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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35 distribute working documents as Internet-Drafts.
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 Client Payload ................................. 31
98 2.3.18 New Server Payload ................................. 32
99 2.3.19 New Channel Payload ................................ 33
100 2.3.20 Key Agreement Payload .............................. XXX
101 2.4 SILC ID Types ............................................. 39
102 2.5 Packet Encryption And Decryption .......................... 39
103 2.5.1 Normal Packet Encryption And Decryption ............. 39
104 2.5.2 Channel Message Encryption And Decryption ........... 40
105 2.5.3 Private Message Encryption And Decryption ........... 41
106 2.6 Packet MAC Generation ..................................... 41
107 2.7 Packet Padding Generation ................................. 42
108 2.8 Packet Compression ........................................ 42
109 2.9 Packet Sending ............................................ 43
110 2.10 Packet Reception ......................................... 43
111 2.11 Packet Routing ........................................... 44
112 2.12 Packet Broadcasting ...................................... 45
113 2.13 Packet Tunneling ......................................... 45
114 3 Security Considerations ....................................... 46
115 4 References .................................................... 46
116 5 Author's Address .............................................. 47
122 Figure 1: Typical SILC Packet
123 Figure 2: SILC Packet Header
125 Figure 4: Argument Payload
126 Figure 5: Disconnect Payload
127 Figure 6: Success Payload
128 Figure 7: Failure Payload
129 Figure 8: Reject Payload
130 Figure 9: Notify Payload
131 Figure 10: Error Payload
132 Figure 11: Channel Message Payload
133 Figure 12: Channel Key Payload
134 Figure 13: Private Message Payload
135 Figure 14: Private Message Key Payload
136 Figure 15: Command Payload
137 Figure 16: Connection Auth Request Payload
138 Figure 17: New Client Payload
139 Figure 18: New Server Payload
140 Figure 19: New Channel Payload
146 This document describes a Packet Protocol used in the Secure Internet
147 Live Conferencing (SILC) protocol specified in the Secure Internet Live
148 Conferencing, Protocol Specification Internet Draft [SILC1]. This
149 protocol describes the packet types and packet payloads which defines
150 the contents of the packets. The protocol provides secure binary packet
151 protocol that assures that the contents of the packets are secured and
154 The basis of SILC protocol relies in the SILC packets and it is with
155 out a doubt the most important part of the protocol. It is also probably
156 the most complicated part of the protocol. Packets are used all the
157 time in the SILC network to send messages, commands and other information.
158 All packets in SILC network are always encrypted and their integrity
159 is assured by computed MACs. The protocol defines several packet types
160 and packet payloads. Each packet type usually has a specific packet
161 payload that actually defines the contents of the packet. Each packet
162 also includes a default SILC Packet Header that provides sufficient
163 information about the origin of the packet and destination of the
168 2 SILC Packet Protocol
173 SILC packets deliver messages from sender to receiver securely by
174 encrypting important fields of the packet. The packet consists of
175 default SILC Packet Header, Padding, Packet Payload data, and, packet
178 The following diagram illustrates typical SILC packet.
183 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
184 | n bytes | 1 - n bytes | n bytes | n bytes
185 | SILC Header | Padding | Data Payload | MAC
186 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
190 Figure 1: Typical SILC Packet
193 SILC Header is always the first part of the packet and its purpose
194 is to provide information about the packet. It provides for example
195 the packet type, origin of the packet and the destination of the packet.
196 The header is variable in length and first two (2) bytes of the
197 header (thus first two bytes of the packet) are not encrypted. The
198 first two (2) bytes are the length of the packet which is not encrypted.
199 See The following section for description of SILC Packet header. Packets
200 without SILC header or with malformed SILC header must be dropped.
202 Padding follows the packet header. The purpose of the padding is to
203 make the packet multiple by eight (8) or by the block size of the
204 cipher used in the encryption, which ever is larger. The maximum
205 length of padding is currently 16 bytes. The padding is always
208 Data payload area follows padding and it is the actual data of the
209 packet. The packet data is the packet payloads defined in this
210 protocol. The data payload area is always encrypted.
212 The last part of SILC packet is the packet MAC that assures the
213 integrity of the packet. The MAC is always computed from the packet
214 before the encryption is applied to the packet. If compression is used
215 in the packet the MAC is computed after the compression has been
216 applied. The compression, on the other hand, is always applied before
219 All fields in all packet payloads are always in MSB (most significant
224 2.2 SILC Packet Header
226 The default SILC packet header is applied to all SILC packets and it is
227 variable in length. The purpose of SILC Packet header is to provide
228 detailed information about the packet. The receiver of the packet uses
229 the packet header to parse the packet and gain other relevant parameters
232 The following diagram represents the default SILC header format.
233 (*) indicates that this field is never encrypted. Other fields are
240 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
241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
242 | Payload Length * | Flags | Packet Type |
243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
244 | Source ID Length | Destination ID Length |
245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
261 Figure 2: SILC Packet Header
265 o Payload Length (2 bytes) - Is the length of the packet
266 not including the padding of the packet. This field must
267 not be encrypted but must always be authenticated.
269 o Flags (1 byte) - Indicates flags to be used in packet
270 processing. Several flags may be set by ORing the flags
273 The following flags are reserved for this field:
278 In this case the field is ignored.
281 Private Message Key 0x01
283 Indicates that the packet must include private
284 message that is encrypted using private key set by
285 client. Servers does not know anything about this
286 key and this causes that the private message is
287 not handled by the server at all, it is just
288 passed along. See section 2.5.3 Private Message
289 Encryption And Decryption for more information.
294 Indicates that the packet consists of list of
295 packet payloads indicated by the Packet Type field.
296 The payloads are added one after the other. Note that
297 there are packet types that must not be used as
298 list. Parsing of list packet is done by calculating
299 the length of each payload and parsing them one by
305 Marks the packet to be broadcasted. Client cannot
306 send broadcast packet and normal server cannot send
307 broadcast packet. Only router server may send broadcast
308 packet. The router receiving of packet with this flag
309 set must send (broadcast) the packet to its primary
310 route. If router has several router connections the
311 packet may be sent only to the primary route. See
312 section 2.13 Packet Broadcasting for description of
318 Marks that the packet is tunneled. Tunneling means
319 that extra SILC Packet Header has been applied to the
320 original packet. The outer header has this flag
321 set. See section 2.14 Packet Tunneling for more
327 o Packet Type (1 byte) - Is the type of the packet. Receiver
328 uses this field to parse the packet. See section 2.3
329 SILC Packets for list of defined packet types.
331 o Source ID Length (2 bytes) - Indicates the length of the
332 Source ID field in the header, not including this or any
335 o Destination ID Length (2 bytes) - Indicates the length of the
336 Destination ID field in the header, not including this or
339 o Src ID Type (1 byte) - Indicates the type of ID in the
340 Source ID field. See section 2.4 SILC ID Types for
343 o Source ID (variable length) - The actual source ID that
344 indicates who is the original sender of the packet.
346 o Dst ID Type (1 byte) - Indicates the type of ID in the
347 Destination ID field. See section 2.4 SILC ID Types for
350 o Destination ID (variable length) - The actual source ID that
351 indicates who is the end receiver of the packet.
355 2.3 SILC Packet Types
357 SILC packet types defines the contents of the packet and it is used by
358 the receiver to parse the packet. The packet type is 8 bits, as a one
359 byte, in length. The range for the packet types are from 0 - 255,
360 where 0 is never sent and 255 is currently reserved for future
361 extensions and must not be defined to any other purpose. Every SILC
362 specification compliant implementation should support all of these packet
365 The below list of the SILC Packet types includes reference to the packet
366 payload as well. Packet payloads are the actual packet, that is, the data
367 that the packet consists of. Each packet type defines packet payload
368 which usually may only be sent with the specific packet type.
370 Most of the packets are packets that must be destined directly to entity
371 that is connected to the sender. It is not allowed, for example, for
372 router to send disconnect packet to client that is not directly connected
373 to the router. However, there are some special packet types that may
374 be destined to some entity that the sender has not direct connection
375 with. These packets are for example private message packets, channel
376 message packets, command packets and some other packets that may be
377 broadcasted in the SILC network. If the packet is allowed to be sent to
378 indirectly connected entity it is mentioned separately in the packet
379 description (unless it is obvious as in private and channel message
380 packets). Other packets must not be sent or accepted, if sent, to
381 indirectly connected entities.
383 List of SILC Packet types are defined as follows.
388 This type is reserved and it is never sent.
391 1 SILC_PACKET_DISCONNECT
393 This packet is sent to disconnect the remote end. Reason of
394 the disconnection is sent inside the packet payload. Client
395 usually does not send this packet.
397 This packet must not be sent as list and the List flag must
400 Payload of the packet: See section 2.3.3 Disconnect Payload
403 2 SILC_PACKET_SUCCESS
405 This packet is sent upon successful execution of some protocol.
406 The status of the success is sent in the packet.
408 This packet must not be sent as list and the List flag must
411 Payload of the packet: See section 2.3.4 Success Payload
414 3 SILC_PACKET_FAILURE
416 This packet is sent upon failure of some protocol. The status
417 of the failure is sent in the packet.
419 This packet must not be sent as list and the List flag must
422 Payload of the packet: See section 2.3.5 Failure Payload
427 This packet may be sent upon rejection of some protocol.
428 The status of the rejection is sent in the packet.
430 This packet must not be sent as list and the List flag must
433 Payload of the packet: See section 2.3.6 Reject Payload
438 This packet is used to send notify message, usually from
439 server to client, although it may be sent from server to another
440 server as well. Client never sends this packet. Server may
441 send this packet to channel as well when the packet is
442 distributed to all clients on the channel.
444 Payload of the packet: See section 2.3.7 Notify Payload.
449 This packet is sent when an error occurs. Server may
450 send this packet. Client never sends this packet. The
451 client may entirely ignore the packet, however, server is
452 most likely to take action anyway. This packet may be sent
453 to entity that is indirectly connected to the sender.
455 This packet must not be sent as list and the List flag must
458 Payload of the packet: See section 2.3.8 Error Payload.
461 7 SILC_PACKET_CHANNEL_MESSAGE
463 This packet is used to send messages to channels. The packet
464 includes Channel ID of the channel and the actual message to
465 the channel. Messages sent to the channel are always protected
466 by channel specific keys. Channel Keys are distributed by
467 SILC_PACKET_CHANNEL_KEY packet.
469 This packet must not be sent as list and the List flag must
472 Payload of the packet: See section 2.3.9 Channel Message
476 8 SILC_PACKET_CHANNEL_KEY
478 This packet is used to distribute new key for particular
479 channel. Each channel has their own independent keys that
480 is used to protect the traffic on the channel. Only server
481 may send this packet. This packet may be sent to entity
482 that is indirectly connected to the sender.
484 This packet must not be sent as list and the List flag must
487 Payload of the packet: See section 2.3.10 Channel Key Payload
490 9 SILC_PACKET_PRIVATE_MESSAGE
492 This packet is used to send private messages from client
493 to another client. By default, private messages are protected
494 by session keys established by normal key exchange protocol.
495 However, it is possible to use specific key to protect private
496 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
497 agree the key with the remote client. Pre-shared key may be
498 used as well if both of the client knows it, however, it needs
499 to be agreed outside SILC. See more of this in [SILC1].
501 This packet must not be sent as list and the List flag must
504 Payload of the packet: See section 2.3.11 Private Message
508 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
510 This packet is used to agree about a key to be used to protect
511 the private messages between two clients. If this is not sent
512 the normal session key is used to protect the private messages
513 inside SILC network. Agreeing to use specific key to protect
514 private messages adds security, as no server between the two
515 clients will be able to decrypt the private message. However,
516 servers inside SILC network are considered to be trusted, thus
517 using normal session key to protect private messages does not
518 degree security. Whether to agree to use specific keys by
519 default or to use normal session keys by default, is
520 implementation specific issue. See more of this in [SILC1].
522 This packet must not be sent as list and the List flag must
525 Payload of the packet: See section 2.3.12 Private Message
529 11 SILC_PACKET_COMMAND
531 This packet is used to send commands from client to server.
532 Server may send this packet to other servers as well. All
533 commands are listed in their own section SILC Command Types
534 in [SILC1]. The contents of this packet is command specific.
535 This packet may be sent to entity that is indirectly connected
538 This packet must not be sent as list and the List flag must
541 Payload of the packet: See section 2.3.13 Command Payload
544 12 SILC_PACKET_COMMAND_REPLY
546 This packet is send as reply to the SILC_PACKET_COMMAND packet.
547 The contents of this packet is command specific. This packet
548 maybe sent to entity that is indirectly connected to the sender.
550 This packet must not be sent as list and the List flag must
553 Payload of the packet: See section 2.3.14 Command Reply
554 Payload and section 2.3.13 Command
558 13 SILC_PACKET_KEY_EXCHANGE
560 This packet is used to start SILC Key Exchange Protocol,
561 described in detail in [SILC3].
563 This packet must not be sent as list and the List flag must
566 Payload of the packet: Payload of this packet is described
567 in the section SILC Key Exchange
568 Protocol and its sub sections in
572 14 SILC_PACKET_KEY_EXCHANGE_1
574 This packet is used as part of the SILC Key Exchange Protocol.
576 This packet must not be sent as list and the List flag must
579 Payload of the packet: Payload of this packet is described
580 in the section SILC Key Exchange
581 Protocol and its sub sections in
585 15 SILC_PACKET_KEY_EXCHANGE_2
587 This packet is used as part of the SILC Key Exchange Protocol.
589 This packet must not be sent as list and the List flag must
592 Payload of the packet: Payload of this packet is described
593 in the section SILC Key Exchange
594 Protocol and its sub sections in
598 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
600 This packet is used to request the authentication method to
601 be used in the SILC Connection Authentication Protocol. If
602 initiator of the protocol does not know the mandatory
603 authentication method this packet is used to determine it.
605 The party receiving this payload must respond with the same
606 packet including the mandatory authentication method.
608 This packet must not be sent as list and the List flag must
611 Payload of the packet: See section 2.3.15 Connection Auth
615 17 SILC_PACKET_CONNECTION_AUTH
617 This packet is used to start and perform the SILC Connection
618 Authentication Protocol. This protocol is used to authenticate
619 the connecting party. The protocol is described in detail in
622 This packet must not be sent as list and the List flag must
625 Payload of the packet: Payload of this packet is described
626 in the section SILC Authentication
627 Protocol and it sub sections in [SILC].
630 18 SILC_PACKET_NEW_ID
632 This packet is used to distribute new ID's from server to
633 router and from router to all routers in the SILC network.
634 This is used when for example new client is registered to
635 SILC network. The newly created ID's of these operations are
636 distributed by this packet. Only server may send this packet,
637 however, client must be able to receive this packet.
639 Payload of the packet: See section 2.3.16 New ID Payload
642 19 SILC_PACKET_NEW_CLIENT
644 This packet is used by client to register itself to the
645 SILC network. This is sent after key exchange and
646 authentication protocols has been completed. Client sends
647 various information about itself in this packet.
649 This packet must not be sent as list and the List flag must
652 Payload of the packet: See section 2.3.17 New Client Payload
655 20 SILC_PACKET_NEW_SERVER
657 This packet is used by server to register itself to the
658 SILC network. This is sent after key exchange and
659 authentication protocols has been completed. Server sends
660 this to the router it connected to, or, if router was
661 connecting, to the connected router. Server sends
662 its Server ID and other information in this packet.
663 Client must not send or receive this packet.
665 This packet must not be sent as list and the List flag must
668 Payload of the packet: See section 2.3.18 New Server Payload
671 21 SILC_PACKET_NEW_CHANNEL
673 This packet is used to notify routers about newly created
674 channel. Channels are always created by the router and it must
675 notify other routers about the created channel. Router sends
676 this packet to its primary route. Client must not send this
677 packet. This packet maybe sent to entity that is indirectly
678 connected to the sender.
680 Payload of the packet: See section 2.3.19 New Channel Payload
685 This packet is used to indicate that re-key must be performed
686 for session keys. See section Session Key Regeneration in
687 [SILC1] for more information. This packet does not have
690 This packet must not be sent as list and the List flag must
694 23 SILC_PACKET_REKEY_DONE
696 This packet is used to indicate that re-key is performed and
697 new keys must be used hereafter. This is sent only if re-key
698 was done without PFS option. If PFS is set, this is not sent
699 as SILC Key Exchange protocol is executed. This packet does
702 This packet must not be sent as list and the List flag must
706 24 SILC_PACKET_HEARTBEAT
708 This packet is used by clients, servers and routers to keep the
709 connection alive. It is recommended that all servers implement
710 keepalive actions and perform it to both direction in a link.
711 This packet does not have a payload.
713 This packet must not be sent as list and the List flag must
717 25 SILC_PACKET_KEY_AGREEMENT
719 This packet is used by clients to request key negotiation
720 between another client in the SILC network. If the negotiation
721 is started it is performed using the SKE protocol. The result of
722 the negotiation, the secret key material, can be used for
723 example as private message key. The server and router must not
726 Payload of the packet: See section 2.3.20 Key Agreement Payload
729 26 SILC_PACKET_CELL_ROUTERS
731 This packet is used by primary router in the cell to notify its
732 primary router what other routers (backup routers) exist in the
733 cell. In case of failure of the primary router in the cell the
734 first router in the list will act as primary router of the cell.
735 This packet may be sent at anytime after connection has been
736 registered to the primary router. The client must not send this
739 Payload of the packet: See section 2.3.21 Cell Routers Payload
744 Currently undefined commands.
749 These packet types are reserved for private use and they will not
750 be defined by this document.
755 This type is reserved for future extensions and currently it
761 2.3.1 SILC Packet Payloads
763 All payloads resides in the main data area of the SILC packet. However
764 all payloads must be at the start of the data area after the default
765 SILC packet header and padding. All fields in the packet payload are
766 always encrypted, as, they reside in the data area of the packet which
769 Payloads described in this section are common payloads that must be
770 accepted anytime during SILC session. Most of the payloads may only
771 be sent with specific packet type which is defined in the description
774 There are a lot of other payloads in the SILC as well. However, they
775 are not common in the sense that they could be sent at any time.
776 These payloads are not described in this section. These are payloads
777 such as SILC Key Exchange payloads and so on. These are described
778 in [SILC1] and [SILC3].
782 2.3.2 Generic payloads
784 This section describes generic payloads that are not associated to any
785 specific packet type. They can be used for example inside some other
792 This payload can be used to send an ID. ID's are variable length thus
793 this payload provides a way to send variable length ID's.
795 The following diagram represents the ID Payload.
800 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
801 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
802 | ID Type | ID Length |
803 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
807 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
815 o ID Type (2 bytes) - Indicates the type of the ID. See
816 section 2.4 SILC ID Types for list of defined ID types.
818 o ID Length (2 bytes) - Length of the ID Data area not
819 including the length of any other fields in the payload.
821 o ID Data (variable length) - The actual ID data.
826 2.3.2.2 Argument Payload
828 Argument Payload is used to set arguments for any packet payload that
829 needs and supports arguments, such as commands. Number of arguments
830 associated with a packet must be indicated by the packet payload who
831 needs the arguments. Argument Payloads must always reside right after
832 the packet payload needing the arguments. Incorrect amount of argument
833 payloads must cause rejection of the packet. The following diagram represents
834 the Argument Payload.
840 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
841 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
842 | Payload Length | Argument Type | |
843 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
847 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
851 Figure 4: Argument Payload
855 o Payload Length (2 bytes) - Length of the argument payload data
856 area not including the length of any other fields in the
859 o Argument Type (1 byte) - Indicates the type of the argument.
860 Every argument may have a specific type that must be defined
861 by the packet payload needing the argument. For example
862 every command specify a number for each argument that maybe
863 associated with the command. By using this number the receiver
864 of the packet knows what type of argument this is. If there is
865 no specific argument type this field is set to zero (0).
867 o Argument Data (variable length) - Argument data.
872 2.3.3 Disconnect Payload
874 Disconnect payload is sent upon disconnection. The payload is simple;
875 reason of disconnection is sent to the disconnected party.
877 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
878 must not be sent in any other packet type. The following diagram represents
879 the Disconnect Payload.
890 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
891 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
893 ~ Disconnect Message ~
895 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
899 Figure 5: Disconnect Payload
905 o Disconnect Message (variable length) - Human readable
906 reason of the disconnection.
911 2.3.4 Success Payload
913 Success payload is sent when some protocol execution is successfully
914 completed. The payload is simple; indication of the success is sent.
915 This maybe any data, including binary or human readable data.
920 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
921 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
923 ~ Success Indication ~
925 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
929 Figure 6: Success Payload
933 o Success Indication (variable length) - Indication of
934 the success. This maybe for example some flag that
935 indicates the protocol and the success status or human
936 readable success message. The true length of this
937 payload is available by calculating it from the SILC
943 2.3.5 Failure Payload
945 This is opposite of Success Payload. Indication of failure of
946 some protocol is sent in the payload.
952 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
953 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
955 ~ Failure Indication ~
957 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
961 Figure 7: Failure Payload
965 o Failure Indication (variable length) - Indication of
966 the failure. This maybe for example some flag that
967 indicates the protocol and the failure status or human
968 readable failure message. The true length of this
969 payload is available by calculating it from the SILC
977 This payload is sent when some protocol is rejected to be executed.
978 Other operations may send this as well that was rejected. The
979 indication of the rejection is sent in the payload. The indication
980 may be binary or human readable data.
986 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
987 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
989 ~ Reject Indication ~
991 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
995 Figure 8: Reject Payload
999 o Reject Indication (variable length) - Indication of
1000 the rejection. This maybe for example some flag that
1001 indicates the protocol and the rejection status or human
1002 readable rejection message. The true length of this
1003 payload is available by calculating it from the SILC
1012 2.3.7 Notify Payload
1014 Notify payload is used to send notify messages. The payload is usually
1015 sent from server to client, however, server may send it to another
1016 server as well. This payload may also be sent to a channel. Client must
1017 not send this payload. The receiver of this payload may totally ignore the
1018 contents of the payload, however, notify message should be audited.
1020 The payload may only be sent with SILC_PACKET_NOTIFY packet. It must
1021 not be sent in any other packet type. The following diagram represents the
1027 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
1028 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1029 | Notify Type | Payload Length |
1030 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1036 Figure 9: Notify Payload
1040 o Notify Type (2 bytes) - Indicates the type of the notify
1043 o Payload Length (2 bytes) - Length of the entire Notify Payload
1044 including any associated Argument Payloads.
1046 o Argument Nums (2 bytes) - Indicates the number of Argument
1047 Payloads associated to this payload. Notify types may define
1048 arguments to be send along the notify message.
1051 The following list of currently defined notify types. The format for notify
1052 arguments is same as in SILC commands described in [SILC1]. Also, all
1053 ID's sent in arguments are sent inside ID Payload.
1056 0 SILC_NOTIFY_TYPE_NONE
1058 If no specific notify type apply for the notify message this type
1062 Arguments: (1) <message>
1064 The <message> is implementation specific free text string. Receiver
1065 may ignore this message.
1068 1 SILC_NOTIFY_TYPE_INVITE
1070 Sent when receiver has been invited to a channel. This type must be
1071 sent directly to the invited client.
1074 Arguments: (1) <Client ID> (2) <Channel ID>
1076 The <Client ID> is the client who invites the receiver of this type
1077 to channel indicated by <Channel ID>.
1080 2 SILC_NOTIFY_TYPE_JOIN
1082 Sent when client has joined to a channel. The server must distribute
1083 this type only to the local clients on the channel and then send
1084 it to its primary router. The router or server receiving the packet
1085 distributes this type to the local clients on the channel and
1086 broadcast it to the network.
1089 Arguments: (1) <Client ID> (2) <Channel ID>
1091 The <Client ID> is the client that joined to the channel indicated
1092 by the <Channel ID>.
1095 3 SILC_NOTIFY_TYPE_LEAVE
1097 Sent when client has left a channel. The server must distribute
1098 this type only to the local clients on the channel and then send
1099 it to its primary router. The router or server receiving the packet
1100 distributes this type to the local clients on the channel and
1101 broadcast it to the network.
1104 Arguments: (1) <Client ID>
1106 The <Client ID> is the client who left the channel.
1109 4 SILC_NOTIFY_TYPE_SIGNOFF
1111 Sent when client signoffs from SILC network. The server must
1112 distribute this type only to the local clients on the channel and
1113 then send it to its primary router. The router or server receiving
1114 the packet distributes this type to the local clients on the channel
1115 and broadcast it to the network.
1118 Arguments: (1) <Client ID> (2) <message>
1120 The <Client ID> is the client who left SILC network. The <message>
1121 is free text string indicating the reason of signoff.
1124 5 SILC_NOTIFY_TYPE_TOPIC_SET
1126 Sent when topic is set/changed on a channel. This type must be sent
1127 only to the clients who is joined on the channel whose topic was
1131 Arguments: (1) <Client ID> (2) <topic>
1133 The <Client ID> is the client who set or changed the <topic>.
1136 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1138 Sent when client changes nick on a channel. The server must
1139 distribute this type only to the local clients on the channel and
1140 then send it to its primary router. The router or server receiving
1141 the packet distributes this type to the local clients on the channel
1142 and broadcast it to the network.
1145 Arguments: (1) <Old Client ID> (2) <New Client ID>
1147 The <Old Client ID> is the old ID of the client who changed the
1148 nickname. The <New Client ID> is the new ID generated by the change
1152 7 SILC_NOTIFY_TYPE_CMODE_CHANGE
1154 Sent when channel mode has changed. This type must be sent only to
1155 the clients who is joined on the channel whose mode was changed.
1158 Arguments: (1) <Client ID> (2) <mode mask>
1160 The <Client ID> is the client who changed the mode. The <mode mask>
1161 is the new mode mask of the channel.
1164 8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
1166 Sent when user mode on channel has changed. This type must be sent
1167 only to the clients who is joined on the channel where the target
1171 Arguments: (1) <Client ID> (2) <mode mask>
1172 (3) <Target Client ID>
1174 The <Client ID> is the client who changed the mode. The <mode mask>
1175 is the new mode mask of the channel. The <Target Client ID> is the
1176 client which mode was changed.
1179 9 SILC_NOTIFY_TYPE_MOTD
1181 Sent when Message of the Day (motd) is sent to client.
1184 Arguments: (1) <motd>
1186 The <motd> is the Message of the Day.
1189 10 SILC_NOTIFY_TYPE_CHANNEL_CHANGE
1191 Sent when channel's ID has changed for a reason or another. This
1192 is sent by noral server to the client. Client must change the
1193 old Channel ID to the new one. This type must be sent only to the
1194 clients who is joined on the channel.
1197 Arguments: (1) <Old Channel ID> (2) <New Channel ID>
1199 The <Old Channel ID> is the channel's old ID and the <New Channel ID>
1200 is the new one that must replace the old one.
1203 11 SILC_NOTIFY_TYPE_SERVER_SIGNOFF
1205 Sent when server quits SILC network. Those clients from this server
1206 that are on channels must be removed from the channel.
1209 Arguments: (1) <Server ID>
1211 The <Server ID> is the server's ID.
1214 12 SILC_NOTIFY_TYPE_KICKED
1216 Sent when a client has been kicked from a channel. This is sent
1217 also to the client who was kicked from the channel. The client
1218 who was kicked from the channel must be removed from the channel.
1219 This notify type is always destined to the channel. The router or
1220 server receiving the packet distributes this type to the local
1221 clients on the channel and broadcast it to the network.
1224 Arguments: (1) <Client ID> (2) [<comment>]
1226 The <Client ID> is the client who was kicked from the channel.
1227 The kicker may have set the <comment> to indicate the reason for
1231 13 SILC_NOTIFY_TYPE_KILLED
1233 Sent when a client has been killed from the network. This is sent
1234 also to the client who was killed from the network. The client
1235 who was killed from the network must be removed from the network.
1236 This notify type is destined directly to the client who was killed
1237 and to channel if the client is on any channel. The router or
1238 server receiving the packet distributes this type to the local
1239 clients on the channel and broadcast it to the network.
1242 Arguments: (1) <Client ID> (2) [<comment>]
1244 The <Client ID> is the client who was killed from the network.
1245 The killer may have set the <comment> to indicate the reason for
1250 Notify types starting from 16384 are reserved for private notify
1257 Error payload is sent upon error. Error may occur in various
1258 conditions when server sends this packet. Client may not send this
1259 payload but must be able to accept it. However, client may
1260 totally ignore the contents of the packet as server is going to
1261 take action on the error anyway. However, it is recommended
1262 that the client takes error packet seriously.
1268 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
1269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1273 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1277 Figure 10: Error Payload
1281 o Error Message (variable length) - Human readable error
1287 2.3.9 Channel Message Payload
1289 Channel messages are the most common messages sent in the SILC.
1290 Channel Message Payload is used to send message to channels. These
1291 messages can only be sent if client has joined to some channel.
1292 Even though this packet is the most common in SILC it is still
1293 special packet. Some special handling on sending and reception
1294 of channel message is required.
1296 Padding must be applied into this payload since the payload is
1297 encrypted separately from other parts of the packet with the
1298 channel specific key. Hence the requirement of the padding.
1299 The padding should be random data. The packet must be made
1300 multiple by eight (8) or by the block size of the cipher, which
1303 The SILC header in this packet is encrypted with the session key
1304 of the next receiver of the packet. Nothing else is encrypted
1305 with that key. Thus, the actual packet and padding to be
1306 encrypted with the session key is SILC Header plus padding to it
1307 to make it multiple by eight (8) or multiple by the block size
1308 of the cipher, which ever is larger.
1310 Receiver of the the channel message packet is able to determine
1311 the channel the message is destined to by checking the destination
1312 ID from the SILC Packet header which tells the destination channel.
1313 The original sender of the packet is also determined by checking
1314 the source ID from the header which tells the client who sent
1317 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1318 It must not be sent in any other packet type. The following diagram
1319 represents the Channel Message Payload.
1321 (*) indicates that the field is not encrypted.
1327 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
1328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1329 | Message Length | |
1330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1335 | Padding Length | |
1336 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1340 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1344 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1346 ~ Initial Vector * ~
1348 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1352 Figure 11: Channel Message Payload
1356 o Message Length (2 bytes) - Indicates the length of the
1357 the Message Data field in the payload, not including any
1360 o Message Data (variable length) - The actual message to
1363 o Padding Length (2 bytes) - Indicates the length of the
1364 Padding field in the payload, not including any other
1367 o Padding (variable length) - The padding that must be
1368 applied because this payload is encrypted separately from
1369 other parts of the packet.
1371 o MAC (variable legnth) - The MAC computed from the
1372 Message Length, Message Data, Padding Length and Padding
1373 fields. This protects the integrity of the plaintext
1374 channel message. The receiver can verify from the MAC
1375 whether the message decrypted correctly. Also, if more than
1376 one private key has been set for the channel, the receiver
1377 can verify which of the keys decrypted the message
1378 correctly. Note that, this field is encrypted and must
1379 be added to the padding calculation.
1381 o Initial Vector (variable length) - The initial vector
1382 that has been used in packet encryption. It needs to be
1383 used in the packet decryption as well. What this field
1384 includes is implementation issue. However, it is
1385 recommended that it would be random data or, perhaps,
1386 a timestamp. It is not recommended to use zero (0) as
1387 initial vector. This field is not encrypted. This field
1388 is not included into the padding calculation. Length
1389 of this field equals the cipher's block size. This field
1390 is, however, authenticated.
1395 2.3.10 Channel Key Payload
1397 All traffic in channels are protected by channel specific keys.
1398 Channel Key Payload is used to distribute channel keys to all
1399 clients on the particular channel. Channel keys are sent when
1400 the channel is created, when new user joins to the channel and
1401 whenever a user has left a channel. Server creates the new
1402 channel key and distributes it to the clients by encrypting this
1403 payload with the session key shared between the server and
1404 the client. After that, client starts using the key received
1405 in this payload to protect the traffic on the channel.
1407 The client who is joining to the channel receives its key in the
1408 SILC_COMMAND_JOIN command reply message thus it is not necessary to
1409 send this payload to the entity who sent the SILC_COMMAND_JOIN command.
1411 Channel keys are cell specific thus every router in cell have
1412 to create a channel key and distribute it if any client in the
1413 cell has joined to a channel. Channel traffic between cell's
1414 are not encrypted using channel keys, they are encrypted using
1415 normal session keys between two routers. Inside a cell, all
1416 channel traffic is encrypted with the specified channel key.
1417 Channel key should expire periodically, say, in one hour, in
1418 which case new channel key is created and distributed.
1420 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1421 It must not be sent in any other packet type. The following diagram
1422 represents the Channel Key Payload.
1439 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
1440 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1441 | Channel ID Length | |
1442 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1446 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1447 | Cipher Name Length | |
1448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1452 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1453 | Channel Key Length | |
1454 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1458 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1462 Figure 12: Channel Key Payload
1467 o Channel ID Length (2 bytes) - Indicates the length of the
1468 Channel ID field in the payload, not including any other
1471 o Channel ID (variable length) - The Channel ID of the
1472 channel this key is meant for.
1474 o Cipher Name Length (2 bytes) - Indicates the length of the
1475 Cipher name field in the payload, not including any other
1478 o Cipher Name (variable length) - Name of the cipher used
1479 in the protection of channel traffic. This name is
1480 initially decided by the creator of the channel but it
1481 may change during the life time of the channel as well.
1483 o Channel Key Length (2 bytes) - Indicates the length of the
1484 Channel Key field in the payload, not including any other
1487 o Channel Key (variable length) - The actual channel key
1488 material. This key is used as such as key material for
1489 encryption function.
1494 2.3.11 Private Message Payload
1496 Private Message Payload is used to send private message between
1497 two clients (or users for that matter). The messages are sent only
1498 to the specified user and no other user inside SILC network is
1499 able to see the message. The message is protected by the session
1500 key established by the SILC Key Exchange Protocol. However,
1501 it is also possible to agree to use specific keys to protect
1502 just the private messages. See section 2.3.11 Private Message
1503 Key Payload for detailed description of how to agree to use
1506 If normal session key is used to protect the message, every
1507 server between the sender client and the receiving client needs
1508 to decrypt the packet and always re-encrypt it with the session
1509 key of the next receiver of the packet. See section Client
1510 To Client in [SILC1].
1512 When specific key is used to protect the message, servers between
1513 the sender and the receiver needs not to decrypt/re-encrypt the
1514 packet. Section 4.8.2 Client To Client in [SILC1] gives example of
1515 this scheme as well.
1517 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1518 packet. It must not be sent in any other packet type. The following
1519 diagram represents the Private Message Payload.
1525 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
1526 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1527 | Nickname Length | |
1528 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1532 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1536 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1540 Figure 13: Private Message Payload
1544 o Nickname Length (2 bytes) - Indicates the length of the
1545 Nickname field, not including any other field.
1547 o Nickname (variable length) - Nickname of the sender of the
1548 private message. This should not be trusted as a definite
1549 sender of the private message. The SILC Packet Header in
1550 the packet indicates the true sender of the packet and
1551 client should verify that the nickname sent here belongs
1552 to the Client ID in the SILC Packet Header. This nickname
1553 is merely provided to be displayed by the client.
1555 o Message Data (variable length) - The actual message to
1556 the client. Rest of the packet is reserved for the message
1562 2.3.12 Private Message Key Payload
1564 This payload is used to send key from client to another client that
1565 is going to be used to protect the private messages between these
1566 two clients. If this payload is not sent normal session key
1567 established by the SILC Key Exchange Protocol is used to protect
1568 the private messages.
1570 This payload may only be sent by client to another client. Server
1571 must not send this payload at any time. After sending this payload
1572 the sender of private messages must set the Private Message Key
1573 flag into SILC Packet Header.
1575 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1576 packet. It must not be sent in any other packet type. The following
1577 diagram represents the Private Message Key Payload.
1583 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
1584 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1585 | Private Message Key Length | |
1586 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1588 ~ Private Message Key ~
1590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1591 | Cipher Name Length | |
1592 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1596 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1600 Figure 14: Private Message Key Payload
1606 o Private Message Key Length (2 bytes) - Indicates the length
1607 of the Private Message Key field in the payload, not including
1610 o Private Message Key (variable length) - The actual private
1611 message key material.
1613 o Cipher Name Length (2 bytes) - Indicates the length of the
1614 Cipher Name field in the payload, not including any other
1617 o Cipher Name (variable length) - Name of the cipher to use
1618 in the private message encryption. If this field does not
1619 exist then the default cipher of the SILC protocol is used.
1620 See the [SILC1] for defined ciphers.
1626 2.3.13 Command Payload
1628 Command Payload is used to send SILC commands from client to server.
1629 Also server may send commands to other servers. The following diagram
1630 represents the Command Payload.
1636 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
1637 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1638 | Payload Length | SILC Command | Arguments Num |
1639 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1640 | Command Identifier |
1641 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1645 Figure 15: Command Payload
1649 o Payload Length (2 bytes) - Length of the entire command
1650 payload including any command argument payloads associated
1653 o SILC Command (1 byte) - Indicates the SILC command. This must
1654 be set to non-zero value. If zero (0) value is found in this
1655 field the packet must be discarded.
1657 o Arguments Num (1 byte) - Indicates the number of arguments
1658 associated with the command. If there are no arguments this
1659 field is set to zero (0). The arguments must follow the
1660 command payload. See section 2.3.2.2 for definition of the
1663 o Command Identifier (2 bytes) - Identifies this command at the
1664 sender's end. The entity who replies to this command must
1665 set the value found from this field into the Command Payload
1666 used to send the reply to the sender. This way the sender
1667 can identify which command reply belongs to which originally
1668 sent command. What this field includes is implementation
1669 issue but it is recommended that wrapping counter value is
1670 used in the field. Value zero (0) in this field means that
1671 no specific value is set.
1674 See [SILC1] for detailed description of different SILC commands,
1675 their arguments and their reply messages.
1679 2.3.14 Command Reply Payload
1681 Command Reply Payload is used to send replies to the commands. The
1682 Command Reply Payload is identical to the Command Payload thus see the
1683 upper sections for Command Payload and for Command Argument Payload
1684 specifications. Command Reply message uses the Command Argument Payload
1687 The entity who sends the reply packet must set the Command Unifier
1688 field in the reply packet's Command Payload to the value it received
1689 in the original command packet.
1691 See SILC Commands in [SILC1] for detailed description of different
1692 SILC commands, their arguments and their reply messages.
1696 2.3.15 Connection Auth Request Payload
1698 Client may send this payload to server to request the authentication
1699 method that must be used in authentication protocol. If client knows
1700 this information beforehand this payload is not necessary to be sent.
1701 Server performing authentication with another server may also send
1702 this payload to request the authentication method. If the connecting
1703 server already knows this information this payload is not necessary
1706 Server receiving this request must reply with same payload sending
1707 the mandatory authentication method. Algorithms that may be required
1708 to be used by the authentication method are the ones already
1709 established by the SILC Key Exchange protocol. See section Key
1710 Exchange Start Payload in [SILC3] for detailed information.
1712 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1713 packet. It must not be sent in any other packet type. The following
1714 diagram represents the Connection Auth Request Payload.
1720 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
1721 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1722 | Connection Type | Authentication Method |
1723 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1727 Figure 16: Connection Auth Request Payload
1731 o Connection Type (2 bytes) - Indicates the type of the ID.
1732 The following connection types are defined:
1738 If any other type is found in this field the packet must be
1739 discarded and the authentication must be failed.
1741 o Authentication Method (2 bytes) - Indicates the authentication
1742 method to be used in the authentication protocol. The following
1743 authentication methods are defined:
1748 1 password (mandatory)
1749 2 public key (mandatory)
1751 If any other type is found in this field the packet must be
1752 discarded and the authentication must be failed. If this
1753 payload is sent as request to receive the mandatory
1754 authentication method this field must be set to zero (0),
1755 indicating that receiver should send the mandatory
1756 authentication method. The receiver sending this payload
1757 to the requesting party, may also set this field to zero (0)
1758 to indicate that authentication is not required. In this
1759 case authentication protocol still must be started but
1760 server is most likely to respond with SILC_PACKET_SUCCESS
1766 2.3.16 New ID Payload
1768 New ID Payload is a multipurpose payload. It is used to send newly
1769 created ID's from clients and servers. When client connects to server
1770 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
1771 packet, server replies with this packet by sending the created ID for
1772 the client. Server always creates the ID for the client.
1774 This payload is also used when server tells its router that new client
1775 has registered to the SILC network. In this case the server sends
1776 the Client ID of the client to the router. Similary when router
1777 distributes information to other routers about the client in the SILC
1778 network this payload is used.
1780 Also, when server connects to router, router uses this payload to inform
1781 other routers about new server in the SILC network. However, every
1782 server (or router) creates their own ID's thus the ID distributed by
1783 this payload is not created by the distributor in this case. Servers
1784 create their own ID's. Server registers itself to the network by sending
1785 SILC_PACKET_NEW_SERVER to the router it connected to. The case is same
1786 when router connects to another router.
1788 However, this payload is not and must not be used to send information
1789 about new channels. New channels are always distributed by sending the
1790 dedicated SILC_PACKET_NEW_CHANNEL packet.
1792 Hence, this payload is very important and used every time when some
1793 new entity is registered to the SILC network. Client never sends this
1794 payload. Both client and server (and router) may receive this payload.
1796 The packet uses generic ID Payload as New ID Payload. See section
1797 2.3.2.1 for generic ID Payload.
1801 2.3.17 New Client Payload
1803 When client is connected to the server, keys has been exchanged and
1804 connection has been authenticated client must register itself to the
1805 server. Clients first packet after key exchange and authentication
1806 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
1807 the relevant information about the connected user. Server creates a new
1808 client ID for the client when received this payload and sends it to the
1809 client in New ID Payload.
1811 This payload sends username and real name of the user on the remote host
1812 which is connected to the SILC server with SILC client. The server
1813 creates the client ID according the information sent in this payload.
1814 The nickname of the user becomes the username sent in this payload.
1815 However, client should call NICK command after sending this payload to
1816 set the real nickname of the user which is then used to create new
1819 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
1820 must not be sent in any other packet type. The following diagram
1821 represents the New Client Payload.
1828 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
1829 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1830 | Username Length | |
1831 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1835 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1836 | Real Name Length | |
1837 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1841 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1845 Figure 17: New Client Payload
1849 o Username Length (2 bytes) - Length of the username.
1851 o Username (variable length) - The username of the user on
1852 the host where connecting to the SILC server.
1854 o Real Name Length (2 bytes) - Length of the Real Name.
1856 o Real Name (variable length) - The real name of the user
1857 on the host where connecting to the SILC server.
1862 2.3.18 New Server Payload
1864 This payload is sent by server when it has completed successfully both
1865 key exchange and connection authentication protocols. The server
1866 uses this payload to register itself to the SILC network. The
1867 first packet after these key exchange and authentication protocols
1868 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
1869 of the server that it has created by itself. It also includes a
1870 name of the server that is associated to the Server ID.
1872 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
1873 must not be sent in any other packet type. The following diagram represents
1874 the New Server Payload.
1883 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
1884 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1885 | Server ID Length | |
1886 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1890 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1891 | Server Name Length | |
1892 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1896 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1900 Figure 18: New Server Payload
1904 o Server ID Length (2 bytes) - Length of the ID Data area not
1905 including the length of any other fields in the payload.
1907 o Server ID Data (variable length) - The actual Server ID
1910 o Server Name Length (2 bytes) - Length of the server name.
1912 o Server Name (variable length) - The server name.
1917 2.3.19 New Channel Payload
1919 Information about newly created channel is broadcasted to all routers
1920 in the SILC network by sending this packet payload. Channels are
1921 created by router of the cell. Server never creates channels unless
1922 it is a standalone server and it does not have router connection,
1923 in this case server acts as router. Normal server send JOIN command
1924 to the router (after it has received JOIN command from client) which
1925 then processes the command and creates the channel. Client never sends
1928 The payload may only be sent with SILC_PACKET_NEW_CHANNEL packet.
1929 It must not be sent in any other packet type. The following diagram
1930 represents the New Channel Payload.
1936 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
1937 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1938 | Channel Name Length | |
1939 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1943 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1944 | Channel ID Length | |
1945 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1949 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1953 Figure 19: New Channel Payload
1958 o Channel Name Length (2 bytes) - Length of the channel name.
1960 o Channel Name (variable length) - The name of the created
1963 o Channel ID Length (2 bytes) - Length of the Channel ID.
1965 o Channel ID (variable length) - The created Channel ID.
1970 2.3.20 Key Agreement Payload
1972 This payload is used by clients to request key negotiation between
1973 another client in the SILC Network. The key agreement protocol used
1974 is the SKE protocol. The result of the protocol, the secret key
1975 material, can be used for example as private message key between the
1976 two clients. This significantly adds security as the key agreement
1977 is performed outside the SILC network. The server and router must not
1980 The sender may tell the receiver of this payload the hostname and the
1981 port where the SKE protocol is running in the sender's end. The
1982 receiver may then initiate the SKE negotiation with the sender. The
1983 sender may also optionally not to include the hostname and the port
1984 of its SKE protocol. In this case the receiver may reply to the
1985 request by sending the same payload filled with the receiver's hostname
1986 and the port where the SKE protocol is running. The sender may then
1987 initiate the SKE negotiation with the receiver.
1989 The payload may only be sent with SILC_PACKET_KEY_AGREEMENT packet.
1990 It must not be sent in any other packet type. The following diagram
1991 represents the Key Agreement Payload.
1997 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
1998 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1999 | Hostname Length | |
2000 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2004 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2006 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2010 Figure 20: Key Agreement Payload
2014 o Hostname Length (2 bytes) - Indicates the length of the Hostname
2017 o Hostname (variable length) - The hostname or IP address where
2018 the SKE protocol is running. The sender may fill this field
2019 when sending the payload. If the receiver sends this payload
2020 as reply to the request it must fill this field.
2022 o Port (4 bytes) - The port where the SKE protocol is bound.
2023 The sender may fill this field when sending the payload. If
2024 the receiver sends this payload as reply to the request it
2025 must fill this field. This is a 32 bit MSB first order value.
2029 After the key material has been received from the SKE protocol it is
2030 processed as the [SILC3] describes. If the key material is used as
2031 channel private key then the Sending Encryption Key, as defined in
2032 [SILC3] is used as the channel private key. Other key material must
2033 be discarded. The [SILC1] defines the way to use the key material if
2034 it is intended to be used as private message keys. Any other use for
2035 the key material is undefined.
2039 2.3.21 Cell Routers Payload
2041 Cell Routers payload is used by router to notify its primary router what
2042 other routers exist in the cell. The other routers are considered to be
2043 backup routers and one of them will come active only in the case of
2044 failure of the primary router. Normal server can send this packet if it
2045 is acting as backup router. Client must not send this packet. To send
2046 more than one backup router set the List flag and assemble the payloads
2049 The payload may only be sent with SILC_PACKET_CELL_ROUTERS packet. It
2050 must not be sent in any other packet type. The Following diagram
2051 represents the Cell Routers Payload.
2057 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
2058 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2059 | Hostname Length | |
2060 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2064 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2066 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2067 | Server ID Length | |
2068 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2072 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2076 Figure 21: Cell Routers Payload
2080 o Hostname Length (2 bytes) - Indicates the length of the Hostname
2083 o Hostname (variable length) - The hostname or IP address of
2086 o Port (4 bytes) - The port of the backup router it currently uses.
2087 This is a 32 bit MSB first order value.
2089 o Server ID Length (2 bytes) - Indicates the length of the Server
2092 o Server ID (variable length) - Consists of the Server ID of the
2100 ID's are extensively used in the SILC network to associate different
2101 entities. The following ID's has been defined to be used in the SILC
2107 When ever specific ID cannot be used this is used.
2111 Server ID to associate servers. See the format of
2116 Client ID to associate clients. See the format of
2121 Channel ID to associate channels. See the format of
2127 2.5 Packet Encryption And Decryption
2129 SILC packets are encrypted almost entirely. Only small part of SILC
2130 header is not encrypted as described in section 5.2 SILC Packet Header.
2131 The SILC Packet header is the first part of a packet to be encrypted
2132 and it is always encrypted with the key of the next receiver of the
2133 packet. The data payload area of the packet is always entirely
2134 encrypted and it is usually encrypted with the next receiver's key.
2135 However, there are some special packet types and packet payloads
2136 that require special encryption process. These special cases are
2137 described in the next sections. First is described the normal packet
2142 2.5.1 Normal Packet Encryption And Decryption
2144 Normal SILC packets are encrypted with the session key of the next
2145 receiver of the packet. The entire SILC Packet header and the packet
2146 data payload is is also encrypted with the same key. Padding of the
2147 packet is also encrypted always with the session key, also in special
2148 cases. Computed MAC of the packet must not be encrypted.
2150 Decryption process in these cases are straightforward. The receiver
2151 of the packet must first decrypt the SILC Packet header, or some parts
2152 of it, usually first 16 bytes of it. Then the receiver checks the
2153 packet type from the decrypted part of the header and can determine
2154 how the rest of the packet must be decrypted. If the packet type is
2155 any of the special cases described in The following sections the packet
2156 decryption is special. If the packet type is not among those special
2157 packet types rest of the packet may be decrypted with the same key.
2159 Also, note that two bytes of the SILC Packet header are not encrypted
2160 thus it must be noticed in the decryption process by starting the
2161 decryption from the second byte of the header. This sets some rules
2162 to padding generation as well, see the section 2.7 Packet Padding
2165 With out a doubt, this sort of decryption processing causes some
2166 overhead to packet decryption, but never the less, is required.
2170 2.5.2 Channel Message Encryption And Decryption
2172 Channel Messages (Channel Message Payload) are always encrypted with
2173 the channel specific key. However, the SILC Packet header is not
2174 encrypted with that key. As in normal case, the header is encrypted
2175 with the key of the next receiver of the packet, who ever that might
2176 be. Note that in this case the encrypted data area is not touched
2177 at all; it must not be re-encrypted with the session key.
2179 Receiver of a channel message, who ever that is, is required to decrypt
2180 the SILC Packet header to be able to even recognize the packet to be as
2181 channel message. This is same procedure as for normal SILC packets.
2182 As the receiver founds the packet to be channel message, rest of the
2183 packet processing is special. Rest of the SILC Packet header is
2184 decrypted with the same session key along with the padding of the
2185 packet. After that the packet is protected with the channel specific
2186 key and thus can be decrypted only if the receiver is the client on
2187 the channel. See section 2.7 Packet Padding Generation for more
2188 information about padding on special packets.
2190 If the receiver of the channel message is router who is routing the
2191 message to another router then it must decrypt the Channel Message
2192 payload. Between routers (that is, between cells) channel messages
2193 are protected with session keys shared between the routers. This
2194 causes another special packet processing for channel messages. If
2195 the channel message is received from another router then the entire
2196 packet, including Channel Message payload, is encrypted with the
2197 session key shared between the routers. In this case the packet
2198 decryption process is as with normal SILC packets. Hence, if the
2199 router is sending channel message to another router the Channel
2200 Message payload must have been decrypted and must be re-encrypted
2201 with the session key shared between the another router. In this
2202 case the packet encryption is as with any normal SILC packet.
2204 It must be noted that this is only when the channel messages are sent
2205 from router to another router. In all other cases the channel
2206 message encryption and decryption is as described above. This
2207 different processing of channel messages with router to router
2208 connection is because channel keys are cell specific. All cells has
2209 their own channel keys thus the channel message traveling from one
2210 cell to another must be protected as it would be any normal SILC
2213 If the SILC_CMODE_PRIVKEY channel mode has been set for the channel
2214 then the router cannot decrypt the packet as it does not know the
2215 private key. In this case the entire packet is encrypted with the
2216 session key and sent to the router. The router receiving the packet
2217 must check the channel mode and decrypt the packet accordingly.
2221 2.5.3 Private Message Encryption And Decryption
2223 By default, private message in SILC are protected by session keys.
2224 In this case the private message encryption and decryption process is
2225 equivalent to normal packet encryption and decryption.
2227 However, private messages can be protected with private message key
2228 which causes the packet to be special packet. The procedure in this
2229 case is very much alike to channel packets. The actual private message
2230 is encrypted with the private message key and other parts of the
2231 packet is encrypted with the session key. See 2.7 Packet Padding
2232 Generation for more information about padding on special packets.
2234 The difference from channel message processing is that server or router
2235 en route never decrypts the actual private message, as it does not
2236 have the key to do that. Thus, when sending packets between router
2237 the processing is same as in any other case as well; the packet's header
2238 and padding is protected by the session key and the data area is not
2241 The true receiver of the private message, client, that is, is able
2242 to decrypt the private message as it shares the key with the sender
2247 2.6 Packet MAC Generation
2249 Data integrity of a packet is protected by including a message
2250 authentication code (MAC) at the end of the packet. The MAC is computed
2251 from shared secret MAC key, that is established by the SILC Key Exchange
2252 protocol, and from the original contents of the packet. The MAC is
2253 always computed before the packet is encrypted, although after it is
2254 compressed if compression is used.
2256 The MAC is computed from entire packet. Every bit of data in the packet,
2257 including SILC Packet Header is used in the MAC computing. This way
2258 the entire packet becomes authenticated.
2260 If the packet is special packet MAC is computed from the entire packet
2261 but part of the packet may be encrypted before the MAC is computed.
2262 This is case, for example, with channel messages where the message data
2263 is encrypted with key that server may not now. In this case the MAC
2264 has been computed from the encrypted data.
2266 See [SILC1] for defined and allowed MAC algorithms.
2270 2.7 Packet Padding Generation
2272 Padding is needed in the packet because the packet is encrypted. It
2273 must always be multiple by eight (8) or multiple by the size of the
2274 cipher's block size, which ever is larger. The padding is always
2277 For normal packets the padding is added after the SILC Packet Header
2278 and between the Data Payload area. The padding for normal packets
2279 are calculated as follows:
2282 padding length = 16 - ((packet length - 2) % 16)
2285 The 16 is the maximum padding allowed in SILC packet. Two (2) is
2286 subtracted from the true length of the packet because two (2) bytes
2287 is not encrypted in SILC Packet Header, see section 2.2 SILC Packet
2288 Header. Those two bytes that are not encrypted must not be calculated
2289 to the padding length.
2291 For special packets the padding calculation may be different as special
2292 packets may be encrypted differently. In these cases the encrypted
2293 data area must already be multiple by the block size thus in this case
2294 the padding is calculated only for SILC Packet Header, not for any
2295 other area of the packet. The same algorithm works in this case as
2296 well, except that the `packet length' is now the SILC Packet Header
2297 length. In this case, as well, two (2) is subtracted from the
2300 The padding must be random data, preferably, generated by
2301 cryptographically strong random number generator.
2305 2.8 Packet Compression
2307 SILC Packets may be compressed. In this case the data payload area
2308 is compressed and all other areas of the packet must remain as they
2309 are. After compression is performed for the data area, the length
2310 field of Packet Header must be set to the compressed length of the
2313 The compression must always be applied before encryption. When
2314 the packet is received and decrypted the data area must be decompressed.
2315 Note that the true sender of the packet must apply the compression and
2316 the true receiver of the packet must apply the decompression. Any
2317 server or router en route must not decompress the packet.
2324 The sender of the packet must assemble the SILC Packet Header with
2325 correct values. It must set the Source ID of the header as its own
2326 ID, unless it is forwarding the packet. It must also set the Destination
2327 ID of the header to the true destination. If the destination is client
2328 it will be Client ID, if it is server it will be Server ID and if it is
2329 channel it will be Channel ID.
2331 If the sender wants to compress the packet it must apply the
2332 compression now. Sender must also compute the padding as described
2333 in above sections. Then sender must compute the MAC of the packet.
2335 Then sender encrypts the packet as has been described in above
2336 sections according whether the packet is normal packet or special
2337 packet. The computed MAC must not be encrypted.
2341 2.10 Packet Reception
2343 On packet reception the receiver must check that all fields in the
2344 SILC Packet Header are valid. It must check the flags of the
2345 header and act accordingly. It must also check the MAC of the packet
2346 and if it is to be failed the packet must be discarded. Also if the
2347 header of the packet includes any bad fields the packet must be
2350 See above sections on the decryption process of the received packet.
2352 The receiver must also check that the ID's in the header are valid
2353 ID's. Unsupported ID types or malformed ID's must cause packet
2354 rejection. The padding on the reception is always ignored.
2356 The receiver must also check the packet type and start parsing the
2357 packet according to the type. However, note the above sections on
2358 special packet types and their parsing.
2364 Routers are the primary entities in the SILC network that takes care
2365 of packet routing. However, normal servers routes packets as well, for
2366 example, when they are routing channel message to the local clients.
2367 Routing is quite simple as every packet tells the true origin and the
2368 true destination of the packet.
2370 It is still recommended for routers that has several routing connections
2371 to create route cache for those destinations that has faster route than
2372 the router's primary route. This information is available for the router
2373 when other router connects to the router. The connecting party then
2374 sends all of its locally connected clients, server and channels. These
2375 informations helps to create the route cache. Also, when new channels
2376 are created to a cell its information is broadcasted to all routers
2377 in the network. Channel ID's are based on router's ID thus it is easy
2378 to create route cache based on these informations. If faster route for
2379 destination does not exist in router's route cache the packet must be
2380 routed to the primary route (default route).
2382 For server who receives a packet to be routed to its locally connected
2383 client the server must check whether the particular packet type is
2384 allowed to be routed to the client. Not all packets may be sent by
2385 some odd entity to client that is indirectly connected to the sender.
2386 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2387 entities and sending packets to them. The section mentions the packets
2388 that may be sent to indirectly connected entities. It is clear that some
2389 server cannot send, for example, disconnect packet to client that is not
2390 directly connected to the server.
2394 2.12 Packet Broadcasting
2396 SILC packets may be broadcasted in SILC network. However, only router
2397 server may send or receive broadcast packets. Client and normal server
2398 must not send broadcast packets and they must ignore broadcast packets
2399 if they receive them. Broadcast packets are sent by setting Broadcast
2400 flag to the SILC packet header.
2402 Broadcasting packets means that the packet is sent to all routers in
2403 the SILC network, except to the router that sent the packet. The router
2404 receiving broadcast packet must send the packet to its primary route.
2405 The fact that SILC routers may have several router connections may
2406 cause problems, such as race conditions inside the SILC network, if
2407 care is not taken when broadcasting packets. Router must not send
2408 the broadcast packet to any other route except to its primary route.
2410 If the primary route of the router is the original sender of the packet
2411 the packet must not be sent to the primary route. This may happen
2412 if router has several router connections and some other router uses
2413 the router as its primary route.
2415 Routers use broadcast packets to broadcast for example information
2416 about newly registered clients, servers, channels etc. so that all the
2417 routers may keep these informations up to date.
2421 2.13 Packet Tunneling
2423 Tunneling is a feature that is available in SILC protocol. Tunneling
2424 means that extra SILC Packet Header is applied to the original packet
2425 and thus hiding the original packet entirely. There can be some
2426 interesting applications using tunneling, such as, using ID's based on
2427 private network IP addresses inside in the tunneled packet. This can
2428 open many interesting features relating to connecting to private network
2429 from the Internet with SILC and many more. However, this feature is
2430 optional currently in SILC as there does not exist thorough analysis of
2431 this feature. It is with out a doubt that there will be many more
2432 applications that has not yet been discovered. Thus, it is left
2433 to Internet Community to investigate the use of tunneling in SILC
2434 protocol. This document is updated according those investigations
2435 and additional documents on the issue may be written.
2439 3 Security Considerations
2441 Security is central to the design of this protocol, and these security
2442 considerations permeate the specification. Common security considerations
2443 such as keeping private keys truly private and using adequate lengths for
2444 symmetric and asymmetric keys must be followed in order to maintain the
2445 security of this protocol.
2451 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2452 Protocol Specification", Internet Draft, June 2000.
2454 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2455 Protocols", Internet Draft, June 2000.
2457 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2460 [IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
2463 [IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
2466 [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
2469 [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
2472 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2475 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2478 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2481 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2482 Infrastructure, Certificate and CRL Profile", RFC 2459,
2485 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2486 John Wiley & Sons, New York, NY, 1996.
2488 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2491 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2492 RFC 2412, November 1998.
2494 [ISAKMP] Maughan D., et al, "Internet Security Association and
2495 Key Management Protocol (ISAKMP)", RFC 2408, November
2498 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2499 (IKE)", RFC 2409, November 1998.
2501 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2502 Authentication", RFC 2104, February 1997.
2504 [PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
2505 Specifications, Version 2.0", RFC 2437, October 1998.
2517 EMail: priikone@poseidon.pspt.fi
2519 This Internet-Draft expires 6 Jun 2001