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 Note that all ID's sent in arguments are sent inside ID Payload. Also
1193 note that all passphrases that may be sent inside arguments MUST be
1194 UTF-8 [RFC2279] encoded.
1197 0 SILC_NOTIFY_TYPE_NONE
1199 If no specific notify type apply for the notify message this type
1203 Arguments: (1) <message>
1205 The <message> is implementation specific free text string.
1206 Receiver MAY ignore this message.
1209 1 SILC_NOTIFY_TYPE_INVITE
1211 Sent when an client is invited to a channel. This is also sent
1212 when the invite list of the channel is changed. This notify type
1213 is sent between routers and if an client was invited, to the
1214 client as well. In this case the packet is destined to the client.
1217 Arguments: (1) <Channel ID> (2) <channel name>
1218 (3) [<sender Client ID>] (4) [<adding client>]
1219 (5) [<removing client>]
1221 The <Channel ID> is the channel. The <channel name> is the name
1222 of the channel and is provided because the client which receives
1223 this notify packet may not have a way to resolve the name of the
1224 channel from the <Channel ID>. The <sender Client ID> is the
1225 Client ID which invited the client to the channel. The <adding
1226 client> and the <removing client> indicates the added or removed
1227 client from the channel's invite list. The format of the <adding
1228 client> and the <removing client> is defined in the [SILC4] with
1229 SILC_COMMAND_INVITE command.
1231 The <adding client> and <removing client> MUST NOT be sent when
1232 the packet is destined to a client.
1235 2 SILC_NOTIFY_TYPE_JOIN
1237 Sent when client has joined to a channel. The server MUST
1238 distribute this type only to the local clients on the channel
1239 and then send it to its primary router. The router or server
1240 receiving the packet distributes this type to the local clients
1241 on the channel and broadcast it to the network.
1244 Arguments: (1) [<Client ID>] (2) <Channel ID>
1246 The <Client ID> is the client that joined to the channel indicated
1247 by the <Channel ID>.
1250 3 SILC_NOTIFY_TYPE_LEAVE
1252 Sent when client has left a channel. The server must distribute
1253 this type only to the local clients on the channel and then send
1254 it to its primary router. The router or server receiving the
1255 packet distributes this type to the local clients on the channel
1256 and broadcast it to the network.
1259 Arguments: (1) <Client ID>
1261 The <Client ID> is the client which left the channel.
1264 4 SILC_NOTIFY_TYPE_SIGNOFF
1266 Sent when client signoff from SILC network. The server MUST
1267 distribute this type only to the local clients on the channel and
1268 then send it to its primary router. The router or server receiving
1269 the packet distributes this type to the local clients on the
1270 channel and broadcast it to the network.
1273 Arguments: (1) <Client ID> (2) <message>
1275 The <Client ID> is the client which left SILC network. The
1276 <message> is free text string indicating the reason of the signoff.
1279 5 SILC_NOTIFY_TYPE_TOPIC_SET
1281 Sent when topic is set/changed on a channel. This type must be
1282 sent only to the clients which is joined on the channel which
1283 topic was set or changed.
1286 Arguments: (1) <ID Payload> (2) <topic>
1288 The <ID Payload> is the ID of the entity who set the topic. It
1289 usually is Client ID but it can be Server ID and Channel ID as well.
1292 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1294 Sent when client changes nick on a channel. The server MUST
1295 distribute this type only to the local clients on the channel
1296 and then send it to its primary router. The router or server
1297 receiving the packet distributes this type to the local clients
1298 on the channel and broadcast it to the network.
1301 Arguments: (1) <Old Client ID> (2) <New Client ID>
1304 The <Old Client ID> is the old ID of the client which changed
1305 the nickname. The <New Client ID> is the new ID generated by
1306 the change of the nickname. The <nickname> is the new nickname.
1309 7 SILC_NOTIFY_TYPE_CMODE_CHANGE
1311 Sent when channel mode has changed. This type MUST be sent only
1312 to the clients which is joined on the channel which mode was
1316 Arguments: (1) <ID Payload> (2) <mode mask>
1317 (3) [<cipher>] (4) <[hmac>]
1320 The <ID Payload> is the ID (usually Client ID but it can be
1321 Server ID as well when the router is enforcing channel mode
1322 change) of the entity which changed the mode. The <mode mask>
1323 is the new mode mask of the channel. The client can safely
1324 ignore the <cipher> argument since the SILC_PACKET_CHANNEL_KEY
1325 packet will force the new channel key change anyway. The <hmac>
1326 argument is important since the client is responsible of setting
1327 the new HMAC and the hmac key into use. The <passphrase> is
1328 the passphrase of the channel, if it was now set.
1331 8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
1333 Sent when user mode on channel has changed. This type MUST be
1334 sent only to the clients which is joined on the channel where
1335 the target client is on.
1338 Arguments: (1) <ID Payload> (2) <mode mask>
1339 (3) <Target Client ID>
1341 The <ID Payload> is the ID (usually Client ID but it can be
1342 Server ID as well when the router is enforcing user's mode
1343 change) of the entity which changed the mode. The <mode mask>
1344 is the new mode mask of the channel. The <Target Client ID>
1345 is the client which mode was changed.
1348 9 SILC_NOTIFY_TYPE_MOTD
1350 Sent when Message of the Day (motd) is sent to a client.
1353 Arguments: (1) <motd>
1355 The <motd> is the Message of the Day.
1358 10 SILC_NOTIFY_TYPE_CHANNEL_CHANGE
1360 Sent when channel's ID has changed for a reason or another.
1361 This is sent by normal server to the client. This can also be
1362 sent by router to other server to force the Channel ID change.
1363 The Channel ID MUST be changed to use the new one. When sent
1364 to clients, this type MUST be sent only to the clients which is
1365 joined on the channel.
1368 Arguments: (1) <Old Channel ID> (2) <New Channel ID>
1370 The <Old Channel ID> is the channel's old ID and the <New
1371 Channel ID> is the new one that MUST replace the old one.
1374 11 SILC_NOTIFY_TYPE_SERVER_SIGNOFF
1376 Sent when server quits SILC network. Those clients from this
1377 server that are on channels must be removed from the channel.
1380 Arguments: (1) <Server ID> (n) [<Client ID>] [...]
1382 The <Server ID> is the server's ID. The rest of the arguments
1383 are the Client ID's of the client's which are coming from this
1384 server and are thus quitting the SILC network also. If the
1385 maximum number of arguments are reached another
1386 SILC_NOTIFY_TYPE_SERVER_SIGNOFF notify packet MUST be sent.
1387 When this notify packet is sent between routers the Client ID's
1388 MAY be omitted. Server receiving the Client ID's in the payload
1389 may use them directly to remove the client.
1392 12 SILC_NOTIFY_TYPE_KICKED
1394 Sent when a client has been kicked from a channel. This is
1395 sent also to the client which was kicked from the channel.
1396 The client which was kicked from the channel MUST be removed
1397 from the channel. This notify type is always destined to the
1398 channel. The router or server receiving the packet distributes
1399 this type to the local clients on the channel and broadcast it
1403 Arguments: (1) <Client ID> (2) [<comment>]
1404 (3) <Kicker's Client ID>
1406 The <Client ID> is the client which was kicked from the channel.
1407 The kicker may have set the <comment> to indicate the reason for
1408 the kicking. The <Kicker's Client ID> is the kicker.
1411 13 SILC_NOTIFY_TYPE_KILLED
1413 Sent when a client has been killed from the network. This is sent
1414 also to the client which was killed from the network. The client
1415 which was killed from the network MUST be removed from the network.
1416 This notify type is destined directly to the client which was
1417 killed and to channel if the client is on any channel. The router
1418 or server receiving the packet distributes this type to the local
1419 clients on the channel and broadcast it to the network.
1422 Arguments: (1) <Client ID> (2) [<comment>]
1423 (3) <Killer's Client ID>
1425 The <Client ID> is the client which was killed from the network.
1426 The killer may have set the <comment> to indicate the reason for
1427 the killing. The <Killer's Client ID> is the killer.
1430 14 SILC_NOTIFY_TYPE_UMODE_CHANGE
1432 Sent when user's mode in the SILC changes. This type is sent
1433 only between routers as broadcast packet.
1436 Arguments: (1) <Client ID> (2) <mode mask>
1438 The <Client ID> is the client which mode was changed. The
1439 <mode mask> is the new mode mask.
1442 15 SILC_NOTIFY_TYPE_BAN
1444 Sent when the ban list of the channel is changed. This type is
1445 sent only between routers as broadcast packet.
1448 Arguments: (1) <Channel ID> (2) [<adding client>]
1449 (3) [<removing client>]
1451 The <Channel ID> is the channel which ban list was changed. The
1452 <adding client> is used to indicate that a ban was added and the
1453 <removing client> is used to indicate that a ban was removed from
1454 the ban list. The format of the <adding client> and the
1455 <removing client> is defined in the [SILC4] with SILC_COMMAND_BAN
1460 Notify types starting from 16384 are reserved for private notify
1467 Error payload is sent upon error. Error may occur in various
1468 conditions when server sends this packet. Client MUST NOT send this
1469 payload but MUST be able to accept it. However, client MAY
1470 totally ignore the contents of the packet as server is going to
1471 take action on the error anyway. However, it is recommended
1472 that the client takes error packet seriously.
1478 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
1479 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1483 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1487 Figure 12: Error Payload
1491 o Error Message (variable length) - Human readable error
1497 2.3.9 Channel Message Payload
1499 Channel messages are the most common messages sent in the SILC.
1500 Channel Message Payload is used to send message to channels. These
1501 messages can only be sent if client has joined to some channel.
1502 Even though this packet is the most common in SILC it is still
1503 special packet. Some special handling on sending and reception
1504 of channel message is required.
1506 Padding MUST be applied into this payload since the payload is
1507 encrypted separately from other parts of the packet with the
1508 channel specific key. Hence the requirement of the padding.
1509 The padding SHOULD be random data. The packet MUST be made
1510 multiple by eight (8) or by the block size of the cipher, which
1513 The SILC header in this packet is encrypted with the session key
1514 of the next receiver of the packet. Nothing else is encrypted
1515 with that key. Thus, the actual packet and padding to be
1516 encrypted with the session key is SILC Header plus padding to it
1517 to make it multiple by eight (8) or multiple by the block size
1518 of the cipher, which ever is larger.
1520 Receiver of the the channel message packet is able to determine
1521 the channel the message is destined to by checking the destination
1522 ID from the SILC Packet header which tells the destination channel.
1523 The original sender of the packet is also determined by checking
1524 the source ID from the header which tells the client which sent
1527 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1528 It MUST NOT be sent in any other packet type. The following diagram
1529 represents the Channel Message Payload.
1531 (*) indicates that the field is not encrypted.
1537 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
1538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1539 | Message Flags | Message Length |
1540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1544 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1545 | Padding Length | |
1546 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1554 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1556 ~ Initial Vector * ~
1558 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1562 Figure 13: Channel Message Payload
1566 o Message Flags (2 bytes) - Includes the Message Flags of
1567 the channel messages. The flags can indicate a reason or
1568 purpose for the channel message. Note that the Private
1569 Message Payload use these same Message Flags for the same
1570 purpose. The following Message Flags are defined:
1572 0x0000 SILC_MESSAGE_FLAG_NONE
1574 No specific flags set.
1576 0x0001 SILC_MESSAGE_FLAG_AUTOREPLY
1578 This message is an automatic reply to an earlier
1581 0x0002 SILC_MESSAGE_FLAG_NOREPLY
1583 There should not be reply messages to this
1586 0x0004 SILC_MESSAGE_FLAG_ACTION
1588 The sender is performing an action and the message
1589 is the indication of the action.
1591 0x0008 SILC_MESSAGE_FLAG_NOTICE
1593 The message is for example an informational notice
1596 0x0010 SILC_MESSAGE_FLAG_REQUEST
1598 This is a generic request flag to send request
1599 messages. A separate document should define any
1600 payloads associated to this flag.
1602 0x0020 SILC_MESSAGE_FLAG_SIGNED
1604 This flag indicates that the message is signed
1605 with sender's private key and thus can be verified
1606 by the receiver using the sender's public key. A
1607 separate document should define the detailed procedure
1608 of the signing process and any associated payloads
1611 0x0040 SILC_MESSAGE_FLAG_REPLY
1613 This is a generic reply flag to send a reply to
1614 previously received request. A separate document
1615 should define any payloads associated to this flag.
1617 0x0080 SILC_MESSAGE_FLAG_DATA
1619 This is a generic data flag, indicating that the
1620 message includes some data which can be interpreted
1621 in a specific way. Using this flag any kind of data
1622 can be delivered inside message payload. A separate
1623 document should define how this flag is interpreted
1624 and define any associated payloads.
1626 0x0100 - 0x0800 RESERVED
1628 Reserved for future flags
1630 0x1000 - 0x8000 PRIVATE RANGE
1632 Private range for free use.
1634 o Message Length (2 bytes) - Indicates the length of the
1635 the Message Data field in the payload, not including any
1638 o Message Data (variable length) - The actual message to
1641 o Padding Length (2 bytes) - Indicates the length of the
1642 Padding field in the payload, not including any other
1645 o Padding (variable length) - The padding that MUST be
1646 applied because this payload is encrypted separately from
1647 other parts of the packet.
1649 o MAC (variable length) - The MAC computed from the
1650 Message Length, Message Data, Padding Length and Padding
1651 fields. This protects the integrity of the plaintext
1652 channel message. The receiver can verify from the MAC
1653 whether the message decrypted correctly. Also, if more than
1654 one private key has been set for the channel, the receiver
1655 can verify which of the keys decrypted the message
1656 correctly. Note that, this field is encrypted and MUST
1657 be added to the padding calculation.
1659 o Initial Vector (variable length) - The initial vector
1660 that has been used in packet encryption. It needs to be
1661 used in the packet decryption as well. What this field
1662 includes is implementation issue. However, it is
1663 RECOMMENDED that it would be random data or, perhaps,
1664 a timestamp. It is NOT RECOMMENDED to use zero (0) as an
1665 initial vector. This field is not encrypted. This field
1666 is not included into the padding calculation. Length
1667 of this field equals the cipher's block size. This field
1668 is, however, authenticated.
1673 2.3.10 Channel Key Payload
1675 All traffic in channels are protected by channel specific keys.
1676 Channel Key Payload is used to distribute channel keys to all
1677 clients on the particular channel. Channel keys are sent when
1678 the channel is created, when new user joins to the channel and
1679 whenever a user has left a channel. Server creates the new
1680 channel key and distributes it to the clients by encrypting this
1681 payload with the session key shared between the server and
1682 the client. After that, client starts using the key received
1683 in this payload to protect the traffic on the channel.
1685 The client which is joining to the channel receives its key in the
1686 SILC_COMMAND_JOIN command reply message thus it is not necessary to
1687 send this payload to the entity which sent the SILC_COMMAND_JOIN
1690 Channel keys are cell specific thus every router in the cell have
1691 to create a channel key and distribute it if any client in the
1692 cell has joined to a channel. Channel traffic between cell's
1693 are not encrypted using channel keys, they are encrypted using
1694 normal session keys between two routers. Inside a cell, all
1695 channel traffic is encrypted with the specified channel key.
1696 Channel key should expire periodically, say, in one hour, in
1697 which case new channel key is created and distributed.
1699 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1700 It MUST NOT be sent in any other packet type. The following diagram
1701 represents the Channel Key Payload.
1707 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
1708 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1709 | Channel ID Length | |
1710 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1714 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1715 | Cipher Name Length | |
1716 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1720 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1721 | Channel Key Length | |
1722 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1726 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1730 Figure 14: Channel Key Payload
1735 o Channel ID Length (2 bytes) - Indicates the length of the
1736 Channel ID field in the payload, not including any other
1739 o Channel ID (variable length) - The Channel ID of the
1740 channel this key is meant for.
1742 o Cipher Name Length (2 bytes) - Indicates the length of the
1743 Cipher name field in the payload, not including any other
1746 o Cipher Name (variable length) - Name of the cipher used
1747 in the protection of channel traffic. This name is
1748 initially decided by the creator of the channel but it
1749 MAY change during the life time of the channel as well.
1751 o Channel Key Length (2 bytes) - Indicates the length of the
1752 Channel Key field in the payload, not including any other
1755 o Channel Key (variable length) - The actual channel key
1761 2.3.11 Private Message Payload
1763 Private Message Payload is used to send private message between
1764 two clients (or users for that matter). The messages are sent only
1765 to the specified user and no other user inside SILC network is
1766 able to see the message. The message is protected by the session
1767 key established by the SILC Key Exchange Protocol. However,
1768 it is also possible to agree to use a private key to protect
1769 just the private messages. See section 2.3.11 Private Message
1770 Key Payload for detailed description of how to agree to use
1773 If normal session key is used to protect the message, every server
1774 between the sender client and the receiving client MUST decrypt the
1775 packet and always re-encrypt it with the session key of the next
1776 receiver of the packet. See section Client To Client in [SILC1].
1778 When private key is used to protect the message, servers between
1779 the sender and the receiver needs not to decrypt/re-encrypt the
1780 packet. Section Client To Client in [SILC1] gives example of this
1783 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1784 packet. It MUST NOT be sent in any other packet type. The following
1785 diagram represents the Private Message Payload.
1797 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
1798 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1799 | Message Flags | Message Data Length |
1800 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1804 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1808 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1812 Figure 15: Private Message Payload
1816 o Message Flags (2 bytes) - This field includes the Message
1817 Flags of the private message. They can indicate a different
1818 reason or purpose for the private message. See the section
1819 2.3.9 Channel Message Payload for defined flags. Note that
1820 the Channel Message Payload use the same flags for the
1823 o Message Data Length (2 bytes) - Indicates the length of the
1824 Message Data field, not includes any other field.
1826 o Message Data (variable length) - The actual message to
1827 the client. Rest of the packet is reserved for the message
1830 o Padding (variable length) - This field is present only
1831 when the private message payload is encrypted with private
1832 message key. In this case the padding is applied to make
1833 the payload multiple by eight (8), or by the block size of
1834 the cipher, which ever is larger. When encrypted with
1835 normal session keys, this field MUST NOT be included.
1840 2.3.12 Private Message Key Payload
1842 This payload is used to send key from client to another client that
1843 is going to be used to protect the private messages between these
1844 two clients. If this payload is not sent normal session key
1845 established by the SILC Key Exchange Protocol is used to protect
1846 the private messages.
1848 This payload may only be sent by client to another client. Server
1849 MUST NOT send this payload at any time. After sending this payload
1850 the sender of private messages must set the Private Message Key
1851 flag into SILC Packet Header.
1853 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1854 packet. It MUST NOT be sent in any other packet type. The following
1855 diagram represents the Private Message Key Payload.
1861 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
1862 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1863 | Private Message Key Length | |
1864 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1866 ~ Private Message Key ~
1868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1869 | Cipher Name Length | |
1870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1874 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1878 Figure 16: Private Message Key Payload
1884 o Private Message Key Length (2 bytes) - Indicates the length
1885 of the Private Message Key field in the payload, not including
1888 o Private Message Key (variable length) - The actual private
1889 message key material.
1891 o Cipher Name Length (2 bytes) - Indicates the length of the
1892 Cipher Name field in the payload, not including any other
1895 o Cipher Name (variable length) - Name of the cipher to use
1896 in the private message encryption. If this field does not
1897 exist then the default cipher of the SILC protocol is used.
1898 See the [SILC1] for defined ciphers.
1904 2.3.13 Command Payload
1906 Command Payload is used to send SILC commands from client to server.
1907 Also server MAY send commands to other servers. The following diagram
1908 represents the Command Payload.
1914 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
1915 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1916 | Payload Length | SILC Command | Arguments Num |
1917 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1918 | Command Identifier |
1919 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1923 Figure 17: Command Payload
1927 o Payload Length (2 bytes) - Length of the entire command
1928 payload including any command argument payloads associated
1931 o SILC Command (1 byte) - Indicates the SILC command. This MUST
1932 be set to non-zero value. If zero (0) value is found in this
1933 field the packet MUST be discarded.
1935 o Arguments Num (1 byte) - Indicates the number of arguments
1936 associated with the command. If there are no arguments this
1937 field is set to zero (0). The arguments MUST follow the
1938 command payload. See section 2.3.2.2 for definition of the
1941 o Command Identifier (2 bytes) - Identifies this command at the
1942 sender's end. The entity which replies to this command MUST
1943 set the value found from this field into the Command Payload
1944 used to send the reply to the sender. This way the sender
1945 can identify which command reply belongs to which originally
1946 sent command. What this field includes is implementation
1947 issue but it is RECOMMENDED that wrapping counter value is
1948 used in the field. Value zero (0) in this field means that
1949 no specific value is set.
1952 See [SILC4] for detailed description of different SILC commands,
1953 their arguments and their reply messages.
1959 2.3.14 Command Reply Payload
1961 Command Reply Payload is used to send replies to the commands. The
1962 Command Reply Payload is identical to the Command Payload thus see
1963 the upper section for the Command Payload specification.
1965 The entity which sends the reply packet MUST set the Command Identifier
1966 field in the reply packet's Command Payload to the value it received
1967 in the original command packet.
1969 See SILC Commands in [SILC4] for detailed description of different
1970 SILC commands, their arguments and their reply messages.
1974 2.3.15 Connection Auth Request Payload
1976 Client MAY send this payload to server to request the authentication
1977 method that must be used in authentication protocol. If client knows
1978 this information beforehand this payload is not necessary to be sent.
1979 Server performing authentication with another server MAY also send
1980 this payload to request the authentication method. If the connecting
1981 server already knows this information this payload is not necessary
1984 Server receiving this request MUST reply with same payload sending
1985 the mandatory authentication method. Algorithms that may be required
1986 to be used by the authentication method are the ones already
1987 established by the SILC Key Exchange protocol. See section Key
1988 Exchange Start Payload in [SILC3] for detailed information.
1990 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1991 packet. It MUST NOT be sent in any other packet type. The following
1992 diagram represents the Connection Auth Request Payload.
1998 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
1999 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2000 | Connection Type | Authentication Method |
2001 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2005 Figure 18: Connection Auth Request Payload
2009 o Connection Type (2 bytes) - Indicates the type of the
2010 connection. The following connection types are defined:
2017 If any other type is found in this field the packet MUST be
2018 discarded and the authentication MUST be failed.
2020 o Authentication Method (2 bytes) - Indicates the authentication
2021 method to be used in the authentication protocol. The following
2022 authentication methods are defined:
2025 1 password (mandatory)
2026 2 public key (mandatory)
2028 If any other type is found in this field the packet MUST be
2029 discarded and the authentication MUST be failed. If this
2030 payload is sent as request to receive the mandatory
2031 authentication method this field MUST be set to zero (0),
2032 indicating that receiver should send the mandatory
2033 authentication method. The receiver sending this payload
2034 to the requesting party, MAY also set this field to zero (0)
2035 to indicate that authentication is not required. In this
2036 case authentication protocol still MUST be started but
2037 server is most likely to respond with SILC_PACKET_SUCCESS
2043 2.3.16 New ID Payload
2045 New ID Payload is a multipurpose payload. It is used to send newly
2046 created ID's from clients and servers. When client connects to server
2047 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
2048 packet, server replies with this packet by sending the created ID for
2049 the client. Server always creates the ID for the client.
2051 This payload is also used when server tells its router that new client
2052 has registered to the SILC network. In this case the server sends
2053 the Client ID of the client to the router. Similarly when router
2054 distributes information to other routers about the client in the SILC
2055 network this payload is used.
2057 Also, when server connects to router, router uses this payload to inform
2058 other routers about new server in the SILC network. However, every
2059 server (or router) creates their own ID's thus the ID distributed by
2060 this payload is not created by the distributor in this case. Servers
2061 create their own ID's. Server registers itself to the network by
2062 sending SILC_PACKET_NEW_SERVER to the router it connected to. The case
2063 is same when router connects to another router.
2065 However, this payload MUST NOT be used to send information about new
2066 channels. New channels are always distributed by sending the dedicated
2067 SILC_PACKET_NEW_CHANNEL packet.
2069 Thus, this payload is very important and used every time when some
2070 new entity is registered to the SILC network. Client MUST NOT send this
2071 payload. Both client and server (and router) MAY receive this payload.
2073 The packet uses generic ID Payload as New ID Payload. See section
2074 2.3.2.1 for generic ID Payload.
2078 2.3.17 New Client Payload
2080 When client is connected to the server, keys has been exchanged and
2081 connection has been authenticated client MUST register itself to the
2082 server. Client's first packet after key exchange and authentication
2083 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
2084 the relevant information about the connected user. Server creates a new
2085 client ID for the client when received this payload and sends it to the
2086 client in New ID Payload.
2088 This payload sends username and real name of the user on the remote host
2089 which is connected to the SILC server with SILC client. The server
2090 creates the client ID according the information sent in this payload.
2091 The nickname of the user becomes the username sent in this payload.
2092 However, client should call NICK command after sending this payload to
2093 set the real nickname of the user which is then used to create new
2096 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
2097 MUST NOT be sent in any other packet type. The following diagram
2098 represents the New Client Payload.
2115 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
2116 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2117 | Username Length | |
2118 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2122 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2123 | Real Name Length | |
2124 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2128 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2132 Figure 19: New Client Payload
2136 o Username Length (2 bytes) - Length of the Username field.
2138 o Username (variable length) - The username of the user on
2139 the host where connecting to the SILC server.
2141 o Real Name Length (2 bytes) - Length of the Real Name field.
2143 o Real Name (variable length) - The real name of the user
2144 on the host where connecting to the SILC server.
2149 2.3.18 New Server Payload
2151 This payload is sent by server when it has completed successfully both
2152 key exchange and connection authentication protocols. The server
2153 MUST register itself to the SILC Network by sending this payload.
2154 The first packet after these key exchange and authentication protocols
2155 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
2156 of the server that it has created by itself. It also includes a
2157 name of the server that is associated to the Server ID.
2159 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
2160 MUST NOT be sent in any other packet type. The following diagram
2161 represents the New Server Payload.
2170 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
2171 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2172 | Server ID Length | |
2173 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2177 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2178 | Server Name Length | |
2179 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2183 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2187 Figure 20: New Server Payload
2191 o Server ID Length (2 bytes) - Length of the Server ID Data
2194 o Server ID Data (variable length) - The actual Server ID
2197 o Server Name Length (2 bytes) - Length of the server name
2200 o Server Name (variable length) - The server name.
2205 2.3.19 New Channel Payload
2207 Information about newly created channel is broadcasted to all routers
2208 in the SILC network by sending this packet payload. Channels are
2209 created by router of the cell. Server never creates channels unless
2210 it is a standalone server and it does not have router connection,
2211 in this case server acts as router. Normal server send JOIN command
2212 to the router (after it has received JOIN command from client) which
2213 then processes the command and creates the channel. Client MUST NOT
2214 send this packet. Server may send this packet to a router when it is
2215 announcing its existing channels to the router after it has connected
2218 The packet uses generic Channel Payload as New Channel Payload. See
2219 section 2.3.2.3 for generic Channel Payload. The Mode Mask field in the
2220 Channel Payload is the mode of the channel.
2224 2.3.20 Key Agreement Payload
2226 This payload is used by clients to request key negotiation between
2227 another client in the SILC Network. The key agreement protocol used
2228 is the SKE protocol. The result of the protocol, the secret key
2229 material, can be used for example as private message key between the
2230 two clients. This significantly adds security as the key agreement
2231 is performed outside the SILC network. The server and router MUST NOT
2234 The sender MAY tell the receiver of this payload the hostname and the
2235 port where the SKE protocol is running in the sender's end. The
2236 receiver MAY then initiate the SKE negotiation with the sender. The
2237 sender MAY also optionally not to include the hostname and the port
2238 of its SKE protocol. In this case the receiver MAY reply to the
2239 request by sending the same payload filled with the receiver's hostname
2240 and the port where the SKE protocol is running. The sender MAY then
2241 initiate the SKE negotiation with the receiver.
2243 This payload may be sent with SILC_PACKET_KEY_AGREEMENT and
2244 SILC_PACKET_FTP packet types. It MUST NOT be sent in any other packet
2245 types. The following diagram represents the Key Agreement Payload.
2251 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
2252 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2253 | Hostname Length | |
2254 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2258 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2260 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2264 Figure 21: Key Agreement Payload
2268 o Hostname Length (2 bytes) - Indicates the length of the
2271 o Hostname (variable length) - The hostname or IP address where
2272 the SKE protocol is running. The sender MAY fill this field
2273 when sending the payload. If the receiver sends this payload
2274 as reply to the request it MUST fill this field.
2276 o Port (4 bytes) - The port where the SKE protocol is bound.
2277 The sender MAY fill this field when sending the payload. If
2278 the receiver sends this payload as reply to the request it
2279 MUST fill this field. This is a 32 bit MSB first order value.
2283 After the key material has been received from the SKE protocol it is
2284 processed as the [SILC3] describes. If the key material is used as
2285 channel private key then the Sending Encryption Key, as defined in
2286 [SILC3] is used as the channel private key. Other key material must
2287 be discarded. The [SILC1] defines the way to use the key material if
2288 it is intended to be used as private message keys. Any other use for
2289 the key material is undefined.
2293 2.3.21 Resume Router Payload
2295 The payload may only be sent with SILC_PACKET_RESUME_ROUTER packet. It
2296 MUST NOT be sent in any other packet type. The Following diagram
2297 represents the Resume Router Payload.
2303 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
2304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2305 | Type | Session ID |
2306 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2310 Figure 22: Resume Router Payload
2314 o Type (1 byte) - Indicates the type of the backup resume
2315 protocol packet. The type values are defined in [SILC1].
2317 o Session ID (1 bytes) - Indicates the session ID for the
2318 backup resume protocol. The sender of the packet sets this
2319 value and the receiver MUST set the same value in subsequent
2325 2.3.22 File Transfer Payload
2327 File Transfer Payload is used to perform file transfer protocol
2328 between two entities in the network. The actual file transfer
2329 protocol is always encapsulated inside the SILC Packet. The actual
2330 data stream is also sent peer to peer outside SILC network.
2332 When an entity, usually a client wishes to perform file transfer
2333 protocol with another client in the network, they perform Key Agreement
2334 protocol as described in the section 2.3.20 Key Agreement Payload and
2335 in [SILC3], inside File Transfer Payload. After the Key Agreement
2336 protocol has been performed the subsequent packets in the data stream
2337 will be protected using the new key material. The actual file transfer
2338 protocol is also initialized in this stage. All file transfer protocol
2339 packets are always encapsulated in the File Transfer Payload and
2340 protected with the negotiated key material.
2342 The payload may only be sent with SILC_PACKET_FTP packet. It MUST NOT
2343 be sent in any other packet type. The following diagram represents the
2344 File Transfer Payload
2349 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
2350 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2356 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2360 Figure 23: File Transfer Payload
2364 o Type (1 byte) - Indicates the type of the file transfer
2365 protocol. The following file transfer protocols has been
2368 1 SSH File Transfer Protocol (SFTP) (mandatory)
2370 If zero (0) value or any unsupported file transfer protocol
2371 type is found in this field the packet must be discarded.
2372 The currently mandatory file transfer protocol is SFTP.
2373 The SFTP protocol is defined in [SFTP].
2375 o Data (variable length) - Arbitrary file transfer data. The
2376 contents and encoding of this field is dependent of the usage
2377 of this payload and the type of the file transfer protocol.
2378 When this payload is used to perform the Key Agreement
2379 protocol, this field include the Key Agreement Payload,
2380 as defined in the section 2.3.20 Key Agreement Payload.
2381 When this payload is used to send the actual file transfer
2382 protocol data, the encoding is defined in the corresponding
2383 file transfer protocol.
2392 ID's are extensively used in the SILC network to associate different
2393 entities. The following ID's has been defined to be used in the SILC
2399 When ever specific ID cannot be used this is used.
2403 Server ID to associate servers. See the format of
2408 Client ID to associate clients. See the format of
2413 Channel ID to associate channels. See the format of
2417 When encoding different IDs into the ID Payload, all fields are always
2418 in MSB first order. The IP address, port, and/or the random number
2419 are encoded in the MSB first order.
2423 2.5 Packet Encryption And Decryption
2425 SILC packets are encrypted almost entirely. Only small part of SILC
2426 header is not encrypted as described in section 5.2 SILC Packet Header.
2427 The SILC Packet header is the first part of a packet to be encrypted
2428 and it is always encrypted with the key of the next receiver of the
2429 packet. The data payload area of the packet is always entirely
2430 encrypted and it is usually encrypted with the next receiver's key.
2431 However, there are some special packet types and packet payloads
2432 that require special encryption process. These special cases are
2433 described in the next sections. First is described the normal packet
2438 2.5.1 Normal Packet Encryption And Decryption
2440 Normal SILC packets are encrypted with the session key of the next
2441 receiver of the packet. The entire SILC Packet header and the packet
2442 data payload is is also encrypted with the same key. Padding of the
2443 packet is also encrypted always with the session key, also in special
2444 cases. Computed MAC of the packet must not be encrypted.
2446 Decryption process in these cases are straightforward. The receiver
2447 of the packet MUST first decrypt the SILC Packet header, or some parts
2448 of it, usually first 16 bytes of it. Then the receiver checks the
2449 packet type from the decrypted part of the header and can determine
2450 how the rest of the packet must be decrypted. If the packet type is
2451 any of the special cases described in the following sections the packet
2452 decryption is special. If the packet type is not among those special
2453 packet types rest of the packet can be decrypted with the same key.
2455 With out a doubt, this sort of decryption processing causes some
2456 overhead to packet decryption, but never the less, is required.
2460 2.5.2 Channel Message Encryption And Decryption
2462 Channel Messages (Channel Message Payload) are always encrypted with
2463 the channel specific key. However, the SILC Packet header is not
2464 encrypted with that key. As in normal case, the header is encrypted
2465 with the key of the next receiver of the packet, who ever that might
2466 be. Note that in this case the encrypted data area is not touched
2467 at all; it MUST NOT be re-encrypted with the session key.
2469 Receiver of a channel message, who ever that is, is REQUIRED to decrypt
2470 the SILC Packet header to be able to even recognize the packet to be as
2471 channel message. This is same procedure as for normal SILC packets.
2472 As the receiver founds the packet to be channel message, rest of the
2473 packet processing is special. Rest of the SILC Packet header is
2474 decrypted with the same session key along with the padding of the
2475 packet. After that the packet is protected with the channel specific
2476 key and thus can be decrypted only if the receiver is the client on
2477 the channel. See section 2.7 Packet Padding Generation for more
2478 information about padding on special packets.
2480 If the receiver of the channel message is router which is routing the
2481 message to another router then it MUST decrypt the Channel Message
2482 payload. Between routers (that is, between cells) channel messages
2483 are protected with session keys shared between the routers. This
2484 causes another special packet processing for channel messages. If
2485 the channel message is received from another router then the entire
2486 packet, including Channel Message payload, MUST be encrypted with the
2487 session key shared between the routers. In this case the packet
2488 decryption process is as with normal SILC packets. Hence, if the
2489 router is sending channel message to another router the Channel
2490 Message payload MUST have been decrypted and MUST be re-encrypted
2491 with the session key shared between the another router. In this
2492 case the packet encryption is as with any normal SILC packet.
2494 It must be noted that this is only when the channel messages are sent
2495 from router to another router. In all other cases the channel
2496 message encryption and decryption is as described above. This
2497 different processing of channel messages with router to router
2498 connection is because channel keys are cell specific. All cells have
2499 their own channel keys thus the channel message traveling from one
2500 cell to another MUST be protected as it would be any normal SILC
2503 If the SILC_CMODE_PRIVKEY channel mode has been set for the channel
2504 then the router cannot decrypt the packet as it does not know the
2505 private key. In this case the entire packet MUST be encrypted with
2506 the session key and sent to the router. The router receiving the
2507 packet MUST check the channel mode and decrypt the packet accordingly.
2511 2.5.3 Private Message Encryption And Decryption
2513 By default, private message in SILC are protected by session keys.
2514 In this case the private message encryption and decryption process is
2515 equivalent to normal packet encryption and decryption.
2517 However, private messages MAY be protected with private message key
2518 which causes the packet to be special packet. The procedure in this
2519 case is very much alike to channel packets. The actual private message
2520 is encrypted with the private message key and other parts of the
2521 packet is encrypted with the session key. See 2.7 Packet Padding
2522 Generation for more information about padding on special packets.
2524 The difference from channel message processing is that server or router
2525 en route never decrypts the actual private message, as it does not
2526 have the key to do that. Thus, when sending packets between router
2527 the processing is same as in any other case as well; the packet's header
2528 and padding is protected by the session key and the data area is not
2531 The true receiver of the private message, client, that is, is able
2532 to decrypt the private message as it shares the key with the sender
2537 2.6 Packet MAC Generation
2539 Data integrity of a packet is protected by including a message
2540 authentication code (MAC) at the end of the packet. The MAC is computed
2541 from shared secret MAC key, that is established by the SILC Key Exchange
2542 protocol, from packet sequence number, and from the original contents
2543 of the packet. The MAC is always computed before the packet is
2544 encrypted, although after it is compressed if compression is used.
2546 The MAC is computed from entire packet. Every bit of data in the packet,
2547 including SILC Packet Header is used in the MAC computing. This way
2548 the entire packet becomes authenticated.
2550 If the packet is special packet MAC is computed from the entire packet
2551 but part of the packet may be encrypted before the MAC is computed.
2552 This is case, for example, with channel messages where the message data
2553 is encrypted with key that server may not now. In this case the MAC
2554 has been computed from the encrypted data.
2556 Hence, packet's MAC generation is as follows:
2558 mac = MAC(key, sequence number | SILC packet)
2560 The MAC key is negotiated during the SKE protocol. The sequence number
2561 is a 32 bit MSB first value starting from zero for first packet and
2562 increasing for subsequent packets, finally wrapping after 2^32 packets.
2563 The value is never reset, not even after rekey has been performed. Note
2564 that the sequence number is incremented only when MAC is computed for a
2565 packet. If packet is not encrypted and MAC is not computed then the
2566 sequence number is not incremented. Hence, the sequence number is zero
2567 for first encrypted packet.
2569 See [SILC1] for defined and allowed MAC algorithms.
2573 2.7 Packet Padding Generation
2575 Padding is needed in the packet because the packet is encrypted. It
2576 MUST always be multiple by eight (8) or multiple by the block size
2577 of the cipher, which ever is larger. The padding is always encrypted.
2579 For normal packets the padding is added after the SILC Packet Header
2580 and between the Data Payload area. The padding for normal packets
2581 may be calculated as follows:
2584 padding length = 16 - (packet_length mod block_size)
2587 The `block_size' is the block size of the cipher. The maximum padding
2588 length is 128 bytes, and minimum is 1 byte. The above algorithm calculates
2589 the padding to the next block size, and always returns the padding
2590 length between 1 - 16 bytes. However, implementations may add padding
2591 up to 128 bytes. For example packets that include a passphrase or a
2592 password for authentication purposes SHOULD pad the packet up to the
2593 maximum padding length.
2595 For special packets the padding calculation is different as special
2596 packets may be encrypted differently. In these cases the encrypted
2597 data area MUST already be multiple by the block size thus in this case
2598 the padding is calculated only for SILC Packet Header, not for any
2599 other area of the packet. The same algorithm works in this case as
2600 well, except that the `packet length' is now the SILC Packet Header
2603 The padding MUST be random data, preferably, generated by
2604 cryptographically strong random number generator.
2608 2.8 Packet Compression
2610 SILC Packets MAY be compressed. In this case the data payload area
2611 is compressed and all other areas of the packet MUST remain as they
2612 are. After compression is performed for the data area, the length
2613 field of Packet Header MUST be set to the compressed length of the
2616 The compression MUST always be applied before encryption. When
2617 the packet is received and decrypted the data area MUST be decompressed.
2618 Note that the true sender of the packet MUST apply the compression and
2619 the true receiver of the packet MUST apply the decompression. Any
2620 server or router en route MUST NOT decompress the packet.
2626 The sender of the packet MUST assemble the SILC Packet Header with
2627 correct values. It MUST set the Source ID of the header as its own
2628 ID, unless it is forwarding the packet. It MUST also set the Destination
2629 ID of the header to the true destination. If the destination is client
2630 it will be Client ID, if it is server it will be Server ID and if it is
2631 channel it will be Channel ID.
2633 If the sender wants to compress the packet it MUST apply the
2634 compression now. Sender MUST also compute the padding as described
2635 in above sections. Then sender MUST compute the MAC of the packet.
2637 Then sender MUST encrypt the packet as has been described in above
2638 sections according whether the packet is normal packet or special
2639 packet. The computed MAC MUST NOT be encrypted.
2643 2.10 Packet Reception
2645 On packet reception the receiver MUST check that all fields in the
2646 SILC Packet Header are valid. It MUST check the flags of the
2647 header and act accordingly. It MUST also check the MAC of the packet
2648 and if it is to be failed the packet MUST be discarded. Also if the
2649 header of the packet includes any bad fields the packet MUST be
2652 See above sections on the decryption process of the received packet.
2654 The receiver MUST also check that the ID's in the header are valid
2655 ID's. Unsupported ID types or malformed ID's MUST cause packet
2656 rejection. The padding on the reception is always ignored.
2658 The receiver MUST also check the packet type and start parsing the
2659 packet according to the type. However, note the above sections on
2660 special packet types and their parsing.
2666 Routers are the primary entities in the SILC network that takes care
2667 of packet routing. However, normal servers routes packets as well, for
2668 example, when they are routing channel message to the local clients.
2669 Routing is quite simple as every packet tells the true origin and the
2670 true destination of the packet.
2672 It is still RECOMMENDED for routers that has several routing connections
2673 to create route cache for those destinations that has faster route than
2674 the router's primary route. This information is available for the router
2675 when other router connects to the router. The connecting party then
2676 sends all of its locally connected clients, servers and channels. These
2677 informations helps to create the route cache. Also, when new channels
2678 are created to a cell its information is broadcasted to all routers
2679 in the network. Channel ID's are based on router's ID thus it is easy
2680 to create route cache based on these informations. If faster route for
2681 destination does not exist in router's route cache the packet MUST be
2682 routed to the primary route (default route).
2684 However, there are some issues when routing channel messages to group
2685 of users. Routers are responsible of routing the channel message to
2686 other routers, local servers and local clients as well. Routers MUST
2687 send the channel message to only one router in the network, preferrably
2688 to the shortest route to reach the channel users. The message can be
2689 routed into either upstream or downstream. After the message is sent
2690 to a router in the network it MUST NOT be sent to any other router in
2691 either same route or other route. The message MUST NOT be routed to
2692 the router it came from.
2694 When routing for example private messages they should be routed to the
2695 shortest route always to reach the destination client as fast as possible.
2697 For server which receives a packet to be routed to its locally connected
2698 client the server MUST check whether the particular packet type is
2699 allowed to be routed to the client. Not all packets may be sent by
2700 some odd entity to client that is indirectly connected to the sender.
2701 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2702 entities and sending packets to them. The section mentions the packets
2703 that may be sent to indirectly connected entities. It is clear that
2704 server cannot send, for example, disconnect packet to client that is not
2705 directly connected to the server.
2707 Routers form a ring in the SILC network. However, routers may have other
2708 direct connections to other routers in the network too. This can cause
2709 interesting routing problems in the network. Since the network is a ring,
2710 the packets usually should be routed into clock-wise direction, or if it
2711 cannot be used then always counter clock-wise (primary route) direction.
2712 Problems may arise when a faster direct route exists and router is routing
2713 a channel message. Currently channel messages must be routed either
2714 in upstream or downstream, they cannot be routed to other direct routes.
2715 The SILC protocol should have a shortest path discovery protocol, and some
2716 existing routing protocol, that can handle a ring network with other
2717 direct routes inside the ring (so called hybrid ring-mesh topology),
2718 MAY be defined to be used with the SILC protocol. Additional
2719 specifications MAY be written on the subject to permeate this
2724 2.12 Packet Broadcasting
2726 SILC packets MAY be broadcasted in SILC network. However, only router
2727 server may send or receive broadcast packets. Client and normal server
2728 MUST NOT send broadcast packets and they MUST ignore broadcast packets
2729 if they receive them. Broadcast packets are sent by setting Broadcast
2730 flag to the SILC packet header.
2732 Broadcasting packets means that the packet is sent to all routers in
2733 the SILC network, except to the router that sent the packet. The router
2734 receiving broadcast packet MUST send the packet to its primary route.
2735 The fact that SILC routers may have several router connections can
2736 cause problems, such as race conditions inside the SILC network, if
2737 care is not taken when broadcasting packets. Router MUST NOT send
2738 the broadcast packet to any other route except to its primary route.
2740 If the primary route of the router is the original sender of the packet
2741 the packet MUST NOT be sent to the primary route. This may happen
2742 if router has several router connections and some other router uses
2743 the router as its primary route.
2745 Routers use broadcast packets to broadcast for example information
2746 about newly registered clients, servers, channels etc. so that all the
2747 routers may keep these informations up to date.
2751 3 Security Considerations
2753 Security is central to the design of this protocol, and these security
2754 considerations permeate the specification. Common security considerations
2755 such as keeping private keys truly private and using adequate lengths for
2756 symmetric and asymmetric keys must be followed in order to maintain the
2757 security of this protocol.
2763 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2764 Protocol Specification", Internet Draft, April 2001.
2766 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2767 Protocols", Internet Draft, April 2001.
2769 [SILC4] Riikonen, P., "SILC Commands", Internet Draft, April 2001.
2771 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2774 [IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
2777 [IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
2780 [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
2783 [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
2786 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2789 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2792 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2795 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2796 Infrastructure, Certificate and CRL Profile", RFC 2459,
2799 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2800 John Wiley & Sons, New York, NY, 1996.
2802 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2805 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2806 RFC 2412, November 1998.
2808 [ISAKMP] Maughan D., et al, "Internet Security Association and
2809 Key Management Protocol (ISAKMP)", RFC 2408, November
2812 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2813 (IKE)", RFC 2409, November 1998.
2815 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2816 Authentication", RFC 2104, February 1997.
2818 [PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
2819 Specifications, Version 2.0", RFC 2437, October 1998.
2821 [RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate
2822 Requirement Levels", BCP 14, RFC 2119, March 1997.
2824 [SFTP] Ylonen T., and Lehtinen S., "Secure Shell File Transfer
2825 Protocol", Internet Draft, March 2001.
2827 [RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO
2828 10646", RFC 2279, January 1998.
2835 Snellmanninkatu 34 A 15
2839 EMail: priikone@iki.fi
2841 This Internet-Draft expires XXX
projects / silc.git / blob