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 2.3.2.4 Public Key Payload .......................... XXX
85 2.3.3 Disconnect Payload .................................. 17
86 2.3.4 Success Payload ..................................... 18
87 2.3.5 Failure Payload ..................................... 18
88 2.3.6 Reject Payload ...................................... 19
89 2.3.7 Notify Payload ...................................... 20
90 2.3.8 Error Payload ....................................... 21
91 2.3.9 Channel Message Payload ............................. 22
92 2.3.10 Channel Key Payload ................................ 24
93 2.3.11 Private Message Payload ............................ 26
94 2.3.12 Private Message Key Payload ........................ 27
95 2.3.13 Command Payload .................................... 28
96 2.3.14 Command Reply Payload .............................. 29
97 2.3.15 Connection Auth Request Payload .................... 29
98 2.3.16 New ID Payload ..................................... 30
99 2.3.17 New Client Payload ................................. 31
100 2.3.18 New Server Payload ................................. 32
101 2.3.19 New Channel Payload ................................ 33
102 2.3.20 Key Agreement Payload .............................. XXX
103 2.4 SILC ID Types ............................................. 39
104 2.5 Packet Encryption And Decryption .......................... 39
105 2.5.1 Normal Packet Encryption And Decryption ............. 39
106 2.5.2 Channel Message Encryption And Decryption ........... 40
107 2.5.3 Private Message Encryption And Decryption ........... 41
108 2.6 Packet MAC Generation ..................................... 41
109 2.7 Packet Padding Generation ................................. 42
110 2.8 Packet Compression ........................................ 42
111 2.9 Packet Sending ............................................ 43
112 2.10 Packet Reception ......................................... 43
113 2.11 Packet Routing ........................................... 44
114 2.12 Packet Broadcasting ...................................... 45
115 3 Security Considerations ....................................... 46
116 4 References .................................................... 46
117 5 Author's Address .............................................. 47
123 Figure 1: Typical SILC Packet
124 Figure 2: SILC Packet Header
126 Figure 4: Argument Payload
127 Figure 5: Channel Payload
128 Figure 6: Public Key Payload
129 Figure 7: Disconnect Payload
130 Figure 8: Success Payload
131 Figure 9: Failure Payload
132 Figure 10: Reject Payload
133 Figure 11: Notify Payload
134 Figure 12: Error Payload
135 Figure 13: Channel Message Payload
136 Figure 14: Channel Key Payload
137 Figure 15: Private Message Payload
138 Figure 16: Private Message Key Payload
139 Figure 17: Command Payload
140 Figure 18: Connection Auth Request Payload
141 Figure 19: New Client Payload
142 Figure 20: New Server Payload
143 Figure 21: Key Agreement Payload
144 Figure 22: Cell Routers Payload
150 This document describes a Packet Protocol used in the Secure Internet
151 Live Conferencing (SILC) protocol specified in the Secure Internet Live
152 Conferencing, Protocol Specification Internet Draft [SILC1]. This
153 protocol describes the packet types and packet payloads which defines
154 the contents of the packets. The protocol provides secure binary packet
155 protocol that assures that the contents of the packets are secured and
158 The basis of SILC protocol relies in the SILC packets and it is with
159 out a doubt the most important part of the protocol. It is also probably
160 the most complicated part of the protocol. Packets are used all the
161 time in the SILC network to send messages, commands and other information.
162 All packets in SILC network are always encrypted and their integrity
163 is assured by computed MACs. The protocol defines several packet types
164 and packet payloads. Each packet type usually has a specific packet
165 payload that actually defines the contents of the packet. Each packet
166 also includes a default SILC Packet Header that provides sufficient
167 information about the origin of the packet and destination of the
172 2 SILC Packet Protocol
177 SILC packets deliver messages from sender to receiver securely by
178 encrypting important fields of the packet. The packet consists of
179 default SILC Packet Header, Padding, Packet Payload data, and, packet
182 The following diagram illustrates typical SILC packet.
187 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
188 | n bytes | 1 - n bytes | n bytes | n bytes
189 | SILC Header | Padding | Data Payload | MAC
190 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
194 Figure 1: Typical SILC Packet
197 SILC Header is always the first part of the packet and its purpose
198 is to provide information about the packet. It provides for example
199 the packet type, origin of the packet and the destination of the packet.
200 The header is variable in length and first two (2) bytes of the
201 header (thus first two bytes of the packet) are not encrypted. The
202 first two (2) bytes are the length of the packet which is not encrypted.
203 See The following section for description of SILC Packet header. Packets
204 without SILC header or with malformed SILC header must be dropped.
206 Padding follows the packet header. The purpose of the padding is to
207 make the packet multiple by eight (8) or by the block size of the
208 cipher used in the encryption, which ever is larger. The maximum
209 length of padding is currently 16 bytes. The padding is always
212 Data payload area follows padding and it is the actual data of the
213 packet. The packet data is the packet payloads defined in this
214 protocol. The data payload area is always encrypted.
216 The last part of SILC packet is the packet MAC that assures the
217 integrity of the packet. The MAC is always computed from the packet
218 before the encryption is applied to the packet. If compression is used
219 in the packet the MAC is computed after the compression has been
220 applied. The compression, on the other hand, is always applied before
223 All fields in all packet payloads are always in MSB (most significant
228 2.2 SILC Packet Header
230 The default SILC packet header is applied to all SILC packets and it is
231 variable in length. The purpose of SILC Packet header is to provide
232 detailed information about the packet. The receiver of the packet uses
233 the packet header to parse the packet and gain other relevant parameters
236 The following diagram represents the default SILC header format.
237 (*) indicates that this field is never encrypted. Other fields are
244 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
245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
246 | Payload Length * | Flags | Packet Type |
247 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
248 | Source ID Length | Destination ID Length |
249 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
265 Figure 2: SILC Packet Header
269 o Payload Length (2 bytes) - Is the length of the packet
270 not including the padding of the packet. This field must
271 not be encrypted but must always be authenticated.
273 o Flags (1 byte) - Indicates flags to be used in packet
274 processing. Several flags may be set by ORing the flags
277 The following flags are reserved for this field:
282 In this case the field is ignored.
285 Private Message Key 0x01
287 Indicates that the packet must include private
288 message that is encrypted using private key set by
289 client. Servers does not know anything about this
290 key and this causes that the private message is
291 not handled by the server at all, it is just
292 passed along. See section 2.5.3 Private Message
293 Encryption And Decryption for more information.
298 Indicates that the packet consists of list of
299 packet payloads indicated by the Packet Type field.
300 The payloads are added one after the other. Note that
301 there are packet types that must not be used as
302 list. Parsing of list packet is done by calculating
303 the length of each payload and parsing them one by
309 Marks the packet to be broadcasted. Client cannot
310 send broadcast packet and normal server cannot send
311 broadcast packet. Only router server may send broadcast
312 packet. The router receiving of packet with this flag
313 set must send (broadcast) the packet to its primary
314 route. If router has several router connections the
315 packet may be sent only to the primary route. See
316 section 2.13 Packet Broadcasting for description of
323 o Packet Type (1 byte) - Is the type of the packet. Receiver
324 uses this field to parse the packet. See section 2.3
325 SILC Packets for list of defined packet types.
327 o Source ID Length (2 bytes) - Indicates the length of the
328 Source ID field in the header, not including this or any
331 o Destination ID Length (2 bytes) - Indicates the length of the
332 Destination ID field in the header, not including this or
335 o Src ID Type (1 byte) - Indicates the type of ID in the
336 Source ID field. See section 2.4 SILC ID Types for
339 o Source ID (variable length) - The actual source ID that
340 indicates who is the original sender of the packet.
342 o Dst ID Type (1 byte) - Indicates the type of ID in the
343 Destination ID field. See section 2.4 SILC ID Types for
346 o Destination ID (variable length) - The actual source ID that
347 indicates who is the end receiver of the packet.
351 2.3 SILC Packet Types
353 SILC packet types defines the contents of the packet and it is used by
354 the receiver to parse the packet. The packet type is 8 bits, as a one
355 byte, in length. The range for the packet types are from 0 - 255,
356 where 0 is never sent and 255 is currently reserved for future
357 extensions and must not be defined to any other purpose. Every SILC
358 specification compliant implementation should support all of these packet
361 The below list of the SILC Packet types includes reference to the packet
362 payload as well. Packet payloads are the actual packet, that is, the data
363 that the packet consists of. Each packet type defines packet payload
364 which usually may only be sent with the specific packet type.
366 Most of the packets are packets that must be destined directly to entity
367 that is connected to the sender. It is not allowed, for example, for
368 router to send disconnect packet to client that is not directly connected
369 to the router. However, there are some special packet types that may
370 be destined to some entity that the sender has not direct connection
371 with. These packets are for example private message packets, channel
372 message packets, command packets and some other packets that may be
373 broadcasted in the SILC network. If the packet is allowed to be sent to
374 indirectly connected entity it is mentioned separately in the packet
375 description (unless it is obvious as in private and channel message
376 packets). Other packets must not be sent or accepted, if sent, to
377 indirectly connected entities.
379 List of SILC Packet types are defined as follows.
384 This type is reserved and it is never sent.
387 1 SILC_PACKET_DISCONNECT
389 This packet is sent to disconnect the remote end. Reason of
390 the disconnection is sent inside the packet payload. Client
391 usually does not send this packet.
393 This packet must not be sent as list and the List flag must
396 Payload of the packet: See section 2.3.3 Disconnect Payload
399 2 SILC_PACKET_SUCCESS
401 This packet is sent upon successful execution of some protocol.
402 The status of the success is sent in the packet.
404 This packet must not be sent as list and the List flag must
407 Payload of the packet: See section 2.3.4 Success Payload
410 3 SILC_PACKET_FAILURE
412 This packet is sent upon failure of some protocol. The status
413 of the failure is sent in the packet.
415 This packet must not be sent as list and the List flag must
418 Payload of the packet: See section 2.3.5 Failure Payload
423 This packet may be sent upon rejection of some protocol.
424 The status of the rejection is sent in the packet.
426 This packet must not be sent as list and the List flag must
429 Payload of the packet: See section 2.3.6 Reject Payload
434 This packet is used to send notify message, usually from
435 server to client, although it may be sent from server to another
436 server as well. Client never sends this packet. Server may
437 send this packet to channel as well when the packet is
438 distributed to all clients on the channel.
440 Payload of the packet: See section 2.3.7 Notify Payload.
445 This packet is sent when an error occurs. Server may
446 send this packet. Client never sends this packet. The
447 client may entirely ignore the packet, however, server is
448 most likely to take action anyway. This packet may be sent
449 to entity that is indirectly connected to the sender.
451 This packet must not be sent as list and the List flag must
454 Payload of the packet: See section 2.3.8 Error Payload.
457 7 SILC_PACKET_CHANNEL_MESSAGE
459 This packet is used to send messages to channels. The packet
460 includes Channel ID of the channel and the actual message to
461 the channel. Messages sent to the channel are always protected
462 by channel specific keys. Channel Keys are distributed by
463 SILC_PACKET_CHANNEL_KEY packet.
465 This packet must not be sent as list and the List flag must
468 Payload of the packet: See section 2.3.9 Channel Message
472 8 SILC_PACKET_CHANNEL_KEY
474 This packet is used to distribute new key for particular
475 channel. Each channel has their own independent keys that
476 is used to protect the traffic on the channel. Only server
477 may send this packet. This packet may be sent to entity
478 that is indirectly connected to the sender.
480 This packet must not be sent as list and the List flag must
483 Payload of the packet: See section 2.3.10 Channel Key Payload
486 9 SILC_PACKET_PRIVATE_MESSAGE
488 This packet is used to send private messages from client
489 to another client. By default, private messages are protected
490 by session keys established by normal key exchange protocol.
491 However, it is possible to use specific key to protect private
492 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
493 agree the key with the remote client. Pre-shared key may be
494 used as well if both of the client knows it, however, it needs
495 to be agreed outside SILC. See more of this in [SILC1].
497 This packet must not be sent as list and the List flag must
500 Payload of the packet: See section 2.3.11 Private Message
504 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
506 This packet is used to agree about a key to be used to protect
507 the private messages between two clients. If this is not sent
508 the normal session key is used to protect the private messages
509 inside SILC network. Agreeing to use specific key to protect
510 private messages adds security, as no server between the two
511 clients will be able to decrypt the private message. However,
512 servers inside SILC network are considered to be trusted, thus
513 using normal session key to protect private messages does not
514 degree security. Whether to agree to use specific keys by
515 default or to use normal session keys by default, is
516 implementation specific issue. See more of this in [SILC1].
518 This packet must not be sent as list and the List flag must
521 Payload of the packet: See section 2.3.12 Private Message
525 11 SILC_PACKET_COMMAND
527 This packet is used to send commands from client to server.
528 Server may send this packet to other servers as well. All
529 commands are listed in their own section SILC Command Types
530 in [SILC1]. The contents of this packet is command specific.
531 This packet may be sent to entity that is indirectly connected
534 This packet must not be sent as list and the List flag must
537 Payload of the packet: See section 2.3.13 Command Payload
540 12 SILC_PACKET_COMMAND_REPLY
542 This packet is send as reply to the SILC_PACKET_COMMAND packet.
543 The contents of this packet is command specific. This packet
544 maybe sent to entity that is indirectly connected to the sender.
546 This packet must not be sent as list and the List flag must
549 Payload of the packet: See section 2.3.14 Command Reply
550 Payload and section 2.3.13 Command
554 13 SILC_PACKET_KEY_EXCHANGE
556 This packet is used to start SILC Key Exchange Protocol,
557 described in detail in [SILC3].
559 This packet must not be sent as list and the List flag must
562 Payload of the packet: Payload of this packet is described
563 in the section SILC Key Exchange
564 Protocol and its sub sections in
568 14 SILC_PACKET_KEY_EXCHANGE_1
570 This packet is used as part of the SILC Key Exchange Protocol.
572 This packet must not be sent as list and the List flag must
575 Payload of the packet: Payload of this packet is described
576 in the section SILC Key Exchange
577 Protocol and its sub sections in
581 15 SILC_PACKET_KEY_EXCHANGE_2
583 This packet is used as part of the SILC Key Exchange Protocol.
585 This packet must not be sent as list and the List flag must
588 Payload of the packet: Payload of this packet is described
589 in the section SILC Key Exchange
590 Protocol and its sub sections in
594 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
596 This packet is used to request the authentication method to
597 be used in the SILC Connection Authentication Protocol. If
598 initiator of the protocol does not know the mandatory
599 authentication method this packet may be used to determine it.
601 The party receiving this payload must respond with the same
602 packet including the mandatory authentication method.
604 This packet must not be sent as list and the List flag must
607 Payload of the packet: See section 2.3.15 Connection Auth
611 17 SILC_PACKET_CONNECTION_AUTH
613 This packet is used to start and perform the SILC Connection
614 Authentication Protocol. This protocol is used to authenticate
615 the connecting party. The protocol is described in detail in
618 This packet must not be sent as list and the List flag must
621 Payload of the packet: Payload of this packet is described
622 in the section SILC Authentication
623 Protocol and it sub sections in [SILC].
626 18 SILC_PACKET_NEW_ID
628 This packet is used to distribute new ID's from server to
629 router and from router to all routers in the SILC network.
630 This is used when for example new client is registered to
631 SILC network. The newly created ID's of these operations are
632 distributed by this packet. Only server may send this packet,
633 however, client must be able to receive this packet.
635 Payload of the packet: See section 2.3.16 New ID Payload
638 19 SILC_PACKET_NEW_CLIENT
640 This packet is used by client to register itself to the
641 SILC network. This is sent after key exchange and
642 authentication protocols has been completed. Client sends
643 various information about itself in this packet.
645 This packet must not be sent as list and the List flag must
648 Payload of the packet: See section 2.3.17 New Client Payload
651 20 SILC_PACKET_NEW_SERVER
653 This packet is used by server to register itself to the
654 SILC network. This is sent after key exchange and
655 authentication protocols has been completed. Server sends
656 this to the router it connected to, or, if router was
657 connecting, to the connected router. Server sends
658 its Server ID and other information in this packet.
659 Client must not send or receive this packet.
661 This packet must not be sent as list and the List flag must
664 Payload of the packet: See section 2.3.18 New Server Payload
667 21 SILC_PACKET_NEW_CHANNEL
669 This packet is used to notify routers about newly created
670 channel. Channels are always created by the router and it must
671 notify other routers about the created channel. Router sends
672 this packet to its primary route. Client must not send this
673 packet. This packet maybe sent to entity that is indirectly
674 connected to the sender.
676 Payload of the packet: See section 2.3.19 New Channel Payload
681 This packet is used to indicate that re-key must be performed
682 for session keys. See section Session Key Regeneration in
683 [SILC1] for more information. This packet does not have
686 This packet must not be sent as list and the List flag must
690 23 SILC_PACKET_REKEY_DONE
692 This packet is used to indicate that re-key is performed and
693 new keys must be used hereafter. This is sent only if re-key
694 was done without PFS option. If PFS is set, this is not sent
695 as SILC Key Exchange protocol is executed. This packet does
698 This packet must not be sent as list and the List flag must
702 24 SILC_PACKET_HEARTBEAT
704 This packet is used by clients, servers and routers to keep the
705 connection alive. It is recommended that all servers implement
706 keepalive actions and perform it to both direction in a link.
707 This packet does not have a payload.
709 This packet must not be sent as list and the List flag must
713 25 SILC_PACKET_KEY_AGREEMENT
715 This packet is used by clients to request key negotiation
716 between another client in the SILC network. If the negotiation
717 is started it is performed using the SKE protocol. The result of
718 the negotiation, the secret key material, can be used for
719 example as private message key. The server and router must not
722 Payload of the packet: See section 2.3.20 Key Agreement Payload
725 26 SILC_PACKET_CELL_ROUTERS
727 This packet is used by primary router in the cell to notify its
728 primary router what other routers (backup routers) exist in the
729 cell. In case of failure of the primary router in the cell the
730 first router in the list will act as primary router of the cell.
731 This packet may be sent at anytime after connection has been
732 registered to the primary router. The client must not send this
735 Payload of the packet: See section 2.3.21 Cell Routers Payload
740 Currently undefined commands.
745 These packet types are reserved for private use and they will not
746 be defined by this document.
751 This type is reserved for future extensions and currently it
757 2.3.1 SILC Packet Payloads
759 All payloads resides in the main data area of the SILC packet. However
760 all payloads must be at the start of the data area after the default
761 SILC packet header and padding. All fields in the packet payload are
762 always encrypted, as, they reside in the data area of the packet which
765 Payloads described in this section are common payloads that must be
766 accepted anytime during SILC session. Most of the payloads may only
767 be sent with specific packet type which is defined in the description
770 There are a lot of other payloads in the SILC as well. However, they
771 are not common in the sense that they could be sent at any time.
772 These payloads are not described in this section. These are payloads
773 such as SILC Key Exchange payloads and so on. These are described
774 in [SILC1] and [SILC3].
778 2.3.2 Generic payloads
780 This section describes generic payloads that are not associated to any
781 specific packet type. They can be used for example inside some other
788 This payload can be used to send an ID. ID's are variable length thus
789 this payload provides a way to send variable length ID's.
791 The following diagram represents the ID Payload.
796 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
797 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
798 | ID Type | ID Length |
799 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
803 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
811 o ID Type (2 bytes) - Indicates the type of the ID. See
812 section 2.4 SILC ID Types for list of defined ID types.
814 o ID Length (2 bytes) - Length of the ID Data area not
815 including the length of any other fields in the payload.
817 o ID Data (variable length) - The actual ID data.
822 2.3.2.2 Argument Payload
824 Argument Payload is used to set arguments for any packet payload that
825 needs and supports arguments, such as commands. Number of arguments
826 associated with a packet must be indicated by the packet payload who
827 needs the arguments. Argument Payloads must always reside right after
828 the packet payload needing the arguments. Incorrect amount of argument
829 payloads must cause rejection of the packet. The following diagram represents
830 the Argument Payload.
832 The following diagram represents the Argument Payload.
837 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
838 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
839 | Payload Length | Argument Type | |
840 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
844 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
848 Figure 4: Argument Payload
852 o Payload Length (2 bytes) - Length of the argument payload data
853 area not including the length of any other fields in the
856 o Argument Type (1 byte) - Indicates the type of the argument.
857 Every argument may have a specific type that must be defined
858 by the packet payload needing the argument. For example
859 every command specify a number for each argument that maybe
860 associated with the command. By using this number the receiver
861 of the packet knows what type of argument this is. If there is
862 no specific argument type this field is set to zero (0).
864 o Argument Data (variable length) - Argument data.
869 2.3.2.3 Channel Payload
871 Generic Channel Payload may be used information about channel, its name,
872 the Channel ID and a mode.
874 The following diagram represents the Channel Payload Payload.
880 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
881 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
882 | Channel Name Length | |
883 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
888 | Channel ID Length | |
889 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
893 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
895 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
899 Figure 5: New Channel Payload
903 o Channel Name Length (2 bytes) - Length of the channel name
906 o Channel Name (variable length) - The name of the channel.
908 o Channel ID Length (2 bytes) - Length of the Channel ID field.
910 o Channel ID (variable length) - The Channel ID.
912 o Mode Mask (4 bytes) - A mode. This can be the mode of the
913 channel but it can also be the mode of the client on the
914 channel. The contents of this field is dependent of the
915 usage of this payload. The usage is defined separately
916 when this payload is used. This is a 32 bit MSB first value.
921 2.3.2.4 Public Key Payload
923 Generic Public Key Payload may be used to send different types of
924 public keys and certificates.
926 The following diagram represents the Channel Payload Payload.
932 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
933 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
934 | Public Key Length | Public Key Type |
935 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
937 ~ Public Key of the party (or certificate) ~
939 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
943 Figure 6: Public Key Payload
947 o Public Key Length (2 bytes) - The length of the Public Key
948 (or certificate) field, not including any other field.
950 o Public Key Type (2 bytes) - The public key (or certificate)
951 type. This field indicates the type of the public key in
952 the packet. See the [SILC3] for defined public key types.
954 o Public Key (or certicicate) (variable length) - The
955 public key or certificate.
960 2.3.3 Disconnect Payload
962 Disconnect payload is sent upon disconnection. The payload is simple;
963 reason of disconnection is sent to the disconnected party.
965 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
966 must not be sent in any other packet type. The following diagram represents
967 the Disconnect Payload.
978 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
979 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
981 ~ Disconnect Message ~
983 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
987 Figure 7: Disconnect Payload
993 o Disconnect Message (variable length) - Human readable
994 reason of the disconnection.
999 2.3.4 Success Payload
1001 Success payload is sent when some protocol execution is successfully
1002 completed. The payload is simple; indication of the success is sent.
1003 This maybe any data, including binary or human readable data.
1008 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
1009 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1011 ~ Success Indication ~
1013 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1017 Figure 8: Success Payload
1021 o Success Indication (variable length) - Indication of
1022 the success. This maybe for example some flag that
1023 indicates the protocol and the success status or human
1024 readable success message. The true length of this
1025 payload is available by calculating it from the SILC
1031 2.3.5 Failure Payload
1033 This is opposite of Success Payload. Indication of failure of
1034 some protocol is sent in the payload.
1040 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
1041 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1043 ~ Failure Indication ~
1045 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1049 Figure 9: Failure Payload
1053 o Failure Indication (variable length) - Indication of
1054 the failure. This maybe for example some flag that
1055 indicates the protocol and the failure status or human
1056 readable failure message. The true length of this
1057 payload is available by calculating it from the SILC
1063 2.3.6 Reject Payload
1065 This payload is sent when some protocol is rejected to be executed.
1066 Other operations may send this as well that was rejected. The
1067 indication of the rejection is sent in the payload. The indication
1068 may be binary or human readable data.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1077 ~ Reject Indication ~
1079 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1083 Figure 10: Reject Payload
1087 o Reject Indication (variable length) - Indication of
1088 the rejection. This maybe for example some flag that
1089 indicates the protocol and the rejection status or human
1090 readable rejection message. The true length of this
1091 payload is available by calculating it from the SILC
1100 2.3.7 Notify Payload
1102 Notify payload is used to send notify messages. The payload is usually
1103 sent from server to client, however, server may send it to another
1104 server as well. This payload may also be sent to a channel. Client must
1105 not send this payload. The receiver of this payload may totally ignore the
1106 contents of the payload, however, notify message should be audited.
1108 The payload may only be sent with SILC_PACKET_NOTIFY packet. It must
1109 not be sent in any other packet type. The following diagram represents the
1115 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
1116 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1117 | Notify Type | Payload Length |
1118 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1124 Figure 11: Notify Payload
1128 o Notify Type (2 bytes) - Indicates the type of the notify
1131 o Payload Length (2 bytes) - Length of the entire Notify Payload
1132 including any associated Argument Payloads.
1134 o Argument Nums (2 bytes) - Indicates the number of Argument
1135 Payloads associated to this payload. Notify types may define
1136 arguments to be send along the notify message.
1139 The following list of currently defined notify types. The format for notify
1140 arguments is same as in SILC commands described in [SILC1]. Also, all
1141 ID's sent in arguments are sent inside ID Payload.
1144 0 SILC_NOTIFY_TYPE_NONE
1146 If no specific notify type apply for the notify message this type
1150 Arguments: (1) <message>
1152 The <message> is implementation specific free text string. Receiver
1153 may ignore this message.
1156 1 SILC_NOTIFY_TYPE_INVITE
1158 Sent when an client is invited to a channel. This is also sent
1159 when the invite list of the channel is changed. This notify type
1160 is sent between routers and if an client was invited to the
1161 client as well. In this case the packet is destined to the client.
1164 Arguments: (1) <Channel ID> (2) <channel name>
1165 (3) [<sender Client ID>] (4) [<adding client>]
1166 (5) [<removing client>]
1168 The <Channel ID> is the channel. The <channel name> is the name
1169 of the channel and is provided because the client which receives
1170 this notify packet may not have a way to resolve the name of the
1171 channel from the <Channel ID>. The <sender Client ID> is the
1172 Client ID who invited the client to the channel. The <adding client>
1173 and the <removing client> indicates the added or removed client
1174 from the channel's invite list. The format of the <adding client
1175 and the <removing client> is defined in the [SILC1] with
1176 SILC_COMMAND_INVITE command.
1178 The <adding client> and <removing client> is never sent when the
1179 packet is destined to a client.
1182 2 SILC_NOTIFY_TYPE_JOIN
1184 Sent when client has joined to a channel. The server must distribute
1185 this type only to the local clients on the channel and then send
1186 it to its primary router. The router or server receiving the packet
1187 distributes this type to the local clients on the channel and
1188 broadcast it to the network.
1191 Arguments: (1) [<Client ID>] (2) <Channel ID>
1193 The <Client ID> is the client that joined to the channel indicated
1194 by the <Channel ID>.
1197 3 SILC_NOTIFY_TYPE_LEAVE
1199 Sent when client has left a channel. The server must distribute
1200 this type only to the local clients on the channel and then send
1201 it to its primary router. The router or server receiving the packet
1202 distributes this type to the local clients on the channel and
1203 broadcast it to the network.
1206 Arguments: (1) <Client ID>
1208 The <Client ID> is the client who left the channel.
1211 4 SILC_NOTIFY_TYPE_SIGNOFF
1213 Sent when client signoffs from SILC network. The server must
1214 distribute this type only to the local clients on the channel and
1215 then send it to its primary router. The router or server receiving
1216 the packet distributes this type to the local clients on the channel
1217 and broadcast it to the network.
1220 Arguments: (1) <Client ID> (2) <message>
1222 The <Client ID> is the client who left SILC network. The <message>
1223 is free text string indicating the reason of signoff.
1226 5 SILC_NOTIFY_TYPE_TOPIC_SET
1228 Sent when topic is set/changed on a channel. This type must be sent
1229 only to the clients who is joined on the channel whose topic was
1233 Arguments: (1) <Client ID> (2) <topic>
1235 The <Client ID> is the client who set or changed the <topic>.
1238 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1240 Sent when client changes nick on a channel. The server must
1241 distribute this type only to the local clients on the channel and
1242 then send it to its primary router. The router or server receiving
1243 the packet distributes this type to the local clients on the channel
1244 and broadcast it to the network.
1247 Arguments: (1) <Old Client ID> (2) <New Client ID>
1249 The <Old Client ID> is the old ID of the client who changed the
1250 nickname. The <New Client ID> is the new ID generated by the change
1254 7 SILC_NOTIFY_TYPE_CMODE_CHANGE
1256 Sent when channel mode has changed. This type must be sent only to
1257 the clients who is joined on the channel whose mode was changed.
1260 Arguments: (1) <ID Payload> (2) <mode mask>
1261 (3) [<cipher>] (4) <[hmac>]
1263 The <ID Payload> is the ID (usually Client ID but it can be Server ID
1264 as well when the router is enforcing channel mode change) of the
1265 entity which changed the mode. The <mode mask> is the new mode mask
1266 of the channel. The client can safely ignore the <cipher> argument
1267 since the SILC_PACKET_CHANNEL_KEY packet will force the new channel
1268 key change anyway. The <hmac> argument is important since the client
1269 is responsible of setting the new HMAC and the hmac key into use.
1272 8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
1274 Sent when user mode on channel has changed. This type must be sent
1275 only to the clients who is joined on the channel where the target
1279 Arguments: (1) <Client ID> (2) <mode mask>
1280 (3) <Target Client ID>
1282 The <Client ID> is the client who changed the mode. The <mode mask>
1283 is the new mode mask of the channel. The <Target Client ID> is the
1284 client which mode was changed.
1287 9 SILC_NOTIFY_TYPE_MOTD
1289 Sent when Message of the Day (motd) is sent to client.
1292 Arguments: (1) <motd>
1294 The <motd> is the Message of the Day.
1297 10 SILC_NOTIFY_TYPE_CHANNEL_CHANGE
1299 Sent when channel's ID has changed for a reason or another. This
1300 is sent by normal server to the client. This can also be sent by
1301 router to other server to force the Channel ID change. The Channel
1302 ID must be changed to use the new one. When sent to clients, this
1303 type must be sent only to the clients who is joined on the channel.
1306 Arguments: (1) <Old Channel ID> (2) <New Channel ID>
1308 The <Old Channel ID> is the channel's old ID and the <New Channel ID>
1309 is the new one that must replace the old one.
1312 11 SILC_NOTIFY_TYPE_SERVER_SIGNOFF
1314 Sent when server quits SILC network. Those clients from this server
1315 that are on channels must be removed from the channel.
1318 Arguments: (1) <Server ID> (n) [<Client ID> [...]
1320 The <Server ID> is the server's ID. The rest of the arguments are
1321 the Client ID's of the client's who are coming from this server and
1322 are thus quitting the SILC network also. If the maximum number of
1323 arguments are reached another SILC_NOTIFY_TYPE_SERVER_SIGNOFF notify
1324 packet must be sent. When this notify packet is sent between routers
1325 the Client ID's may be omitted.
1328 12 SILC_NOTIFY_TYPE_KICKED
1330 Sent when a client has been kicked from a channel. This is sent
1331 also to the client who was kicked from the channel. The client
1332 who was kicked from the channel must be removed from the channel.
1333 This notify type is always destined to the channel. The router or
1334 server receiving the packet distributes this type to the local
1335 clients on the channel and broadcast it to the network.
1338 Arguments: (1) <Client ID> (2) [<comment>]
1340 The <Client ID> is the client who was kicked from the channel.
1341 The kicker may have set the <comment> to indicate the reason for
1345 13 SILC_NOTIFY_TYPE_KILLED
1347 Sent when a client has been killed from the network. This is sent
1348 also to the client who was killed from the network. The client
1349 who was killed from the network must be removed from the network.
1350 This notify type is destined directly to the client who was killed
1351 and to channel if the client is on any channel. The router or
1352 server receiving the packet distributes this type to the local
1353 clients on the channel and broadcast it to the network.
1356 Arguments: (1) <Client ID> (2) [<comment>]
1358 The <Client ID> is the client who was killed from the network.
1359 The killer may have set the <comment> to indicate the reason for
1363 14 SILC_NOTIFY_TYPE_UMODE_CHANGE
1365 Sent when user's mode in the SILC changes. This type is sent only
1366 between routers as broadcast packet.
1369 Arguments: (1) <Client ID> (2) <mode mask>
1371 The <Client ID> is the client which mode was changed. The <mode mask>
1372 is the new mode mask.
1375 15 SILC_NOTIFY_TYPE_BAN
1377 Sent when the ban list of the channel is changed. This type is sent
1378 only between routers as broadcast packet.
1381 Arguments: (1) <Channel ID> (2) [<adding client>]
1382 (3) [<removing client>]
1384 The <Channel ID> is the channel which ban list was changed. The
1385 <adding client> is used to indicate the a ban was added and the
1386 <removing client> is used to indicate that a ban was removed from
1387 the ban list. The format of the <adding client> and the
1388 <removing client> is defined in the [SILC1] with SILC_COMMAND_BAN
1393 Notify types starting from 16384 are reserved for private notify
1400 Error payload is sent upon error. Error may occur in various
1401 conditions when server sends this packet. Client may not send this
1402 payload but must be able to accept it. However, client may
1403 totally ignore the contents of the packet as server is going to
1404 take action on the error anyway. However, it is recommended
1405 that the client takes error packet seriously.
1411 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
1412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1416 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1420 Figure 12: Error Payload
1424 o Error Message (variable length) - Human readable error
1430 2.3.9 Channel Message Payload
1432 Channel messages are the most common messages sent in the SILC.
1433 Channel Message Payload is used to send message to channels. These
1434 messages can only be sent if client has joined to some channel.
1435 Even though this packet is the most common in SILC it is still
1436 special packet. Some special handling on sending and reception
1437 of channel message is required.
1439 Padding must be applied into this payload since the payload is
1440 encrypted separately from other parts of the packet with the
1441 channel specific key. Hence the requirement of the padding.
1442 The padding should be random data. The packet must be made
1443 multiple by eight (8) or by the block size of the cipher, which
1446 The SILC header in this packet is encrypted with the session key
1447 of the next receiver of the packet. Nothing else is encrypted
1448 with that key. Thus, the actual packet and padding to be
1449 encrypted with the session key is SILC Header plus padding to it
1450 to make it multiple by eight (8) or multiple by the block size
1451 of the cipher, which ever is larger.
1453 Receiver of the the channel message packet is able to determine
1454 the channel the message is destined to by checking the destination
1455 ID from the SILC Packet header which tells the destination channel.
1456 The original sender of the packet is also determined by checking
1457 the source ID from the header which tells the client who sent
1460 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1461 It must not be sent in any other packet type. The following diagram
1462 represents the Channel Message Payload.
1464 (*) indicates that the field is not encrypted.
1470 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
1471 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1472 | Flags | Message Length |
1473 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1477 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1478 | Padding Length | |
1479 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1483 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1487 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1489 ~ Initial Vector * ~
1491 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1495 Figure 13: Channel Message Payload
1499 o Flags (2 bytes) - Includes the flags of the channel
1500 messages. The flags can indicate a reason or purpose
1501 for the channel message. Note, that the Private Message
1502 Payload use these same flags for the same purpose. The
1503 following flags are defined:
1505 0x0000 SILC_MESSAGE_FLAG_NONE
1507 No specific flags set.
1509 0x0001 SILC_MESSAGE_FLAG_AUTREPLY
1511 This message is an automatic reply to a earlier
1514 0x0002 SILC_MESSAGE_FLAG_NOREPLY
1516 There should not be reply messages to this
1519 0x0004 SILC_MESSAGE_FLAG_ACTION
1521 The sender is performing an action and the message
1522 is the indication of the action.
1524 0x0008 SILC_MESSAGE_FLAG_NOTICE
1526 The message is for example and informational notice
1529 0x0010 SILC_MESSAGE_FLAG_REQUEST
1531 This is a generic request flag to send request
1534 0x0020 - 0x0200 RESERVED
1536 Reserved for future flags
1538 0x0400 - 0x8000 PRIVATE RANGE
1540 Private range for free use.
1542 o Message Length (2 bytes) - Indicates the length of the
1543 the Message Data field in the payload, not including any
1546 o Message Data (variable length) - The actual message to
1549 o Padding Length (2 bytes) - Indicates the length of the
1550 Padding field in the payload, not including any other
1553 o Padding (variable length) - The padding that must be
1554 applied because this payload is encrypted separately from
1555 other parts of the packet.
1557 o MAC (variable legnth) - The MAC computed from the
1558 Message Length, Message Data, Padding Length and Padding
1559 fields. This protects the integrity of the plaintext
1560 channel message. The receiver can verify from the MAC
1561 whether the message decrypted correctly. Also, if more than
1562 one private key has been set for the channel, the receiver
1563 can verify which of the keys decrypted the message
1564 correctly. Note that, this field is encrypted and must
1565 be added to the padding calculation.
1567 o Initial Vector (variable length) - The initial vector
1568 that has been used in packet encryption. It needs to be
1569 used in the packet decryption as well. What this field
1570 includes is implementation issue. However, it is
1571 recommended that it would be random data or, perhaps,
1572 a timestamp. It is not recommended to use zero (0) as
1573 initial vector. This field is not encrypted. This field
1574 is not included into the padding calculation. Length
1575 of this field equals the cipher's block size. This field
1576 is, however, authenticated.
1581 2.3.10 Channel Key Payload
1583 All traffic in channels are protected by channel specific keys.
1584 Channel Key Payload is used to distribute channel keys to all
1585 clients on the particular channel. Channel keys are sent when
1586 the channel is created, when new user joins to the channel and
1587 whenever a user has left a channel. Server creates the new
1588 channel key and distributes it to the clients by encrypting this
1589 payload with the session key shared between the server and
1590 the client. After that, client starts using the key received
1591 in this payload to protect the traffic on the channel.
1593 The client who is joining to the channel receives its key in the
1594 SILC_COMMAND_JOIN command reply message thus it is not necessary to
1595 send this payload to the entity who sent the SILC_COMMAND_JOIN command.
1597 Channel keys are cell specific thus every router in cell have
1598 to create a channel key and distribute it if any client in the
1599 cell has joined to a channel. Channel traffic between cell's
1600 are not encrypted using channel keys, they are encrypted using
1601 normal session keys between two routers. Inside a cell, all
1602 channel traffic is encrypted with the specified channel key.
1603 Channel key should expire periodically, say, in one hour, in
1604 which case new channel key is created and distributed.
1606 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1607 It must not be sent in any other packet type. The following diagram
1608 represents the Channel Key Payload.
1625 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
1626 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1627 | Channel ID Length | |
1628 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1632 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1633 | Cipher Name Length | |
1634 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1638 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1639 | Channel Key Length | |
1640 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1644 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1648 Figure 14: Channel Key Payload
1653 o Channel ID Length (2 bytes) - Indicates the length of the
1654 Channel ID field in the payload, not including any other
1657 o Channel ID (variable length) - The Channel ID of the
1658 channel this key is meant for.
1660 o Cipher Name Length (2 bytes) - Indicates the length of the
1661 Cipher name field in the payload, not including any other
1664 o Cipher Name (variable length) - Name of the cipher used
1665 in the protection of channel traffic. This name is
1666 initially decided by the creator of the channel but it
1667 may change during the life time of the channel as well.
1669 o Channel Key Length (2 bytes) - Indicates the length of the
1670 Channel Key field in the payload, not including any other
1673 o Channel Key (variable length) - The actual channel key
1674 material. This key is used as such as key material for
1675 encryption function.
1680 2.3.11 Private Message Payload
1682 Private Message Payload is used to send private message between
1683 two clients (or users for that matter). The messages are sent only
1684 to the specified user and no other user inside SILC network is
1685 able to see the message. The message is protected by the session
1686 key established by the SILC Key Exchange Protocol. However,
1687 it is also possible to agree to use specific keys to protect
1688 just the private messages. See section 2.3.11 Private Message
1689 Key Payload for detailed description of how to agree to use
1692 If normal session key is used to protect the message, every
1693 server between the sender client and the receiving client needs
1694 to decrypt the packet and always re-encrypt it with the session
1695 key of the next receiver of the packet. See section Client
1696 To Client in [SILC1].
1698 When specific key is used to protect the message, servers between
1699 the sender and the receiver needs not to decrypt/re-encrypt the
1700 packet. Section 4.8.2 Client To Client in [SILC1] gives example of
1701 this scheme as well.
1703 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1704 packet. It must not be sent in any other packet type. The following
1705 diagram represents the Private Message Payload.
1711 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
1712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1713 | Flags | Nickname Length |
1714 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1718 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1719 | Message Data Length | |
1720 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1724 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1728 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1732 Figure 15: Private Message Payload
1736 o Flags (2 bytes) - This field includes the flags of the
1737 private message. They can indicate a different reason or
1738 purpose for the private message. See the section 2.3.9
1739 Channel Message Payload for defined flags. Note, that
1740 the Channel Message Payload use the same flags for the
1743 o Nickname Length (2 bytes) - Indicates the length of the
1744 Nickname field, not including any other field.
1746 o Nickname (variable length) - Nickname of the sender of the
1747 private message. This should not be trusted as a definite
1748 sender of the private message. The SILC Packet Header in
1749 the packet indicates the true sender of the packet and
1750 client should verify that the nickname sent here belongs
1751 to the Client ID in the SILC Packet Header. This nickname
1752 is merely provided to be displayed by the client.
1754 o Message Data Length (2 bytes) - Indicates the length of the
1755 Message Data field, not includes any other field.
1757 o Message Data (variable length) - The actual message to
1758 the client. Rest of the packet is reserved for the message
1761 o Padding (variable length) - This field is present only
1762 when the private message payload is encrypted with private
1763 message key. In this case the padding is applied to make
1764 the packet multiple by eight (8), or by the block size of
1765 the cipher, which ever is larger. When encrypted with
1766 normal session keys, this field must not be included.
1771 2.3.12 Private Message Key Payload
1773 This payload is used to send key from client to another client that
1774 is going to be used to protect the private messages between these
1775 two clients. If this payload is not sent normal session key
1776 established by the SILC Key Exchange Protocol is used to protect
1777 the private messages.
1779 This payload may only be sent by client to another client. Server
1780 must not send this payload at any time. After sending this payload
1781 the sender of private messages must set the Private Message Key
1782 flag into SILC Packet Header.
1784 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1785 packet. It must not be sent in any other packet type. The following
1786 diagram represents the Private Message Key Payload.
1792 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
1793 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1794 | Private Message Key Length | |
1795 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1797 ~ Private Message Key ~
1799 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1800 | Cipher Name Length | |
1801 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1805 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1809 Figure 16: Private Message Key Payload
1815 o Private Message Key Length (2 bytes) - Indicates the length
1816 of the Private Message Key field in the payload, not including
1819 o Private Message Key (variable length) - The actual private
1820 message key material.
1822 o Cipher Name Length (2 bytes) - Indicates the length of the
1823 Cipher Name field in the payload, not including any other
1826 o Cipher Name (variable length) - Name of the cipher to use
1827 in the private message encryption. If this field does not
1828 exist then the default cipher of the SILC protocol is used.
1829 See the [SILC1] for defined ciphers.
1835 2.3.13 Command Payload
1837 Command Payload is used to send SILC commands from client to server.
1838 Also server may send commands to other servers. The following diagram
1839 represents the Command Payload.
1845 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
1846 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1847 | Payload Length | SILC Command | Arguments Num |
1848 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1849 | Command Identifier |
1850 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1854 Figure 17: Command Payload
1858 o Payload Length (2 bytes) - Length of the entire command
1859 payload including any command argument payloads associated
1862 o SILC Command (1 byte) - Indicates the SILC command. This must
1863 be set to non-zero value. If zero (0) value is found in this
1864 field the packet must be discarded.
1866 o Arguments Num (1 byte) - Indicates the number of arguments
1867 associated with the command. If there are no arguments this
1868 field is set to zero (0). The arguments must follow the
1869 command payload. See section 2.3.2.2 for definition of the
1872 o Command Identifier (2 bytes) - Identifies this command at the
1873 sender's end. The entity who replies to this command must
1874 set the value found from this field into the Command Payload
1875 used to send the reply to the sender. This way the sender
1876 can identify which command reply belongs to which originally
1877 sent command. What this field includes is implementation
1878 issue but it is recommended that wrapping counter value is
1879 used in the field. Value zero (0) in this field means that
1880 no specific value is set.
1883 See [SILC1] for detailed description of different SILC commands,
1884 their arguments and their reply messages.
1888 2.3.14 Command Reply Payload
1890 Command Reply Payload is used to send replies to the commands. The
1891 Command Reply Payload is identical to the Command Payload thus see the
1892 upper sections for Command Payload and for Command Argument Payload
1893 specifications. Command Reply message uses the Command Argument Payload
1896 The entity who sends the reply packet must set the Command Unifier
1897 field in the reply packet's Command Payload to the value it received
1898 in the original command packet.
1900 See SILC Commands in [SILC1] for detailed description of different
1901 SILC commands, their arguments and their reply messages.
1905 2.3.15 Connection Auth Request Payload
1907 Client may send this payload to server to request the authentication
1908 method that must be used in authentication protocol. If client knows
1909 this information beforehand this payload is not necessary to be sent.
1910 Server performing authentication with another server may also send
1911 this payload to request the authentication method. If the connecting
1912 server already knows this information this payload is not necessary
1915 Server receiving this request must reply with same payload sending
1916 the mandatory authentication method. Algorithms that may be required
1917 to be used by the authentication method are the ones already
1918 established by the SILC Key Exchange protocol. See section Key
1919 Exchange Start Payload in [SILC3] for detailed information.
1921 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1922 packet. It must not be sent in any other packet type. The following
1923 diagram represents the Connection Auth Request Payload.
1929 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
1930 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1931 | Connection Type | Authentication Method |
1932 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1936 Figure 18: Connection Auth Request Payload
1940 o Connection Type (2 bytes) - Indicates the type of the ID.
1941 The following connection types are defined:
1947 If any other type is found in this field the packet must be
1948 discarded and the authentication must be failed.
1950 o Authentication Method (2 bytes) - Indicates the authentication
1951 method to be used in the authentication protocol. The following
1952 authentication methods are defined:
1957 1 password (mandatory)
1958 2 public key (mandatory)
1960 If any other type is found in this field the packet must be
1961 discarded and the authentication must be failed. If this
1962 payload is sent as request to receive the mandatory
1963 authentication method this field must be set to zero (0),
1964 indicating that receiver should send the mandatory
1965 authentication method. The receiver sending this payload
1966 to the requesting party, may also set this field to zero (0)
1967 to indicate that authentication is not required. In this
1968 case authentication protocol still must be started but
1969 server is most likely to respond with SILC_PACKET_SUCCESS
1975 2.3.16 New ID Payload
1977 New ID Payload is a multipurpose payload. It is used to send newly
1978 created ID's from clients and servers. When client connects to server
1979 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
1980 packet, server replies with this packet by sending the created ID for
1981 the client. Server always creates the ID for the client.
1983 This payload is also used when server tells its router that new client
1984 has registered to the SILC network. In this case the server sends
1985 the Client ID of the client to the router. Similary when router
1986 distributes information to other routers about the client in the SILC
1987 network this payload is used.
1989 Also, when server connects to router, router uses this payload to inform
1990 other routers about new server in the SILC network. However, every
1991 server (or router) creates their own ID's thus the ID distributed by
1992 this payload is not created by the distributor in this case. Servers
1993 create their own ID's. Server registers itself to the network by sending
1994 SILC_PACKET_NEW_SERVER to the router it connected to. The case is same
1995 when router connects to another router.
1997 However, this payload is not and must not be used to send information
1998 about new channels. New channels are always distributed by sending the
1999 dedicated SILC_PACKET_NEW_CHANNEL packet.
2001 Hence, this payload is very important and used every time when some
2002 new entity is registered to the SILC network. Client never sends this
2003 payload. Both client and server (and router) may receive this payload.
2005 The packet uses generic ID Payload as New ID Payload. See section
2006 2.3.2.1 for generic ID Payload.
2010 2.3.17 New Client Payload
2012 When client is connected to the server, keys has been exchanged and
2013 connection has been authenticated client must register itself to the
2014 server. Clients first packet after key exchange and authentication
2015 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
2016 the relevant information about the connected user. Server creates a new
2017 client ID for the client when received this payload and sends it to the
2018 client in New ID Payload.
2020 This payload sends username and real name of the user on the remote host
2021 which is connected to the SILC server with SILC client. The server
2022 creates the client ID according the information sent in this payload.
2023 The nickname of the user becomes the username sent in this payload.
2024 However, client should call NICK command after sending this payload to
2025 set the real nickname of the user which is then used to create new
2028 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
2029 must not be sent in any other packet type. The following diagram
2030 represents the New Client Payload.
2037 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
2038 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2039 | Username Length | |
2040 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2044 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2045 | Real Name Length | |
2046 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2050 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2054 Figure 19: New Client Payload
2058 o Username Length (2 bytes) - Length of the username.
2060 o Username (variable length) - The username of the user on
2061 the host where connecting to the SILC server.
2063 o Real Name Length (2 bytes) - Length of the Real Name.
2065 o Real Name (variable length) - The real name of the user
2066 on the host where connecting to the SILC server.
2071 2.3.18 New Server Payload
2073 This payload is sent by server when it has completed successfully both
2074 key exchange and connection authentication protocols. The server
2075 uses this payload to register itself to the SILC network. The
2076 first packet after these key exchange and authentication protocols
2077 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
2078 of the server that it has created by itself. It also includes a
2079 name of the server that is associated to the Server ID.
2081 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
2082 must not be sent in any other packet type. The following diagram represents
2083 the New Server Payload.
2092 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
2093 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2094 | Server ID Length | |
2095 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2099 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2100 | Server Name Length | |
2101 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2105 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2109 Figure 20: New Server Payload
2113 o Server ID Length (2 bytes) - Length of the ID Data area not
2114 including the length of any other fields in the payload.
2116 o Server ID Data (variable length) - The actual Server ID
2119 o Server Name Length (2 bytes) - Length of the server name.
2121 o Server Name (variable length) - The server name.
2126 2.3.19 New Channel Payload
2128 Information about newly created channel is broadcasted to all routers
2129 in the SILC network by sending this packet payload. Channels are
2130 created by router of the cell. Server never creates channels unless
2131 it is a standalone server and it does not have router connection,
2132 in this case server acts as router. Normal server send JOIN command
2133 to the router (after it has received JOIN command from client) which
2134 then processes the command and creates the channel. Client never sends
2137 The packet uses generic Channel Payload as New Channel Payload. See
2138 section 2.3.2.3 for generic Channel Payload. The Mode Mask field in the
2139 Channel Payload is the mode of the channel.
2143 2.3.20 Key Agreement Payload
2145 This payload is used by clients to request key negotiation between
2146 another client in the SILC Network. The key agreement protocol used
2147 is the SKE protocol. The result of the protocol, the secret key
2148 material, can be used for example as private message key between the
2149 two clients. This significantly adds security as the key agreement
2150 is performed outside the SILC network. The server and router must not
2153 The sender may tell the receiver of this payload the hostname and the
2154 port where the SKE protocol is running in the sender's end. The
2155 receiver may then initiate the SKE negotiation with the sender. The
2156 sender may also optionally not to include the hostname and the port
2157 of its SKE protocol. In this case the receiver may reply to the
2158 request by sending the same payload filled with the receiver's hostname
2159 and the port where the SKE protocol is running. The sender may then
2160 initiate the SKE negotiation with the receiver.
2162 The payload may only be sent with SILC_PACKET_KEY_AGREEMENT packet.
2163 It must not be sent in any other packet type. The following diagram
2164 represents the Key Agreement Payload.
2170 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
2171 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2172 | Hostname Length | |
2173 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2177 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2179 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2183 Figure 21: Key Agreement Payload
2187 o Hostname Length (2 bytes) - Indicates the length of the Hostname
2190 o Hostname (variable length) - The hostname or IP address where
2191 the SKE protocol is running. The sender may fill this field
2192 when sending the payload. If the receiver sends this payload
2193 as reply to the request it must fill this field.
2195 o Port (4 bytes) - The port where the SKE protocol is bound.
2196 The sender may fill this field when sending the payload. If
2197 the receiver sends this payload as reply to the request it
2198 must fill this field. This is a 32 bit MSB first order value.
2202 After the key material has been received from the SKE protocol it is
2203 processed as the [SILC3] describes. If the key material is used as
2204 channel private key then the Sending Encryption Key, as defined in
2205 [SILC3] is used as the channel private key. Other key material must
2206 be discarded. The [SILC1] defines the way to use the key material if
2207 it is intended to be used as private message keys. Any other use for
2208 the key material is undefined.
2212 2.3.21 Cell Routers Payload
2214 Cell Routers payload is used by router to notify its primary router what
2215 other routers exist in the cell. The other routers are considered to be
2216 backup routers and one of them will come active only in the case of
2217 failure of the primary router. Normal server can send this packet if it
2218 is acting as backup router. Client must not send this packet. To send
2219 more than one backup router set the List flag and assemble the payloads
2222 The payload may only be sent with SILC_PACKET_CELL_ROUTERS packet. It
2223 must not be sent in any other packet type. The Following diagram
2224 represents the Cell Routers Payload.
2230 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
2231 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2232 | Hostname Length | |
2233 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2237 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2239 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2240 | Server ID Length | |
2241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2249 Figure 22: Cell Routers Payload
2253 o Hostname Length (2 bytes) - Indicates the length of the Hostname
2256 o Hostname (variable length) - The hostname or IP address of
2259 o Port (4 bytes) - The port of the backup router it currently uses.
2260 This is a 32 bit MSB first order value.
2262 o Server ID Length (2 bytes) - Indicates the length of the Server
2265 o Server ID (variable length) - Consists of the Server ID of the
2273 ID's are extensively used in the SILC network to associate different
2274 entities. The following ID's has been defined to be used in the SILC
2280 When ever specific ID cannot be used this is used.
2284 Server ID to associate servers. See the format of
2289 Client ID to associate clients. See the format of
2294 Channel ID to associate channels. See the format of
2300 2.5 Packet Encryption And Decryption
2302 SILC packets are encrypted almost entirely. Only small part of SILC
2303 header is not encrypted as described in section 5.2 SILC Packet Header.
2304 The SILC Packet header is the first part of a packet to be encrypted
2305 and it is always encrypted with the key of the next receiver of the
2306 packet. The data payload area of the packet is always entirely
2307 encrypted and it is usually encrypted with the next receiver's key.
2308 However, there are some special packet types and packet payloads
2309 that require special encryption process. These special cases are
2310 described in the next sections. First is described the normal packet
2315 2.5.1 Normal Packet Encryption And Decryption
2317 Normal SILC packets are encrypted with the session key of the next
2318 receiver of the packet. The entire SILC Packet header and the packet
2319 data payload is is also encrypted with the same key. Padding of the
2320 packet is also encrypted always with the session key, also in special
2321 cases. Computed MAC of the packet must not be encrypted.
2323 Decryption process in these cases are straightforward. The receiver
2324 of the packet must first decrypt the SILC Packet header, or some parts
2325 of it, usually first 16 bytes of it. Then the receiver checks the
2326 packet type from the decrypted part of the header and can determine
2327 how the rest of the packet must be decrypted. If the packet type is
2328 any of the special cases described in The following sections the packet
2329 decryption is special. If the packet type is not among those special
2330 packet types rest of the packet may be decrypted with the same key.
2332 Also, note that two bytes of the SILC Packet header are not encrypted
2333 thus it must be noticed in the decryption process by starting the
2334 decryption from the second byte of the header. This sets some rules
2335 to padding generation as well, see the section 2.7 Packet Padding
2338 With out a doubt, this sort of decryption processing causes some
2339 overhead to packet decryption, but never the less, is required.
2343 2.5.2 Channel Message Encryption And Decryption
2345 Channel Messages (Channel Message Payload) are always encrypted with
2346 the channel specific key. However, the SILC Packet header is not
2347 encrypted with that key. As in normal case, the header is encrypted
2348 with the key of the next receiver of the packet, who ever that might
2349 be. Note that in this case the encrypted data area is not touched
2350 at all; it must not be re-encrypted with the session key.
2352 Receiver of a channel message, who ever that is, is required to decrypt
2353 the SILC Packet header to be able to even recognize the packet to be as
2354 channel message. This is same procedure as for normal SILC packets.
2355 As the receiver founds the packet to be channel message, rest of the
2356 packet processing is special. Rest of the SILC Packet header is
2357 decrypted with the same session key along with the padding of the
2358 packet. After that the packet is protected with the channel specific
2359 key and thus can be decrypted only if the receiver is the client on
2360 the channel. See section 2.7 Packet Padding Generation for more
2361 information about padding on special packets.
2363 If the receiver of the channel message is router who is routing the
2364 message to another router then it must decrypt the Channel Message
2365 payload. Between routers (that is, between cells) channel messages
2366 are protected with session keys shared between the routers. This
2367 causes another special packet processing for channel messages. If
2368 the channel message is received from another router then the entire
2369 packet, including Channel Message payload, is encrypted with the
2370 session key shared between the routers. In this case the packet
2371 decryption process is as with normal SILC packets. Hence, if the
2372 router is sending channel message to another router the Channel
2373 Message payload must have been decrypted and must be re-encrypted
2374 with the session key shared between the another router. In this
2375 case the packet encryption is as with any normal SILC packet.
2377 It must be noted that this is only when the channel messages are sent
2378 from router to another router. In all other cases the channel
2379 message encryption and decryption is as described above. This
2380 different processing of channel messages with router to router
2381 connection is because channel keys are cell specific. All cells has
2382 their own channel keys thus the channel message traveling from one
2383 cell to another must be protected as it would be any normal SILC
2386 If the SILC_CMODE_PRIVKEY channel mode has been set for the channel
2387 then the router cannot decrypt the packet as it does not know the
2388 private key. In this case the entire packet is encrypted with the
2389 session key and sent to the router. The router receiving the packet
2390 must check the channel mode and decrypt the packet accordingly.
2394 2.5.3 Private Message Encryption And Decryption
2396 By default, private message in SILC are protected by session keys.
2397 In this case the private message encryption and decryption process is
2398 equivalent to normal packet encryption and decryption.
2400 However, private messages can be protected with private message key
2401 which causes the packet to be special packet. The procedure in this
2402 case is very much alike to channel packets. The actual private message
2403 is encrypted with the private message key and other parts of the
2404 packet is encrypted with the session key. See 2.7 Packet Padding
2405 Generation for more information about padding on special packets.
2407 The difference from channel message processing is that server or router
2408 en route never decrypts the actual private message, as it does not
2409 have the key to do that. Thus, when sending packets between router
2410 the processing is same as in any other case as well; the packet's header
2411 and padding is protected by the session key and the data area is not
2414 The true receiver of the private message, client, that is, is able
2415 to decrypt the private message as it shares the key with the sender
2420 2.6 Packet MAC Generation
2422 Data integrity of a packet is protected by including a message
2423 authentication code (MAC) at the end of the packet. The MAC is computed
2424 from shared secret MAC key, that is established by the SILC Key Exchange
2425 protocol, and from the original contents of the packet. The MAC is
2426 always computed before the packet is encrypted, although after it is
2427 compressed if compression is used.
2429 The MAC is computed from entire packet. Every bit of data in the packet,
2430 including SILC Packet Header is used in the MAC computing. This way
2431 the entire packet becomes authenticated.
2433 If the packet is special packet MAC is computed from the entire packet
2434 but part of the packet may be encrypted before the MAC is computed.
2435 This is case, for example, with channel messages where the message data
2436 is encrypted with key that server may not now. In this case the MAC
2437 has been computed from the encrypted data.
2439 See [SILC1] for defined and allowed MAC algorithms.
2443 2.7 Packet Padding Generation
2445 Padding is needed in the packet because the packet is encrypted. It
2446 must always be multiple by eight (8) or multiple by the size of the
2447 cipher's block size, which ever is larger. The padding is always
2450 For normal packets the padding is added after the SILC Packet Header
2451 and between the Data Payload area. The padding for normal packets
2452 are calculated as follows:
2455 padding length = 16 - ((packet length - 2) % 16)
2458 The 16 is the maximum padding allowed in SILC packet. Two (2) is
2459 subtracted from the true length of the packet because two (2) bytes
2460 is not encrypted in SILC Packet Header, see section 2.2 SILC Packet
2461 Header. Those two bytes that are not encrypted must not be calculated
2462 to the padding length.
2464 For special packets the padding calculation may be different as special
2465 packets may be encrypted differently. In these cases the encrypted
2466 data area must already be multiple by the block size thus in this case
2467 the padding is calculated only for SILC Packet Header, not for any
2468 other area of the packet. The same algorithm works in this case as
2469 well, except that the `packet length' is now the SILC Packet Header
2470 length. In this case, as well, two (2) is subtracted from the
2473 The padding must be random data, preferably, generated by
2474 cryptographically strong random number generator.
2478 2.8 Packet Compression
2480 SILC Packets may be compressed. In this case the data payload area
2481 is compressed and all other areas of the packet must remain as they
2482 are. After compression is performed for the data area, the length
2483 field of Packet Header must be set to the compressed length of the
2486 The compression must always be applied before encryption. When
2487 the packet is received and decrypted the data area must be decompressed.
2488 Note that the true sender of the packet must apply the compression and
2489 the true receiver of the packet must apply the decompression. Any
2490 server or router en route must not decompress the packet.
2497 The sender of the packet must assemble the SILC Packet Header with
2498 correct values. It must set the Source ID of the header as its own
2499 ID, unless it is forwarding the packet. It must also set the Destination
2500 ID of the header to the true destination. If the destination is client
2501 it will be Client ID, if it is server it will be Server ID and if it is
2502 channel it will be Channel ID.
2504 If the sender wants to compress the packet it must apply the
2505 compression now. Sender must also compute the padding as described
2506 in above sections. Then sender must compute the MAC of the packet.
2508 Then sender encrypts the packet as has been described in above
2509 sections according whether the packet is normal packet or special
2510 packet. The computed MAC must not be encrypted.
2514 2.10 Packet Reception
2516 On packet reception the receiver must check that all fields in the
2517 SILC Packet Header are valid. It must check the flags of the
2518 header and act accordingly. It must also check the MAC of the packet
2519 and if it is to be failed the packet must be discarded. Also if the
2520 header of the packet includes any bad fields the packet must be
2523 See above sections on the decryption process of the received packet.
2525 The receiver must also check that the ID's in the header are valid
2526 ID's. Unsupported ID types or malformed ID's must cause packet
2527 rejection. The padding on the reception is always ignored.
2529 The receiver must also check the packet type and start parsing the
2530 packet according to the type. However, note the above sections on
2531 special packet types and their parsing.
2537 Routers are the primary entities in the SILC network that takes care
2538 of packet routing. However, normal servers routes packets as well, for
2539 example, when they are routing channel message to the local clients.
2540 Routing is quite simple as every packet tells the true origin and the
2541 true destination of the packet.
2543 It is still recommended for routers that has several routing connections
2544 to create route cache for those destinations that has faster route than
2545 the router's primary route. This information is available for the router
2546 when other router connects to the router. The connecting party then
2547 sends all of its locally connected clients, server and channels. These
2548 informations helps to create the route cache. Also, when new channels
2549 are created to a cell its information is broadcasted to all routers
2550 in the network. Channel ID's are based on router's ID thus it is easy
2551 to create route cache based on these informations. If faster route for
2552 destination does not exist in router's route cache the packet must be
2553 routed to the primary route (default route).
2555 For server who receives a packet to be routed to its locally connected
2556 client the server must check whether the particular packet type is
2557 allowed to be routed to the client. Not all packets may be sent by
2558 some odd entity to client that is indirectly connected to the sender.
2559 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2560 entities and sending packets to them. The section mentions the packets
2561 that may be sent to indirectly connected entities. It is clear that some
2562 server cannot send, for example, disconnect packet to client that is not
2563 directly connected to the server.
2567 2.12 Packet Broadcasting
2569 SILC packets may be broadcasted in SILC network. However, only router
2570 server may send or receive broadcast packets. Client and normal server
2571 must not send broadcast packets and they must ignore broadcast packets
2572 if they receive them. Broadcast packets are sent by setting Broadcast
2573 flag to the SILC packet header.
2575 Broadcasting packets means that the packet is sent to all routers in
2576 the SILC network, except to the router that sent the packet. The router
2577 receiving broadcast packet must send the packet to its primary route.
2578 The fact that SILC routers may have several router connections may
2579 cause problems, such as race conditions inside the SILC network, if
2580 care is not taken when broadcasting packets. Router must not send
2581 the broadcast packet to any other route except to its primary route.
2583 If the primary route of the router is the original sender of the packet
2584 the packet must not be sent to the primary route. This may happen
2585 if router has several router connections and some other router uses
2586 the router as its primary route.
2588 Routers use broadcast packets to broadcast for example information
2589 about newly registered clients, servers, channels etc. so that all the
2590 routers may keep these informations up to date.
2594 3 Security Considerations
2596 Security is central to the design of this protocol, and these security
2597 considerations permeate the specification. Common security considerations
2598 such as keeping private keys truly private and using adequate lengths for
2599 symmetric and asymmetric keys must be followed in order to maintain the
2600 security of this protocol.
2606 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2607 Protocol Specification", Internet Draft, June 2000.
2609 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2610 Protocols", Internet Draft, June 2000.
2612 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2615 [IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
2618 [IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
2621 [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
2624 [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
2627 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2630 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2633 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2636 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2637 Infrastructure, Certificate and CRL Profile", RFC 2459,
2640 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2641 John Wiley & Sons, New York, NY, 1996.
2643 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2646 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2647 RFC 2412, November 1998.
2649 [ISAKMP] Maughan D., et al, "Internet Security Association and
2650 Key Management Protocol (ISAKMP)", RFC 2408, November
2653 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2654 (IKE)", RFC 2409, November 1998.
2656 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2657 Authentication", RFC 2104, February 1997.
2659 [PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
2660 Specifications, Version 2.0", RFC 2437, October 1998.
2672 EMail: priikone@poseidon.pspt.fi
2674 This Internet-Draft expires 6 Jun 2001