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
771 Currently undefined commands.
776 These packet types are reserved for private use and they will not
777 be defined by this document.
782 This type is reserved for future extensions and currently it
788 2.3.1 SILC Packet Payloads
790 All payloads resides in the main data area of the SILC packet. However
791 all payloads must be at the start of the data area after the default
792 SILC packet header and padding. All fields in the packet payload are
793 always encrypted, as, they reside in the data area of the packet which
796 Payloads described in this section are common payloads that must be
797 accepted anytime during SILC session. Most of the payloads may only
798 be sent with specific packet type which is defined in the description
801 There are a lot of other payloads in the SILC as well. However, they
802 are not common in the sense that they could be sent at any time.
803 These payloads are not described in this section. These are payloads
804 such as SILC Key Exchange payloads and so on. These are described
805 in [SILC1] and [SILC3].
809 2.3.2 Generic payloads
811 This section describes generic payloads that are not associated to any
812 specific packet type. They can be used for example inside some other
819 This payload can be used to send an ID. ID's are variable length thus
820 this payload provides a way to send variable length ID's.
822 Following diagram represents the ID Payload.
827 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
828 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
829 | ID Type | ID Length |
830 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
834 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
842 o ID Type (2 bytes) - Indicates the type of the ID. See
843 section 2.4 SILC ID Types for list of defined ID types.
845 o ID Length (2 bytes) - Length of the ID Data area not
846 including the length of any other fields in the payload.
848 o ID Data (variable length) - The actual ID data.
853 2.3.2.2 Argument Payload
855 Argument Payload is used to set arguments for any packet payload that
856 needs and supports arguments, such as commands. Number of arguments
857 associated with a packet must be indicated by the packet payload who
858 needs the arguments. Argument Payloads must always reside right after
859 the packet payload needing the arguments. Incorrect amount of argument
860 payloads must cause rejection of the packet. Following diagram represents
861 the Argument Payload.
867 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
868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
869 | Payload Length | Argument Type | |
870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
874 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
878 Figure 4: Argument Payload
882 o Payload Length (2 bytes) - Length of the argument payload data
883 area not including the length of any other fields in the
886 o Argument Type (1 byte) - Indicates the type of the argument.
887 Every argument may have a specific type that must be defined
888 by the packet payload needing the argument. For example
889 every command specify a number for each argument that maybe
890 associated with the command. By using this number the receiver
891 of the packet knows what type of argument this is. If there is
892 no specific argument type this field is set to zero (0).
894 o Argument Data (variable length) - Argument data.
899 2.3.3 Disconnect Payload
901 Disconnect payload is sent upon disconnection. The payload is simple;
902 reason of disconnection is sent to the disconnected party.
904 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
905 must not be sent in any other packet type. Following diagram represents
906 the Disconnect Payload.
917 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
918 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
920 ~ Disconnect Message ~
922 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
926 Figure 5: Disconnect Payload
932 o Disconnect Message (variable length) - Human readable
933 reason of the disconnection.
938 2.3.4 Success Payload
940 Success payload is sent when some protocol execution is successfully
941 completed. The payload is simple; indication of the success is sent.
942 This maybe any data, including binary or human readable data.
947 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
948 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
950 ~ Success Indication ~
952 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
956 Figure 6: Success Payload
960 o Success Indication (variable length) - Indication of
961 the success. This maybe for example some flag that
962 indicates the protocol and the success status or human
963 readable success message. The true length of this
964 payload is available by calculating it from the SILC
970 2.3.5 Failure Payload
972 This is opposite of Success Payload. Indication of failure of
973 some protocol is sent in the payload.
979 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
980 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
982 ~ Failure Indication ~
984 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
988 Figure 7: Failure Payload
992 o Failure Indication (variable length) - Indication of
993 the failure. This maybe for example some flag that
994 indicates the protocol and the failure status or human
995 readable failure message. The true length of this
996 payload is available by calculating it from the SILC
1002 2.3.6 Reject Payload
1004 This payload is sent when some protocol is rejected to be executed.
1005 Other operations may send this as well that was rejected. The
1006 indication of the rejection is sent in the payload. The indication
1007 may be binary or human readable data.
1013 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
1014 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1016 ~ Reject Indication ~
1018 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1022 Figure 8: Reject Payload
1026 o Reject Indication (variable length) - Indication of
1027 the rejection. This maybe for example some flag that
1028 indicates the protocol and the rejection status or human
1029 readable rejection message. The true length of this
1030 payload is available by calculating it from the SILC
1039 2.3.7 Notify Payload
1041 Notify payload is used to send notify messages. The payload is usually
1042 sent from server to client, however, server may send it to another
1043 server as well. This payload may also be sent to a channel. Client must
1044 not send this payload. The receiver of this payload may totally ignore the
1045 contents of the payload, however, notify message should be audited.
1047 The payload may only be sent with SILC_PACKET_NOTIFY packet. It must
1048 not be sent in any other packet type. Following diagram represents the
1054 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
1055 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1056 | Notify Type | Payload Length |
1057 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1063 Figure 9: Notify Payload
1067 o Notify Type (2 bytes) - Indicates the type of the notify
1070 o Payload Length (2 bytes) - Length of the entire Notify Payload
1071 including any associated Argument Payloads.
1073 o Argument Nums (2 bytes) - Indicates the number of Argument
1074 Payloads associated to this payload. Notify types may define
1075 arguments to be send along the notify message.
1078 Following list of currently defined notify types. The format for notify
1079 arguments is same as in SILC commands described in [SILC1]. Also, all
1080 ID's sent in arguments are sent inside ID Payload.
1083 0 SILC_NOTIFY_TYPE_NONE
1085 If no specific notify type apply for the notify message this type
1089 Arguments: (1) <message>
1091 The <message> is implementation specific free text string. Receiver
1092 may ignore this message.
1095 1 SILC_NOTIFY_TYPE_INVITE
1097 Sent when receiver has been invited to a channel. This type must be
1098 sent directly to the invited client.
1101 Arguments: (1) <Client ID> (2) <Channel ID>
1103 The <Client ID> is the client who invites the receiver of this type
1104 to channel indicated by <Channel ID>.
1107 2 SILC_NOTIFY_TYPE_JOIN
1109 Sent when client has joined to a channel. The server must distribute
1110 this type only to the local clients on the channel and then send
1111 SILC_PACKET_NEW_CHANNEL_USER packet to its primary route. The router
1112 or server receiving the packet distributes this type to the local
1113 clients on the channel. See description of SILC_PACKET_NEW_CHANNEL_USER
1114 packet for more information.
1117 Arguments: (1) <Client ID>
1119 The <Client ID> is the client that joined to the channel.
1122 3 SILC_NOTIFY_TYPE_LEAVE
1124 Sent when client has left a channel. The server must distribute
1125 this type only to the local clients on the channel and then send
1126 SILC_PACKET_REMOVE_CHANNEL_USER packet to its primary route. The
1127 router or server receiving the packet distributes this type to the
1128 local clients on the channel. See description of
1129 SILC_PACKET_REMOVE_CHANNEL_USER packet for more information.
1132 Arguments: (1) <Client ID>
1134 The <Client ID> is the client who left the channel.
1137 4 SILC_NOTIFY_TYPE_SIGNOFF
1139 Sent when client signoffs from SILC network. This type is sent only
1140 if the client was joined to any channel. This type is sent by server
1141 or router when SILC_PACKET_REMOVE_ID packet has been received. See
1142 detailed information from description of SILC_PACKET_REMOVE_ID packet.
1145 Arguments: (1) <Client ID>
1147 The <Client ID> is the client who left SILC network.
1150 5 SILC_NOTIFY_TYPE_TOPIC_SET
1152 Sent when topic is set/changed on a channel. This type must be sent
1153 only to the clients who is joined on the channel whose topic was
1157 Arguments: (1) <Client ID> (2) <topic>
1159 The <Client ID> is the client who set or changed the <topic>.
1162 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1164 Sent when client changes nick on a channel. This type is sent only if
1165 the client has joined to any channel. This type is sent by server or
1166 router when SILC_PACKET_REPLACE_ID packet has been received. See
1167 detailed information from description of SILC_PACKET_REPLACE_ID packet.
1170 Arguments: (1) <Old Client ID> (2) <New Client ID>
1172 The <Old Client ID> is the old ID of the client who changed the
1173 nickname. The <New Client ID> is the new ID generated by the change
1177 7 SILC_NOTIFY_TYPE_CMODE_CHANGE
1179 Sent when channel mode has changed. This type must be sent only to
1180 the clients who is joined on the channel whose mode was changed.
1183 Arguments: (1) <Client ID> (2) <mode mask>
1185 The <Client ID> is the client who changed the mode. The <mode mask>
1186 is the new mode mask of the channel.
1189 8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
1191 Sent when user mode on channel has changed. This type must be sent
1192 only to the clients who is joined on the channel where the target
1196 Arguments: (1) <Client ID> (2) <mode mask>
1197 (3) <Target Client ID>
1199 The <Client ID> is the client who changed the mode. The <mode mask>
1200 is the new mode mask of the channel. The <Target Client ID> is the
1201 client which mode was changed.
1204 9 SILC_NOTIFY_TYPE_MOTD
1206 Sent when Message of the Day (motd) is sent to client.
1209 Arguments: (1) <motd>
1211 The <motd> is the Message of the Day.
1214 Notify types starting from 16384 are reserved for private notify
1221 Error payload is sent upon error. Error may occur in various
1222 conditions when server sends this packet. Client may not send this
1223 payload but must be able to accept it. However, client may
1224 totally ignore the contents of the packet as server is going to
1225 take action on the error anyway. However, it is recommended
1226 that the client takes error packet seriously.
1232 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
1233 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1237 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1241 Figure 10: Error Payload
1245 o Error Message (variable length) - Human readable error
1251 2.3.9 Channel Message Payload
1253 Channel messages are the most common messages sent in the SILC.
1254 Channel Message Payload is used to send message to channels. These
1255 messages can only be sent if client has joined to some channel.
1256 Even though this packet is the most common in SILC it is still
1257 special packet. Some special handling on sending and reception
1258 of channel message is required.
1260 Padding must be applied into this payload since the payload is
1261 encrypted separately from other parts of the packet with the
1262 channel specific key. Hence the requirement of the padding.
1263 The padding should be random data. The packet must be made
1264 multiple by eight (8) or by the block size of the cipher, which
1267 The SILC header in this packet is encrypted with the session key
1268 of the next receiver of the packet. Nothing else is encrypted
1269 with that key. Thus, the actual packet and padding to be
1270 encrypted with the session key is SILC Header plus padding to it
1271 to make it multiple by eight (8) or multiple by the block size
1272 of the cipher, which ever is larger.
1274 Receiver of the the channel message packet is able to determine
1275 the channel the message is destined to by checking the destination
1276 ID from the SILC Packet header which tells the destination channel.
1277 The original sender of the packet is also determined by checking
1278 the source ID from the header which tells the client who sent
1281 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1282 It must not be sent in any other packet type. Following diagram
1283 represents the Channel Message Payload.
1285 (*) indicates that the field is not encrypted.
1291 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
1292 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1293 | Message Length | |
1294 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1298 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1299 | Padding Length | |
1300 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1306 ~ Initial Vector * ~
1308 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1312 Figure 11: Channel Message Payload
1316 o Message Length (2 bytes) - Indicates the length of the
1317 the Message Data field in the payload, not including any
1320 o Message Data (variable length) - The actual message to
1323 o Padding Length (2 bytes) - Indicates the length of the
1324 Padding field in the payload, not including any other
1327 o Padding (variable length) - The padding that must be
1328 applied because this payload is encrypted separately from
1329 other parts of the packet.
1331 o Initial Vector (variable length) - The initial vector
1332 that has been used in packet encryption. It needs to be
1333 used in the packet decryption as well. What this field
1334 includes is implementation issue. However, it is
1335 recommended that it would be random data or, perhaps,
1336 a timestamp. It is not recommended to use zero (0) as
1337 initial vector. This field is not encrypted. This field
1338 is not included into the padding calculation. Length
1339 of this field equals the cipher's block size. This field
1340 is, however, authenticated.
1345 2.3.10 Channel Key Payload
1347 All traffic in channels are protected by channel specific keys.
1348 Channel Key Payload is used to distribute channel keys to all
1349 clients on the particular channel. Channel keys are sent when
1350 the channel is created, when new user joins to the channel and
1351 whenever a user has left a channel. Server creates the new
1352 channel key and distributes it to the clients by encrypting this
1353 payload with the session key shared between the server and
1354 the client. After that, client starts using the key received
1355 in this payload to protect the traffic on the channel.
1357 The client who is joining to the channel receives its key in the
1358 SILC_COMMAND_JOIN command reply message thus it is not necessary to
1359 send this payload to the entity who sent the SILC_COMMAND_JOIN command.
1361 Channel keys are cell specific thus every router in cell have
1362 to create a channel key and distribute it if any client in the
1363 cell has joined to a channel. Channel traffic between cell's
1364 are not encrypted using channel keys, they are encrypted using
1365 normal session keys between two routers. Inside a cell, all
1366 channel traffic is encrypted with the specified channel key.
1367 Channel key should expire periodically, say, in one hour, in
1368 which case new channel key is created and distributed.
1370 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1371 It must not be sent in any other packet type. Following diagram
1372 represents the Channel Key Payload.
1389 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
1390 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1391 | Channel ID Length | |
1392 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1396 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1397 | Cipher Name Length | |
1398 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1402 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1403 | Channel Key Length | |
1404 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1408 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1412 Figure 12: Channel Key Payload
1417 o Channel ID Length (2 bytes) - Indicates the length of the
1418 Channel ID field in the payload, not including any other
1421 o Channel ID (variable length) - The Channel ID of the
1422 channel this key is meant for.
1424 o Cipher Name Length (2 bytes) - Indicates the length of the
1425 Cipher name field in the payload, not including any other
1428 o Cipher Name (variable length) - Name of the cipher used
1429 in the protection of channel traffic. This name is
1430 initially decided by the creator of the channel but it
1431 may change during the life time of the channel as well.
1433 o Channel Key Length (2 bytes) - Indicates the length of the
1434 Channel Key field in the payload, not including any other
1437 o Channel Key (variable length) - The actual channel key
1438 material. This key is used as such as key material for
1439 encryption function.
1444 2.3.11 Private Message Payload
1446 Private Message Payload is used to send private message between
1447 two clients (or users for that matter). The messages are sent only
1448 to the specified user and no other user inside SILC network is
1449 able to see the message. The message is protected by the session
1450 key established by the SILC Key Exchange Protocol. However,
1451 it is also possible to agree to use specific keys to protect
1452 just the private messages. See section 2.3.11 Private Message
1453 Key Payload for detailed description of how to agree to use
1456 If normal session key is used to protect the message, every
1457 server between the sender client and the receiving client needs
1458 to decrypt the packet and always re-encrypt it with the session
1459 key of the next receiver of the packet. See section Client
1460 To Client in [SILC1].
1462 When specific key is used to protect the message, servers between
1463 the sender and the receiver needs not to decrypt/re-encrypt the
1464 packet. Section 4.8.2 Client To Client in [SILC1] gives example of
1465 this scheme as well.
1467 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1468 packet. It must not be sent in any other packet type. Following
1469 diagram represents the Private Message Payload.
1475 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
1476 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1477 | Nickname Length | |
1478 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1482 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1486 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1490 Figure 13: Private Message Payload
1494 o Nickname Length (2 bytes) - Indicates the length of the
1495 Nickname field, not including any other field.
1497 o Nickname (variable length) - Nickname of the sender of the
1498 private message. This should not be trusted as a definite
1499 sender of the private message. The SILC Packet Header in
1500 the packet indicates the true sender of the packet and
1501 client should verify that the nickname sent here belongs
1502 to the Client ID in the SILC Packet Header. This nickname
1503 is merely provided to be displayed by the client.
1505 o Message Data (variable length) - The actual message to
1506 the client. Rest of the packet is reserved for the message
1512 2.3.12 Private Message Key Payload
1514 This payload is used to send key from client to another client that
1515 is going to be used to protect the private messages between these
1516 two clients. If this payload is not sent normal session key
1517 established by the SILC Key Exchange Protocol is used to protect
1518 the private messages.
1520 This payload may only be sent by client to another client. Server
1521 must not send this payload at any time. After sending this payload
1522 the sender of private messages must set the Private Message Key
1523 flag into SILC Packet Header.
1525 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1526 packet. It must not be sent in any other packet type. Following
1527 diagram represents the Private Message Key Payload.
1533 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
1534 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1535 | Private Message Key Length | |
1536 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1538 ~ Private Message Key ~
1540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1544 Figure 14: Private Message Key Payload
1550 o Private Message Key Length (2 bytes) - Indicates the length
1551 of the Private Message Key field in the payload, not including
1554 o Private Message Key (variable length) - The actual private
1555 message key material. This key is used as such as key material
1556 for encryption function.
1561 2.3.13 Command Payload
1563 Command Payload is used to send SILC commands from client to server.
1564 Also server may send commands to other servers. Following diagram
1565 represents the Command Payload.
1571 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
1572 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1573 | Payload Length | SILC Command | Arguments Num |
1574 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1576 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1580 Figure 15: Command Payload
1584 o Payload Length (2 bytes) - Length of the entire command
1585 payload including any command argument payloads associated
1588 o SILC Command (1 byte) - SILC Command identifier. This must
1589 be set to non-zero value. If zero (0) value is found in this
1590 field the packet must be discarded.
1592 o Arguments Num (1 byte) - Indicates the number of arguments
1593 associated with the command. If there are no arguments this
1594 field is set to zero (0). The arguments must follow the
1595 command payload. See section 2.3.2.2 for definition of the
1598 o Command Unifier (2 bytes) - Unifies this command at the
1599 sender's end. The entity who replies to this command must
1600 set the value found from this field into the Command Payload
1601 used to send the reply to the sender. This way the sender
1602 can identify which command reply belongs to which originally
1603 sent command. What this field includes is implementation
1604 issue but it is recommended that wrapping counter value is
1605 used in the field. Value zero (0) in this field means that
1606 no specific value is set.
1609 See [SILC1] for detailed description of different SILC commands,
1610 their arguments and their reply messages.
1614 2.3.14 Command Reply Payload
1616 Command Reply Payload is used to send replies to the commands. The
1617 Command Reply Payload is identical to the Command Payload thus see the
1618 upper sections for Command Payload and for Command Argument Payload
1619 specifications. Command Reply message uses the Command Argument Payload
1622 The entity who sends the reply packet must set the Command Unifier
1623 field in the reply packet's Command Payload to the value it received
1624 in the original command packet.
1626 See SILC Commands in [SILC1] for detailed description of different
1627 SILC commands, their arguments and their reply messages.
1631 2.3.15 Connection Auth Request Payload
1633 Client may send this payload to server to request the authentication
1634 method that must be used in authentication protocol. If client knows
1635 this information beforehand this payload is not necessary to be sent.
1636 Server performing authentication with another server may also send
1637 this payload to request the authentication method. If the connecting
1638 server already knows this information this payload is not necessary
1641 Server receiving this request must reply with same payload sending
1642 the mandatory authentication method. Algorithms that may be required
1643 to be used by the authentication method are the ones already
1644 established by the SILC Key Exchange protocol. See section Key
1645 Exchange Start Payload in [SILC3] for detailed information.
1647 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1648 packet. It must not be sent in any other packet type. Following
1649 diagram represents the Connection Auth Request Payload.
1655 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
1656 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1657 | Connection Type | Authentication Method |
1658 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1662 Figure 16: Connection Auth Request Payload
1666 o Connection Type (2 bytes) - Indicates the type of the ID.
1667 Following connection types are defined:
1673 If any other type is found in this field the packet must be
1674 discarded and the authentication must be failed.
1676 o Authentication Method (2 bytes) - Indicates the authentication
1677 method to be used in the authentication protocol. Following
1678 authentication methods are defined:
1683 1 password (mandatory)
1684 2 public key (mandatory)
1686 If any other type is found in this field the packet must be
1687 discarded and the authentication must be failed. If this
1688 payload is sent as request to receive the mandatory
1689 authentication method this field must be set to zero (0),
1690 indicating that receiver should send the mandatory
1691 authentication method. The receiver sending this payload
1692 to the requesting party, may also set this field to zero (0)
1693 to indicate that authentication is not required. In this
1694 case authentication protocol still must be started but
1695 server is most likely to respond with SILC_PACKET_SUCCESS
1701 2.3.16 New ID Payload
1703 New ID Payload is a multipurpose payload. It is used to send newly
1704 created ID's from clients and servers. When client connects to server
1705 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
1706 packet, server replies with this packet by sending the created ID for
1707 the client. Server always creates the ID for the client.
1709 This payload is also used when server tells its router that new client
1710 has registered to the SILC network. In this case the server sends
1711 the Client ID of the client to the router. Similary when router
1712 distributes information to other routers about the client in the SILC
1713 network this payload is used.
1715 Also, when server connects to router, router uses this payload to inform
1716 other routers about new server in the SILC network. However, every
1717 server (or router) creates their own ID's thus the ID distributed by
1718 this payload is not created by the distributor in this case. Servers
1719 create their own ID's. Server registers itself to the network by sending
1720 SILC_PACKET_NEW_SERVER to the router it connected to. The case is same
1721 when router connects to another router.
1723 However, this payload is not and must not be used to send information
1724 about new channels. New channels are always distributed by sending the
1725 dedicated SILC_PACKET_NEW_CHANNEL packet.
1727 Hence, this payload is very important and used every time when some
1728 new entity is registered to the SILC network. Client never sends this
1729 payload. Both client and server (and router) may receive this payload.
1731 The packet uses generic ID Payload as New ID Payload. See section
1732 2.3.2.1 for generic ID Payload.
1736 2.3.17 New ID List Payload
1738 New ID List Payload is used to distribute list of ID's usually from
1739 server to router but also from router to other routers in the network.
1740 This payload is used, for example, when server is connected to router
1741 and the server wants to distribute all of its locally connected clients
1742 and locally created channels to the router. It is convenient in this
1743 case to use this payload instead of sending all the information one
1744 by one using New ID Payload.
1746 There is no specific payload for this packet type. The packet type
1747 uses same payload as described in previous section. To form a list
1748 several payloads is put in the packet each after each. The payload
1749 is variable in length but can be calculated by calculating the ID
1750 Type field, Length field and the ID Data fields together. This forms
1751 one New ID Payload in the list.
1753 The list of payloads may only be sent with SILC_PACKET_NEW_ID_LIST
1754 packet. They must not be sent in any other packet type.
1758 2.3.18 New Client Payload
1760 When client is connected to the server, keys has been exchanged and
1761 connection has been authenticated client must register itself to the
1762 server. Clients first packet after key exchange and authentication
1763 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
1764 the relevant information about the connected user. Server creates a new
1765 client ID for the client when received this payload and sends it to the
1766 client in New ID Payload.
1768 This payload sends username and real name of the user on the remote host
1769 which is connected to the SILC server with SILC client. The server
1770 creates the client ID according the information sent in this payload.
1771 The nickname of the user becomes the username sent in this payload.
1772 However, client should call NICK command after sending this payload to
1773 set the real nickname of the user which is then used to create new
1776 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
1777 must not be sent in any other packet type. Following diagram represents
1778 the New Client Payload.
1785 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
1786 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1787 | Username Length | |
1788 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1792 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1793 | Real Name Length | |
1794 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1798 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1802 Figure 17: New Client Payload
1806 o Username Length (2 bytes) - Length of the username.
1808 o Username (variable length) - The username of the user on
1809 the host where connecting to the SILC server.
1811 o Real Name Length (2 bytes) - Length of the Real Name.
1813 o Real Name (variable length) - The real name of the user
1814 on the host where connecting to the SILC server.
1819 2.3.19 New Server Payload
1821 This payload is sent by server when it has completed successfully both
1822 key exchange and connection authentication protocols. The server
1823 uses this payload to register itself to the SILC network. The
1824 first packet after these key exchange and authentication protocols
1825 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
1826 of the server that it has created by itself. It also includes a
1827 name of the server that is associated to the Server ID.
1829 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
1830 must not be sent in any other packet type. Following diagram represents
1831 the New Server Payload.
1840 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
1841 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1842 | Server ID Length | |
1843 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1847 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1848 | Server Name Length | |
1849 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1853 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1857 Figure 18: New Server Payload
1861 o Server ID Length (2 bytes) - Length of the ID Data area not
1862 including the length of any other fields in the payload.
1864 o Server ID Data (variable length) - The actual Server ID
1867 o Server Name Length (2 bytes) - Length of the server name.
1869 o Server Name (variable length) - The server name.
1874 2.3.20 New Channel Payload
1876 Information about newly created channel is broadcasted to all routers
1877 in the SILC network by sending this packet payload. Channels are
1878 created by router of the cell. Server never creates channels unless
1879 it is a standalone server and it does not have router connection,
1880 in this case server acts as router. Normal server forwards JOIN command
1881 to the router (after it has received JOIN command from client) which
1882 then processes the command and creates the channel. Client never sends
1885 The payload may only be sent with SILC_PACKET_NEW_CHANNEL packet.
1886 It must not be sent in any other packet type. Following diagram
1887 represents the New Channel Payload.
1895 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
1896 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1897 | Channel Name Length | |
1898 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1902 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1903 | Channel ID Length | |
1904 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1908 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1912 Figure 19: New Channel Payload
1917 o Channel Name Length (2 bytes) - Length of the channel name.
1919 o Channel Name (variable length) - The name of the created
1922 o Channel ID Length (2 bytes) - Length of the Channel ID.
1924 o Channel ID (variable length) - The created Channel ID.
1929 2.3.21 New Channel User Payload
1931 When client (user) joins to a channel, server must notify routers
1932 about the new user on the channel. Normal server sends this packet
1933 payload to its router which then broadcasts the packet further.
1934 Router sends this packet always to its primary router. Client must
1935 not send this packet payload. The mode of the user is NONE after
1936 user has joined to the channel.
1938 The payload may only be sent with SILC_PACKET_NEW_CHANNEL_USER
1939 packet. It must not be sent in any other packet type. Following
1940 diagram represents the New Channel User Payload.
1950 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
1951 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1952 | Channel ID Length | |
1953 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1957 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1958 | Client ID Length | |
1959 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1963 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1967 Figure 20: New Channel User Payload
1971 o Channel ID Length (2 bytes) - Length of the Channel ID.
1973 o Channel ID (variable length) - The Channel ID of the channel
1974 to which the client has joined.
1976 o Client ID Length (2 bytes) - Length of the Client ID.
1978 o Client ID (variable length) - The Client ID of the client
1979 who has joined the channel.
1984 2.3.22 New Channel List Payload
1986 This payload is used to distribute list of new channels from server
1987 to routers. It might convenient to send list of new channels when
1988 existing server connects to router, instead of sending them one
1991 There is no specific payload for this packet type. The packet type
1992 uses same payload as described in 2.3.19 New Channel Payload. To form
1993 a list several payloads is put in the packet each after each. The
1994 payload is variable in length but can be calculated by calculating
1995 the length of the fields together. This forms one New Channel Payload
1998 The list of payloads may only be sent with SILC_PACKET_NEW_CHANNEL_LIST
1999 packet. They must not be sent in any other packet type.
2003 2.3.23 New Channel User List Payload
2005 This payload is used to distribute list of channel users on specific
2006 channel from server to routers. It might convenient to send list of
2007 channel users when existing server connects to router, instead of
2008 sending them one by one.
2010 There is no specific payload for this packet type. The packet type
2011 uses same payload as described in 2.3.20 New Channel User Payload.
2012 To form a list several payloads is put in the packet each after each.
2013 The payload is variable in length but can be calculated by calculating
2014 the length of the fields together. This forms one New Channel User
2015 Payload in the list.
2017 The list of payloads may only be sent with packet
2018 SILC_PACKET_NEW_CHANNEL_USER_LIST. They must not be sent in any other
2023 2.3.24 Replace ID Payload
2025 This payload is used to replace old ID with new ID sent in the payload.
2026 When ID changes for some entity and the new ID is wanted to replace the
2027 old one this payload must be used. Client cannot send or receive this
2028 payload. Normal server and router server may send and receive this
2029 payload. After this packet has been sent the old ID must not be used
2032 The payload may only be sent with SILC_PACKET_REPLACE_ID packet. It must
2033 not be sent in any other packet type. Following diagram represents the
2034 Replace Payload Payload.
2041 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
2042 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2043 | Old ID Type | Old ID Length |
2044 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2048 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2049 | New ID Type | New ID Length |
2050 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2054 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2058 Figure 21: Replace ID Payload
2062 o Old ID Type (2 bytes) - Indicates the type of the old ID. See
2063 section 2.4 SILC ID Types for list of defined ID types.
2065 o Old ID Length (2 bytes) - Length of the old ID Data area not
2066 including the length of any other fields in the payload.
2068 o Old ID Data (variable length) - The actual old ID data.
2070 o New ID Type (2 bytes) - Indicates the type of the new ID. See
2071 section 2.4 SILC ID Types for list of defined ID types.
2073 o New ID Length (2 bytes) - Length of the new ID Data area not
2074 including the length of any other fields in the payload.
2076 o New ID Data (variable length) - The actual new ID data.
2081 2.3.25 Remove ID Payload
2083 Remove ID payload is used to remove ID from SILC network. This is used
2084 when client, server, router or channel is removed from the SILC network.
2085 After this payload has been send the old ID must not be used anymore.
2086 Client must not send or receive this payload.
2088 The packet uses generic ID Payload as New ID Payload. See section
2089 2.3.2.1 for generic ID Payload.
2093 2.3.26 Remove Channel User Payload
2095 Remove Channel User payload is used to remove a user from a channel network
2096 wide. This is used by routers to notify other routers that a user has
2097 left a channel. As routers keep information about users on channels a
2098 user leaving channel must be removed from all routers. Normal server may
2099 send this payload as well. Client must not send this payload.
2101 The payload may only be sent with SILC_PACKET_REMOVE_CHANNEL USER packet.
2102 It must not be sent in any other packet type. Following diagram
2103 represents the Remove Payload Payload.
2112 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
2113 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2114 | Client ID Length | |
2115 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2119 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2120 | Channel ID Length | |
2121 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2125 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2129 Figure 22: Remove Channel User Payload
2133 o Client ID Length (2 bytes) - Length of the Client ID Data area
2134 not including the length of any other fields in the payload.
2136 o Client ID Data (variable length) - The Client ID of the user
2137 that has left the channel.
2139 o Channel ID Length (2 bytes) - Length of the Channel ID Data area
2140 not including the length of any other fields in the payload.
2142 o Channel ID Data (variable length) - The Channel ID of the channel
2148 2.3.27 Set Mode Payload
2150 Set Mode Payload is used by servers and routers to distribute to each
2151 other the information about changed modes in the SILC network. The
2152 payload is sent when channel's or client's channel mode is changed.
2153 Server can send this to router which will broadcast it further to other
2154 routers. However, normal server must not reiceve this payload. Client
2155 must not send or receive this payload.
2157 The payload may only be sent with SILC_PACKET_SET_MODE packet.
2158 It must not be sent in any other packet type. Following diagram
2159 represents the Set Mode Payload.
2168 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
2169 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2170 | Mode Type | Payload Length |
2171 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2173 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2179 Figure 23: Set Mode Payload
2183 o Mode type (2 bytes) - Indicates the type of the mode that was
2184 changed. Every type has arguments associated to the type which
2185 are defined below. The following types are defined:
2187 0 SILC_MODE_TYPE_CHANNEL
2190 Arguments: (1) <Channel ID> (2) <Client ID>
2192 The <Channel ID> is the channel which mode was set and the
2193 <Client ID> is the client who set it.
2196 1 SILC_MODE_TYPE_UCHANNEL
2199 Arguments: (1) <Channel ID> (2) <Client ID>
2200 (3) <Target Client ID>
2202 The <Channel ID> is the channel where the <Client ID> and
2203 the <Target Client ID> is on. The <Client ID> is the client
2204 who set the <Target Client ID> mode.
2212 32768 - Private range
2214 Rest of the types are reserved for private use.
2216 o Payload Length (2 bytes) - Length of the entire Set Mode Payload
2217 including any associated Argument Payloads.
2219 o Mode Mask (4 bytes) - Indicates the set mode mask. This is
2220 specified by the mode type. See definitions of SILC_COMMAND_UMODE
2221 for client modes, SILC_COMMAND_CMODE for channel modes and
2222 SILC_COMMAND_CUMODE for client's channel modes in [SILC1].
2224 o Argument Nums (2 bytes) - Indicates the number of Argument
2225 Payloads associated to this payload. Mode types may define
2226 arguments to be send along this payload.
2234 ID's are extensively used in the SILC network to associate different
2235 entities. Following ID's has been defined to be used in the SILC
2241 When ever specific ID cannot be used this is used.
2245 Server ID to associate servers. See the format of
2250 Client ID to associate clients. See the format of
2255 Channel ID to associate channels. See the format of
2261 2.5 Packet Encryption And Decryption
2263 SILC packets are encrypted almost entirely. Only small part of SILC
2264 header is not encrypted as described in section 5.2 SILC Packet Header.
2265 The SILC Packet header is the first part of a packet to be encrypted
2266 and it is always encrypted with the key of the next receiver of the
2267 packet. The data payload area of the packet is always entirely
2268 encrypted and it is usually encrypted with the next receiver's key.
2269 However, there are some special packet types and packet payloads
2270 that require special encryption process. These special cases are
2271 described in the next sections. First is described the normal packet
2276 2.5.1 Normal Packet Encryption And Decryption
2278 Normal SILC packets are encrypted with the session key of the next
2279 receiver of the packet. The entire SILC Packet header and the packet
2280 data payload is is also encrypted with the same key. Padding of the
2281 packet is also encrypted always with the session key, also in special
2282 cases. Computed MAC of the packet must not be encrypted.
2284 Decryption process in these cases are straightforward. The receiver
2285 of the packet must first decrypt the SILC Packet header, or some parts
2286 of it, usually first 16 bytes of it. Then the receiver checks the
2287 packet type from the decrypted part of the header and can determine
2288 how the rest of the packet must be decrypted. If the packet type is
2289 any of the special cases described in following sections the packet
2290 decryption is special. If the packet type is not among those special
2291 packet types rest of the packet may be decrypted with the same key.
2293 Also, note that two bytes of the SILC Packet header are not encrypted
2294 thus it must be noticed in the decryption process by starting the
2295 decryption from the second byte of the header. This sets some rules
2296 to padding generation as well, see the section 2.7 Packet Padding
2299 With out a doubt, this sort of decryption processing causes some
2300 overhead to packet decryption, but never the less, is required.
2304 2.5.2 Channel Message Encryption And Decryption
2306 Channel Messages (Channel Message Payload) are always encrypted with
2307 the channel specific key. However, the SILC Packet header is not
2308 encrypted with that key. As in normal case, the header is encrypted
2309 with the key of the next receiver of the packet, who ever that might
2310 be. Note that in this case the encrypted data area is not touched
2311 at all; it must not be re-encrypted with the session key.
2313 Receiver of a channel message, who ever that is, is required to decrypt
2314 the SILC Packet header to be able to even recognize the packet to be as
2315 channel message. This is same procedure as for normal SILC packets.
2316 As the receiver founds the packet to be channel message, rest of the
2317 packet processing is special. Rest of the SILC Packet header is
2318 decrypted with the same session key along with the padding of the
2319 packet. After that the packet is protected with the channel specific
2320 key and hence can be decrypted only if the receiver is the client on
2321 the channel. See section 2.7 Packet Padding Generation for more
2322 information about padding on special packets.
2324 If the receiver of the channel message is router who is routing the
2325 message to another router then it must decrypt the Channel Message
2326 payload. Between routers (that is, between cells) channel messages
2327 are protected with session keys shared between the routers. This
2328 causes another special packet processing for channel messages. If
2329 the channel message is received from another router then the entire
2330 packet, including Channel Message payload, is encrypted with the
2331 session key shared between the routers. In this case the packet
2332 decryption process is as with normal SILC packets. Hence, if the
2333 router is sending channel message to another router the Channel
2334 Message payload must have been decrypted and must be re-encrypted
2335 with the session key shared between the another router. In this
2336 case the packet encryption is as with any normal SILC packet.
2338 It must be noted that this is only when the channel messages are sent
2339 from router to another router. In all other cases the channel
2340 message encryption and decryption is as described above. This
2341 different processing of channel messages with router to router
2342 connection is because channel keys are cell specific. All cells has
2343 their own channel keys thus the channel message traveling from one
2344 cell to another must be protected as it would be any normal SILC
2349 2.5.3 Private Message Encryption And Decryption
2351 By default, private message in SILC are protected by session keys.
2352 In this case the private message encryption and decryption process is
2353 equivalent to normal packet encryption and decryption.
2355 However, private messages can be protected with private message key
2356 which causes the packet to be special packet. The procedure in this
2357 case is very much alike to channel packets. The actual private message
2358 is encrypted with the private message key and other parts of the
2359 packet is encrypted with the session key. See 2.7 Packet Padding
2360 Generation for more information about padding on special packets.
2362 The difference from channel message processing is that server or router
2363 en route never decrypts the actual private message, as it does not
2364 have the key to do that. Thus, when sending packets between router
2365 the processing is same as in any other case as well; the packet's header
2366 and padding is protected by the session key and the data area is not
2369 The true receiver of the private message, client, that is, is able
2370 to decrypt the private message as it shares the key with the sender
2375 2.6 Packet MAC Generation
2377 Data integrity of a packet is protected by including a message
2378 authentication code (MAC) at the end of the packet. The MAC is computed
2379 from shared secret MAC key, that is established by the SILC Key Exchange
2380 protocol, and from the original contents of the packet. The MAC is
2381 always computed before the packet is encrypted, although after it is
2382 compressed if compression is used.
2384 The MAC is computed from entire packet. Every bit of data in the packet,
2385 including SILC Packet Header is used in the MAC computing. This way
2386 the entire packet becomes authenticated.
2388 If the packet is special packet MAC is computed from the entire packet
2389 but part of the packet may be encrypted before the MAC is computed.
2390 This is case, for example, with channel messages where the message data
2391 is encrypted with key that server may not now. In this case the MAC
2392 has been computed from the encrypted data.
2394 See [SILC1] for defined and allowed MAC algorithms.
2398 2.7 Packet Padding Generation
2400 Padding is needed in the packet because the packet is encrypted. It
2401 must always be multiple by eight (8) or multiple by the size of the
2402 cipher's block size, which ever is larger. The padding is always
2405 For normal packets the padding is added after the SILC Packet Header
2406 and between the Data Payload area. The padding for normal packets
2407 are calculated as follows:
2410 padding length = 16 - ((packet length - 2) % 16)
2413 The 16 is the maximum padding allowed in SILC packet. Two (2) is
2414 subtracted from the true length of the packet because two (2) bytes
2415 is not encrypted in SILC Packet Header, see section 2.2 SILC Packet
2416 Header. Those two bytes that are not encrypted must not be calculated
2417 to the padding length.
2419 For special packets the padding calculation may be different as special
2420 packets may be encrypted differently. In these cases the encrypted
2421 data area must already be multiple by the block size thus in this case
2422 the padding is calculated only for SILC Packet Header, not for any
2423 other area of the packet. The same algorithm works in this case as
2424 well, except that the `packet length' is now the SILC Packet Header
2425 length. In this case, as well, two (2) is subtracted from the
2428 The padding must be random data, preferably, generated by
2429 cryptographically strong random number generator.
2433 2.8 Packet Compression
2435 SILC Packets may be compressed. In this case the data payload area
2436 is compressed and all other areas of the packet must remain as they
2437 are. After compression is performed for the data area, the length
2438 field of Packet Header must be set to the compressed length of the
2441 The compression must always be applied before encryption. When
2442 the packet is received and decrypted the data area must be decompressed.
2443 Note that the true sender of the packet must apply the compression and
2444 the true receiver of the packet must apply the decompression. Any
2445 server or router en route must not decompress the packet.
2452 The sender of the packet must assemble the SILC Packet Header with
2453 correct values. It must set the Source ID of the header as its own
2454 ID, unless it is forwarding the packet. It must also set the Destination
2455 ID of the header to the true destination. If the destination is client
2456 it will be Client ID, if it is server it will be Server ID and if it is
2457 channel it will be Channel ID.
2459 If the sender wants to compress the packet it must apply the
2460 compression now. Sender must also compute the padding as described
2461 in above sections. Then sender must compute the MAC of the packet.
2463 Then sender encrypts the packet as has been described in above
2464 sections according whether the packet is normal packet or special
2465 packet. The computed MAC must not be encrypted.
2469 2.10 Packet Reception
2471 On packet reception the receiver must check that all fields in the
2472 SILC Packet Header are valid. It must check the flags of the
2473 header and act accordingly. It must also check the MAC of the packet
2474 and if it is to be failed the packet must be discarded. Also if the
2475 header of the packet includes any bad fields the packet must be
2478 See above sections on the decryption process of the received packet.
2480 The receiver must also check that the ID's in the header are valid
2481 ID's. Unsupported ID types or malformed ID's must cause packet
2482 rejection. The padding on the reception is always ignored.
2484 The receiver must also check the packet type and start parsing the
2485 packet according to the type. However, note the above sections on
2486 special packet types and their parsing.
2492 Routers are the primary entities in the SILC network that takes care
2493 of packet routing. However, normal servers routes packets as well, for
2494 example, when they are routing channel message to the local clients.
2495 Routing is quite simple as every packet tells the true origin and the
2496 true destination of the packet.
2498 It is still recommended for routers that has several routing connections
2499 to create route cache for those destinations that has faster route than
2500 the router's primary route. This information is available for the router
2501 when other router connects to the router. The connecting party then
2502 sends all of its locally connected clients, server and channels. These
2503 informations helps to create the route cache. Also, when new channels
2504 are created to a cell its information is broadcasted to all routers
2505 in the network. Channel ID's are based on router's ID thus it is easy
2506 to create route cache based on these informations. If faster route for
2507 destination does not exist in router's route cache the packet must be
2508 routed to the primary route (default route).
2510 For server who receives a packet to be routed to its locally connected
2511 client the server must check whether the particular packet type is
2512 allowed to be routed to the client. Not all packets may be sent by
2513 some odd entity to client that is indirectly connected to the sender.
2514 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2515 entities and sending packets to them. The section mentions the packets
2516 that may be sent to indirectly connected entities. It is clear that some
2517 server cannot send, for example, disconnect packet to client that is not
2518 directly connected to the server.
2522 2.12 Packet Forwarding
2524 Currently SILC command packets may be forwarded from one entity to another.
2525 Any other packet currently cannot be forwarded but support for more packet
2526 types may be added if needed. Forwarding is usually used by server to
2527 forward some command request coming from client to the router as the server
2528 may be incapable to handle the request. Forwarding may be only one hop
2529 long; the receiver of the packet with Forwarded flag set in the SILC
2530 Packet header must not forward the packet any further.
2532 The normal scenario is that client sends JOIN command to the server which
2533 is not able to create the channel as there are no local clients on the
2534 channel. Channels are created always by the router of the cell thus the
2535 packet must be forwarded to the router. The server forwards the original
2536 packet coming from client to the router after it has set the Forwarded
2537 flag to the SILC Packet header.
2539 Router receiving the packet knows that the packet has to be processed
2540 specially by checking the flags and the Forwarded flag in the SILC Packet
2541 header. After router has joined the client to the channel (and perhaps
2542 created a new channel) it sends normal command reply packet to the
2543 client. However, as the router doesn't have direct connection to the
2544 client the packet is sent through the server. Server detects that
2545 the command reply packet is destined to the client and sends it to
2550 2.13 Packet Broadcasting
2552 SILC packets may be broadcasted in SILC network. However, only router
2553 server may send or receive broadcast packets. Client and normal server
2554 must not send broadcast packets and they must ignore broadcast packets
2555 if they receive them. Broadcast packets are sent by setting Broadcast
2556 flag to the SILC packet header.
2558 Broadcasting packets means that the packet is sent to all routers in
2559 the SILC network, except to the router that sent the packet. The router
2560 receiving broadcast packet must send the packet to its primary route.
2561 The fact that SILC routers may have several router connections may
2562 cause problems, such as race conditions inside the SILC network, if
2563 care is not taken when broadcasting packets. Router must not send
2564 the broadcast packet to any other route except to its primary route.
2566 If the primary route of the router is the original sender of the packet
2567 the packet must not be sent to the primary route. This may happen
2568 if router has several router connections and some other router uses
2569 the router as its primary route.
2571 Routers use broadcast packets to broadcast for example information
2572 about newly registered clients, servers, channels etc. so that all the
2573 routers may keep these informations up to date.
2577 2.14 Packet Tunneling
2579 Tunneling is a feature that is available in SILC protocol. Tunneling
2580 means that extra SILC Packet Header is applied to the original packet
2581 and thus hiding the original packet entirely. There can be some
2582 interesting applications using tunneling, such as, using ID's based on
2583 private network IP addresses inside in the tunneled packet. This can
2584 open many interesting features relating to connecting to private network
2585 from the Internet with SILC and many more. However, this feature is
2586 optional currently in SILC as there does not exist thorough analysis of
2587 this feature. It is with out a doubt that there will be many more
2588 applications that has not yet been discovered. Thus, it is left
2589 to Internet Community to investigate the use of tunneling in SILC
2590 protocol. This document is updated according those investigations
2591 and additional documents on the issue may be written.
2595 3 Security Considerations
2597 Security is central to the design of this protocol, and these security
2598 considerations permeate the specification. Common security considerations
2599 such as keeping private keys truly private and using adequate lengths for
2600 symmetric and asymmetric keys must be followed in order to maintain the
2601 security of this protocol.
2607 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2608 Protocol Specification", Internet Draft, June 2000.
2610 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2611 Protocols", Internet Draft, June 2000.
2613 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2616 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2619 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2622 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2625 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2626 Infrastructure, Certificate and CRL Profile", RFC 2459,
2629 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2630 John Wiley & Sons, New York, NY, 1996.
2632 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2635 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2636 RFC 2412, November 1998.
2638 [ISAKMP] Maughan D., et al, "Internet Security Association and
2639 Key Management Protocol (ISAKMP)", RFC 2408, November
2642 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2643 (IKE)", RFC 2409, November 1998.
2645 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2646 Authentication", RFC 2104, February 1997.
2662 EMail: priikone@poseidon.pspt.fi
2664 This Internet-Draft expires 6 Jun 2001