ID> (2) [<comment>]
1402 (3) <Kicker's Client ID>
1404 The <Client ID> is the client which was kicked from the channel.
1405 The kicker may have set the <comment> to indicate the reason for
1406 the kicking. The <Kicker's Client ID> is the kicker.
1409 13 SILC_NOTIFY_TYPE_KILLED
1411 Sent when a client has been killed from the network. This is sent
1412 also to the client which was killed from the network. The client
1413 which was killed from the network MUST be removed from the network.
1414 This notify type is destined directly to the client which was
1415 killed and to channel if the client is on any channel. The router
1416 or server receiving the packet distributes this type to the local
1417 clients on the channel and broadcast it to the network.
1420 Arguments: (1) <Client ID> (2) [<comment>]
1421 (3) <Killer's Client ID>
1423 The <Client ID> is the client which was killed from the network.
1424 The killer may have set the <comment> to indicate the reason for
1425 the killing. The <Killer's Client ID> is the killer.
1428 14 SILC_NOTIFY_TYPE_UMODE_CHANGE
1430 Sent when user's mode in the SILC changes. This type is sent
1431 only between routers as broadcast packet.
1434 Arguments: (1) <Client ID> (2) <mode mask>
1436 The <Client ID> is the client which mode was changed. The
1437 <mode mask> is the new mode mask.
1440 15 SILC_NOTIFY_TYPE_BAN
1442 Sent when the ban list of the channel is changed. This type is
1443 sent only between routers as broadcast packet.
1446 Arguments: (1) <Channel ID> (2) [<adding client>]
1447 (3) [<removing client>]
1449 The <Channel ID> is the channel which ban list was changed. The
1450 <adding client> is used to indicate that a ban was added and the
1451 <removing client> is used to indicate that a ban was removed from
1452 the ban list. The format of the <adding client> and the
1453 <removing client> is defined in the [SILC4] with SILC_COMMAND_BAN
1458 Notify types starting from 16384 are reserved for private notify
1465 Error payload is sent upon error. Error may occur in various
1466 conditions when server sends this packet. Client MUST NOT send this
1467 payload but MUST be able to accept it. However, client MAY
1468 totally ignore the contents of the packet as server is going to
1469 take action on the error anyway. However, it is recommended
1470 that the client takes error packet seriously.
1476 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
1477 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1481 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1485 Figure 12: Error Payload
1489 o Error Message (variable length) - Human readable error
1495 2.3.9 Channel Message Payload
1497 Channel messages are the most common messages sent in the SILC.
1498 Channel Message Payload is used to send message to channels. These
1499 messages can only be sent if client has joined to some channel.
1500 Even though this packet is the most common in SILC it is still
1501 special packet. Some special handling on sending and reception
1502 of channel message is required.
1504 Padding MUST be applied into this payload since the payload is
1505 encrypted separately from other parts of the packet with the
1506 channel specific key. Hence the requirement of the padding.
1507 The padding SHOULD be random data. The packet MUST be made
1508 multiple by eight (8) or by the block size of the cipher, which
1511 The SILC header in this packet is encrypted with the session key
1512 of the next receiver of the packet. Nothing else is encrypted
1513 with that key. Thus, the actual packet and padding to be
1514 encrypted with the session key is SILC Header plus padding to it
1515 to make it multiple by eight (8) or multiple by the block size
1516 of the cipher, which ever is larger.
1518 Receiver of the the channel message packet is able to determine
1519 the channel the message is destined to by checking the destination
1520 ID from the SILC Packet header which tells the destination channel.
1521 The original sender of the packet is also determined by checking
1522 the source ID from the header which tells the client which sent
1525 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1526 It MUST NOT be sent in any other packet type. The following diagram
1527 represents the Channel Message Payload.
1529 (*) indicates that the field is not encrypted.
1535 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
1536 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1537 | Message Flags | Message Length |
1538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1542 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1543 | Padding Length | |
1544 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1548 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1552 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1554 ~ Initial Vector * ~
1556 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1560 Figure 13: Channel Message Payload
1564 o Message Flags (2 bytes) - Includes the Message Flags of
1565 the channel messages. The flags can indicate a reason or
1566 purpose for the channel message. Note that the Private
1567 Message Payload use these same Message Flags for the same
1568 purpose. The following Message Flags are defined:
1570 0x0000 SILC_MESSAGE_FLAG_NONE
1572 No specific flags set.
1574 0x0001 SILC_MESSAGE_FLAG_AUTOREPLY
1576 This message is an automatic reply to an earlier
1579 0x0002 SILC_MESSAGE_FLAG_NOREPLY
1581 There should not be reply messages to this
1584 0x0004 SILC_MESSAGE_FLAG_ACTION
1586 The sender is performing an action and the message
1587 is the indication of the action.
1589 0x0008 SILC_MESSAGE_FLAG_NOTICE
1591 The message is for example an informational notice
1594 0x0010 SILC_MESSAGE_FLAG_REQUEST
1596 This is a generic request flag to send request
1597 messages. A separate document should define any
1598 payloads associated to this flag.
1600 0x0020 SILC_MESSAGE_FLAG_SIGNED
1602 This flag indicates that the message is signed
1603 with sender's private key and thus can be verified
1604 by the receiver using the sender's public key. A
1605 separate document should define the detailed procedure
1606 of the signing process and any associated payloads
1609 0x0040 SILC_MESSAGE_FLAG_REPLY
1611 This is a generic reply flag to send a reply to
1612 previously received request. A separate document
1613 should define any payloads associated to this flag.
1615 0x0080 SILC_MESSAGE_FLAG_DATA
1617 This is a generic data flag, indicating that the
1618 message includes some data which can be interpreted
1619 in a specific way. Using this flag any kind of data
1620 can be delivered inside message payload. A separate
1621 document should define how this flag is interpreted
1622 and define any associated payloads.
1624 0x0100 - 0x0800 RESERVED
1626 Reserved for future flags
1628 0x1000 - 0x8000 PRIVATE RANGE
1630 Private range for free use.
1632 o Message Length (2 bytes) - Indicates the length of the
1633 the Message Data field in the payload, not including any
1636 o Message Data (variable length) - The actual message to
1639 o Padding Length (2 bytes) - Indicates the length of the
1640 Padding field in the payload, not including any other
1643 o Padding (variable length) - The padding that MUST be
1644 applied because this payload is encrypted separately from
1645 other parts of the packet.
1647 o MAC (variable length) - The MAC computed from the
1648 Message Length, Message Data, Padding Length and Padding
1649 fields. This protects the integrity of the plaintext
1650 channel message. The receiver can verify from the MAC
1651 whether the message decrypted correctly. Also, if more than
1652 one private key has been set for the channel, the receiver
1653 can verify which of the keys decrypted the message
1654 correctly. Note that, this field is encrypted and MUST
1655 be added to the padding calculation.
1657 o Initial Vector (variable length) - The initial vector
1658 that has been used in packet encryption. It needs to be
1659 used in the packet decryption as well. What this field
1660 includes is implementation issue. However, it is
1661 RECOMMENDED that it would be random data or, perhaps,
1662 a timestamp. It is NOT RECOMMENDED to use zero (0) as an
1663 initial vector. This field is not encrypted. This field
1664 is not included into the padding calculation. Length
1665 of this field equals the cipher's block size. This field
1666 is, however, authenticated.
1671 2.3.10 Channel Key Payload
1673 All traffic in channels are protected by channel specific keys.
1674 Channel Key Payload is used to distribute channel keys to all
1675 clients on the particular channel. Channel keys are sent when
1676 the channel is created, when new user joins to the channel and
1677 whenever a user has left a channel. Server creates the new
1678 channel key and distributes it to the clients by encrypting this
1679 payload with the session key shared between the server and
1680 the client. After that, client starts using the key received
1681 in this payload to protect the traffic on the channel.
1683 The client which is joining to the channel receives its key in the
1684 SILC_COMMAND_JOIN command reply message thus it is not necessary to
1685 send this payload to the entity which sent the SILC_COMMAND_JOIN
1688 Channel keys are cell specific thus every router in the cell have
1689 to create a channel key and distribute it if any client in the
1690 cell has joined to a channel. Channel traffic between cell's
1691 are not encrypted using channel keys, they are encrypted using
1692 normal session keys between two routers. Inside a cell, all
1693 channel traffic is encrypted with the specified channel key.
1694 Channel key should expire periodically, say, in one hour, in
1695 which case new channel key is created and distributed.
1697 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1698 It MUST NOT be sent in any other packet type. The following diagram
1699 represents the Channel Key Payload.
1705 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
1706 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1707 | Channel ID Length | |
1708 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1713 | Cipher Name Length | |
1714 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1718 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1719 | Channel Key Length | |
1720 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1724 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1728 Figure 14: Channel Key Payload
1733 o Channel ID Length (2 bytes) - Indicates the length of the
1734 Channel ID field in the payload, not including any other
1737 o Channel ID (variable length) - The Channel ID of the
1738 channel this key is meant for.
1740 o Cipher Name Length (2 bytes) - Indicates the length of the
1741 Cipher name field in the payload, not including any other
1744 o Cipher Name (variable length) - Name of the cipher used
1745 in the protection of channel traffic. This name is
1746 initially decided by the creator of the channel but it
1747 MAY change during the life time of the channel as well.
1749 o Channel Key Length (2 bytes) - Indicates the length of the
1750 Channel Key field in the payload, not including any other
1753 o Channel Key (variable length) - The actual channel key
1759 2.3.11 Private Message Payload
1761 Private Message Payload is used to send private message between
1762 two clients (or users for that matter). The messages are sent only
1763 to the specified user and no other user inside SILC network is
1764 able to see the message. The message is protected by the session
1765 key established by the SILC Key Exchange Protocol. However,
1766 it is also possible to agree to use a private key to protect
1767 just the private messages. See section 2.3.11 Private Message
1768 Key Payload for detailed description of how to agree to use
1771 If normal session key is used to protect the message, every server
1772 between the sender client and the receiving client MUST decrypt the
1773 packet and always re-encrypt it with the session key of the next
1774 receiver of the packet. See section Client To Client in [SILC1].
1776 When private key is used to protect the message, servers between
1777 the sender and the receiver needs not to decrypt/re-encrypt the
1778 packet. Section Client To Client in [SILC1] gives example of this
1781 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1782 packet. It MUST NOT be sent in any other packet type. The following
1783 diagram represents the Private Message Payload.
1795 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
1796 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1797 | Message Flags | Message Data Length |
1798 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1802 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1806 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1810 Figure 15: Private Message Payload
1814 o Message Flags (2 bytes) - This field includes the Message
1815 Flags of the private message. They can indicate a different
1816 reason or purpose for the private message. See the section
1817 2.3.9 Channel Message Payload for defined flags. Note that
1818 the Channel Message Payload use the same flags for the
1821 o Message Data Length (2 bytes) - Indicates the length of the
1822 Message Data field, not includes any other field.
1824 o Message Data (variable length) - The actual message to
1825 the client. Rest of the packet is reserved for the message
1828 o Padding (variable length) - This field is present only
1829 when the private message payload is encrypted with private
1830 message key. In this case the padding is applied to make
1831 the payload multiple by eight (8), or by the block size of
1832 the cipher, which ever is larger. When encrypted with
1833 normal session keys, this field MUST NOT be included.
1838 2.3.12 Private Message Key Payload
1840 This payload is used to send key from client to another client that
1841 is going to be used to protect the private messages between these
1842 two clients. If this payload is not sent normal session key
1843 established by the SILC Key Exchange Protocol is used to protect
1844 the private messages.
1846 This payload may only be sent by client to another client. Server
1847 MUST NOT send this payload at any time. After sending this payload
1848 the sender of private messages must set the Private Message Key
1849 flag into SILC Packet Header.
1851 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1852 packet. It MUST NOT be sent in any other packet type. The following
1853 diagram represents the Private Message Key Payload.
1859 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
1860 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1861 | Private Message Key Length | |
1862 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1864 ~ Private Message Key ~
1866 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1867 | Cipher Name Length | |
1868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1872 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1876 Figure 16: Private Message Key Payload
1882 o Private Message Key Length (2 bytes) - Indicates the length
1883 of the Private Message Key field in the payload, not including
1886 o Private Message Key (variable length) - The actual private
1887 message key material.
1889 o Cipher Name Length (2 bytes) - Indicates the length of the
1890 Cipher Name field in the payload, not including any other
1893 o Cipher Name (variable length) - Name of the cipher to use
1894 in the private message encryption. If this field does not
1895 exist then the default cipher of the SILC protocol is used.
1896 See the [SILC1] for defined ciphers.
1902 2.3.13 Command Payload
1904 Command Payload is used to send SILC commands from client to server.
1905 Also server MAY send commands to other servers. The following diagram
1906 represents the Command Payload.
1912 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
1913 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1914 | Payload Length | SILC Command | Arguments Num |
1915 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1916 | Command Identifier |
1917 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1921 Figure 17: Command Payload
1925 o Payload Length (2 bytes) - Length of the entire command
1926 payload including any command argument payloads associated
1929 o SILC Command (1 byte) - Indicates the SILC command. This MUST
1930 be set to non-zero value. If zero (0) value is found in this
1931 field the packet MUST be discarded.
1933 o Arguments Num (1 byte) - Indicates the number of arguments
1934 associated with the command. If there are no arguments this
1935 field is set to zero (0). The arguments MUST follow the
1936 command payload. See section 2.3.2.2 for definition of the
1939 o Command Identifier (2 bytes) - Identifies this command at the
1940 sender's end. The entity which replies to this command MUST
1941 set the value found from this field into the Command Payload
1942 used to send the reply to the sender. This way the sender
1943 can identify which command reply belongs to which originally
1944 sent command. What this field includes is implementation
1945 issue but it is RECOMMENDED that wrapping counter value is
1946 used in the field. Value zero (0) in this field means that
1947 no specific value is set.
1950 See [SILC4] for detailed description of different SILC commands,
1951 their arguments and their reply messages.
1957 2.3.14 Command Reply Payload
1959 Command Reply Payload is used to send replies to the commands. The
1960 Command Reply Payload is identical to the Command Payload thus see
1961 the upper section for the Command Payload specification.
1963 The entity which sends the reply packet MUST set the Command Identifier
1964 field in the reply packet's Command Payload to the value it received
1965 in the original command packet.
1967 See SILC Commands in [SILC4] for detailed description of different
1968 SILC commands, their arguments and their reply messages.
1972 2.3.15 Connection Auth Request Payload
1974 Client MAY send this payload to server to request the authentication
1975 method that must be used in authentication protocol. If client knows
1976 this information beforehand this payload is not necessary to be sent.
1977 Server performing authentication with another server MAY also send
1978 this payload to request the authentication method. If the connecting
1979 server already knows this information this payload is not necessary
1982 Server receiving this request MUST reply with same payload sending
1983 the mandatory authentication method. Algorithms that may be required
1984 to be used by the authentication method are the ones already
1985 established by the SILC Key Exchange protocol. See section Key
1986 Exchange Start Payload in [SILC3] for detailed information.
1988 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1989 packet. It MUST NOT be sent in any other packet type. The following
1990 diagram represents the Connection Auth Request Payload.
1996 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
1997 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1998 | Connection Type | Authentication Method |
1999 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2003 Figure 18: Connection Auth Request Payload
2007 o Connection Type (2 bytes) - Indicates the type of the
2008 connection. The following connection types are defined:
2015 If any other type is found in this field the packet MUST be
2016 discarded and the authentication MUST be failed.
2018 o Authentication Method (2 bytes) - Indicates the authentication
2019 method to be used in the authentication protocol. The following
2020 authentication methods are defined:
2023 1 password (mandatory)
2024 2 public key (mandatory)
2026 If any other type is found in this field the packet MUST be
2027 discarded and the authentication MUST be failed. If this
2028 payload is sent as request to receive the mandatory
2029 authentication method this field MUST be set to zero (0),
2030 indicating that receiver should send the mandatory
2031 authentication method. The receiver sending this payload
2032 to the requesting party, MAY also set this field to zero (0)
2033 to indicate that authentication is not required. In this
2034 case authentication protocol still MUST be started but
2035 server is most likely to respond with SILC_PACKET_SUCCESS
2041 2.3.16 New ID Payload
2043 New ID Payload is a multipurpose payload. It is used to send newly
2044 created ID's from clients and servers. When client connects to server
2045 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
2046 packet, server replies with this packet by sending the created ID for
2047 the client. Server always creates the ID for the client.
2049 This payload is also used when server tells its router that new client
2050 has registered to the SILC network. In this case the server sends
2051 the Client ID of the client to the router. Similarly when router
2052 distributes information to other routers about the client in the SILC
2053 network this payload is used.
2055 Also, when server connects to router, router uses this payload to inform
2056 other routers about new server in the SILC network. However, every
2057 server (or router) creates their own ID's thus the ID distributed by
2058 this payload is not created by the distributor in this case. Servers
2059 create their own ID's. Server registers itself to the network by
2060 sending SILC_PACKET_NEW_SERVER to the router it connected to. The case
2061 is same when router connects to another router.
2063 However, this payload MUST NOT be used to send information about new
2064 channels. New channels are always distributed by sending the dedicated
2065 SILC_PACKET_NEW_CHANNEL packet.
2067 Thus, this payload is very important and used every time when some
2068 new entity is registered to the SILC network. Client MUST NOT send this
2069 payload. Both client and server (and router) MAY receive this payload.
2071 The packet uses generic ID Payload as New ID Payload. See section
2072 2.3.2.1 for generic ID Payload.
2076 2.3.17 New Client Payload
2078 When client is connected to the server, keys has been exchanged and
2079 connection has been authenticated client MUST register itself to the
2080 server. Client's first packet after key exchange and authentication
2081 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
2082 the relevant information about the connected user. Server creates a new
2083 client ID for the client when received this payload and sends it to the
2084 client in New ID Payload.
2086 This payload sends username and real name of the user on the remote host
2087 which is connected to the SILC server with SILC client. The server
2088 creates the client ID according the information sent in this payload.
2089 The nickname of the user becomes the username sent in this payload.
2090 However, client should call NICK command after sending this payload to
2091 set the real nickname of the user which is then used to create new
2094 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
2095 MUST NOT be sent in any other packet type. The following diagram
2096 represents the New Client Payload.
2113 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
2114 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2115 | Username Length | |
2116 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2120 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2121 | Real Name Length | |
2122 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2126 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2130 Figure 19: New Client Payload
2134 o Username Length (2 bytes) - Length of the Username field.
2136 o Username (variable length) - The username of the user on
2137 the host where connecting to the SILC server.
2139 o Real Name Length (2 bytes) - Length of the Real Name field.
2141 o Real Name (variable length) - The real name of the user
2142 on the host where connecting to the SILC server.
2147 2.3.18 New Server Payload
2149 This payload is sent by server when it has completed successfully both
2150 key exchange and connection authentication protocols. The server
2151 MUST register itself to the SILC Network by sending this payload.
2152 The first packet after these key exchange and authentication protocols
2153 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
2154 of the server that it has created by itself. It also includes a
2155 name of the server that is associated to the Server ID.
2157 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
2158 MUST NOT be sent in any other packet type. The following diagram
2159 represents the New Server Payload.
2168 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
2169 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2170 | Server ID Length | |
2171 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2175 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2176 | Server Name Length | |
2177 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2181 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2185 Figure 20: New Server Payload
2189 o Server ID Length (2 bytes) - Length of the Server ID Data
2192 o Server ID Data (variable length) - The actual Server ID
2195 o Server Name Length (2 bytes) - Length of the server name
2198 o Server Name (variable length) - The server name.
2203 2.3.19 New Channel Payload
2205 Information about newly created channel is broadcasted to all routers
2206 in the SILC network by sending this packet payload. Channels are
2207 created by router of the cell. Server never creates channels unless
2208 it is a standalone server and it does not have router connection,
2209 in this case server acts as router. Normal server send JOIN command
2210 to the router (after it has received JOIN command from client) which
2211 then processes the command and creates the channel. Client MUST NOT
2212 send this packet. Server may send this packet to a router when it is
2213 announcing its existing channels to the router after it has connected
2216 The packet uses generic Channel Payload as New Channel Payload. See
2217 section 2.3.2.3 for generic Channel Payload. The Mode Mask field in the
2218 Channel Payload is the mode of the channel.
2222 2.3.20 Key Agreement Payload
2224 This payload is used by clients to request key negotiation between
2225 another client in the SILC Network. The key agreement protocol used
2226 is the SKE protocol. The result of the protocol, the secret key
2227 material, can be used for example as private message key between the
2228 two clients. This significantly adds security as the key agreement
2229 is performed outside the SILC network. The server and router MUST NOT
2232 The sender MAY tell the receiver of this payload the hostname and the
2233 port where the SKE protocol is running in the sender's end. The
2234 receiver MAY then initiate the SKE negotiation with the sender. The
2235 sender MAY also optionally not to include the hostname and the port
2236 of its SKE protocol. In this case the receiver MAY reply to the
2237 request by sending the same payload filled with the receiver's hostname
2238 and the port where the SKE protocol is running. The sender MAY then
2239 initiate the SKE negotiation with the receiver.
2241 This payload may be sent with SILC_PACKET_KEY_AGREEMENT and
2242 SILC_PACKET_FTP packet types. It MUST NOT be sent in any other packet
2243 types. The following diagram represents the Key Agreement Payload.
2249 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
2250 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2251 | Hostname Length | |
2252 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2256 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2258 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2262 Figure 21: Key Agreement Payload
2266 o Hostname Length (2 bytes) - Indicates the length of the
2269 o Hostname (variable length) - The hostname or IP address where
2270 the SKE protocol is running. The sender MAY fill this field
2271 when sending the payload. If the receiver sends this payload
2272 as reply to the request it MUST fill this field.
2274 o Port (4 bytes) - The port where the SKE protocol is bound.
2275 The sender MAY fill this field when sending the payload. If
2276 the receiver sends this payload as reply to the request it
2277 MUST fill this field. This is a 32 bit MSB first order value.
2281 After the key material has been received from the SKE protocol it is
2282 processed as the [SILC3] describes. If the key material is used as
2283 channel private key then the Sending Encryption Key, as defined in
2284 [SILC3] is used as the channel private key. Other key material must
2285 be discarded. The [SILC1] defines the way to use the key material if
2286 it is intended to be used as private message keys. Any other use for
2287 the key material is undefined.
2291 2.3.21 Resume Router Payload
2293 The payload may only be sent with SILC_PACKET_RESUME_ROUTER packet. It
2294 MUST NOT be sent in any other packet type. The Following diagram
2295 represents the Resume Router Payload.
2301 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
2302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2303 | Type | Session ID |
2304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2308 Figure 22: Resume Router Payload
2312 o Type (1 byte) - Indicates the type of the backup resume
2313 protocol packet. The type values are defined in [SILC1].
2315 o Session ID (1 bytes) - Indicates the session ID for the
2316 backup resume protocol. The sender of the packet sets this
2317 value and the receiver MUST set the same value in subsequent
2323 2.3.22 File Transfer Payload
2325 File Transfer Payload is used to perform file transfer protocol
2326 between two entities in the network. The actual file transfer
2327 protocol is always encapsulated inside the SILC Packet. The actual
2328 data stream is also sent peer to peer outside SILC network.
2330 When an entity, usually a client wishes to perform file transfer
2331 protocol with another client in the network, they perform Key Agreement
2332 protocol as described in the section 2.3.20 Key Agreement Payload and
2333 in [SILC3], inside File Transfer Payload. After the Key Agreement
2334 protocol has been performed the subsequent packets in the data stream
2335 will be protected using the new key material. The actual file transfer
2336 protocol is also initialized in this stage. All file transfer protocol
2337 packets are always encapsulated in the File Transfer Payload and
2338 protected with the negotiated key material.
2340 The payload may only be sent with SILC_PACKET_FTP packet. It MUST NOT
2341 be sent in any other packet type. The following diagram represents the
2342 File Transfer Payload
2347 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
2348 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2354 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2358 Figure 23: File Transfer Payload
2362 o Type (1 byte) - Indicates the type of the file transfer
2363 protocol. The following file transfer protocols has been
2366 1 SSH File Transfer Protocol (SFTP) (mandatory)
2368 If zero (0) value or any unsupported file transfer protocol
2369 type is found in this field the packet must be discarded.
2370 The currently mandatory file transfer protocol is SFTP.
2371 The SFTP protocol is defined in [SFTP].
2373 o Data (variable length) - Arbitrary file transfer data. The
2374 contents and encoding of this field is dependent of the usage
2375 of this payload and the type of the file transfer protocol.
2376 When this payload is used to perform the Key Agreement
2377 protocol, this field include the Key Agreement Payload,
2378 as defined in the section 2.3.20 Key Agreement Payload.
2379 When this payload is used to send the actual file transfer
2380 protocol data, the encoding is defined in the corresponding
2381 file transfer protocol.
2390 ID's are extensively used in the SILC network to associate different
2391 entities. The following ID's has been defined to be used in the SILC
2397 When ever specific ID cannot be used this is used.
2401 Server ID to associate servers. See the format of
2406 Client ID to associate clients. See the format of
2411 Channel ID to associate channels. See the format of
2415 When encoding different IDs into the ID Payload, all fields are always
2416 in MSB first order. The IP address, port, and/or the random number
2417 are encoded in the MSB first order.
2421 2.5 Packet Encryption And Decryption
2423 SILC packets are encrypted almost entirely. Only small part of SILC
2424 header is not encrypted as described in section 5.2 SILC Packet Header.
2425 The SILC Packet header is the first part of a packet to be encrypted
2426 and it is always encrypted with the key of the next receiver of the
2427 packet. The data payload area of the packet is always entirely
2428 encrypted and it is usually encrypted with the next receiver's key.
2429 However, there are some special packet types and packet payloads
2430 that require special encryption process. These special cases are
2431 described in the next sections. First is described the normal packet
2436 2.5.1 Normal Packet Encryption And Decryption
2438 Normal SILC packets are encrypted with the session key of the next
2439 receiver of the packet. The entire SILC Packet header and the packet
2440 data payload is is also encrypted with the same key. Padding of the
2441 packet is also encrypted always with the session key, also in special
2442 cases. Computed MAC of the packet must not be encrypted.
2444 Decryption process in these cases are straightforward. The receiver
2445 of the packet MUST first decrypt the SILC Packet header, or some parts
2446 of it, usually first 16 bytes of it. Then the receiver checks the
2447 packet type from the decrypted part of the header and can determine
2448 how the rest of the packet must be decrypted. If the packet type is
2449 any of the special cases described in the following sections the packet
2450 decryption is special. If the packet type is not among those special
2451 packet types rest of the packet can be decrypted with the same key.
2453 With out a doubt, this sort of decryption processing causes some
2454 overhead to packet decryption, but never the less, is required.
2458 2.5.2 Channel Message Encryption And Decryption
2460 Channel Messages (Channel Message Payload) are always encrypted with
2461 the channel specific key. However, the SILC Packet header is not
2462 encrypted with that key. As in normal case, the header is encrypted
2463 with the key of the next receiver of the packet, who ever that might
2464 be. Note that in this case the encrypted data area is not touched
2465 at all; it MUST NOT be re-encrypted with the session key.
2467 Receiver of a channel message, who ever that is, is REQUIRED to decrypt
2468 the SILC Packet header to be able to even recognize the packet to be as
2469 channel message. This is same procedure as for normal SILC packets.
2470 As the receiver founds the packet to be channel message, rest of the
2471 packet processing is special. Rest of the SILC Packet header is
2472 decrypted with the same session key along with the padding of the
2473 packet. After that the packet is protected with the channel specific
2474 key and thus can be decrypted only if the receiver is the client on
2475 the channel. See section 2.7 Packet Padding Generation for more
2476 information about padding on special packets.
2478 If the receiver of the channel message is router which is routing the
2479 message to another router then it MUST decrypt the Channel Message
2480 payload. Between routers (that is, between cells) channel messages
2481 are protected with session keys shared between the routers. This
2482 causes another special packet processing for channel messages. If
2483 the channel message is received from another router then the entire
2484 packet, including Channel Message payload, MUST be encrypted with the
2485 session key shared between the routers. In this case the packet
2486 decryption process is as with normal SILC packets. Hence, if the
2487 router is sending channel message to another router the Channel
2488 Message payload MUST have been decrypted and MUST be re-encrypted
2489 with the session key shared between the another router. In this
2490 case the packet encryption is as with any normal SILC packet.
2492 It must be noted that this is only when the channel messages are sent
2493 from router to another router. In all other cases the channel
2494 message encryption and decryption is as described above. This
2495 different processing of channel messages with router to router
2496 connection is because channel keys are cell specific. All cells have
2497 their own channel keys thus the channel message traveling from one
2498 cell to another MUST be protected as it would be any normal SILC
2501 If the SILC_CMODE_PRIVKEY channel mode has been set for the channel
2502 then the router cannot decrypt the packet as it does not know the
2503 private key. In this case the entire packet MUST be encrypted with
2504 the session key and sent to the router. The router receiving the
2505 packet MUST check the channel mode and decrypt the packet accordingly.
2509 2.5.3 Private Message Encryption And Decryption
2511 By default, private message in SILC are protected by session keys.
2512 In this case the private message encryption and decryption process is
2513 equivalent to normal packet encryption and decryption.
2515 However, private messages MAY be protected with private message key
2516 which causes the packet to be special packet. The procedure in this
2517 case is very much alike to channel packets. The actual private message
2518 is encrypted with the private message key and other parts of the
2519 packet is encrypted with the session key. See 2.7 Packet Padding
2520 Generation for more information about padding on special packets.
2522 The difference from channel message processing is that server or router
2523 en route never decrypts the actual private message, as it does not
2524 have the key to do that. Thus, when sending packets between router
2525 the processing is same as in any other case as well; the packet's header
2526 and padding is protected by the session key and the data area is not
2529 The true receiver of the private message, client, that is, is able
2530 to decrypt the private message as it shares the key with the sender
2535 2.6 Packet MAC Generation
2537 Data integrity of a packet is protected by including a message
2538 authentication code (MAC) at the end of the packet. The MAC is computed
2539 from shared secret MAC key, that is established by the SILC Key Exchange
2540 protocol, from packet sequence number, and from the original contents
2541 of the packet. The MAC is always computed before the packet is
2542 encrypted, although after it is compressed if compression is used.
2544 The MAC is computed from entire packet. Every bit of data in the packet,
2545 including SILC Packet Header is used in the MAC computing. This way
2546 the entire packet becomes authenticated.
2548 If the packet is special packet MAC is computed from the entire packet
2549 but part of the packet may be encrypted before the MAC is computed.
2550 This is case, for example, with channel messages where the message data
2551 is encrypted with key that server may not now. In this case the MAC
2552 has been computed from the encrypted data.
2554 Hence, packet's MAC generation is as follows:
2556 mac = MAC(key, sequence number | SILC packet)
2558 The MAC key is negotiated during the SKE protocol. The sequence number
2559 is a 32 bit MSB first value starting from zero for first packet and
2560 increasing for subsequent packets, finally wrapping after 2^32 packets.
2561 The value is never reset, not even after rekey has been performed. Note
2562 that the sequence number is incremented only when MAC is computed for a
2563 packet. If packet is not encrypted and MAC is not computed then the
2564 sequence number is not incremented. Hence, the sequence number is zero
2565 for first encrypted packet.
2567 See [SILC1] for defined and allowed MAC algorithms.
2571 2.7 Packet Padding Generation
2573 Padding is needed in the packet because the packet is encrypted. It
2574 MUST always be multiple by eight (8) or multiple by the block size
2575 of the cipher, which ever is larger. The padding is always encrypted.
2577 For normal packets the padding is added after the SILC Packet Header
2578 and between the Data Payload area. The padding for normal packets
2579 may be calculated as follows:
2582 padding length = 16 - (packet_length mod block_size)
2585 The `block_size' is the block size of the cipher. The maximum padding
2586 length is 128 bytes, and minimum is 1 byte. The above algorithm calculates
2587 the padding to the next block size, and always returns the padding
2588 length between 1 - 16 bytes. However, implementations may add padding
2589 up to 128 bytes. For example packets that include a passphrase or a
2590 password for authentication purposes SHOULD pad the packet up to the
2591 maximum padding length.
2593 For special packets the padding calculation is different as special
2594 packets may be encrypted differently. In these cases the encrypted
2595 data area MUST already be multiple by the block size thus in this case
2596 the padding is calculated only for SILC Packet Header, not for any
2597 other area of the packet. The same algorithm works in this case as
2598 well, except that the `packet length' is now the SILC Packet Header
2601 The padding MUST be random data, preferably, generated by
2602 cryptographically strong random number generator.
2606 2.8 Packet Compression
2608 SILC Packets MAY be compressed. In this case the data payload area
2609 is compressed and all other areas of the packet MUST remain as they
2610 are. After compression is performed for the data area, the length
2611 field of Packet Header MUST be set to the compressed length of the
2614 The compression MUST always be applied before encryption. When
2615 the packet is received and decrypted the data area MUST be decompressed.
2616 Note that the true sender of the packet MUST apply the compression and
2617 the true receiver of the packet MUST apply the decompression. Any
2618 server or router en route MUST NOT decompress the packet.
2624 The sender of the packet MUST assemble the SILC Packet Header with
2625 correct values. It MUST set the Source ID of the header as its own
2626 ID, unless it is forwarding the packet. It MUST also set the Destination
2627 ID of the header to the true destination. If the destination is client
2628 it will be Client ID, if it is server it will be Server ID and if it is
2629 channel it will be Channel ID.
2631 If the sender wants to compress the packet it MUST apply the
2632 compression now. Sender MUST also compute the padding as described
2633 in above sections. Then sender MUST compute the MAC of the packet.
2635 Then sender MUST encrypt the packet as has been described in above
2636 sections according whether the packet is normal packet or special
2637 packet. The computed MAC MUST NOT be encrypted.
2641 2.10 Packet Reception
2643 On packet reception the receiver MUST check that all fields in the
2644 SILC Packet Header are valid. It MUST check the flags of the
2645 header and act accordingly. It MUST also check the MAC of the packet
2646 and if it is to be failed the packet MUST be discarded. Also if the
2647 header of the packet includes any bad fields the packet MUST be
2650 See above sections on the decryption process of the received packet.
2652 The receiver MUST also check that the ID's in the header are valid
2653 ID's. Unsupported ID types or malformed ID's MUST cause packet
2654 rejection. The padding on the reception is always ignored.
2656 The receiver MUST also check the packet type and start parsing the
2657 packet according to the type. However, note the above sections on
2658 special packet types and their parsing.
2664 Routers are the primary entities in the SILC network that takes care
2665 of packet routing. However, normal servers routes packets as well, for
2666 example, when they are routing channel message to the local clients.
2667 Routing is quite simple as every packet tells the true origin and the
2668 true destination of the packet.
2670 It is still RECOMMENDED for routers that has several routing connections
2671 to create route cache for those destinations that has faster route than
2672 the router's primary route. This information is available for the router
2673 when other router connects to the router. The connecting party then
2674 sends all of its locally connected clients, servers and channels. These
2675 informations helps to create the route cache. Also, when new channels
2676 are created to a cell its information is broadcasted to all routers
2677 in the network. Channel ID's are based on router's ID thus it is easy
2678 to create route cache based on these informations. If faster route for
2679 destination does not exist in router's route cache the packet MUST be
2680 routed to the primary route (default route).
2682 However, there are some issues when routing channel messages to group
2683 of users. Routers are responsible of routing the channel message to
2684 other routers, local servers and local clients as well. Routers MUST
2685 send the channel message to only one router in the network, preferrably
2686 to the shortest route to reach the channel users. The message can be
2687 routed into either upstream or downstream. After the message is sent
2688 to a router in the network it MUST NOT be sent to any other router in
2689 either same route or other route. The message MUST NOT be routed to
2690 the router it came from.
2692 When routing for example private messages they should be routed to the
2693 shortest route always to reach the destination client as fast as possible.
2695 For server which receives a packet to be routed to its locally connected
2696 client the server MUST check whether the particular packet type is
2697 allowed to be routed to the client. Not all packets may be sent by
2698 some odd entity to client that is indirectly connected to the sender.
2699 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2700 entities and sending packets to them. The section mentions the packets
2701 that may be sent to indirectly connected entities. It is clear that
2702 server cannot send, for example, disconnect packet to client that is not
2703 directly connected to the server.
2705 Routers form a ring in the SILC network. However, routers may have other
2706 direct connections to other routers in the network too. This can cause
2707 interesting routing problems in the network. Since the network is a ring,
2708 the packets usually should be routed into clock-wise direction, or if it
2709 cannot be used then always counter clock-wise (primary route) direction.
2710 Problems may arise when a faster direct route exists and router is routing
2711 a channel message. Currently channel messages must be routed either
2712 in upstream or downstream, they cannot be routed to other direct routes.
2713 The SILC protocol should have a shortest path discovery protocol, and some
2714 existing routing protocol, that can handle a ring network with other
2715 direct routes inside the ring (so called hybrid ring-mesh topology),
2716 MAY be defined to be used with the SILC protocol. Additional
2717 specifications MAY be written on the subject to permeate this
2722 2.12 Packet Broadcasting
2724 SILC packets MAY be broadcasted in SILC network. However, only router
2725 server may send or receive broadcast packets. Client and normal server
2726 MUST NOT send broadcast packets and they MUST ignore broadcast packets
2727 if they receive them. Broadcast packets are sent by setting Broadcast
2728 flag to the SILC packet header.
2730 Broadcasting packets means that the packet is sent to all routers in
2731 the SILC network, except to the router that sent the packet. The router
2732 receiving broadcast packet MUST send the packet to its primary route.
2733 The fact that SILC routers may have several router connections can
2734 cause problems, such as race conditions inside the SILC network, if
2735 care is not taken when broadcasting packets. Router MUST NOT send
2736 the broadcast packet to any other route except to its primary route.
2738 If the primary route of the router is the original sender of the packet
2739 the packet MUST NOT be sent to the primary route. This may happen
2740 if router has several router connections and some other router uses
2741 the router as its primary route.
2743 Routers use broadcast packets to broadcast for example information
2744 about newly registered clients, servers, channels etc. so that all the
2745 routers may keep these informations up to date.
2749 3 Security Considerations
2751 Security is central to the design of this protocol, and these security
2752 considerations permeate the specification. Common security considerations
2753 such as keeping private keys truly private and using adequate lengths for
2754 symmetric and asymmetric keys must be followed in order to maintain the
2755 security of this protocol.
2761 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2762 Protocol Specification", Internet Draft, April 2001.
2764 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2765 Protocols", Internet Draft, April 2001.
2767 [SILC4] Riikonen, P., "SILC Commands", Internet Draft, April 2001.
2769 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2772 [IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
2775 [IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
2778 [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
2781 [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
2784 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2787 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2790 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2793 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2794 Infrastructure, Certificate and CRL Profile", RFC 2459,
2797 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2798 John Wiley & Sons, New York, NY, 1996.
2800 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2803 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2804 RFC 2412, November 1998.
2806 [ISAKMP] Maughan D., et al, "Internet Security Association and
2807 Key Management Protocol (ISAKMP)", RFC 2408, November
2810 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2811 (IKE)", RFC 2409, November 1998.
2813 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2814 Authentication", RFC 2104, February 1997.
2816 [PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
2817 Specifications, Version 2.0", RFC 2437, October 1998.
2819 [RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate
2820 Requirement Levels", BCP 14, RFC 2119, March 1997.
2822 [SFTP] Ylonen T., and Lehtinen S., "Secure Shell File Transfer
2823 Protocol", Internet Draft, March 2001.
2830 Snellmanninkatu 34 A 15
2834 EMail: priikone@iki.fi
2836 This Internet-Draft expires XXX
projects / silc.git / blob