8 .ds RF FORMFEED[Page %]
17 Network Working Group P. Riikonen
19 draft-riikonen-silc-pp-02.txt XX April 2001
20 Expires: XX October 2001
26 <draft-riikonen-silc-pp-02.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
34 areas, and its working groups. Note that other groups may also
35 distribute working documents as Internet-Drafts.
37 Internet-Drafts are draft documents valid for a maximum of six months
38 and may be updated, replaced, or obsoleted by other documents at any
39 time. It is inappropriate to use Internet-Drafts as reference
40 material or to cite them other than as "work in progress."
42 The list of current Internet-Drafts can be accessed at
43 http://www.ietf.org/ietf/1id-abstracts.txt
45 The list of Internet-Draft Shadow Directories can be accessed at
46 http://www.ietf.org/shadow.html
48 The distribution of this memo is unlimited.
54 This memo describes a Packet Protocol used in the Secure Internet Live
55 Conferencing (SILC) protocol, specified in the Secure Internet Live
56 Conferencing, Protocol Specification Internet Draft [SILC1]. This
57 protocol describes the packet types and packet payloads which defines
58 the contents of the packets. The protocol provides secure binary packet
59 protocol that assures that the contents of the packets are secured and
74 1 Introduction .................................................. 3
75 1.1 Requirements Terminology .................................. 4
76 2 SILC Packet Protocol .......................................... 4
77 2.1 SILC Packet ............................................... 4
78 2.2 SILC Packet Header ........................................ 5
79 2.3 SILC Packet Types ......................................... 7
80 2.3.1 SILC Packet Payloads ................................ 16
81 2.3.2 Generic payloads .................................... 16
82 2.3.2.1 ID Payload .................................. 16
83 2.3.2.2 Argument Payload ............................ 17
84 2.3.2.3 Channel Payload ............................. 18
85 2.3.2.4 Public Key Payload .......................... 19
86 2.3.3 Disconnect Payload .................................. 19
87 2.3.4 Success Payload ..................................... 19
88 2.3.5 Failure Payload ..................................... 20
89 2.3.6 Reject Payload ...................................... 21
90 2.3.7 Notify Payload ...................................... 22
91 2.3.8 Error Payload ....................................... 21
92 2.3.9 Channel Message Payload ............................. 28
93 2.3.10 Channel Key Payload ................................ 31
94 2.3.11 Private Message Payload ............................ 33
95 2.3.12 Private Message Key Payload ........................ 34
96 2.3.13 Command Payload .................................... 36
97 2.3.14 Command Reply Payload .............................. 37
98 2.3.15 Connection Auth Request Payload .................... 37
99 2.3.16 New ID Payload ..................................... 38
100 2.3.17 New Client Payload ................................. 39
101 2.3.18 New Server Payload ................................. 40
102 2.3.19 New Channel Payload ................................ 41
103 2.3.20 Key Agreement Payload .............................. 42
104 2.3.21 Cell Routers Payload ............................... 43
105 2.4 SILC ID Types ............................................. 44
106 2.5 Packet Encryption And Decryption .......................... 44
107 2.5.1 Normal Packet Encryption And Decryption ............. 45
108 2.5.2 Channel Message Encryption And Decryption ........... 45
109 2.5.3 Private Message Encryption And Decryption ........... 46
110 2.6 Packet MAC Generation ..................................... 47
111 2.7 Packet Padding Generation ................................. 47
112 2.8 Packet Compression ........................................ 48
113 2.9 Packet Sending ............................................ 48
114 2.10 Packet Reception ......................................... 49
115 2.11 Packet Routing ........................................... 49
116 2.12 Packet Broadcasting ...................................... 50
117 3 Security Considerations ....................................... 50
118 4 References .................................................... 50
119 5 Author's Address .............................................. 52
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: Cell Routers Payload
152 This document describes a Packet Protocol used in the Secure Internet
153 Live Conferencing (SILC) protocol specified in the Secure Internet Live
154 Conferencing, Protocol Specification Internet Draft [SILC1]. This
155 protocol describes the packet types and packet payloads which defines
156 the contents of the packets. The protocol provides secure binary packet
157 protocol that assures that the contents of the packets are secured and
160 The basis of SILC protocol relies in the SILC packets and it is with
161 out a doubt the most important part of the protocol. It is also probably
162 the most complicated part of the protocol. Packets are used all the
163 time in the SILC network to send messages, commands and other information.
164 All packets in SILC network are always encrypted and their integrity
165 is assured by computed MACs. The protocol defines several packet types
166 and packet payloads. Each packet type usually has a specific packet
167 payload that actually defines the contents of the packet. Each packet
168 also includes a default SILC Packet Header that provides sufficient
169 information about the origin of the packet and destination of the
174 1.1 Requirements Terminology
176 The keywords MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED,
177 MAY, and OPTIONAL, when they appear in this document, are to be
178 interpreted as described in [RFC2119].
182 2 SILC Packet Protocol
187 SILC packets deliver messages from sender to receiver securely by
188 encrypting important fields of the packet. The packet consists of
189 default SILC Packet Header, Padding, Packet Payload data, and, packet
192 The following diagram illustrates typical SILC packet.
197 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
198 | n bytes | 1 - n bytes | n bytes | n bytes
199 | SILC Header | Padding | Data Payload | MAC
200 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
204 Figure 1: Typical SILC Packet
207 SILC Header is always the first part of the packet and its purpose
208 is to provide information about the packet. It provides for example
209 the packet type, origin of the packet and the destination of the packet.
210 The header is variable in length and first two (2) bytes of the
211 header (thus first two bytes of the packet) are not encrypted. The
212 first two (2) bytes are the length of the packet which is not encrypted.
213 See the following section for description of SILC Packet header. Packets
214 without SILC header or with malformed SILC header must be dropped.
216 Padding follows the packet header. The purpose of the padding is to
217 make the packet multiple by eight (8) or by the block size of the
218 cipher used in the encryption, which ever is larger. The maximum
219 length of padding is currently 16 bytes. The padding is always
222 Data payload area follows padding and it is the actual data of the
223 packet. The packet data is the packet payloads defined in this
224 protocol. The data payload area is always encrypted.
226 The last part of SILC packet is the packet MAC that assures the
227 integrity of the packet. The MAC is always computed from the packet
228 before the encryption is applied to the packet. If compression is used
229 in the packet the MAC is computed after the compression has been
230 applied. The compression, on the other hand, is always applied before
233 All fields in all packet payloads are always in MSB (most significant
238 2.2 SILC Packet Header
240 The SILC packet header is applied to all SILC packets and it is
241 variable in length. The purpose of SILC Packet header is to provide
242 detailed information about the packet. The receiver of the packet
243 uses the packet header to parse the packet and gain other relevant
244 parameters of the packet.
246 The following diagram represents the SILC packet header. (*) indicates
247 that this field is never encrypted. Other fields are always encrypted.
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 | Source ID Length | Destination ID Length |
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. This field must
279 not be encrypted but must always be authenticated.
281 o Flags (1 byte) - Indicates flags to be used in packet
282 processing. Several flags may be set by ORing the flags
285 The following flags are reserved for this field:
290 In this case the field is ignored.
293 Private Message Key 0x01
295 Indicates that the packet must include private
296 message that is encrypted using private key set by
297 client. Servers does not know anything about this
298 key and this causes that the private message is
299 not handled by the server at all, it is just
300 passed along. See section 2.5.3 Private Message
301 Encryption And Decryption for more information.
306 Indicates that the packet consists of list of
307 packet payloads indicated by the Packet Type field.
308 The payloads are added one after the other. Note that
309 there are packet types that must not be used as
310 list. Parsing of list packet is done by calculating
311 the length of each payload and parsing them one by
317 Marks the packet to be broadcasted. Client cannot
318 send broadcast packet and normal server cannot send
319 broadcast packet. Only router server may send broadcast
320 packet. The router receiving of packet with this flag
321 set MUST send (broadcast) the packet to its primary
322 route. If router has several router connections the
323 packet may be sent only to the primary route. See
324 section 2.13 Packet Broadcasting for description of
332 o Packet Type (1 byte) - Is the type of the packet. Receiver
333 uses this field to parse the packet. See section 2.3
334 SILC Packets for list of defined packet types.
336 o Source ID Length (2 bytes) - Indicates the length of the
337 Source ID field in the header, not including this or any
340 o Destination ID Length (2 bytes) - Indicates the length of the
341 Destination ID field in the header, not including this or
344 o Src ID Type (1 byte) - Indicates the type of ID in the
345 Source ID field. See section 2.4 SILC ID Types for
348 o Source ID (variable length) - The actual source ID that
349 indicates which is the original sender of the packet.
351 o Dst ID Type (1 byte) - Indicates the type of ID in the
352 Destination ID field. See section 2.4 SILC ID Types for
355 o Destination ID (variable length) - The actual source ID that
356 indicates which is the end receiver of the packet.
360 2.3 SILC Packet Types
362 SILC packet types defines the contents of the packet and it is used by
363 the receiver to parse the packet. The packet type is 8 bits, as a one
364 byte, in length. The range for the packet types are from 0 - 255,
365 where 0 is never sent and 255 is currently reserved for future
366 extensions and MUST NOT be defined to any other purpose. Every SILC
367 specification compliant implementation SHOULD support all of these packet
370 The below list of the SILC Packet types includes reference to the packet
371 payload as well. Packet payloads are the actual packet, that is, the data
372 that the packet consists of. Each packet type defines packet payload
373 which usually may only be sent with the specific packet type.
375 Most of the packets are packets that must be destined directly to entity
376 that is connected to the sender. It is not allowed, for example, for
377 router to send disconnect packet to client that is not directly connected
378 to the router. However, there are some special packet types that may
379 be destined to some entity that the sender has not direct connection
380 with. These packets are for example private message packets, channel
381 message packets, command packets and some other packets that may be
382 broadcasted in the SILC network. If the packet is allowed to be sent to
383 indirectly connected entity it is mentioned separately in the packet
384 description (unless it is obvious as in private and channel message
385 packets). Other packets MUST NOT be sent or accepted, if sent, to
386 indirectly connected entities.
388 List of SILC Packet types are defined as follows.
393 This type is reserved and it is never sent.
396 1 SILC_PACKET_DISCONNECT
398 This packet is sent to disconnect the remote end. Reason of
399 the disconnection is sent inside the packet payload. Client
400 usually does not send this packet.
402 This packet MUST NOT be sent as list and the List flag MUST
405 Payload of the packet: See section 2.3.3 Disconnect Payload
408 2 SILC_PACKET_SUCCESS
410 This packet is sent upon successful execution of some protocol.
411 The status of the success is sent in the packet.
413 This packet MUST NOT be sent as list and the List flag MUST
416 Payload of the packet: See section 2.3.4 Success Payload
419 3 SILC_PACKET_FAILURE
421 This packet is sent upon failure of some protocol. The status
422 of the failure is sent in the packet.
424 This packet MUST NOT be sent as list and the List flag MUST
427 Payload of the packet: See section 2.3.5 Failure Payload
432 This packet MAY be sent upon rejection of some protocol.
433 The status of the rejection is sent in the packet.
435 This packet MUST NOT be sent as list and the List flag MUST
438 Payload of the packet: See section 2.3.6 Reject Payload
443 This packet is used to send notify message, usually from
444 server to client, although it MAY be sent from server to another
445 server as well. Client MUST NOT send this packet. Server MAY
446 send this packet to channel as well when the packet is
447 distributed to all clients on the channel.
449 Payload of the packet: See section 2.3.7 Notify Payload.
454 This packet is sent when an error occurs. Server MAY
455 send this packet. Client MUST NOT send this packet. The
456 client MAY entirely ignore the packet, however, server is
457 most likely to take action anyway. This packet MAY be sent
458 to entity that is indirectly connected to the sender.
460 This packet MUST NOT be sent as list and the List flag MUST
463 Payload of the packet: See section 2.3.8 Error Payload.
466 7 SILC_PACKET_CHANNEL_MESSAGE
468 This packet is used to send messages to channels. The packet
469 includes Channel ID of the channel and the actual message to
470 the channel. Messages sent to the channel are always protected
471 by channel specific keys. Channel Keys are distributed by
472 SILC_PACKET_CHANNEL_KEY packet.
474 This packet MUST NOT be sent as list and the List flag MUST
477 Payload of the packet: See section 2.3.9 Channel Message
481 8 SILC_PACKET_CHANNEL_KEY
483 This packet is used to distribute new key for particular
484 channel. Each channel has their own independent keys that
485 is used to protect the traffic on the channel. Only server
486 may send this packet. This packet MAY be sent to entity
487 that is indirectly connected to the sender.
489 This packet MUST NOT be sent as list and the List flag MUST
492 Payload of the packet: See section 2.3.10 Channel Key Payload
495 9 SILC_PACKET_PRIVATE_MESSAGE
497 This packet is used to send private messages from client
498 to another client. By default, private messages are protected
499 by session keys established by normal key exchange protocol.
500 However, it is possible to use specific key to protect private
501 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
502 agree the key with the remote client. Pre-shared key MAY be
503 used as well if both of the client knows it, however, it needs
504 to be agreed outside SILC. See more of this in [SILC1].
506 This packet MUST NOT be sent as list and the List flag MUST
509 Payload of the packet: See section 2.3.11 Private Message
513 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
515 This packet is used to agree about a key to be used to protect
516 the private messages between two clients. If this is not sent
517 the normal session key is used to protect the private messages
518 inside SILC network. Agreeing to use specific key to protect
519 private messages adds security, as no server between the two
520 clients will be able to decrypt the private message. However,
521 servers inside SILC network are considered to be trusted, thus
522 using normal session key to protect private messages does not
523 degree security. Whether to agree to use specific keys by
524 default or to use normal session keys by default, is
525 implementation specific issue. See more of this in [SILC1].
527 This packet MUST NOT be sent as list and the List flag MUST
530 Payload of the packet: See section 2.3.12 Private Message
534 11 SILC_PACKET_COMMAND
536 This packet is used to send commands from client to server.
537 Server MAY send this packet to other servers as well. All
538 commands are listed in their own section SILC Command Types
539 in [SILC4]. The contents of this packet is command specific.
540 This packet MAY be sent to entity that is indirectly connected
543 This packet MUST NOT be sent as list and the List flag MUST
546 Payload of the packet: See section 2.3.13 Command Payload
549 12 SILC_PACKET_COMMAND_REPLY
551 This packet is send as reply to the SILC_PACKET_COMMAND packet.
552 The contents of this packet is command specific. This packet
553 MAY be sent to entity that is indirectly connected to the
556 This packet MUST NOT be sent as list and the List flag MUST
559 Payload of the packet: See section 2.3.14 Command Reply
560 Payload and section 2.3.13 Command
564 13 SILC_PACKET_KEY_EXCHANGE
566 This packet is used to start SILC Key Exchange Protocol,
567 described in detail in [SILC3].
569 This packet MUST NOT be sent as list and the List flag MUST
572 Payload of the packet: Payload of this packet is described
573 in the section SILC Key Exchange
574 Protocol and its sub sections in
578 14 SILC_PACKET_KEY_EXCHANGE_1
580 This packet is used as part of the SILC Key Exchange Protocol.
582 This packet MUST NOT be sent as list and the List flag MUST
585 Payload of the packet: Payload of this packet is described
586 in the section SILC Key Exchange
587 Protocol and its sub sections in
591 15 SILC_PACKET_KEY_EXCHANGE_2
593 This packet is used as part of the SILC Key Exchange Protocol.
595 This packet MUST NOT be sent as list and the List flag MUST
598 Payload of the packet: Payload of this packet is described
599 in the section SILC Key Exchange
600 Protocol and its sub sections in
604 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
606 This packet is used to request the authentication method to
607 be used in the SILC Connection Authentication Protocol. If
608 initiator of the protocol does not know the mandatory
609 authentication method this packet MAY be used to determine it.
611 The party receiving this payload MUST respond with the same
612 packet including the mandatory authentication method.
614 This packet MUST NOT be sent as list and the List flag MUST
617 Payload of the packet: See section 2.3.15 Connection Auth
623 17 SILC_PACKET_CONNECTION_AUTH
625 This packet is used to start and perform the SILC Connection
626 Authentication Protocol. This protocol is used to authenticate
627 the connecting party. The protocol is described in detail in
630 This packet MUST NOT be sent as list and the List flag MUST
633 Payload of the packet: Payload of this packet is described
634 in the section SILC Authentication
635 Protocol and it sub sections in [SILC].
638 18 SILC_PACKET_NEW_ID
640 This packet is used to distribute new ID's from server to
641 router and from router to all routers in the SILC network.
642 This is used when for example new client is registered to
643 SILC network. The newly created ID's of these operations are
644 distributed by this packet. Only server may send this packet,
645 however, client MUST be able to receive this packet.
647 Payload of the packet: See section 2.3.16 New ID Payload
650 19 SILC_PACKET_NEW_CLIENT
652 This packet is used by client to register itself to the
653 SILC network. This is sent after key exchange and
654 authentication protocols has been completed. Client sends
655 various information about itself in this packet.
657 This packet MUST NOT be sent as list and the List flag MUST
660 Payload of the packet: See section 2.3.17 New Client Payload
663 20 SILC_PACKET_NEW_SERVER
665 This packet is used by server to register itself to the
666 SILC network. This is sent after key exchange and
667 authentication protocols has been completed. Server sends
668 this to the router it connected to, or, if router was
669 connecting, to the connected router. Server sends its
670 Server ID and other information in this packet. The client
671 MUST NOT send or receive this packet.
673 This packet MUST NOT be sent as list and the List flag MUST
676 Payload of the packet: See section 2.3.18 New Server Payload
679 21 SILC_PACKET_NEW_CHANNEL
681 This packet is used to notify routers about newly created
682 channel. Channels are always created by the router and it must
683 notify other routers about the created channel. Router sends
684 this packet to its primary route. Client MUST NOT send this
685 packet. This packet MAY be sent to entity that is indirectly
686 connected to the sender.
688 Payload of the packet: See section 2.3.19 New Channel Payload
693 This packet is used to indicate that re-key must be performed
694 for session keys. See section Session Key Regeneration in
695 [SILC1] for more information. This packet does not have
698 This packet MUST NOT be sent as list and the List flag MUST
702 23 SILC_PACKET_REKEY_DONE
704 This packet is used to indicate that re-key is performed and
705 new keys must be used hereafter. This is sent only if re-key
706 was done without PFS option.
708 This packet MUST NOT be sent as list and the List flag MUST
712 24 SILC_PACKET_HEARTBEAT
714 This packet is used by clients, servers and routers to keep the
715 connection alive. It is recommended that all servers implement
716 keepalive actions and perform it to both direction in a link.
717 This packet does not have a payload.
719 This packet MUST NOT be sent as list and the List flag MUST
723 25 SILC_PACKET_KEY_AGREEMENT
725 This packet is used by clients to request key negotiation
726 between another client in the SILC network. If the negotiation
727 is started it is performed using the SKE protocol. The result of
728 the negotiation, the secret key material, can be used for
729 example as private message key. The server and router MUST NOT
732 This packet MUST NOT be sent as list and the List flag MUST
735 Payload of the packet: See section 2.3.20 Key Agreement Payload
738 26 SILC_PACKET_CELL_ROUTERS
740 This packet is used by primary router in the cell to notify its
741 primary router what other routers (backup routers) exist in the
742 cell. In case of failure of the primary router in the cell the
743 first router in the list will act as primary router of the cell.
744 This packet MAY be sent at anytime after connection has been
745 registered to the primary router. The client MUST NOT send this
748 This packet MUST NOT be sent as list and the List flag MUST
751 Payload of the packet: See section 2.3.21 Cell Routers Payload
756 Currently undefined commands.
761 These packet types are reserved for private use and they will
762 not be defined by this document.
769 This type is reserved for future extensions and currently it
775 2.3.1 SILC Packet Payloads
777 All payloads resides in the main data area of the SILC packet. However
778 all payloads MUST be at the start of the data area after the SILC
779 packet header and padding. All fields in the packet payload are always
780 encrypted, as, they reside in the data area of the packet which is
783 Payloads described in this section are common payloads that MUST be
784 accepted anytime during SILC session. Most of the payloads may only
785 be sent with specific packet type which is defined in the description
788 There are a lot of other payloads in the SILC as well. However, they
789 are not common in the sense that they could be sent at any time.
790 These payloads are not described in this section. These are payloads
791 such as SILC Key Exchange payloads and so on. These are described
792 in [SILC1], [SILC3] and [SILC4].
796 2.3.2 Generic payloads
798 This section describes generic payloads that are not associated to any
799 specific packet type. They can be used for example inside some other
806 This payload can be used to send an ID. ID's are variable length thus
807 this payload provides a way to send variable length ID's.
820 The following diagram represents the ID Payload.
825 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
826 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
827 | ID Type | ID Length |
828 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
832 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
840 o ID Type (2 bytes) - Indicates the type of the ID. See
841 section 2.4 SILC ID Types for list of defined ID types.
843 o ID Length (2 bytes) - Length of the ID Data area not
844 including the length of any other fields in the payload.
846 o ID Data (variable length) - The actual ID data.
851 2.3.2.2 Argument Payload
853 Argument Payload is used to set arguments for any packet payload that
854 needs and supports arguments, such as commands. Number of arguments
855 associated with a packet MUST be indicated by the packet payload which
856 needs the arguments. Argument Payloads MUST always reside right after
857 the packet payload needing the arguments. Incorrect amount of argument
858 payloads MUST cause rejection of the packet. The following diagram
859 represents the Argument Payload.
861 The following diagram represents the Argument Payload.
866 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
867 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
868 | Payload Length | Argument Type | |
869 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
873 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
877 Figure 4: Argument Payload
881 o Payload Length (2 bytes) - Length of the argument payload data
882 area not including the length of any other fields in the
885 o Argument Type (1 byte) - Indicates the type of the argument.
886 Every argument may have a specific type that MUST be defined
887 by the packet payload needing the argument. For example
888 every command specify a number for each argument that maybe
889 associated with the command. By using this number the receiver
890 of the packet knows what type of argument this is. If there is
891 no specific argument type this field is set to zero (0).
893 o Argument Data (variable length) - Argument data.
898 2.3.2.3 Channel Payload
900 Generic Channel Payload may be used to send information about channel,
901 its name, the Channel ID and a mode.
903 The following diagram represents the Channel Payload Payload.
909 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
910 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
911 | Channel Name Length | |
912 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
916 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
917 | Channel ID Length | |
918 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
922 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
924 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
928 Figure 5: New Channel Payload
932 o Channel Name Length (2 bytes) - Length of the channel name
935 o Channel Name (variable length) - The name of the channel.
937 o Channel ID Length (2 bytes) - Length of the Channel ID field.
939 o Channel ID (variable length) - The Channel ID.
941 o Mode Mask (4 bytes) - A mode. This can be the mode of the
942 channel but it can also be the mode of the client on the
943 channel. The contents of this field is dependent of the
944 usage of this payload. The usage is defined separately
945 when this payload is used. This is a 32 bit MSB first value.
950 2.3.2.4 Public Key Payload
952 Generic Public Key Payload may be used to send different types of
953 public keys and certificates.
955 The following diagram represents the Channel Payload Payload.
961 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
962 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
963 | Public Key Length | Public Key Type |
964 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
966 ~ Public Key of the party (or certificate) ~
968 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
972 Figure 6: Public Key Payload
976 o Public Key Length (2 bytes) - The length of the Public Key
977 (or certificate) field, not including any other field.
979 o Public Key Type (2 bytes) - The public key (or certificate)
980 type. This field indicates the type of the public key in
981 the packet. See the [SILC3] for defined public key types.
983 o Public Key (or certificate) (variable length) - The
984 public key or certificate.
989 2.3.3 Disconnect Payload
991 Disconnect payload is sent upon disconnection. The payload is simple;
992 reason of disconnection is sent to the disconnected party.
994 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
995 MUST NOT be sent in any other packet type. The following diagram
996 represents the Disconnect Payload.
1002 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
1003 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1005 ~ Disconnect Message ~
1007 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1011 Figure 7: Disconnect Payload
1017 o Disconnect Message (variable length) - Human readable
1018 reason of the disconnection.
1023 2.3.4 Success Payload
1025 Success payload is sent when some protocol execution is successfully
1026 completed. The payload is simple; indication of the success is sent.
1027 This may be any data, including binary or human readable data.
1032 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
1033 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1035 ~ Success Indication ~
1037 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1041 Figure 8: Success Payload
1045 o Success Indication (variable length) - Indication of
1046 the success. This may be for example some flag that
1047 indicates the protocol and the success status or human
1048 readable success message. The true length of this
1049 payload is available by calculating it from the SILC
1056 2.3.5 Failure Payload
1058 This is opposite of Success Payload. Indication of failure of
1059 some protocol is sent in the payload.
1065 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
1066 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1068 ~ Failure Indication ~
1070 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1074 Figure 9: Failure Payload
1078 o Failure Indication (variable length) - Indication of
1079 the failure. This may be for example some flag that
1080 indicates the protocol and the failure status or human
1081 readable failure message. The true length of this
1082 payload is available by calculating it from the SILC
1088 2.3.6 Reject Payload
1090 This payload is sent when some protocol is rejected to be executed.
1091 Other operations MAY send this as well that was rejected. The
1092 indication of the rejection is sent in the payload. The indication
1093 may be binary or human readable data.
1099 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
1100 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1102 ~ Reject Indication ~
1104 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1108 Figure 10: Reject Payload
1112 o Reject Indication (variable length) - Indication of
1113 the rejection. This maybe for example some flag that
1114 indicates the protocol and the rejection status or human
1115 readable rejection message. The true length of this
1116 payload is available by calculating it from the SILC
1122 2.3.7 Notify Payload
1124 Notify payload is used to send notify messages. The payload is usually
1125 sent from server to client, however, server MAY send it to another
1126 server as well. This payload MAY also be sent to a channel. Client
1127 MUST NOT send this payload. The receiver of this payload MAY ignore
1128 the contents of the payload, however, notify message should be audited.
1130 The payload may only be sent with SILC_PACKET_NOTIFY packet. It MUST
1131 not be sent in any other packet type. The following diagram represents
1137 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
1138 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1139 | Notify Type | Payload Length |
1140 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1146 Figure 11: Notify Payload
1150 o Notify Type (2 bytes) - Indicates the type of the notify
1153 o Payload Length (2 bytes) - Length of the entire Notify Payload
1154 including any associated Argument Payloads.
1156 o Argument Nums (2 bytes) - Indicates the number of Argument
1157 Payloads associated to this payload. Notify types may define
1158 arguments to be send along the notify message.
1161 The following list of currently defined notify types. The format for
1162 notify arguments is same as in SILC commands described in [SILC4].
1163 Also, all ID's sent in arguments are sent inside ID Payload.
1166 0 SILC_NOTIFY_TYPE_NONE
1168 If no specific notify type apply for the notify message this type
1172 Arguments: (1) <message>
1174 The <message> is implementation specific free text string.
1175 Receiver MAY ignore this message.
1178 1 SILC_NOTIFY_TYPE_INVITE
1180 Sent when an client is invited to a channel. This is also sent
1181 when the invite list of the channel is changed. This notify type
1182 is sent between routers and if an client was invited, to the
1183 client as well. In this case the packet is destined to the client.
1186 Arguments: (1) <Channel ID> (2) <channel name>
1187 (3) [<sender Client ID>] (4) [<adding client>]
1188 (5) [<removing client>]
1190 The <Channel ID> is the channel. The <channel name> is the name
1191 of the channel and is provided because the client which receives
1192 this notify packet may not have a way to resolve the name of the
1193 channel from the <Channel ID>. The <sender Client ID> is the
1194 Client ID which invited the client to the channel. The <adding
1195 client> and the <removing client> indicates the added or removed
1196 client from the channel's invite list. The format of the <adding
1197 client> and the <removing client> is defined in the [SILC4] with
1198 SILC_COMMAND_INVITE command.
1200 The <adding client> and <removing client> MUST NOT be sent when
1201 the packet is destined to a client.
1204 2 SILC_NOTIFY_TYPE_JOIN
1206 Sent when client has joined to a channel. The server MUST
1207 distribute this type only to the local clients on the channel
1208 and then send it to its primary router. The router or server
1209 receiving the packet distributes this type to the local clients
1210 on the channel and broadcast it to the network.
1213 Arguments: (1) [<Client ID>] (2) <Channel ID>
1215 The <Client ID> is the client that joined to the channel indicated
1216 by the <Channel ID>.
1219 3 SILC_NOTIFY_TYPE_LEAVE
1221 Sent when client has left a channel. The server must distribute
1222 this type only to the local clients on the channel and then send
1223 it to its primary router. The router or server receiving the
1224 packet distributes this type to the local clients on the channel
1225 and broadcast it to the network.
1228 Arguments: (1) <Client ID>
1230 The <Client ID> is the client which left the channel.
1233 4 SILC_NOTIFY_TYPE_SIGNOFF
1235 Sent when client signoff from SILC network. The server MUST
1236 distribute this type only to the local clients on the channel and
1237 then send it to its primary router. The router or server receiving
1238 the packet distributes this type to the local clients on the
1239 channel and broadcast it to the network.
1242 Arguments: (1) <Client ID> (2) <message>
1244 The <Client ID> is the client which left SILC network. The
1245 <message> is free text string indicating the reason of the signoff.
1248 5 SILC_NOTIFY_TYPE_TOPIC_SET
1250 Sent when topic is set/changed on a channel. This type must be
1251 sent only to the clients which is joined on the channel which
1252 topic was set or changed.
1255 Arguments: (1) <Client ID> (2) <topic>
1257 The <Client ID> is the client which set or changed the <topic>.
1260 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1262 Sent when client changes nick on a channel. The server MUST
1263 distribute this type only to the local clients on the channel
1264 and then send it to its primary router. The router or server
1265 receiving the packet distributes this type to the local clients
1266 on the channel and broadcast it to the network.
1269 Arguments: (1) <Old Client ID> (2) <New Client ID>
1271 The <Old Client ID> is the old ID of the client which changed
1272 the nickname. The <New Client ID> is the new ID generated by
1273 the change of the nickname.
1276 7 SILC_NOTIFY_TYPE_CMODE_CHANGE
1278 Sent when channel mode has changed. This type MUST be sent only
1279 to the clients which is joined on the channel which mode was
1283 Arguments: (1) <ID Payload> (2) <mode mask>
1284 (3) [<cipher>] (4) <[hmac>]
1286 The <ID Payload> is the ID (usually Client ID but it can be
1287 Server ID as well when the router is enforcing channel mode
1288 change) of the entity which changed the mode. The <mode mask>
1289 is the new mode mask of the channel. The client can safely
1290 ignore the <cipher> argument since the SILC_PACKET_CHANNEL_KEY
1291 packet will force the new channel key change anyway. The <hmac>
1292 argument is important since the client is responsible of setting
1293 the new HMAC and the hmac key into use.
1296 8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
1298 Sent when user mode on channel has changed. This type MUST be
1299 sent only to the clients which is joined on the channel where
1300 the target client is on.
1303 Arguments: (1) <Client ID> (2) <mode mask>
1304 (3) <Target Client ID>
1306 The <Client ID> is the client which changed the mode. The
1307 <mode mask> is the new mode mask of the channel. The <Target
1308 Client ID> is the client which mode was changed.
1311 9 SILC_NOTIFY_TYPE_MOTD
1313 Sent when Message of the Day (motd) is sent to a client.
1316 Arguments: (1) <motd>
1318 The <motd> is the Message of the Day.
1321 10 SILC_NOTIFY_TYPE_CHANNEL_CHANGE
1323 Sent when channel's ID has changed for a reason or another.
1324 This is sent by normal server to the client. This can also be
1325 sent by router to other server to force the Channel ID change.
1326 The Channel ID MUST be changed to use the new one. When sent
1327 to clients, this type MUST be sent only to the clients which is
1328 joined on the channel.
1331 Arguments: (1) <Old Channel ID> (2) <New Channel ID>
1333 The <Old Channel ID> is the channel's old ID and the <New
1334 Channel ID> is the new one that MUST replace the old one.
1337 11 SILC_NOTIFY_TYPE_SERVER_SIGNOFF
1339 Sent when server quits SILC network. Those clients from this
1340 server that are on channels must be removed from the channel.
1343 Arguments: (1) <Server ID> (n) [<Client ID> [...]
1345 The <Server ID> is the server's ID. The rest of the arguments
1346 are the Client ID's of the client's which are coming from this
1347 server and are thus quitting the SILC network also. If the
1348 maximum number of arguments are reached another
1349 SILC_NOTIFY_TYPE_SERVER_SIGNOFF notify packet MUST be sent.
1350 When this notify packet is sent between routers the Client ID's
1354 12 SILC_NOTIFY_TYPE_KICKED
1356 Sent when a client has been kicked from a channel. This is
1357 sent also to the client which was kicked from the channel.
1358 The client which was kicked from the channel MUST be removed
1359 from the channel. This notify type is always destined to the
1360 channel. The router or server receiving the packet distributes
1361 this type to the local clients on the channel and broadcast it
1365 Arguments: (1) <Client ID> (2) [<comment>]
1367 The <Client ID> is the client which was kicked from the channel.
1368 The kicker may have set the <comment> to indicate the reason for
1372 13 SILC_NOTIFY_TYPE_KILLED
1374 Sent when a client has been killed from the network. This is sent
1375 also to the client which was killed from the network. The client
1376 which was killed from the network MUST be removed from the network.
1377 This notify type is destined directly to the client which was
1378 killed and to channel if the client is on any channel. The router
1379 or server receiving the packet distributes this type to the local
1380 clients on the channel and broadcast it to the network.
1383 Arguments: (1) <Client ID> (2) [<comment>]
1385 The <Client ID> is the client which was killed from the network.
1386 The killer may have set the <comment> to indicate the reason for
1390 14 SILC_NOTIFY_TYPE_UMODE_CHANGE
1392 Sent when user's mode in the SILC changes. This type is sent
1393 only between routers as broadcast packet.
1396 Arguments: (1) <Client ID> (2) <mode mask>
1398 The <Client ID> is the client which mode was changed. The
1399 <mode mask> is the new mode mask.
1402 15 SILC_NOTIFY_TYPE_BAN
1404 Sent when the ban list of the channel is changed. This type is
1405 sent only between routers as broadcast packet.
1408 Arguments: (1) <Channel ID> (2) [<adding client>]
1409 (3) [<removing client>]
1411 The <Channel ID> is the channel which ban list was changed. The
1412 <adding client> is used to indicate the a ban was added and the
1413 <removing client> is used to indicate that a ban was removed from
1414 the ban list. The format of the <adding client> and the
1415 <removing client> is defined in the [SILC4] with SILC_COMMAND_BAN
1420 Notify types starting from 16384 are reserved for private notify
1427 Error payload is sent upon error. Error may occur in various
1428 conditions when server sends this packet. Client MUST NOT send this
1429 payload but MUST be able to accept it. However, client MAY
1430 totally ignore the contents of the packet as server is going to
1431 take action on the error anyway. However, it is recommended
1432 that the client takes error packet seriously.
1438 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
1439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1447 Figure 12: Error Payload
1451 o Error Message (variable length) - Human readable error
1457 2.3.9 Channel Message Payload
1459 Channel messages are the most common messages sent in the SILC.
1460 Channel Message Payload is used to send message to channels. These
1461 messages can only be sent if client has joined to some channel.
1462 Even though this packet is the most common in SILC it is still
1463 special packet. Some special handling on sending and reception
1464 of channel message is required.
1466 Padding MUST be applied into this payload since the payload is
1467 encrypted separately from other parts of the packet with the
1468 channel specific key. Hence the requirement of the padding.
1469 The padding SHOULD be random data. The packet MUST be made
1470 multiple by eight (8) or by the block size of the cipher, which
1473 The SILC header in this packet is encrypted with the session key
1474 of the next receiver of the packet. Nothing else is encrypted
1475 with that key. Thus, the actual packet and padding to be
1476 encrypted with the session key is SILC Header plus padding to it
1477 to make it multiple by eight (8) or multiple by the block size
1478 of the cipher, which ever is larger.
1480 Receiver of the the channel message packet is able to determine
1481 the channel the message is destined to by checking the destination
1482 ID from the SILC Packet header which tells the destination channel.
1483 The original sender of the packet is also determined by checking
1484 the source ID from the header which tells the client which sent
1487 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1488 It MUST NOT be sent in any other packet type. The following diagram
1489 represents the Channel Message Payload.
1491 (*) indicates that the field is not encrypted.
1497 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
1498 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1499 | Flags | Message Length |
1500 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1504 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1505 | Padding Length | |
1506 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1510 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1514 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1516 ~ Initial Vector * ~
1518 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1522 Figure 13: Channel Message Payload
1526 o Flags (2 bytes) - Includes the flags of the channel
1527 messages. The flags can indicate a reason or purpose
1528 for the channel message. Note that the Private Message
1529 Payload use these same flags for the same purpose. The
1530 following flags are defined:
1532 0x0000 SILC_MESSAGE_FLAG_NONE
1534 No specific flags set.
1536 0x0001 SILC_MESSAGE_FLAG_AUTREPLY
1538 This message is an automatic reply to a earlier
1541 0x0002 SILC_MESSAGE_FLAG_NOREPLY
1543 There should not be reply messages to this
1546 0x0004 SILC_MESSAGE_FLAG_ACTION
1548 The sender is performing an action and the message
1549 is the indication of the action.
1551 0x0008 SILC_MESSAGE_FLAG_NOTICE
1553 The message is for example and informational notice
1556 0x0010 SILC_MESSAGE_FLAG_REQUEST
1558 This is a generic request flag to send request
1561 0x0020 - 0x0200 RESERVED
1563 Reserved for future flags
1565 0x0400 - 0x8000 PRIVATE RANGE
1567 Private range for free use.
1569 o Message Length (2 bytes) - Indicates the length of the
1570 the Message Data field in the payload, not including any
1573 o Message Data (variable length) - The actual message to
1576 o Padding Length (2 bytes) - Indicates the length of the
1577 Padding field in the payload, not including any other
1580 o Padding (variable length) - The padding that MUST be
1581 applied because this payload is encrypted separately from
1582 other parts of the packet.
1584 o MAC (variable length) - The MAC computed from the
1585 Message Length, Message Data, Padding Length and Padding
1586 fields. This protects the integrity of the plaintext
1587 channel message. The receiver can verify from the MAC
1588 whether the message decrypted correctly. Also, if more than
1589 one private key has been set for the channel, the receiver
1590 can verify which of the keys decrypted the message
1591 correctly. Note that, this field is encrypted and MUST
1592 be added to the padding calculation.
1594 o Initial Vector (variable length) - The initial vector
1595 that has been used in packet encryption. It needs to be
1596 used in the packet decryption as well. What this field
1597 includes is implementation issue. However, it is
1598 RECOMMENDED that it would be random data or, perhaps,
1599 a timestamp. It is NOT RECOMMENDED to use zero (0) as
1600 initial vector. This field is not encrypted. This field
1601 is not included into the padding calculation. Length
1602 of this field equals the cipher's block size. This field
1603 is, however, authenticated.
1608 2.3.10 Channel Key Payload
1610 All traffic in channels are protected by channel specific keys.
1611 Channel Key Payload is used to distribute channel keys to all
1612 clients on the particular channel. Channel keys are sent when
1613 the channel is created, when new user joins to the channel and
1614 whenever a user has left a channel. Server creates the new
1615 channel key and distributes it to the clients by encrypting this
1616 payload with the session key shared between the server and
1617 the client. After that, client starts using the key received
1618 in this payload to protect the traffic on the channel.
1620 The client which is joining to the channel receives its key in the
1621 SILC_COMMAND_JOIN command reply message thus it is not necessary to
1622 send this payload to the entity which sent the SILC_COMMAND_JOIN
1625 Channel keys are cell specific thus every router in the cell have
1626 to create a channel key and distribute it if any client in the
1627 cell has joined to a channel. Channel traffic between cell's
1628 are not encrypted using channel keys, they are encrypted using
1629 normal session keys between two routers. Inside a cell, all
1630 channel traffic is encrypted with the specified channel key.
1631 Channel key should expire periodically, say, in one hour, in
1632 which case new channel key is created and distributed.
1634 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1635 It MUST NOT be sent in any other packet type. The following diagram
1636 represents the Channel Key Payload.
1642 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
1643 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1644 | Channel ID Length | |
1645 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1649 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1650 | Cipher Name Length | |
1651 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1655 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1656 | Channel Key Length | |
1657 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1661 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1665 Figure 14: Channel Key Payload
1670 o Channel ID Length (2 bytes) - Indicates the length of the
1671 Channel ID field in the payload, not including any other
1674 o Channel ID (variable length) - The Channel ID of the
1675 channel this key is meant for.
1677 o Cipher Name Length (2 bytes) - Indicates the length of the
1678 Cipher name field in the payload, not including any other
1681 o Cipher Name (variable length) - Name of the cipher used
1682 in the protection of channel traffic. This name is
1683 initially decided by the creator of the channel but it
1684 MAY change during the life time of the channel as well.
1686 o Channel Key Length (2 bytes) - Indicates the length of the
1687 Channel Key field in the payload, not including any other
1690 o Channel Key (variable length) - The actual channel key
1691 material. This key is used as such as key material for
1692 encryption function.
1697 2.3.11 Private Message Payload
1699 Private Message Payload is used to send private message between
1700 two clients (or users for that matter). The messages are sent only
1701 to the specified user and no other user inside SILC network is
1702 able to see the message. The message is protected by the session
1703 key established by the SILC Key Exchange Protocol. However,
1704 it is also possible to agree to use a private key to protect
1705 just the private messages. See section 2.3.11 Private Message
1706 Key Payload for detailed description of how to agree to use
1709 If normal session key is used to protect the message, every server
1710 between the sender client and the receiving client MUST decrypt the
1711 packet and always re-encrypt it with the session key of the next
1712 receiver of the packet. See section Client To Client in [SILC1].
1714 When private key is used to protect the message, servers between
1715 the sender and the receiver needs not to decrypt/re-encrypt the
1716 packet. Section 4.8.2 Client To Client in [SILC1] gives example of
1717 this scheme as well.
1719 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1720 packet. It MUST NOT be sent in any other packet type. The following
1721 diagram represents the Private Message Payload.
1734 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
1735 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1736 | Flags | Message Data Length |
1737 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1741 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1745 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1749 Figure 15: Private Message Payload
1753 o Flags (2 bytes) - This field includes the flags of the
1754 private message. They can indicate a different reason or
1755 purpose for the private message. See the section 2.3.9
1756 Channel Message Payload for defined flags. Note that
1757 the Channel Message Payload use the same flags for the
1760 o Message Data Length (2 bytes) - Indicates the length of the
1761 Message Data field, not includes any other field.
1763 o Message Data (variable length) - The actual message to
1764 the client. Rest of the packet is reserved for the message
1767 o Padding (variable length) - This field is present only
1768 when the private message payload is encrypted with private
1769 message key. In this case the padding is applied to make
1770 the packet multiple by eight (8), or by the block size of
1771 the cipher, which ever is larger. When encrypted with
1772 normal session keys, this field MUST NOT be included.
1777 2.3.12 Private Message Key Payload
1779 This payload is used to send key from client to another client that
1780 is going to be used to protect the private messages between these
1781 two clients. If this payload is not sent normal session key
1782 established by the SILC Key Exchange Protocol is used to protect
1783 the private messages.
1785 This payload may only be sent by client to another client. Server
1786 MUST NOT send this payload at any time. After sending this payload
1787 the sender of private messages must set the Private Message Key
1788 flag into SILC Packet Header.
1790 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1791 packet. It MUST NOT be sent in any other packet type. The following
1792 diagram represents the Private Message Key Payload.
1798 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
1799 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1800 | Private Message Key Length | |
1801 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1803 ~ Private Message Key ~
1805 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1806 | Cipher Name Length | |
1807 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1811 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1815 Figure 16: Private Message Key Payload
1821 o Private Message Key Length (2 bytes) - Indicates the length
1822 of the Private Message Key field in the payload, not including
1825 o Private Message Key (variable length) - The actual private
1826 message key material.
1828 o Cipher Name Length (2 bytes) - Indicates the length of the
1829 Cipher Name field in the payload, not including any other
1832 o Cipher Name (variable length) - Name of the cipher to use
1833 in the private message encryption. If this field does not
1834 exist then the default cipher of the SILC protocol is used.
1835 See the [SILC1] for defined ciphers.
1841 2.3.13 Command Payload
1843 Command Payload is used to send SILC commands from client to server.
1844 Also server MAY send commands to other servers. The following diagram
1845 represents the Command Payload.
1851 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
1852 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1853 | Payload Length | SILC Command | Arguments Num |
1854 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1855 | Command Identifier |
1856 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1860 Figure 17: Command Payload
1864 o Payload Length (2 bytes) - Length of the entire command
1865 payload including any command argument payloads associated
1868 o SILC Command (1 byte) - Indicates the SILC command. This MUST
1869 be set to non-zero value. If zero (0) value is found in this
1870 field the packet MUST be discarded.
1872 o Arguments Num (1 byte) - Indicates the number of arguments
1873 associated with the command. If there are no arguments this
1874 field is set to zero (0). The arguments MUST follow the
1875 command payload. See section 2.3.2.2 for definition of the
1878 o Command Identifier (2 bytes) - Identifies this command at the
1879 sender's end. The entity which replies to this command MUST
1880 set the value found from this field into the Command Payload
1881 used to send the reply to the sender. This way the sender
1882 can identify which command reply belongs to which originally
1883 sent command. What this field includes is implementation
1884 issue but it is RECOMMENDED that wrapping counter value is
1885 used in the field. Value zero (0) in this field means that
1886 no specific value is set.
1889 See [SILC4] for detailed description of different SILC commands,
1890 their arguments and their reply messages.
1896 2.3.14 Command Reply Payload
1898 Command Reply Payload is used to send replies to the commands. The
1899 Command Reply Payload is identical to the Command Payload thus see
1900 the upper sections for Command Payload and for Command Argument
1901 Payload specifications. Command Reply message uses the Command
1902 Argument Payload as well.
1904 The entity which sends the reply packet MUST set the Command Identifier
1905 field in the reply packet's Command Payload to the value it received
1906 in the original command packet.
1908 See SILC Commands in [SILC4] for detailed description of different
1909 SILC commands, their arguments and their reply messages.
1913 2.3.15 Connection Auth Request Payload
1915 Client MAY send this payload to server to request the authentication
1916 method that must be used in authentication protocol. If client knows
1917 this information beforehand this payload is not necessary to be sent.
1918 Server performing authentication with another server MAY also send
1919 this payload to request the authentication method. If the connecting
1920 server already knows this information this payload is not necessary
1923 Server receiving this request MUST reply with same payload sending
1924 the mandatory authentication method. Algorithms that may be required
1925 to be used by the authentication method are the ones already
1926 established by the SILC Key Exchange protocol. See section Key
1927 Exchange Start Payload in [SILC3] for detailed information.
1929 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1930 packet. It MUST NOT be sent in any other packet type. The following
1931 diagram represents the Connection Auth Request Payload.
1937 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
1938 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1939 | Connection Type | Authentication Method |
1940 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1944 Figure 18: Connection Auth Request Payload
1948 o Connection Type (2 bytes) - Indicates the type of the ID.
1949 The following connection types are defined:
1955 If any other type is found in this field the packet must be
1956 discarded and the authentication must be failed.
1958 o Authentication Method (2 bytes) - Indicates the authentication
1959 method to be used in the authentication protocol. The following
1960 authentication methods are defined:
1963 1 password (mandatory)
1964 2 public key (mandatory)
1966 If any other type is found in this field the packet MUST be
1967 discarded and the authentication MUST be failed. If this
1968 payload is sent as request to receive the mandatory
1969 authentication method this field MUST be set to zero (0),
1970 indicating that receiver should send the mandatory
1971 authentication method. The receiver sending this payload
1972 to the requesting party, MAY also set this field to zero (0)
1973 to indicate that authentication is not required. In this
1974 case authentication protocol still MUST be started but
1975 server is most likely to respond with SILC_PACKET_SUCCESS
1981 2.3.16 New ID Payload
1983 New ID Payload is a multipurpose payload. It is used to send newly
1984 created ID's from clients and servers. When client connects to server
1985 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
1986 packet, server replies with this packet by sending the created ID for
1987 the client. Server always creates the ID for the client.
1989 This payload is also used when server tells its router that new client
1990 has registered to the SILC network. In this case the server sends
1991 the Client ID of the client to the router. Similarly when router
1992 distributes information to other routers about the client in the SILC
1993 network this payload is used.
1995 Also, when server connects to router, router uses this payload to inform
1996 other routers about new server in the SILC network. However, every
1997 server (or router) creates their own ID's thus the ID distributed by
1998 this payload is not created by the distributor in this case. Servers
1999 create their own ID's. Server registers itself to the network by sending
2000 SILC_PACKET_NEW_SERVER to the router it connected to. The case is same
2001 when router connects to another router.
2003 However, this payload MUST NOT be used to send information about new
2004 channels. New channels are always distributed by sending the dedicated
2005 SILC_PACKET_NEW_CHANNEL packet.
2007 Thus, this payload is very important and used every time when some
2008 new entity is registered to the SILC network. Client MUST NOT send this
2009 payload. Both client and server (and router) MAY receive this payload.
2011 The packet uses generic ID Payload as New ID Payload. See section
2012 2.3.2.1 for generic ID Payload.
2016 2.3.17 New Client Payload
2018 When client is connected to the server, keys has been exchanged and
2019 connection has been authenticated client MUST register itself to the
2020 server. Clients first packet after key exchange and authentication
2021 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
2022 the relevant information about the connected user. Server creates a new
2023 client ID for the client when received this payload and sends it to the
2024 client in New ID Payload.
2026 This payload sends username and real name of the user on the remote host
2027 which is connected to the SILC server with SILC client. The server
2028 creates the client ID according the information sent in this payload.
2029 The nickname of the user becomes the username sent in this payload.
2030 However, client should call NICK command after sending this payload to
2031 set the real nickname of the user which is then used to create new
2034 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
2035 MUST NOT be sent in any other packet type. The following diagram
2036 represents the New Client Payload.
2053 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
2054 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2055 | Username Length | |
2056 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2060 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2061 | Real Name Length | |
2062 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2066 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2070 Figure 19: New Client Payload
2074 o Username Length (2 bytes) - Length of the username.
2076 o Username (variable length) - The username of the user on
2077 the host where connecting to the SILC server.
2079 o Real Name Length (2 bytes) - Length of the Real Name.
2081 o Real Name (variable length) - The real name of the user
2082 on the host where connecting to the SILC server.
2087 2.3.18 New Server Payload
2089 This payload is sent by server when it has completed successfully both
2090 key exchange and connection authentication protocols. The server
2091 MUST register itself to the SILC Network by sending this payload.
2092 The first packet after these key exchange and authentication protocols
2093 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
2094 of the server that it has created by itself. It also includes a
2095 name of the server that is associated to the Server ID.
2097 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
2098 MUST NOT be sent in any other packet type. The following diagram
2099 represents the New Server Payload.
2108 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
2109 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2110 | Server ID Length | |
2111 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2115 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2116 | Server Name Length | |
2117 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2121 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2125 Figure 20: New Server Payload
2129 o Server ID Length (2 bytes) - Length of the ID Data area not
2130 including the length of any other fields in the payload.
2132 o Server ID Data (variable length) - The actual Server ID
2135 o Server Name Length (2 bytes) - Length of the server name.
2137 o Server Name (variable length) - The server name.
2142 2.3.19 New Channel Payload
2144 Information about newly created channel is broadcasted to all routers
2145 in the SILC network by sending this packet payload. Channels are
2146 created by router of the cell. Server never creates channels unless
2147 it is a standalone server and it does not have router connection,
2148 in this case server acts as router. Normal server send JOIN command
2149 to the router (after it has received JOIN command from client) which
2150 then processes the command and creates the channel. Client MUST NOT
2153 The packet uses generic Channel Payload as New Channel Payload. See
2154 section 2.3.2.3 for generic Channel Payload. The Mode Mask field in the
2155 Channel Payload is the mode of the channel.
2161 2.3.20 Key Agreement Payload
2163 This payload is used by clients to request key negotiation between
2164 another client in the SILC Network. The key agreement protocol used
2165 is the SKE protocol. The result of the protocol, the secret key
2166 material, can be used for example as private message key between the
2167 two clients. This significantly adds security as the key agreement
2168 is performed outside the SILC network. The server and router MUST NOT
2171 The sender MAY tell the receiver of this payload the hostname and the
2172 port where the SKE protocol is running in the sender's end. The
2173 receiver MAY then initiate the SKE negotiation with the sender. The
2174 sender MAY also optionally not to include the hostname and the port
2175 of its SKE protocol. In this case the receiver MAY reply to the
2176 request by sending the same payload filled with the receiver's hostname
2177 and the port where the SKE protocol is running. The sender MAY then
2178 initiate the SKE negotiation with the receiver.
2180 The payload may only be sent with SILC_PACKET_KEY_AGREEMENT packet.
2181 It MUST NOT be sent in any other packet type. The following diagram
2182 represents the Key Agreement Payload.
2188 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
2189 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2190 | Hostname Length | |
2191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2195 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2197 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2201 Figure 21: Key Agreement Payload
2205 o Hostname Length (2 bytes) - Indicates the length of the
2208 o Hostname (variable length) - The hostname or IP address where
2209 the SKE protocol is running. The sender MAY fill this field
2210 when sending the payload. If the receiver sends this payload
2211 as reply to the request it must fill this field.
2213 o Port (4 bytes) - The port where the SKE protocol is bound.
2214 The sender MAY fill this field when sending the payload. If
2215 the receiver sends this payload as reply to the request it
2216 MUST fill this field. This is a 32 bit MSB first order value.
2220 After the key material has been received from the SKE protocol it is
2221 processed as the [SILC3] describes. If the key material is used as
2222 channel private key then the Sending Encryption Key, as defined in
2223 [SILC3] is used as the channel private key. Other key material must
2224 be discarded. The [SILC1] defines the way to use the key material if
2225 it is intended to be used as private message keys. Any other use for
2226 the key material is undefined.
2230 2.3.21 Cell Routers Payload
2232 Cell Routers payload is used by router to notify its primary router what
2233 other routers exist in the cell. The other routers are considered to be
2234 backup routers and one of them will come active only in the case of
2235 failure of the primary router. Normal server MAY send this packet if it
2236 is acting as backup router. Client MUST NOT send this packet. To send
2237 more than one backup router set the List flag and assemble the payloads
2240 The payload may only be sent with SILC_PACKET_CELL_ROUTERS packet. It
2241 MUST NOT be sent in any other packet type. The Following diagram
2242 represents the Cell Routers Payload.
2248 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
2249 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2250 | Hostname Length | |
2251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2258 | Server ID Length | |
2259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2267 Figure 22: Cell Routers Payload
2271 o Hostname Length (2 bytes) - Indicates the length of the Hostname
2274 o Hostname (variable length) - The hostname or IP address of
2277 o Port (4 bytes) - The port of the backup router it currently uses.
2278 This is a 32 bit MSB first order value.
2280 o Server ID Length (2 bytes) - Indicates the length of the Server
2283 o Server ID (variable length) - Consists of the Server ID of the
2291 ID's are extensively used in the SILC network to associate different
2292 entities. The following ID's has been defined to be used in the SILC
2298 When ever specific ID cannot be used this is used.
2302 Server ID to associate servers. See the format of
2307 Client ID to associate clients. See the format of
2312 Channel ID to associate channels. See the format of
2318 2.5 Packet Encryption And Decryption
2320 SILC packets are encrypted almost entirely. Only small part of SILC
2321 header is not encrypted as described in section 5.2 SILC Packet Header.
2322 The SILC Packet header is the first part of a packet to be encrypted
2323 and it is always encrypted with the key of the next receiver of the
2324 packet. The data payload area of the packet is always entirely
2325 encrypted and it is usually encrypted with the next receiver's key.
2326 However, there are some special packet types and packet payloads
2327 that require special encryption process. These special cases are
2328 described in the next sections. First is described the normal packet
2333 2.5.1 Normal Packet Encryption And Decryption
2335 Normal SILC packets are encrypted with the session key of the next
2336 receiver of the packet. The entire SILC Packet header and the packet
2337 data payload is is also encrypted with the same key. Padding of the
2338 packet is also encrypted always with the session key, also in special
2339 cases. Computed MAC of the packet must not be encrypted.
2341 Decryption process in these cases are straightforward. The receiver
2342 of the packet MUST first decrypt the SILC Packet header, or some parts
2343 of it, usually first 16 bytes of it. Then the receiver checks the
2344 packet type from the decrypted part of the header and can determine
2345 how the rest of the packet must be decrypted. If the packet type is
2346 any of the special cases described in the following sections the packet
2347 decryption is special. If the packet type is not among those special
2348 packet types rest of the packet can be decrypted with the same key.
2350 Also, note that two bytes of the SILC Packet header are not encrypted
2351 thus it must be noticed in the decryption process by starting the
2352 decryption from the second byte of the header. This sets some rules
2353 to padding generation as well, see the section 2.7 Packet Padding
2356 With out a doubt, this sort of decryption processing causes some
2357 overhead to packet decryption, but never the less, is required.
2361 2.5.2 Channel Message Encryption And Decryption
2363 Channel Messages (Channel Message Payload) are always encrypted with
2364 the channel specific key. However, the SILC Packet header is not
2365 encrypted with that key. As in normal case, the header is encrypted
2366 with the key of the next receiver of the packet, who ever that might
2367 be. Note that in this case the encrypted data area is not touched
2368 at all; it MUST NOT be re-encrypted with the session key.
2370 Receiver of a channel message, who ever that is, is REQUIRED to decrypt
2371 the SILC Packet header to be able to even recognize the packet to be as
2372 channel message. This is same procedure as for normal SILC packets.
2373 As the receiver founds the packet to be channel message, rest of the
2374 packet processing is special. Rest of the SILC Packet header is
2375 decrypted with the same session key along with the padding of the
2376 packet. After that the packet is protected with the channel specific
2377 key and thus can be decrypted only if the receiver is the client on
2378 the channel. See section 2.7 Packet Padding Generation for more
2379 information about padding on special packets.
2381 If the receiver of the channel message is router which is routing the
2382 message to another router then it MUST decrypt the Channel Message
2383 payload. Between routers (that is, between cells) channel messages
2384 are protected with session keys shared between the routers. This
2385 causes another special packet processing for channel messages. If
2386 the channel message is received from another router then the entire
2387 packet, including Channel Message payload, MUST be encrypted with the
2388 session key shared between the routers. In this case the packet
2389 decryption process is as with normal SILC packets. Hence, if the
2390 router is sending channel message to another router the Channel
2391 Message payload MUST have been decrypted and MUST be re-encrypted
2392 with the session key shared between the another router. In this
2393 case the packet encryption is as with any normal SILC packet.
2395 It must be noted that this is only when the channel messages are sent
2396 from router to another router. In all other cases the channel
2397 message encryption and decryption is as described above. This
2398 different processing of channel messages with router to router
2399 connection is because channel keys are cell specific. All cells has
2400 their own channel keys thus the channel message traveling from one
2401 cell to another MUST be protected as it would be any normal SILC
2404 If the SILC_CMODE_PRIVKEY channel mode has been set for the channel
2405 then the router cannot decrypt the packet as it does not know the
2406 private key. In this case the entire packet MUST be encrypted with
2407 the session key and sent to the router. The router receiving the
2408 packet MUST check the channel mode and decrypt the packet accordingly.
2412 2.5.3 Private Message Encryption And Decryption
2414 By default, private message in SILC are protected by session keys.
2415 In this case the private message encryption and decryption process is
2416 equivalent to normal packet encryption and decryption.
2418 However, private messages MAY be protected with private message key
2419 which causes the packet to be special packet. The procedure in this
2420 case is very much alike to channel packets. The actual private message
2421 is encrypted with the private message key and other parts of the
2422 packet is encrypted with the session key. See 2.7 Packet Padding
2423 Generation for more information about padding on special packets.
2425 The difference from channel message processing is that server or router
2426 en route never decrypts the actual private message, as it does not
2427 have the key to do that. Thus, when sending packets between router
2428 the processing is same as in any other case as well; the packet's header
2429 and padding is protected by the session key and the data area is not
2432 The true receiver of the private message, client, that is, is able
2433 to decrypt the private message as it shares the key with the sender
2438 2.6 Packet MAC Generation
2440 Data integrity of a packet is protected by including a message
2441 authentication code (MAC) at the end of the packet. The MAC is computed
2442 from shared secret MAC key, that is established by the SILC Key Exchange
2443 protocol, and from the original contents of the packet. The MAC is
2444 always computed before the packet is encrypted, although after it is
2445 compressed if compression is used.
2447 The MAC is computed from entire packet. Every bit of data in the packet,
2448 including SILC Packet Header is used in the MAC computing. This way
2449 the entire packet becomes authenticated.
2451 If the packet is special packet MAC is computed from the entire packet
2452 but part of the packet may be encrypted before the MAC is computed.
2453 This is case, for example, with channel messages where the message data
2454 is encrypted with key that server may not now. In this case the MAC
2455 has been computed from the encrypted data.
2457 See [SILC1] for defined and allowed MAC algorithms.
2461 2.7 Packet Padding Generation
2463 Padding is needed in the packet because the packet is encrypted. It
2464 MUST always be multiple by eight (8) or multiple by the size of the
2465 cipher's block size, which ever is larger. The padding is always
2468 For normal packets the padding is added after the SILC Packet Header
2469 and between the Data Payload area. The padding for normal packets
2470 are calculated as follows:
2473 padding length = 16 - ((packet length - 2) mod 16)
2476 The 16 is the maximum padding allowed in SILC packet. Two (2) is
2477 subtracted from the true length of the packet because two (2) bytes
2478 is not encrypted in SILC Packet Header, see section 2.2 SILC Packet
2479 Header. Those two bytes that are not encrypted MUST NOT be calculated
2480 to the padding length.
2482 For special packets the padding calculation MAY be different as special
2483 packets may be encrypted differently. In these cases the encrypted
2484 data area MUST already be multiple by the block size thus in this case
2485 the padding is calculated only for SILC Packet Header, not for any
2486 other area of the packet. The same algorithm works in this case as
2487 well, except that the `packet length' is now the SILC Packet Header
2488 length. In this case, as well, two (2) is subtracted from the
2491 The padding MUST be random data, preferably, generated by
2492 cryptographically strong random number generator.
2496 2.8 Packet Compression
2498 SILC Packets MAY be compressed. In this case the data payload area
2499 is compressed and all other areas of the packet MUST remain as they
2500 are. After compression is performed for the data area, the length
2501 field of Packet Header MUST be set to the compressed length of the
2504 The compression MUST always be applied before encryption. When
2505 the packet is received and decrypted the data area MUST be decompressed.
2506 Note that the true sender of the packet MUST apply the compression and
2507 the true receiver of the packet MUST apply the decompression. Any
2508 server or router en route MUST NOT decompress the packet.
2514 The sender of the packet MUST assemble the SILC Packet Header with
2515 correct values. It MUST set the Source ID of the header as its own
2516 ID, unless it is forwarding the packet. It MUST also set the Destination
2517 ID of the header to the true destination. If the destination is client
2518 it will be Client ID, if it is server it will be Server ID and if it is
2519 channel it will be Channel ID.
2521 If the sender wants to compress the packet it MUST apply the
2522 compression now. Sender MUST also compute the padding as described
2523 in above sections. Then sender MUST compute the MAC of the packet.
2525 Then sender MUST encrypt the packet as has been described in above
2526 sections according whether the packet is normal packet or special
2527 packet. The computed MAC MUST NOT be encrypted.
2531 2.10 Packet Reception
2533 On packet reception the receiver MUST check that all fields in the
2534 SILC Packet Header are valid. It MUST check the flags of the
2535 header and act accordingly. It MUST also check the MAC of the packet
2536 and if it is to be failed the packet MUST be discarded. Also if the
2537 header of the packet includes any bad fields the packet MUST be
2540 See above sections on the decryption process of the received packet.
2542 The receiver MUST also check that the ID's in the header are valid
2543 ID's. Unsupported ID types or malformed ID's MUST cause packet
2544 rejection. The padding on the reception is always ignored.
2546 The receiver MUST also check the packet type and start parsing the
2547 packet according to the type. However, note the above sections on
2548 special packet types and their parsing.
2554 Routers are the primary entities in the SILC network that takes care
2555 of packet routing. However, normal servers routes packets as well, for
2556 example, when they are routing channel message to the local clients.
2557 Routing is quite simple as every packet tells the true origin and the
2558 true destination of the packet.
2560 It is still RECOMMENDED for routers that has several routing connections
2561 to create route cache for those destinations that has faster route than
2562 the router's primary route. This information is available for the router
2563 when other router connects to the router. The connecting party then
2564 sends all of its locally connected clients, server and channels. These
2565 informations helps to create the route cache. Also, when new channels
2566 are created to a cell its information is broadcasted to all routers
2567 in the network. Channel ID's are based on router's ID thus it is easy
2568 to create route cache based on these informations. If faster route for
2569 destination does not exist in router's route cache the packet MUST be
2570 routed to the primary route (default route).
2572 For server which receives a packet to be routed to its locally connected
2573 client the server MUST check whether the particular packet type is
2574 allowed to be routed to the client. Not all packets may be sent by
2575 some odd entity to client that is indirectly connected to the sender.
2576 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2577 entities and sending packets to them. The section mentions the packets
2578 that may be sent to indirectly connected entities. It is clear that some
2579 server cannot send, for example, disconnect packet to client that is not
2580 directly connected to the server.
2584 2.12 Packet Broadcasting
2586 SILC packets MAY be broadcasted in SILC network. However, only router
2587 server may send or receive broadcast packets. Client and normal server
2588 MUST NOT send broadcast packets and they MUST ignore broadcast packets
2589 if they receive them. Broadcast packets are sent by setting Broadcast
2590 flag to the SILC packet header.
2592 Broadcasting packets means that the packet is sent to all routers in
2593 the SILC network, except to the router that sent the packet. The router
2594 receiving broadcast packet MUST send the packet to its primary route.
2595 The fact that SILC routers may have several router connections can
2596 cause problems, such as race conditions inside the SILC network, if
2597 care is not taken when broadcasting packets. Router MUST NOT send
2598 the broadcast packet to any other route except to its primary route.
2600 If the primary route of the router is the original sender of the packet
2601 the packet MUST NOT be sent to the primary route. This may happen
2602 if router has several router connections and some other router uses
2603 the router as its primary route.
2605 Routers use broadcast packets to broadcast for example information
2606 about newly registered clients, servers, channels etc. so that all the
2607 routers may keep these informations up to date.
2611 3 Security Considerations
2613 Security is central to the design of this protocol, and these security
2614 considerations permeate the specification. Common security considerations
2615 such as keeping private keys truly private and using adequate lengths for
2616 symmetric and asymmetric keys must be followed in order to maintain the
2617 security of this protocol.
2623 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2624 Protocol Specification", Internet Draft, April 2001.
2626 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2627 Protocols", Internet Draft, April 2001.
2629 [SILC4] Riikonen, P., "SILC Commands", Internet Draft, April 2001.
2631 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2634 [IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
2637 [IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
2640 [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
2643 [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
2646 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2649 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2652 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2655 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2656 Infrastructure, Certificate and CRL Profile", RFC 2459,
2659 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2660 John Wiley & Sons, New York, NY, 1996.
2662 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2665 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2666 RFC 2412, November 1998.
2668 [ISAKMP] Maughan D., et al, "Internet Security Association and
2669 Key Management Protocol (ISAKMP)", RFC 2408, November
2672 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2673 (IKE)", RFC 2409, November 1998.
2675 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2676 Authentication", RFC 2104, February 1997.
2678 [PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
2679 Specifications, Version 2.0", RFC 2437, October 1998.
2681 [RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate
2682 Requirement Levels", BCP 14, RFC 2119, March 1997.
2694 EMail: priikone@poseidon.pspt.fi
2696 This Internet-Draft expires XX October 2001