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
34 areas, and its working groups. Note that other groups may also
35 distribute working documents as Internet-Drafts.
37 Internet-Drafts are draft documents valid for a maximum of six months
38 and may be updated, replaced, or obsoleted by other documents at any
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
43 http://www.ietf.org/ietf/1id-abstracts.txt
45 The list of Internet-Draft Shadow Directories can be accessed at
46 http://www.ietf.org/shadow.html
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 2.3.28 Set Mode List Payload .............................. XXX
109 2.4 SILC ID Types ............................................. 39
110 2.5 Packet Encryption And Decryption .......................... 39
111 2.5.1 Normal Packet Encryption And Decryption ............. 39
112 2.5.2 Channel Message Encryption And Decryption ........... 40
113 2.5.3 Private Message Encryption And Decryption ........... 41
114 2.6 Packet MAC Generation ..................................... 41
115 2.7 Packet Padding Generation ................................. 42
116 2.8 Packet Compression ........................................ 42
117 2.9 Packet Sending ............................................ 43
118 2.10 Packet Reception ......................................... 43
119 2.11 Packet Routing ........................................... 44
120 2.12 Packet Forwarding ........................................ 44
121 2.13 Packet Broadcasting ...................................... 45
122 2.14 Packet Tunneling ......................................... 45
123 3 Security Considerations ....................................... 46
124 4 References .................................................... 46
125 5 Author's Address .............................................. 47
131 Figure 1: Typical SILC Packet
132 Figure 2: SILC Packet Header
134 Figure 4: Argument Payload
135 Figure 5: Disconnect Payload
136 Figure 6: Success Payload
137 Figure 7: Failure Payload
138 Figure 8: Reject Payload
139 Figure 9: Notify Payload
140 Figure 10: Error Payload
141 Figure 11: Channel Message Payload
142 Figure 12: Channel Key Payload
143 Figure 13: Private Message Payload
144 Figure 14: Private Message Key Payload
145 Figure 15: Command Payload
146 Figure 16: Connection Auth Request Payload
147 Figure 17: New Client Payload
148 Figure 18: New Server Payload
149 Figure 19: New Channel Payload
150 Figure 20: New Channel User Payload
151 Figure 21: Replace ID Payload
152 Figure 22: Remove Channel User Payload
153 Figure 23: Set Mode Payload
159 This document describes a Packet Protocol used in the Secure Internet
160 Live Conferencing (SILC) protocol specified in the Secure Internet Live
161 Conferencing, Protocol Specification Internet Draft [SILC1]. This
162 protocol describes the packet types and packet payloads which defines
163 the contents of the packets. The protocol provides secure binary packet
164 protocol that assures that the contents of the packets are secured and
167 The basis of SILC protocol relies in the SILC packets and it is with
168 out a doubt the most important part of the protocol. It is also probably
169 the most complicated part of the protocol. Packets are used all the
170 time in the SILC network to send messages, commands and other information.
171 All packets in SILC network are always encrypted and their integrity
172 is assured by computed MACs. The protocol defines several packet types
173 and packet payloads. Each packet type usually has a specific packet
174 payload that actually defines the contents of the packet. Each packet
175 also includes a default SILC Packet Header that provides sufficient
176 information about the origin of the packet and destination of the
181 2 SILC Packet Protocol
186 SILC packets deliver messages from sender to receiver securely by
187 encrypting important fields of the packet. The packet consists of
188 default SILC Packet Header, Padding, Packet Payload data, and, packet
191 The following diagram illustrates typical SILC packet.
196 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
197 | n bytes | 1 - n bytes | n bytes | n bytes
198 | SILC Header | Padding | Data Payload | MAC
199 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
203 Figure 1: Typical SILC Packet
206 SILC Header is always the first part of the packet and its purpose
207 is to provide information about the packet. It provides for example
208 the packet type, origin of the packet and the destination of the packet.
209 The header is variable in length and first two (2) bytes of the
210 header (thus first two bytes of the packet) are not encrypted. The
211 first two (2) bytes are the length of the packet which is not encrypted.
212 See following section for description of SILC Packet header. Packets
213 without SILC header or with malformed SILC header must be dropped.
215 Padding follows the packet header. The purpose of the padding is to
216 make the packet multiple by eight (8) or by the block size of the
217 cipher used in the encryption, which ever is larger. The maximum
218 length of padding is currently 16 bytes. The padding is always
221 Data payload area follows padding and it is the actual data of the
222 packet. The packet data is the packet payloads defined in this
223 protocol. The data payload area is always encrypted.
225 The last part of SILC packet is the packet MAC that assures the
226 integrity of the packet. The MAC is always computed from the packet
227 before the encryption is applied to the packet. If compression is used
228 in the packet the MAC is computed after the compression has been
229 applied. The compression, on the other hand, is always applied before
232 All fields in all packet payloads are always in MSB (most significant
237 2.2 SILC Packet Header
239 The default SILC packet header is applied to all SILC packets and it is
240 variable in length. The purpose of SILC Packet header is to provide
241 detailed information about the packet. The receiver of the packet uses
242 the packet header to parse the packet and gain other relevant parameters
245 Following diagram represents the default SILC header format.
246 (*) indicates that this field is never encrypted. Other fields are
253 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
254 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
255 | Payload Length * | Flags | Packet Type |
256 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
257 | Source ID Length | Destination ID Length |
258 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
270 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
274 Figure 2: SILC Packet Header
278 o Payload Length (2 bytes) - Is the length of the packet
279 not including the padding of the packet. This field must
280 not be encrypted but must always be authenticated.
282 o Flags (1 byte) - Indicates flags to be used in packet
283 processing. Several flags may be set by ORing the flags
286 Following flags are reserved for this field:
291 In this case the field is ignored.
294 Private Message Key 0x01
296 Indicates that the packet must include private
297 message that is encrypted using private key set by
298 client. Servers does not know anything about this
299 key and this causes that the private message is
300 not handled by the server at all, it is just
301 passed along. See section 2.5.3 Private Message
302 Encryption And Decryption for more information.
307 Marks the packet to be forwarded. Some specific
308 packet types may be forwarded. Receiver of packet
309 with this flag set must not forward the packet any
310 further. See section 2.12 Packet Forwarding for
311 description of packet forwarding.
316 Marks the packet to be broadcasted. Client cannot
317 send broadcast packet and normal server cannot send
318 broadcast packet. Only router server may send broadcast
319 packet. The router receiving of packet with this flag
320 set must send (broadcast) the packet to its primary
321 route. If router has several router connections the
322 packet may be sent only to the primary route. See
323 section 2.13 Packet Broadcasting for description of
329 Marks that the packet is tunneled. Tunneling means
330 that extra SILC Packet Header has been applied to the
331 original packet. The outer header has this flag
332 set. See section 2.14 Packet Tunneling for more
338 o Packet Type (1 byte) - Is the type of the packet. Receiver
339 uses this field to parse the packet. See section 2.3
340 SILC Packets for list of defined packet types.
342 o Source ID Length (2 bytes) - Indicates the length of the
343 Source ID field in the header, not including this or any
346 o Destination ID Length (2 bytes) - Indicates the length of the
347 Destination ID field in the header, not including this or
350 o Src ID Type (1 byte) - Indicates the type of ID in the
351 Source ID field. See section 2.4 SILC ID Types for
354 o Source ID (variable length) - The actual source ID that
355 indicates who is the original sender of the packet.
357 o Dst ID Type (1 byte) - Indicates the type of ID in the
358 Destination ID field. See section 2.4 SILC ID Types for
361 o Destination ID (variable length) - The actual source ID that
362 indicates who is the end receiver of the packet.
366 2.3 SILC Packet Types
368 SILC packet types defines the contents of the packet and it is used by
369 the receiver to parse the packet. The packet type is 8 bits, as a one
370 byte, in length. The range for the packet types are from 0 - 255,
371 where 0 is never sent and 255 is currently reserved for future
372 extensions and must not be defined to any other purpose. Every SILC
373 specification compliant implementation should support all of these packet
376 The below list of the SILC Packet types includes reference to the packet
377 payload as well. Packet payloads are the actual packet, that is, the data
378 that the packet consists of. Each packet type defines packet payload
379 which usually may only be sent with the specific packet type.
381 Most of the packets are packets that must be destined directly to entity
382 that is connected to the sender. It is not allowed, for example, for
383 router to send disconnect packet to client that is not directly connected
384 to the router. However, there are some special packet types that may
385 be destined to some entity that the sender has not direct connection
386 with. These packets are for example private message packets, channel
387 message packets, command packets and some other packets that may be
388 broadcasted in the SILC network. If the packet is allowed to be sent to
389 indirectly connected entity it is mentioned separately in the packet
390 description (unless it is obvious as in private and channel message
391 packets). Other packets must not be sent or accepted, if sent, to
392 indirectly connected entities.
394 List of SILC Packet types are defined as follows.
399 This type is reserved and it is never sent.
402 1 SILC_PACKET_DISCONNECT
404 This packet is sent to disconnect the remote end. Reason of
405 the disconnection is sent inside the packet payload. Client
406 usually does not send this packet.
408 Payload of the packet: See section 2.3.3 Disconnect Payload
411 2 SILC_PACKET_SUCCESS
413 This packet is sent upon successful execution of some protocol.
414 The status of the success is sent in the packet.
416 Payload of the packet: See section 2.3.4 Success Payload
419 3 SILC_PACKET_FAILURE
421 This packet is sent upon failure of some protocol. The status
422 of the failure is sent in the packet.
424 Payload of the packet: See section 2.3.5 Failure Payload
429 This packet may be sent upon rejection of some protocol.
430 The status of the rejection is sent in the packet.
432 Payload of the packet: See section 2.3.6 Reject Payload
437 This packet is used to send notify message, usually from
438 server to client, although it may be sent from server to another
439 server as well. Client never sends this packet. Server may
440 send this packet to channel as well when the packet is
441 distributed to all clients on the channel.
443 Payload of the packet: See section 2.3.7 Notify Payload.
448 This packet is sent when an error occurs. Server may
449 send this packet. Client never sends this packet. The
450 client may entirely ignore the packet, however, server is
451 most likely to take action anyway. This packet may be sent
452 to entity that is indirectly connected to the sender.
454 Payload of the packet: See section 2.3.8 Error Payload.
457 7 SILC_PACKET_CHANNEL_MESSAGE
459 This packet is used to send messages to channels. The packet
460 includes Channel ID of the channel and the actual message to
461 the channel. Messages sent to the channel are always protected
462 by channel specific keys. Channel Keys are distributed by
463 SILC_PACKET_CHANNEL_KEY packet.
465 Payload of the packet: See section 2.3.9 Channel Message
469 8 SILC_PACKET_CHANNEL_KEY
471 This packet is used to distribute new key for particular
472 channel. Each channel has their own independent keys that
473 is used to protect the traffic on the channel. Only server
474 may send this packet. This packet may be sent to entity
475 that is indirectly connected to the sender.
477 Payload of the packet: See section 2.3.10 Channel Key Payload
480 9 SILC_PACKET_PRIVATE_MESSAGE
482 This packet is used to send private messages from client
483 to another client. By default, private messages are protected
484 by session keys established by normal key exchange protocol.
485 However, it is possible to use specific key to protect private
486 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
487 agree the key with the remote client. Pre-shared key may be
488 used as well if both of the client knows it, however, it needs
489 to be agreed outside SILC. See more of this in [SILC1].
491 Payload of the packet: See section 2.3.11 Private Message
495 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
497 This packet is used to agree about a key to be used to protect
498 the private messages between two clients. If this is not sent
499 the normal session key is used to protect the private messages
500 inside SILC network. Agreeing to use specific key to protect
501 private messages adds security, as no server between the two
502 clients will be able to decrypt the private message. However,
503 servers inside SILC network are considered to be trusted, thus
504 using normal session key to protect private messages does not
505 degree security. Whether to agree to use specific keys by
506 default or to use normal session keys by default, is
507 implementation specific issue. See more of this in [SILC1].
509 Payload of the packet: See section 2.3.12 Private Message
513 11 SILC_PACKET_COMMAND
515 This packet is used to send commands from client to server.
516 Server may send this packet to other servers as well. All
517 commands are listed in their own section SILC Command Types
518 in [SILC1]. The contents of this packet is command specific.
519 This packet may be sent to entity that is indirectly connected
522 Payload of the packet: See section 2.3.13 Command Payload
525 12 SILC_PACKET_COMMAND_REPLY
527 This packet is send as reply to the SILC_PACKET_COMMAND packet.
528 The contents of this packet is command specific. This packet
529 maybe sent to entity that is indirectly connected to the sender.
531 Payload of the packet: See section 2.3.14 Command Reply
532 Payload and section 2.3.13 Command
536 13 SILC_PACKET_KEY_EXCHANGE
538 This packet is used to start SILC Key Exchange Protocol,
539 described in detail in [SILC3].
541 Payload of the packet: Payload of this packet is described
542 in the section SILC Key Exchange
543 Protocol and its sub sections in
547 14 SILC_PACKET_KEY_EXCHANGE_1
549 This packet is used as part of the SILC Key Exchange Protocol.
551 Payload of the packet: Payload of this packet is described
552 in the section SILC Key Exchange
553 Protocol and its sub sections in
557 15 SILC_PACKET_KEY_EXCHANGE_2
559 This packet is used as part of the SILC Key Exchange Protocol.
561 Payload of the packet: Payload of this packet is described
562 in the section SILC Key Exchange
563 Protocol and its sub sections in
567 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
569 This packet is used to request the authentication method to
570 be used in the SILC Connection Authentication Protocol. If
571 initiator of the protocol does not know the mandatory
572 authentication method this packet is used to determine it.
574 The party receiving this payload must respond with the same
575 packet including the mandatory authentication method.
577 Payload of the packet: See section 2.3.15 Connection Auth
581 17 SILC_PACKET_CONNECTION_AUTH
583 This packet is used to start and perform the SILC Connection
584 Authentication Protocol. This protocol is used to authenticate
585 the connecting party. The protocol is described in detail in
588 Payload of the packet: Payload of this packet is described
589 in the section SILC Authentication
590 Protocol and it sub sections in [SILC].
593 18 SILC_PACKET_NEW_ID
595 This packet is used to distribute new ID's from server to
596 router and from router to all routers in the SILC network.
597 This is used when for example new client is registered to
598 SILC network. The newly created ID's of these operations are
599 distributed by this packet. Only server may send this packet,
600 however, client must be able to receive this packet.
602 Payload of the packet: See section 2.3.16 New ID Payload
605 19 SILC_PACKET_NEW_ID_LIST
607 This packet is used to distribute list of new ID's from
608 server to routers. This is equivalent to previous packet
609 type except that it may include several ID's. Client must
610 not send this packet.
612 Payload of the packet: See section 2.3.17 New ID List
616 20 SILC_PACKET_NEW_CLIENT
618 This packet is used by client to register itself to the
619 SILC network. This is sent after key exchange and
620 authentication protocols has been completed. Client sends
621 various information about itself in this packet.
623 Payload of the packet: See section 2.3.18 New Client Payload
626 21 SILC_PACKET_NEW_SERVER
628 This packet is used by server to register itself to the
629 SILC network. This is sent after key exchange and
630 authentication protocols has been completed. Server sends
631 this to the router it connected to, or, if router was
632 connecting, to the connected router. Server sends
633 its Server ID and other information in this packet.
634 Client must not send or receive this packet.
636 Payload of the packet: See section 2.3.19 New Server Payload
639 22 SILC_PACKET_NEW_CHANNEL
641 This packet is used to notify routers about newly created
642 channel. Channels are always created by the router and it must
643 notify other routers about the created channel. Router sends
644 this packet to its primary route. Client must not send this
645 packet. This packet maybe sent to entity that is indirectly
646 connected to the sender.
648 Payload of the packet: See section 2.3.20 New Channel Payload
651 23 SILC_PACKET_NEW_CHANNEL_USER
653 This packet is used to notify routers about new user on channel.
654 The packet is sent after user has joined to the channel. Server
655 may send this packet to its router and router may send this to
656 its primary router. Client must not send this packet. This
657 packet maybe sent to entity that is indirectly connected to
660 When received, the server or router must distribute
661 SILC_NOTIFY_TYPE_JOIN to local clients on the channel.
663 Payload of the packet: See section 2.3.21 New Channel User
667 24 SILC_PACKET_NEW_CHANNEL_LIST
669 This packet is used to distribute list of created channels
670 from server to routers. This is equivalent to the packet
671 SILC_PACKET_NEW_CHANNEL except that it may include several
672 payloads. Client must not send this packet.
674 Payload of the packet: See section 2.3.22 New Channel List
678 25 SILC_PACKET_NEW_CHANNEL_USER_LIST
680 This packet is used to distribute list of users on specific
681 channel from server to routers. This is equivalent to the
682 packet SILC_PACKET_NEW_CHANNEL_USER except that it may
683 include several payloads. Client must not send this packet.
685 When received, the server or router must distribute
686 SILC_NOTIFY_TYPE_JOIN to local clients on the channel.
688 Payload of the packet: See section 2.3.23 New Channel User
692 26 SILC_PACKET_REPLACE_ID
694 This packet is used to replace old ID with new ID sent in
695 the packet payload. For example, when client changes its
696 nickname new ID is created and this packet can be used to
697 distribute the new ID and the old ID is removed when it is
698 send in the packet. Client cannot send or receive this
699 packet. This packet maybe sent to entity that is indirectly
700 connected to the sender.
702 When received and the replaced ID is Client ID the server or
703 router must distribute SILC_NOTIFY_TYPE_NICK_CHANGE to the
704 local clients on the channels (if any) of the client whose
705 ID was changed. However, the notify type must be sent only
708 Payload of the packet: See section 2.3.24 Replace ID Payload
711 27 SILC_PACKET_REMOVE_ID
713 This packet is used to removed ID. For example, when client
714 exits SILC network its ID is removed. Client must not send
715 this packet. This packet maybe sent to entity that is
716 indirectly connected to the sender.
718 When received and the removed ID is Client ID the server or
719 router must distribute SILC_NOTIFY_TYPE_SIGNOFF to the
720 local clients on the channels (if any) of the client whose
721 ID was removed. However, the notify type must be sent only
724 Payload of the packet: See section 2.3.25 Remove ID Payload
727 28 SILC_PACKET_REMOVE_CHANNEL_USER
729 This packet is used to remove user from a channel. This is
730 used by router to notify other routers in the network that a
731 client has left a channel. This packet maybe sent to entity
732 that is indirectly connected to the sender.
734 When received, the server or router must distribute
735 SILC_NOTIFY_TYPE_LEAVE to local clients on the channel.
737 Payload of the packet: See section 2.3.26 Remove Channel User
743 This packet is used to indicate that re-key must be performed
744 for session keys. See section Session Key Regeneration in
745 [SILC1] for more information. This packet does not have
749 30 SILC_PACKET_REKEY_DONE
751 This packet is used to indicate that re-key is performed and
752 new keys must be used hereafter. This is sent only if re-key
753 was done without PFS option. If PFS is set, this is not sent
754 as SILC Key Exchange protocol is executed. This packet does
758 31 SILC_PACKET_SET_MODE
760 This packet is used by servers and routers to inform each
761 other about changed modes. When channel's and client'c channel
762 mode is changed this packet is used to distribute the information
763 to all routers in the network. Server can send this packet but
764 must not receive it. Router can send and receive this packet.
765 Client must not send or receive this packet.
767 Payload of the packet: See section 2.3.27 Set Mode Payload
770 32 SILC_PACKET_SET_MODE_LIST
772 This packet is used to distribute list of Set Mode payloads
773 from server to routers. This is equivalent to the packet
774 SILC_PACKET_SET_MODE except that it may include several
775 payloads. Client must not send this packet.
777 Payload of the packet: See section 2.3.28 Set Mode List
780 33 SILC_PACKET_HEARTBEAT
782 This packet is used by clients, servers and routers to keep the
783 connection alive. It is recommended that all servers implement
784 keepalive actions and perform it to both direction in a link.
785 This packet does not have a payload.
790 Currently undefined commands.
795 These packet types are reserved for private use and they will not
796 be defined by this document.
801 This type is reserved for future extensions and currently it
807 2.3.1 SILC Packet Payloads
809 All payloads resides in the main data area of the SILC packet. However
810 all payloads must be at the start of the data area after the default
811 SILC packet header and padding. All fields in the packet payload are
812 always encrypted, as, they reside in the data area of the packet which
815 Payloads described in this section are common payloads that must be
816 accepted anytime during SILC session. Most of the payloads may only
817 be sent with specific packet type which is defined in the description
820 There are a lot of other payloads in the SILC as well. However, they
821 are not common in the sense that they could be sent at any time.
822 These payloads are not described in this section. These are payloads
823 such as SILC Key Exchange payloads and so on. These are described
824 in [SILC1] and [SILC3].
828 2.3.2 Generic payloads
830 This section describes generic payloads that are not associated to any
831 specific packet type. They can be used for example inside some other
838 This payload can be used to send an ID. ID's are variable length thus
839 this payload provides a way to send variable length ID's.
841 Following diagram represents the ID Payload.
846 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
847 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
848 | ID Type | ID Length |
849 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
853 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
861 o ID Type (2 bytes) - Indicates the type of the ID. See
862 section 2.4 SILC ID Types for list of defined ID types.
864 o ID Length (2 bytes) - Length of the ID Data area not
865 including the length of any other fields in the payload.
867 o ID Data (variable length) - The actual ID data.
872 2.3.2.2 Argument Payload
874 Argument Payload is used to set arguments for any packet payload that
875 needs and supports arguments, such as commands. Number of arguments
876 associated with a packet must be indicated by the packet payload who
877 needs the arguments. Argument Payloads must always reside right after
878 the packet payload needing the arguments. Incorrect amount of argument
879 payloads must cause rejection of the packet. Following diagram represents
880 the Argument Payload.
886 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
887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
888 | Payload Length | Argument Type | |
889 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
893 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
897 Figure 4: Argument Payload
901 o Payload Length (2 bytes) - Length of the argument payload data
902 area not including the length of any other fields in the
905 o Argument Type (1 byte) - Indicates the type of the argument.
906 Every argument may have a specific type that must be defined
907 by the packet payload needing the argument. For example
908 every command specify a number for each argument that maybe
909 associated with the command. By using this number the receiver
910 of the packet knows what type of argument this is. If there is
911 no specific argument type this field is set to zero (0).
913 o Argument Data (variable length) - Argument data.
918 2.3.3 Disconnect Payload
920 Disconnect payload is sent upon disconnection. The payload is simple;
921 reason of disconnection is sent to the disconnected party.
923 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
924 must not be sent in any other packet type. Following diagram represents
925 the Disconnect Payload.
936 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
937 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
939 ~ Disconnect Message ~
941 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
945 Figure 5: Disconnect Payload
951 o Disconnect Message (variable length) - Human readable
952 reason of the disconnection.
957 2.3.4 Success Payload
959 Success payload is sent when some protocol execution is successfully
960 completed. The payload is simple; indication of the success is sent.
961 This maybe any data, including binary or human readable data.
966 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
967 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
969 ~ Success Indication ~
971 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
975 Figure 6: Success Payload
979 o Success Indication (variable length) - Indication of
980 the success. This maybe for example some flag that
981 indicates the protocol and the success status or human
982 readable success message. The true length of this
983 payload is available by calculating it from the SILC
989 2.3.5 Failure Payload
991 This is opposite of Success Payload. Indication of failure of
992 some protocol is sent in the payload.
998 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
999 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1001 ~ Failure Indication ~
1003 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1007 Figure 7: Failure Payload
1011 o Failure Indication (variable length) - Indication of
1012 the failure. This maybe for example some flag that
1013 indicates the protocol and the failure status or human
1014 readable failure message. The true length of this
1015 payload is available by calculating it from the SILC
1021 2.3.6 Reject Payload
1023 This payload is sent when some protocol is rejected to be executed.
1024 Other operations may send this as well that was rejected. The
1025 indication of the rejection is sent in the payload. The indication
1026 may be binary or human readable data.
1032 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
1033 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1035 ~ Reject Indication ~
1037 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1041 Figure 8: Reject Payload
1045 o Reject Indication (variable length) - Indication of
1046 the rejection. This maybe for example some flag that
1047 indicates the protocol and the rejection status or human
1048 readable rejection message. The true length of this
1049 payload is available by calculating it from the SILC
1058 2.3.7 Notify Payload
1060 Notify payload is used to send notify messages. The payload is usually
1061 sent from server to client, however, server may send it to another
1062 server as well. This payload may also be sent to a channel. Client must
1063 not send this payload. The receiver of this payload may totally ignore the
1064 contents of the payload, however, notify message should be audited.
1066 The payload may only be sent with SILC_PACKET_NOTIFY packet. It must
1067 not be sent in any other packet type. Following diagram represents the
1073 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
1074 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1075 | Notify Type | Payload Length |
1076 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1082 Figure 9: Notify Payload
1086 o Notify Type (2 bytes) - Indicates the type of the notify
1089 o Payload Length (2 bytes) - Length of the entire Notify Payload
1090 including any associated Argument Payloads.
1092 o Argument Nums (2 bytes) - Indicates the number of Argument
1093 Payloads associated to this payload. Notify types may define
1094 arguments to be send along the notify message.
1097 Following list of currently defined notify types. The format for notify
1098 arguments is same as in SILC commands described in [SILC1]. Also, all
1099 ID's sent in arguments are sent inside ID Payload.
1102 0 SILC_NOTIFY_TYPE_NONE
1104 If no specific notify type apply for the notify message this type
1108 Arguments: (1) <message>
1110 The <message> is implementation specific free text string. Receiver
1111 may ignore this message.
1114 1 SILC_NOTIFY_TYPE_INVITE
1116 Sent when receiver has been invited to a channel. This type must be
1117 sent directly to the invited client.
1120 Arguments: (1) <Client ID> (2) <Channel ID>
1122 The <Client ID> is the client who invites the receiver of this type
1123 to channel indicated by <Channel ID>.
1126 2 SILC_NOTIFY_TYPE_JOIN
1128 Sent when client has joined to a channel. The server must distribute
1129 this type only to the local clients on the channel and then send
1130 SILC_PACKET_NEW_CHANNEL_USER packet to its primary route. The router
1131 or server receiving the packet distributes this type to the local
1132 clients on the channel. See description of SILC_PACKET_NEW_CHANNEL_USER
1133 packet for more information.
1136 Arguments: (1) <Client ID>
1138 The <Client ID> is the client that joined to the channel.
1141 3 SILC_NOTIFY_TYPE_LEAVE
1143 Sent when client has left a channel. The server must distribute
1144 this type only to the local clients on the channel and then send
1145 SILC_PACKET_REMOVE_CHANNEL_USER packet to its primary route. The
1146 router or server receiving the packet distributes this type to the
1147 local clients on the channel. See description of
1148 SILC_PACKET_REMOVE_CHANNEL_USER packet for more information.
1151 Arguments: (1) <Client ID>
1153 The <Client ID> is the client who left the channel.
1156 4 SILC_NOTIFY_TYPE_SIGNOFF
1158 Sent when client signoffs from SILC network. This type is sent only
1159 if the client was joined to any channel. This type is sent by server
1160 or router when SILC_PACKET_REMOVE_ID packet has been received. See
1161 detailed information from description of SILC_PACKET_REMOVE_ID packet.
1164 Arguments: (1) <Client ID>
1166 The <Client ID> is the client who left SILC network.
1169 5 SILC_NOTIFY_TYPE_TOPIC_SET
1171 Sent when topic is set/changed on a channel. This type must be sent
1172 only to the clients who is joined on the channel whose topic was
1176 Arguments: (1) <Client ID> (2) <topic>
1178 The <Client ID> is the client who set or changed the <topic>.
1181 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1183 Sent when client changes nick on a channel. This type is sent only if
1184 the client has joined to any channel. This type is sent by server or
1185 router when SILC_PACKET_REPLACE_ID packet has been received. See
1186 detailed information from description of SILC_PACKET_REPLACE_ID packet.
1189 Arguments: (1) <Old Client ID> (2) <New Client ID>
1191 The <Old Client ID> is the old ID of the client who changed the
1192 nickname. The <New Client ID> is the new ID generated by the change
1196 7 SILC_NOTIFY_TYPE_CMODE_CHANGE
1198 Sent when channel mode has changed. This type must be sent only to
1199 the clients who is joined on the channel whose mode was changed.
1202 Arguments: (1) <Client ID> (2) <mode mask>
1204 The <Client ID> is the client who changed the mode. The <mode mask>
1205 is the new mode mask of the channel.
1208 8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
1210 Sent when user mode on channel has changed. This type must be sent
1211 only to the clients who is joined on the channel where the target
1215 Arguments: (1) <Client ID> (2) <mode mask>
1216 (3) <Target Client ID>
1218 The <Client ID> is the client who changed the mode. The <mode mask>
1219 is the new mode mask of the channel. The <Target Client ID> is the
1220 client which mode was changed.
1223 9 SILC_NOTIFY_TYPE_MOTD
1225 Sent when Message of the Day (motd) is sent to client.
1228 Arguments: (1) <motd>
1230 The <motd> is the Message of the Day.
1233 10 SILC_NOTIFY_TYPE_CHANNEL_CHANGE
1235 Sent when channel's ID has changed for a reason or another. This
1236 is sent by noral server to the client. Client must change the
1237 old Channel ID to the new one. This type must be sent only to the
1238 clients who is joined on the channel.
1241 Arguments: (1) <Old Channel ID> (2) <New Channel ID>
1243 The <Old Channel ID> is the channel's old ID and the <New Channel ID>
1244 is the new one that must replace the old one.
1248 Notify types starting from 16384 are reserved for private notify
1255 Error payload is sent upon error. Error may occur in various
1256 conditions when server sends this packet. Client may not send this
1257 payload but must be able to accept it. However, client may
1258 totally ignore the contents of the packet as server is going to
1259 take action on the error anyway. However, it is recommended
1260 that the client takes error packet seriously.
1266 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
1267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1271 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1275 Figure 10: Error Payload
1279 o Error Message (variable length) - Human readable error
1285 2.3.9 Channel Message Payload
1287 Channel messages are the most common messages sent in the SILC.
1288 Channel Message Payload is used to send message to channels. These
1289 messages can only be sent if client has joined to some channel.
1290 Even though this packet is the most common in SILC it is still
1291 special packet. Some special handling on sending and reception
1292 of channel message is required.
1294 Padding must be applied into this payload since the payload is
1295 encrypted separately from other parts of the packet with the
1296 channel specific key. Hence the requirement of the padding.
1297 The padding should be random data. The packet must be made
1298 multiple by eight (8) or by the block size of the cipher, which
1301 The SILC header in this packet is encrypted with the session key
1302 of the next receiver of the packet. Nothing else is encrypted
1303 with that key. Thus, the actual packet and padding to be
1304 encrypted with the session key is SILC Header plus padding to it
1305 to make it multiple by eight (8) or multiple by the block size
1306 of the cipher, which ever is larger.
1308 Receiver of the the channel message packet is able to determine
1309 the channel the message is destined to by checking the destination
1310 ID from the SILC Packet header which tells the destination channel.
1311 The original sender of the packet is also determined by checking
1312 the source ID from the header which tells the client who sent
1315 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1316 It must not be sent in any other packet type. Following diagram
1317 represents the Channel Message Payload.
1319 (*) indicates that the field is not encrypted.
1325 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
1326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1327 | Message Length | |
1328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1333 | Padding Length | |
1334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1338 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1340 ~ Initial Vector * ~
1342 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1346 Figure 11: Channel Message Payload
1350 o Message Length (2 bytes) - Indicates the length of the
1351 the Message Data field in the payload, not including any
1354 o Message Data (variable length) - The actual message to
1357 o Padding Length (2 bytes) - Indicates the length of the
1358 Padding field in the payload, not including any other
1361 o Padding (variable length) - The padding that must be
1362 applied because this payload is encrypted separately from
1363 other parts of the packet.
1365 o Initial Vector (variable length) - The initial vector
1366 that has been used in packet encryption. It needs to be
1367 used in the packet decryption as well. What this field
1368 includes is implementation issue. However, it is
1369 recommended that it would be random data or, perhaps,
1370 a timestamp. It is not recommended to use zero (0) as
1371 initial vector. This field is not encrypted. This field
1372 is not included into the padding calculation. Length
1373 of this field equals the cipher's block size. This field
1374 is, however, authenticated.
1379 2.3.10 Channel Key Payload
1381 All traffic in channels are protected by channel specific keys.
1382 Channel Key Payload is used to distribute channel keys to all
1383 clients on the particular channel. Channel keys are sent when
1384 the channel is created, when new user joins to the channel and
1385 whenever a user has left a channel. Server creates the new
1386 channel key and distributes it to the clients by encrypting this
1387 payload with the session key shared between the server and
1388 the client. After that, client starts using the key received
1389 in this payload to protect the traffic on the channel.
1391 The client who is joining to the channel receives its key in the
1392 SILC_COMMAND_JOIN command reply message thus it is not necessary to
1393 send this payload to the entity who sent the SILC_COMMAND_JOIN command.
1395 Channel keys are cell specific thus every router in cell have
1396 to create a channel key and distribute it if any client in the
1397 cell has joined to a channel. Channel traffic between cell's
1398 are not encrypted using channel keys, they are encrypted using
1399 normal session keys between two routers. Inside a cell, all
1400 channel traffic is encrypted with the specified channel key.
1401 Channel key should expire periodically, say, in one hour, in
1402 which case new channel key is created and distributed.
1404 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1405 It must not be sent in any other packet type. Following diagram
1406 represents the Channel Key Payload.
1423 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
1424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1425 | Channel ID Length | |
1426 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1430 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1431 | Cipher Name Length | |
1432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1436 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1437 | Channel Key Length | |
1438 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1442 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1446 Figure 12: Channel Key Payload
1451 o Channel ID Length (2 bytes) - Indicates the length of the
1452 Channel ID field in the payload, not including any other
1455 o Channel ID (variable length) - The Channel ID of the
1456 channel this key is meant for.
1458 o Cipher Name Length (2 bytes) - Indicates the length of the
1459 Cipher name field in the payload, not including any other
1462 o Cipher Name (variable length) - Name of the cipher used
1463 in the protection of channel traffic. This name is
1464 initially decided by the creator of the channel but it
1465 may change during the life time of the channel as well.
1467 o Channel Key Length (2 bytes) - Indicates the length of the
1468 Channel Key field in the payload, not including any other
1471 o Channel Key (variable length) - The actual channel key
1472 material. This key is used as such as key material for
1473 encryption function.
1478 2.3.11 Private Message Payload
1480 Private Message Payload is used to send private message between
1481 two clients (or users for that matter). The messages are sent only
1482 to the specified user and no other user inside SILC network is
1483 able to see the message. The message is protected by the session
1484 key established by the SILC Key Exchange Protocol. However,
1485 it is also possible to agree to use specific keys to protect
1486 just the private messages. See section 2.3.11 Private Message
1487 Key Payload for detailed description of how to agree to use
1490 If normal session key is used to protect the message, every
1491 server between the sender client and the receiving client needs
1492 to decrypt the packet and always re-encrypt it with the session
1493 key of the next receiver of the packet. See section Client
1494 To Client in [SILC1].
1496 When specific key is used to protect the message, servers between
1497 the sender and the receiver needs not to decrypt/re-encrypt the
1498 packet. Section 4.8.2 Client To Client in [SILC1] gives example of
1499 this scheme as well.
1501 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1502 packet. It must not be sent in any other packet type. Following
1503 diagram represents the Private Message Payload.
1509 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
1510 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1511 | Nickname Length | |
1512 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1516 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1524 Figure 13: Private Message Payload
1528 o Nickname Length (2 bytes) - Indicates the length of the
1529 Nickname field, not including any other field.
1531 o Nickname (variable length) - Nickname of the sender of the
1532 private message. This should not be trusted as a definite
1533 sender of the private message. The SILC Packet Header in
1534 the packet indicates the true sender of the packet and
1535 client should verify that the nickname sent here belongs
1536 to the Client ID in the SILC Packet Header. This nickname
1537 is merely provided to be displayed by the client.
1539 o Message Data (variable length) - The actual message to
1540 the client. Rest of the packet is reserved for the message
1546 2.3.12 Private Message Key Payload
1548 This payload is used to send key from client to another client that
1549 is going to be used to protect the private messages between these
1550 two clients. If this payload is not sent normal session key
1551 established by the SILC Key Exchange Protocol is used to protect
1552 the private messages.
1554 This payload may only be sent by client to another client. Server
1555 must not send this payload at any time. After sending this payload
1556 the sender of private messages must set the Private Message Key
1557 flag into SILC Packet Header.
1559 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1560 packet. It must not be sent in any other packet type. Following
1561 diagram represents the Private Message Key Payload.
1567 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
1568 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1569 | Private Message Key Length | |
1570 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1572 ~ Private Message Key ~
1574 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1578 Figure 14: Private Message Key Payload
1584 o Private Message Key Length (2 bytes) - Indicates the length
1585 of the Private Message Key field in the payload, not including
1588 o Private Message Key (variable length) - The actual private
1589 message key material. This key is used as such as key material
1590 for encryption function.
1595 2.3.13 Command Payload
1597 Command Payload is used to send SILC commands from client to server.
1598 Also server may send commands to other servers. Following diagram
1599 represents the Command Payload.
1605 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
1606 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1607 | Payload Length | SILC Command | Arguments Num |
1608 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1610 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1614 Figure 15: Command Payload
1618 o Payload Length (2 bytes) - Length of the entire command
1619 payload including any command argument payloads associated
1622 o SILC Command (1 byte) - SILC Command identifier. This must
1623 be set to non-zero value. If zero (0) value is found in this
1624 field the packet must be discarded.
1626 o Arguments Num (1 byte) - Indicates the number of arguments
1627 associated with the command. If there are no arguments this
1628 field is set to zero (0). The arguments must follow the
1629 command payload. See section 2.3.2.2 for definition of the
1632 o Command Unifier (2 bytes) - Unifies this command at the
1633 sender's end. The entity who replies to this command must
1634 set the value found from this field into the Command Payload
1635 used to send the reply to the sender. This way the sender
1636 can identify which command reply belongs to which originally
1637 sent command. What this field includes is implementation
1638 issue but it is recommended that wrapping counter value is
1639 used in the field. Value zero (0) in this field means that
1640 no specific value is set.
1643 See [SILC1] for detailed description of different SILC commands,
1644 their arguments and their reply messages.
1648 2.3.14 Command Reply Payload
1650 Command Reply Payload is used to send replies to the commands. The
1651 Command Reply Payload is identical to the Command Payload thus see the
1652 upper sections for Command Payload and for Command Argument Payload
1653 specifications. Command Reply message uses the Command Argument Payload
1656 The entity who sends the reply packet must set the Command Unifier
1657 field in the reply packet's Command Payload to the value it received
1658 in the original command packet.
1660 See SILC Commands in [SILC1] for detailed description of different
1661 SILC commands, their arguments and their reply messages.
1665 2.3.15 Connection Auth Request Payload
1667 Client may send this payload to server to request the authentication
1668 method that must be used in authentication protocol. If client knows
1669 this information beforehand this payload is not necessary to be sent.
1670 Server performing authentication with another server may also send
1671 this payload to request the authentication method. If the connecting
1672 server already knows this information this payload is not necessary
1675 Server receiving this request must reply with same payload sending
1676 the mandatory authentication method. Algorithms that may be required
1677 to be used by the authentication method are the ones already
1678 established by the SILC Key Exchange protocol. See section Key
1679 Exchange Start Payload in [SILC3] for detailed information.
1681 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1682 packet. It must not be sent in any other packet type. Following
1683 diagram represents the Connection Auth Request Payload.
1689 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
1690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1691 | Connection Type | Authentication Method |
1692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1696 Figure 16: Connection Auth Request Payload
1700 o Connection Type (2 bytes) - Indicates the type of the ID.
1701 Following connection types are defined:
1707 If any other type is found in this field the packet must be
1708 discarded and the authentication must be failed.
1710 o Authentication Method (2 bytes) - Indicates the authentication
1711 method to be used in the authentication protocol. Following
1712 authentication methods are defined:
1717 1 password (mandatory)
1718 2 public key (mandatory)
1720 If any other type is found in this field the packet must be
1721 discarded and the authentication must be failed. If this
1722 payload is sent as request to receive the mandatory
1723 authentication method this field must be set to zero (0),
1724 indicating that receiver should send the mandatory
1725 authentication method. The receiver sending this payload
1726 to the requesting party, may also set this field to zero (0)
1727 to indicate that authentication is not required. In this
1728 case authentication protocol still must be started but
1729 server is most likely to respond with SILC_PACKET_SUCCESS
1735 2.3.16 New ID Payload
1737 New ID Payload is a multipurpose payload. It is used to send newly
1738 created ID's from clients and servers. When client connects to server
1739 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
1740 packet, server replies with this packet by sending the created ID for
1741 the client. Server always creates the ID for the client.
1743 This payload is also used when server tells its router that new client
1744 has registered to the SILC network. In this case the server sends
1745 the Client ID of the client to the router. Similary when router
1746 distributes information to other routers about the client in the SILC
1747 network this payload is used.
1749 Also, when server connects to router, router uses this payload to inform
1750 other routers about new server in the SILC network. However, every
1751 server (or router) creates their own ID's thus the ID distributed by
1752 this payload is not created by the distributor in this case. Servers
1753 create their own ID's. Server registers itself to the network by sending
1754 SILC_PACKET_NEW_SERVER to the router it connected to. The case is same
1755 when router connects to another router.
1757 However, this payload is not and must not be used to send information
1758 about new channels. New channels are always distributed by sending the
1759 dedicated SILC_PACKET_NEW_CHANNEL packet.
1761 Hence, this payload is very important and used every time when some
1762 new entity is registered to the SILC network. Client never sends this
1763 payload. Both client and server (and router) may receive this payload.
1765 The packet uses generic ID Payload as New ID Payload. See section
1766 2.3.2.1 for generic ID Payload.
1770 2.3.17 New ID List Payload
1772 New ID List Payload is used to distribute list of ID's usually from
1773 server to router but also from router to other routers in the network.
1774 This payload is used, for example, when server is connected to router
1775 and the server wants to distribute all of its locally connected clients
1776 and locally created channels to the router. It is convenient in this
1777 case to use this payload instead of sending all the information one
1778 by one using New ID Payload.
1780 There is no specific payload for this packet type. The packet type
1781 uses same payload as described in previous section. To form a list
1782 several payloads is put in the packet each after each. The payload
1783 is variable in length but can be calculated by calculating the ID
1784 Type field, Length field and the ID Data fields together. This forms
1785 one New ID Payload in the list.
1787 The list of payloads may only be sent with SILC_PACKET_NEW_ID_LIST
1788 packet. They must not be sent in any other packet type.
1792 2.3.18 New Client Payload
1794 When client is connected to the server, keys has been exchanged and
1795 connection has been authenticated client must register itself to the
1796 server. Clients first packet after key exchange and authentication
1797 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
1798 the relevant information about the connected user. Server creates a new
1799 client ID for the client when received this payload and sends it to the
1800 client in New ID Payload.
1802 This payload sends username and real name of the user on the remote host
1803 which is connected to the SILC server with SILC client. The server
1804 creates the client ID according the information sent in this payload.
1805 The nickname of the user becomes the username sent in this payload.
1806 However, client should call NICK command after sending this payload to
1807 set the real nickname of the user which is then used to create new
1810 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
1811 must not be sent in any other packet type. Following diagram represents
1812 the New Client Payload.
1819 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
1820 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1821 | Username Length | |
1822 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1826 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1827 | Real Name Length | |
1828 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1832 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1836 Figure 17: New Client Payload
1840 o Username Length (2 bytes) - Length of the username.
1842 o Username (variable length) - The username of the user on
1843 the host where connecting to the SILC server.
1845 o Real Name Length (2 bytes) - Length of the Real Name.
1847 o Real Name (variable length) - The real name of the user
1848 on the host where connecting to the SILC server.
1853 2.3.19 New Server Payload
1855 This payload is sent by server when it has completed successfully both
1856 key exchange and connection authentication protocols. The server
1857 uses this payload to register itself to the SILC network. The
1858 first packet after these key exchange and authentication protocols
1859 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
1860 of the server that it has created by itself. It also includes a
1861 name of the server that is associated to the Server ID.
1863 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
1864 must not be sent in any other packet type. Following diagram represents
1865 the New Server Payload.
1874 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
1875 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1876 | Server ID Length | |
1877 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1881 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1882 | Server Name Length | |
1883 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1891 Figure 18: New Server Payload
1895 o Server ID Length (2 bytes) - Length of the ID Data area not
1896 including the length of any other fields in the payload.
1898 o Server ID Data (variable length) - The actual Server ID
1901 o Server Name Length (2 bytes) - Length of the server name.
1903 o Server Name (variable length) - The server name.
1908 2.3.20 New Channel Payload
1910 Information about newly created channel is broadcasted to all routers
1911 in the SILC network by sending this packet payload. Channels are
1912 created by router of the cell. Server never creates channels unless
1913 it is a standalone server and it does not have router connection,
1914 in this case server acts as router. Normal server forwards JOIN command
1915 to the router (after it has received JOIN command from client) which
1916 then processes the command and creates the channel. Client never sends
1919 The payload may only be sent with SILC_PACKET_NEW_CHANNEL packet.
1920 It must not be sent in any other packet type. Following diagram
1921 represents the New Channel Payload.
1929 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
1930 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1931 | Channel Name Length | |
1932 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1936 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1937 | Channel ID Length | |
1938 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1942 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1946 Figure 19: New Channel Payload
1951 o Channel Name Length (2 bytes) - Length of the channel name.
1953 o Channel Name (variable length) - The name of the created
1956 o Channel ID Length (2 bytes) - Length of the Channel ID.
1958 o Channel ID (variable length) - The created Channel ID.
1963 2.3.21 New Channel User Payload
1965 When client (user) joins to a channel, server must notify routers
1966 about the new user on the channel. Normal server sends this packet
1967 payload to its router which then broadcasts the packet further.
1968 Router sends this packet always to its primary router. Client must
1969 not send this packet payload. The mode of the user is NONE after
1970 user has joined to the channel.
1972 The payload may only be sent with SILC_PACKET_NEW_CHANNEL_USER
1973 packet. It must not be sent in any other packet type. Following
1974 diagram represents the New Channel User Payload.
1984 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
1985 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1986 | Channel ID Length | |
1987 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1991 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1992 | Client ID Length | |
1993 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1997 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2001 Figure 20: New Channel User Payload
2005 o Channel ID Length (2 bytes) - Length of the Channel ID.
2007 o Channel ID (variable length) - The Channel ID of the channel
2008 to which the client has joined.
2010 o Client ID Length (2 bytes) - Length of the Client ID.
2012 o Client ID (variable length) - The Client ID of the client
2013 who has joined the channel.
2018 2.3.22 New Channel List Payload
2020 This payload is used to distribute list of new channels from server
2021 to routers. It might be convenient to send list of new channels when
2022 existing server connects to router, instead of sending them one
2025 There is no specific payload for this packet type. The packet type
2026 uses same payload as described in 2.3.19 New Channel Payload. To form
2027 a list several payloads is put in the packet each after each. The
2028 payload is variable in length but can be calculated by calculating
2029 the length of the fields together. This forms one New Channel Payload
2032 The list of payloads may only be sent with SILC_PACKET_NEW_CHANNEL_LIST
2033 packet. They must not be sent in any other packet type.
2037 2.3.23 New Channel User List Payload
2039 This payload is used to distribute list of channel users on a channel
2040 from server to routers. It might convenient to send list of channel
2041 users when existing server connects to router, instead of sending them
2042 one by one. One list may include users for several different channels.
2044 There is no specific payload for this packet type. The packet type
2045 uses same payload as described in 2.3.20 New Channel User Payload.
2046 To form a list several payloads is put in the packet one after another.
2047 The payload is variable in length but can be calculated by calculating
2048 the length of the fields together. This forms one New Channel User
2049 Payload in the list.
2051 The list of payloads may only be sent with packet
2052 SILC_PACKET_NEW_CHANNEL_USER_LIST. They must not be sent in any other
2057 2.3.24 Replace ID Payload
2059 This payload is used to replace old ID with new ID sent in the payload.
2060 When ID changes for some entity and the new ID is wanted to replace the
2061 old one this payload must be used. Client cannot send or receive this
2062 payload. Normal server and router server may send and receive this
2063 payload. After this packet has been sent the old ID must not be used
2066 The payload may only be sent with SILC_PACKET_REPLACE_ID packet. It must
2067 not be sent in any other packet type. Following diagram represents the
2068 Replace Payload Payload.
2075 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
2076 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2077 | Old ID Type | Old ID Length |
2078 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2082 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2083 | New ID Type | New ID Length |
2084 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2088 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2092 Figure 21: Replace ID Payload
2096 o Old ID Type (2 bytes) - Indicates the type of the old ID. See
2097 section 2.4 SILC ID Types for list of defined ID types.
2099 o Old ID Length (2 bytes) - Length of the old ID Data area not
2100 including the length of any other fields in the payload.
2102 o Old ID Data (variable length) - The actual old ID data.
2104 o New ID Type (2 bytes) - Indicates the type of the new ID. See
2105 section 2.4 SILC ID Types for list of defined ID types.
2107 o New ID Length (2 bytes) - Length of the new ID Data area not
2108 including the length of any other fields in the payload.
2110 o New ID Data (variable length) - The actual new ID data.
2115 2.3.25 Remove ID Payload
2117 Remove ID payload is used to remove ID from SILC network. This is used
2118 when client, server, router or channel is removed from the SILC network.
2119 After this payload has been send the old ID must not be used anymore.
2120 Client must not send or receive this payload.
2122 The packet uses generic ID Payload as New ID Payload. See section
2123 2.3.2.1 for generic ID Payload.
2127 2.3.26 Remove Channel User Payload
2129 Remove Channel User payload is used to remove a user from a channel network
2130 wide. This is used by routers to notify other routers that a user has
2131 left a channel. As routers keep information about users on channels a
2132 user leaving channel must be removed from all routers. Normal server may
2133 send this payload as well. Client must not send this payload.
2135 The payload may only be sent with SILC_PACKET_REMOVE_CHANNEL USER packet.
2136 It must not be sent in any other packet type. Following diagram
2137 represents the Remove Payload Payload.
2146 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
2147 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2148 | Client ID Length | |
2149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2153 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2154 | Channel ID Length | |
2155 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2159 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2163 Figure 22: Remove Channel User Payload
2167 o Client ID Length (2 bytes) - Length of the Client ID Data area
2168 not including the length of any other fields in the payload.
2170 o Client ID Data (variable length) - The Client ID of the user
2171 that has left the channel.
2173 o Channel ID Length (2 bytes) - Length of the Channel ID Data area
2174 not including the length of any other fields in the payload.
2176 o Channel ID Data (variable length) - The Channel ID of the channel
2182 2.3.27 Set Mode Payload
2184 Set Mode Payload is used by servers and routers to distribute to each
2185 other the information about changed modes in the SILC network. The
2186 payload is sent when channel's or client's channel mode is changed.
2187 Server can send this to router which will broadcast it further to other
2188 routers. However, normal server must not reiceve this payload. Client
2189 must not send or receive this payload.
2191 The payload may only be sent with SILC_PACKET_SET_MODE packet.
2192 It must not be sent in any other packet type. Following diagram
2193 represents the Set Mode Payload.
2202 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
2203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2204 | Mode Type | Payload Length |
2205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2207 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2213 Figure 23: Set Mode Payload
2217 o Mode type (2 bytes) - Indicates the type of the mode that was
2218 changed. Every type has arguments associated to the type which
2219 are defined below. The following types are defined:
2221 0 SILC_MODE_TYPE_CHANNEL
2224 Arguments: (1) <Channel ID> (2) <Client ID>
2226 The <Channel ID> is the channel which mode was set and the
2227 <Client ID> is the client who set it.
2230 1 SILC_MODE_TYPE_UCHANNEL
2233 Arguments: (1) <Channel ID> (2) <Client ID>
2234 (3) <Target Client ID>
2236 The <Channel ID> is the channel where the <Client ID> and
2237 the <Target Client ID> is on. The <Client ID> is the client
2238 who set the <Target Client ID> mode.
2246 32768 - Private range
2248 Rest of the types are reserved for private use.
2250 o Payload Length (2 bytes) - Length of the entire Set Mode Payload
2251 including any associated Argument Payloads.
2253 o Mode Mask (4 bytes) - Indicates the set mode mask. This is
2254 specified by the mode type. See definitions of SILC_COMMAND_UMODE
2255 for client modes, SILC_COMMAND_CMODE for channel modes and
2256 SILC_COMMAND_CUMODE for client's channel modes in [SILC1].
2258 o Argument Nums (2 bytes) - Indicates the number of Argument
2259 Payloads associated to this payload. Mode types may define
2260 arguments to be send along this payload.
2265 2.3.28 Set Mode List Payload
2267 This paylaod is used to distribute list of Set Mode payloads inside
2268 one packet. When server announces channels and client's on those
2269 channels to its primary router when it connects to it, it is convenient
2270 to send list of Set Mode payloads to set the modes for the channel
2271 and clients on those channel. One list may include several mode
2274 There is no specific payload for this packet type. The packet type
2275 uses same payload as described in 2.3.27 Set Mode Payload. To form a
2276 list several payloads are put in the packet one after another. The
2277 payload is variable in length but can be calculated by calculating the
2278 length of the fields together. This forms one Set Mode payload in the
2281 The list of payloads may only be sent with packet SILC_PACKET_SET_MODE_LIST.
2282 They must not be sent in any other packet type.
2288 ID's are extensively used in the SILC network to associate different
2289 entities. Following ID's has been defined to be used in the SILC
2295 When ever specific ID cannot be used this is used.
2299 Server ID to associate servers. See the format of
2304 Client ID to associate clients. See the format of
2309 Channel ID to associate channels. See the format of
2315 2.5 Packet Encryption And Decryption
2317 SILC packets are encrypted almost entirely. Only small part of SILC
2318 header is not encrypted as described in section 5.2 SILC Packet Header.
2319 The SILC Packet header is the first part of a packet to be encrypted
2320 and it is always encrypted with the key of the next receiver of the
2321 packet. The data payload area of the packet is always entirely
2322 encrypted and it is usually encrypted with the next receiver's key.
2323 However, there are some special packet types and packet payloads
2324 that require special encryption process. These special cases are
2325 described in the next sections. First is described the normal packet
2330 2.5.1 Normal Packet Encryption And Decryption
2332 Normal SILC packets are encrypted with the session key of the next
2333 receiver of the packet. The entire SILC Packet header and the packet
2334 data payload is is also encrypted with the same key. Padding of the
2335 packet is also encrypted always with the session key, also in special
2336 cases. Computed MAC of the packet must not be encrypted.
2338 Decryption process in these cases are straightforward. The receiver
2339 of the packet must first decrypt the SILC Packet header, or some parts
2340 of it, usually first 16 bytes of it. Then the receiver checks the
2341 packet type from the decrypted part of the header and can determine
2342 how the rest of the packet must be decrypted. If the packet type is
2343 any of the special cases described in following sections the packet
2344 decryption is special. If the packet type is not among those special
2345 packet types rest of the packet may be decrypted with the same key.
2347 Also, note that two bytes of the SILC Packet header are not encrypted
2348 thus it must be noticed in the decryption process by starting the
2349 decryption from the second byte of the header. This sets some rules
2350 to padding generation as well, see the section 2.7 Packet Padding
2353 With out a doubt, this sort of decryption processing causes some
2354 overhead to packet decryption, but never the less, is required.
2358 2.5.2 Channel Message Encryption And Decryption
2360 Channel Messages (Channel Message Payload) are always encrypted with
2361 the channel specific key. However, the SILC Packet header is not
2362 encrypted with that key. As in normal case, the header is encrypted
2363 with the key of the next receiver of the packet, who ever that might
2364 be. Note that in this case the encrypted data area is not touched
2365 at all; it must not be re-encrypted with the session key.
2367 Receiver of a channel message, who ever that is, is required to decrypt
2368 the SILC Packet header to be able to even recognize the packet to be as
2369 channel message. This is same procedure as for normal SILC packets.
2370 As the receiver founds the packet to be channel message, rest of the
2371 packet processing is special. Rest of the SILC Packet header is
2372 decrypted with the same session key along with the padding of the
2373 packet. After that the packet is protected with the channel specific
2374 key and hence can be decrypted only if the receiver is the client on
2375 the channel. See section 2.7 Packet Padding Generation for more
2376 information about padding on special packets.
2378 If the receiver of the channel message is router who is routing the
2379 message to another router then it must decrypt the Channel Message
2380 payload. Between routers (that is, between cells) channel messages
2381 are protected with session keys shared between the routers. This
2382 causes another special packet processing for channel messages. If
2383 the channel message is received from another router then the entire
2384 packet, including Channel Message payload, is encrypted with the
2385 session key shared between the routers. In this case the packet
2386 decryption process is as with normal SILC packets. Hence, if the
2387 router is sending channel message to another router the Channel
2388 Message payload must have been decrypted and must be re-encrypted
2389 with the session key shared between the another router. In this
2390 case the packet encryption is as with any normal SILC packet.
2392 It must be noted that this is only when the channel messages are sent
2393 from router to another router. In all other cases the channel
2394 message encryption and decryption is as described above. This
2395 different processing of channel messages with router to router
2396 connection is because channel keys are cell specific. All cells has
2397 their own channel keys thus the channel message traveling from one
2398 cell to another must be protected as it would be any normal SILC
2403 2.5.3 Private Message Encryption And Decryption
2405 By default, private message in SILC are protected by session keys.
2406 In this case the private message encryption and decryption process is
2407 equivalent to normal packet encryption and decryption.
2409 However, private messages can be protected with private message key
2410 which causes the packet to be special packet. The procedure in this
2411 case is very much alike to channel packets. The actual private message
2412 is encrypted with the private message key and other parts of the
2413 packet is encrypted with the session key. See 2.7 Packet Padding
2414 Generation for more information about padding on special packets.
2416 The difference from channel message processing is that server or router
2417 en route never decrypts the actual private message, as it does not
2418 have the key to do that. Thus, when sending packets between router
2419 the processing is same as in any other case as well; the packet's header
2420 and padding is protected by the session key and the data area is not
2423 The true receiver of the private message, client, that is, is able
2424 to decrypt the private message as it shares the key with the sender
2429 2.6 Packet MAC Generation
2431 Data integrity of a packet is protected by including a message
2432 authentication code (MAC) at the end of the packet. The MAC is computed
2433 from shared secret MAC key, that is established by the SILC Key Exchange
2434 protocol, and from the original contents of the packet. The MAC is
2435 always computed before the packet is encrypted, although after it is
2436 compressed if compression is used.
2438 The MAC is computed from entire packet. Every bit of data in the packet,
2439 including SILC Packet Header is used in the MAC computing. This way
2440 the entire packet becomes authenticated.
2442 If the packet is special packet MAC is computed from the entire packet
2443 but part of the packet may be encrypted before the MAC is computed.
2444 This is case, for example, with channel messages where the message data
2445 is encrypted with key that server may not now. In this case the MAC
2446 has been computed from the encrypted data.
2448 See [SILC1] for defined and allowed MAC algorithms.
2452 2.7 Packet Padding Generation
2454 Padding is needed in the packet because the packet is encrypted. It
2455 must always be multiple by eight (8) or multiple by the size of the
2456 cipher's block size, which ever is larger. The padding is always
2459 For normal packets the padding is added after the SILC Packet Header
2460 and between the Data Payload area. The padding for normal packets
2461 are calculated as follows:
2464 padding length = 16 - ((packet length - 2) % 16)
2467 The 16 is the maximum padding allowed in SILC packet. Two (2) is
2468 subtracted from the true length of the packet because two (2) bytes
2469 is not encrypted in SILC Packet Header, see section 2.2 SILC Packet
2470 Header. Those two bytes that are not encrypted must not be calculated
2471 to the padding length.
2473 For special packets the padding calculation may be different as special
2474 packets may be encrypted differently. In these cases the encrypted
2475 data area must already be multiple by the block size thus in this case
2476 the padding is calculated only for SILC Packet Header, not for any
2477 other area of the packet. The same algorithm works in this case as
2478 well, except that the `packet length' is now the SILC Packet Header
2479 length. In this case, as well, two (2) is subtracted from the
2482 The padding must be random data, preferably, generated by
2483 cryptographically strong random number generator.
2487 2.8 Packet Compression
2489 SILC Packets may be compressed. In this case the data payload area
2490 is compressed and all other areas of the packet must remain as they
2491 are. After compression is performed for the data area, the length
2492 field of Packet Header must be set to the compressed length of the
2495 The compression must always be applied before encryption. When
2496 the packet is received and decrypted the data area must be decompressed.
2497 Note that the true sender of the packet must apply the compression and
2498 the true receiver of the packet must apply the decompression. Any
2499 server or router en route must not decompress the packet.
2506 The sender of the packet must assemble the SILC Packet Header with
2507 correct values. It must set the Source ID of the header as its own
2508 ID, unless it is forwarding the packet. It must also set the Destination
2509 ID of the header to the true destination. If the destination is client
2510 it will be Client ID, if it is server it will be Server ID and if it is
2511 channel it will be Channel ID.
2513 If the sender wants to compress the packet it must apply the
2514 compression now. Sender must also compute the padding as described
2515 in above sections. Then sender must compute the MAC of the packet.
2517 Then sender encrypts the packet as has been described in above
2518 sections according whether the packet is normal packet or special
2519 packet. The computed MAC must not be encrypted.
2523 2.10 Packet Reception
2525 On packet reception the receiver must check that all fields in the
2526 SILC Packet Header are valid. It must check the flags of the
2527 header and act accordingly. It must also check the MAC of the packet
2528 and if it is to be failed the packet must be discarded. Also if the
2529 header of the packet includes any bad fields the packet must be
2532 See above sections on the decryption process of the received packet.
2534 The receiver must also check that the ID's in the header are valid
2535 ID's. Unsupported ID types or malformed ID's must cause packet
2536 rejection. The padding on the reception is always ignored.
2538 The receiver must also check the packet type and start parsing the
2539 packet according to the type. However, note the above sections on
2540 special packet types and their parsing.
2546 Routers are the primary entities in the SILC network that takes care
2547 of packet routing. However, normal servers routes packets as well, for
2548 example, when they are routing channel message to the local clients.
2549 Routing is quite simple as every packet tells the true origin and the
2550 true destination of the packet.
2552 It is still recommended for routers that has several routing connections
2553 to create route cache for those destinations that has faster route than
2554 the router's primary route. This information is available for the router
2555 when other router connects to the router. The connecting party then
2556 sends all of its locally connected clients, server and channels. These
2557 informations helps to create the route cache. Also, when new channels
2558 are created to a cell its information is broadcasted to all routers
2559 in the network. Channel ID's are based on router's ID thus it is easy
2560 to create route cache based on these informations. If faster route for
2561 destination does not exist in router's route cache the packet must be
2562 routed to the primary route (default route).
2564 For server who receives a packet to be routed to its locally connected
2565 client the server must check whether the particular packet type is
2566 allowed to be routed to the client. Not all packets may be sent by
2567 some odd entity to client that is indirectly connected to the sender.
2568 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2569 entities and sending packets to them. The section mentions the packets
2570 that may be sent to indirectly connected entities. It is clear that some
2571 server cannot send, for example, disconnect packet to client that is not
2572 directly connected to the server.
2576 2.12 Packet Forwarding
2578 Currently SILC command packets may be forwarded from one entity to another.
2579 Any other packet currently cannot be forwarded but support for more packet
2580 types may be added if needed. Forwarding is usually used by server to
2581 forward some command request coming from client to the router as the server
2582 may be incapable to handle the request. Forwarding may be only one hop
2583 long; the receiver of the packet with Forwarded flag set in the SILC
2584 Packet header must not forward the packet any further.
2586 The normal scenario is that client sends JOIN command to the server which
2587 is not able to create the channel as there are no local clients on the
2588 channel. Channels are created always by the router of the cell thus the
2589 packet must be forwarded to the router. The server forwards the original
2590 packet coming from client to the router after it has set the Forwarded
2591 flag to the SILC Packet header.
2593 Router receiving the packet knows that the packet has to be processed
2594 specially by checking the flags and the Forwarded flag in the SILC Packet
2595 header. After router has joined the client to the channel (and perhaps
2596 created a new channel) it sends normal command reply packet to the
2597 client. However, as the router doesn't have direct connection to the
2598 client the packet is sent through the server. Server detects that
2599 the command reply packet is destined to the client and sends it to
2604 2.13 Packet Broadcasting
2606 SILC packets may be broadcasted in SILC network. However, only router
2607 server may send or receive broadcast packets. Client and normal server
2608 must not send broadcast packets and they must ignore broadcast packets
2609 if they receive them. Broadcast packets are sent by setting Broadcast
2610 flag to the SILC packet header.
2612 Broadcasting packets means that the packet is sent to all routers in
2613 the SILC network, except to the router that sent the packet. The router
2614 receiving broadcast packet must send the packet to its primary route.
2615 The fact that SILC routers may have several router connections may
2616 cause problems, such as race conditions inside the SILC network, if
2617 care is not taken when broadcasting packets. Router must not send
2618 the broadcast packet to any other route except to its primary route.
2620 If the primary route of the router is the original sender of the packet
2621 the packet must not be sent to the primary route. This may happen
2622 if router has several router connections and some other router uses
2623 the router as its primary route.
2625 Routers use broadcast packets to broadcast for example information
2626 about newly registered clients, servers, channels etc. so that all the
2627 routers may keep these informations up to date.
2631 2.14 Packet Tunneling
2633 Tunneling is a feature that is available in SILC protocol. Tunneling
2634 means that extra SILC Packet Header is applied to the original packet
2635 and thus hiding the original packet entirely. There can be some
2636 interesting applications using tunneling, such as, using ID's based on
2637 private network IP addresses inside in the tunneled packet. This can
2638 open many interesting features relating to connecting to private network
2639 from the Internet with SILC and many more. However, this feature is
2640 optional currently in SILC as there does not exist thorough analysis of
2641 this feature. It is with out a doubt that there will be many more
2642 applications that has not yet been discovered. Thus, it is left
2643 to Internet Community to investigate the use of tunneling in SILC
2644 protocol. This document is updated according those investigations
2645 and additional documents on the issue may be written.
2649 3 Security Considerations
2651 Security is central to the design of this protocol, and these security
2652 considerations permeate the specification. Common security considerations
2653 such as keeping private keys truly private and using adequate lengths for
2654 symmetric and asymmetric keys must be followed in order to maintain the
2655 security of this protocol.
2661 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2662 Protocol Specification", Internet Draft, June 2000.
2664 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2665 Protocols", Internet Draft, June 2000.
2667 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2670 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2673 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2676 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2679 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2680 Infrastructure, Certificate and CRL Profile", RFC 2459,
2683 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2684 John Wiley & Sons, New York, NY, 1996.
2686 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2689 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2690 RFC 2412, November 1998.
2692 [ISAKMP] Maughan D., et al, "Internet Security Association and
2693 Key Management Protocol (ISAKMP)", RFC 2408, November
2696 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2697 (IKE)", RFC 2409, November 1998.
2699 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2700 Authentication", RFC 2104, February 1997.
2716 EMail: priikone@poseidon.pspt.fi
2718 This Internet-Draft expires 6 Jun 2001