8 .ds RF FORMFEED[Page %]
17 Network Working Group P. Riikonen
19 draft-riikonen-silc-pp-02.txt XXXXXXXXXXXXXX
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
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37 Internet-Drafts are draft documents valid for a maximum of six months
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39 time. It is inappropriate to use Internet-Drafts as reference
40 material or to cite them other than as "work in progress."
42 The list of current Internet-Drafts can be accessed at
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45 The list of Internet-Draft Shadow Directories can be accessed at
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48 The distribution of this memo is unlimited.
54 This memo describes a Packet Protocol used in the Secure Internet Live
55 Conferencing (SILC) protocol specified in the Secure Internet Live
56 Conferencing, Protocol Specification Internet Draft [SILC1]. This
57 protocol describes the packet types and packet payloads which defines
58 the contents of the packets. The protocol provides secure binary packet
59 protocol that assures that the contents of the packets are secured and
74 1 Introduction .................................................. 3
75 2 SILC Packet Protocol .......................................... 4
76 2.1 SILC Packet ............................................... 4
77 2.2 SILC Packet Header ........................................ 5
78 2.3 SILC Packet Types ......................................... 7
79 2.3.1 SILC Packet Payloads ................................ 15
80 2.3.2 Generic payloads .................................... 16
81 2.3.2.1 ID Payload .................................. 16
82 2.3.2.2 Argument Payload ............................ 16
83 2.3.2.3 Channel Payload ............................. XXX
84 2.3.3 Disconnect Payload .................................. 17
85 2.3.4 Success Payload ..................................... 18
86 2.3.5 Failure Payload ..................................... 18
87 2.3.6 Reject Payload ...................................... 19
88 2.3.7 Notify Payload ...................................... 20
89 2.3.8 Error Payload ....................................... 21
90 2.3.9 Channel Message Payload ............................. 22
91 2.3.10 Channel Key Payload ................................ 24
92 2.3.11 Private Message Payload ............................ 26
93 2.3.12 Private Message Key Payload ........................ 27
94 2.3.13 Command Payload .................................... 28
95 2.3.14 Command Reply Payload .............................. 29
96 2.3.15 Connection Auth Request Payload .................... 29
97 2.3.16 New ID Payload ..................................... 30
98 2.3.17 New Client Payload ................................. 31
99 2.3.18 New Server Payload ................................. 32
100 2.3.19 New Channel Payload ................................ 33
101 2.3.20 Key Agreement Payload .............................. XXX
102 2.4 SILC ID Types ............................................. 39
103 2.5 Packet Encryption And Decryption .......................... 39
104 2.5.1 Normal Packet Encryption And Decryption ............. 39
105 2.5.2 Channel Message Encryption And Decryption ........... 40
106 2.5.3 Private Message Encryption And Decryption ........... 41
107 2.6 Packet MAC Generation ..................................... 41
108 2.7 Packet Padding Generation ................................. 42
109 2.8 Packet Compression ........................................ 42
110 2.9 Packet Sending ............................................ 43
111 2.10 Packet Reception ......................................... 43
112 2.11 Packet Routing ........................................... 44
113 2.12 Packet Broadcasting ...................................... 45
114 3 Security Considerations ....................................... 46
115 4 References .................................................... 46
116 5 Author's Address .............................................. 47
122 Figure 1: Typical SILC Packet
123 Figure 2: SILC Packet Header
125 Figure 4: Argument Payload
126 Figure 5: Channel Payload
127 Figure 6: Disconnect Payload
128 Figure 7: Success Payload
129 Figure 8: Failure Payload
130 Figure 9: Reject Payload
131 Figure 10: Notify Payload
132 Figure 11: Error Payload
133 Figure 12: Channel Message Payload
134 Figure 13: Channel Key Payload
135 Figure 14: Private Message Payload
136 Figure 15: Private Message Key Payload
137 Figure 16: Command Payload
138 Figure 17: Connection Auth Request Payload
139 Figure 18: New Client Payload
140 Figure 19: New Server Payload
141 Figure 20: Key Agreement Payload
142 Figure 21: Cell Routers Payload
148 This document describes a Packet Protocol used in the Secure Internet
149 Live Conferencing (SILC) protocol specified in the Secure Internet Live
150 Conferencing, Protocol Specification Internet Draft [SILC1]. This
151 protocol describes the packet types and packet payloads which defines
152 the contents of the packets. The protocol provides secure binary packet
153 protocol that assures that the contents of the packets are secured and
156 The basis of SILC protocol relies in the SILC packets and it is with
157 out a doubt the most important part of the protocol. It is also probably
158 the most complicated part of the protocol. Packets are used all the
159 time in the SILC network to send messages, commands and other information.
160 All packets in SILC network are always encrypted and their integrity
161 is assured by computed MACs. The protocol defines several packet types
162 and packet payloads. Each packet type usually has a specific packet
163 payload that actually defines the contents of the packet. Each packet
164 also includes a default SILC Packet Header that provides sufficient
165 information about the origin of the packet and destination of the
170 2 SILC Packet Protocol
175 SILC packets deliver messages from sender to receiver securely by
176 encrypting important fields of the packet. The packet consists of
177 default SILC Packet Header, Padding, Packet Payload data, and, packet
180 The following diagram illustrates typical SILC packet.
185 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
186 | n bytes | 1 - n bytes | n bytes | n bytes
187 | SILC Header | Padding | Data Payload | MAC
188 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
192 Figure 1: Typical SILC Packet
195 SILC Header is always the first part of the packet and its purpose
196 is to provide information about the packet. It provides for example
197 the packet type, origin of the packet and the destination of the packet.
198 The header is variable in length and first two (2) bytes of the
199 header (thus first two bytes of the packet) are not encrypted. The
200 first two (2) bytes are the length of the packet which is not encrypted.
201 See The following section for description of SILC Packet header. Packets
202 without SILC header or with malformed SILC header must be dropped.
204 Padding follows the packet header. The purpose of the padding is to
205 make the packet multiple by eight (8) or by the block size of the
206 cipher used in the encryption, which ever is larger. The maximum
207 length of padding is currently 16 bytes. The padding is always
210 Data payload area follows padding and it is the actual data of the
211 packet. The packet data is the packet payloads defined in this
212 protocol. The data payload area is always encrypted.
214 The last part of SILC packet is the packet MAC that assures the
215 integrity of the packet. The MAC is always computed from the packet
216 before the encryption is applied to the packet. If compression is used
217 in the packet the MAC is computed after the compression has been
218 applied. The compression, on the other hand, is always applied before
221 All fields in all packet payloads are always in MSB (most significant
226 2.2 SILC Packet Header
228 The default SILC packet header is applied to all SILC packets and it is
229 variable in length. The purpose of SILC Packet header is to provide
230 detailed information about the packet. The receiver of the packet uses
231 the packet header to parse the packet and gain other relevant parameters
234 The following diagram represents the default SILC header format.
235 (*) indicates that this field is never encrypted. Other fields are
242 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
243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
244 | Payload Length * | Flags | Packet Type |
245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
246 | Source ID Length | Destination ID Length |
247 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
263 Figure 2: SILC Packet Header
267 o Payload Length (2 bytes) - Is the length of the packet
268 not including the padding of the packet. This field must
269 not be encrypted but must always be authenticated.
271 o Flags (1 byte) - Indicates flags to be used in packet
272 processing. Several flags may be set by ORing the flags
275 The following flags are reserved for this field:
280 In this case the field is ignored.
283 Private Message Key 0x01
285 Indicates that the packet must include private
286 message that is encrypted using private key set by
287 client. Servers does not know anything about this
288 key and this causes that the private message is
289 not handled by the server at all, it is just
290 passed along. See section 2.5.3 Private Message
291 Encryption And Decryption for more information.
296 Indicates that the packet consists of list of
297 packet payloads indicated by the Packet Type field.
298 The payloads are added one after the other. Note that
299 there are packet types that must not be used as
300 list. Parsing of list packet is done by calculating
301 the length of each payload and parsing them one by
307 Marks the packet to be broadcasted. Client cannot
308 send broadcast packet and normal server cannot send
309 broadcast packet. Only router server may send broadcast
310 packet. The router receiving of packet with this flag
311 set must send (broadcast) the packet to its primary
312 route. If router has several router connections the
313 packet may be sent only to the primary route. See
314 section 2.13 Packet Broadcasting for description of
321 o Packet Type (1 byte) - Is the type of the packet. Receiver
322 uses this field to parse the packet. See section 2.3
323 SILC Packets for list of defined packet types.
325 o Source ID Length (2 bytes) - Indicates the length of the
326 Source ID field in the header, not including this or any
329 o Destination ID Length (2 bytes) - Indicates the length of the
330 Destination ID field in the header, not including this or
333 o Src ID Type (1 byte) - Indicates the type of ID in the
334 Source ID field. See section 2.4 SILC ID Types for
337 o Source ID (variable length) - The actual source ID that
338 indicates who is the original sender of the packet.
340 o Dst ID Type (1 byte) - Indicates the type of ID in the
341 Destination ID field. See section 2.4 SILC ID Types for
344 o Destination ID (variable length) - The actual source ID that
345 indicates who is the end receiver of the packet.
349 2.3 SILC Packet Types
351 SILC packet types defines the contents of the packet and it is used by
352 the receiver to parse the packet. The packet type is 8 bits, as a one
353 byte, in length. The range for the packet types are from 0 - 255,
354 where 0 is never sent and 255 is currently reserved for future
355 extensions and must not be defined to any other purpose. Every SILC
356 specification compliant implementation should support all of these packet
359 The below list of the SILC Packet types includes reference to the packet
360 payload as well. Packet payloads are the actual packet, that is, the data
361 that the packet consists of. Each packet type defines packet payload
362 which usually may only be sent with the specific packet type.
364 Most of the packets are packets that must be destined directly to entity
365 that is connected to the sender. It is not allowed, for example, for
366 router to send disconnect packet to client that is not directly connected
367 to the router. However, there are some special packet types that may
368 be destined to some entity that the sender has not direct connection
369 with. These packets are for example private message packets, channel
370 message packets, command packets and some other packets that may be
371 broadcasted in the SILC network. If the packet is allowed to be sent to
372 indirectly connected entity it is mentioned separately in the packet
373 description (unless it is obvious as in private and channel message
374 packets). Other packets must not be sent or accepted, if sent, to
375 indirectly connected entities.
377 List of SILC Packet types are defined as follows.
382 This type is reserved and it is never sent.
385 1 SILC_PACKET_DISCONNECT
387 This packet is sent to disconnect the remote end. Reason of
388 the disconnection is sent inside the packet payload. Client
389 usually does not send this packet.
391 This packet must not be sent as list and the List flag must
394 Payload of the packet: See section 2.3.3 Disconnect Payload
397 2 SILC_PACKET_SUCCESS
399 This packet is sent upon successful execution of some protocol.
400 The status of the success is sent in the packet.
402 This packet must not be sent as list and the List flag must
405 Payload of the packet: See section 2.3.4 Success Payload
408 3 SILC_PACKET_FAILURE
410 This packet is sent upon failure of some protocol. The status
411 of the failure 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 2.3.5 Failure Payload
421 This packet may be sent upon rejection of some protocol.
422 The status of the rejection 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 2.3.6 Reject Payload
432 This packet is used to send notify message, usually from
433 server to client, although it may be sent from server to another
434 server as well. Client never sends this packet. Server may
435 send this packet to channel as well when the packet is
436 distributed to all clients on the channel.
438 Payload of the packet: See section 2.3.7 Notify Payload.
443 This packet is sent when an error occurs. Server may
444 send this packet. Client never sends this packet. The
445 client may entirely ignore the packet, however, server is
446 most likely to take action anyway. This packet may be sent
447 to entity that is indirectly connected to the sender.
449 This packet must not be sent as list and the List flag must
452 Payload of the packet: See section 2.3.8 Error Payload.
455 7 SILC_PACKET_CHANNEL_MESSAGE
457 This packet is used to send messages to channels. The packet
458 includes Channel ID of the channel and the actual message to
459 the channel. Messages sent to the channel are always protected
460 by channel specific keys. Channel Keys are distributed by
461 SILC_PACKET_CHANNEL_KEY packet.
463 This packet must not be sent as list and the List flag must
466 Payload of the packet: See section 2.3.9 Channel Message
470 8 SILC_PACKET_CHANNEL_KEY
472 This packet is used to distribute new key for particular
473 channel. Each channel has their own independent keys that
474 is used to protect the traffic on the channel. Only server
475 may send this packet. This packet may be sent to entity
476 that is indirectly connected to the sender.
478 This packet must not be sent as list and the List flag must
481 Payload of the packet: See section 2.3.10 Channel Key Payload
484 9 SILC_PACKET_PRIVATE_MESSAGE
486 This packet is used to send private messages from client
487 to another client. By default, private messages are protected
488 by session keys established by normal key exchange protocol.
489 However, it is possible to use specific key to protect private
490 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
491 agree the key with the remote client. Pre-shared key may be
492 used as well if both of the client knows it, however, it needs
493 to be agreed outside SILC. See more of this in [SILC1].
495 This packet must not be sent as list and the List flag must
498 Payload of the packet: See section 2.3.11 Private Message
502 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
504 This packet is used to agree about a key to be used to protect
505 the private messages between two clients. If this is not sent
506 the normal session key is used to protect the private messages
507 inside SILC network. Agreeing to use specific key to protect
508 private messages adds security, as no server between the two
509 clients will be able to decrypt the private message. However,
510 servers inside SILC network are considered to be trusted, thus
511 using normal session key to protect private messages does not
512 degree security. Whether to agree to use specific keys by
513 default or to use normal session keys by default, is
514 implementation specific issue. See more of this in [SILC1].
516 This packet must not be sent as list and the List flag must
519 Payload of the packet: See section 2.3.12 Private Message
523 11 SILC_PACKET_COMMAND
525 This packet is used to send commands from client to server.
526 Server may send this packet to other servers as well. All
527 commands are listed in their own section SILC Command Types
528 in [SILC1]. The contents of this packet is command specific.
529 This packet may be sent to entity that is indirectly connected
532 This packet must not be sent as list and the List flag must
535 Payload of the packet: See section 2.3.13 Command Payload
538 12 SILC_PACKET_COMMAND_REPLY
540 This packet is send as reply to the SILC_PACKET_COMMAND packet.
541 The contents of this packet is command specific. This packet
542 maybe sent to entity that is indirectly connected to the sender.
544 This packet must not be sent as list and the List flag must
547 Payload of the packet: See section 2.3.14 Command Reply
548 Payload and section 2.3.13 Command
552 13 SILC_PACKET_KEY_EXCHANGE
554 This packet is used to start SILC Key Exchange Protocol,
555 described in detail in [SILC3].
557 This packet must not be sent as list and the List flag must
560 Payload of the packet: Payload of this packet is described
561 in the section SILC Key Exchange
562 Protocol and its sub sections in
566 14 SILC_PACKET_KEY_EXCHANGE_1
568 This packet is used as part of the SILC Key Exchange Protocol.
570 This packet must not be sent as list and the List flag must
573 Payload of the packet: Payload of this packet is described
574 in the section SILC Key Exchange
575 Protocol and its sub sections in
579 15 SILC_PACKET_KEY_EXCHANGE_2
581 This packet is used as part of the SILC Key Exchange Protocol.
583 This packet must not be sent as list and the List flag must
586 Payload of the packet: Payload of this packet is described
587 in the section SILC Key Exchange
588 Protocol and its sub sections in
592 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
594 This packet is used to request the authentication method to
595 be used in the SILC Connection Authentication Protocol. If
596 initiator of the protocol does not know the mandatory
597 authentication method this packet may be used to determine it.
599 The party receiving this payload must respond with the same
600 packet including the mandatory authentication method.
602 This packet must not be sent as list and the List flag must
605 Payload of the packet: See section 2.3.15 Connection Auth
609 17 SILC_PACKET_CONNECTION_AUTH
611 This packet is used to start and perform the SILC Connection
612 Authentication Protocol. This protocol is used to authenticate
613 the connecting party. The protocol is described in detail in
616 This packet must not be sent as list and the List flag must
619 Payload of the packet: Payload of this packet is described
620 in the section SILC Authentication
621 Protocol and it sub sections in [SILC].
624 18 SILC_PACKET_NEW_ID
626 This packet is used to distribute new ID's from server to
627 router and from router to all routers in the SILC network.
628 This is used when for example new client is registered to
629 SILC network. The newly created ID's of these operations are
630 distributed by this packet. Only server may send this packet,
631 however, client must be able to receive this packet.
633 Payload of the packet: See section 2.3.16 New ID Payload
636 19 SILC_PACKET_NEW_CLIENT
638 This packet is used by client to register itself to the
639 SILC network. This is sent after key exchange and
640 authentication protocols has been completed. Client sends
641 various information about itself in this packet.
643 This packet must not be sent as list and the List flag must
646 Payload of the packet: See section 2.3.17 New Client Payload
649 20 SILC_PACKET_NEW_SERVER
651 This packet is used by server to register itself to the
652 SILC network. This is sent after key exchange and
653 authentication protocols has been completed. Server sends
654 this to the router it connected to, or, if router was
655 connecting, to the connected router. Server sends
656 its Server ID and other information in this packet.
657 Client must not send or receive this packet.
659 This packet must not be sent as list and the List flag must
662 Payload of the packet: See section 2.3.18 New Server Payload
665 21 SILC_PACKET_NEW_CHANNEL
667 This packet is used to notify routers about newly created
668 channel. Channels are always created by the router and it must
669 notify other routers about the created channel. Router sends
670 this packet to its primary route. Client must not send this
671 packet. This packet maybe sent to entity that is indirectly
672 connected to the sender.
674 Payload of the packet: See section 2.3.19 New Channel Payload
679 This packet is used to indicate that re-key must be performed
680 for session keys. See section Session Key Regeneration in
681 [SILC1] for more information. This packet does not have
684 This packet must not be sent as list and the List flag must
688 23 SILC_PACKET_REKEY_DONE
690 This packet is used to indicate that re-key is performed and
691 new keys must be used hereafter. This is sent only if re-key
692 was done without PFS option. If PFS is set, this is not sent
693 as SILC Key Exchange protocol is executed. This packet does
696 This packet must not be sent as list and the List flag must
700 24 SILC_PACKET_HEARTBEAT
702 This packet is used by clients, servers and routers to keep the
703 connection alive. It is recommended that all servers implement
704 keepalive actions and perform it to both direction in a link.
705 This packet does not have a payload.
707 This packet must not be sent as list and the List flag must
711 25 SILC_PACKET_KEY_AGREEMENT
713 This packet is used by clients to request key negotiation
714 between another client in the SILC network. If the negotiation
715 is started it is performed using the SKE protocol. The result of
716 the negotiation, the secret key material, can be used for
717 example as private message key. The server and router must not
720 Payload of the packet: See section 2.3.20 Key Agreement Payload
723 26 SILC_PACKET_CELL_ROUTERS
725 This packet is used by primary router in the cell to notify its
726 primary router what other routers (backup routers) exist in the
727 cell. In case of failure of the primary router in the cell the
728 first router in the list will act as primary router of the cell.
729 This packet may be sent at anytime after connection has been
730 registered to the primary router. The client must not send this
733 Payload of the packet: See section 2.3.21 Cell Routers Payload
738 Currently undefined commands.
743 These packet types are reserved for private use and they will not
744 be defined by this document.
749 This type is reserved for future extensions and currently it
755 2.3.1 SILC Packet Payloads
757 All payloads resides in the main data area of the SILC packet. However
758 all payloads must be at the start of the data area after the default
759 SILC packet header and padding. All fields in the packet payload are
760 always encrypted, as, they reside in the data area of the packet which
763 Payloads described in this section are common payloads that must be
764 accepted anytime during SILC session. Most of the payloads may only
765 be sent with specific packet type which is defined in the description
768 There are a lot of other payloads in the SILC as well. However, they
769 are not common in the sense that they could be sent at any time.
770 These payloads are not described in this section. These are payloads
771 such as SILC Key Exchange payloads and so on. These are described
772 in [SILC1] and [SILC3].
776 2.3.2 Generic payloads
778 This section describes generic payloads that are not associated to any
779 specific packet type. They can be used for example inside some other
786 This payload can be used to send an ID. ID's are variable length thus
787 this payload provides a way to send variable length ID's.
789 The following diagram represents the ID Payload.
794 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
795 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
796 | ID Type | ID Length |
797 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
801 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
809 o ID Type (2 bytes) - Indicates the type of the ID. See
810 section 2.4 SILC ID Types for list of defined ID types.
812 o ID Length (2 bytes) - Length of the ID Data area not
813 including the length of any other fields in the payload.
815 o ID Data (variable length) - The actual ID data.
820 2.3.2.2 Argument Payload
822 Argument Payload is used to set arguments for any packet payload that
823 needs and supports arguments, such as commands. Number of arguments
824 associated with a packet must be indicated by the packet payload who
825 needs the arguments. Argument Payloads must always reside right after
826 the packet payload needing the arguments. Incorrect amount of argument
827 payloads must cause rejection of the packet. The following diagram represents
828 the Argument Payload.
830 The following diagram represents the Argument Payload.
835 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
836 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
837 | Payload Length | Argument Type | |
838 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
842 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
846 Figure 4: Argument Payload
850 o Payload Length (2 bytes) - Length of the argument payload data
851 area not including the length of any other fields in the
854 o Argument Type (1 byte) - Indicates the type of the argument.
855 Every argument may have a specific type that must be defined
856 by the packet payload needing the argument. For example
857 every command specify a number for each argument that maybe
858 associated with the command. By using this number the receiver
859 of the packet knows what type of argument this is. If there is
860 no specific argument type this field is set to zero (0).
862 o Argument Data (variable length) - Argument data.
867 2.3.2.3 Channel Payload
869 Generic Channel Payload may be used information about channel, its name,
870 the Channel ID and a mode.
872 The following diagram represents the Channel Payload Payload.
878 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
879 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
880 | Channel Name Length | |
881 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
885 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
886 | Channel ID Length | |
887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
891 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
893 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
897 Figure 5: New Channel Payload
901 o Channel Name Length (2 bytes) - Length of the channel name
904 o Channel Name (variable length) - The name of the channel.
906 o Channel ID Length (2 bytes) - Length of the Channel ID field.
908 o Channel ID (variable length) - The Channel ID.
910 o Mode Mask (4 bytes) - A mode. This can be the mode of the
911 channel but it can also be the mode of the client on the
912 channel. The contents of this field is dependent of the
913 usage of this payload. The usage is defined separately
914 when this payload is used. This is a 32 bit MSB first value.
919 2.3.3 Disconnect Payload
921 Disconnect payload is sent upon disconnection. The payload is simple;
922 reason of disconnection is sent to the disconnected party.
924 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
925 must not be sent in any other packet type. The following diagram represents
926 the Disconnect Payload.
937 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
938 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
940 ~ Disconnect Message ~
942 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
946 Figure 6: Disconnect Payload
952 o Disconnect Message (variable length) - Human readable
953 reason of the disconnection.
958 2.3.4 Success Payload
960 Success payload is sent when some protocol execution is successfully
961 completed. The payload is simple; indication of the success is sent.
962 This maybe any data, including binary or human readable data.
967 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
968 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
970 ~ Success Indication ~
972 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
976 Figure 7: Success Payload
980 o Success Indication (variable length) - Indication of
981 the success. This maybe for example some flag that
982 indicates the protocol and the success status or human
983 readable success message. The true length of this
984 payload is available by calculating it from the SILC
990 2.3.5 Failure Payload
992 This is opposite of Success Payload. Indication of failure of
993 some protocol is sent in the payload.
999 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
1000 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1002 ~ Failure Indication ~
1004 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1008 Figure 8: Failure Payload
1012 o Failure Indication (variable length) - Indication of
1013 the failure. This maybe for example some flag that
1014 indicates the protocol and the failure status or human
1015 readable failure message. The true length of this
1016 payload is available by calculating it from the SILC
1022 2.3.6 Reject Payload
1024 This payload is sent when some protocol is rejected to be executed.
1025 Other operations may send this as well that was rejected. The
1026 indication of the rejection is sent in the payload. The indication
1027 may be binary or human readable data.
1033 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
1034 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1036 ~ Reject Indication ~
1038 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1042 Figure 9: Reject Payload
1046 o Reject Indication (variable length) - Indication of
1047 the rejection. This maybe for example some flag that
1048 indicates the protocol and the rejection status or human
1049 readable rejection message. The true length of this
1050 payload is available by calculating it from the SILC
1059 2.3.7 Notify Payload
1061 Notify payload is used to send notify messages. The payload is usually
1062 sent from server to client, however, server may send it to another
1063 server as well. This payload may also be sent to a channel. Client must
1064 not send this payload. The receiver of this payload may totally ignore the
1065 contents of the payload, however, notify message should be audited.
1067 The payload may only be sent with SILC_PACKET_NOTIFY packet. It must
1068 not be sent in any other packet type. The following diagram represents the
1074 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
1075 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1076 | Notify Type | Payload Length |
1077 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1083 Figure 10: Notify Payload
1087 o Notify Type (2 bytes) - Indicates the type of the notify
1090 o Payload Length (2 bytes) - Length of the entire Notify Payload
1091 including any associated Argument Payloads.
1093 o Argument Nums (2 bytes) - Indicates the number of Argument
1094 Payloads associated to this payload. Notify types may define
1095 arguments to be send along the notify message.
1098 The following list of currently defined notify types. The format for notify
1099 arguments is same as in SILC commands described in [SILC1]. Also, all
1100 ID's sent in arguments are sent inside ID Payload.
1103 0 SILC_NOTIFY_TYPE_NONE
1105 If no specific notify type apply for the notify message this type
1109 Arguments: (1) <message>
1111 The <message> is implementation specific free text string. Receiver
1112 may ignore this message.
1115 1 SILC_NOTIFY_TYPE_INVITE
1117 Sent when an client is invited to a channel. This is also sent
1118 when the invite list of the channel is changed. This notify type
1119 is sent between routers and if an client was invited to the
1120 client as well. In this case the packet is destined to the client.
1123 Arguments: (1) <Channel ID> (2) <channel name>
1124 (3) [<sender Client ID>] (4) [<adding client>]
1125 (5) [<removing client>]
1127 The <Channel ID> is the channel. The <channel name> is the name
1128 of the channel and is provided because the client which receives
1129 this notify packet may not have a way to resolve the name of the
1130 channel from the <Channel ID>. The <sender Client ID> is the
1131 Client ID who invited the client to the channel. The <adding client>
1132 and the <removing client> indicates the added or removed client
1133 from the channel's invite list. The format of the <adding client
1134 and the <removing client> is defined in the [SILC1] with
1135 SILC_COMMAND_INVITE command.
1137 The <adding client> and <removing client> is never sent when the
1138 packet is destined to a client.
1141 2 SILC_NOTIFY_TYPE_JOIN
1143 Sent when client has joined to a channel. The server must distribute
1144 this type only to the local clients on the channel and then send
1145 it to its primary router. The router or server receiving the packet
1146 distributes this type to the local clients on the channel and
1147 broadcast it to the network.
1150 Arguments: (1) [<Client ID>] (2) <Channel ID>
1152 The <Client ID> is the client that joined to the channel indicated
1153 by the <Channel ID>.
1156 3 SILC_NOTIFY_TYPE_LEAVE
1158 Sent when client has left a channel. The server must distribute
1159 this type only to the local clients on the channel and then send
1160 it to its primary router. The router or server receiving the packet
1161 distributes this type to the local clients on the channel and
1162 broadcast it to the network.
1165 Arguments: (1) <Client ID>
1167 The <Client ID> is the client who left the channel.
1170 4 SILC_NOTIFY_TYPE_SIGNOFF
1172 Sent when client signoffs from SILC network. The server must
1173 distribute this type only to the local clients on the channel and
1174 then send it to its primary router. The router or server receiving
1175 the packet distributes this type to the local clients on the channel
1176 and broadcast it to the network.
1179 Arguments: (1) <Client ID> (2) <message>
1181 The <Client ID> is the client who left SILC network. The <message>
1182 is free text string indicating the reason of signoff.
1185 5 SILC_NOTIFY_TYPE_TOPIC_SET
1187 Sent when topic is set/changed on a channel. This type must be sent
1188 only to the clients who is joined on the channel whose topic was
1192 Arguments: (1) <Client ID> (2) <topic>
1194 The <Client ID> is the client who set or changed the <topic>.
1197 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1199 Sent when client changes nick on a channel. The server must
1200 distribute this type only to the local clients on the channel and
1201 then send it to its primary router. The router or server receiving
1202 the packet distributes this type to the local clients on the channel
1203 and broadcast it to the network.
1206 Arguments: (1) <Old Client ID> (2) <New Client ID>
1208 The <Old Client ID> is the old ID of the client who changed the
1209 nickname. The <New Client ID> is the new ID generated by the change
1213 7 SILC_NOTIFY_TYPE_CMODE_CHANGE
1215 Sent when channel mode has changed. This type must be sent only to
1216 the clients who is joined on the channel whose mode was changed.
1219 Arguments: (1) <ID Payload> (2) <mode mask>
1220 (3) [<cipher>] (4) <[hmac>]
1222 The <ID Payload> is the ID (usually Client ID but it can be Server ID
1223 as well when the router is enforcing channel mode change) of the
1224 entity which changed the mode. The <mode mask> is the new mode mask
1225 of the channel. The client can safely ignore the <cipher> argument
1226 since the SILC_PACKET_CHANNEL_KEY packet will force the new channel
1227 key change anyway. The <hmac> argument is important since the client
1228 is responsible of setting the new HMAC and the hmac key into use.
1231 8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
1233 Sent when user mode on channel has changed. This type must be sent
1234 only to the clients who is joined on the channel where the target
1238 Arguments: (1) <Client ID> (2) <mode mask>
1239 (3) <Target Client ID>
1241 The <Client ID> is the client who changed the mode. The <mode mask>
1242 is the new mode mask of the channel. The <Target Client ID> is the
1243 client which mode was changed.
1246 9 SILC_NOTIFY_TYPE_MOTD
1248 Sent when Message of the Day (motd) is sent to client.
1251 Arguments: (1) <motd>
1253 The <motd> is the Message of the Day.
1256 10 SILC_NOTIFY_TYPE_CHANNEL_CHANGE
1258 Sent when channel's ID has changed for a reason or another. This
1259 is sent by normal server to the client. This can also be sent by
1260 router to other server to force the Channel ID change. The Channel
1261 ID must be changed to use the new one. When sent to clients, this
1262 type must be sent only to the clients who is joined on the channel.
1265 Arguments: (1) <Old Channel ID> (2) <New Channel ID>
1267 The <Old Channel ID> is the channel's old ID and the <New Channel ID>
1268 is the new one that must replace the old one.
1271 11 SILC_NOTIFY_TYPE_SERVER_SIGNOFF
1273 Sent when server quits SILC network. Those clients from this server
1274 that are on channels must be removed from the channel.
1277 Arguments: (1) <Server ID> (n) [<Client ID> [...]
1279 The <Server ID> is the server's ID. The rest of the arguments are
1280 the Client ID's of the client's who are coming from this server and
1281 are thus quitting the SILC network also. If the maximum number of
1282 arguments are reached another SILC_NOTIFY_TYPE_SERVER_SIGNOFF notify
1283 packet must be sent. When this notify packet is sent between routers
1284 the Client ID's may be omitted.
1287 12 SILC_NOTIFY_TYPE_KICKED
1289 Sent when a client has been kicked from a channel. This is sent
1290 also to the client who was kicked from the channel. The client
1291 who was kicked from the channel must be removed from the channel.
1292 This notify type is always destined to the channel. The router or
1293 server receiving the packet distributes this type to the local
1294 clients on the channel and broadcast it to the network.
1297 Arguments: (1) <Client ID> (2) [<comment>]
1299 The <Client ID> is the client who was kicked from the channel.
1300 The kicker may have set the <comment> to indicate the reason for
1304 13 SILC_NOTIFY_TYPE_KILLED
1306 Sent when a client has been killed from the network. This is sent
1307 also to the client who was killed from the network. The client
1308 who was killed from the network must be removed from the network.
1309 This notify type is destined directly to the client who was killed
1310 and to channel if the client is on any channel. The router or
1311 server receiving the packet distributes this type to the local
1312 clients on the channel and broadcast it to the network.
1315 Arguments: (1) <Client ID> (2) [<comment>]
1317 The <Client ID> is the client who was killed from the network.
1318 The killer may have set the <comment> to indicate the reason for
1322 14 SILC_NOTIFY_TYPE_UMODE_CHANGE
1324 Sent when user's mode in the SILC changes. This type is sent only
1325 between routers as broadcast packet.
1328 Arguments: (1) <Client ID> (2) <mode mask>
1330 The <Client ID> is the client which mode was changed. The <mode mask>
1331 is the new mode mask.
1334 15 SILC_NOTIFY_TYPE_BAN
1336 Sent when the ban list of the channel is changed. This type is sent
1337 only between routers as broadcast packet.
1340 Arguments: (1) <Channel ID> (2) [<adding client>]
1341 (3) [<removing client>]
1343 The <Channel ID> is the channel which ban list was changed. The
1344 <adding client> is used to indicate the a ban was added and the
1345 <removing client> is used to indicate that a ban was removed from
1346 the ban list. The format of the <adding client> and the
1347 <removing client> is defined in the [SILC1] with SILC_COMMAND_BAN
1352 Notify types starting from 16384 are reserved for private notify
1359 Error payload is sent upon error. Error may occur in various
1360 conditions when server sends this packet. Client may not send this
1361 payload but must be able to accept it. However, client may
1362 totally ignore the contents of the packet as server is going to
1363 take action on the error anyway. However, it is recommended
1364 that the client takes error packet seriously.
1370 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
1371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1375 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1379 Figure 11: Error Payload
1383 o Error Message (variable length) - Human readable error
1389 2.3.9 Channel Message Payload
1391 Channel messages are the most common messages sent in the SILC.
1392 Channel Message Payload is used to send message to channels. These
1393 messages can only be sent if client has joined to some channel.
1394 Even though this packet is the most common in SILC it is still
1395 special packet. Some special handling on sending and reception
1396 of channel message is required.
1398 Padding must be applied into this payload since the payload is
1399 encrypted separately from other parts of the packet with the
1400 channel specific key. Hence the requirement of the padding.
1401 The padding should be random data. The packet must be made
1402 multiple by eight (8) or by the block size of the cipher, which
1405 The SILC header in this packet is encrypted with the session key
1406 of the next receiver of the packet. Nothing else is encrypted
1407 with that key. Thus, the actual packet and padding to be
1408 encrypted with the session key is SILC Header plus padding to it
1409 to make it multiple by eight (8) or multiple by the block size
1410 of the cipher, which ever is larger.
1412 Receiver of the the channel message packet is able to determine
1413 the channel the message is destined to by checking the destination
1414 ID from the SILC Packet header which tells the destination channel.
1415 The original sender of the packet is also determined by checking
1416 the source ID from the header which tells the client who sent
1419 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1420 It must not be sent in any other packet type. The following diagram
1421 represents the Channel Message Payload.
1423 (*) indicates that the field is not encrypted.
1429 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
1430 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1431 | Flags | Message Length |
1432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1436 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1437 | Padding Length | |
1438 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1442 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1446 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1448 ~ Initial Vector * ~
1450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1454 Figure 12: Channel Message Payload
1458 o Flags (2 bytes) - Includes the flags of the channel
1459 messages. The flags can indicate a reason or purpose
1460 for the channel message. Note, that the Private Message
1461 Payload use these same flags for the same purpose. The
1462 following flags are defined:
1464 0x0000 SILC_MESSAGE_FLAG_NONE
1466 No specific flags set.
1468 0x0001 SILC_MESSAGE_FLAG_AUTREPLY
1470 This message is an automatic reply to a earlier
1473 0x0002 SILC_MESSAGE_FLAG_NOREPLY
1475 There should not be reply messages to this
1478 0x0004 SILC_MESSAGE_FLAG_ACTION
1480 The sender is performing an action and the message
1481 is the indication of the action.
1483 0x0008 SILC_MESSAGE_FLAG_NOTICE
1485 The message is for example and informational notice
1488 0x0010 SILC_MESSAGE_FLAG_REQUEST
1490 This is a generic request flag to send request
1493 0x0020 - 0x0200 RESERVED
1495 Reserved for future flags
1497 0x0400 - 0x8000 PRIVATE RANGE
1499 Private range for free use.
1501 o Message Length (2 bytes) - Indicates the length of the
1502 the Message Data field in the payload, not including any
1505 o Message Data (variable length) - The actual message to
1508 o Padding Length (2 bytes) - Indicates the length of the
1509 Padding field in the payload, not including any other
1512 o Padding (variable length) - The padding that must be
1513 applied because this payload is encrypted separately from
1514 other parts of the packet.
1516 o MAC (variable legnth) - The MAC computed from the
1517 Message Length, Message Data, Padding Length and Padding
1518 fields. This protects the integrity of the plaintext
1519 channel message. The receiver can verify from the MAC
1520 whether the message decrypted correctly. Also, if more than
1521 one private key has been set for the channel, the receiver
1522 can verify which of the keys decrypted the message
1523 correctly. Note that, this field is encrypted and must
1524 be added to the padding calculation.
1526 o Initial Vector (variable length) - The initial vector
1527 that has been used in packet encryption. It needs to be
1528 used in the packet decryption as well. What this field
1529 includes is implementation issue. However, it is
1530 recommended that it would be random data or, perhaps,
1531 a timestamp. It is not recommended to use zero (0) as
1532 initial vector. This field is not encrypted. This field
1533 is not included into the padding calculation. Length
1534 of this field equals the cipher's block size. This field
1535 is, however, authenticated.
1540 2.3.10 Channel Key Payload
1542 All traffic in channels are protected by channel specific keys.
1543 Channel Key Payload is used to distribute channel keys to all
1544 clients on the particular channel. Channel keys are sent when
1545 the channel is created, when new user joins to the channel and
1546 whenever a user has left a channel. Server creates the new
1547 channel key and distributes it to the clients by encrypting this
1548 payload with the session key shared between the server and
1549 the client. After that, client starts using the key received
1550 in this payload to protect the traffic on the channel.
1552 The client who is joining to the channel receives its key in the
1553 SILC_COMMAND_JOIN command reply message thus it is not necessary to
1554 send this payload to the entity who sent the SILC_COMMAND_JOIN command.
1556 Channel keys are cell specific thus every router in cell have
1557 to create a channel key and distribute it if any client in the
1558 cell has joined to a channel. Channel traffic between cell's
1559 are not encrypted using channel keys, they are encrypted using
1560 normal session keys between two routers. Inside a cell, all
1561 channel traffic is encrypted with the specified channel key.
1562 Channel key should expire periodically, say, in one hour, in
1563 which case new channel key is created and distributed.
1565 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1566 It must not be sent in any other packet type. The following diagram
1567 represents the Channel Key Payload.
1584 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
1585 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1586 | Channel ID Length | |
1587 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1591 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1592 | Cipher Name Length | |
1593 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1598 | Channel Key Length | |
1599 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1603 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1607 Figure 13: Channel Key Payload
1612 o Channel ID Length (2 bytes) - Indicates the length of the
1613 Channel ID field in the payload, not including any other
1616 o Channel ID (variable length) - The Channel ID of the
1617 channel this key is meant for.
1619 o Cipher Name Length (2 bytes) - Indicates the length of the
1620 Cipher name field in the payload, not including any other
1623 o Cipher Name (variable length) - Name of the cipher used
1624 in the protection of channel traffic. This name is
1625 initially decided by the creator of the channel but it
1626 may change during the life time of the channel as well.
1628 o Channel Key Length (2 bytes) - Indicates the length of the
1629 Channel Key field in the payload, not including any other
1632 o Channel Key (variable length) - The actual channel key
1633 material. This key is used as such as key material for
1634 encryption function.
1639 2.3.11 Private Message Payload
1641 Private Message Payload is used to send private message between
1642 two clients (or users for that matter). The messages are sent only
1643 to the specified user and no other user inside SILC network is
1644 able to see the message. The message is protected by the session
1645 key established by the SILC Key Exchange Protocol. However,
1646 it is also possible to agree to use specific keys to protect
1647 just the private messages. See section 2.3.11 Private Message
1648 Key Payload for detailed description of how to agree to use
1651 If normal session key is used to protect the message, every
1652 server between the sender client and the receiving client needs
1653 to decrypt the packet and always re-encrypt it with the session
1654 key of the next receiver of the packet. See section Client
1655 To Client in [SILC1].
1657 When specific key is used to protect the message, servers between
1658 the sender and the receiver needs not to decrypt/re-encrypt the
1659 packet. Section 4.8.2 Client To Client in [SILC1] gives example of
1660 this scheme as well.
1662 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1663 packet. It must not be sent in any other packet type. The following
1664 diagram represents the Private Message Payload.
1670 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
1671 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1672 | Flags | Nickname Length |
1673 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1677 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1678 | Message Data Length | |
1679 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1683 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1687 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1691 Figure 14: Private Message Payload
1695 o Flags (2 bytes) - This field includes the flags of the
1696 private message. They can indicate a different reason or
1697 purpose for the private message. See the section 2.3.9
1698 Channel Message Payload for defined flags. Note, that
1699 the Channel Message Payload use the same flags for the
1702 o Nickname Length (2 bytes) - Indicates the length of the
1703 Nickname field, not including any other field.
1705 o Nickname (variable length) - Nickname of the sender of the
1706 private message. This should not be trusted as a definite
1707 sender of the private message. The SILC Packet Header in
1708 the packet indicates the true sender of the packet and
1709 client should verify that the nickname sent here belongs
1710 to the Client ID in the SILC Packet Header. This nickname
1711 is merely provided to be displayed by the client.
1713 o Message Data Length (2 bytes) - Indicates the length of the
1714 Message Data field, not includes any other field.
1716 o Message Data (variable length) - The actual message to
1717 the client. Rest of the packet is reserved for the message
1720 o Padding (variable length) - This field is present only
1721 when the private message payload is encrypted with private
1722 message key. In this case the padding is applied to make
1723 the packet multiple by eight (8), or by the block size of
1724 the cipher, which ever is larger. When encrypted with
1725 normal session keys, this field must not be included.
1730 2.3.12 Private Message Key Payload
1732 This payload is used to send key from client to another client that
1733 is going to be used to protect the private messages between these
1734 two clients. If this payload is not sent normal session key
1735 established by the SILC Key Exchange Protocol is used to protect
1736 the private messages.
1738 This payload may only be sent by client to another client. Server
1739 must not send this payload at any time. After sending this payload
1740 the sender of private messages must set the Private Message Key
1741 flag into SILC Packet Header.
1743 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1744 packet. It must not be sent in any other packet type. The following
1745 diagram represents the Private Message Key Payload.
1751 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
1752 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1753 | Private Message Key Length | |
1754 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1756 ~ Private Message Key ~
1758 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1759 | Cipher Name Length | |
1760 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1764 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1768 Figure 15: Private Message Key Payload
1774 o Private Message Key Length (2 bytes) - Indicates the length
1775 of the Private Message Key field in the payload, not including
1778 o Private Message Key (variable length) - The actual private
1779 message key material.
1781 o Cipher Name Length (2 bytes) - Indicates the length of the
1782 Cipher Name field in the payload, not including any other
1785 o Cipher Name (variable length) - Name of the cipher to use
1786 in the private message encryption. If this field does not
1787 exist then the default cipher of the SILC protocol is used.
1788 See the [SILC1] for defined ciphers.
1794 2.3.13 Command Payload
1796 Command Payload is used to send SILC commands from client to server.
1797 Also server may send commands to other servers. The following diagram
1798 represents the Command Payload.
1804 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
1805 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1806 | Payload Length | SILC Command | Arguments Num |
1807 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1808 | Command Identifier |
1809 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1813 Figure 16: Command Payload
1817 o Payload Length (2 bytes) - Length of the entire command
1818 payload including any command argument payloads associated
1821 o SILC Command (1 byte) - Indicates the SILC command. This must
1822 be set to non-zero value. If zero (0) value is found in this
1823 field the packet must be discarded.
1825 o Arguments Num (1 byte) - Indicates the number of arguments
1826 associated with the command. If there are no arguments this
1827 field is set to zero (0). The arguments must follow the
1828 command payload. See section 2.3.2.2 for definition of the
1831 o Command Identifier (2 bytes) - Identifies this command at the
1832 sender's end. The entity who replies to this command must
1833 set the value found from this field into the Command Payload
1834 used to send the reply to the sender. This way the sender
1835 can identify which command reply belongs to which originally
1836 sent command. What this field includes is implementation
1837 issue but it is recommended that wrapping counter value is
1838 used in the field. Value zero (0) in this field means that
1839 no specific value is set.
1842 See [SILC1] for detailed description of different SILC commands,
1843 their arguments and their reply messages.
1847 2.3.14 Command Reply Payload
1849 Command Reply Payload is used to send replies to the commands. The
1850 Command Reply Payload is identical to the Command Payload thus see the
1851 upper sections for Command Payload and for Command Argument Payload
1852 specifications. Command Reply message uses the Command Argument Payload
1855 The entity who sends the reply packet must set the Command Unifier
1856 field in the reply packet's Command Payload to the value it received
1857 in the original command packet.
1859 See SILC Commands in [SILC1] for detailed description of different
1860 SILC commands, their arguments and their reply messages.
1864 2.3.15 Connection Auth Request Payload
1866 Client may send this payload to server to request the authentication
1867 method that must be used in authentication protocol. If client knows
1868 this information beforehand this payload is not necessary to be sent.
1869 Server performing authentication with another server may also send
1870 this payload to request the authentication method. If the connecting
1871 server already knows this information this payload is not necessary
1874 Server receiving this request must reply with same payload sending
1875 the mandatory authentication method. Algorithms that may be required
1876 to be used by the authentication method are the ones already
1877 established by the SILC Key Exchange protocol. See section Key
1878 Exchange Start Payload in [SILC3] for detailed information.
1880 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1881 packet. It must not be sent in any other packet type. The following
1882 diagram represents the Connection Auth Request Payload.
1888 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
1889 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1890 | Connection Type | Authentication Method |
1891 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1895 Figure 17: Connection Auth Request Payload
1899 o Connection Type (2 bytes) - Indicates the type of the ID.
1900 The following connection types are defined:
1906 If any other type is found in this field the packet must be
1907 discarded and the authentication must be failed.
1909 o Authentication Method (2 bytes) - Indicates the authentication
1910 method to be used in the authentication protocol. The following
1911 authentication methods are defined:
1916 1 password (mandatory)
1917 2 public key (mandatory)
1919 If any other type is found in this field the packet must be
1920 discarded and the authentication must be failed. If this
1921 payload is sent as request to receive the mandatory
1922 authentication method this field must be set to zero (0),
1923 indicating that receiver should send the mandatory
1924 authentication method. The receiver sending this payload
1925 to the requesting party, may also set this field to zero (0)
1926 to indicate that authentication is not required. In this
1927 case authentication protocol still must be started but
1928 server is most likely to respond with SILC_PACKET_SUCCESS
1934 2.3.16 New ID Payload
1936 New ID Payload is a multipurpose payload. It is used to send newly
1937 created ID's from clients and servers. When client connects to server
1938 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
1939 packet, server replies with this packet by sending the created ID for
1940 the client. Server always creates the ID for the client.
1942 This payload is also used when server tells its router that new client
1943 has registered to the SILC network. In this case the server sends
1944 the Client ID of the client to the router. Similary when router
1945 distributes information to other routers about the client in the SILC
1946 network this payload is used.
1948 Also, when server connects to router, router uses this payload to inform
1949 other routers about new server in the SILC network. However, every
1950 server (or router) creates their own ID's thus the ID distributed by
1951 this payload is not created by the distributor in this case. Servers
1952 create their own ID's. Server registers itself to the network by sending
1953 SILC_PACKET_NEW_SERVER to the router it connected to. The case is same
1954 when router connects to another router.
1956 However, this payload is not and must not be used to send information
1957 about new channels. New channels are always distributed by sending the
1958 dedicated SILC_PACKET_NEW_CHANNEL packet.
1960 Hence, this payload is very important and used every time when some
1961 new entity is registered to the SILC network. Client never sends this
1962 payload. Both client and server (and router) may receive this payload.
1964 The packet uses generic ID Payload as New ID Payload. See section
1965 2.3.2.1 for generic ID Payload.
1969 2.3.17 New Client Payload
1971 When client is connected to the server, keys has been exchanged and
1972 connection has been authenticated client must register itself to the
1973 server. Clients first packet after key exchange and authentication
1974 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
1975 the relevant information about the connected user. Server creates a new
1976 client ID for the client when received this payload and sends it to the
1977 client in New ID Payload.
1979 This payload sends username and real name of the user on the remote host
1980 which is connected to the SILC server with SILC client. The server
1981 creates the client ID according the information sent in this payload.
1982 The nickname of the user becomes the username sent in this payload.
1983 However, client should call NICK command after sending this payload to
1984 set the real nickname of the user which is then used to create new
1987 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
1988 must not be sent in any other packet type. The following diagram
1989 represents the New Client Payload.
1996 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
1997 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1998 | Username Length | |
1999 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2003 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2004 | Real Name Length | |
2005 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2009 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2013 Figure 18: New Client Payload
2017 o Username Length (2 bytes) - Length of the username.
2019 o Username (variable length) - The username of the user on
2020 the host where connecting to the SILC server.
2022 o Real Name Length (2 bytes) - Length of the Real Name.
2024 o Real Name (variable length) - The real name of the user
2025 on the host where connecting to the SILC server.
2030 2.3.18 New Server Payload
2032 This payload is sent by server when it has completed successfully both
2033 key exchange and connection authentication protocols. The server
2034 uses this payload to register itself to the SILC network. The
2035 first packet after these key exchange and authentication protocols
2036 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
2037 of the server that it has created by itself. It also includes a
2038 name of the server that is associated to the Server ID.
2040 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
2041 must not be sent in any other packet type. The following diagram represents
2042 the New Server Payload.
2051 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
2052 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2053 | Server ID Length | |
2054 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2058 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2059 | Server Name Length | |
2060 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2064 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2068 Figure 19: New Server Payload
2072 o Server ID Length (2 bytes) - Length of the ID Data area not
2073 including the length of any other fields in the payload.
2075 o Server ID Data (variable length) - The actual Server ID
2078 o Server Name Length (2 bytes) - Length of the server name.
2080 o Server Name (variable length) - The server name.
2085 2.3.19 New Channel Payload
2087 Information about newly created channel is broadcasted to all routers
2088 in the SILC network by sending this packet payload. Channels are
2089 created by router of the cell. Server never creates channels unless
2090 it is a standalone server and it does not have router connection,
2091 in this case server acts as router. Normal server send JOIN command
2092 to the router (after it has received JOIN command from client) which
2093 then processes the command and creates the channel. Client never sends
2096 The packet uses generic Channel Payload as New Channel Payload. See
2097 section 2.3.2.3 for generic Channel Payload. The Mode Mask field in the
2098 Channel Payload is the mode of the channel.
2102 2.3.20 Key Agreement Payload
2104 This payload is used by clients to request key negotiation between
2105 another client in the SILC Network. The key agreement protocol used
2106 is the SKE protocol. The result of the protocol, the secret key
2107 material, can be used for example as private message key between the
2108 two clients. This significantly adds security as the key agreement
2109 is performed outside the SILC network. The server and router must not
2112 The sender may tell the receiver of this payload the hostname and the
2113 port where the SKE protocol is running in the sender's end. The
2114 receiver may then initiate the SKE negotiation with the sender. The
2115 sender may also optionally not to include the hostname and the port
2116 of its SKE protocol. In this case the receiver may reply to the
2117 request by sending the same payload filled with the receiver's hostname
2118 and the port where the SKE protocol is running. The sender may then
2119 initiate the SKE negotiation with the receiver.
2121 The payload may only be sent with SILC_PACKET_KEY_AGREEMENT packet.
2122 It must not be sent in any other packet type. The following diagram
2123 represents the Key Agreement Payload.
2129 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
2130 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2131 | Hostname Length | |
2132 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2136 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2138 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2142 Figure 20: Key Agreement Payload
2146 o Hostname Length (2 bytes) - Indicates the length of the Hostname
2149 o Hostname (variable length) - The hostname or IP address where
2150 the SKE protocol is running. The sender may fill this field
2151 when sending the payload. If the receiver sends this payload
2152 as reply to the request it must fill this field.
2154 o Port (4 bytes) - The port where the SKE protocol is bound.
2155 The sender may fill this field when sending the payload. If
2156 the receiver sends this payload as reply to the request it
2157 must fill this field. This is a 32 bit MSB first order value.
2161 After the key material has been received from the SKE protocol it is
2162 processed as the [SILC3] describes. If the key material is used as
2163 channel private key then the Sending Encryption Key, as defined in
2164 [SILC3] is used as the channel private key. Other key material must
2165 be discarded. The [SILC1] defines the way to use the key material if
2166 it is intended to be used as private message keys. Any other use for
2167 the key material is undefined.
2171 2.3.21 Cell Routers Payload
2173 Cell Routers payload is used by router to notify its primary router what
2174 other routers exist in the cell. The other routers are considered to be
2175 backup routers and one of them will come active only in the case of
2176 failure of the primary router. Normal server can send this packet if it
2177 is acting as backup router. Client must not send this packet. To send
2178 more than one backup router set the List flag and assemble the payloads
2181 The payload may only be sent with SILC_PACKET_CELL_ROUTERS packet. It
2182 must not be sent in any other packet type. The Following diagram
2183 represents the Cell Routers Payload.
2189 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
2190 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2191 | Hostname Length | |
2192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2198 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2199 | Server ID Length | |
2200 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2204 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2208 Figure 21: Cell Routers Payload
2212 o Hostname Length (2 bytes) - Indicates the length of the Hostname
2215 o Hostname (variable length) - The hostname or IP address of
2218 o Port (4 bytes) - The port of the backup router it currently uses.
2219 This is a 32 bit MSB first order value.
2221 o Server ID Length (2 bytes) - Indicates the length of the Server
2224 o Server ID (variable length) - Consists of the Server ID of the
2232 ID's are extensively used in the SILC network to associate different
2233 entities. The following ID's has been defined to be used in the SILC
2239 When ever specific ID cannot be used this is used.
2243 Server ID to associate servers. See the format of
2248 Client ID to associate clients. See the format of
2253 Channel ID to associate channels. See the format of
2259 2.5 Packet Encryption And Decryption
2261 SILC packets are encrypted almost entirely. Only small part of SILC
2262 header is not encrypted as described in section 5.2 SILC Packet Header.
2263 The SILC Packet header is the first part of a packet to be encrypted
2264 and it is always encrypted with the key of the next receiver of the
2265 packet. The data payload area of the packet is always entirely
2266 encrypted and it is usually encrypted with the next receiver's key.
2267 However, there are some special packet types and packet payloads
2268 that require special encryption process. These special cases are
2269 described in the next sections. First is described the normal packet
2274 2.5.1 Normal Packet Encryption And Decryption
2276 Normal SILC packets are encrypted with the session key of the next
2277 receiver of the packet. The entire SILC Packet header and the packet
2278 data payload is is also encrypted with the same key. Padding of the
2279 packet is also encrypted always with the session key, also in special
2280 cases. Computed MAC of the packet must not be encrypted.
2282 Decryption process in these cases are straightforward. The receiver
2283 of the packet must first decrypt the SILC Packet header, or some parts
2284 of it, usually first 16 bytes of it. Then the receiver checks the
2285 packet type from the decrypted part of the header and can determine
2286 how the rest of the packet must be decrypted. If the packet type is
2287 any of the special cases described in The following sections the packet
2288 decryption is special. If the packet type is not among those special
2289 packet types rest of the packet may be decrypted with the same key.
2291 Also, note that two bytes of the SILC Packet header are not encrypted
2292 thus it must be noticed in the decryption process by starting the
2293 decryption from the second byte of the header. This sets some rules
2294 to padding generation as well, see the section 2.7 Packet Padding
2297 With out a doubt, this sort of decryption processing causes some
2298 overhead to packet decryption, but never the less, is required.
2302 2.5.2 Channel Message Encryption And Decryption
2304 Channel Messages (Channel Message Payload) are always encrypted with
2305 the channel specific key. However, the SILC Packet header is not
2306 encrypted with that key. As in normal case, the header is encrypted
2307 with the key of the next receiver of the packet, who ever that might
2308 be. Note that in this case the encrypted data area is not touched
2309 at all; it must not be re-encrypted with the session key.
2311 Receiver of a channel message, who ever that is, is required to decrypt
2312 the SILC Packet header to be able to even recognize the packet to be as
2313 channel message. This is same procedure as for normal SILC packets.
2314 As the receiver founds the packet to be channel message, rest of the
2315 packet processing is special. Rest of the SILC Packet header is
2316 decrypted with the same session key along with the padding of the
2317 packet. After that the packet is protected with the channel specific
2318 key and thus can be decrypted only if the receiver is the client on
2319 the channel. See section 2.7 Packet Padding Generation for more
2320 information about padding on special packets.
2322 If the receiver of the channel message is router who is routing the
2323 message to another router then it must decrypt the Channel Message
2324 payload. Between routers (that is, between cells) channel messages
2325 are protected with session keys shared between the routers. This
2326 causes another special packet processing for channel messages. If
2327 the channel message is received from another router then the entire
2328 packet, including Channel Message payload, is encrypted with the
2329 session key shared between the routers. In this case the packet
2330 decryption process is as with normal SILC packets. Hence, if the
2331 router is sending channel message to another router the Channel
2332 Message payload must have been decrypted and must be re-encrypted
2333 with the session key shared between the another router. In this
2334 case the packet encryption is as with any normal SILC packet.
2336 It must be noted that this is only when the channel messages are sent
2337 from router to another router. In all other cases the channel
2338 message encryption and decryption is as described above. This
2339 different processing of channel messages with router to router
2340 connection is because channel keys are cell specific. All cells has
2341 their own channel keys thus the channel message traveling from one
2342 cell to another must be protected as it would be any normal SILC
2345 If the SILC_CMODE_PRIVKEY channel mode has been set for the channel
2346 then the router cannot decrypt the packet as it does not know the
2347 private key. In this case the entire packet is encrypted with the
2348 session key and sent to the router. The router receiving the packet
2349 must check the channel mode and decrypt the packet accordingly.
2353 2.5.3 Private Message Encryption And Decryption
2355 By default, private message in SILC are protected by session keys.
2356 In this case the private message encryption and decryption process is
2357 equivalent to normal packet encryption and decryption.
2359 However, private messages can be protected with private message key
2360 which causes the packet to be special packet. The procedure in this
2361 case is very much alike to channel packets. The actual private message
2362 is encrypted with the private message key and other parts of the
2363 packet is encrypted with the session key. See 2.7 Packet Padding
2364 Generation for more information about padding on special packets.
2366 The difference from channel message processing is that server or router
2367 en route never decrypts the actual private message, as it does not
2368 have the key to do that. Thus, when sending packets between router
2369 the processing is same as in any other case as well; the packet's header
2370 and padding is protected by the session key and the data area is not
2373 The true receiver of the private message, client, that is, is able
2374 to decrypt the private message as it shares the key with the sender
2379 2.6 Packet MAC Generation
2381 Data integrity of a packet is protected by including a message
2382 authentication code (MAC) at the end of the packet. The MAC is computed
2383 from shared secret MAC key, that is established by the SILC Key Exchange
2384 protocol, and from the original contents of the packet. The MAC is
2385 always computed before the packet is encrypted, although after it is
2386 compressed if compression is used.
2388 The MAC is computed from entire packet. Every bit of data in the packet,
2389 including SILC Packet Header is used in the MAC computing. This way
2390 the entire packet becomes authenticated.
2392 If the packet is special packet MAC is computed from the entire packet
2393 but part of the packet may be encrypted before the MAC is computed.
2394 This is case, for example, with channel messages where the message data
2395 is encrypted with key that server may not now. In this case the MAC
2396 has been computed from the encrypted data.
2398 See [SILC1] for defined and allowed MAC algorithms.
2402 2.7 Packet Padding Generation
2404 Padding is needed in the packet because the packet is encrypted. It
2405 must always be multiple by eight (8) or multiple by the size of the
2406 cipher's block size, which ever is larger. The padding is always
2409 For normal packets the padding is added after the SILC Packet Header
2410 and between the Data Payload area. The padding for normal packets
2411 are calculated as follows:
2414 padding length = 16 - ((packet length - 2) % 16)
2417 The 16 is the maximum padding allowed in SILC packet. Two (2) is
2418 subtracted from the true length of the packet because two (2) bytes
2419 is not encrypted in SILC Packet Header, see section 2.2 SILC Packet
2420 Header. Those two bytes that are not encrypted must not be calculated
2421 to the padding length.
2423 For special packets the padding calculation may be different as special
2424 packets may be encrypted differently. In these cases the encrypted
2425 data area must already be multiple by the block size thus in this case
2426 the padding is calculated only for SILC Packet Header, not for any
2427 other area of the packet. The same algorithm works in this case as
2428 well, except that the `packet length' is now the SILC Packet Header
2429 length. In this case, as well, two (2) is subtracted from the
2432 The padding must be random data, preferably, generated by
2433 cryptographically strong random number generator.
2437 2.8 Packet Compression
2439 SILC Packets may be compressed. In this case the data payload area
2440 is compressed and all other areas of the packet must remain as they
2441 are. After compression is performed for the data area, the length
2442 field of Packet Header must be set to the compressed length of the
2445 The compression must always be applied before encryption. When
2446 the packet is received and decrypted the data area must be decompressed.
2447 Note that the true sender of the packet must apply the compression and
2448 the true receiver of the packet must apply the decompression. Any
2449 server or router en route must not decompress the packet.
2456 The sender of the packet must assemble the SILC Packet Header with
2457 correct values. It must set the Source ID of the header as its own
2458 ID, unless it is forwarding the packet. It must also set the Destination
2459 ID of the header to the true destination. If the destination is client
2460 it will be Client ID, if it is server it will be Server ID and if it is
2461 channel it will be Channel ID.
2463 If the sender wants to compress the packet it must apply the
2464 compression now. Sender must also compute the padding as described
2465 in above sections. Then sender must compute the MAC of the packet.
2467 Then sender encrypts the packet as has been described in above
2468 sections according whether the packet is normal packet or special
2469 packet. The computed MAC must not be encrypted.
2473 2.10 Packet Reception
2475 On packet reception the receiver must check that all fields in the
2476 SILC Packet Header are valid. It must check the flags of the
2477 header and act accordingly. It must also check the MAC of the packet
2478 and if it is to be failed the packet must be discarded. Also if the
2479 header of the packet includes any bad fields the packet must be
2482 See above sections on the decryption process of the received packet.
2484 The receiver must also check that the ID's in the header are valid
2485 ID's. Unsupported ID types or malformed ID's must cause packet
2486 rejection. The padding on the reception is always ignored.
2488 The receiver must also check the packet type and start parsing the
2489 packet according to the type. However, note the above sections on
2490 special packet types and their parsing.
2496 Routers are the primary entities in the SILC network that takes care
2497 of packet routing. However, normal servers routes packets as well, for
2498 example, when they are routing channel message to the local clients.
2499 Routing is quite simple as every packet tells the true origin and the
2500 true destination of the packet.
2502 It is still recommended for routers that has several routing connections
2503 to create route cache for those destinations that has faster route than
2504 the router's primary route. This information is available for the router
2505 when other router connects to the router. The connecting party then
2506 sends all of its locally connected clients, server and channels. These
2507 informations helps to create the route cache. Also, when new channels
2508 are created to a cell its information is broadcasted to all routers
2509 in the network. Channel ID's are based on router's ID thus it is easy
2510 to create route cache based on these informations. If faster route for
2511 destination does not exist in router's route cache the packet must be
2512 routed to the primary route (default route).
2514 For server who receives a packet to be routed to its locally connected
2515 client the server must check whether the particular packet type is
2516 allowed to be routed to the client. Not all packets may be sent by
2517 some odd entity to client that is indirectly connected to the sender.
2518 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2519 entities and sending packets to them. The section mentions the packets
2520 that may be sent to indirectly connected entities. It is clear that some
2521 server cannot send, for example, disconnect packet to client that is not
2522 directly connected to the server.
2526 2.12 Packet Broadcasting
2528 SILC packets may be broadcasted in SILC network. However, only router
2529 server may send or receive broadcast packets. Client and normal server
2530 must not send broadcast packets and they must ignore broadcast packets
2531 if they receive them. Broadcast packets are sent by setting Broadcast
2532 flag to the SILC packet header.
2534 Broadcasting packets means that the packet is sent to all routers in
2535 the SILC network, except to the router that sent the packet. The router
2536 receiving broadcast packet must send the packet to its primary route.
2537 The fact that SILC routers may have several router connections may
2538 cause problems, such as race conditions inside the SILC network, if
2539 care is not taken when broadcasting packets. Router must not send
2540 the broadcast packet to any other route except to its primary route.
2542 If the primary route of the router is the original sender of the packet
2543 the packet must not be sent to the primary route. This may happen
2544 if router has several router connections and some other router uses
2545 the router as its primary route.
2547 Routers use broadcast packets to broadcast for example information
2548 about newly registered clients, servers, channels etc. so that all the
2549 routers may keep these informations up to date.
2553 3 Security Considerations
2555 Security is central to the design of this protocol, and these security
2556 considerations permeate the specification. Common security considerations
2557 such as keeping private keys truly private and using adequate lengths for
2558 symmetric and asymmetric keys must be followed in order to maintain the
2559 security of this protocol.
2565 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2566 Protocol Specification", Internet Draft, June 2000.
2568 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2569 Protocols", Internet Draft, June 2000.
2571 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2574 [IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
2577 [IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
2580 [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
2583 [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
2586 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2589 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2592 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2595 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2596 Infrastructure, Certificate and CRL Profile", RFC 2459,
2599 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2600 John Wiley & Sons, New York, NY, 1996.
2602 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2605 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2606 RFC 2412, November 1998.
2608 [ISAKMP] Maughan D., et al, "Internet Security Association and
2609 Key Management Protocol (ISAKMP)", RFC 2408, November
2612 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2613 (IKE)", RFC 2409, November 1998.
2615 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2616 Authentication", RFC 2104, February 1997.
2618 [PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
2619 Specifications, Version 2.0", RFC 2437, October 1998.
2631 EMail: priikone@poseidon.pspt.fi
2633 This Internet-Draft expires 6 Jun 2001