8 .ds RF FORMFEED[Page %]
17 Network Working Group P. Riikonen
19 draft-riikonen-silc-pp-01.txt 6 October 2000
26 <draft-riikonen-silc-pp-01.txt>
31 This document is an Internet-Draft and is in full conformance with
32 all provisions of Section 10 of RFC 2026. Internet-Drafts are
33 working documents of the Internet Engineering Task Force (IETF), its
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37 Internet-Drafts are draft documents valid for a maximum of six months
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39 time. It is inappropriate to use Internet-Drafts as reference
40 material or to cite them other than as "work in progress."
42 The list of current Internet-Drafts can be accessed at
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45 The list of Internet-Draft Shadow Directories can be accessed at
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48 The distribution of this memo is unlimited.
54 This memo describes a Packet Protocol used in the Secure Internet Live
55 Conferencing (SILC) protocol specified in the Secure Internet Live
56 Conferencing, Protocol Specification Internet Draft [SILC1]. This
57 protocol describes the packet types and packet payloads which defines
58 the contents of the packets. The protocol provides secure binary packet
59 protocol that assures that the contents of the packets are secured and
74 1 Introduction .................................................. 3
75 2 SILC Packet Protocol .......................................... 4
76 2.1 SILC Packet ............................................... 4
77 2.2 SILC Packet Header ........................................ 5
78 2.3 SILC Packet Types ......................................... 7
79 2.3.1 SILC Packet Payloads ................................ 15
80 2.3.2 Generic payloads .................................... 16
81 2.3.2.1 ID Payload .................................. 16
82 2.3.2.2 Argument Payload ............................ 16
83 2.3.3 Disconnect Payload .................................. 17
84 2.3.4 Success Payload ..................................... 18
85 2.3.5 Failure Payload ..................................... 18
86 2.3.6 Reject Payload ...................................... 19
87 2.3.7 Notify Payload ...................................... 20
88 2.3.8 Error Payload ....................................... 21
89 2.3.9 Channel Message Payload ............................. 22
90 2.3.10 Channel Key Payload ................................ 24
91 2.3.11 Private Message Payload ............................ 26
92 2.3.12 Private Message Key Payload ........................ 27
93 2.3.13 Command Payload .................................... 28
94 2.3.14 Command Reply Payload .............................. 29
95 2.3.15 Connection Auth Request Payload .................... 29
96 2.3.16 New ID Payload ..................................... 30
97 2.3.17 New ID List Payload ................................ 31
98 2.3.18 New Client Payload ................................. 31
99 2.3.19 New Server Payload ................................. 32
100 2.3.20 New Channel Payload ................................ 33
101 2.3.21 New Channel User Payload ........................... 34
102 2.3.22 New Channel List Payload ........................... 35
103 2.3.23 New Channel User List Payload ...................... 36
104 2.3.24 Replace ID Payload ................................. 36
105 2.3.25 Remove ID Payload .................................. 37
106 2.3.26 Remove Channel User Payload ........................ 38
107 2.3.27 Set Mode Payload ................................... XXX
108 2.4 SILC ID Types ............................................. 39
109 2.5 Packet Encryption And Decryption .......................... 39
110 2.5.1 Normal Packet Encryption And Decryption ............. 39
111 2.5.2 Channel Message Encryption And Decryption ........... 40
112 2.5.3 Private Message Encryption And Decryption ........... 41
113 2.6 Packet MAC Generation ..................................... 41
114 2.7 Packet Padding Generation ................................. 42
115 2.8 Packet Compression ........................................ 42
116 2.9 Packet Sending ............................................ 43
117 2.10 Packet Reception ......................................... 43
118 2.11 Packet Routing ........................................... 44
119 2.12 Packet Forwarding ........................................ 44
120 2.13 Packet Broadcasting ...................................... 45
121 2.14 Packet Tunneling ......................................... 45
122 3 Security Considerations ....................................... 46
123 4 References .................................................... 46
124 5 Author's Address .............................................. 47
130 Figure 1: Typical SILC Packet
131 Figure 2: SILC Packet Header
133 Figure 4: Argument Payload
134 Figure 5: Disconnect Payload
135 Figure 6: Success Payload
136 Figure 7: Failure Payload
137 Figure 8: Reject Payload
138 Figure 9: Notify Payload
139 Figure 10: Error Payload
140 Figure 11: Channel Message Payload
141 Figure 12: Channel Key Payload
142 Figure 13: Private Message Payload
143 Figure 14: Private Message Key Payload
144 Figure 15: Command Payload
145 Figure 16: Connection Auth Request Payload
146 Figure 17: New Client Payload
147 Figure 18: New Server Payload
148 Figure 19: New Channel Payload
149 Figure 20: New Channel User Payload
150 Figure 21: Replace ID Payload
151 Figure 22: Remove Channel User Payload
152 Figure 23: Set Mode Payload
158 This document describes a Packet Protocol used in the Secure Internet
159 Live Conferencing (SILC) protocol specified in the Secure Internet Live
160 Conferencing, Protocol Specification Internet Draft [SILC1]. This
161 protocol describes the packet types and packet payloads which defines
162 the contents of the packets. The protocol provides secure binary packet
163 protocol that assures that the contents of the packets are secured and
166 The basis of SILC protocol relies in the SILC packets and it is with
167 out a doubt the most important part of the protocol. It is also probably
168 the most complicated part of the protocol. Packets are used all the
169 time in the SILC network to send messages, commands and other information.
170 All packets in SILC network are always encrypted and their integrity
171 is assured by computed MACs. The protocol defines several packet types
172 and packet payloads. Each packet type usually has a specific packet
173 payload that actually defines the contents of the packet. Each packet
174 also includes a default SILC Packet Header that provides sufficient
175 information about the origin of the packet and destination of the
180 2 SILC Packet Protocol
185 SILC packets deliver messages from sender to receiver securely by
186 encrypting important fields of the packet. The packet consists of
187 default SILC Packet Header, Padding, Packet Payload data, and, packet
190 The following diagram illustrates typical SILC packet.
195 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
196 | n bytes | 1 - n bytes | n bytes | n bytes
197 | SILC Header | Padding | Data Payload | MAC
198 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
202 Figure 1: Typical SILC Packet
205 SILC Header is always the first part of the packet and its purpose
206 is to provide information about the packet. It provides for example
207 the packet type, origin of the packet and the destination of the packet.
208 The header is variable in length and first two (2) bytes of the
209 header (thus first two bytes of the packet) are not encrypted. The
210 first two (2) bytes are the length of the packet which is not encrypted.
211 See following section for description of SILC Packet header. Packets
212 without SILC header or with malformed SILC header must be dropped.
214 Padding follows the packet header. The purpose of the padding is to
215 make the packet multiple by eight (8) or by the block size of the
216 cipher used in the encryption, which ever is larger. The maximum
217 length of padding is currently 16 bytes. The padding is always
220 Data payload area follows padding and it is the actual data of the
221 packet. The packet data is the packet payloads defined in this
222 protocol. The data payload area is always encrypted.
224 The last part of SILC packet is the packet MAC that assures the
225 integrity of the packet. The MAC is always computed from the packet
226 before the encryption is applied to the packet. If compression is used
227 in the packet the MAC is computed after the compression has been
228 applied. The compression, on the other hand, is always applied before
231 All fields in all packet payloads are always in MSB (most significant
236 2.2 SILC Packet Header
238 The default SILC packet header is applied to all SILC packets and it is
239 variable in length. The purpose of SILC Packet header is to provide
240 detailed information about the packet. The receiver of the packet uses
241 the packet header to parse the packet and gain other relevant parameters
244 Following diagram represents the default SILC header format.
245 (*) indicates that this field is never encrypted. Other fields are
252 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
254 | Payload Length * | Flags | Packet Type |
255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
256 | Source ID Length | Destination ID Length |
257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
273 Figure 2: SILC Packet Header
277 o Payload Length (2 bytes) - Is the length of the packet
278 not including the padding of the packet. This field must
279 not be encrypted but must always be authenticated.
281 o Flags (1 byte) - Indicates flags to be used in packet
282 processing. Several flags may be set by ORing the flags
285 Following flags are reserved for this field:
290 In this case the field is ignored.
293 Private Message Key 0x01
295 Indicates that the packet must include private
296 message that is encrypted using private key set by
297 client. Servers does not know anything about this
298 key and this causes that the private message is
299 not handled by the server at all, it is just
300 passed along. See section 2.5.3 Private Message
301 Encryption And Decryption for more information.
306 Marks the packet to be forwarded. Some specific
307 packet types may be forwarded. Receiver of packet
308 with this flag set must not forward the packet any
309 further. See section 2.12 Packet Forwarding for
310 description of packet forwarding.
315 Marks the packet to be broadcasted. Client cannot
316 send broadcast packet and normal server cannot send
317 broadcast packet. Only router server may send broadcast
318 packet. The router receiving of packet with this flag
319 set must send (broadcast) the packet to its primary
320 route. If router has several router connections the
321 packet may be sent only to the primary route. See
322 section 2.13 Packet Broadcasting for description of
328 Marks that the packet is tunneled. Tunneling means
329 that extra SILC Packet Header has been applied to the
330 original packet. The outer header has this flag
331 set. See section 2.14 Packet Tunneling for more
337 o Packet Type (1 byte) - Is the type of the packet. Receiver
338 uses this field to parse the packet. See section 2.3
339 SILC Packets for list of defined packet types.
341 o Source ID Length (2 bytes) - Indicates the length of the
342 Source ID field in the header, not including this or any
345 o Destination ID Length (2 bytes) - Indicates the length of the
346 Destination ID field in the header, not including this or
349 o Src ID Type (1 byte) - Indicates the type of ID in the
350 Source ID field. See section 2.4 SILC ID Types for
353 o Source ID (variable length) - The actual source ID that
354 indicates who is the original sender of the packet.
356 o Dst ID Type (1 byte) - Indicates the type of ID in the
357 Destination ID field. See section 2.4 SILC ID Types for
360 o Destination ID (variable length) - The actual source ID that
361 indicates who is the end receiver of the packet.
365 2.3 SILC Packet Types
367 SILC packet types defines the contents of the packet and it is used by
368 the receiver to parse the packet. The packet type is 8 bits, as a one
369 byte, in length. The range for the packet types are from 0 - 255,
370 where 0 is never sent and 255 is currently reserved for future
371 extensions and must not be defined to any other purpose. Every SILC
372 specification compliant implementation should support all of these packet
375 The below list of the SILC Packet types includes reference to the packet
376 payload as well. Packet payloads are the actual packet, that is, the data
377 that the packet consists of. Each packet type defines packet payload
378 which usually may only be sent with the specific packet type.
380 Most of the packets are packets that must be destined directly to entity
381 that is connected to the sender. It is not allowed, for example, for
382 router to send disconnect packet to client that is not directly connected
383 to the router. However, there are some special packet types that may
384 be destined to some entity that the sender has not direct connection
385 with. These packets are for example private message packets, channel
386 message packets, command packets and some other packets that may be
387 broadcasted in the SILC network. If the packet is allowed to be sent to
388 indirectly connected entity it is mentioned separately in the packet
389 description (unless it is obvious as in private and channel message
390 packets). Other packets must not be sent or accepted, if sent, to
391 indirectly connected entities.
393 List of SILC Packet types are defined as follows.
398 This type is reserved and it is never sent.
401 1 SILC_PACKET_DISCONNECT
403 This packet is sent to disconnect the remote end. Reason of
404 the disconnection is sent inside the packet payload. Client
405 usually does not send this packet.
407 Payload of the packet: See section 2.3.3 Disconnect Payload
410 2 SILC_PACKET_SUCCESS
412 This packet is sent upon successful execution of some protocol.
413 The status of the success is sent in the packet.
415 Payload of the packet: See section 2.3.4 Success Payload
418 3 SILC_PACKET_FAILURE
420 This packet is sent upon failure of some protocol. The status
421 of the failure is sent in the packet.
423 Payload of the packet: See section 2.3.5 Failure Payload
428 This packet may be sent upon rejection of some protocol.
429 The status of the rejection is sent in the packet.
431 Payload of the packet: See section 2.3.6 Reject Payload
436 This packet is used to send notify message, usually from
437 server to client, although it may be sent from server to another
438 server as well. Client never sends this packet. Server may
439 send this packet to channel as well when the packet is
440 distributed to all clients on the channel.
442 Payload of the packet: See section 2.3.7 Notify Payload.
447 This packet is sent when an error occurs. Server may
448 send this packet. Client never sends this packet. The
449 client may entirely ignore the packet, however, server is
450 most likely to take action anyway. This packet may be sent
451 to entity that is indirectly connected to the sender.
453 Payload of the packet: See section 2.3.8 Error Payload.
456 7 SILC_PACKET_CHANNEL_MESSAGE
458 This packet is used to send messages to channels. The packet
459 includes Channel ID of the channel and the actual message to
460 the channel. Messages sent to the channel are always protected
461 by channel specific keys. Channel Keys are distributed by
462 SILC_PACKET_CHANNEL_KEY packet.
464 Payload of the packet: See section 2.3.9 Channel Message
468 8 SILC_PACKET_CHANNEL_KEY
470 This packet is used to distribute new key for particular
471 channel. Each channel has their own independent keys that
472 is used to protect the traffic on the channel. Only server
473 may send this packet. This packet may be sent to entity
474 that is indirectly connected to the sender.
476 Payload of the packet: See section 2.3.10 Channel Key Payload
479 9 SILC_PACKET_PRIVATE_MESSAGE
481 This packet is used to send private messages from client
482 to another client. By default, private messages are protected
483 by session keys established by normal key exchange protocol.
484 However, it is possible to use specific key to protect private
485 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
486 agree the key with the remote client. Pre-shared key may be
487 used as well if both of the client knows it, however, it needs
488 to be agreed outside SILC. See more of this in [SILC1].
490 Payload of the packet: See section 2.3.11 Private Message
494 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
496 This packet is used to agree about a key to be used to protect
497 the private messages between two clients. If this is not sent
498 the normal session key is used to protect the private messages
499 inside SILC network. Agreeing to use specific key to protect
500 private messages adds security, as no server between the two
501 clients will be able to decrypt the private message. However,
502 servers inside SILC network are considered to be trusted, thus
503 using normal session key to protect private messages does not
504 degree security. Whether to agree to use specific keys by
505 default or to use normal session keys by default, is
506 implementation specific issue. See more of this in [SILC1].
508 Payload of the packet: See section 2.3.12 Private Message
512 11 SILC_PACKET_COMMAND
514 This packet is used to send commands from client to server.
515 Server may send this packet to other servers as well. All
516 commands are listed in their own section SILC Command Types
517 in [SILC1]. The contents of this packet is command specific.
518 This packet may be sent to entity that is indirectly connected
521 Payload of the packet: See section 2.3.13 Command Payload
524 12 SILC_PACKET_COMMAND_REPLY
526 This packet is send as reply to the SILC_PACKET_COMMAND packet.
527 The contents of this packet is command specific. This packet
528 maybe sent to entity that is indirectly connected to the sender.
530 Payload of the packet: See section 2.3.14 Command Reply
531 Payload and section 2.3.13 Command
535 13 SILC_PACKET_KEY_EXCHANGE
537 This packet is used to start SILC Key Exchange Protocol,
538 described in detail in [SILC3].
540 Payload of the packet: Payload of this packet is described
541 in the section SILC Key Exchange
542 Protocol and its sub sections in
546 14 SILC_PACKET_KEY_EXCHANGE_1
548 This packet is used as part of the SILC Key Exchange Protocol.
550 Payload of the packet: Payload of this packet is described
551 in the section SILC Key Exchange
552 Protocol and its sub sections in
556 15 SILC_PACKET_KEY_EXCHANGE_2
558 This packet is used as part of the SILC Key Exchange Protocol.
560 Payload of the packet: Payload of this packet is described
561 in the section SILC Key Exchange
562 Protocol and its sub sections in
566 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
568 This packet is used to request the authentication method to
569 be used in the SILC Connection Authentication Protocol. If
570 initiator of the protocol does not know the mandatory
571 authentication method this packet is used to determine it.
573 The party receiving this payload must respond with the same
574 packet including the mandatory authentication method.
576 Payload of the packet: See section 2.3.15 Connection Auth
580 17 SILC_PACKET_CONNECTION_AUTH
582 This packet is used to start and perform the SILC Connection
583 Authentication Protocol. This protocol is used to authenticate
584 the connecting party. The protocol is described in detail in
587 Payload of the packet: Payload of this packet is described
588 in the section SILC Authentication
589 Protocol and it sub sections in [SILC].
592 18 SILC_PACKET_NEW_ID
594 This packet is used to distribute new ID's from server to
595 router and from router to all routers in the SILC network.
596 This is used when for example new client is registered to
597 SILC network. The newly created ID's of these operations are
598 distributed by this packet. Only server may send this packet,
599 however, client must be able to receive this packet.
601 Payload of the packet: See section 2.3.16 New ID Payload
604 19 SILC_PACKET_NEW_ID_LIST
606 This packet is used to distribute list of new ID's from
607 server to routers. This is equivalent to previous packet
608 type except that it may include several ID's. Client must
609 not send this packet.
611 Payload of the packet: See section 2.3.17 New ID List
615 20 SILC_PACKET_NEW_CLIENT
617 This packet is used by client to register itself to the
618 SILC network. This is sent after key exchange and
619 authentication protocols has been completed. Client sends
620 various information about itself in this packet.
622 Payload of the packet: See section 2.3.18 New Client Payload
625 21 SILC_PACKET_NEW_SERVER
627 This packet is used by server to register itself to the
628 SILC network. This is sent after key exchange and
629 authentication protocols has been completed. Server sends
630 this to the router it connected to, or, if router was
631 connecting, to the connected router. Server sends
632 its Server ID and other information in this packet.
633 Client must not send or receive this packet.
635 Payload of the packet: See section 2.3.19 New Server Payload
638 22 SILC_PACKET_NEW_CHANNEL
640 This packet is used to notify routers about newly created
641 channel. Channels are always created by the router and it must
642 notify other routers about the created channel. Router sends
643 this packet to its primary route. Client must not send this
644 packet. This packet maybe sent to entity that is indirectly
645 connected to the sender.
647 Payload of the packet: See section 2.3.20 New Channel Payload
650 23 SILC_PACKET_NEW_CHANNEL_USER
652 This packet is used to notify routers about new user on channel.
653 The packet is sent after user has joined to the channel. Server
654 may send this packet to its router and router may send this to
655 its primary router. Client must not send this packet. This
656 packet maybe sent to entity that is indirectly connected to
659 When received, the server or router must distribute
660 SILC_NOTIFY_TYPE_JOIN to local clients on the channel.
662 Payload of the packet: See section 2.3.21 New Channel User
666 24 SILC_PACKET_NEW_CHANNEL_LIST
668 This packet is used to distribute list of created channels
669 from server to routers. This is equivalent to the packet
670 SILC_PACKET_NEW_CHANNEL except that it may include several
671 payloads. Client must not send this packet.
673 Payload of the packet: See section 2.3.22 New Channel List
677 25 SILC_PACKET_NEW_CHANNEL_USER_LIST
679 This packet is used to distribute list of users on specific
680 channel from server to routers. This is equivalent to the
681 packet SILC_PACKET_NEW_CHANNEL_USER except that it may
682 include several payloads. Client must not send this packet.
684 When received, the server or router must distribute
685 SILC_NOTIFY_TYPE_JOIN to local clients on the channel.
687 Payload of the packet: See section 2.3.23 New Channel User
691 26 SILC_PACKET_REPLACE_ID
693 This packet is used to replace old ID with new ID sent in
694 the packet payload. For example, when client changes its
695 nickname new ID is created and this packet can be used to
696 distribute the new ID and the old ID is removed when it is
697 send in the packet. Client cannot send or receive this
698 packet. This packet maybe sent to entity that is indirectly
699 connected to the sender.
701 When received and the replaced ID is Client ID the server or
702 router must distribute SILC_NOTIFY_TYPE_NICK_CHANGE to the
703 local clients on the channels (if any) of the client whose
704 ID was changed. However, the notify type must be sent only
707 Payload of the packet: See section 2.3.24 Replace ID Payload
710 27 SILC_PACKET_REMOVE_ID
712 This packet is used to removed ID. For example, when client
713 exits SILC network its ID is removed. Client must not send
714 this packet. This packet maybe sent to entity that is
715 indirectly connected to the sender.
717 When received and the removed ID is Client ID the server or
718 router must distribute SILC_NOTIFY_TYPE_SIGNOFF to the
719 local clients on the channels (if any) of the client whose
720 ID was removed. However, the notify type must be sent only
723 Payload of the packet: See section 2.3.25 Remove ID Payload
726 28 SILC_PACKET_REMOVE_CHANNEL_USER
728 This packet is used to remove user from a channel. This is
729 used by router to notify other routers in the network that a
730 client has left a channel. This packet maybe sent to entity
731 that is indirectly connected to the sender.
733 When received, the server or router must distribute
734 SILC_NOTIFY_TYPE_LEAVE to local clients on the channel.
736 Payload of the packet: See section 2.3.26 Remove Channel User
742 This packet is used to indicate that re-key must be performed
743 for session keys. See section Session Key Regeneration in
744 [SILC1] for more information. This packet does not have
748 30 SILC_PACKET_REKEY_DONE
750 This packet is used to indicate that re-key is performed and
751 new keys must be used hereafter. This is sent only if re-key
752 was done without PFS option. If PFS is set, this is not sent
753 as SILC Key Exchange protocol is executed. This packet does
757 31 SILC_PACKET_SET_MODE
759 This packet is used by servers and routers to inform each
760 other about changed modes. When channel's and client'c channel
761 mode is changed this packet is used to distribute the information
762 to all routers in the network. Server can send this packet but
763 must not receive it. Router can send and receive this packet.
764 Client must not send or receive this packet.
766 Payload of the packet: See section 2.3.27 Set Mode Payload
769 32 SILC_PACKET_HEARTBEAT
771 This packet is used by clients, servers and routers to keep the
772 connection alive. It is recommended that all servers implement
773 keepalive actions and perform it to both direction in a link.
774 This packet does not have a payload.
779 Currently undefined commands.
784 These packet types are reserved for private use and they will not
785 be defined by this document.
790 This type is reserved for future extensions and currently it
796 2.3.1 SILC Packet Payloads
798 All payloads resides in the main data area of the SILC packet. However
799 all payloads must be at the start of the data area after the default
800 SILC packet header and padding. All fields in the packet payload are
801 always encrypted, as, they reside in the data area of the packet which
804 Payloads described in this section are common payloads that must be
805 accepted anytime during SILC session. Most of the payloads may only
806 be sent with specific packet type which is defined in the description
809 There are a lot of other payloads in the SILC as well. However, they
810 are not common in the sense that they could be sent at any time.
811 These payloads are not described in this section. These are payloads
812 such as SILC Key Exchange payloads and so on. These are described
813 in [SILC1] and [SILC3].
817 2.3.2 Generic payloads
819 This section describes generic payloads that are not associated to any
820 specific packet type. They can be used for example inside some other
827 This payload can be used to send an ID. ID's are variable length thus
828 this payload provides a way to send variable length ID's.
830 Following diagram represents the ID Payload.
835 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
836 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
837 | ID Type | ID Length |
838 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
842 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
850 o ID Type (2 bytes) - Indicates the type of the ID. See
851 section 2.4 SILC ID Types for list of defined ID types.
853 o ID Length (2 bytes) - Length of the ID Data area not
854 including the length of any other fields in the payload.
856 o ID Data (variable length) - The actual ID data.
861 2.3.2.2 Argument Payload
863 Argument Payload is used to set arguments for any packet payload that
864 needs and supports arguments, such as commands. Number of arguments
865 associated with a packet must be indicated by the packet payload who
866 needs the arguments. Argument Payloads must always reside right after
867 the packet payload needing the arguments. Incorrect amount of argument
868 payloads must cause rejection of the packet. Following diagram represents
869 the Argument Payload.
875 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
876 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
877 | Payload Length | Argument Type | |
878 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
882 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
886 Figure 4: Argument Payload
890 o Payload Length (2 bytes) - Length of the argument payload data
891 area not including the length of any other fields in the
894 o Argument Type (1 byte) - Indicates the type of the argument.
895 Every argument may have a specific type that must be defined
896 by the packet payload needing the argument. For example
897 every command specify a number for each argument that maybe
898 associated with the command. By using this number the receiver
899 of the packet knows what type of argument this is. If there is
900 no specific argument type this field is set to zero (0).
902 o Argument Data (variable length) - Argument data.
907 2.3.3 Disconnect Payload
909 Disconnect payload is sent upon disconnection. The payload is simple;
910 reason of disconnection is sent to the disconnected party.
912 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
913 must not be sent in any other packet type. Following diagram represents
914 the Disconnect Payload.
925 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
926 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
928 ~ Disconnect Message ~
930 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
934 Figure 5: Disconnect Payload
940 o Disconnect Message (variable length) - Human readable
941 reason of the disconnection.
946 2.3.4 Success Payload
948 Success payload is sent when some protocol execution is successfully
949 completed. The payload is simple; indication of the success is sent.
950 This maybe any data, including binary or human readable data.
955 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
956 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
958 ~ Success Indication ~
960 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
964 Figure 6: Success Payload
968 o Success Indication (variable length) - Indication of
969 the success. This maybe for example some flag that
970 indicates the protocol and the success status or human
971 readable success message. The true length of this
972 payload is available by calculating it from the SILC
978 2.3.5 Failure Payload
980 This is opposite of Success Payload. Indication of failure of
981 some protocol is sent in the payload.
987 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
988 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
990 ~ Failure Indication ~
992 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
996 Figure 7: Failure Payload
1000 o Failure Indication (variable length) - Indication of
1001 the failure. This maybe for example some flag that
1002 indicates the protocol and the failure status or human
1003 readable failure message. The true length of this
1004 payload is available by calculating it from the SILC
1010 2.3.6 Reject Payload
1012 This payload is sent when some protocol is rejected to be executed.
1013 Other operations may send this as well that was rejected. The
1014 indication of the rejection is sent in the payload. The indication
1015 may be binary or human readable data.
1021 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
1022 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1024 ~ Reject Indication ~
1026 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1030 Figure 8: Reject Payload
1034 o Reject Indication (variable length) - Indication of
1035 the rejection. This maybe for example some flag that
1036 indicates the protocol and the rejection status or human
1037 readable rejection message. The true length of this
1038 payload is available by calculating it from the SILC
1047 2.3.7 Notify Payload
1049 Notify payload is used to send notify messages. The payload is usually
1050 sent from server to client, however, server may send it to another
1051 server as well. This payload may also be sent to a channel. Client must
1052 not send this payload. The receiver of this payload may totally ignore the
1053 contents of the payload, however, notify message should be audited.
1055 The payload may only be sent with SILC_PACKET_NOTIFY packet. It must
1056 not be sent in any other packet type. Following diagram represents the
1062 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
1063 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1064 | Notify Type | Payload Length |
1065 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1071 Figure 9: Notify Payload
1075 o Notify Type (2 bytes) - Indicates the type of the notify
1078 o Payload Length (2 bytes) - Length of the entire Notify Payload
1079 including any associated Argument Payloads.
1081 o Argument Nums (2 bytes) - Indicates the number of Argument
1082 Payloads associated to this payload. Notify types may define
1083 arguments to be send along the notify message.
1086 Following list of currently defined notify types. The format for notify
1087 arguments is same as in SILC commands described in [SILC1]. Also, all
1088 ID's sent in arguments are sent inside ID Payload.
1091 0 SILC_NOTIFY_TYPE_NONE
1093 If no specific notify type apply for the notify message this type
1097 Arguments: (1) <message>
1099 The <message> is implementation specific free text string. Receiver
1100 may ignore this message.
1103 1 SILC_NOTIFY_TYPE_INVITE
1105 Sent when receiver has been invited to a channel. This type must be
1106 sent directly to the invited client.
1109 Arguments: (1) <Client ID> (2) <Channel ID>
1111 The <Client ID> is the client who invites the receiver of this type
1112 to channel indicated by <Channel ID>.
1115 2 SILC_NOTIFY_TYPE_JOIN
1117 Sent when client has joined to a channel. The server must distribute
1118 this type only to the local clients on the channel and then send
1119 SILC_PACKET_NEW_CHANNEL_USER packet to its primary route. The router
1120 or server receiving the packet distributes this type to the local
1121 clients on the channel. See description of SILC_PACKET_NEW_CHANNEL_USER
1122 packet for more information.
1125 Arguments: (1) <Client ID>
1127 The <Client ID> is the client that joined to the channel.
1130 3 SILC_NOTIFY_TYPE_LEAVE
1132 Sent when client has left a channel. The server must distribute
1133 this type only to the local clients on the channel and then send
1134 SILC_PACKET_REMOVE_CHANNEL_USER packet to its primary route. The
1135 router or server receiving the packet distributes this type to the
1136 local clients on the channel. See description of
1137 SILC_PACKET_REMOVE_CHANNEL_USER packet for more information.
1140 Arguments: (1) <Client ID>
1142 The <Client ID> is the client who left the channel.
1145 4 SILC_NOTIFY_TYPE_SIGNOFF
1147 Sent when client signoffs from SILC network. This type is sent only
1148 if the client was joined to any channel. This type is sent by server
1149 or router when SILC_PACKET_REMOVE_ID packet has been received. See
1150 detailed information from description of SILC_PACKET_REMOVE_ID packet.
1153 Arguments: (1) <Client ID>
1155 The <Client ID> is the client who left SILC network.
1158 5 SILC_NOTIFY_TYPE_TOPIC_SET
1160 Sent when topic is set/changed on a channel. This type must be sent
1161 only to the clients who is joined on the channel whose topic was
1165 Arguments: (1) <Client ID> (2) <topic>
1167 The <Client ID> is the client who set or changed the <topic>.
1170 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1172 Sent when client changes nick on a channel. This type is sent only if
1173 the client has joined to any channel. This type is sent by server or
1174 router when SILC_PACKET_REPLACE_ID packet has been received. See
1175 detailed information from description of SILC_PACKET_REPLACE_ID packet.
1178 Arguments: (1) <Old Client ID> (2) <New Client ID>
1180 The <Old Client ID> is the old ID of the client who changed the
1181 nickname. The <New Client ID> is the new ID generated by the change
1185 7 SILC_NOTIFY_TYPE_CMODE_CHANGE
1187 Sent when channel mode has changed. This type must be sent only to
1188 the clients who is joined on the channel whose mode was changed.
1191 Arguments: (1) <Client ID> (2) <mode mask>
1193 The <Client ID> is the client who changed the mode. The <mode mask>
1194 is the new mode mask of the channel.
1197 8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
1199 Sent when user mode on channel has changed. This type must be sent
1200 only to the clients who is joined on the channel where the target
1204 Arguments: (1) <Client ID> (2) <mode mask>
1205 (3) <Target Client ID>
1207 The <Client ID> is the client who changed the mode. The <mode mask>
1208 is the new mode mask of the channel. The <Target Client ID> is the
1209 client which mode was changed.
1212 9 SILC_NOTIFY_TYPE_MOTD
1214 Sent when Message of the Day (motd) is sent to client.
1217 Arguments: (1) <motd>
1219 The <motd> is the Message of the Day.
1222 Notify types starting from 16384 are reserved for private notify
1229 Error payload is sent upon error. Error may occur in various
1230 conditions when server sends this packet. Client may not send this
1231 payload but must be able to accept it. However, client may
1232 totally ignore the contents of the packet as server is going to
1233 take action on the error anyway. However, it is recommended
1234 that the client takes error packet seriously.
1240 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
1241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1249 Figure 10: Error Payload
1253 o Error Message (variable length) - Human readable error
1259 2.3.9 Channel Message Payload
1261 Channel messages are the most common messages sent in the SILC.
1262 Channel Message Payload is used to send message to channels. These
1263 messages can only be sent if client has joined to some channel.
1264 Even though this packet is the most common in SILC it is still
1265 special packet. Some special handling on sending and reception
1266 of channel message is required.
1268 Padding must be applied into this payload since the payload is
1269 encrypted separately from other parts of the packet with the
1270 channel specific key. Hence the requirement of the padding.
1271 The padding should be random data. The packet must be made
1272 multiple by eight (8) or by the block size of the cipher, which
1275 The SILC header in this packet is encrypted with the session key
1276 of the next receiver of the packet. Nothing else is encrypted
1277 with that key. Thus, the actual packet and padding to be
1278 encrypted with the session key is SILC Header plus padding to it
1279 to make it multiple by eight (8) or multiple by the block size
1280 of the cipher, which ever is larger.
1282 Receiver of the the channel message packet is able to determine
1283 the channel the message is destined to by checking the destination
1284 ID from the SILC Packet header which tells the destination channel.
1285 The original sender of the packet is also determined by checking
1286 the source ID from the header which tells the client who sent
1289 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1290 It must not be sent in any other packet type. Following diagram
1291 represents the Channel Message Payload.
1293 (*) indicates that the field is not encrypted.
1299 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
1300 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1301 | Message Length | |
1302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1306 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1307 | Padding Length | |
1308 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1312 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1314 ~ Initial Vector * ~
1316 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1320 Figure 11: Channel Message Payload
1324 o Message Length (2 bytes) - Indicates the length of the
1325 the Message Data field in the payload, not including any
1328 o Message Data (variable length) - The actual message to
1331 o Padding Length (2 bytes) - Indicates the length of the
1332 Padding field in the payload, not including any other
1335 o Padding (variable length) - The padding that must be
1336 applied because this payload is encrypted separately from
1337 other parts of the packet.
1339 o Initial Vector (variable length) - The initial vector
1340 that has been used in packet encryption. It needs to be
1341 used in the packet decryption as well. What this field
1342 includes is implementation issue. However, it is
1343 recommended that it would be random data or, perhaps,
1344 a timestamp. It is not recommended to use zero (0) as
1345 initial vector. This field is not encrypted. This field
1346 is not included into the padding calculation. Length
1347 of this field equals the cipher's block size. This field
1348 is, however, authenticated.
1353 2.3.10 Channel Key Payload
1355 All traffic in channels are protected by channel specific keys.
1356 Channel Key Payload is used to distribute channel keys to all
1357 clients on the particular channel. Channel keys are sent when
1358 the channel is created, when new user joins to the channel and
1359 whenever a user has left a channel. Server creates the new
1360 channel key and distributes it to the clients by encrypting this
1361 payload with the session key shared between the server and
1362 the client. After that, client starts using the key received
1363 in this payload to protect the traffic on the channel.
1365 The client who is joining to the channel receives its key in the
1366 SILC_COMMAND_JOIN command reply message thus it is not necessary to
1367 send this payload to the entity who sent the SILC_COMMAND_JOIN command.
1369 Channel keys are cell specific thus every router in cell have
1370 to create a channel key and distribute it if any client in the
1371 cell has joined to a channel. Channel traffic between cell's
1372 are not encrypted using channel keys, they are encrypted using
1373 normal session keys between two routers. Inside a cell, all
1374 channel traffic is encrypted with the specified channel key.
1375 Channel key should expire periodically, say, in one hour, in
1376 which case new channel key is created and distributed.
1378 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1379 It must not be sent in any other packet type. Following diagram
1380 represents the Channel Key Payload.
1397 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
1398 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1399 | Channel ID Length | |
1400 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1404 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1405 | Cipher Name Length | |
1406 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1410 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1411 | Channel Key Length | |
1412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1416 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1420 Figure 12: Channel Key Payload
1425 o Channel ID Length (2 bytes) - Indicates the length of the
1426 Channel ID field in the payload, not including any other
1429 o Channel ID (variable length) - The Channel ID of the
1430 channel this key is meant for.
1432 o Cipher Name Length (2 bytes) - Indicates the length of the
1433 Cipher name field in the payload, not including any other
1436 o Cipher Name (variable length) - Name of the cipher used
1437 in the protection of channel traffic. This name is
1438 initially decided by the creator of the channel but it
1439 may change during the life time of the channel as well.
1441 o Channel Key Length (2 bytes) - Indicates the length of the
1442 Channel Key field in the payload, not including any other
1445 o Channel Key (variable length) - The actual channel key
1446 material. This key is used as such as key material for
1447 encryption function.
1452 2.3.11 Private Message Payload
1454 Private Message Payload is used to send private message between
1455 two clients (or users for that matter). The messages are sent only
1456 to the specified user and no other user inside SILC network is
1457 able to see the message. The message is protected by the session
1458 key established by the SILC Key Exchange Protocol. However,
1459 it is also possible to agree to use specific keys to protect
1460 just the private messages. See section 2.3.11 Private Message
1461 Key Payload for detailed description of how to agree to use
1464 If normal session key is used to protect the message, every
1465 server between the sender client and the receiving client needs
1466 to decrypt the packet and always re-encrypt it with the session
1467 key of the next receiver of the packet. See section Client
1468 To Client in [SILC1].
1470 When specific key is used to protect the message, servers between
1471 the sender and the receiver needs not to decrypt/re-encrypt the
1472 packet. Section 4.8.2 Client To Client in [SILC1] gives example of
1473 this scheme as well.
1475 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1476 packet. It must not be sent in any other packet type. Following
1477 diagram represents the Private Message Payload.
1483 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
1484 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1485 | Nickname Length | |
1486 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1490 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1494 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1498 Figure 13: Private Message Payload
1502 o Nickname Length (2 bytes) - Indicates the length of the
1503 Nickname field, not including any other field.
1505 o Nickname (variable length) - Nickname of the sender of the
1506 private message. This should not be trusted as a definite
1507 sender of the private message. The SILC Packet Header in
1508 the packet indicates the true sender of the packet and
1509 client should verify that the nickname sent here belongs
1510 to the Client ID in the SILC Packet Header. This nickname
1511 is merely provided to be displayed by the client.
1513 o Message Data (variable length) - The actual message to
1514 the client. Rest of the packet is reserved for the message
1520 2.3.12 Private Message Key Payload
1522 This payload is used to send key from client to another client that
1523 is going to be used to protect the private messages between these
1524 two clients. If this payload is not sent normal session key
1525 established by the SILC Key Exchange Protocol is used to protect
1526 the private messages.
1528 This payload may only be sent by client to another client. Server
1529 must not send this payload at any time. After sending this payload
1530 the sender of private messages must set the Private Message Key
1531 flag into SILC Packet Header.
1533 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1534 packet. It must not be sent in any other packet type. Following
1535 diagram represents the Private Message Key Payload.
1541 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
1542 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1543 | Private Message Key Length | |
1544 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1546 ~ Private Message Key ~
1548 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1552 Figure 14: Private Message Key Payload
1558 o Private Message Key Length (2 bytes) - Indicates the length
1559 of the Private Message Key field in the payload, not including
1562 o Private Message Key (variable length) - The actual private
1563 message key material. This key is used as such as key material
1564 for encryption function.
1569 2.3.13 Command Payload
1571 Command Payload is used to send SILC commands from client to server.
1572 Also server may send commands to other servers. Following diagram
1573 represents the Command Payload.
1579 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
1580 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1581 | Payload Length | SILC Command | Arguments Num |
1582 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1584 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1588 Figure 15: Command Payload
1592 o Payload Length (2 bytes) - Length of the entire command
1593 payload including any command argument payloads associated
1596 o SILC Command (1 byte) - SILC Command identifier. This must
1597 be set to non-zero value. If zero (0) value is found in this
1598 field the packet must be discarded.
1600 o Arguments Num (1 byte) - Indicates the number of arguments
1601 associated with the command. If there are no arguments this
1602 field is set to zero (0). The arguments must follow the
1603 command payload. See section 2.3.2.2 for definition of the
1606 o Command Unifier (2 bytes) - Unifies this command at the
1607 sender's end. The entity who replies to this command must
1608 set the value found from this field into the Command Payload
1609 used to send the reply to the sender. This way the sender
1610 can identify which command reply belongs to which originally
1611 sent command. What this field includes is implementation
1612 issue but it is recommended that wrapping counter value is
1613 used in the field. Value zero (0) in this field means that
1614 no specific value is set.
1617 See [SILC1] for detailed description of different SILC commands,
1618 their arguments and their reply messages.
1622 2.3.14 Command Reply Payload
1624 Command Reply Payload is used to send replies to the commands. The
1625 Command Reply Payload is identical to the Command Payload thus see the
1626 upper sections for Command Payload and for Command Argument Payload
1627 specifications. Command Reply message uses the Command Argument Payload
1630 The entity who sends the reply packet must set the Command Unifier
1631 field in the reply packet's Command Payload to the value it received
1632 in the original command packet.
1634 See SILC Commands in [SILC1] for detailed description of different
1635 SILC commands, their arguments and their reply messages.
1639 2.3.15 Connection Auth Request Payload
1641 Client may send this payload to server to request the authentication
1642 method that must be used in authentication protocol. If client knows
1643 this information beforehand this payload is not necessary to be sent.
1644 Server performing authentication with another server may also send
1645 this payload to request the authentication method. If the connecting
1646 server already knows this information this payload is not necessary
1649 Server receiving this request must reply with same payload sending
1650 the mandatory authentication method. Algorithms that may be required
1651 to be used by the authentication method are the ones already
1652 established by the SILC Key Exchange protocol. See section Key
1653 Exchange Start Payload in [SILC3] for detailed information.
1655 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1656 packet. It must not be sent in any other packet type. Following
1657 diagram represents the Connection Auth Request Payload.
1663 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
1664 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1665 | Connection Type | Authentication Method |
1666 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1670 Figure 16: Connection Auth Request Payload
1674 o Connection Type (2 bytes) - Indicates the type of the ID.
1675 Following connection types are defined:
1681 If any other type is found in this field the packet must be
1682 discarded and the authentication must be failed.
1684 o Authentication Method (2 bytes) - Indicates the authentication
1685 method to be used in the authentication protocol. Following
1686 authentication methods are defined:
1691 1 password (mandatory)
1692 2 public key (mandatory)
1694 If any other type is found in this field the packet must be
1695 discarded and the authentication must be failed. If this
1696 payload is sent as request to receive the mandatory
1697 authentication method this field must be set to zero (0),
1698 indicating that receiver should send the mandatory
1699 authentication method. The receiver sending this payload
1700 to the requesting party, may also set this field to zero (0)
1701 to indicate that authentication is not required. In this
1702 case authentication protocol still must be started but
1703 server is most likely to respond with SILC_PACKET_SUCCESS
1709 2.3.16 New ID Payload
1711 New ID Payload is a multipurpose payload. It is used to send newly
1712 created ID's from clients and servers. When client connects to server
1713 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
1714 packet, server replies with this packet by sending the created ID for
1715 the client. Server always creates the ID for the client.
1717 This payload is also used when server tells its router that new client
1718 has registered to the SILC network. In this case the server sends
1719 the Client ID of the client to the router. Similary when router
1720 distributes information to other routers about the client in the SILC
1721 network this payload is used.
1723 Also, when server connects to router, router uses this payload to inform
1724 other routers about new server in the SILC network. However, every
1725 server (or router) creates their own ID's thus the ID distributed by
1726 this payload is not created by the distributor in this case. Servers
1727 create their own ID's. Server registers itself to the network by sending
1728 SILC_PACKET_NEW_SERVER to the router it connected to. The case is same
1729 when router connects to another router.
1731 However, this payload is not and must not be used to send information
1732 about new channels. New channels are always distributed by sending the
1733 dedicated SILC_PACKET_NEW_CHANNEL packet.
1735 Hence, this payload is very important and used every time when some
1736 new entity is registered to the SILC network. Client never sends this
1737 payload. Both client and server (and router) may receive this payload.
1739 The packet uses generic ID Payload as New ID Payload. See section
1740 2.3.2.1 for generic ID Payload.
1744 2.3.17 New ID List Payload
1746 New ID List Payload is used to distribute list of ID's usually from
1747 server to router but also from router to other routers in the network.
1748 This payload is used, for example, when server is connected to router
1749 and the server wants to distribute all of its locally connected clients
1750 and locally created channels to the router. It is convenient in this
1751 case to use this payload instead of sending all the information one
1752 by one using New ID Payload.
1754 There is no specific payload for this packet type. The packet type
1755 uses same payload as described in previous section. To form a list
1756 several payloads is put in the packet each after each. The payload
1757 is variable in length but can be calculated by calculating the ID
1758 Type field, Length field and the ID Data fields together. This forms
1759 one New ID Payload in the list.
1761 The list of payloads may only be sent with SILC_PACKET_NEW_ID_LIST
1762 packet. They must not be sent in any other packet type.
1766 2.3.18 New Client Payload
1768 When client is connected to the server, keys has been exchanged and
1769 connection has been authenticated client must register itself to the
1770 server. Clients first packet after key exchange and authentication
1771 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
1772 the relevant information about the connected user. Server creates a new
1773 client ID for the client when received this payload and sends it to the
1774 client in New ID Payload.
1776 This payload sends username and real name of the user on the remote host
1777 which is connected to the SILC server with SILC client. The server
1778 creates the client ID according the information sent in this payload.
1779 The nickname of the user becomes the username sent in this payload.
1780 However, client should call NICK command after sending this payload to
1781 set the real nickname of the user which is then used to create new
1784 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
1785 must not be sent in any other packet type. Following diagram represents
1786 the New Client Payload.
1793 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
1794 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1795 | Username Length | |
1796 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1800 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1801 | Real Name Length | |
1802 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1806 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1810 Figure 17: New Client Payload
1814 o Username Length (2 bytes) - Length of the username.
1816 o Username (variable length) - The username of the user on
1817 the host where connecting to the SILC server.
1819 o Real Name Length (2 bytes) - Length of the Real Name.
1821 o Real Name (variable length) - The real name of the user
1822 on the host where connecting to the SILC server.
1827 2.3.19 New Server Payload
1829 This payload is sent by server when it has completed successfully both
1830 key exchange and connection authentication protocols. The server
1831 uses this payload to register itself to the SILC network. The
1832 first packet after these key exchange and authentication protocols
1833 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
1834 of the server that it has created by itself. It also includes a
1835 name of the server that is associated to the Server ID.
1837 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
1838 must not be sent in any other packet type. Following diagram represents
1839 the New Server Payload.
1848 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
1849 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1850 | Server ID Length | |
1851 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1855 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1856 | Server Name Length | |
1857 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1861 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1865 Figure 18: New Server Payload
1869 o Server ID Length (2 bytes) - Length of the ID Data area not
1870 including the length of any other fields in the payload.
1872 o Server ID Data (variable length) - The actual Server ID
1875 o Server Name Length (2 bytes) - Length of the server name.
1877 o Server Name (variable length) - The server name.
1882 2.3.20 New Channel Payload
1884 Information about newly created channel is broadcasted to all routers
1885 in the SILC network by sending this packet payload. Channels are
1886 created by router of the cell. Server never creates channels unless
1887 it is a standalone server and it does not have router connection,
1888 in this case server acts as router. Normal server forwards JOIN command
1889 to the router (after it has received JOIN command from client) which
1890 then processes the command and creates the channel. Client never sends
1893 The payload may only be sent with SILC_PACKET_NEW_CHANNEL packet.
1894 It must not be sent in any other packet type. Following diagram
1895 represents the New Channel Payload.
1903 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
1904 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1905 | Channel Name Length | |
1906 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1910 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1911 | Channel ID Length | |
1912 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1916 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1920 Figure 19: New Channel Payload
1925 o Channel Name Length (2 bytes) - Length of the channel name.
1927 o Channel Name (variable length) - The name of the created
1930 o Channel ID Length (2 bytes) - Length of the Channel ID.
1932 o Channel ID (variable length) - The created Channel ID.
1937 2.3.21 New Channel User Payload
1939 When client (user) joins to a channel, server must notify routers
1940 about the new user on the channel. Normal server sends this packet
1941 payload to its router which then broadcasts the packet further.
1942 Router sends this packet always to its primary router. Client must
1943 not send this packet payload. The mode of the user is NONE after
1944 user has joined to the channel.
1946 The payload may only be sent with SILC_PACKET_NEW_CHANNEL_USER
1947 packet. It must not be sent in any other packet type. Following
1948 diagram represents the New Channel User Payload.
1958 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
1959 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1960 | Channel ID Length | |
1961 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1965 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1966 | Client ID Length | |
1967 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1971 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1975 Figure 20: New Channel User Payload
1979 o Channel ID Length (2 bytes) - Length of the Channel ID.
1981 o Channel ID (variable length) - The Channel ID of the channel
1982 to which the client has joined.
1984 o Client ID Length (2 bytes) - Length of the Client ID.
1986 o Client ID (variable length) - The Client ID of the client
1987 who has joined the channel.
1992 2.3.22 New Channel List Payload
1994 This payload is used to distribute list of new channels from server
1995 to routers. It might convenient to send list of new channels when
1996 existing server connects to router, instead of sending them one
1999 There is no specific payload for this packet type. The packet type
2000 uses same payload as described in 2.3.19 New Channel Payload. To form
2001 a list several payloads is put in the packet each after each. The
2002 payload is variable in length but can be calculated by calculating
2003 the length of the fields together. This forms one New Channel Payload
2006 The list of payloads may only be sent with SILC_PACKET_NEW_CHANNEL_LIST
2007 packet. They must not be sent in any other packet type.
2011 2.3.23 New Channel User List Payload
2013 This payload is used to distribute list of channel users on specific
2014 channel from server to routers. It might convenient to send list of
2015 channel users when existing server connects to router, instead of
2016 sending them one by one.
2018 There is no specific payload for this packet type. The packet type
2019 uses same payload as described in 2.3.20 New Channel User Payload.
2020 To form a list several payloads is put in the packet each after each.
2021 The payload is variable in length but can be calculated by calculating
2022 the length of the fields together. This forms one New Channel User
2023 Payload in the list.
2025 The list of payloads may only be sent with packet
2026 SILC_PACKET_NEW_CHANNEL_USER_LIST. They must not be sent in any other
2031 2.3.24 Replace ID Payload
2033 This payload is used to replace old ID with new ID sent in the payload.
2034 When ID changes for some entity and the new ID is wanted to replace the
2035 old one this payload must be used. Client cannot send or receive this
2036 payload. Normal server and router server may send and receive this
2037 payload. After this packet has been sent the old ID must not be used
2040 The payload may only be sent with SILC_PACKET_REPLACE_ID packet. It must
2041 not be sent in any other packet type. Following diagram represents the
2042 Replace Payload Payload.
2049 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
2050 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2051 | Old ID Type | Old ID Length |
2052 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2056 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2057 | New ID Type | New ID Length |
2058 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2062 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2066 Figure 21: Replace ID Payload
2070 o Old ID Type (2 bytes) - Indicates the type of the old ID. See
2071 section 2.4 SILC ID Types for list of defined ID types.
2073 o Old ID Length (2 bytes) - Length of the old ID Data area not
2074 including the length of any other fields in the payload.
2076 o Old ID Data (variable length) - The actual old ID data.
2078 o New ID Type (2 bytes) - Indicates the type of the new ID. See
2079 section 2.4 SILC ID Types for list of defined ID types.
2081 o New ID Length (2 bytes) - Length of the new ID Data area not
2082 including the length of any other fields in the payload.
2084 o New ID Data (variable length) - The actual new ID data.
2089 2.3.25 Remove ID Payload
2091 Remove ID payload is used to remove ID from SILC network. This is used
2092 when client, server, router or channel is removed from the SILC network.
2093 After this payload has been send the old ID must not be used anymore.
2094 Client must not send or receive this payload.
2096 The packet uses generic ID Payload as New ID Payload. See section
2097 2.3.2.1 for generic ID Payload.
2101 2.3.26 Remove Channel User Payload
2103 Remove Channel User payload is used to remove a user from a channel network
2104 wide. This is used by routers to notify other routers that a user has
2105 left a channel. As routers keep information about users on channels a
2106 user leaving channel must be removed from all routers. Normal server may
2107 send this payload as well. Client must not send this payload.
2109 The payload may only be sent with SILC_PACKET_REMOVE_CHANNEL USER packet.
2110 It must not be sent in any other packet type. Following diagram
2111 represents the Remove Payload Payload.
2120 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
2121 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2122 | Client ID Length | |
2123 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2127 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2128 | Channel ID Length | |
2129 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2133 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2137 Figure 22: Remove Channel User Payload
2141 o Client ID Length (2 bytes) - Length of the Client ID Data area
2142 not including the length of any other fields in the payload.
2144 o Client ID Data (variable length) - The Client ID of the user
2145 that has left the channel.
2147 o Channel ID Length (2 bytes) - Length of the Channel ID Data area
2148 not including the length of any other fields in the payload.
2150 o Channel ID Data (variable length) - The Channel ID of the channel
2156 2.3.27 Set Mode Payload
2158 Set Mode Payload is used by servers and routers to distribute to each
2159 other the information about changed modes in the SILC network. The
2160 payload is sent when channel's or client's channel mode is changed.
2161 Server can send this to router which will broadcast it further to other
2162 routers. However, normal server must not reiceve this payload. Client
2163 must not send or receive this payload.
2165 The payload may only be sent with SILC_PACKET_SET_MODE packet.
2166 It must not be sent in any other packet type. Following diagram
2167 represents the Set Mode Payload.
2176 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
2177 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2178 | Mode Type | Payload Length |
2179 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2181 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2187 Figure 23: Set Mode Payload
2191 o Mode type (2 bytes) - Indicates the type of the mode that was
2192 changed. Every type has arguments associated to the type which
2193 are defined below. The following types are defined:
2195 0 SILC_MODE_TYPE_CHANNEL
2198 Arguments: (1) <Channel ID> (2) <Client ID>
2200 The <Channel ID> is the channel which mode was set and the
2201 <Client ID> is the client who set it.
2204 1 SILC_MODE_TYPE_UCHANNEL
2207 Arguments: (1) <Channel ID> (2) <Client ID>
2208 (3) <Target Client ID>
2210 The <Channel ID> is the channel where the <Client ID> and
2211 the <Target Client ID> is on. The <Client ID> is the client
2212 who set the <Target Client ID> mode.
2220 32768 - Private range
2222 Rest of the types are reserved for private use.
2224 o Payload Length (2 bytes) - Length of the entire Set Mode Payload
2225 including any associated Argument Payloads.
2227 o Mode Mask (4 bytes) - Indicates the set mode mask. This is
2228 specified by the mode type. See definitions of SILC_COMMAND_UMODE
2229 for client modes, SILC_COMMAND_CMODE for channel modes and
2230 SILC_COMMAND_CUMODE for client's channel modes in [SILC1].
2232 o Argument Nums (2 bytes) - Indicates the number of Argument
2233 Payloads associated to this payload. Mode types may define
2234 arguments to be send along this payload.
2242 ID's are extensively used in the SILC network to associate different
2243 entities. Following ID's has been defined to be used in the SILC
2249 When ever specific ID cannot be used this is used.
2253 Server ID to associate servers. See the format of
2258 Client ID to associate clients. See the format of
2263 Channel ID to associate channels. See the format of
2269 2.5 Packet Encryption And Decryption
2271 SILC packets are encrypted almost entirely. Only small part of SILC
2272 header is not encrypted as described in section 5.2 SILC Packet Header.
2273 The SILC Packet header is the first part of a packet to be encrypted
2274 and it is always encrypted with the key of the next receiver of the
2275 packet. The data payload area of the packet is always entirely
2276 encrypted and it is usually encrypted with the next receiver's key.
2277 However, there are some special packet types and packet payloads
2278 that require special encryption process. These special cases are
2279 described in the next sections. First is described the normal packet
2284 2.5.1 Normal Packet Encryption And Decryption
2286 Normal SILC packets are encrypted with the session key of the next
2287 receiver of the packet. The entire SILC Packet header and the packet
2288 data payload is is also encrypted with the same key. Padding of the
2289 packet is also encrypted always with the session key, also in special
2290 cases. Computed MAC of the packet must not be encrypted.
2292 Decryption process in these cases are straightforward. The receiver
2293 of the packet must first decrypt the SILC Packet header, or some parts
2294 of it, usually first 16 bytes of it. Then the receiver checks the
2295 packet type from the decrypted part of the header and can determine
2296 how the rest of the packet must be decrypted. If the packet type is
2297 any of the special cases described in following sections the packet
2298 decryption is special. If the packet type is not among those special
2299 packet types rest of the packet may be decrypted with the same key.
2301 Also, note that two bytes of the SILC Packet header are not encrypted
2302 thus it must be noticed in the decryption process by starting the
2303 decryption from the second byte of the header. This sets some rules
2304 to padding generation as well, see the section 2.7 Packet Padding
2307 With out a doubt, this sort of decryption processing causes some
2308 overhead to packet decryption, but never the less, is required.
2312 2.5.2 Channel Message Encryption And Decryption
2314 Channel Messages (Channel Message Payload) are always encrypted with
2315 the channel specific key. However, the SILC Packet header is not
2316 encrypted with that key. As in normal case, the header is encrypted
2317 with the key of the next receiver of the packet, who ever that might
2318 be. Note that in this case the encrypted data area is not touched
2319 at all; it must not be re-encrypted with the session key.
2321 Receiver of a channel message, who ever that is, is required to decrypt
2322 the SILC Packet header to be able to even recognize the packet to be as
2323 channel message. This is same procedure as for normal SILC packets.
2324 As the receiver founds the packet to be channel message, rest of the
2325 packet processing is special. Rest of the SILC Packet header is
2326 decrypted with the same session key along with the padding of the
2327 packet. After that the packet is protected with the channel specific
2328 key and hence can be decrypted only if the receiver is the client on
2329 the channel. See section 2.7 Packet Padding Generation for more
2330 information about padding on special packets.
2332 If the receiver of the channel message is router who is routing the
2333 message to another router then it must decrypt the Channel Message
2334 payload. Between routers (that is, between cells) channel messages
2335 are protected with session keys shared between the routers. This
2336 causes another special packet processing for channel messages. If
2337 the channel message is received from another router then the entire
2338 packet, including Channel Message payload, is encrypted with the
2339 session key shared between the routers. In this case the packet
2340 decryption process is as with normal SILC packets. Hence, if the
2341 router is sending channel message to another router the Channel
2342 Message payload must have been decrypted and must be re-encrypted
2343 with the session key shared between the another router. In this
2344 case the packet encryption is as with any normal SILC packet.
2346 It must be noted that this is only when the channel messages are sent
2347 from router to another router. In all other cases the channel
2348 message encryption and decryption is as described above. This
2349 different processing of channel messages with router to router
2350 connection is because channel keys are cell specific. All cells has
2351 their own channel keys thus the channel message traveling from one
2352 cell to another must be protected as it would be any normal SILC
2357 2.5.3 Private Message Encryption And Decryption
2359 By default, private message in SILC are protected by session keys.
2360 In this case the private message encryption and decryption process is
2361 equivalent to normal packet encryption and decryption.
2363 However, private messages can be protected with private message key
2364 which causes the packet to be special packet. The procedure in this
2365 case is very much alike to channel packets. The actual private message
2366 is encrypted with the private message key and other parts of the
2367 packet is encrypted with the session key. See 2.7 Packet Padding
2368 Generation for more information about padding on special packets.
2370 The difference from channel message processing is that server or router
2371 en route never decrypts the actual private message, as it does not
2372 have the key to do that. Thus, when sending packets between router
2373 the processing is same as in any other case as well; the packet's header
2374 and padding is protected by the session key and the data area is not
2377 The true receiver of the private message, client, that is, is able
2378 to decrypt the private message as it shares the key with the sender
2383 2.6 Packet MAC Generation
2385 Data integrity of a packet is protected by including a message
2386 authentication code (MAC) at the end of the packet. The MAC is computed
2387 from shared secret MAC key, that is established by the SILC Key Exchange
2388 protocol, and from the original contents of the packet. The MAC is
2389 always computed before the packet is encrypted, although after it is
2390 compressed if compression is used.
2392 The MAC is computed from entire packet. Every bit of data in the packet,
2393 including SILC Packet Header is used in the MAC computing. This way
2394 the entire packet becomes authenticated.
2396 If the packet is special packet MAC is computed from the entire packet
2397 but part of the packet may be encrypted before the MAC is computed.
2398 This is case, for example, with channel messages where the message data
2399 is encrypted with key that server may not now. In this case the MAC
2400 has been computed from the encrypted data.
2402 See [SILC1] for defined and allowed MAC algorithms.
2406 2.7 Packet Padding Generation
2408 Padding is needed in the packet because the packet is encrypted. It
2409 must always be multiple by eight (8) or multiple by the size of the
2410 cipher's block size, which ever is larger. The padding is always
2413 For normal packets the padding is added after the SILC Packet Header
2414 and between the Data Payload area. The padding for normal packets
2415 are calculated as follows:
2418 padding length = 16 - ((packet length - 2) % 16)
2421 The 16 is the maximum padding allowed in SILC packet. Two (2) is
2422 subtracted from the true length of the packet because two (2) bytes
2423 is not encrypted in SILC Packet Header, see section 2.2 SILC Packet
2424 Header. Those two bytes that are not encrypted must not be calculated
2425 to the padding length.
2427 For special packets the padding calculation may be different as special
2428 packets may be encrypted differently. In these cases the encrypted
2429 data area must already be multiple by the block size thus in this case
2430 the padding is calculated only for SILC Packet Header, not for any
2431 other area of the packet. The same algorithm works in this case as
2432 well, except that the `packet length' is now the SILC Packet Header
2433 length. In this case, as well, two (2) is subtracted from the
2436 The padding must be random data, preferably, generated by
2437 cryptographically strong random number generator.
2441 2.8 Packet Compression
2443 SILC Packets may be compressed. In this case the data payload area
2444 is compressed and all other areas of the packet must remain as they
2445 are. After compression is performed for the data area, the length
2446 field of Packet Header must be set to the compressed length of the
2449 The compression must always be applied before encryption. When
2450 the packet is received and decrypted the data area must be decompressed.
2451 Note that the true sender of the packet must apply the compression and
2452 the true receiver of the packet must apply the decompression. Any
2453 server or router en route must not decompress the packet.
2460 The sender of the packet must assemble the SILC Packet Header with
2461 correct values. It must set the Source ID of the header as its own
2462 ID, unless it is forwarding the packet. It must also set the Destination
2463 ID of the header to the true destination. If the destination is client
2464 it will be Client ID, if it is server it will be Server ID and if it is
2465 channel it will be Channel ID.
2467 If the sender wants to compress the packet it must apply the
2468 compression now. Sender must also compute the padding as described
2469 in above sections. Then sender must compute the MAC of the packet.
2471 Then sender encrypts the packet as has been described in above
2472 sections according whether the packet is normal packet or special
2473 packet. The computed MAC must not be encrypted.
2477 2.10 Packet Reception
2479 On packet reception the receiver must check that all fields in the
2480 SILC Packet Header are valid. It must check the flags of the
2481 header and act accordingly. It must also check the MAC of the packet
2482 and if it is to be failed the packet must be discarded. Also if the
2483 header of the packet includes any bad fields the packet must be
2486 See above sections on the decryption process of the received packet.
2488 The receiver must also check that the ID's in the header are valid
2489 ID's. Unsupported ID types or malformed ID's must cause packet
2490 rejection. The padding on the reception is always ignored.
2492 The receiver must also check the packet type and start parsing the
2493 packet according to the type. However, note the above sections on
2494 special packet types and their parsing.
2500 Routers are the primary entities in the SILC network that takes care
2501 of packet routing. However, normal servers routes packets as well, for
2502 example, when they are routing channel message to the local clients.
2503 Routing is quite simple as every packet tells the true origin and the
2504 true destination of the packet.
2506 It is still recommended for routers that has several routing connections
2507 to create route cache for those destinations that has faster route than
2508 the router's primary route. This information is available for the router
2509 when other router connects to the router. The connecting party then
2510 sends all of its locally connected clients, server and channels. These
2511 informations helps to create the route cache. Also, when new channels
2512 are created to a cell its information is broadcasted to all routers
2513 in the network. Channel ID's are based on router's ID thus it is easy
2514 to create route cache based on these informations. If faster route for
2515 destination does not exist in router's route cache the packet must be
2516 routed to the primary route (default route).
2518 For server who receives a packet to be routed to its locally connected
2519 client the server must check whether the particular packet type is
2520 allowed to be routed to the client. Not all packets may be sent by
2521 some odd entity to client that is indirectly connected to the sender.
2522 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2523 entities and sending packets to them. The section mentions the packets
2524 that may be sent to indirectly connected entities. It is clear that some
2525 server cannot send, for example, disconnect packet to client that is not
2526 directly connected to the server.
2530 2.12 Packet Forwarding
2532 Currently SILC command packets may be forwarded from one entity to another.
2533 Any other packet currently cannot be forwarded but support for more packet
2534 types may be added if needed. Forwarding is usually used by server to
2535 forward some command request coming from client to the router as the server
2536 may be incapable to handle the request. Forwarding may be only one hop
2537 long; the receiver of the packet with Forwarded flag set in the SILC
2538 Packet header must not forward the packet any further.
2540 The normal scenario is that client sends JOIN command to the server which
2541 is not able to create the channel as there are no local clients on the
2542 channel. Channels are created always by the router of the cell thus the
2543 packet must be forwarded to the router. The server forwards the original
2544 packet coming from client to the router after it has set the Forwarded
2545 flag to the SILC Packet header.
2547 Router receiving the packet knows that the packet has to be processed
2548 specially by checking the flags and the Forwarded flag in the SILC Packet
2549 header. After router has joined the client to the channel (and perhaps
2550 created a new channel) it sends normal command reply packet to the
2551 client. However, as the router doesn't have direct connection to the
2552 client the packet is sent through the server. Server detects that
2553 the command reply packet is destined to the client and sends it to
2558 2.13 Packet Broadcasting
2560 SILC packets may be broadcasted in SILC network. However, only router
2561 server may send or receive broadcast packets. Client and normal server
2562 must not send broadcast packets and they must ignore broadcast packets
2563 if they receive them. Broadcast packets are sent by setting Broadcast
2564 flag to the SILC packet header.
2566 Broadcasting packets means that the packet is sent to all routers in
2567 the SILC network, except to the router that sent the packet. The router
2568 receiving broadcast packet must send the packet to its primary route.
2569 The fact that SILC routers may have several router connections may
2570 cause problems, such as race conditions inside the SILC network, if
2571 care is not taken when broadcasting packets. Router must not send
2572 the broadcast packet to any other route except to its primary route.
2574 If the primary route of the router is the original sender of the packet
2575 the packet must not be sent to the primary route. This may happen
2576 if router has several router connections and some other router uses
2577 the router as its primary route.
2579 Routers use broadcast packets to broadcast for example information
2580 about newly registered clients, servers, channels etc. so that all the
2581 routers may keep these informations up to date.
2585 2.14 Packet Tunneling
2587 Tunneling is a feature that is available in SILC protocol. Tunneling
2588 means that extra SILC Packet Header is applied to the original packet
2589 and thus hiding the original packet entirely. There can be some
2590 interesting applications using tunneling, such as, using ID's based on
2591 private network IP addresses inside in the tunneled packet. This can
2592 open many interesting features relating to connecting to private network
2593 from the Internet with SILC and many more. However, this feature is
2594 optional currently in SILC as there does not exist thorough analysis of
2595 this feature. It is with out a doubt that there will be many more
2596 applications that has not yet been discovered. Thus, it is left
2597 to Internet Community to investigate the use of tunneling in SILC
2598 protocol. This document is updated according those investigations
2599 and additional documents on the issue may be written.
2603 3 Security Considerations
2605 Security is central to the design of this protocol, and these security
2606 considerations permeate the specification. Common security considerations
2607 such as keeping private keys truly private and using adequate lengths for
2608 symmetric and asymmetric keys must be followed in order to maintain the
2609 security of this protocol.
2615 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2616 Protocol Specification", Internet Draft, June 2000.
2618 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2619 Protocols", Internet Draft, June 2000.
2621 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2624 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2627 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2630 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2633 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2634 Infrastructure, Certificate and CRL Profile", RFC 2459,
2637 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2638 John Wiley & Sons, New York, NY, 1996.
2640 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2643 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2644 RFC 2412, November 1998.
2646 [ISAKMP] Maughan D., et al, "Internet Security Association and
2647 Key Management Protocol (ISAKMP)", RFC 2408, November
2650 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2651 (IKE)", RFC 2409, November 1998.
2653 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2654 Authentication", RFC 2104, February 1997.
2670 EMail: priikone@poseidon.pspt.fi
2672 This Internet-Draft expires 6 Jun 2001