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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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 2.3.2.3 Channel Payload ............................. XXX
84 2.3.3 Disconnect Payload .................................. 17
85 2.3.4 Success Payload ..................................... 18
86 2.3.5 Failure Payload ..................................... 18
87 2.3.6 Reject Payload ...................................... 19
88 2.3.7 Notify Payload ...................................... 20
89 2.3.8 Error Payload ....................................... 21
90 2.3.9 Channel Message Payload ............................. 22
91 2.3.10 Channel Key Payload ................................ 24
92 2.3.11 Private Message Payload ............................ 26
93 2.3.12 Private Message Key Payload ........................ 27
94 2.3.13 Command Payload .................................... 28
95 2.3.14 Command Reply Payload .............................. 29
96 2.3.15 Connection Auth Request Payload .................... 29
97 2.3.16 New ID Payload ..................................... 30
98 2.3.17 New Client Payload ................................. 31
99 2.3.18 New Server Payload ................................. 32
100 2.3.19 New Channel Payload ................................ 33
101 2.3.20 Key Agreement Payload .............................. XXX
102 2.4 SILC ID Types ............................................. 39
103 2.5 Packet Encryption And Decryption .......................... 39
104 2.5.1 Normal Packet Encryption And Decryption ............. 39
105 2.5.2 Channel Message Encryption And Decryption ........... 40
106 2.5.3 Private Message Encryption And Decryption ........... 41
107 2.6 Packet MAC Generation ..................................... 41
108 2.7 Packet Padding Generation ................................. 42
109 2.8 Packet Compression ........................................ 42
110 2.9 Packet Sending ............................................ 43
111 2.10 Packet Reception ......................................... 43
112 2.11 Packet Routing ........................................... 44
113 2.12 Packet Broadcasting ...................................... 45
114 2.13 Packet Tunneling ......................................... 45
115 3 Security Considerations ....................................... 46
116 4 References .................................................... 46
117 5 Author's Address .............................................. 47
123 Figure 1: Typical SILC Packet
124 Figure 2: SILC Packet Header
126 Figure 4: Argument Payload
127 Figure 5: Channel Payload
128 Figure 6: Disconnect Payload
129 Figure 7: Success Payload
130 Figure 8: Failure Payload
131 Figure 9: Reject Payload
132 Figure 10: Notify Payload
133 Figure 11: Error Payload
134 Figure 12: Channel Message Payload
135 Figure 13: Channel Key Payload
136 Figure 14: Private Message Payload
137 Figure 15: Private Message Key Payload
138 Figure 16: Command Payload
139 Figure 17: Connection Auth Request Payload
140 Figure 18: New Client Payload
141 Figure 19: New Server Payload
142 Figure 20: Key Agreement Payload
143 Figure 21: Cell Routers Payload
149 This document describes a Packet Protocol used in the Secure Internet
150 Live Conferencing (SILC) protocol specified in the Secure Internet Live
151 Conferencing, Protocol Specification Internet Draft [SILC1]. This
152 protocol describes the packet types and packet payloads which defines
153 the contents of the packets. The protocol provides secure binary packet
154 protocol that assures that the contents of the packets are secured and
157 The basis of SILC protocol relies in the SILC packets and it is with
158 out a doubt the most important part of the protocol. It is also probably
159 the most complicated part of the protocol. Packets are used all the
160 time in the SILC network to send messages, commands and other information.
161 All packets in SILC network are always encrypted and their integrity
162 is assured by computed MACs. The protocol defines several packet types
163 and packet payloads. Each packet type usually has a specific packet
164 payload that actually defines the contents of the packet. Each packet
165 also includes a default SILC Packet Header that provides sufficient
166 information about the origin of the packet and destination of the
171 2 SILC Packet Protocol
176 SILC packets deliver messages from sender to receiver securely by
177 encrypting important fields of the packet. The packet consists of
178 default SILC Packet Header, Padding, Packet Payload data, and, packet
181 The following diagram illustrates typical SILC packet.
186 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
187 | n bytes | 1 - n bytes | n bytes | n bytes
188 | SILC Header | Padding | Data Payload | MAC
189 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
193 Figure 1: Typical SILC Packet
196 SILC Header is always the first part of the packet and its purpose
197 is to provide information about the packet. It provides for example
198 the packet type, origin of the packet and the destination of the packet.
199 The header is variable in length and first two (2) bytes of the
200 header (thus first two bytes of the packet) are not encrypted. The
201 first two (2) bytes are the length of the packet which is not encrypted.
202 See The following section for description of SILC Packet header. Packets
203 without SILC header or with malformed SILC header must be dropped.
205 Padding follows the packet header. The purpose of the padding is to
206 make the packet multiple by eight (8) or by the block size of the
207 cipher used in the encryption, which ever is larger. The maximum
208 length of padding is currently 16 bytes. The padding is always
211 Data payload area follows padding and it is the actual data of the
212 packet. The packet data is the packet payloads defined in this
213 protocol. The data payload area is always encrypted.
215 The last part of SILC packet is the packet MAC that assures the
216 integrity of the packet. The MAC is always computed from the packet
217 before the encryption is applied to the packet. If compression is used
218 in the packet the MAC is computed after the compression has been
219 applied. The compression, on the other hand, is always applied before
222 All fields in all packet payloads are always in MSB (most significant
227 2.2 SILC Packet Header
229 The default SILC packet header is applied to all SILC packets and it is
230 variable in length. The purpose of SILC Packet header is to provide
231 detailed information about the packet. The receiver of the packet uses
232 the packet header to parse the packet and gain other relevant parameters
235 The following diagram represents the default SILC header format.
236 (*) indicates that this field is never encrypted. Other fields are
243 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
244 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
245 | Payload Length * | Flags | Packet Type |
246 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
247 | Source ID Length | Destination ID Length |
248 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
254 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
260 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
264 Figure 2: SILC Packet Header
268 o Payload Length (2 bytes) - Is the length of the packet
269 not including the padding of the packet. This field must
270 not be encrypted but must always be authenticated.
272 o Flags (1 byte) - Indicates flags to be used in packet
273 processing. Several flags may be set by ORing the flags
276 The following flags are reserved for this field:
281 In this case the field is ignored.
284 Private Message Key 0x01
286 Indicates that the packet must include private
287 message that is encrypted using private key set by
288 client. Servers does not know anything about this
289 key and this causes that the private message is
290 not handled by the server at all, it is just
291 passed along. See section 2.5.3 Private Message
292 Encryption And Decryption for more information.
297 Indicates that the packet consists of list of
298 packet payloads indicated by the Packet Type field.
299 The payloads are added one after the other. Note that
300 there are packet types that must not be used as
301 list. Parsing of list packet is done by calculating
302 the length of each payload and parsing them one by
308 Marks the packet to be broadcasted. Client cannot
309 send broadcast packet and normal server cannot send
310 broadcast packet. Only router server may send broadcast
311 packet. The router receiving of packet with this flag
312 set must send (broadcast) the packet to its primary
313 route. If router has several router connections the
314 packet may be sent only to the primary route. See
315 section 2.13 Packet Broadcasting for description of
321 Marks that the packet is tunneled. Tunneling means
322 that extra SILC Packet Header has been applied to the
323 original packet. The outer header has this flag
324 set. See section 2.14 Packet Tunneling for more
330 o Packet Type (1 byte) - Is the type of the packet. Receiver
331 uses this field to parse the packet. See section 2.3
332 SILC Packets for list of defined packet types.
334 o Source ID Length (2 bytes) - Indicates the length of the
335 Source ID field in the header, not including this or any
338 o Destination ID Length (2 bytes) - Indicates the length of the
339 Destination ID field in the header, not including this or
342 o Src ID Type (1 byte) - Indicates the type of ID in the
343 Source ID field. See section 2.4 SILC ID Types for
346 o Source ID (variable length) - The actual source ID that
347 indicates who is the original sender of the packet.
349 o Dst ID Type (1 byte) - Indicates the type of ID in the
350 Destination ID field. See section 2.4 SILC ID Types for
353 o Destination ID (variable length) - The actual source ID that
354 indicates who is the end receiver of the packet.
358 2.3 SILC Packet Types
360 SILC packet types defines the contents of the packet and it is used by
361 the receiver to parse the packet. The packet type is 8 bits, as a one
362 byte, in length. The range for the packet types are from 0 - 255,
363 where 0 is never sent and 255 is currently reserved for future
364 extensions and must not be defined to any other purpose. Every SILC
365 specification compliant implementation should support all of these packet
368 The below list of the SILC Packet types includes reference to the packet
369 payload as well. Packet payloads are the actual packet, that is, the data
370 that the packet consists of. Each packet type defines packet payload
371 which usually may only be sent with the specific packet type.
373 Most of the packets are packets that must be destined directly to entity
374 that is connected to the sender. It is not allowed, for example, for
375 router to send disconnect packet to client that is not directly connected
376 to the router. However, there are some special packet types that may
377 be destined to some entity that the sender has not direct connection
378 with. These packets are for example private message packets, channel
379 message packets, command packets and some other packets that may be
380 broadcasted in the SILC network. If the packet is allowed to be sent to
381 indirectly connected entity it is mentioned separately in the packet
382 description (unless it is obvious as in private and channel message
383 packets). Other packets must not be sent or accepted, if sent, to
384 indirectly connected entities.
386 List of SILC Packet types are defined as follows.
391 This type is reserved and it is never sent.
394 1 SILC_PACKET_DISCONNECT
396 This packet is sent to disconnect the remote end. Reason of
397 the disconnection is sent inside the packet payload. Client
398 usually does not send this packet.
400 This packet must not be sent as list and the List flag must
403 Payload of the packet: See section 2.3.3 Disconnect Payload
406 2 SILC_PACKET_SUCCESS
408 This packet is sent upon successful execution of some protocol.
409 The status of the success is sent in the packet.
411 This packet must not be sent as list and the List flag must
414 Payload of the packet: See section 2.3.4 Success Payload
417 3 SILC_PACKET_FAILURE
419 This packet is sent upon failure of some protocol. The status
420 of the failure is sent in the packet.
422 This packet must not be sent as list and the List flag must
425 Payload of the packet: See section 2.3.5 Failure Payload
430 This packet may be sent upon rejection of some protocol.
431 The status of the rejection is sent in the packet.
433 This packet must not be sent as list and the List flag must
436 Payload of the packet: See section 2.3.6 Reject Payload
441 This packet is used to send notify message, usually from
442 server to client, although it may be sent from server to another
443 server as well. Client never sends this packet. Server may
444 send this packet to channel as well when the packet is
445 distributed to all clients on the channel.
447 Payload of the packet: See section 2.3.7 Notify Payload.
452 This packet is sent when an error occurs. Server may
453 send this packet. Client never sends this packet. The
454 client may entirely ignore the packet, however, server is
455 most likely to take action anyway. This packet may be sent
456 to entity that is indirectly connected to the sender.
458 This packet must not be sent as list and the List flag must
461 Payload of the packet: See section 2.3.8 Error Payload.
464 7 SILC_PACKET_CHANNEL_MESSAGE
466 This packet is used to send messages to channels. The packet
467 includes Channel ID of the channel and the actual message to
468 the channel. Messages sent to the channel are always protected
469 by channel specific keys. Channel Keys are distributed by
470 SILC_PACKET_CHANNEL_KEY packet.
472 This packet must not be sent as list and the List flag must
475 Payload of the packet: See section 2.3.9 Channel Message
479 8 SILC_PACKET_CHANNEL_KEY
481 This packet is used to distribute new key for particular
482 channel. Each channel has their own independent keys that
483 is used to protect the traffic on the channel. Only server
484 may send this packet. This packet may be sent to entity
485 that is indirectly connected to the sender.
487 This packet must not be sent as list and the List flag must
490 Payload of the packet: See section 2.3.10 Channel Key Payload
493 9 SILC_PACKET_PRIVATE_MESSAGE
495 This packet is used to send private messages from client
496 to another client. By default, private messages are protected
497 by session keys established by normal key exchange protocol.
498 However, it is possible to use specific key to protect private
499 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
500 agree the key with the remote client. Pre-shared key may be
501 used as well if both of the client knows it, however, it needs
502 to be agreed outside SILC. See more of this in [SILC1].
504 This packet must not be sent as list and the List flag must
507 Payload of the packet: See section 2.3.11 Private Message
511 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
513 This packet is used to agree about a key to be used to protect
514 the private messages between two clients. If this is not sent
515 the normal session key is used to protect the private messages
516 inside SILC network. Agreeing to use specific key to protect
517 private messages adds security, as no server between the two
518 clients will be able to decrypt the private message. However,
519 servers inside SILC network are considered to be trusted, thus
520 using normal session key to protect private messages does not
521 degree security. Whether to agree to use specific keys by
522 default or to use normal session keys by default, is
523 implementation specific issue. See more of this in [SILC1].
525 This packet must not be sent as list and the List flag must
528 Payload of the packet: See section 2.3.12 Private Message
532 11 SILC_PACKET_COMMAND
534 This packet is used to send commands from client to server.
535 Server may send this packet to other servers as well. All
536 commands are listed in their own section SILC Command Types
537 in [SILC1]. The contents of this packet is command specific.
538 This packet may be sent to entity that is indirectly connected
541 This packet must not be sent as list and the List flag must
544 Payload of the packet: See section 2.3.13 Command Payload
547 12 SILC_PACKET_COMMAND_REPLY
549 This packet is send as reply to the SILC_PACKET_COMMAND packet.
550 The contents of this packet is command specific. This packet
551 maybe sent to entity that is indirectly connected to the sender.
553 This packet must not be sent as list and the List flag must
556 Payload of the packet: See section 2.3.14 Command Reply
557 Payload and section 2.3.13 Command
561 13 SILC_PACKET_KEY_EXCHANGE
563 This packet is used to start SILC Key Exchange Protocol,
564 described in detail in [SILC3].
566 This packet must not be sent as list and the List flag must
569 Payload of the packet: Payload of this packet is described
570 in the section SILC Key Exchange
571 Protocol and its sub sections in
575 14 SILC_PACKET_KEY_EXCHANGE_1
577 This packet is used as part of the SILC Key Exchange Protocol.
579 This packet must not be sent as list and the List flag must
582 Payload of the packet: Payload of this packet is described
583 in the section SILC Key Exchange
584 Protocol and its sub sections in
588 15 SILC_PACKET_KEY_EXCHANGE_2
590 This packet is used as part of the SILC Key Exchange Protocol.
592 This packet must not be sent as list and the List flag must
595 Payload of the packet: Payload of this packet is described
596 in the section SILC Key Exchange
597 Protocol and its sub sections in
601 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
603 This packet is used to request the authentication method to
604 be used in the SILC Connection Authentication Protocol. If
605 initiator of the protocol does not know the mandatory
606 authentication method this packet may be used to determine it.
608 The party receiving this payload must respond with the same
609 packet including the mandatory authentication method.
611 This packet must not be sent as list and the List flag must
614 Payload of the packet: See section 2.3.15 Connection Auth
618 17 SILC_PACKET_CONNECTION_AUTH
620 This packet is used to start and perform the SILC Connection
621 Authentication Protocol. This protocol is used to authenticate
622 the connecting party. The protocol is described in detail in
625 This packet must not be sent as list and the List flag must
628 Payload of the packet: Payload of this packet is described
629 in the section SILC Authentication
630 Protocol and it sub sections in [SILC].
633 18 SILC_PACKET_NEW_ID
635 This packet is used to distribute new ID's from server to
636 router and from router to all routers in the SILC network.
637 This is used when for example new client is registered to
638 SILC network. The newly created ID's of these operations are
639 distributed by this packet. Only server may send this packet,
640 however, client must be able to receive this packet.
642 Payload of the packet: See section 2.3.16 New ID Payload
645 19 SILC_PACKET_NEW_CLIENT
647 This packet is used by client to register itself to the
648 SILC network. This is sent after key exchange and
649 authentication protocols has been completed. Client sends
650 various information about itself in this packet.
652 This packet must not be sent as list and the List flag must
655 Payload of the packet: See section 2.3.17 New Client Payload
658 20 SILC_PACKET_NEW_SERVER
660 This packet is used by server to register itself to the
661 SILC network. This is sent after key exchange and
662 authentication protocols has been completed. Server sends
663 this to the router it connected to, or, if router was
664 connecting, to the connected router. Server sends
665 its Server ID and other information in this packet.
666 Client must not send or receive this packet.
668 This packet must not be sent as list and the List flag must
671 Payload of the packet: See section 2.3.18 New Server Payload
674 21 SILC_PACKET_NEW_CHANNEL
676 This packet is used to notify routers about newly created
677 channel. Channels are always created by the router and it must
678 notify other routers about the created channel. Router sends
679 this packet to its primary route. Client must not send this
680 packet. This packet maybe sent to entity that is indirectly
681 connected to the sender.
683 Payload of the packet: See section 2.3.19 New Channel Payload
688 This packet is used to indicate that re-key must be performed
689 for session keys. See section Session Key Regeneration in
690 [SILC1] for more information. This packet does not have
693 This packet must not be sent as list and the List flag must
697 23 SILC_PACKET_REKEY_DONE
699 This packet is used to indicate that re-key is performed and
700 new keys must be used hereafter. This is sent only if re-key
701 was done without PFS option. If PFS is set, this is not sent
702 as SILC Key Exchange protocol is executed. This packet does
705 This packet must not be sent as list and the List flag must
709 24 SILC_PACKET_HEARTBEAT
711 This packet is used by clients, servers and routers to keep the
712 connection alive. It is recommended that all servers implement
713 keepalive actions and perform it to both direction in a link.
714 This packet does not have a payload.
716 This packet must not be sent as list and the List flag must
720 25 SILC_PACKET_KEY_AGREEMENT
722 This packet is used by clients to request key negotiation
723 between another client in the SILC network. If the negotiation
724 is started it is performed using the SKE protocol. The result of
725 the negotiation, the secret key material, can be used for
726 example as private message key. The server and router must not
729 Payload of the packet: See section 2.3.20 Key Agreement Payload
732 26 SILC_PACKET_CELL_ROUTERS
734 This packet is used by primary router in the cell to notify its
735 primary router what other routers (backup routers) exist in the
736 cell. In case of failure of the primary router in the cell the
737 first router in the list will act as primary router of the cell.
738 This packet may be sent at anytime after connection has been
739 registered to the primary router. The client must not send this
742 Payload of the packet: See section 2.3.21 Cell Routers Payload
747 Currently undefined commands.
752 These packet types are reserved for private use and they will not
753 be defined by this document.
758 This type is reserved for future extensions and currently it
764 2.3.1 SILC Packet Payloads
766 All payloads resides in the main data area of the SILC packet. However
767 all payloads must be at the start of the data area after the default
768 SILC packet header and padding. All fields in the packet payload are
769 always encrypted, as, they reside in the data area of the packet which
772 Payloads described in this section are common payloads that must be
773 accepted anytime during SILC session. Most of the payloads may only
774 be sent with specific packet type which is defined in the description
777 There are a lot of other payloads in the SILC as well. However, they
778 are not common in the sense that they could be sent at any time.
779 These payloads are not described in this section. These are payloads
780 such as SILC Key Exchange payloads and so on. These are described
781 in [SILC1] and [SILC3].
785 2.3.2 Generic payloads
787 This section describes generic payloads that are not associated to any
788 specific packet type. They can be used for example inside some other
795 This payload can be used to send an ID. ID's are variable length thus
796 this payload provides a way to send variable length ID's.
798 The following diagram represents the ID Payload.
803 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
804 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
805 | ID Type | ID Length |
806 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
810 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
818 o ID Type (2 bytes) - Indicates the type of the ID. See
819 section 2.4 SILC ID Types for list of defined ID types.
821 o ID Length (2 bytes) - Length of the ID Data area not
822 including the length of any other fields in the payload.
824 o ID Data (variable length) - The actual ID data.
829 2.3.2.2 Argument Payload
831 Argument Payload is used to set arguments for any packet payload that
832 needs and supports arguments, such as commands. Number of arguments
833 associated with a packet must be indicated by the packet payload who
834 needs the arguments. Argument Payloads must always reside right after
835 the packet payload needing the arguments. Incorrect amount of argument
836 payloads must cause rejection of the packet. The following diagram represents
837 the Argument Payload.
839 The following diagram represents the Argument Payload.
844 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
845 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
846 | Payload Length | Argument Type | |
847 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
851 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
855 Figure 4: Argument Payload
859 o Payload Length (2 bytes) - Length of the argument payload data
860 area not including the length of any other fields in the
863 o Argument Type (1 byte) - Indicates the type of the argument.
864 Every argument may have a specific type that must be defined
865 by the packet payload needing the argument. For example
866 every command specify a number for each argument that maybe
867 associated with the command. By using this number the receiver
868 of the packet knows what type of argument this is. If there is
869 no specific argument type this field is set to zero (0).
871 o Argument Data (variable length) - Argument data.
876 2.3.2.3 Channel Payload
878 Generic Channel Payload may be used information about channel, its name,
879 the Channel ID and a mode.
881 The following diagram represents the Channel Payload Payload.
887 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
888 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
889 | Channel Name Length | |
890 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
894 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
895 | Channel ID Length | |
896 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
900 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
902 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
906 Figure 5: New Channel Payload
910 o Channel Name Length (2 bytes) - Length of the channel name
913 o Channel Name (variable length) - The name of the channel.
915 o Channel ID Length (2 bytes) - Length of the Channel ID field.
917 o Channel ID (variable length) - The Channel ID.
919 o Mode Mask (4 bytes) - A mode. This can be the mode of the
920 channel but it can also be the mode of the client on the
921 channel. The contents of this field is dependent of the
922 usage of this payload. The usage is defined separately
923 when this payload is used. This is a 32 bit MSB first value.
928 2.3.3 Disconnect Payload
930 Disconnect payload is sent upon disconnection. The payload is simple;
931 reason of disconnection is sent to the disconnected party.
933 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
934 must not be sent in any other packet type. The following diagram represents
935 the Disconnect 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 ~ Disconnect Message ~
951 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
955 Figure 6: Disconnect Payload
961 o Disconnect Message (variable length) - Human readable
962 reason of the disconnection.
967 2.3.4 Success Payload
969 Success payload is sent when some protocol execution is successfully
970 completed. The payload is simple; indication of the success is sent.
971 This maybe any data, including binary or human readable data.
976 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
977 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
979 ~ Success Indication ~
981 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
985 Figure 7: Success Payload
989 o Success Indication (variable length) - Indication of
990 the success. This maybe for example some flag that
991 indicates the protocol and the success status or human
992 readable success message. The true length of this
993 payload is available by calculating it from the SILC
999 2.3.5 Failure Payload
1001 This is opposite of Success Payload. Indication of failure of
1002 some protocol is sent in the payload.
1008 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
1009 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1011 ~ Failure Indication ~
1013 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1017 Figure 8: Failure Payload
1021 o Failure Indication (variable length) - Indication of
1022 the failure. This maybe for example some flag that
1023 indicates the protocol and the failure status or human
1024 readable failure message. The true length of this
1025 payload is available by calculating it from the SILC
1031 2.3.6 Reject Payload
1033 This payload is sent when some protocol is rejected to be executed.
1034 Other operations may send this as well that was rejected. The
1035 indication of the rejection is sent in the payload. The indication
1036 may be binary or human readable data.
1042 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
1043 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1045 ~ Reject Indication ~
1047 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1051 Figure 9: Reject Payload
1055 o Reject Indication (variable length) - Indication of
1056 the rejection. This maybe for example some flag that
1057 indicates the protocol and the rejection status or human
1058 readable rejection message. The true length of this
1059 payload is available by calculating it from the SILC
1068 2.3.7 Notify Payload
1070 Notify payload is used to send notify messages. The payload is usually
1071 sent from server to client, however, server may send it to another
1072 server as well. This payload may also be sent to a channel. Client must
1073 not send this payload. The receiver of this payload may totally ignore the
1074 contents of the payload, however, notify message should be audited.
1076 The payload may only be sent with SILC_PACKET_NOTIFY packet. It must
1077 not be sent in any other packet type. The following diagram represents the
1083 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
1084 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1085 | Notify Type | Payload Length |
1086 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1092 Figure 10: Notify Payload
1096 o Notify Type (2 bytes) - Indicates the type of the notify
1099 o Payload Length (2 bytes) - Length of the entire Notify Payload
1100 including any associated Argument Payloads.
1102 o Argument Nums (2 bytes) - Indicates the number of Argument
1103 Payloads associated to this payload. Notify types may define
1104 arguments to be send along the notify message.
1107 The following list of currently defined notify types. The format for notify
1108 arguments is same as in SILC commands described in [SILC1]. Also, all
1109 ID's sent in arguments are sent inside ID Payload.
1112 0 SILC_NOTIFY_TYPE_NONE
1114 If no specific notify type apply for the notify message this type
1118 Arguments: (1) <message>
1120 The <message> is implementation specific free text string. Receiver
1121 may ignore this message.
1124 1 SILC_NOTIFY_TYPE_INVITE
1126 Sent when an client is invited to a channel. This is also sent
1127 when the invite list of the channel is changed. This notify type
1128 is sent between routers and if the <Client ID> is argument is
1129 provided to the client as well. In this case the packet is
1130 destined to the client.
1133 Arguments: (1) <Channel ID> (2) <channel name>
1134 (3) [<sender Client ID>] (4) [<adding client>]
1135 (5) [<removing client>]
1137 The <Channel ID> is the channel. The <channel name> is the name
1138 of the channel and is provided because the client which receives
1139 this notify packet may not have a way to resolve the name of the
1140 channel from the <Channel ID>. The <sender Client ID> is the
1141 Client ID who invited the client to the channel. The <adding client>
1142 and the <removing client> indicates the added or removed client
1143 from the channel's invite list. The format of the <adding client
1144 and the <removing client> is defined in the [SILC1] with
1145 SILC_COMMAND_INVITE command.
1147 The <adding client> and <removing client> is never sent to the
1148 client indicated by the <Client ID>.
1151 2 SILC_NOTIFY_TYPE_JOIN
1153 Sent when client has joined to a channel. The server must distribute
1154 this type only to the local clients on the channel and then send
1155 it to its primary router. The router or server receiving the packet
1156 distributes this type to the local clients on the channel and
1157 broadcast it to the network.
1160 Arguments: (1) [<Client ID>] (2) <Channel ID>
1162 The <Client ID> is the client that joined to the channel indicated
1163 by the <Channel ID>.
1166 3 SILC_NOTIFY_TYPE_LEAVE
1168 Sent when client has left a channel. The server must distribute
1169 this type only to the local clients on the channel and then send
1170 it to its primary router. The router or server receiving the packet
1171 distributes this type to the local clients on the channel and
1172 broadcast it to the network.
1175 Arguments: (1) <Client ID>
1177 The <Client ID> is the client who left the channel.
1180 4 SILC_NOTIFY_TYPE_SIGNOFF
1182 Sent when client signoffs from SILC network. The server must
1183 distribute this type only to the local clients on the channel and
1184 then send it to its primary router. The router or server receiving
1185 the packet distributes this type to the local clients on the channel
1186 and broadcast it to the network.
1189 Arguments: (1) <Client ID> (2) <message>
1191 The <Client ID> is the client who left SILC network. The <message>
1192 is free text string indicating the reason of signoff.
1195 5 SILC_NOTIFY_TYPE_TOPIC_SET
1197 Sent when topic is set/changed on a channel. This type must be sent
1198 only to the clients who is joined on the channel whose topic was
1202 Arguments: (1) <Client ID> (2) <topic>
1204 The <Client ID> is the client who set or changed the <topic>.
1207 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1209 Sent when client changes nick on a channel. The server must
1210 distribute this type only to the local clients on the channel and
1211 then send it to its primary router. The router or server receiving
1212 the packet distributes this type to the local clients on the channel
1213 and broadcast it to the network.
1216 Arguments: (1) <Old Client ID> (2) <New Client ID>
1218 The <Old Client ID> is the old ID of the client who changed the
1219 nickname. The <New Client ID> is the new ID generated by the change
1223 7 SILC_NOTIFY_TYPE_CMODE_CHANGE
1225 Sent when channel mode has changed. This type must be sent only to
1226 the clients who is joined on the channel whose mode was changed.
1229 Arguments: (1) <ID Payload> (2) <mode mask>
1230 (3) [<cipher>] (4) <[hmac>]
1232 The <ID Payload> is the ID (usually Client ID but it can be Server ID
1233 as well when the router is enforcing channel mode change) of the
1234 entity which changed the mode. The <mode mask> is the new mode mask
1235 of the channel. The client can safely ignore the <cipher> argument
1236 since the SILC_PACKET_CHANNEL_KEY packet will force the new channel
1237 key change anyway. The <hmac> argument is important since the client
1238 is responsible of setting the new HMAC and the hmac key into use.
1241 8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
1243 Sent when user mode on channel has changed. This type must be sent
1244 only to the clients who is joined on the channel where the target
1248 Arguments: (1) <Client ID> (2) <mode mask>
1249 (3) <Target Client ID>
1251 The <Client ID> is the client who changed the mode. The <mode mask>
1252 is the new mode mask of the channel. The <Target Client ID> is the
1253 client which mode was changed.
1256 9 SILC_NOTIFY_TYPE_MOTD
1258 Sent when Message of the Day (motd) is sent to client.
1261 Arguments: (1) <motd>
1263 The <motd> is the Message of the Day.
1266 10 SILC_NOTIFY_TYPE_CHANNEL_CHANGE
1268 Sent when channel's ID has changed for a reason or another. This
1269 is sent by normal server to the client. This can also be sent by
1270 router to other server to force the Channel ID change. The Channel
1271 ID must be changed to use the new one. When sent to clients, this
1272 type must be sent only to the clients who is joined on the channel.
1275 Arguments: (1) <Old Channel ID> (2) <New Channel ID>
1277 The <Old Channel ID> is the channel's old ID and the <New Channel ID>
1278 is the new one that must replace the old one.
1281 11 SILC_NOTIFY_TYPE_SERVER_SIGNOFF
1283 Sent when server quits SILC network. Those clients from this server
1284 that are on channels must be removed from the channel.
1287 Arguments: (1) <Server ID>
1289 The <Server ID> is the server's ID.
1292 12 SILC_NOTIFY_TYPE_KICKED
1294 Sent when a client has been kicked from a channel. This is sent
1295 also to the client who was kicked from the channel. The client
1296 who was kicked from the channel must be removed from the channel.
1297 This notify type is always destined to the channel. The router or
1298 server receiving the packet distributes this type to the local
1299 clients on the channel and broadcast it to the network.
1302 Arguments: (1) <Client ID> (2) [<comment>]
1304 The <Client ID> is the client who was kicked from the channel.
1305 The kicker may have set the <comment> to indicate the reason for
1309 13 SILC_NOTIFY_TYPE_KILLED
1311 Sent when a client has been killed from the network. This is sent
1312 also to the client who was killed from the network. The client
1313 who was killed from the network must be removed from the network.
1314 This notify type is destined directly to the client who was killed
1315 and to channel if the client is on any channel. The router or
1316 server receiving the packet distributes this type to the local
1317 clients on the channel and broadcast it to the network.
1320 Arguments: (1) <Client ID> (2) [<comment>]
1322 The <Client ID> is the client who was killed from the network.
1323 The killer may have set the <comment> to indicate the reason for
1327 14 SILC_NOTIFY_TYPE_UMODE_CHANGE
1329 Sent when user's mode in the SILC changes. This type is sent only
1330 between routers as broadcast packet.
1333 Arguments: (1) <Client ID> (2) <mode mask>
1335 The <Client ID> is the client which mode was changed. The <mode mask>
1336 is the new mode mask.
1339 15 SILC_NOTIFY_TYPE_BAN
1341 Sent when the ban list of the channel is changed. This type is sent
1342 only between routers as broadcast packet.
1345 Arguments: (1) <Channel ID> (2) [<adding client>]
1346 (3) [<removing client>]
1348 The <Channel ID> is the channel which ban list was changed. The
1349 <adding client> is used to indicate the a ban was added and the
1350 <removing client> is used to indicate that a ban was removed from
1351 the ban list. The format of the <adding client> and the
1352 <removing client> is defined in the [SILC1] with SILC_COMMAND_BAN
1357 Notify types starting from 16384 are reserved for private notify
1364 Error payload is sent upon error. Error may occur in various
1365 conditions when server sends this packet. Client may not send this
1366 payload but must be able to accept it. However, client may
1367 totally ignore the contents of the packet as server is going to
1368 take action on the error anyway. However, it is recommended
1369 that the client takes error packet seriously.
1375 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
1376 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1384 Figure 11: Error Payload
1388 o Error Message (variable length) - Human readable error
1394 2.3.9 Channel Message Payload
1396 Channel messages are the most common messages sent in the SILC.
1397 Channel Message Payload is used to send message to channels. These
1398 messages can only be sent if client has joined to some channel.
1399 Even though this packet is the most common in SILC it is still
1400 special packet. Some special handling on sending and reception
1401 of channel message is required.
1403 Padding must be applied into this payload since the payload is
1404 encrypted separately from other parts of the packet with the
1405 channel specific key. Hence the requirement of the padding.
1406 The padding should be random data. The packet must be made
1407 multiple by eight (8) or by the block size of the cipher, which
1410 The SILC header in this packet is encrypted with the session key
1411 of the next receiver of the packet. Nothing else is encrypted
1412 with that key. Thus, the actual packet and padding to be
1413 encrypted with the session key is SILC Header plus padding to it
1414 to make it multiple by eight (8) or multiple by the block size
1415 of the cipher, which ever is larger.
1417 Receiver of the the channel message packet is able to determine
1418 the channel the message is destined to by checking the destination
1419 ID from the SILC Packet header which tells the destination channel.
1420 The original sender of the packet is also determined by checking
1421 the source ID from the header which tells the client who sent
1424 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1425 It must not be sent in any other packet type. The following diagram
1426 represents the Channel Message Payload.
1428 (*) indicates that the field is not encrypted.
1434 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
1435 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1436 | Flags | Message Length |
1437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1442 | Padding Length | |
1443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1447 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1453 ~ Initial Vector * ~
1455 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1459 Figure 12: Channel Message Payload
1463 o Flags (2 bytes) - Includes the flags of the channel
1464 messages. The flags can indicate a reason or purpose
1465 for the channel message. Note, that the Private Message
1466 Payload use these same flags for the same purpose. The
1467 following flags are defined:
1469 0x0000 SILC_MESSAGE_FLAG_NONE
1471 No specific flags set.
1473 0x0001 SILC_MESSAGE_FLAG_AUTREPLY
1475 This message is an automatic reply to a earlier
1478 0x0002 SILC_MESSAGE_FLAG_NOREPLY
1480 There should not be reply messages to this
1483 0x0004 SILC_MESSAGE_FLAG_ACTION
1485 The sender is performing an action and the message
1486 is the indication of the action.
1488 0x0008 SILC_MESSAGE_FLAG_NOTICE
1490 The message is for example and informational notice
1493 0x0010 SILC_MESSAGE_FLAG_REQUEST
1495 This is a generic request flag to send request
1498 0x0020 - 0x0200 RESERVED
1500 Reserved for future flags
1502 0x0400 - 0x8000 PRIVATE RANGE
1504 Private range for free use.
1506 o Message Length (2 bytes) - Indicates the length of the
1507 the Message Data field in the payload, not including any
1510 o Message Data (variable length) - The actual message to
1513 o Padding Length (2 bytes) - Indicates the length of the
1514 Padding field in the payload, not including any other
1517 o Padding (variable length) - The padding that must be
1518 applied because this payload is encrypted separately from
1519 other parts of the packet.
1521 o MAC (variable legnth) - The MAC computed from the
1522 Message Length, Message Data, Padding Length and Padding
1523 fields. This protects the integrity of the plaintext
1524 channel message. The receiver can verify from the MAC
1525 whether the message decrypted correctly. Also, if more than
1526 one private key has been set for the channel, the receiver
1527 can verify which of the keys decrypted the message
1528 correctly. Note that, this field is encrypted and must
1529 be added to the padding calculation.
1531 o Initial Vector (variable length) - The initial vector
1532 that has been used in packet encryption. It needs to be
1533 used in the packet decryption as well. What this field
1534 includes is implementation issue. However, it is
1535 recommended that it would be random data or, perhaps,
1536 a timestamp. It is not recommended to use zero (0) as
1537 initial vector. This field is not encrypted. This field
1538 is not included into the padding calculation. Length
1539 of this field equals the cipher's block size. This field
1540 is, however, authenticated.
1545 2.3.10 Channel Key Payload
1547 All traffic in channels are protected by channel specific keys.
1548 Channel Key Payload is used to distribute channel keys to all
1549 clients on the particular channel. Channel keys are sent when
1550 the channel is created, when new user joins to the channel and
1551 whenever a user has left a channel. Server creates the new
1552 channel key and distributes it to the clients by encrypting this
1553 payload with the session key shared between the server and
1554 the client. After that, client starts using the key received
1555 in this payload to protect the traffic on the channel.
1557 The client who is joining to the channel receives its key in the
1558 SILC_COMMAND_JOIN command reply message thus it is not necessary to
1559 send this payload to the entity who sent the SILC_COMMAND_JOIN command.
1561 Channel keys are cell specific thus every router in cell have
1562 to create a channel key and distribute it if any client in the
1563 cell has joined to a channel. Channel traffic between cell's
1564 are not encrypted using channel keys, they are encrypted using
1565 normal session keys between two routers. Inside a cell, all
1566 channel traffic is encrypted with the specified channel key.
1567 Channel key should expire periodically, say, in one hour, in
1568 which case new channel key is created and distributed.
1570 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1571 It must not be sent in any other packet type. The following diagram
1572 represents the Channel Key Payload.
1589 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
1590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1591 | Channel ID Length | |
1592 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1596 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1597 | Cipher Name Length | |
1598 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1602 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1603 | Channel Key Length | |
1604 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1608 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1612 Figure 13: Channel Key Payload
1617 o Channel ID Length (2 bytes) - Indicates the length of the
1618 Channel ID field in the payload, not including any other
1621 o Channel ID (variable length) - The Channel ID of the
1622 channel this key is meant for.
1624 o Cipher Name Length (2 bytes) - Indicates the length of the
1625 Cipher name field in the payload, not including any other
1628 o Cipher Name (variable length) - Name of the cipher used
1629 in the protection of channel traffic. This name is
1630 initially decided by the creator of the channel but it
1631 may change during the life time of the channel as well.
1633 o Channel Key Length (2 bytes) - Indicates the length of the
1634 Channel Key field in the payload, not including any other
1637 o Channel Key (variable length) - The actual channel key
1638 material. This key is used as such as key material for
1639 encryption function.
1644 2.3.11 Private Message Payload
1646 Private Message Payload is used to send private message between
1647 two clients (or users for that matter). The messages are sent only
1648 to the specified user and no other user inside SILC network is
1649 able to see the message. The message is protected by the session
1650 key established by the SILC Key Exchange Protocol. However,
1651 it is also possible to agree to use specific keys to protect
1652 just the private messages. See section 2.3.11 Private Message
1653 Key Payload for detailed description of how to agree to use
1656 If normal session key is used to protect the message, every
1657 server between the sender client and the receiving client needs
1658 to decrypt the packet and always re-encrypt it with the session
1659 key of the next receiver of the packet. See section Client
1660 To Client in [SILC1].
1662 When specific key is used to protect the message, servers between
1663 the sender and the receiver needs not to decrypt/re-encrypt the
1664 packet. Section 4.8.2 Client To Client in [SILC1] gives example of
1665 this scheme as well.
1667 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1668 packet. It must not be sent in any other packet type. The following
1669 diagram represents the Private Message Payload.
1675 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
1676 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1677 | Flags | Nickname Length |
1678 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1682 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1683 | Message Data Length | |
1684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1688 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1696 Figure 14: Private Message Payload
1700 o Flags (2 bytes) - This field includes the flags of the
1701 private message. They can indicate a different reason or
1702 purpose for the private message. See the section 2.3.9
1703 Channel Message Payload for defined flags. Note, that
1704 the Channel Message Payload use the same flags for the
1707 o Nickname Length (2 bytes) - Indicates the length of the
1708 Nickname field, not including any other field.
1710 o Nickname (variable length) - Nickname of the sender of the
1711 private message. This should not be trusted as a definite
1712 sender of the private message. The SILC Packet Header in
1713 the packet indicates the true sender of the packet and
1714 client should verify that the nickname sent here belongs
1715 to the Client ID in the SILC Packet Header. This nickname
1716 is merely provided to be displayed by the client.
1718 o Message Data Length (2 bytes) - Indicates the length of the
1719 Message Data field, not includes any other field.
1721 o Message Data (variable length) - The actual message to
1722 the client. Rest of the packet is reserved for the message
1725 o Padding (variable length) - This field is present only
1726 when the private message payload is encrypted with private
1727 message key. In this case the padding is applied to make
1728 the packet multiple by eight (8), or by the block size of
1729 the cipher, which ever is larger. When encrypted with
1730 normal session keys, this field must not be included.
1735 2.3.12 Private Message Key Payload
1737 This payload is used to send key from client to another client that
1738 is going to be used to protect the private messages between these
1739 two clients. If this payload is not sent normal session key
1740 established by the SILC Key Exchange Protocol is used to protect
1741 the private messages.
1743 This payload may only be sent by client to another client. Server
1744 must not send this payload at any time. After sending this payload
1745 the sender of private messages must set the Private Message Key
1746 flag into SILC Packet Header.
1748 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1749 packet. It must not be sent in any other packet type. The following
1750 diagram represents the Private Message Key Payload.
1756 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
1757 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1758 | Private Message Key Length | |
1759 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1761 ~ Private Message Key ~
1763 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1764 | Cipher Name Length | |
1765 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1769 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1773 Figure 15: Private Message Key Payload
1779 o Private Message Key Length (2 bytes) - Indicates the length
1780 of the Private Message Key field in the payload, not including
1783 o Private Message Key (variable length) - The actual private
1784 message key material.
1786 o Cipher Name Length (2 bytes) - Indicates the length of the
1787 Cipher Name field in the payload, not including any other
1790 o Cipher Name (variable length) - Name of the cipher to use
1791 in the private message encryption. If this field does not
1792 exist then the default cipher of the SILC protocol is used.
1793 See the [SILC1] for defined ciphers.
1799 2.3.13 Command Payload
1801 Command Payload is used to send SILC commands from client to server.
1802 Also server may send commands to other servers. The following diagram
1803 represents the Command Payload.
1809 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
1810 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1811 | Payload Length | SILC Command | Arguments Num |
1812 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1813 | Command Identifier |
1814 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1818 Figure 16: Command Payload
1822 o Payload Length (2 bytes) - Length of the entire command
1823 payload including any command argument payloads associated
1826 o SILC Command (1 byte) - Indicates the SILC command. This must
1827 be set to non-zero value. If zero (0) value is found in this
1828 field the packet must be discarded.
1830 o Arguments Num (1 byte) - Indicates the number of arguments
1831 associated with the command. If there are no arguments this
1832 field is set to zero (0). The arguments must follow the
1833 command payload. See section 2.3.2.2 for definition of the
1836 o Command Identifier (2 bytes) - Identifies this command at the
1837 sender's end. The entity who replies to this command must
1838 set the value found from this field into the Command Payload
1839 used to send the reply to the sender. This way the sender
1840 can identify which command reply belongs to which originally
1841 sent command. What this field includes is implementation
1842 issue but it is recommended that wrapping counter value is
1843 used in the field. Value zero (0) in this field means that
1844 no specific value is set.
1847 See [SILC1] for detailed description of different SILC commands,
1848 their arguments and their reply messages.
1852 2.3.14 Command Reply Payload
1854 Command Reply Payload is used to send replies to the commands. The
1855 Command Reply Payload is identical to the Command Payload thus see the
1856 upper sections for Command Payload and for Command Argument Payload
1857 specifications. Command Reply message uses the Command Argument Payload
1860 The entity who sends the reply packet must set the Command Unifier
1861 field in the reply packet's Command Payload to the value it received
1862 in the original command packet.
1864 See SILC Commands in [SILC1] for detailed description of different
1865 SILC commands, their arguments and their reply messages.
1869 2.3.15 Connection Auth Request Payload
1871 Client may send this payload to server to request the authentication
1872 method that must be used in authentication protocol. If client knows
1873 this information beforehand this payload is not necessary to be sent.
1874 Server performing authentication with another server may also send
1875 this payload to request the authentication method. If the connecting
1876 server already knows this information this payload is not necessary
1879 Server receiving this request must reply with same payload sending
1880 the mandatory authentication method. Algorithms that may be required
1881 to be used by the authentication method are the ones already
1882 established by the SILC Key Exchange protocol. See section Key
1883 Exchange Start Payload in [SILC3] for detailed information.
1885 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1886 packet. It must not be sent in any other packet type. The following
1887 diagram represents the Connection Auth Request Payload.
1893 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
1894 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1895 | Connection Type | Authentication Method |
1896 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1900 Figure 17: Connection Auth Request Payload
1904 o Connection Type (2 bytes) - Indicates the type of the ID.
1905 The following connection types are defined:
1911 If any other type is found in this field the packet must be
1912 discarded and the authentication must be failed.
1914 o Authentication Method (2 bytes) - Indicates the authentication
1915 method to be used in the authentication protocol. The following
1916 authentication methods are defined:
1921 1 password (mandatory)
1922 2 public key (mandatory)
1924 If any other type is found in this field the packet must be
1925 discarded and the authentication must be failed. If this
1926 payload is sent as request to receive the mandatory
1927 authentication method this field must be set to zero (0),
1928 indicating that receiver should send the mandatory
1929 authentication method. The receiver sending this payload
1930 to the requesting party, may also set this field to zero (0)
1931 to indicate that authentication is not required. In this
1932 case authentication protocol still must be started but
1933 server is most likely to respond with SILC_PACKET_SUCCESS
1939 2.3.16 New ID Payload
1941 New ID Payload is a multipurpose payload. It is used to send newly
1942 created ID's from clients and servers. When client connects to server
1943 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
1944 packet, server replies with this packet by sending the created ID for
1945 the client. Server always creates the ID for the client.
1947 This payload is also used when server tells its router that new client
1948 has registered to the SILC network. In this case the server sends
1949 the Client ID of the client to the router. Similary when router
1950 distributes information to other routers about the client in the SILC
1951 network this payload is used.
1953 Also, when server connects to router, router uses this payload to inform
1954 other routers about new server in the SILC network. However, every
1955 server (or router) creates their own ID's thus the ID distributed by
1956 this payload is not created by the distributor in this case. Servers
1957 create their own ID's. Server registers itself to the network by sending
1958 SILC_PACKET_NEW_SERVER to the router it connected to. The case is same
1959 when router connects to another router.
1961 However, this payload is not and must not be used to send information
1962 about new channels. New channels are always distributed by sending the
1963 dedicated SILC_PACKET_NEW_CHANNEL packet.
1965 Hence, this payload is very important and used every time when some
1966 new entity is registered to the SILC network. Client never sends this
1967 payload. Both client and server (and router) may receive this payload.
1969 The packet uses generic ID Payload as New ID Payload. See section
1970 2.3.2.1 for generic ID Payload.
1974 2.3.17 New Client Payload
1976 When client is connected to the server, keys has been exchanged and
1977 connection has been authenticated client must register itself to the
1978 server. Clients first packet after key exchange and authentication
1979 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
1980 the relevant information about the connected user. Server creates a new
1981 client ID for the client when received this payload and sends it to the
1982 client in New ID Payload.
1984 This payload sends username and real name of the user on the remote host
1985 which is connected to the SILC server with SILC client. The server
1986 creates the client ID according the information sent in this payload.
1987 The nickname of the user becomes the username sent in this payload.
1988 However, client should call NICK command after sending this payload to
1989 set the real nickname of the user which is then used to create new
1992 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
1993 must not be sent in any other packet type. The following diagram
1994 represents the New Client Payload.
2001 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
2002 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2003 | Username Length | |
2004 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2008 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2009 | Real Name Length | |
2010 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2014 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2018 Figure 18: New Client Payload
2022 o Username Length (2 bytes) - Length of the username.
2024 o Username (variable length) - The username of the user on
2025 the host where connecting to the SILC server.
2027 o Real Name Length (2 bytes) - Length of the Real Name.
2029 o Real Name (variable length) - The real name of the user
2030 on the host where connecting to the SILC server.
2035 2.3.18 New Server Payload
2037 This payload is sent by server when it has completed successfully both
2038 key exchange and connection authentication protocols. The server
2039 uses this payload to register itself to the SILC network. The
2040 first packet after these key exchange and authentication protocols
2041 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
2042 of the server that it has created by itself. It also includes a
2043 name of the server that is associated to the Server ID.
2045 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
2046 must not be sent in any other packet type. The following diagram represents
2047 the New Server Payload.
2056 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
2057 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2058 | Server ID Length | |
2059 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2063 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2064 | Server Name Length | |
2065 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2069 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2073 Figure 19: New Server Payload
2077 o Server ID Length (2 bytes) - Length of the ID Data area not
2078 including the length of any other fields in the payload.
2080 o Server ID Data (variable length) - The actual Server ID
2083 o Server Name Length (2 bytes) - Length of the server name.
2085 o Server Name (variable length) - The server name.
2090 2.3.19 New Channel Payload
2092 Information about newly created channel is broadcasted to all routers
2093 in the SILC network by sending this packet payload. Channels are
2094 created by router of the cell. Server never creates channels unless
2095 it is a standalone server and it does not have router connection,
2096 in this case server acts as router. Normal server send JOIN command
2097 to the router (after it has received JOIN command from client) which
2098 then processes the command and creates the channel. Client never sends
2101 The packet uses generic Channel Payload as New Channel Payload. See
2102 section 2.3.2.3 for generic Channel Payload. The Mode Mask field in the
2103 Channel Payload is the mode of the channel.
2107 2.3.20 Key Agreement Payload
2109 This payload is used by clients to request key negotiation between
2110 another client in the SILC Network. The key agreement protocol used
2111 is the SKE protocol. The result of the protocol, the secret key
2112 material, can be used for example as private message key between the
2113 two clients. This significantly adds security as the key agreement
2114 is performed outside the SILC network. The server and router must not
2117 The sender may tell the receiver of this payload the hostname and the
2118 port where the SKE protocol is running in the sender's end. The
2119 receiver may then initiate the SKE negotiation with the sender. The
2120 sender may also optionally not to include the hostname and the port
2121 of its SKE protocol. In this case the receiver may reply to the
2122 request by sending the same payload filled with the receiver's hostname
2123 and the port where the SKE protocol is running. The sender may then
2124 initiate the SKE negotiation with the receiver.
2126 The payload may only be sent with SILC_PACKET_KEY_AGREEMENT packet.
2127 It must not be sent in any other packet type. The following diagram
2128 represents the Key Agreement Payload.
2134 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
2135 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2136 | Hostname Length | |
2137 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2141 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2147 Figure 20: Key Agreement Payload
2151 o Hostname Length (2 bytes) - Indicates the length of the Hostname
2154 o Hostname (variable length) - The hostname or IP address where
2155 the SKE protocol is running. The sender may fill this field
2156 when sending the payload. If the receiver sends this payload
2157 as reply to the request it must fill this field.
2159 o Port (4 bytes) - The port where the SKE protocol is bound.
2160 The sender may fill this field when sending the payload. If
2161 the receiver sends this payload as reply to the request it
2162 must fill this field. This is a 32 bit MSB first order value.
2166 After the key material has been received from the SKE protocol it is
2167 processed as the [SILC3] describes. If the key material is used as
2168 channel private key then the Sending Encryption Key, as defined in
2169 [SILC3] is used as the channel private key. Other key material must
2170 be discarded. The [SILC1] defines the way to use the key material if
2171 it is intended to be used as private message keys. Any other use for
2172 the key material is undefined.
2176 2.3.21 Cell Routers Payload
2178 Cell Routers payload is used by router to notify its primary router what
2179 other routers exist in the cell. The other routers are considered to be
2180 backup routers and one of them will come active only in the case of
2181 failure of the primary router. Normal server can send this packet if it
2182 is acting as backup router. Client must not send this packet. To send
2183 more than one backup router set the List flag and assemble the payloads
2186 The payload may only be sent with SILC_PACKET_CELL_ROUTERS packet. It
2187 must not be sent in any other packet type. The Following diagram
2188 represents the Cell Routers Payload.
2194 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
2195 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2196 | Hostname Length | |
2197 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2204 | Server ID Length | |
2205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2209 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2213 Figure 21: Cell Routers Payload
2217 o Hostname Length (2 bytes) - Indicates the length of the Hostname
2220 o Hostname (variable length) - The hostname or IP address of
2223 o Port (4 bytes) - The port of the backup router it currently uses.
2224 This is a 32 bit MSB first order value.
2226 o Server ID Length (2 bytes) - Indicates the length of the Server
2229 o Server ID (variable length) - Consists of the Server ID of the
2237 ID's are extensively used in the SILC network to associate different
2238 entities. The following ID's has been defined to be used in the SILC
2244 When ever specific ID cannot be used this is used.
2248 Server ID to associate servers. See the format of
2253 Client ID to associate clients. See the format of
2258 Channel ID to associate channels. See the format of
2264 2.5 Packet Encryption And Decryption
2266 SILC packets are encrypted almost entirely. Only small part of SILC
2267 header is not encrypted as described in section 5.2 SILC Packet Header.
2268 The SILC Packet header is the first part of a packet to be encrypted
2269 and it is always encrypted with the key of the next receiver of the
2270 packet. The data payload area of the packet is always entirely
2271 encrypted and it is usually encrypted with the next receiver's key.
2272 However, there are some special packet types and packet payloads
2273 that require special encryption process. These special cases are
2274 described in the next sections. First is described the normal packet
2279 2.5.1 Normal Packet Encryption And Decryption
2281 Normal SILC packets are encrypted with the session key of the next
2282 receiver of the packet. The entire SILC Packet header and the packet
2283 data payload is is also encrypted with the same key. Padding of the
2284 packet is also encrypted always with the session key, also in special
2285 cases. Computed MAC of the packet must not be encrypted.
2287 Decryption process in these cases are straightforward. The receiver
2288 of the packet must first decrypt the SILC Packet header, or some parts
2289 of it, usually first 16 bytes of it. Then the receiver checks the
2290 packet type from the decrypted part of the header and can determine
2291 how the rest of the packet must be decrypted. If the packet type is
2292 any of the special cases described in The following sections the packet
2293 decryption is special. If the packet type is not among those special
2294 packet types rest of the packet may be decrypted with the same key.
2296 Also, note that two bytes of the SILC Packet header are not encrypted
2297 thus it must be noticed in the decryption process by starting the
2298 decryption from the second byte of the header. This sets some rules
2299 to padding generation as well, see the section 2.7 Packet Padding
2302 With out a doubt, this sort of decryption processing causes some
2303 overhead to packet decryption, but never the less, is required.
2307 2.5.2 Channel Message Encryption And Decryption
2309 Channel Messages (Channel Message Payload) are always encrypted with
2310 the channel specific key. However, the SILC Packet header is not
2311 encrypted with that key. As in normal case, the header is encrypted
2312 with the key of the next receiver of the packet, who ever that might
2313 be. Note that in this case the encrypted data area is not touched
2314 at all; it must not be re-encrypted with the session key.
2316 Receiver of a channel message, who ever that is, is required to decrypt
2317 the SILC Packet header to be able to even recognize the packet to be as
2318 channel message. This is same procedure as for normal SILC packets.
2319 As the receiver founds the packet to be channel message, rest of the
2320 packet processing is special. Rest of the SILC Packet header is
2321 decrypted with the same session key along with the padding of the
2322 packet. After that the packet is protected with the channel specific
2323 key and thus can be decrypted only if the receiver is the client on
2324 the channel. See section 2.7 Packet Padding Generation for more
2325 information about padding on special packets.
2327 If the receiver of the channel message is router who is routing the
2328 message to another router then it must decrypt the Channel Message
2329 payload. Between routers (that is, between cells) channel messages
2330 are protected with session keys shared between the routers. This
2331 causes another special packet processing for channel messages. If
2332 the channel message is received from another router then the entire
2333 packet, including Channel Message payload, is encrypted with the
2334 session key shared between the routers. In this case the packet
2335 decryption process is as with normal SILC packets. Hence, if the
2336 router is sending channel message to another router the Channel
2337 Message payload must have been decrypted and must be re-encrypted
2338 with the session key shared between the another router. In this
2339 case the packet encryption is as with any normal SILC packet.
2341 It must be noted that this is only when the channel messages are sent
2342 from router to another router. In all other cases the channel
2343 message encryption and decryption is as described above. This
2344 different processing of channel messages with router to router
2345 connection is because channel keys are cell specific. All cells has
2346 their own channel keys thus the channel message traveling from one
2347 cell to another must be protected as it would be any normal SILC
2350 If the SILC_CMODE_PRIVKEY channel mode has been set for the channel
2351 then the router cannot decrypt the packet as it does not know the
2352 private key. In this case the entire packet is encrypted with the
2353 session key and sent to the router. The router receiving the packet
2354 must check the channel mode and decrypt the packet accordingly.
2358 2.5.3 Private Message Encryption And Decryption
2360 By default, private message in SILC are protected by session keys.
2361 In this case the private message encryption and decryption process is
2362 equivalent to normal packet encryption and decryption.
2364 However, private messages can be protected with private message key
2365 which causes the packet to be special packet. The procedure in this
2366 case is very much alike to channel packets. The actual private message
2367 is encrypted with the private message key and other parts of the
2368 packet is encrypted with the session key. See 2.7 Packet Padding
2369 Generation for more information about padding on special packets.
2371 The difference from channel message processing is that server or router
2372 en route never decrypts the actual private message, as it does not
2373 have the key to do that. Thus, when sending packets between router
2374 the processing is same as in any other case as well; the packet's header
2375 and padding is protected by the session key and the data area is not
2378 The true receiver of the private message, client, that is, is able
2379 to decrypt the private message as it shares the key with the sender
2384 2.6 Packet MAC Generation
2386 Data integrity of a packet is protected by including a message
2387 authentication code (MAC) at the end of the packet. The MAC is computed
2388 from shared secret MAC key, that is established by the SILC Key Exchange
2389 protocol, and from the original contents of the packet. The MAC is
2390 always computed before the packet is encrypted, although after it is
2391 compressed if compression is used.
2393 The MAC is computed from entire packet. Every bit of data in the packet,
2394 including SILC Packet Header is used in the MAC computing. This way
2395 the entire packet becomes authenticated.
2397 If the packet is special packet MAC is computed from the entire packet
2398 but part of the packet may be encrypted before the MAC is computed.
2399 This is case, for example, with channel messages where the message data
2400 is encrypted with key that server may not now. In this case the MAC
2401 has been computed from the encrypted data.
2403 See [SILC1] for defined and allowed MAC algorithms.
2407 2.7 Packet Padding Generation
2409 Padding is needed in the packet because the packet is encrypted. It
2410 must always be multiple by eight (8) or multiple by the size of the
2411 cipher's block size, which ever is larger. The padding is always
2414 For normal packets the padding is added after the SILC Packet Header
2415 and between the Data Payload area. The padding for normal packets
2416 are calculated as follows:
2419 padding length = 16 - ((packet length - 2) % 16)
2422 The 16 is the maximum padding allowed in SILC packet. Two (2) is
2423 subtracted from the true length of the packet because two (2) bytes
2424 is not encrypted in SILC Packet Header, see section 2.2 SILC Packet
2425 Header. Those two bytes that are not encrypted must not be calculated
2426 to the padding length.
2428 For special packets the padding calculation may be different as special
2429 packets may be encrypted differently. In these cases the encrypted
2430 data area must already be multiple by the block size thus in this case
2431 the padding is calculated only for SILC Packet Header, not for any
2432 other area of the packet. The same algorithm works in this case as
2433 well, except that the `packet length' is now the SILC Packet Header
2434 length. In this case, as well, two (2) is subtracted from the
2437 The padding must be random data, preferably, generated by
2438 cryptographically strong random number generator.
2442 2.8 Packet Compression
2444 SILC Packets may be compressed. In this case the data payload area
2445 is compressed and all other areas of the packet must remain as they
2446 are. After compression is performed for the data area, the length
2447 field of Packet Header must be set to the compressed length of the
2450 The compression must always be applied before encryption. When
2451 the packet is received and decrypted the data area must be decompressed.
2452 Note that the true sender of the packet must apply the compression and
2453 the true receiver of the packet must apply the decompression. Any
2454 server or router en route must not decompress the packet.
2461 The sender of the packet must assemble the SILC Packet Header with
2462 correct values. It must set the Source ID of the header as its own
2463 ID, unless it is forwarding the packet. It must also set the Destination
2464 ID of the header to the true destination. If the destination is client
2465 it will be Client ID, if it is server it will be Server ID and if it is
2466 channel it will be Channel ID.
2468 If the sender wants to compress the packet it must apply the
2469 compression now. Sender must also compute the padding as described
2470 in above sections. Then sender must compute the MAC of the packet.
2472 Then sender encrypts the packet as has been described in above
2473 sections according whether the packet is normal packet or special
2474 packet. The computed MAC must not be encrypted.
2478 2.10 Packet Reception
2480 On packet reception the receiver must check that all fields in the
2481 SILC Packet Header are valid. It must check the flags of the
2482 header and act accordingly. It must also check the MAC of the packet
2483 and if it is to be failed the packet must be discarded. Also if the
2484 header of the packet includes any bad fields the packet must be
2487 See above sections on the decryption process of the received packet.
2489 The receiver must also check that the ID's in the header are valid
2490 ID's. Unsupported ID types or malformed ID's must cause packet
2491 rejection. The padding on the reception is always ignored.
2493 The receiver must also check the packet type and start parsing the
2494 packet according to the type. However, note the above sections on
2495 special packet types and their parsing.
2501 Routers are the primary entities in the SILC network that takes care
2502 of packet routing. However, normal servers routes packets as well, for
2503 example, when they are routing channel message to the local clients.
2504 Routing is quite simple as every packet tells the true origin and the
2505 true destination of the packet.
2507 It is still recommended for routers that has several routing connections
2508 to create route cache for those destinations that has faster route than
2509 the router's primary route. This information is available for the router
2510 when other router connects to the router. The connecting party then
2511 sends all of its locally connected clients, server and channels. These
2512 informations helps to create the route cache. Also, when new channels
2513 are created to a cell its information is broadcasted to all routers
2514 in the network. Channel ID's are based on router's ID thus it is easy
2515 to create route cache based on these informations. If faster route for
2516 destination does not exist in router's route cache the packet must be
2517 routed to the primary route (default route).
2519 For server who receives a packet to be routed to its locally connected
2520 client the server must check whether the particular packet type is
2521 allowed to be routed to the client. Not all packets may be sent by
2522 some odd entity to client that is indirectly connected to the sender.
2523 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2524 entities and sending packets to them. The section mentions the packets
2525 that may be sent to indirectly connected entities. It is clear that some
2526 server cannot send, for example, disconnect packet to client that is not
2527 directly connected to the server.
2531 2.12 Packet Broadcasting
2533 SILC packets may be broadcasted in SILC network. However, only router
2534 server may send or receive broadcast packets. Client and normal server
2535 must not send broadcast packets and they must ignore broadcast packets
2536 if they receive them. Broadcast packets are sent by setting Broadcast
2537 flag to the SILC packet header.
2539 Broadcasting packets means that the packet is sent to all routers in
2540 the SILC network, except to the router that sent the packet. The router
2541 receiving broadcast packet must send the packet to its primary route.
2542 The fact that SILC routers may have several router connections may
2543 cause problems, such as race conditions inside the SILC network, if
2544 care is not taken when broadcasting packets. Router must not send
2545 the broadcast packet to any other route except to its primary route.
2547 If the primary route of the router is the original sender of the packet
2548 the packet must not be sent to the primary route. This may happen
2549 if router has several router connections and some other router uses
2550 the router as its primary route.
2552 Routers use broadcast packets to broadcast for example information
2553 about newly registered clients, servers, channels etc. so that all the
2554 routers may keep these informations up to date.
2558 2.13 Packet Tunneling
2560 Tunneling is a feature that is available in SILC protocol. Tunneling
2561 means that extra SILC Packet Header is applied to the original packet
2562 and thus hiding the original packet entirely. There can be some
2563 interesting applications using tunneling, such as, using ID's based on
2564 private network IP addresses inside in the tunneled packet. This can
2565 open many interesting features relating to connecting to private network
2566 from the Internet with SILC and many more. However, this feature is
2567 optional currently in SILC as there does not exist thorough analysis of
2568 this feature. It is with out a doubt that there will be many more
2569 applications that has not yet been discovered. Thus, it is left
2570 to Internet Community to investigate the use of tunneling in SILC
2571 protocol. This document is updated according those investigations
2572 and additional documents on the issue may be written.
2576 3 Security Considerations
2578 Security is central to the design of this protocol, and these security
2579 considerations permeate the specification. Common security considerations
2580 such as keeping private keys truly private and using adequate lengths for
2581 symmetric and asymmetric keys must be followed in order to maintain the
2582 security of this protocol.
2588 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2589 Protocol Specification", Internet Draft, June 2000.
2591 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2592 Protocols", Internet Draft, June 2000.
2594 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2597 [IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
2600 [IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
2603 [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
2606 [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
2609 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2612 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2615 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2618 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2619 Infrastructure, Certificate and CRL Profile", RFC 2459,
2622 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2623 John Wiley & Sons, New York, NY, 1996.
2625 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2628 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2629 RFC 2412, November 1998.
2631 [ISAKMP] Maughan D., et al, "Internet Security Association and
2632 Key Management Protocol (ISAKMP)", RFC 2408, November
2635 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2636 (IKE)", RFC 2409, November 1998.
2638 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2639 Authentication", RFC 2104, February 1997.
2641 [PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
2642 Specifications, Version 2.0", RFC 2437, October 1998.
2654 EMail: priikone@poseidon.pspt.fi
2656 This Internet-Draft expires 6 Jun 2001