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 2.4 SILC ID Types ............................................. 39
108 2.5 Packet Encryption And Decryption .......................... 39
109 2.5.1 Normal Packet Encryption And Decryption ............. 39
110 2.5.2 Channel Message Encryption And Decryption ........... 40
111 2.5.3 Private Message Encryption And Decryption ........... 41
112 2.6 Packet MAC Generation ..................................... 41
113 2.7 Packet Padding Generation ................................. 42
114 2.8 Packet Compression ........................................ 42
115 2.9 Packet Sending ............................................ 43
116 2.10 Packet Reception ......................................... 43
117 2.11 Packet Routing ........................................... 44
118 2.12 Packet Forwarding ........................................ 44
119 2.13 Packet Broadcasting ...................................... 45
120 2.14 Packet Tunneling ......................................... 45
121 3 Security Considerations ....................................... 46
122 4 References .................................................... 46
123 5 Author's Address .............................................. 47
129 Figure 1: Typical SILC Packet
130 Figure 2: SILC Packet Header
132 Figure 4: Argument Payload
133 Figure 5: Disconnect Payload
134 Figure 6: Success Payload
135 Figure 7: Failure Payload
136 Figure 8: Reject Payload
137 Figure 9: Notify Payload
138 Figure 10: Error Payload
139 Figure 11: Channel Message Payload
140 Figure 12: Channel Key Payload
141 Figure 13: Private Message Payload
142 Figure 14: Private Message Key Payload
143 Figure 15: Command Payload
144 Figure 16: Connection Auth Request Payload
145 Figure 17: New Client Payload
146 Figure 18: New Server Payload
147 Figure 19: New Channel Payload
148 Figure 20: New Channel User Payload
149 Figure 21: Replace ID Payload
150 Figure 22: Remove Channel User Payload
156 This document describes a Packet Protocol used in the Secure Internet
157 Live Conferencing (SILC) protocol specified in the Secure Internet Live
158 Conferencing, Protocol Specification Internet Draft [SILC1]. This
159 protocol describes the packet types and packet payloads which defines
160 the contents of the packets. The protocol provides secure binary packet
161 protocol that assures that the contents of the packets are secured and
164 The basis of SILC protocol relies in the SILC packets and it is with
165 out a doubt the most important part of the protocol. It is also probably
166 the most complicated part of the protocol. Packets are used all the
167 time in the SILC network to send messages, commands and other information.
168 All packets in SILC network are always encrypted and their integrity
169 is assured by computed MACs. The protocol defines several packet types
170 and packet payloads. Each packet type usually has a specific packet
171 payload that actually defines the contents of the packet. Each packet
172 also includes a default SILC Packet Header that provides sufficient
173 information about the origin of the packet and destination of the
178 2 SILC Packet Protocol
183 SILC packets deliver messages from sender to receiver securely by
184 encrypting important fields of the packet. The packet consists of
185 default SILC Packet Header, Padding, Packet Payload data, and, packet
188 The following diagram illustrates typical SILC packet.
193 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
194 | n bytes | 1 - n bytes | n bytes | n bytes
195 | SILC Header | Padding | Data Payload | MAC
196 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
200 Figure 1: Typical SILC Packet
203 SILC Header is always the first part of the packet and its purpose
204 is to provide information about the packet. It provides for example
205 the packet type, origin of the packet and the destination of the packet.
206 The header is variable in length and first two (2) bytes of the
207 header (thus first two bytes of the packet) are not encrypted. The
208 first two (2) bytes are the length of the packet which is not encrypted.
209 See following section for description of SILC Packet header. Packets
210 without SILC header or with malformed SILC header must be dropped.
212 Padding follows the packet header. The purpose of the padding is to
213 make the packet multiple by eight (8) or by the block size of the
214 cipher used in the encryption, which ever is larger. The maximum
215 length of padding is currently 16 bytes. The padding is always
218 Data payload area follows padding and it is the actual data of the
219 packet. The packet data is the packet payloads defined in this
220 protocol. The data payload area is always encrypted.
222 The last part of SILC packet is the packet MAC that assures the
223 integrity of the packet. The MAC is always computed from the packet
224 before the encryption is applied to the packet. If compression is used
225 in the packet the MAC is computed after the compression has been
226 applied. The compression, on the other hand, is always applied before
229 All fields in all packet payloads are always in MSB (most significant
234 2.2 SILC Packet Header
236 The default SILC packet header is applied to all SILC packets and it is
237 variable in length. The purpose of SILC Packet header is to provide
238 detailed information about the packet. The receiver of the packet uses
239 the packet header to parse the packet and gain other relevant parameters
242 Following diagram represents the default SILC header format.
243 (*) indicates that this field is never encrypted. Other fields are
250 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
251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
252 | Payload Length * | Flags | Packet Type |
253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
254 | Source ID Length | Destination ID Length |
255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
271 Figure 2: SILC Packet Header
275 o Payload Length (2 bytes) - Is the length of the packet
276 not including the padding of the packet. This field must
277 not be encrypted but must always be authenticated.
279 o Flags (1 byte) - Indicates flags to be used in packet
280 processing. Several flags may be set by ORing the flags
283 Following flags are reserved for this field:
288 In this case the field is ignored.
291 Private Message Key 0x01
293 Indicates that the packet must include private
294 message that is encrypted using private key set by
295 client. Servers does not know anything about this
296 key and this causes that the private message is
297 not handled by the server at all, it is just
298 passed along. See section 2.5.3 Private Message
299 Encryption And Decryption for more information.
304 Marks the packet to be forwarded. Some specific
305 packet types may be forwarded. Receiver of packet
306 with this flag set must not forward the packet any
307 further. See section 2.12 Packet Forwarding for
308 description of packet forwarding.
313 Marks the packet to be broadcasted. Client cannot
314 send broadcast packet and normal server cannot send
315 broadcast packet. Only router server may send broadcast
316 packet. The router receiving of packet with this flag
317 set must send (broadcast) the packet to its primary
318 route. If router has several router connections the
319 packet may be sent only to the primary route. See
320 section 2.13 Packet Broadcasting for description of
326 Marks that the packet is tunneled. Tunneling means
327 that extra SILC Packet Header has been applied to the
328 original packet. The outer header has this flag
329 set. See section 2.14 Packet Tunneling for more
335 o Packet Type (1 byte) - Is the type of the packet. Receiver
336 uses this field to parse the packet. See section 2.3
337 SILC Packets for list of defined packet types.
339 o Source ID Length (2 bytes) - Indicates the length of the
340 Source ID field in the header, not including this or any
343 o Destination ID Length (2 bytes) - Indicates the length of the
344 Destination ID field in the header, not including this or
347 o Src ID Type (1 byte) - Indicates the type of ID in the
348 Source ID field. See section 2.4 SILC ID Types for
351 o Source ID (variable length) - The actual source ID that
352 indicates who is the original sender of the packet.
354 o Dst ID Type (1 byte) - Indicates the type of ID in the
355 Destination ID field. See section 2.4 SILC ID Types for
358 o Destination ID (variable length) - The actual source ID that
359 indicates who is the end receiver of the packet.
363 2.3 SILC Packet Types
365 SILC packet types defines the contents of the packet and it is used by
366 the receiver to parse the packet. The packet type is 8 bits, as a one
367 byte, in length. The range for the packet types are from 0 - 255,
368 where 0 is never sent and 255 is currently reserved for future
369 extensions and must not be defined to any other purpose. Every SILC
370 specification compliant implementation should support all of these packet
373 The below list of the SILC Packet types includes reference to the packet
374 payload as well. Packet payloads are the actual packet, that is, the data
375 that the packet consists of. Each packet type defines packet payload
376 which usually may only be sent with the specific packet type.
378 Most of the packets are packets that must be destined directly to entity
379 that is connected to the sender. It is not allowed, for example, for
380 router to send disconnect packet to client that is not directly connected
381 to the router. However, there are some special packet types that may
382 be destined to some entity that the sender has not direct connection
383 with. These packets are for example private message packets, channel
384 message packets, command packets and some other packets that may be
385 broadcasted in the SILC network. If the packet is allowed to be sent to
386 indirectly connected entity it is mentioned separately in the packet
387 description (unless it is obvious as in private and channel message
388 packets). Other packets must not be sent or accepted, if sent, to
389 indirectly connected entities.
391 List of SILC Packet types are defined as follows.
396 This type is reserved and it is never sent.
399 1 SILC_PACKET_DISCONNECT
401 This packet is sent to disconnect the remote end. Reason of
402 the disconnection is sent inside the packet payload. Client
403 usually does not send this packet.
405 Payload of the packet: See section 2.3.3 Disconnect Payload
408 2 SILC_PACKET_SUCCESS
410 This packet is sent upon successful execution of some protocol.
411 The status of the success is sent in the packet.
413 Payload of the packet: See section 2.3.4 Success Payload
416 3 SILC_PACKET_FAILURE
418 This packet is sent upon failure of some protocol. The status
419 of the failure is sent in the packet.
421 Payload of the packet: See section 2.3.5 Failure Payload
426 This packet may be sent upon rejection of some protocol.
427 The status of the rejection is sent in the packet.
429 Payload of the packet: See section 2.3.6 Reject Payload
434 This packet is used to send notify message, usually from
435 server to client, although it may be sent from server to another
436 server as well. Client never sends this packet. Server may
437 send this packet to channel as well when the packet is
438 distributed to all clients on the channel. Receiver of this
439 packet may ignore the packet if it chooses so. However, it
440 should not be ignored.
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 Payload of the packet: See section 2.3.21 New Channel User
663 24 SILC_PACKET_NEW_CHANNEL_LIST
665 This packet is used to distribute list of created channels
666 from server to routers. This is equivalent to the packet
667 SILC_PACKET_NEW_CHANNEL except that it may include several
668 payloads. Client must not send this packet.
670 Payload of the packet: See section 2.3.22 New Channel List
674 25 SILC_PACKET_NEW_CHANNEL_USER_LIST
676 This packet is used to distribute list of users on specific
677 channel from server to routers. This is equivalent to the
678 packet SILC_PACKET_NEW_CHANNEL_USER except that it may
679 include several payloads. Client must not send this packet.
681 Payload of the packet: See section 2.3.23 New Channel User
685 26 SILC_PACKET_REPLACE_ID
687 This packet is used to replace old ID with new ID sent in
688 the packet payload. For example, when client changes its
689 nickname new ID is created and this packet can be used to
690 distribute the new ID and the old ID is removed when it is
691 send in the packet. Client cannot send or receive this
692 packet. This packet maybe sent to entity that is indirectly
693 connected to the sender.
695 Payload of the packet: See section 2.3.24 Replace ID Payload
698 27 SILC_PACKET_REMOVE_ID
700 This packet is used to removed ID. For example, when client
701 exits SILC network its ID is removed. Client must not send
702 this packet. This packet maybe sent to entity that is
703 indirectly connected to the sender.
705 Payload of the packet: See section 2.3.25 Remove ID Payload
708 28 SILC_PACKET_REMOVE_CHANNEL_USER
710 This packet is used to remove user from a channel. This is
711 used by router to notify other routers in the network that a
712 client has left a channel. This packet maybe sent to entity
713 that is indirectly connected to the sender.
715 Payload of the packet: See section 2.3.26 Remove Channel User
721 This packet is used to indicate that re-key must be performed
722 for session keys. See section Session Key Regeneration in
723 [SILC1] for more information. This packet does not have
727 30 SILC_PACKET_REKEY_DONE
729 This packet is used to indicate that re-key is performed and
730 new keys must be used hereafter. This is sent only if re-key
731 was done without PFS option. If PFS is set, this is not sent
732 as SILC Key Exchange protocol is executed. This packet does
738 Currently undefined commands.
743 These packet types are reserved for private use and they will not
744 be defined by this document.
749 This type is reserved for future extensions and currently it
755 2.3.1 SILC Packet Payloads
757 All payloads resides in the main data area of the SILC packet. However
758 all payloads must be at the start of the data area after the default
759 SILC packet header and padding. All fields in the packet payload are
760 always encrypted, as, they reside in the data area of the packet which
763 Payloads described in this section are common payloads that must be
764 accepted anytime during SILC session. Most of the payloads may only
765 be sent with specific packet type which is defined in the description
768 There are a lot of other payloads in the SILC as well. However, they
769 are not common in the sense that they could be sent at any time.
770 These payloads are not described in this section. These are payloads
771 such as SILC Key Exchange payloads and so on. These are described
772 in [SILC1] and [SILC3].
776 2.3.2 Generic payloads
778 This section describes generic payloads that are not associated to any
779 specific packet type. They can be used for example inside some other
786 This payload can be used to send an ID. ID's are variable length thus
787 this payload provides a way to send variable length ID's.
789 Following diagram represents the ID Payload.
794 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
795 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
796 | ID Type | ID Length |
797 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
801 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
809 o ID Type (2 bytes) - Indicates the type of the ID. See
810 section 2.4 SILC ID Types for list of defined ID types.
812 o ID Length (2 bytes) - Length of the ID Data area not
813 including the length of any other fields in the payload.
815 o ID Data (variable length) - The actual ID data.
820 2.3.2.2 Argument Payload
822 Argument Payload is used to set arguments for any packet payload that
823 needs and supports arguments, such as commands. Number of arguments
824 associated with a packet must be indicated by the packet payload who
825 needs the arguments. Argument Payloads must always reside right after
826 the packet payload needing the arguments. Incorrect amount of argument
827 payloads must cause rejection of the packet. Following diagram represents
828 the Argument Payload.
834 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
835 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
836 | Payload Length | Argument Type | |
837 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
841 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
845 Figure 4: Argument Payload
849 o Payload Length (2 bytes) - Length of the argument payload data
850 area not including the length of any other fields in the
853 o Argument Type (1 byte) - Indicates the type of the argument.
854 Every argument may have a specific type that must be defined
855 by the packet payload needing the argument. For example
856 every command specify a number for each argument that maybe
857 associated with the command. By using this number the receiver
858 of the packet knows what type of argument this is. If there is
859 no specific argument type this field is set to zero (0).
861 o Argument Data (variable length) - Argument data.
866 2.3.3 Disconnect Payload
868 Disconnect payload is sent upon disconnection. The payload is simple;
869 reason of disconnection is sent to the disconnected party.
871 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
872 must not be sent in any other packet type. Following diagram represents
873 the Disconnect Payload.
884 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
885 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
887 ~ Disconnect Message ~
889 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
893 Figure 5: Disconnect Payload
899 o Disconnect Message (variable length) - Human readable
900 reason of the disconnection.
905 2.3.4 Success Payload
907 Success payload is sent when some protocol execution is successfully
908 completed. The payload is simple; indication of the success is sent.
909 This maybe any data, including binary or human readable data.
914 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
915 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
917 ~ Success Indication ~
919 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
923 Figure 6: Success Payload
927 o Success Indication (variable length) - Indication of
928 the success. This maybe for example some flag that
929 indicates the protocol and the success status or human
930 readable success message. The true length of this
931 payload is available by calculating it from the SILC
937 2.3.5 Failure Payload
939 This is opposite of Success Payload. Indication of failure of
940 some protocol is sent in the payload.
946 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
947 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
949 ~ Failure Indication ~
951 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
955 Figure 7: Failure Payload
959 o Failure Indication (variable length) - Indication of
960 the failure. This maybe for example some flag that
961 indicates the protocol and the failure status or human
962 readable failure message. The true length of this
963 payload is available by calculating it from the SILC
971 This payload is sent when some protocol is rejected to be executed.
972 Other operations may send this as well that was rejected. The
973 indication of the rejection is sent in the payload. The indication
974 may be binary or human readable data.
980 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
981 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
983 ~ Reject Indication ~
985 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
989 Figure 8: Reject Payload
993 o Reject Indication (variable length) - Indication of
994 the rejection. This maybe for example some flag that
995 indicates the protocol and the rejection status or human
996 readable rejection message. The true length of this
997 payload is available by calculating it from the SILC
1006 2.3.7 Notify Payload
1008 Notify payload is used to send notify messages. The payload is usually
1009 sent from server to client, however, server may send it to another
1010 server as well. Client must not send this payload. The receiver of
1011 this payload may totally ignore the contents of the payload, however,
1012 notify message should be noted and possibly logged.
1014 The payload may only be sent with SILC_PACKET_NOTIFY packet. It must
1015 not be sent in any other packet type. Following diagram represents the
1021 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
1022 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1023 | Notify Type | Argument Nums | |
1024 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1028 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1032 Figure 9: Notify Payload
1036 o Notify Type (2 bytes) - Indicates the type of the notify
1039 o Argument Nums (2 bytes) - Indicates the number of Argument
1040 Payloads associated to this payload. Notify types may define
1041 arguments to be send along the notify message.
1043 o Notify Message (variable length) - Human readable notify
1044 message. The format of this message is implementation specific.
1045 The message can be for example "%s has joined channel %s".
1048 Following notify types has been defined:
1051 0 SILC_NOTIFY_TYPE_NONE
1053 If no specific notify type apply for the notify
1054 message this type may be used.
1056 No arguments associated to this type.
1058 1 SILC_NOTIFY_TYPE_INVITE
1060 Sent when receiver has been invited to a channel.
1062 This type includes three arguments: nickname and channel name.
1064 2 SILC_NOTIFY_TYPE_JOIN
1066 Sent when client has joined to a channel.
1068 This type includes six arguments: Client ID, nickname, username,
1069 hostname, Channel ID and channel name. The Client ID and Channel ID
1070 are sent inside ID Payload.
1072 3 SILC_NOTIFY_TYPE_LEAVE
1074 Sent when client has left a channel.
1076 This type includes three arguments: nickname, server name,
1077 Channel ID and channel name. The Channel ID is sent inside ID
1080 4 SILC_NOTIFY_TYPE_SIGNOFF
1082 Sent when client signoffs from SILC network.
1084 This type includes three arguments: nickname, server name and
1085 Channel ID. The Channel ID is sent inside ID Payload.
1087 5 SILC_NOTIFY_TYPE_TOPIC_SET
1089 Sent when topic is set/changed on a channel.
1091 This type includes three arguments: Channel ID, topic, nickname and
1092 hostname. The Channel ID is sent inside ID Payload.
1094 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1096 Sent when client changes nick on a channel.
1098 This type includes three arguments: nickname and Channel ID.
1099 The Channel ID is sent inside ID Payload.
1102 Notify types starting from 16384 are reserved for private notify
1109 Error payload is sent upon error. Error may occur in various
1110 conditions when server sends this packet. Client may not send this
1111 payload but must be able to accept it. However, client may
1112 totally ignore the contents of the packet as server is going to
1113 take action on the error anyway. However, it is recommended
1114 that the client takes error packet seriously.
1120 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
1121 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1125 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1129 Figure 10: Error Payload
1133 o Error Message (variable length) - Human readable error
1139 2.3.9 Channel Message Payload
1141 Channel messages are the most common messages sent in the SILC.
1142 Channel Message Payload is used to send message to channels. These
1143 messages can only be sent if client has joined to some channel.
1144 Even though this packet is the most common in SILC it is still
1145 special packet. Some special handling on sending and reception
1146 of channel message is required.
1148 Padding must be applied into this payload since the payload is
1149 encrypted separately from other parts of the packet with the
1150 channel specific key. Hence the requirement of the padding.
1151 The padding should be random data. The packet must be made
1152 multiple by eight (8) or by the block size of the cipher, which
1155 The SILC header in this packet is encrypted with the session key
1156 of the next receiver of the packet. Nothing else is encrypted
1157 with that key. Thus, the actual packet and padding to be
1158 encrypted with the session key is SILC Header plus padding to it
1159 to make it multiple by eight (8) or multiple by the block size
1160 of the cipher, which ever is larger.
1162 Receiver of the the channel message packet is able to determine
1163 the channel the message is destined to by checking the destination
1164 ID from the SILC Packet header which tells the destination channel.
1165 The original sender of the packet is also determined by checking
1166 the source ID from the header which tells the client who sent
1169 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1170 It must not be sent in any other packet type. Following diagram
1171 represents the Channel Message Payload.
1173 (*) indicates that the field is not encrypted.
1179 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
1180 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1181 | Message Length | |
1182 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1187 | Padding Length | |
1188 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1194 ~ Initial Vector * ~
1196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1200 Figure 11: Channel Message Payload
1204 o Message Length (2 bytes) - Indicates the length of the
1205 the Message Data field in the payload, not including any
1208 o Message Data (variable length) - The actual message to
1211 o Padding Length (2 bytes) - Indicates the length of the
1212 Padding field in the payload, not including any other
1215 o Padding (variable length) - The padding that must be
1216 applied because this payload is encrypted separately from
1217 other parts of the packet.
1219 o Initial Vector (variable length) - The initial vector
1220 that has been used in packet encryption. It needs to be
1221 used in the packet decryption as well. What this field
1222 includes is implementation issue. However, it is
1223 recommended that it would be random data or, perhaps,
1224 a timestamp. It is not recommended to use zero (0) as
1225 initial vector. This field is not encrypted. This field
1226 is not included into the padding calculation. Length
1227 of this field equals the cipher's block size. This field
1228 is, however, authenticated.
1233 2.3.10 Channel Key Payload
1235 All traffic in channels are protected by channel specific keys.
1236 Channel Key Payload is used to distribute channel keys to all
1237 clients on the particular channel. Channel keys are sent when
1238 the channel is created, when new user joins to the channel and
1239 whenever a user has left a channel. Server creates the new
1240 channel key and distributes it to the clients by encrypting this
1241 payload with the session key shared between the server and
1242 the client. After that, client starts using the key received
1243 in this payload to protect the traffic on the channel.
1245 Channel keys are cell specific thus every router in cell have
1246 to create a channel key and distribute it if any client in the
1247 cell has joined to a channel. Channel traffic between cell's
1248 are not encrypted using channel keys, they are encrypted using
1249 normal session keys between two routers. Inside a cell, all
1250 channel traffic is encrypted with the specified channel key.
1251 Channel key should expire periodically, say, in one hour, in
1252 which case new channel key is created and distributed.
1254 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1255 It must not be sent in any other packet type. Following diagram
1256 represents the Channel Key Payload.
1273 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
1274 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1275 | Channel ID Length | |
1276 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1280 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1281 | Cipher Name Length | |
1282 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1286 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1287 | Channel Key Length | |
1288 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1292 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1296 Figure 12: Channel Key Payload
1301 o Channel ID Length (2 bytes) - Indicates the length of the
1302 Channel ID field in the payload, not including any other
1305 o Channel ID (variable length) - The Channel ID of the
1306 channel this key is meant for.
1308 o Cipher Name Length (2 bytes) - Indicates the length of the
1309 Cipher name field in the payload, not including any other
1312 o Cipher Name (variable length) - Name of the cipher used
1313 in the protection of channel traffic. This name is
1314 initially decided by the creator of the channel but it
1315 may change during the life time of the channel as well.
1317 o Channel Key Length (2 bytes) - Indicates the length of the
1318 Channel Key field in the payload, not including any other
1321 o Channel Key (variable length) - The actual channel key
1322 material. This key is used as such as key material for
1323 encryption function.
1328 2.3.11 Private Message Payload
1330 Private Message Payload is used to send private message between
1331 two clients (or users for that matter). The messages are sent only
1332 to the specified user and no other user inside SILC network is
1333 able to see the message. The message is protected by the session
1334 key established by the SILC Key Exchange Protocol. However,
1335 it is also possible to agree to use specific keys to protect
1336 just the private messages. See section 2.3.11 Private Message
1337 Key Payload for detailed description of how to agree to use
1340 If normal session key is used to protect the message, every
1341 server between the sender client and the receiving client needs
1342 to decrypt the packet and always re-encrypt it with the session
1343 key of the next receiver of the packet. See section Client
1344 To Client in [SILC1].
1346 When specific key is used to protect the message, servers between
1347 the sender and the receiver needs not to decrypt/re-encrypt the
1348 packet. Section 4.8.2 Client To Client in [SILC1] gives example of
1349 this scheme as well.
1351 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1352 packet. It must not be sent in any other packet type. Following
1353 diagram represents the Private Message Payload.
1359 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
1360 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1361 | Nickname Length | |
1362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1366 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1370 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1374 Figure 13: Private Message Payload
1378 o Nickname Length (2 bytes) - Indicates the length of the
1379 Nickname field, not including any other field.
1381 o Nickname (variable length) - Nickname of the sender of the
1382 private message. This should not be trusted as a definite
1383 sender of the private message. The SILC Packet Header in
1384 the packet indicates the true sender of the packet and
1385 client should verify that the nickname sent here belongs
1386 to the Client ID in the SILC Packet Header. This nickname
1387 is merely provided to be displayed by the client.
1389 o Message Data (variable length) - The actual message to
1390 the client. Rest of the packet is reserved for the message
1396 2.3.12 Private Message Key Payload
1398 This payload is used to send key from client to another client that
1399 is going to be used to protect the private messages between these
1400 two clients. If this payload is not sent normal session key
1401 established by the SILC Key Exchange Protocol is used to protect
1402 the private messages.
1404 This payload may only be sent by client to another client. Server
1405 must not send this payload at any time. After sending this payload
1406 the sender of private messages must set the Private Message Key
1407 flag into SILC Packet Header.
1409 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1410 packet. It must not be sent in any other packet type. Following
1411 diagram represents the Private Message Key Payload.
1417 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
1418 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1419 | Private Message Key Length | |
1420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1422 ~ Private Message Key ~
1424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1428 Figure 14: Private Message Key Payload
1434 o Private Message Key Length (2 bytes) - Indicates the length
1435 of the Private Message Key field in the payload, not including
1438 o Private Message Key (variable length) - The actual private
1439 message key material. This key is used as such as key material
1440 for encryption function.
1445 2.3.13 Command Payload
1447 Command Payload is used to send SILC commands from client to server.
1448 Also server may send commands to other servers. Following diagram
1449 represents the Command Payload.
1455 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
1456 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1457 | Payload Length | SILC Command | Arguments Num |
1458 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1460 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1464 Figure 15: Command Payload
1468 o Payload Length (2 bytes) - Length of the entire command
1469 payload including any command argument payloads associated
1472 o SILC Command (1 byte) - SILC Command identifier. This must
1473 be set to non-zero value. If zero (0) value is found in this
1474 field the packet must be discarded.
1476 o Arguments Num (1 byte) - Indicates the number of arguments
1477 associated with the command. If there are no arguments this
1478 field is set to zero (0). The arguments must follow the
1479 command payload. See section 2.3.2.2 for definition of the
1482 o Command Unifier (2 bytes) - Unifies this command at the
1483 sender's end. The entity who replies to this command must
1484 set the value found from this field into the Command Payload
1485 used to send the reply to the sender. This way the sender
1486 can identify which command reply belongs to which originally
1487 sent command. What this field includes is implementation
1488 issue but it is recommended that wrapping counter value is
1492 See [SILC1] for detailed description of different SILC commands,
1493 their arguments and their reply messages.
1497 2.3.14 Command Reply Payload
1499 Command Reply Payload is used to send replies to the commands. The
1500 Command Reply Payload is identical to the Command Payload thus see the
1501 upper sections for Command Payload and for Command Argument Payload
1502 specifications. Command Reply message uses the Command Argument Payload
1505 The entity who sends the reply packet must set the Command Unifier
1506 field in the reply packet's Command Payload to the value it received
1507 in the original command packet.
1509 See SILC Commands in [SILC1] for detailed description of different
1510 SILC commands, their arguments and their reply messages.
1514 2.3.15 Connection Auth Request Payload
1516 Client may send this payload to server to request the authentication
1517 method that must be used in authentication protocol. If client knows
1518 this information beforehand this payload is not necessary to be sent.
1519 Server performing authentication with another server may also send
1520 this payload to request the authentication method. If the connecting
1521 server already knows this information this payload is not necessary
1524 Server receiving this request must reply with same payload sending
1525 the mandatory authentication method. Algorithms that may be required
1526 to be used by the authentication method are the ones already
1527 established by the SILC Key Exchange protocol. See section Key
1528 Exchange Start Payload in [SILC3] for detailed information.
1530 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1531 packet. It must not be sent in any other packet type. Following
1532 diagram represents the Connection Auth Request Payload.
1538 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
1539 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1540 | Connection Type | Authentication Method |
1541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1545 Figure 16: Connection Auth Request Payload
1549 o Connection Type (2 bytes) - Indicates the type of the ID.
1550 Following connection types are defined:
1556 If any other type is found in this field the packet must be
1557 discarded and the authentication must be failed.
1559 o Authentication Method (2 bytes) - Indicates the authentication
1560 method to be used in the authentication protocol. Following
1561 authentication methods are defined:
1566 1 password (mandatory)
1567 2 public key (mandatory)
1569 If any other type is found in this field the packet must be
1570 discarded and the authentication must be failed. If this
1571 payload is sent as request to receive the mandatory
1572 authentication method this field must be set to zero (0),
1573 indicating that receiver should send the mandatory
1574 authentication method. The receiver sending this payload
1575 to the requesting party, may also set this field to zero (0)
1576 to indicate that authentication is not required. In this
1577 case authentication protocol still must be started but
1578 server is most likely to respond with SILC_PACKET_SUCCESS
1584 2.3.16 New ID Payload
1586 New ID Payload is a multipurpose payload. It is used to send newly
1587 created ID's from clients and servers. When client connects to server
1588 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
1589 packet, server replies with this packet by sending the created ID for
1590 the client. Server always creates the ID for the client.
1592 This payload is also used when server tells its router that new client
1593 has registered to the SILC network. In this case the server sends
1594 the Client ID of the client to the router. Similary when router
1595 distributes information to other routers about the client in the SILC
1596 network this payload is used.
1598 Also, when server connects to router, router uses this payload to inform
1599 other routers about new server in the SILC network. However, every
1600 server (or router) creates their own ID's thus the ID distributed by
1601 this payload is not created by the distributor in this case. Servers
1602 create their own ID's. Server registers itself to the network by sending
1603 SILC_PACKET_NEW_SERVER to the router it connected to. The case is same
1604 when router connects to another router.
1606 Hence, this payload is very important and used every time when some
1607 new entity is registered to the SILC network. Client never sends this
1608 payload. Both client and server (and router) may receive this payload.
1610 The packet uses generic ID Payload as New ID Payload. See section
1611 2.3.2.1 for generic ID Payload.
1615 2.3.17 New ID List Payload
1617 New ID List Payload is used to distribute list of ID's usually from
1618 server to router but also from router to other routers in the network.
1619 This payload is used, for example, when server is connected to router
1620 and the server wants to distribute all of its locally connected clients
1621 and locally created channels to the router. It is convenient in this
1622 case to use this payload instead of sending all the information one
1623 by one using New ID Payload.
1625 There is no specific payload for this packet type. The packet type
1626 uses same payload as described in previous section. To form a list
1627 several payloads is put in the packet each after each. The payload
1628 is variable in length but can be calculated by calculating the ID
1629 Type field, Length field and the ID Data fields together. This forms
1630 one New ID Payload in the list.
1632 The list of payloads may only be sent with SILC_PACKET_NEW_ID_LIST
1633 packet. They must not be sent in any other packet type.
1637 2.3.18 New Client Payload
1639 When client is connected to the server, keys has been exchanged and
1640 connection has been authenticated client must register itself to the
1641 server. Clients first packet after key exchange and authentication
1642 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
1643 the relevant information about the connected user. Server creates a new
1644 client ID for the client when received this payload and sends it to the
1645 client in New ID Payload.
1647 This payload sends username and real name of the user on the remote host
1648 which is connected to the SILC server with SILC client. The server
1649 creates the client ID according the information sent in this payload.
1650 The nickname of the user becomes the username sent in this payload.
1651 However, client should call NICK command after sending this payload to
1652 set the real nickname of the user which is then used to create new
1655 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
1656 must not be sent in any other packet type. Following diagram represents
1657 the New Client Payload.
1664 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
1665 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1666 | Username Length | |
1667 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1671 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1672 | Real Name Length | |
1673 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1677 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1681 Figure 17: New Client Payload
1685 o Username Length (2 bytes) - Length of the username.
1687 o Username (variable length) - The username of the user on
1688 the host where connecting to the SILC server.
1690 o Real Name Length (2 bytes) - Length of the Real Name.
1692 o Real Name (variable length) - The real name of the user
1693 on the host where connecting to the SILC server.
1698 2.3.19 New Server Payload
1700 This payload is sent by server when it has completed successfully both
1701 key exchange and connection authentication protocols. The server
1702 uses this payload to register itself to the SILC network. The
1703 first packet after these key exchange and authentication protocols
1704 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
1705 of the server that it has created by itself. It also includes a
1706 name of the server that is associated to the Server ID.
1708 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
1709 must not be sent in any other packet type. Following diagram represents
1710 the New Server Payload.
1719 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
1720 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1721 | Server ID Length | |
1722 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1726 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1727 | Server Name Length | |
1728 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1732 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1736 Figure 18: New Server Payload
1740 o Server ID Length (2 bytes) - Length of the ID Data area not
1741 including the length of any other fields in the payload.
1743 o Server ID Data (variable length) - The actual Server ID
1746 o Server Name Length (2 bytes) - Length of the server name.
1748 o Server Name (variable length) - The server name.
1753 2.3.20 New Channel Payload
1755 Information about newly created channel is broadcasted to all routers
1756 in the SILC network by sending this packet payload. Channels are
1757 created by router of the cell. Server never creates channels unless
1758 it is a standalone server and it does not have router connection,
1759 in this case server acts as router. Normal server forwards JOIN command
1760 to the router (after it has received JOIN command from client) which
1761 then processes the command and creates the channel. Client never sends
1764 The payload may only be sent with SILC_PACKET_NEW_CHANNEL packet.
1765 It must not be sent in any other packet type. Following diagram
1766 represents the New Channel Payload.
1774 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
1775 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1776 | Channel Name Length | |
1777 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1781 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1782 | Channel ID Length | |
1783 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1787 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1791 Figure 19: New Channel Payload
1796 o Channel Name Length (2 bytes) - Length of the channel name.
1798 o Channel Name (variable length) - The name of the created
1801 o Channel ID Length (2 bytes) - Length of the Channel ID.
1803 o Channel ID (variable length) - The created Channel ID.
1808 2.3.21 New Channel User Payload
1810 When client (user) joins to a channel, server must notify routers
1811 about the new user on the channel. Normal server sends this packet
1812 payload to its router which then broadcasts the packet further.
1813 Router sends this packet always to its primary router. Client must
1814 not send this packet payload. The mode of the user is NONE after
1815 user has joined to the channel.
1817 The payload may only be sent with SILC_PACKET_NEW_CHANNEL_USER
1818 packet. It must not be sent in any other packet type. Following
1819 diagram represents the New Channel User Payload.
1829 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
1830 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1831 | Channel ID Length | |
1832 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1836 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1837 | Client ID Length | |
1838 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1842 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1846 Figure 20: New Channel User Payload
1850 o Channel ID Length (2 bytes) - Length of the Channel ID.
1852 o Channel ID (variable length) - The Channel ID of the channel
1853 to which the client has joined.
1855 o Client ID Length (2 bytes) - Length of the Client ID.
1857 o Client ID (variable length) - The Client ID of the client
1858 who has joined the channel.
1863 2.3.22 New Channel List Payload
1865 This payload is used to distribute list of new channels from server
1866 to routers. It might convenient to send list of new channels when
1867 existing server connects to router, instead of sending them one
1870 There is no specific payload for this packet type. The packet type
1871 uses same payload as described in 2.3.19 New Channel Payload. To form
1872 a list several payloads is put in the packet each after each. The
1873 payload is variable in length but can be calculated by calculating
1874 the length of the fields together. This forms one New Channel Payload
1877 The list of payloads may only be sent with SILC_PACKET_NEW_CHANNEL_LIST
1878 packet. They must not be sent in any other packet type.
1882 2.3.23 New Channel User List Payload
1884 This payload is used to distribute list of channel users on specific
1885 channel from server to routers. It might convenient to send list of
1886 channel users when existing server connects to router, instead of
1887 sending them one by one.
1889 There is no specific payload for this packet type. The packet type
1890 uses same payload as described in 2.3.20 New Channel User Payload.
1891 To form a list several payloads is put in the packet each after each.
1892 The payload is variable in length but can be calculated by calculating
1893 the length of the fields together. This forms one New Channel User
1894 Payload in the list.
1896 The list of payloads may only be sent with packet
1897 SILC_PACKET_NEW_CHANNEL_USER_LIST. They must not be sent in any other
1902 2.3.24 Replace ID Payload
1904 This payload is used to replace old ID with new ID sent in the payload.
1905 When ID changes for some entity and the new ID is wanted to replace the
1906 old one this payload must be used. Client cannot send or receive this
1907 payload. Normal server and router server may send and receive this
1908 payload. After this packet has been sent the old ID must not be used
1911 The payload may only be sent with SILC_PACKET_REPLACE_ID packet. It must
1912 not be sent in any other packet type. Following diagram represents the
1913 Replace Payload Payload.
1920 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
1921 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1922 | Old ID Type | Old ID Length |
1923 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1927 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1928 | New ID Type | New ID Length |
1929 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1933 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1937 Figure 21: Replace ID Payload
1941 o Old ID Type (2 bytes) - Indicates the type of the old ID. See
1942 section 2.4 SILC ID Types for list of defined ID types.
1944 o Old ID Length (2 bytes) - Length of the old ID Data area not
1945 including the length of any other fields in the payload.
1947 o Old ID Data (variable length) - The actual old ID data.
1949 o New ID Type (2 bytes) - Indicates the type of the new ID. See
1950 section 2.4 SILC ID Types for list of defined ID types.
1952 o New ID Length (2 bytes) - Length of the new ID Data area not
1953 including the length of any other fields in the payload.
1955 o New ID Data (variable length) - The actual new ID data.
1960 2.3.25 Remove ID Payload
1962 Remove ID payload is used to remove ID from SILC network. This is used
1963 for example when client exits SILC network. The server must in this
1964 case send this payload to notify that this ID is not valid anymore.
1965 After this has been send the old ID must not be used anymore. Client
1966 must not send this payload.
1968 The packet uses generic ID Payload as New ID Payload. See section
1969 2.3.2.1 for generic ID Payload.
1973 2.3.26 Remove Channel User Payload
1975 Remove Channel User payload is used to remove a user from a channel network
1976 wide. This is used by routers to notify other routers that a user has
1977 left a channel. As routers keep information about users on channels a
1978 user leaving channel must be removed from all routers. Normal server may
1979 send this payload as well. Client must not send this payload.
1981 The payload may only be sent with SILC_PACKET_REMOVE_CHANNEL USER packet.
1982 It must not be sent in any other packet type. Following diagram
1983 represents the Remove Payload Payload.
1992 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
1993 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1994 | Client ID Length | |
1995 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1999 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2000 | Channel ID Length | |
2001 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2005 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2009 Figure 22: Remove Channel User Payload
2013 o Client ID Length (2 bytes) - Length of the Client ID Data area
2014 not including the length of any other fields in the payload.
2016 o Client ID Data (variable length) - The Client ID of the user
2017 that has left the channel.
2019 o Channel ID Length (2 bytes) - Length of the Channel ID Data area
2020 not including the length of any other fields in the payload.
2022 o Channel ID Data (variable length) - The Channel ID of the channel
2031 ID's are extensively used in the SILC network to associate different
2032 entities. Following ID's has been defined to be used in the SILC
2038 When ever specific ID cannot be used this is used.
2042 Server ID to associate servers. See the format of
2047 Client ID to associate clients. See the format of
2052 Channel ID to associate channels. See the format of
2058 2.5 Packet Encryption And Decryption
2060 SILC packets are encrypted almost entirely. Only small part of SILC
2061 header is not encrypted as described in section 5.2 SILC Packet Header.
2062 The SILC Packet header is the first part of a packet to be encrypted
2063 and it is always encrypted with the key of the next receiver of the
2064 packet. The data payload area of the packet is always entirely
2065 encrypted and it is usually encrypted with the next receiver's key.
2066 However, there are some special packet types and packet payloads
2067 that require special encryption process. These special cases are
2068 described in the next sections. First is described the normal packet
2073 2.5.1 Normal Packet Encryption And Decryption
2075 Normal SILC packets are encrypted with the session key of the next
2076 receiver of the packet. The entire SILC Packet header and the packet
2077 data payload is is also encrypted with the same key. Padding of the
2078 packet is also encrypted always with the session key, also in special
2079 cases. Computed MAC of the packet must not be encrypted.
2081 Decryption process in these cases are straightforward. The receiver
2082 of the packet must first decrypt the SILC Packet header, or some parts
2083 of it, usually first 16 bytes of it. Then the receiver checks the
2084 packet type from the decrypted part of the header and can determine
2085 how the rest of the packet must be decrypted. If the packet type is
2086 any of the special cases described in following sections the packet
2087 decryption is special. If the packet type is not among those special
2088 packet types rest of the packet may be decrypted with the same key.
2090 Also, note that two bytes of the SILC Packet header are not encrypted
2091 thus it must be noticed in the decryption process by starting the
2092 decryption from the second byte of the header. This sets some rules
2093 to padding generation as well, see the section 2.7 Packet Padding
2096 With out a doubt, this sort of decryption processing causes some
2097 overhead to packet decryption, but never the less, is required.
2101 2.5.2 Channel Message Encryption And Decryption
2103 Channel Messages (Channel Message Payload) are always encrypted with
2104 the channel specific key. However, the SILC Packet header is not
2105 encrypted with that key. As in normal case, the header is encrypted
2106 with the key of the next receiver of the packet, who ever that might
2107 be. Note that in this case the encrypted data area is not touched
2108 at all; it must not be re-encrypted with the session key.
2110 Receiver of a channel message, who ever that is, is required to decrypt
2111 the SILC Packet header to be able to even recognize the packet to be as
2112 channel message. This is same procedure as for normal SILC packets.
2113 As the receiver founds the packet to be channel message, rest of the
2114 packet processing is special. Rest of the SILC Packet header is
2115 decrypted with the same session key along with the padding of the
2116 packet. After that the packet is protected with the channel specific
2117 key and hence can be decrypted only if the receiver is the client on
2118 the channel. See section 2.7 Packet Padding Generation for more
2119 information about padding on special packets.
2121 If the receiver of the channel message is router who is routing the
2122 message to another router then it must decrypt the Channel Message
2123 payload. Between routers (that is, between cells) channel messages
2124 are protected with session keys shared between the routers. This
2125 causes another special packet processing for channel messages. If
2126 the channel message is received from another router then the entire
2127 packet, including Channel Message payload, is encrypted with the
2128 session key shared between the routers. In this case the packet
2129 decryption process is as with normal SILC packets. Hence, if the
2130 router is sending channel message to another router the Channel
2131 Message payload must have been decrypted and must be re-encrypted
2132 with the session key shared between the another router. In this
2133 case the packet encryption is as with any normal SILC packet.
2135 It must be noted that this is only when the channel messages are sent
2136 from router to another router. In all other cases the channel
2137 message encryption and decryption is as described above. This
2138 different processing of channel messages with router to router
2139 connection is because channel keys are cell specific. All cells has
2140 their own channel keys thus the channel message traveling from one
2141 cell to another must be protected as it would be any normal SILC
2146 2.5.3 Private Message Encryption And Decryption
2148 By default, private message in SILC are protected by session keys.
2149 In this case the private message encryption and decryption process is
2150 equivalent to normal packet encryption and decryption.
2152 However, private messages can be protected with private message key
2153 which causes the packet to be special packet. The procedure in this
2154 case is very much alike to channel packets. The actual private message
2155 is encrypted with the private message key and other parts of the
2156 packet is encrypted with the session key. See 2.7 Packet Padding
2157 Generation for more information about padding on special packets.
2159 The difference from channel message processing is that server or router
2160 en route never decrypts the actual private message, as it does not
2161 have the key to do that. Thus, when sending packets between router
2162 the processing is same as in any other case as well; the packet's header
2163 and padding is protected by the session key and the data area is not
2166 The true receiver of the private message, client, that is, is able
2167 to decrypt the private message as it shares the key with the sender
2172 2.6 Packet MAC Generation
2174 Data integrity of a packet is protected by including a message
2175 authentication code (MAC) at the end of the packet. The MAC is computed
2176 from shared secret MAC key, that is established by the SILC Key Exchange
2177 protocol, and from the original contents of the packet. The MAC is
2178 always computed before the packet is encrypted, although after it is
2179 compressed if compression is used.
2181 The MAC is computed from entire packet. Every bit of data in the packet,
2182 including SILC Packet Header is used in the MAC computing. This way
2183 the entire packet becomes authenticated.
2185 If the packet is special packet MAC is computed from the entire packet
2186 but part of the packet may be encrypted before the MAC is computed.
2187 This is case, for example, with channel messages where the message data
2188 is encrypted with key that server may not now. In this case the MAC
2189 has been computed from the encrypted data.
2191 See [SILC1] for defined and allowed MAC algorithms.
2195 2.7 Packet Padding Generation
2197 Padding is needed in the packet because the packet is encrypted. It
2198 must always be multiple by eight (8) or multiple by the size of the
2199 cipher's block size, which ever is larger. The padding is always
2202 For normal packets the padding is added after the SILC Packet Header
2203 and between the Data Payload area. The padding for normal packets
2204 are calculated as follows:
2207 padding length = 16 - ((packet length - 2) % 16)
2210 The 16 is the maximum padding allowed in SILC packet. Two (2) is
2211 subtracted from the true length of the packet because two (2) bytes
2212 is not encrypted in SILC Packet Header, see section 2.2 SILC Packet
2213 Header. Those two bytes that are not encrypted must not be calculated
2214 to the padding length.
2216 For special packets the padding calculation may be different as special
2217 packets may be encrypted differently. In these cases the encrypted
2218 data area must already be multiple by the block size thus in this case
2219 the padding is calculated only for SILC Packet Header, not for any
2220 other area of the packet. The same algorithm works in this case as
2221 well, except that the `packet length' is now the SILC Packet Header
2222 length. In this case, as well, two (2) is subtracted from the
2225 The padding must be random data, preferably, generated by
2226 cryptographically strong random number generator.
2230 2.8 Packet Compression
2232 SILC Packets may be compressed. In this case the data payload area
2233 is compressed and all other areas of the packet must remain as they
2234 are. After compression is performed for the data area, the length
2235 field of Packet Header must be set to the compressed length of the
2238 The compression must always be applied before encryption. When
2239 the packet is received and decrypted the data area must be decompressed.
2240 Note that the true sender of the packet must apply the compression and
2241 the true receiver of the packet must apply the decompression. Any
2242 server or router en route must not decompress the packet.
2249 The sender of the packet must assemble the SILC Packet Header with
2250 correct values. It must set the Source ID of the header as its own
2251 ID, unless it is forwarding the packet. It must also set the Destination
2252 ID of the header to the true destination. If the destination is client
2253 it will be Client ID, if it is server it will be Server ID and if it is
2254 channel it will be Channel ID.
2256 If the sender wants to compress the packet it must apply the
2257 compression now. Sender must also compute the padding as described
2258 in above sections. Then sender must compute the MAC of the packet.
2260 Then sender encrypts the packet as has been described in above
2261 sections according whether the packet is normal packet or special
2262 packet. The computed MAC must not be encrypted.
2266 2.10 Packet Reception
2268 On packet reception the receiver must check that all fields in the
2269 SILC Packet Header are valid. It must check the flags of the
2270 header and act accordingly. It must also check the MAC of the packet
2271 and if it is to be failed the packet must be discarded. Also if the
2272 header of the packet includes any bad fields the packet must be
2275 See above sections on the decryption process of the received packet.
2277 The receiver must also check that the ID's in the header are valid
2278 ID's. Unsupported ID types or malformed ID's must cause packet
2279 rejection. The padding on the reception is always ignored.
2281 The receiver must also check the packet type and start parsing the
2282 packet according to the type. However, note the above sections on
2283 special packet types and their parsing.
2289 Routers are the primary entities in the SILC network that takes care
2290 of packet routing. However, normal servers routes packets as well, for
2291 example, when they are routing channel message to the local clients.
2292 Routing is quite simple as every packet tells the true origin and the
2293 true destination of the packet.
2295 It is still recommended for routers that has several routing connections
2296 to create route cache for those destinations that has faster route than
2297 the router's primary route. This information is available for the router
2298 when other router connects to the router. The connecting party then
2299 sends all of its locally connected clients, server and channels. These
2300 informations helps to create the route cache. Also, when new channels
2301 are created to a cell its information is broadcasted to all routers
2302 in the network. Channel ID's are based on router's ID thus it is easy
2303 to create route cache based on these informations. If faster route for
2304 destination does not exist in router's route cache the packet must be
2305 routed to the primary route (default route).
2307 For server who receives a packet to be routed to its locally connected
2308 client the server must check whether the particular packet type is
2309 allowed to be routed to the client. Not all packets may be sent by
2310 some odd entity to client that is indirectly connected to the sender.
2311 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2312 entities and sending packets to them. The section mentions the packets
2313 that may be sent to indirectly connected entities. It is clear that some
2314 server cannot send, for example, disconnect packet to client that is not
2315 directly connected to the server.
2319 2.12 Packet Forwarding
2321 Currently SILC command packets may be forwarded from one entity to another.
2322 Any other packet currently cannot be forwarded but support for more packet
2323 types may be added if needed. Forwarding is usually used by server to
2324 forward some command request coming from client to the router as the server
2325 may be incapable to handle the request. Forwarding may be only one hop
2326 long; the receiver of the packet with Forwarded flag set in the SILC
2327 Packet header must not forward the packet any further.
2329 The normal scenario is that client sends JOIN command to the server which
2330 is not able to create the channel as there are no local clients on the
2331 channel. Channels are created always by the router of the cell thus the
2332 packet must be forwarded to the router. The server forwards the original
2333 packet coming from client to the router after it has set the Forwarded
2334 flag to the SILC Packet header.
2336 Router receiving the packet knows that the packet has to be processed
2337 specially by checking the flags and the Forwarded flag in the SILC Packet
2338 header. After router has joined the client to the channel (and perhaps
2339 created a new channel) it sends normal command reply packet to the
2340 client. However, as the router doesn't have direct connection to the
2341 client the packet is sent through the server. Server detects that
2342 the command reply packet is destined to the client and sends it to
2347 2.13 Packet Broadcasting
2349 SILC packets may be broadcasted in SILC network. However, only router
2350 server may send or receive broadcast packets. Client and normal server
2351 must not send broadcast packets and they must ignore broadcast packets
2352 if they receive them. Broadcast packets are sent by setting Broadcast
2353 flag to the SILC packet header.
2355 Broadcasting packets means that the packet is sent to all routers in
2356 the SILC network, except to the router that sent the packet. The router
2357 receiving broadcast packet must send the packet to its primary route.
2358 The fact that SILC routers may have several router connections may
2359 cause problems, such as race conditions inside the SILC network, if
2360 care is not taken when broadcasting packets. Router must not send
2361 the broadcast packet to any other route except to its primary route.
2363 If the primary route of the router is the original sender of the packet
2364 the packet must not be sent to the primary route. This may happen
2365 if router has several router connections and some other router uses
2366 the router as its primary route.
2368 Routers use broadcast packets to broadcast for example information
2369 about newly registered clients, servers, channels etc. so that all the
2370 routers may keep these informations up to date.
2374 2.14 Packet Tunneling
2376 Tunneling is a feature that is available in SILC protocol. Tunneling
2377 means that extra SILC Packet Header is applied to the original packet
2378 and thus hiding the original packet entirely. There can be some
2379 interesting applications using tunneling, such as, using ID's based on
2380 private network IP addresses inside in the tunneled packet. This can
2381 open many interesting features relating to connecting to private network
2382 from the Internet with SILC and many more. However, this feature is
2383 optional currently in SILC as there does not exist thorough analysis of
2384 this feature. It is with out a doubt that there will be many more
2385 applications that has not yet been discovered. Thus, it is left
2386 to Internet Community to investigate the use of tunneling in SILC
2387 protocol. This document is updated according those investigations
2388 and additional documents on the issue may be written.
2392 3 Security Considerations
2394 Security is central to the design of this protocol, and these security
2395 considerations permeate the specification.
2401 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2402 Protocol Specification", Internet Draft, June 2000.
2404 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2405 Protocols", Internet Draft, June 2000.
2407 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2410 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2413 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2416 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2419 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2420 Infrastructure, Certificate and CRL Profile", RFC 2459,
2423 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2424 John Wiley & Sons, New York, NY, 1996.
2426 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2429 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2430 RFC 2412, November 1998.
2432 [ISAKMP] Maughan D., et al, "Internet Security Association and
2433 Key Management Protocol (ISAKMP)", RFC 2408, November
2436 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2437 (IKE)", RFC 2409, November 1998.
2439 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2440 Authentication", RFC 2104, February 1997.
2456 EMail: priikone@poseidon.pspt.fi
2458 This Internet-Draft expires 6 Jun 2001
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