8 .ds RF FORMFEED[Page %]
17 Network Working Group P. Riikonen
19 draft-riikonen-silc-pp-05.txt XXX
26 <draft-riikonen-silc-pp-05.txt>
31 This document is an Internet-Draft and is in full conformance with
32 all provisions of Section 10 of RFC 2026. Internet-Drafts are
33 working documents of the Internet Engineering Task Force (IETF), its
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37 Internet-Drafts are draft documents valid for a maximum of six months
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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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48 The distribution of this memo is unlimited.
54 This memo describes a Packet Protocol used in the Secure Internet Live
55 Conferencing (SILC) protocol, specified in the Secure Internet Live
56 Conferencing, Protocol Specification Internet Draft [SILC1]. This
57 protocol describes the packet types and packet payloads which defines
58 the contents of the packets. The protocol provides secure binary packet
59 protocol that assures that the contents of the packets are secured and
73 1 Introduction .................................................. 3
74 1.1 Requirements Terminology .................................. 4
75 2 SILC Packet Protocol .......................................... 4
76 2.1 SILC Packet ............................................... 4
77 2.2 SILC Packet Header ........................................ 5
78 2.3 SILC Packet Types ......................................... 7
79 2.3.1 SILC Packet Payloads ................................ 16
80 2.3.2 Generic payloads .................................... 16
81 2.3.2.1 ID Payload .................................. 17
82 2.3.2.2 Argument Payload ............................ 18
83 2.3.2.3 Channel Payload ............................. 18
84 2.3.2.4 Public Key Payload .......................... 19
85 2.3.3 Disconnect Payload .................................. 20
86 2.3.4 Success Payload ..................................... 21
87 2.3.5 Failure Payload ..................................... 21
88 2.3.6 Reject Payload ...................................... 22
89 2.3.7 Notify Payload ...................................... 22
90 2.3.8 Error Payload ....................................... 28
91 2.3.9 Channel Message Payload ............................. 29
92 2.3.10 Channel Key Payload ................................ 32
93 2.3.11 Private Message Payload ............................ 34
94 2.3.12 Private Message Key Payload ........................ 35
95 2.3.13 Command Payload .................................... 37
96 2.3.14 Command Reply Payload .............................. 38
97 2.3.15 Connection Auth Request Payload .................... 38
98 2.3.16 New ID Payload ..................................... 39
99 2.3.17 New Client Payload ................................. 40
100 2.3.18 New Server Payload ................................. 41
101 2.3.19 New Channel Payload ................................ 42
102 2.3.20 Key Agreement Payload .............................. 43
103 2.3.21 Resume Router Payload .............................. 44
104 2.3.22 File Transfer Payload .............................. 44
105 2.3.23 Resume Client Payload .............................. XXXXXX
106 2.4 SILC ID Types ............................................. 46
107 2.5 Packet Encryption And Decryption .......................... 46
108 2.5.1 Normal Packet Encryption And Decryption ............. 46
109 2.5.2 Channel Message Encryption And Decryption ........... 47
110 2.5.3 Private Message Encryption And Decryption ........... 48
111 2.6 Packet MAC Generation ..................................... 48
112 2.7 Packet Padding Generation ................................. 49
113 2.8 Packet Compression ........................................ 50
114 2.9 Packet Sending ............................................ 50
115 2.10 Packet Reception ......................................... 51
116 2.11 Packet Routing ........................................... 51
117 2.12 Packet Broadcasting ...................................... 52
118 3 Security Considerations ....................................... 53
119 4 References .................................................... 53
120 5 Author's Address .............................................. 54
126 Figure 1: Typical SILC Packet
127 Figure 2: SILC Packet Header
129 Figure 4: Argument Payload
130 Figure 5: Channel Payload
131 Figure 6: Public Key Payload
132 Figure 7: Disconnect Payload
133 Figure 8: Success Payload
134 Figure 9: Failure Payload
135 Figure 10: Reject Payload
136 Figure 11: Notify Payload
137 Figure 12: Error Payload
138 Figure 13: Channel Message Payload
139 Figure 14: Channel Key Payload
140 Figure 15: Private Message Payload
141 Figure 16: Private Message Key Payload
142 Figure 17: Command Payload
143 Figure 18: Connection Auth Request Payload
144 Figure 19: New Client Payload
145 Figure 20: New Server Payload
146 Figure 21: Key Agreement Payload
147 Figure 22: Resume Router Payload
148 Figure 23: File Transfer Payload
149 Figure 24: Resume Client Payload
155 This document describes a Packet Protocol used in the Secure Internet
156 Live Conferencing (SILC) protocol specified in the Secure Internet Live
157 Conferencing, Protocol Specification Internet Draft [SILC1]. This
158 protocol describes the packet types and packet payloads which defines
159 the contents of the packets. The protocol provides secure binary packet
160 protocol that assures that the contents of the packets are secured and
163 The basis of SILC protocol relies in the SILC packets and it is with
164 out a doubt the most important part of the protocol. It is also probably
165 the most complicated part of the protocol. Packets are used all the
166 time in the SILC network to send messages, commands and other information.
167 All packets in SILC network are always encrypted and their integrity
168 is assured by computed MACs. The protocol defines several packet types
169 and packet payloads. Each packet type usually has a specific packet
170 payload that actually defines the contents of the packet. Each packet
171 also includes a default SILC Packet Header that provides sufficient
172 information about the origin of the packet and destination of the
177 1.1 Requirements Terminology
179 The keywords MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED,
180 MAY, and OPTIONAL, when they appear in this document, are to be
181 interpreted as described in [RFC2119].
185 2 SILC Packet Protocol
190 SILC packets deliver messages from sender to receiver securely by
191 encrypting important fields of the packet. The packet consists of
192 default SILC Packet Header, Padding, Packet Payload data, and, packet
195 The following diagram illustrates typical SILC packet.
200 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
201 | n bytes | 1 - n bytes | n bytes | n bytes
202 | SILC Header | Padding | Data Payload | MAC
203 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
207 Figure 1: Typical SILC Packet
210 SILC Header is always the first part of the packet and its purpose
211 is to provide information about the packet. It provides for example
212 the packet type, origin of the packet and the destination of the packet.
213 The header is variable in length. See the following section for
214 description of SILC Packet header. Packets without SILC header or
215 with malformed SILC header MUST be dropped.
217 Padding follows the packet header. The purpose of the padding is to
218 make the packet multiple by eight (8) or by the block size of the
219 cipher used in the encryption, which ever is larger. The maximum
220 length of padding is currently 128 bytes. The padding is always
221 encrypted. The padding is applied always, even if the packet is
222 not encrypted. See the section 2.7 Padding Generation for more
223 detailed information.
225 Data payload area follows padding and it is the actual data of the
226 packet. The packet data is the packet payloads defined in this
227 protocol. The data payload area is always encrypted.
229 The last part of SILC packet is the packet MAC that assures the
230 integrity of the packet. The MAC is always computed from the packet
231 before the encryption is applied to the packet. If compression is used
232 in the packet the MAC is computed after the compression has been
233 applied. The compression, on the other hand, is always applied before
234 encryption. See more details in the section 2.6 Packet MAC Generation.
236 All fields in all packet payloads are always in MSB (most significant
241 2.2 SILC Packet Header
243 The SILC packet header is applied to all SILC packets and it is
244 variable in length. The purpose of SILC Packet header is to provide
245 detailed information about the packet. The receiver of the packet
246 uses the packet header to parse the packet and gain other relevant
247 parameters of the packet.
249 The following diagram represents the SILC packet header.
254 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
255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
256 | Payload Length | Flags | Packet Type |
257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
258 | Pad Length | RESERVED | Source ID Len | Dest ID Len |
259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
271 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
275 Figure 2: SILC Packet Header
279 o Payload Length (2 bytes) - Is the length of the packet
280 not including the padding of the packet.
282 o Flags (1 byte) - Indicates flags to be used in packet
283 processing. Several flags may be set by ORing the flags
286 The following flags are reserved for this field:
291 In this case the field is ignored.
294 Private Message Key 0x01
296 Indicates that the packet must include private
297 message that is encrypted using private key set by
298 client. Servers does not know anything about this
299 key and this causes that the private message is
300 not handled by the server at all, it is just
301 passed along. See section 2.5.3 Private Message
302 Encryption And Decryption for more information.
307 Indicates that the packet consists of list of
308 packet payloads indicated by the Packet Type field.
309 The payloads are added one after the other. Note that
310 there are packet types that must not be used as
311 list. Parsing of list packet is done by calculating
312 the length of each payload and parsing them one by
318 Marks the packet to be broadcasted. Client cannot
319 send broadcast packet and normal server cannot send
320 broadcast packet. Only router server may send broadcast
321 packet. The router receiving of packet with this flag
322 set MUST send (broadcast) the packet to its primary
323 route. If router has several router connections the
324 packet may be sent only to the primary route. See
325 section 2.12 Packet Broadcasting for description of
333 o Packet Type (1 byte) - Is the type of the packet. Receiver
334 uses this field to parse the packet. See section 2.3
335 SILC Packets for list of defined packet types.
337 o Pad Length (1 byte) - Indicates the length of the padding
338 applied after the SILC Packet header. Maximum length for
339 padding is 128 bytes.
341 o RESERVED (1 byte) - Reserved field and must include a
344 o Source ID Length (1 byte) - Indicates the length of the
345 Source ID field in the header, not including this or any
348 o Destination ID Length (1 byte) - Indicates the length of the
349 Destination ID field in the header, not including this or
352 o Src ID Type (1 byte) - Indicates the type of ID in the
353 Source ID field. See section 2.4 SILC ID Types for
356 o Source ID (variable length) - The actual source ID that
357 indicates which is the original sender of the packet.
359 o Dst ID Type (1 byte) - Indicates the type of ID in the
360 Destination ID field. See section 2.4 SILC ID Types for
363 o Destination ID (variable length) - The actual destination
364 ID that indicates which is the end receiver of the packet.
369 2.3 SILC Packet Types
371 SILC packet types defines the contents of the packet and it is used by
372 the receiver to parse the packet. The packet type is 8 bits, as a one
373 byte, in length. The range for the packet types are from 0 - 255,
374 where 0 is never sent and 255 is currently reserved for future
375 extensions and MUST NOT be defined to any other purpose. Every SILC
376 specification compliant implementation SHOULD support all of these packet
379 The below list of the SILC Packet types includes reference to the packet
380 payload as well. Packet payloads are the actual packet, that is, the data
381 that the packet consists of. Each packet type defines packet payload
382 which usually may only be sent with the specific packet type.
384 Most of the packets are packets that must be destined directly to entity
385 that is connected to the sender. It is not allowed, for example, for
386 router to send disconnect packet to client that is not directly connected
387 to the router. However, there are some special packet types that may
388 be destined to some entity that the sender has not direct connection
389 with. These packets are for example private message packets, channel
390 message packets, command packets and some other packets that may be
391 broadcasted in the SILC network. If the packet is allowed to be sent to
392 indirectly connected entity it is mentioned separately in the packet
393 description (unless it is obvious as in private and channel message
394 packets). Other packets MUST NOT be sent or accepted, if sent, to
395 indirectly connected entities.
397 List of SILC Packet types are defined as follows.
402 This type is reserved and it is never sent.
405 1 SILC_PACKET_DISCONNECT
407 This packet is sent to disconnect the remote end. Reason of
408 the disconnection is sent inside the packet payload. Client
409 usually does not send this packet.
411 This packet MUST NOT be sent as list and the List flag MUST
414 Payload of the packet: See section 2.3.3 Disconnect Payload
417 2 SILC_PACKET_SUCCESS
419 This packet is sent upon successful execution of some protocol.
420 The status of the success is sent in the packet.
422 This packet MUST NOT be sent as list and the List flag MUST
425 Payload of the packet: See section 2.3.4 Success Payload
428 3 SILC_PACKET_FAILURE
430 This packet is sent upon failure of some protocol. The status
431 of the failure is sent in the packet.
433 This packet MUST NOT be sent as list and the List flag MUST
436 Payload of the packet: See section 2.3.5 Failure Payload
441 This packet MAY be sent upon rejection of some protocol.
442 The status of the rejection is sent in the packet.
444 This packet MUST NOT be sent as list and the List flag MUST
447 Payload of the packet: See section 2.3.6 Reject Payload
452 This packet is used to send notify message, usually from
453 server to client, although it MAY be sent from server to another
454 server as well. Client MUST NOT send this packet. Server MAY
455 send this packet to channel as well when the packet is
456 distributed to all clients on the channel.
458 Payload of the packet: See section 2.3.7 Notify Payload.
463 This packet is sent when an error occurs. Server MAY
464 send this packet. Client MUST NOT send this packet. The
465 client MAY entirely ignore the packet, however, server is
466 most likely to take action anyway. This packet MAY be sent
467 to entity that is indirectly connected to the sender.
469 This packet MUST NOT be sent as list and the List flag MUST
472 Payload of the packet: See section 2.3.8 Error Payload.
475 7 SILC_PACKET_CHANNEL_MESSAGE
477 This packet is used to send messages to channels. The packet
478 includes Channel ID of the channel and the actual message to
479 the channel. Messages sent to the channel are always protected
480 by channel specific keys. Channel Keys are distributed by
481 SILC_PACKET_CHANNEL_KEY packet.
483 This packet MUST NOT be sent as list and the List flag MUST
486 Payload of the packet: See section 2.3.9 Channel Message
490 8 SILC_PACKET_CHANNEL_KEY
492 This packet is used to distribute new key for particular
493 channel. Each channel has their own independent keys that
494 is used to protect the traffic on the channel. Only server
495 may send this packet. This packet MAY be sent to entity
496 that is indirectly connected to the sender.
498 This packet MUST NOT be sent as list and the List flag MUST
501 Payload of the packet: See section 2.3.10 Channel Key Payload
504 9 SILC_PACKET_PRIVATE_MESSAGE
506 This packet is used to send private messages from client
507 to another client. By default, private messages are protected
508 by session keys established by normal key exchange protocol.
509 However, it is possible to use specific key to protect private
510 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
511 agree the key with the remote client. Pre-shared key MAY be
512 used as well if both of the client knows it, however, it needs
513 to be agreed outside SILC. See more of this in [SILC1].
515 This packet MUST NOT be sent as list and the List flag MUST
518 Payload of the packet: See section 2.3.11 Private Message
522 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
524 This packet is used to agree about a key to be used to protect
525 the private messages between two clients. If this is not sent
526 the normal session key is used to protect the private messages
527 inside SILC network. Agreeing to use specific key to protect
528 private messages adds security, as no server between the two
529 clients will be able to decrypt the private message. However,
530 servers inside SILC network are considered to be trusted, thus
531 using normal session key to protect private messages does not
532 degrade security. Whether to agree to use specific keys by
533 default or to use normal session keys by default, is
534 implementation specific issue. See more of this in [SILC1].
536 This packet MUST NOT be sent as list and the List flag MUST
539 Payload of the packet: See section 2.3.12 Private Message
543 11 SILC_PACKET_COMMAND
545 This packet is used to send commands from client to server.
546 Server MAY send this packet to other servers as well. All
547 commands are listed in their own section SILC Command Types
548 in [SILC4]. The contents of this packet is command specific.
549 This packet MAY be sent to entity that is indirectly connected
552 This packet MUST NOT be sent as list and the List flag MUST
555 Payload of the packet: See section 2.3.13 Command Payload
558 12 SILC_PACKET_COMMAND_REPLY
560 This packet is sent as reply to the SILC_PACKET_COMMAND packet.
561 The contents of this packet is command specific. This packet
562 MAY be sent to entity that is indirectly connected to the
565 This packet MUST NOT be sent as list and the List flag MUST
568 Payload of the packet: See section 2.3.14 Command Reply
569 Payload and section 2.3.13 Command
575 13 SILC_PACKET_KEY_EXCHANGE
577 This packet is used to start SILC Key Exchange Protocol,
578 described in detail in [SILC3].
580 This packet MUST NOT be sent as list and the List flag MUST
583 Payload of the packet: Payload of this packet is described
584 in the section SILC Key Exchange
585 Protocol and its sub sections in
589 14 SILC_PACKET_KEY_EXCHANGE_1
591 This packet is used as part of the SILC Key Exchange Protocol.
593 This packet MUST NOT be sent as list and the List flag MUST
596 Payload of the packet: Payload of this packet is described
597 in the section SILC Key Exchange
598 Protocol and its sub sections in
602 15 SILC_PACKET_KEY_EXCHANGE_2
604 This packet is used as part of the SILC Key Exchange Protocol.
606 This packet MUST NOT be sent as list and the List flag MUST
609 Payload of the packet: Payload of this packet is described
610 in the section SILC Key Exchange
611 Protocol and its sub sections in
615 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
617 This packet is used to request the authentication method to
618 be used in the SILC Connection Authentication Protocol. If
619 initiator of the protocol does not know the mandatory
620 authentication method this packet MAY be used to determine it.
622 The party receiving this payload MUST respond with the same
623 packet including the mandatory authentication method.
625 This packet MUST NOT be sent as list and the List flag MUST
628 Payload of the packet: See section 2.3.15 Connection Auth
634 17 SILC_PACKET_CONNECTION_AUTH
636 This packet is used to start and perform the SILC Connection
637 Authentication Protocol. This protocol is used to authenticate
638 the connecting party. The protocol is described in detail in
641 This packet MUST NOT be sent as list and the List flag MUST
644 Payload of the packet: Payload of this packet is described
645 in the section SILC Authentication
646 Protocol and it sub sections in [SILC].
649 18 SILC_PACKET_NEW_ID
651 This packet is used to distribute new ID's from server to
652 router and from router to all routers in the SILC network.
653 This is used when for example new client is registered to
654 SILC network. The newly created ID's of these operations are
655 distributed by this packet. Only server may send this packet,
656 however, client MUST be able to receive this packet. This
657 packet MAY be sent to entity that is indirectly connected
660 Payload of the packet: See section 2.3.16 New ID Payload
663 19 SILC_PACKET_NEW_CLIENT
665 This packet is used by client to register itself to the
666 SILC network. This is sent after key exchange and
667 authentication protocols has been completed. Client sends
668 various information about itself in this packet.
670 This packet MUST NOT be sent as list and the List flag MUST
673 Payload of the packet: See section 2.3.17 New Client Payload
676 20 SILC_PACKET_NEW_SERVER
678 This packet is used by server to register itself to the
679 SILC network. This is sent after key exchange and
680 authentication protocols has been completed. Server sends
681 this to the router it connected to, or, if router was
682 connecting, to the connected router. Server sends its
683 Server ID and other information in this packet. The client
684 MUST NOT send or receive this packet.
686 This packet MUST NOT be sent as list and the List flag MUST
689 Payload of the packet: See section 2.3.18 New Server Payload
692 21 SILC_PACKET_NEW_CHANNEL
694 This packet is used to notify routers about newly created
695 channel. Channels are always created by the router and it MUST
696 notify other routers about the created channel. Router sends
697 this packet to its primary route. Client MUST NOT send this
698 packet. This packet MAY be sent to entity that is indirectly
699 connected to the sender.
701 Payload of the packet: See section 2.3.19 New Channel Payload
706 This packet is used to indicate that re-key must be performed
707 for session keys. See section Session Key Regeneration in
708 [SILC1] for more information. This packet does not have
711 This packet MUST NOT be sent as list and the List flag MUST
715 23 SILC_PACKET_REKEY_DONE
717 This packet is used to indicate that re-key is performed and
718 new keys must be used hereafter.
720 This packet MUST NOT be sent as list and the List flag MUST
724 24 SILC_PACKET_HEARTBEAT
726 This packet is used by clients, servers and routers to keep the
727 connection alive. It is recommended that all servers implement
728 keepalive actions and perform it to both direction in a link.
729 This packet does not have a payload.
731 This packet MUST NOT be sent as list and the List flag MUST
735 25 SILC_PACKET_KEY_AGREEMENT
737 This packet is used by clients to request key negotiation
738 between another client in the SILC network. If the negotiation
739 is started it is performed using the SKE protocol. The result of
740 the negotiation, the secret key material, can be used for
741 example as private message key. The server and router MUST NOT
744 This packet MUST NOT be sent as list and the List flag MUST
747 Payload of the packet: See section 2.3.20 Key Agreement Payload
750 26 SILC_PACKET_RESUME_ROUTER
752 This packet is used during backup router protocol when the
753 original primary router of the cell comes back online and wishes
754 to resume the position as being the primary router of the cell.
756 Payload of the packet: See section 2.3.21 Resume Router Payload
761 This packet is used to perform an file transfer protocol in the
762 SILC session with some entity in the network. The packet is
763 multi purpose. The packet is used to tell other entity in the
764 network that the sender wishes to perform an file transfer
765 protocol. The packet is also used to actually tunnel the
766 file transfer protocol stream. The file transfer protocol
767 stream is always protected with the SILC packet.
769 This packet MUST NOT be sent as list and the List flag MUST
772 Payload of the packet: See section 2.3.22 File Transfer Payload
775 28 SILC_PACKET_RESUME_CLIENT
777 This packet is used to resume a client back to the network
778 after it has been detached. A client is able to detach from
779 the network but the client is still valid client in the network.
780 The client may then later resume its session back by sending
781 this packet to a server. Routers also use this packet to notify
782 other routers in the network that the detached client has resumed.
784 This packet MUST NOT be sent as list and the List flag MUST
787 Payload of the packet: See section 2.3.23 Resume Client Payload
792 Currently undefined commands.
797 These packet types are reserved for private use and they will
798 not be defined by this document.
805 This type is reserved for future extensions and currently it
811 2.3.1 SILC Packet Payloads
813 All payloads resides in the main data area of the SILC packet. However
814 all payloads MUST be at the start of the data area after the SILC
815 packet header and padding. All fields in the packet payload are always
816 encrypted, as they reside in the data area of the packet which is
819 Payloads described in this section are common payloads that MUST be
820 accepted anytime during SILC session. Most of the payloads may only
821 be sent with specific packet type which is defined in the description
824 There are a lot of other payloads in the SILC as well. However, they
825 are not common in the sense that they could be sent at any time.
826 These payloads are not described in this section. These are payloads
827 such as SILC Key Exchange payloads and so on. These are described
828 in [SILC1], [SILC3] and [SILC4].
832 2.3.2 Generic payloads
834 This section describes generic payloads that are not associated to any
835 specific packet type. They can be used for example inside some other
842 This payload can be used to send an ID. ID's are variable in length
843 thus this payload provides a way to send variable length ID's.
845 The following diagram represents the ID Payload.
850 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
851 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
852 | ID Type | ID Length |
853 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
857 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
865 o ID Type (2 bytes) - Indicates the type of the ID. See
866 section 2.4 SILC ID Types for list of defined ID types.
868 o ID Length (2 bytes) - Length of the ID Data area not
869 including the length of any other fields in the payload.
871 o ID Data (variable length) - The actual ID data.
876 2.3.2.2 Argument Payload
878 Argument Payload is used to set arguments for any packet payload that
879 needs and supports arguments, such as commands. Number of arguments
880 associated with a packet MUST be indicated by the packet payload which
881 needs the arguments. Argument Payloads MUST always reside right after
882 the packet payload needing the arguments. Incorrect amount of argument
883 payloads MUST cause rejection of the packet.
891 The following diagram represents the Argument Payload.
896 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
897 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
898 | Payload Length | Argument Type | |
899 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
903 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
907 Figure 4: Argument Payload
911 o Payload Length (2 bytes) - Length of the argument payload data
912 area not including the length of any other fields in the
915 o Argument Type (1 byte) - Indicates the type of the argument.
916 Every argument may have a specific type that MUST be defined
917 by the packet payload needing the argument. For example
918 every command specify a number for each argument that maybe
919 associated with the command. By using this number the receiver
920 of the packet knows what type of argument this is. If there is
921 no specific argument type this field is set to zero (0).
923 o Argument Data (variable length) - Argument data.
928 2.3.2.3 Channel Payload
930 Generic Channel Payload may be used to send information about channel,
931 its name, the Channel ID and a mode.
933 The following diagram represents the Channel Payload.
949 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
950 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
951 | Channel Name Length | |
952 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
956 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
957 | Channel ID Length | |
958 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
962 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
964 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
968 Figure 5: New Channel Payload
972 o Channel Name Length (2 bytes) - Length of the channel name
975 o Channel Name (variable length) - The name of the channel.
977 o Channel ID Length (2 bytes) - Length of the Channel ID field.
979 o Channel ID (variable length) - The Channel ID.
981 o Mode Mask (4 bytes) - A mode. This can be the mode of the
982 channel but it can also be the mode of the client on the
983 channel. The contents of this field is dependent of the
984 usage of this payload. The usage is defined separately
985 when this payload is used. This is a 32 bit MSB first value.
990 2.3.2.4 Public Key Payload
992 Generic Public Key Payload may be used to send different types of
993 public keys and certificates.
995 The following diagram represents the Public Key Payload.
1004 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
1005 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1006 | Public Key Length | Public Key Type |
1007 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1009 ~ Public Key of the party (or certificate) ~
1011 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1015 Figure 6: Public Key Payload
1019 o Public Key Length (2 bytes) - The length of the Public Key
1020 (or certificate) field, not including any other field.
1022 o Public Key Type (2 bytes) - The public key (or certificate)
1023 type. This field indicates the type of the public key in
1024 the packet. See the [SILC3] for defined public key types.
1026 o Public Key (or certificate) (variable length) - The
1027 public key or certificate.
1032 2.3.3 Disconnect Payload
1034 Disconnect payload is sent upon disconnection. The payload is simple;
1035 reason of disconnection is sent to the disconnected party.
1037 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
1038 MUST NOT be sent in any other packet type. The following diagram
1039 represents the Disconnect Payload.
1045 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
1046 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1048 ~ Disconnect Message ~
1050 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1054 Figure 7: Disconnect Payload
1060 o Disconnect Message (variable length) - Human readable
1061 reason of the disconnection.
1066 2.3.4 Success Payload
1068 Success payload is sent when some protocol execution is successfully
1069 completed. The payload is simple; indication of the success is sent.
1070 This may be any data, including binary or human readable data.
1075 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
1076 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1078 ~ Success Indication ~
1080 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1084 Figure 8: Success Payload
1088 o Success Indication (variable length) - Indication of
1089 the success. This may be for example some flag that
1090 indicates the protocol and the success status or human
1091 readable success message. The true length of this
1092 payload is available by calculating it from the SILC
1099 2.3.5 Failure Payload
1101 This is opposite of Success Payload. Indication of failure of
1102 some protocol is sent in the payload.
1108 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
1109 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1111 ~ Failure Indication ~
1113 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1117 Figure 9: Failure Payload
1121 o Failure Indication (variable length) - Indication of
1122 the failure. This may be for example some flag that
1123 indicates the protocol and the failure status or human
1124 readable failure message. The true length of this
1125 payload is available by calculating it from the SILC
1131 2.3.6 Reject Payload
1133 This payload is sent when some protocol is rejected to be executed.
1134 Other operations MAY send this as well that was rejected. The
1135 indication of the rejection is sent in the payload. The indication
1136 may be binary or human readable data.
1142 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
1143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1145 ~ Reject Indication ~
1147 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1151 Figure 10: Reject Payload
1155 o Reject Indication (variable length) - Indication of
1156 the rejection. This maybe for example some flag that
1157 indicates the protocol and the rejection status or human
1158 readable rejection message. The true length of this
1159 payload is available by calculating it from the SILC
1165 2.3.7 Notify Payload
1167 Notify payload is used to send notify messages. The payload is usually
1168 sent from server to client, however, server MAY send it to another
1169 server as well. This payload MAY also be sent to a channel. Client
1170 MUST NOT send this payload. The receiver of this payload MAY ignore
1171 the contents of the payload, however, notify message SHOULD be audited.
1173 The payload may only be sent with SILC_PACKET_NOTIFY packet. It MUST
1174 not be sent in any other packet type. The following diagram represents
1183 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
1184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1185 | Notify Type | Payload Length |
1186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1192 Figure 11: Notify Payload
1196 o Notify Type (2 bytes) - Indicates the type of the notify
1199 o Payload Length (2 bytes) - Length of the entire Notify Payload
1200 including any associated Argument Payloads.
1202 o Argument Nums (2 bytes) - Indicates the number of Argument
1203 Payloads associated to this payload. Notify types may define
1204 arguments to be send along the notify message.
1207 The following list of currently defined notify types. The format for
1208 notify arguments is same as in SILC commands described in [SILC4].
1209 Note that all ID's sent in arguments are sent inside ID Payload. Also
1210 note that all passphrases that may be sent inside arguments MUST be
1211 UTF-8 [RFC2279] encoded.
1214 0 SILC_NOTIFY_TYPE_NONE
1216 If no specific notify type apply for the notify message this type
1220 Arguments: (1) <message>
1222 The <message> is implementation specific free text string.
1223 Receiver MAY ignore this message.
1226 1 SILC_NOTIFY_TYPE_INVITE
1228 Sent when an client is invited to a channel. This is also sent
1229 when the invite list of the channel is changed. This notify type
1230 is sent between routers and if an client was invited, to the
1231 client as well. In this case the packet is destined to the client.
1234 Arguments: (1) <Channel ID> (2) <channel name>
1235 (3) [<sender Client ID>] (4) [<adding client>]
1236 (5) [<removing client>]
1238 The <Channel ID> is the channel. The <channel name> is the name
1239 of the channel and is provided because the client which receives
1240 this notify packet may not have a way to resolve the name of the
1241 channel from the <Channel ID>. The <sender Client ID> is the
1242 Client ID which invited the client to the channel. The <adding
1243 client> and the <removing client> indicates the added or removed
1244 client from the channel's invite list. The format of the <adding
1245 client> and the <removing client> is defined in the [SILC4] with
1246 SILC_COMMAND_INVITE command.
1248 The <adding client> and <removing client> MUST NOT be sent when
1249 the packet is destined to a client.
1252 2 SILC_NOTIFY_TYPE_JOIN
1254 Sent when client has joined to a channel. The server MUST
1255 distribute this type only to the local clients on the channel
1256 and then send it to its primary router. The router or server
1257 receiving the packet distributes this type to the local clients
1258 on the channel and broadcast it to the network.
1261 Arguments: (1) [<Client ID>] (2) <Channel ID>
1263 The <Client ID> is the client that joined to the channel indicated
1264 by the <Channel ID>.
1267 3 SILC_NOTIFY_TYPE_LEAVE
1269 Sent when client has left a channel. The server must distribute
1270 this type only to the local clients on the channel and then send
1271 it to its primary router. The router or server receiving the
1272 packet distributes this type to the local clients on the channel
1273 and broadcast it to the network.
1276 Arguments: (1) <Client ID>
1278 The <Client ID> is the client which left the channel.
1281 4 SILC_NOTIFY_TYPE_SIGNOFF
1283 Sent when client signoff from SILC network. The server MUST
1284 distribute this type only to the local clients on the channel and
1285 then send it to its primary router. The router or server receiving
1286 the packet distributes this type to the local clients on the
1287 channel and broadcast it to the network.
1290 Arguments: (1) <Client ID> (2) <message>
1292 The <Client ID> is the client which left SILC network. The
1293 <message> is free text string indicating the reason of the signoff.
1296 5 SILC_NOTIFY_TYPE_TOPIC_SET
1298 Sent when topic is set/changed on a channel. This type must be
1299 sent only to the clients which is joined on the channel which
1300 topic was set or changed.
1303 Arguments: (1) <ID Payload> (2) <topic>
1305 The <ID Payload> is the ID of the entity who set the topic. It
1306 usually is Client ID but it can be Server ID and Channel ID as well.
1309 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1311 Sent when client changes nick on a channel. The server MUST
1312 distribute this type only to the local clients on the channel
1313 and then send it to its primary router. The router or server
1314 receiving the packet distributes this type to the local clients
1315 on the channel and broadcast it to the network.
1318 Arguments: (1) <Old Client ID> (2) <New Client ID>
1321 The <Old Client ID> is the old ID of the client which changed
1322 the nickname. The <New Client ID> is the new ID generated by
1323 the change of the nickname. The <nickname> is the new nickname.
1326 7 SILC_NOTIFY_TYPE_CMODE_CHANGE
1328 Sent when channel mode has changed. This type MUST be sent only
1329 to the clients which is joined on the channel which mode was
1333 Arguments: (1) <ID Payload> (2) <mode mask>
1334 (3) [<cipher>] (4) <[hmac>]
1337 The <ID Payload> is the ID (usually Client ID but it can be
1338 Server ID as well when the router is enforcing channel mode
1339 change) of the entity which changed the mode. The <mode mask>
1340 is the new mode mask of the channel. The client can safely
1341 ignore the <cipher> argument since the SILC_PACKET_CHANNEL_KEY
1342 packet will force the new channel key change anyway. The <hmac>
1343 argument is important since the client is responsible of setting
1344 the new HMAC and the hmac key into use. The <passphrase> is
1345 the passphrase of the channel, if it was now set.
1348 8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
1350 Sent when user mode on channel has changed. This type MUST be
1351 sent only to the clients which is joined on the channel where
1352 the target client is on.
1355 Arguments: (1) <ID Payload> (2) <mode mask>
1356 (3) <Target Client ID>
1358 The <ID Payload> is the ID (usually Client ID but it can be
1359 Server ID as well when the router is enforcing user's mode
1360 change) of the entity which changed the mode. The <mode mask>
1361 is the new mode mask of the channel. The <Target Client ID>
1362 is the client which mode was changed.
1365 9 SILC_NOTIFY_TYPE_MOTD
1367 Sent when Message of the Day (motd) is sent to a client.
1370 Arguments: (1) <motd>
1372 The <motd> is the Message of the Day.
1375 10 SILC_NOTIFY_TYPE_CHANNEL_CHANGE
1377 Sent when channel's ID has changed for a reason or another.
1378 This is sent by normal server to the client. This can also be
1379 sent by router to other server to force the Channel ID change.
1380 The Channel ID MUST be changed to use the new one. When sent
1381 to clients, this type MUST be sent only to the clients which is
1382 joined on the channel.
1385 Arguments: (1) <Old Channel ID> (2) <New Channel ID>
1387 The <Old Channel ID> is the channel's old ID and the <New
1388 Channel ID> is the new one that MUST replace the old one.
1391 11 SILC_NOTIFY_TYPE_SERVER_SIGNOFF
1393 Sent when server quits SILC network. Those clients from this
1394 server that are on channels must be removed from the channel.
1397 Arguments: (1) <Server ID> (n) [<Client ID>] [...]
1399 The <Server ID> is the server's ID. The rest of the arguments
1400 are the Client ID's of the client's which are coming from this
1401 server and are thus quitting the SILC network also. If the
1402 maximum number of arguments are reached another
1403 SILC_NOTIFY_TYPE_SERVER_SIGNOFF notify packet MUST be sent.
1404 When this notify packet is sent between routers the Client ID's
1405 MAY be omitted. Server receiving the Client ID's in the payload
1406 may use them directly to remove the client.
1409 12 SILC_NOTIFY_TYPE_KICKED
1411 Sent when a client has been kicked from a channel. This is
1412 sent also to the client which was kicked from the channel.
1413 The client which was kicked from the channel MUST be removed
1414 from the channel. This notify type is always destined to the
1415 channel. The router or server receiving the packet distributes
1416 this type to the local clients on the channel and broadcast it
1420 Arguments: (1) <Client ID> (2) [<comment>]
1421 (3) <Kicker's Client ID>
1423 The <Client ID> is the client which was kicked from the channel.
1424 The kicker may have set the <comment> to indicate the reason for
1425 the kicking. The <Kicker's Client ID> is the kicker.
1428 13 SILC_NOTIFY_TYPE_KILLED
1430 Sent when a client has been killed from the network. This is sent
1431 also to the client which was killed from the network. The client
1432 which was killed from the network MUST be removed from the network.
1433 This notify type is destined directly to the client which was
1434 killed and to channel if the client is on any channel. The router
1435 or server receiving the packet distributes this type to the local
1436 clients on the channel and broadcast it to the network.
1439 Arguments: (1) <Client ID> (2) [<comment>]
1442 The <Client ID> is the client which was killed from the network.
1443 The killer may have set the <comment> to indicate the reason for
1444 the killing. The <Killer's ID> is the killer, which may be
1445 client but also router server.
1448 14 SILC_NOTIFY_TYPE_UMODE_CHANGE
1450 Sent when user's mode in the SILC changes. This type is sent
1451 only between routers as broadcast packet.
1454 Arguments: (1) <Client ID> (2) <mode mask>
1456 The <Client ID> is the client which mode was changed. The
1457 <mode mask> is the new mode mask.
1460 15 SILC_NOTIFY_TYPE_BAN
1462 Sent when the ban list of the channel is changed. This type is
1463 sent only between routers as broadcast packet.
1466 Arguments: (1) <Channel ID> (2) [<adding client>]
1467 (3) [<removing client>]
1469 The <Channel ID> is the channel which ban list was changed. The
1470 <adding client> is used to indicate that a ban was added and the
1471 <removing client> is used to indicate that a ban was removed from
1472 the ban list. The format of the <adding client> and the
1473 <removing client> is defined in the [SILC4] with SILC_COMMAND_BAN
1478 Notify types starting from 16384 are reserved for private notify
1485 Error payload is sent upon error. Error may occur in various
1486 conditions when server sends this packet. Client MUST NOT send this
1487 payload but MUST be able to accept it. However, client MAY
1488 totally ignore the contents of the packet as server is going to
1489 take action on the error anyway. However, it is recommended
1490 that the client takes error packet seriously.
1496 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
1497 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1501 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1505 Figure 12: Error Payload
1509 o Error Message (variable length) - Human readable error
1515 2.3.9 Channel Message Payload
1517 Channel messages are the most common messages sent in the SILC.
1518 Channel Message Payload is used to send message to channels. These
1519 messages can only be sent if client has joined to some channel.
1520 Even though this packet is the most common in SILC it is still
1521 special packet. Some special handling on sending and reception
1522 of channel message is required.
1524 Padding MUST be applied into this payload since the payload is
1525 encrypted separately from other parts of the packet with the
1526 channel specific key. Hence the requirement of the padding.
1527 The padding SHOULD be random data. The packet MUST be made
1528 multiple by eight (8) or by the block size of the cipher, which
1531 The SILC header in this packet is encrypted with the session key
1532 of the next receiver of the packet. Nothing else is encrypted
1533 with that key. Thus, the actual packet and padding to be
1534 encrypted with the session key is SILC Header plus padding to it
1535 to make it multiple by eight (8) or multiple by the block size
1536 of the cipher, which ever is larger.
1538 Receiver of the the channel message packet is able to determine
1539 the channel the message is destined to by checking the destination
1540 ID from the SILC Packet header which tells the destination channel.
1541 The original sender of the packet is also determined by checking
1542 the source ID from the header which tells the client which sent
1545 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1546 It MUST NOT be sent in any other packet type. The following diagram
1547 represents the Channel Message Payload.
1549 (*) indicates that the field is not encrypted.
1555 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
1556 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1557 | Message Flags | Message Length |
1558 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1562 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1563 | Padding Length | |
1564 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1568 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1572 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1574 ~ Initial Vector * ~
1576 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1580 Figure 13: Channel Message Payload
1584 o Message Flags (2 bytes) - Includes the Message Flags of
1585 the channel messages. The flags can indicate a reason or
1586 purpose for the channel message. Note that the Private
1587 Message Payload use these same Message Flags for the same
1588 purpose. The following Message Flags are defined:
1590 0x0000 SILC_MESSAGE_FLAG_NONE
1592 No specific flags set.
1594 0x0001 SILC_MESSAGE_FLAG_AUTOREPLY
1596 This message is an automatic reply to an earlier
1599 0x0002 SILC_MESSAGE_FLAG_NOREPLY
1601 There should not be reply messages to this
1604 0x0004 SILC_MESSAGE_FLAG_ACTION
1606 The sender is performing an action and the message
1607 is the indication of the action.
1609 0x0008 SILC_MESSAGE_FLAG_NOTICE
1611 The message is for example an informational notice
1614 0x0010 SILC_MESSAGE_FLAG_REQUEST
1616 This is a generic request flag to send request
1617 messages. A separate document should define any
1618 payloads associated to this flag.
1620 0x0020 SILC_MESSAGE_FLAG_SIGNED
1622 This flag indicates that the message is signed
1623 with sender's private key and thus can be verified
1624 by the receiver using the sender's public key. A
1625 separate document should define the detailed procedure
1626 of the signing process and any associated payloads
1629 0x0040 SILC_MESSAGE_FLAG_REPLY
1631 This is a generic reply flag to send a reply to
1632 previously received request. A separate document
1633 should define any payloads associated to this flag.
1635 0x0080 SILC_MESSAGE_FLAG_DATA
1637 This is a generic data flag, indicating that the
1638 message includes some data which can be interpreted
1639 in a specific way. Using this flag any kind of data
1640 can be delivered inside message payload. A separate
1641 document should define how this flag is interpreted
1642 and define any associated payloads.
1644 0x0100 - 0x0800 RESERVED
1646 Reserved for future flags
1648 0x1000 - 0x8000 PRIVATE RANGE
1650 Private range for free use.
1652 o Message Length (2 bytes) - Indicates the length of the
1653 the Message Data field in the payload, not including any
1656 o Message Data (variable length) - The actual message to
1659 o Padding Length (2 bytes) - Indicates the length of the
1660 Padding field in the payload, not including any other
1663 o Padding (variable length) - The padding that MUST be
1664 applied because this payload is encrypted separately from
1665 other parts of the packet.
1667 o MAC (variable length) - The MAC computed from the
1668 Message Length, Message Data, Padding Length, Padding and
1669 Initial Vector fields. This protects the integrity of the
1670 plaintext channel message. The receiver can verify from
1671 the MAC whether the message decrypted correctly. Also, if
1672 more than one private key has been set for the channel, the
1673 receiver can verify which of the keys decrypted the message
1674 correctly. Note that, this field is encrypted and MUST
1675 be added to the padding calculation.
1677 o Initial Vector (variable length) - The initial vector
1678 that has been used in packet encryption. It needs to be
1679 used in the packet decryption as well. What this field
1680 includes is implementation issue. However, it is
1681 RECOMMENDED that it would be random data or, perhaps,
1682 a timestamp. It is NOT RECOMMENDED to use zero (0) as an
1683 initial vector. This field is not encrypted. This field
1684 is not included into the padding calculation. Length
1685 of this field equals the cipher's block size. This field
1686 is, however, authenticated.
1691 2.3.10 Channel Key Payload
1693 All traffic in channels are protected by channel specific keys.
1694 Channel Key Payload is used to distribute channel keys to all
1695 clients on the particular channel. Channel keys are sent when
1696 the channel is created, when new user joins to the channel and
1697 whenever a user has left a channel. Server creates the new
1698 channel key and distributes it to the clients by encrypting this
1699 payload with the session key shared between the server and
1700 the client. After that, client starts using the key received
1701 in this payload to protect the traffic on the channel.
1703 The client which is joining to the channel receives its key in the
1704 SILC_COMMAND_JOIN command reply message thus it is not necessary to
1705 send this payload to the entity which sent the SILC_COMMAND_JOIN
1708 Channel keys are cell specific thus every router in the cell have
1709 to create a channel key and distribute it if any client in the
1710 cell has joined to a channel. Channel traffic between cell's
1711 are not encrypted using channel keys, they are encrypted using
1712 normal session keys between two routers. Inside a cell, all
1713 channel traffic is encrypted with the specified channel key.
1714 Channel key should expire periodically, say, in one hour, in
1715 which case new channel key is created and distributed.
1717 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1718 It MUST NOT be sent in any other packet type. The following diagram
1719 represents the Channel Key Payload.
1725 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
1726 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1727 | Channel ID Length | |
1728 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1732 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1733 | Cipher Name Length | |
1734 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1738 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1739 | Channel Key Length | |
1740 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1744 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1748 Figure 14: Channel Key Payload
1753 o Channel ID Length (2 bytes) - Indicates the length of the
1754 Channel ID field in the payload, not including any other
1757 o Channel ID (variable length) - The Channel ID of the
1758 channel this key is meant for.
1760 o Cipher Name Length (2 bytes) - Indicates the length of the
1761 Cipher name field in the payload, not including any other
1764 o Cipher Name (variable length) - Name of the cipher used
1765 in the protection of channel traffic. This name is
1766 initially decided by the creator of the channel but it
1767 MAY change during the life time of the channel as well.
1769 o Channel Key Length (2 bytes) - Indicates the length of the
1770 Channel Key field in the payload, not including any other
1773 o Channel Key (variable length) - The actual channel key
1779 2.3.11 Private Message Payload
1781 Private Message Payload is used to send private message between
1782 two clients (or users for that matter). The messages are sent only
1783 to the specified user and no other user inside SILC network is
1784 able to see the message. The message is protected by the session
1785 key established by the SILC Key Exchange Protocol. However,
1786 it is also possible to agree to use a private key to protect
1787 just the private messages. See section 2.3.11 Private Message
1788 Key Payload for detailed description of how to agree to use
1791 If normal session key is used to protect the message, every server
1792 between the sender client and the receiving client MUST decrypt the
1793 packet and always re-encrypt it with the session key of the next
1794 receiver of the packet. See section Client To Client in [SILC1].
1796 When private key is used to protect the message, servers between
1797 the sender and the receiver needs not to decrypt/re-encrypt the
1798 packet. Section Client To Client in [SILC1] gives example of this
1801 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1802 packet. It MUST NOT be sent in any other packet type. The following
1803 diagram represents the Private Message Payload.
1815 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
1816 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1817 | Message Flags | Message Data Length |
1818 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1822 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1826 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1830 Figure 15: Private Message Payload
1834 o Message Flags (2 bytes) - This field includes the Message
1835 Flags of the private message. They can indicate a different
1836 reason or purpose for the private message. See the section
1837 2.3.9 Channel Message Payload for defined flags. Note that
1838 the Channel Message Payload use the same flags for the
1841 o Message Data Length (2 bytes) - Indicates the length of the
1842 Message Data field, not includes any other field.
1844 o Message Data (variable length) - The actual message to
1845 the client. Rest of the packet is reserved for the message
1848 o Padding (variable length) - This field is present only
1849 when the private message payload is encrypted with private
1850 message key. In this case the padding is applied to make
1851 the payload multiple by eight (8), or by the block size of
1852 the cipher, which ever is larger. When encrypted with
1853 normal session keys, this field MUST NOT be included.
1858 2.3.12 Private Message Key Payload
1860 This payload is optional and can be used to send private message
1861 key between two clients in the network. The packet is secured with
1862 normal session keys. By default private messages are encrypted
1863 with session keys, and with this payload it is possible to set
1864 private key for private message encryption between two clients.
1866 The receiver of this payload SHOULD verify for example from user
1867 whether user wants to receive private message key. Note that there
1868 are other, more secure ways of exchanging private message keys in
1869 the SILC network. Instead of sending this payload it is possible to
1870 negotiate the private message key with SKE protocol using the Key
1871 Agreement payload directly peer to peer.
1873 This payload may only be sent by client to another client. Server
1874 MUST NOT send this payload at any time. After sending this payload
1875 the sender of private messages must set the Private Message Key
1876 flag into SILC Packet Header.
1878 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1879 packet. It MUST NOT be sent in any other packet type. The following
1880 diagram represents the Private Message Key Payload.
1886 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
1887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1888 | Private Message Key Length | |
1889 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1891 ~ Private Message Key ~
1893 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1894 | Cipher Name Length | |
1895 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1899 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1903 Figure 16: Private Message Key Payload
1909 o Private Message Key Length (2 bytes) - Indicates the length
1910 of the Private Message Key field in the payload, not including
1913 o Private Message Key (variable length) - The actual private
1914 message key material.
1916 o Cipher Name Length (2 bytes) - Indicates the length of the
1917 Cipher Name field in the payload, not including any other
1920 o Cipher Name (variable length) - Name of the cipher to use
1921 in the private message encryption. If this field does not
1922 exist then the default cipher of the SILC protocol is used.
1923 See the [SILC1] for defined ciphers.
1929 2.3.13 Command Payload
1931 Command Payload is used to send SILC commands from client to server.
1932 Also server MAY send commands to other servers. The following diagram
1933 represents the Command Payload.
1939 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
1940 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1941 | Payload Length | SILC Command | Arguments Num |
1942 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1943 | Command Identifier |
1944 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1948 Figure 17: Command Payload
1952 o Payload Length (2 bytes) - Length of the entire command
1953 payload including any command argument payloads associated
1956 o SILC Command (1 byte) - Indicates the SILC command. This MUST
1957 be set to non-zero value. If zero (0) value is found in this
1958 field the packet MUST be discarded.
1960 o Arguments Num (1 byte) - Indicates the number of arguments
1961 associated with the command. If there are no arguments this
1962 field is set to zero (0). The arguments MUST follow the
1963 command payload. See section 2.3.2.2 for definition of the
1966 o Command Identifier (2 bytes) - Identifies this command at the
1967 sender's end. The entity which replies to this command MUST
1968 set the value found from this field into the Command Payload
1969 used to send the reply to the sender. This way the sender
1970 can identify which command reply belongs to which originally
1971 sent command. What this field includes is implementation
1972 issue but it is RECOMMENDED that wrapping counter value is
1973 used in the field. Value zero (0) in this field means that
1974 no specific value is set.
1977 See [SILC4] for detailed description of different SILC commands,
1978 their arguments and their reply messages.
1984 2.3.14 Command Reply Payload
1986 Command Reply Payload is used to send replies to the commands. The
1987 Command Reply Payload is identical to the Command Payload thus see
1988 the upper section for the Command Payload specification.
1990 The entity which sends the reply packet MUST set the Command Identifier
1991 field in the reply packet's Command Payload to the value it received
1992 in the original command packet.
1994 See SILC Commands in [SILC4] for detailed description of different
1995 SILC commands, their arguments and their reply messages.
1999 2.3.15 Connection Auth Request Payload
2001 Client MAY send this payload to server to request the authentication
2002 method that must be used in authentication protocol. If client knows
2003 this information beforehand this payload is not necessary to be sent.
2004 Server performing authentication with another server MAY also send
2005 this payload to request the authentication method. If the connecting
2006 server already knows this information this payload is not necessary
2009 Server receiving this request MUST reply with same payload sending
2010 the mandatory authentication method. Algorithms that may be required
2011 to be used by the authentication method are the ones already
2012 established by the SILC Key Exchange protocol. See section Key
2013 Exchange Start Payload in [SILC3] for detailed information.
2015 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
2016 packet. It MUST NOT be sent in any other packet type. The following
2017 diagram represents the Connection Auth Request Payload.
2023 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
2024 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2025 | Connection Type | Authentication Method |
2026 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2030 Figure 18: Connection Auth Request Payload
2034 o Connection Type (2 bytes) - Indicates the type of the
2035 connection. The following connection types are defined:
2042 If any other type is found in this field the packet MUST be
2043 discarded and the authentication MUST be failed.
2045 o Authentication Method (2 bytes) - Indicates the authentication
2046 method to be used in the authentication protocol. The following
2047 authentication methods are defined:
2050 1 password (mandatory)
2051 2 public key (mandatory)
2053 If any other type is found in this field the packet MUST be
2054 discarded and the authentication MUST be failed. If this
2055 payload is sent as request to receive the mandatory
2056 authentication method this field MUST be set to zero (0),
2057 indicating that receiver should send the mandatory
2058 authentication method. The receiver sending this payload
2059 to the requesting party, MAY also set this field to zero (0)
2060 to indicate that authentication is not required. In this
2061 case authentication protocol still MUST be started but
2062 server is most likely to respond with SILC_PACKET_SUCCESS
2068 2.3.16 New ID Payload
2070 New ID Payload is a multipurpose payload. It is used to send newly
2071 created ID's from clients and servers. When client connects to server
2072 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
2073 packet, server replies with this packet by sending the created ID for
2074 the client. Server always creates the ID for the client.
2076 This payload is also used when server tells its router that new client
2077 has registered to the SILC network. In this case the server sends
2078 the Client ID of the client to the router. Similarly when router
2079 distributes information to other routers about the client in the SILC
2080 network this payload is used.
2082 Also, when server connects to router, router uses this payload to inform
2083 other routers about new server in the SILC network. However, every
2084 server (or router) creates their own ID's thus the ID distributed by
2085 this payload is not created by the distributor in this case. Servers
2086 create their own ID's. Server registers itself to the network by
2087 sending SILC_PACKET_NEW_SERVER to the router it connected to. The case
2088 is same when router connects to another router.
2090 However, this payload MUST NOT be used to send information about new
2091 channels. New channels are always distributed by sending the dedicated
2092 SILC_PACKET_NEW_CHANNEL packet.
2094 Thus, this payload is very important and used every time when some
2095 new entity is registered to the SILC network. Client MUST NOT send this
2096 payload. Both client and server (and router) MAY receive this payload.
2098 The packet uses generic ID Payload as New ID Payload. See section
2099 2.3.2.1 for generic ID Payload.
2103 2.3.17 New Client Payload
2105 When client is connected to the server, keys has been exchanged and
2106 connection has been authenticated client MUST register itself to the
2107 server. Client's first packet after key exchange and authentication
2108 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
2109 the relevant information about the connected user. Server creates a new
2110 client ID for the client when received this payload and sends it to the
2111 client in New ID Payload.
2113 This payload sends username and real name of the user on the remote host
2114 which is connected to the SILC server with SILC client. The server
2115 creates the client ID according the information sent in this payload.
2116 The nickname of the user becomes the username sent in this payload.
2117 However, client should call NICK command after sending this payload to
2118 set the real nickname of the user which is then used to create new
2121 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
2122 MUST NOT be sent in any other packet type. The following diagram
2123 represents the New Client Payload.
2140 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
2141 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2142 | Username Length | |
2143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2147 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2148 | Real Name Length | |
2149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2153 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2157 Figure 19: New Client Payload
2161 o Username Length (2 bytes) - Length of the Username field.
2163 o Username (variable length) - The username of the user on
2164 the host where connecting to the SILC server.
2166 o Real Name Length (2 bytes) - Length of the Real Name field.
2168 o Real Name (variable length) - The real name of the user
2169 on the host where connecting to the SILC server.
2174 2.3.18 New Server Payload
2176 This payload is sent by server when it has completed successfully both
2177 key exchange and connection authentication protocols. The server
2178 MUST register itself to the SILC Network by sending this payload.
2179 The first packet after these key exchange and authentication protocols
2180 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
2181 of the server that it has created by itself. It also includes a
2182 name of the server that is associated to the Server ID.
2184 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
2185 MUST NOT be sent in any other packet type. The following diagram
2186 represents the New Server Payload.
2195 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
2196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2197 | Server ID Length | |
2198 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2202 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2203 | Server Name Length | |
2204 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2208 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2212 Figure 20: New Server Payload
2216 o Server ID Length (2 bytes) - Length of the Server ID Data
2219 o Server ID Data (variable length) - The actual Server ID
2222 o Server Name Length (2 bytes) - Length of the server name
2225 o Server Name (variable length) - The server name.
2230 2.3.19 New Channel Payload
2232 Information about newly created channel is broadcasted to all routers
2233 in the SILC network by sending this packet payload. Channels are
2234 created by router of the cell. Server never creates channels unless
2235 it is a standalone server and it does not have router connection,
2236 in this case server acts as router. Normal server send JOIN command
2237 to the router (after it has received JOIN command from client) which
2238 then processes the command and creates the channel. Client MUST NOT
2239 send this packet. Server may send this packet to a router when it is
2240 announcing its existing channels to the router after it has connected
2243 The packet uses generic Channel Payload as New Channel Payload. See
2244 section 2.3.2.3 for generic Channel Payload. The Mode Mask field in the
2245 Channel Payload is the mode of the channel.
2249 2.3.20 Key Agreement Payload
2251 This payload is used by clients to request key negotiation between
2252 another client in the SILC Network. The key agreement protocol used
2253 is the SKE protocol. The result of the protocol, the secret key
2254 material, can be used for example as private message key between the
2255 two clients. This significantly adds security as the key agreement
2256 is performed outside the SILC network. The server and router MUST NOT
2259 The sender MAY tell the receiver of this payload the hostname and the
2260 port where the SKE protocol is running in the sender's end. The
2261 receiver MAY then initiate the SKE negotiation with the sender. The
2262 sender MAY also optionally not to include the hostname and the port
2263 of its SKE protocol. In this case the receiver MAY reply to the
2264 request by sending the same payload filled with the receiver's hostname
2265 and the port where the SKE protocol is running. The sender MAY then
2266 initiate the SKE negotiation with the receiver.
2268 This payload may be sent with SILC_PACKET_KEY_AGREEMENT and
2269 SILC_PACKET_FTP packet types. It MUST NOT be sent in any other packet
2270 types. The following diagram represents the Key Agreement Payload.
2276 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
2277 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2278 | Hostname Length | |
2279 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2283 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2285 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2289 Figure 21: Key Agreement Payload
2293 o Hostname Length (2 bytes) - Indicates the length of the
2296 o Hostname (variable length) - The hostname or IP address where
2297 the SKE protocol is running. The sender MAY fill this field
2298 when sending the payload. If the receiver sends this payload
2299 as reply to the request it MUST fill this field.
2301 o Port (4 bytes) - The port where the SKE protocol is bound.
2302 The sender MAY fill this field when sending the payload. If
2303 the receiver sends this payload as reply to the request it
2304 MUST fill this field. This is a 32 bit MSB first order value.
2308 After the key material has been received from the SKE protocol it is
2309 processed as the [SILC3] describes. If the key material is used as
2310 channel private key then the Sending Encryption Key, as defined in
2311 [SILC3] is used as the channel private key. Other key material must
2312 be discarded. The [SILC1] defines the way to use the key material if
2313 it is intended to be used as private message keys. Any other use for
2314 the key material is undefined.
2318 2.3.21 Resume Router Payload
2320 The payload may only be sent with SILC_PACKET_RESUME_ROUTER packet. It
2321 MUST NOT be sent in any other packet type. The Following diagram
2322 represents the Resume Router Payload.
2328 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
2329 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2330 | Type | Session ID |
2331 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2335 Figure 22: Resume Router Payload
2339 o Type (1 byte) - Indicates the type of the backup resume
2340 protocol packet. The type values are defined in [SILC1].
2342 o Session ID (1 bytes) - Indicates the session ID for the
2343 backup resume protocol. The sender of the packet sets this
2344 value and the receiver MUST set the same value in subsequent
2350 2.3.22 File Transfer Payload
2352 File Transfer Payload is used to perform file transfer protocol
2353 between two entities in the network. The actual file transfer
2354 protocol is always encapsulated inside the SILC Packet. The actual
2355 data stream is also sent peer to peer outside SILC network.
2357 When an entity, usually a client wishes to perform file transfer
2358 protocol with another client in the network, they perform Key Agreement
2359 protocol as described in the section 2.3.20 Key Agreement Payload and
2360 in [SILC3], inside File Transfer Payload. After the Key Agreement
2361 protocol has been performed the subsequent packets in the data stream
2362 will be protected using the new key material. The actual file transfer
2363 protocol is also initialized in this stage. All file transfer protocol
2364 packets are always encapsulated in the File Transfer Payload and
2365 protected with the negotiated key material.
2367 The payload may only be sent with SILC_PACKET_FTP packet. It MUST NOT
2368 be sent in any other packet type. The following diagram represents the
2369 File Transfer Payload.
2374 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
2375 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2381 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2385 Figure 23: File Transfer Payload
2389 o Type (1 byte) - Indicates the type of the file transfer
2390 protocol. The following file transfer protocols has been
2393 1 SSH File Transfer Protocol (SFTP) (mandatory)
2395 If zero (0) value or any unsupported file transfer protocol
2396 type is found in this field the packet must be discarded.
2397 The currently mandatory file transfer protocol is SFTP.
2398 The SFTP protocol is defined in [SFTP].
2400 o Data (variable length) - Arbitrary file transfer data. The
2401 contents and encoding of this field is dependent of the usage
2402 of this payload and the type of the file transfer protocol.
2403 When this payload is used to perform the Key Agreement
2404 protocol, this field include the Key Agreement Payload,
2405 as defined in the section 2.3.20 Key Agreement Payload.
2406 When this payload is used to send the actual file transfer
2407 protocol data, the encoding is defined in the corresponding
2408 file transfer protocol.
2413 2.3.23 Resume Client Payload
2415 This payload is used by client to resume its detached session in the
2416 SILC Network. A client is able to detach itself from the network by
2417 sending SILC_COMMAND_DETACH command to its server. The network
2418 connection to the client is lost but the client remains as valid
2419 client in the network. The client is able to resume the session back
2420 by sending this packet and including the old Client ID, and an
2421 Authentication Payload [SILC1] which the server uses to verify with
2422 the detached client's public key. This also implies that the
2423 mandatory authentication method is public key authentication.
2425 Server or router that receives this from the client also sends this,
2426 without the Authentication Payload, to routers in the network so that
2427 they know the detached client has resumed. Refer to the [SILC1] for
2428 detailed description how the detaching and resuming prodecure is
2431 The payload may only be sent with SILC_PACKET_RESUME CLIENT packet. It
2432 MUST NOT be sent in any other packet type. The following diagram
2433 represents the Resume Client Payload.
2438 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
2439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2440 | Client ID Length | |
2441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2447 ~ Authentication Payload ~
2449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2453 Figure 24: Resume Client Payload
2457 o Client ID Length (1 byte) - The length of the Client ID
2458 field not including any other field.
2460 o Client ID (variable length) - The detached client's Client
2461 ID. The client that sends this payload must know the Client
2464 o Authentication Payload (variable length) - The authentication
2465 payload that the server will verify with the detached client's
2466 public key. If the server doesn't know the public key, it must
2467 retrieve it for example with SILC_COMMAND_GETKEY command.
2475 ID's are extensively used in the SILC network to associate different
2476 entities. The following ID's has been defined to be used in the SILC
2482 When ever specific ID cannot be used this is used.
2486 Server ID to associate servers. See the format of
2491 Client ID to associate clients. See the format of
2496 Channel ID to associate channels. See the format of
2500 When encoding different IDs into the ID Payload, all fields are always
2501 in MSB first order. The IP address, port, and/or the random number
2502 are encoded in the MSB first order.
2506 2.5 Packet Encryption And Decryption
2508 SILC packets are encrypted almost entirely. Only small part of SILC
2509 header is not encrypted as described in section 5.2 SILC Packet Header.
2510 The SILC Packet header is the first part of a packet to be encrypted
2511 and it is always encrypted with the key of the next receiver of the
2512 packet. The data payload area of the packet is always entirely
2513 encrypted and it is usually encrypted with the next receiver's key.
2514 However, there are some special packet types and packet payloads
2515 that require special encryption process. These special cases are
2516 described in the next sections. First is described the normal packet
2521 2.5.1 Normal Packet Encryption And Decryption
2523 Normal SILC packets are encrypted with the session key of the next
2524 receiver of the packet. The entire SILC Packet header and the packet
2525 data payload is is also encrypted with the same key. Padding of the
2526 packet is also encrypted always with the session key, also in special
2527 cases. Computed MAC of the packet must not be encrypted.
2529 Decryption process in these cases are straightforward. The receiver
2530 of the packet MUST first decrypt the SILC Packet header, or some parts
2531 of it, usually first 16 bytes of it. Then the receiver checks the
2532 packet type from the decrypted part of the header and can determine
2533 how the rest of the packet must be decrypted. If the packet type is
2534 any of the special cases described in the following sections the packet
2535 decryption is special. If the packet type is not among those special
2536 packet types rest of the packet can be decrypted with the same key.
2538 With out a doubt, this sort of decryption processing causes some
2539 overhead to packet decryption, but never the less, is required.
2543 2.5.2 Channel Message Encryption And Decryption
2545 Channel Messages (Channel Message Payload) are always encrypted with
2546 the channel specific key. However, the SILC Packet header is not
2547 encrypted with that key. As in normal case, the header is encrypted
2548 with the key of the next receiver of the packet, who ever that might
2549 be. Note that in this case the encrypted data area is not touched
2550 at all; it MUST NOT be re-encrypted with the session key.
2552 Receiver of a channel message, who ever that is, is REQUIRED to decrypt
2553 the SILC Packet header to be able to even recognize the packet to be as
2554 channel message. This is same procedure as for normal SILC packets.
2555 As the receiver founds the packet to be channel message, rest of the
2556 packet processing is special. Rest of the SILC Packet header is
2557 decrypted with the same session key along with the padding of the
2558 packet. After that the packet is protected with the channel specific
2559 key and thus can be decrypted only if the receiver is the client on
2560 the channel. See section 2.7 Packet Padding Generation for more
2561 information about padding on special packets.
2563 If the receiver of the channel message is router which is routing the
2564 message to another router then it MUST decrypt the Channel Message
2565 payload. Between routers (that is, between cells) channel messages
2566 are protected with session keys shared between the routers. This
2567 causes another special packet processing for channel messages. If
2568 the channel message is received from another router then the entire
2569 packet, including Channel Message payload, MUST be encrypted with the
2570 session key shared between the routers. In this case the packet
2571 decryption process is as with normal SILC packets. Hence, if the
2572 router is sending channel message to another router the Channel
2573 Message payload MUST have been decrypted and MUST be re-encrypted
2574 with the session key shared between the another router. In this
2575 case the packet encryption is as with any normal SILC packet.
2577 It must be noted that this is only when the channel messages are sent
2578 from router to another router. In all other cases the channel
2579 message encryption and decryption is as described above. This
2580 different processing of channel messages with router to router
2581 connection is because channel keys are cell specific. All cells have
2582 their own channel keys thus the channel message traveling from one
2583 cell to another MUST be protected as it would be any normal SILC
2586 If the SILC_CMODE_PRIVKEY channel mode has been set for the channel
2587 then the router cannot decrypt the packet as it does not know the
2588 private key. In this case the entire packet MUST be encrypted with
2589 the session key and sent to the router. The router receiving the
2590 packet MUST check the channel mode and decrypt the packet accordingly.
2594 2.5.3 Private Message Encryption And Decryption
2596 By default, private message in SILC are protected by session keys.
2597 In this case the private message encryption and decryption process is
2598 equivalent to normal packet encryption and decryption.
2600 However, private messages MAY be protected with private message key
2601 which causes the packet to be special packet. The procedure in this
2602 case is very much alike to channel packets. The actual private message
2603 is encrypted with the private message key and other parts of the
2604 packet is encrypted with the session key. See 2.7 Packet Padding
2605 Generation for more information about padding on special packets.
2607 The difference from channel message processing is that server or router
2608 en route never decrypts the actual private message, as it does not
2609 have the key to do that. Thus, when sending packets between router
2610 the processing is same as in any other case as well; the packet's header
2611 and padding is protected by the session key and the data area is not
2614 The true receiver of the private message, client, that is, is able
2615 to decrypt the private message as it shares the key with the sender
2620 2.6 Packet MAC Generation
2622 Data integrity of a packet is protected by including a message
2623 authentication code (MAC) at the end of the packet. The MAC is computed
2624 from shared secret MAC key, that is established by the SILC Key Exchange
2625 protocol, from packet sequence number, and from the original contents
2626 of the packet. The MAC is always computed before the packet is
2627 encrypted, although after it is compressed if compression is used.
2629 The MAC is computed from entire packet. Every bit of data in the packet,
2630 including SILC Packet Header is used in the MAC computing. This way
2631 the entire packet becomes authenticated.
2633 If the packet is special packet MAC is computed from the entire packet
2634 but part of the packet may be encrypted before the MAC is computed.
2635 This is case, for example, with channel messages where the message data
2636 is encrypted with key that server may not now. In this case the MAC
2637 has been computed from the encrypted data.
2639 Hence, packet's MAC generation is as follows:
2641 mac = MAC(key, sequence number | SILC packet)
2643 The MAC key is negotiated during the SKE protocol. The sequence number
2644 is a 32 bit MSB first value starting from zero for first packet and
2645 increasing for subsequent packets, finally wrapping after 2^32 packets.
2646 The value is never reset, not even after rekey has been performed. Note
2647 that the sequence number is incremented only when MAC is computed for a
2648 packet. If packet is not encrypted and MAC is not computed then the
2649 sequence number is not incremented. Hence, the sequence number is zero
2650 for first encrypted packet.
2652 See [SILC1] for defined and allowed MAC algorithms.
2656 2.7 Packet Padding Generation
2658 Padding is needed in the packet because the packet is encrypted. It
2659 MUST always be multiple by eight (8) or multiple by the block size
2660 of the cipher, which ever is larger. The padding is always encrypted.
2662 For normal packets the padding is added after the SILC Packet Header
2663 and between the Data Payload area. The padding for normal packets
2664 may be calculated as follows:
2667 padding length = 16 - (packet_length mod block_size)
2670 The `block_size' is the block size of the cipher. The maximum padding
2671 length is 128 bytes, and minimum is 1 byte. The above algorithm calculates
2672 the padding to the next block size, and always returns the padding
2673 length between 1 - 16 bytes. However, implementations may add padding
2674 up to 128 bytes. For example packets that include a passphrase or a
2675 password for authentication purposes SHOULD pad the packet up to the
2676 maximum padding length.
2678 For special packets the padding calculation is different as special
2679 packets may be encrypted differently. In these cases the encrypted
2680 data area MUST already be multiple by the block size thus in this case
2681 the padding is calculated only for SILC Packet Header, not for any
2682 other area of the packet. The same algorithm works in this case as
2683 well, except that the `packet length' is now the SILC Packet Header
2686 The padding MUST be random data, preferably, generated by
2687 cryptographically strong random number generator.
2691 2.8 Packet Compression
2693 SILC Packets MAY be compressed. In this case the data payload area
2694 is compressed and all other areas of the packet MUST remain as they
2695 are. After compression is performed for the data area, the length
2696 field of Packet Header MUST be set to the compressed length of the
2699 The compression MUST always be applied before encryption. When
2700 the packet is received and decrypted the data area MUST be decompressed.
2701 Note that the true sender of the packet MUST apply the compression and
2702 the true receiver of the packet MUST apply the decompression. Any
2703 server or router en route MUST NOT decompress the packet.
2709 The sender of the packet MUST assemble the SILC Packet Header with
2710 correct values. It MUST set the Source ID of the header as its own
2711 ID, unless it is forwarding the packet. It MUST also set the Destination
2712 ID of the header to the true destination. If the destination is client
2713 it will be Client ID, if it is server it will be Server ID and if it is
2714 channel it will be Channel ID.
2716 If the sender wants to compress the packet it MUST apply the
2717 compression now. Sender MUST also compute the padding as described
2718 in above sections. Then sender MUST compute the MAC of the packet.
2720 Then sender MUST encrypt the packet as has been described in above
2721 sections according whether the packet is normal packet or special
2722 packet. The computed MAC MUST NOT be encrypted.
2726 2.10 Packet Reception
2728 On packet reception the receiver MUST check that all fields in the
2729 SILC Packet Header are valid. It MUST check the flags of the
2730 header and act accordingly. It MUST also check the MAC of the packet
2731 and if it is to be failed the packet MUST be discarded. Also if the
2732 header of the packet includes any bad fields the packet MUST be
2735 See above sections on the decryption process of the received packet.
2737 The receiver MUST also check that the ID's in the header are valid
2738 ID's. Unsupported ID types or malformed ID's MUST cause packet
2739 rejection. The padding on the reception is always ignored.
2741 The receiver MUST also check the packet type and start parsing the
2742 packet according to the type. However, note the above sections on
2743 special packet types and their parsing.
2749 Routers are the primary entities in the SILC network that takes care
2750 of packet routing. However, normal servers routes packets as well, for
2751 example, when they are routing channel message to the local clients.
2752 Routing is quite simple as every packet tells the true origin and the
2753 true destination of the packet.
2755 It is still RECOMMENDED for routers that has several routing connections
2756 to create route cache for those destinations that has faster route than
2757 the router's primary route. This information is available for the router
2758 when other router connects to the router. The connecting party then
2759 sends all of its locally connected clients, servers and channels. These
2760 informations helps to create the route cache. Also, when new channels
2761 are created to a cell its information is broadcasted to all routers
2762 in the network. Channel ID's are based on router's ID thus it is easy
2763 to create route cache based on these informations. If faster route for
2764 destination does not exist in router's route cache the packet MUST be
2765 routed to the primary route (default route).
2767 However, there are some issues when routing channel messages to group
2768 of users. Routers are responsible of routing the channel message to
2769 other routers, local servers and local clients as well. Routers MUST
2770 send the channel message to only one router in the network, preferrably
2771 to the shortest route to reach the channel users. The message can be
2772 routed into either upstream or downstream. After the message is sent
2773 to a router in the network it MUST NOT be sent to any other router in
2774 either same route or other route. The message MUST NOT be routed to
2775 the router it came from.
2777 When routing for example private messages they should be routed to the
2778 shortest route always to reach the destination client as fast as possible.
2780 For server which receives a packet to be routed to its locally connected
2781 client the server MUST check whether the particular packet type is
2782 allowed to be routed to the client. Not all packets may be sent by
2783 some odd entity to client that is indirectly connected to the sender.
2784 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2785 entities and sending packets to them. The section mentions the packets
2786 that may be sent to indirectly connected entities. It is clear that
2787 server cannot send, for example, disconnect packet to client that is not
2788 directly connected to the server.
2790 Routers form a ring in the SILC network. However, routers may have other
2791 direct connections to other routers in the network too. This can cause
2792 interesting routing problems in the network. Since the network is a ring,
2793 the packets usually should be routed into clock-wise direction, or if it
2794 cannot be used then always counter clock-wise (primary route) direction.
2795 Problems may arise when a faster direct route exists and router is routing
2796 a channel message. Currently channel messages must be routed either
2797 in upstream or downstream, they cannot be routed to other direct routes.
2798 The SILC protocol should have a shortest path discovery protocol, and some
2799 existing routing protocol, that can handle a ring network with other
2800 direct routes inside the ring (so called hybrid ring-mesh topology),
2801 MAY be defined to be used with the SILC protocol. Additional
2802 specifications MAY be written on the subject to permeate this
2807 2.12 Packet Broadcasting
2809 SILC packets MAY be broadcasted in SILC network. However, only router
2810 server may send or receive broadcast packets. Client and normal server
2811 MUST NOT send broadcast packets and they MUST ignore broadcast packets
2812 if they receive them. Broadcast packets are sent by setting Broadcast
2813 flag to the SILC packet header.
2815 Broadcasting packets means that the packet is sent to all routers in
2816 the SILC network, except to the router that sent the packet. The router
2817 receiving broadcast packet MUST send the packet to its primary route.
2818 The fact that SILC routers may have several router connections can
2819 cause problems, such as race conditions inside the SILC network, if
2820 care is not taken when broadcasting packets. Router MUST NOT send
2821 the broadcast packet to any other route except to its primary route.
2823 If the primary route of the router is the original sender of the packet
2824 the packet MUST NOT be sent to the primary route. This may happen
2825 if router has several router connections and some other router uses
2826 the router as its primary route.
2828 Routers use broadcast packets to broadcast for example information
2829 about newly registered clients, servers, channels etc. so that all the
2830 routers may keep these informations up to date.
2834 3 Security Considerations
2836 Security is central to the design of this protocol, and these security
2837 considerations permeate the specification. Common security considerations
2838 such as keeping private keys truly private and using adequate lengths for
2839 symmetric and asymmetric keys must be followed in order to maintain the
2840 security of this protocol.
2846 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2847 Protocol Specification", Internet Draft, April 2001.
2849 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2850 Protocols", Internet Draft, April 2001.
2852 [SILC4] Riikonen, P., "SILC Commands", Internet Draft, April 2001.
2854 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2857 [IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
2860 [IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
2863 [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
2866 [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
2869 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2872 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2875 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2878 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2879 Infrastructure, Certificate and CRL Profile", RFC 2459,
2882 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2883 John Wiley & Sons, New York, NY, 1996.
2885 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2888 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2889 RFC 2412, November 1998.
2891 [ISAKMP] Maughan D., et al, "Internet Security Association and
2892 Key Management Protocol (ISAKMP)", RFC 2408, November
2895 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2896 (IKE)", RFC 2409, November 1998.
2898 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2899 Authentication", RFC 2104, February 1997.
2901 [PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
2902 Specifications, Version 2.0", RFC 2437, October 1998.
2904 [RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate
2905 Requirement Levels", BCP 14, RFC 2119, March 1997.
2907 [SFTP] Ylonen T., and Lehtinen S., "Secure Shell File Transfer
2908 Protocol", Internet Draft, March 2001.
2910 [RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO
2911 10646", RFC 2279, January 1998.
2918 Snellmanninkatu 34 A 15
2922 EMail: priikone@iki.fi
2924 This Internet-Draft expires XXX