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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48 The distribution of this memo is unlimited.
54 This memo describes a Packet Protocol used in the Secure Internet Live
55 Conferencing (SILC) protocol specified in the Secure Internet Live
56 Conferencing, Protocol Specification Internet Draft [SILC1]. This
57 protocol describes the packet types and packet payloads which defines
58 the contents of the packets. The protocol provides secure binary packet
59 protocol that assures that the contents of the packets are secured and
74 1 Introduction .................................................. 3
75 2 SILC Packet Protocol .......................................... 4
76 2.1 SILC Packet ............................................... 4
77 2.2 SILC Packet Header ........................................ 5
78 2.3 SILC Packet Types ......................................... 7
79 2.3.1 SILC Packet Payloads ................................ 15
80 2.3.2 Generic payloads .................................... 16
81 2.3.2.1 ID Payload .................................. 16
82 2.3.2.2 Argument Payload ............................ 16
83 2.3.3 Disconnect Payload .................................. 17
84 2.3.4 Success Payload ..................................... 18
85 2.3.5 Failure Payload ..................................... 18
86 2.3.6 Reject Payload ...................................... 19
87 2.3.7 Notify Payload ...................................... 20
88 2.3.8 Error Payload ....................................... 21
89 2.3.9 Channel Message Payload ............................. 22
90 2.3.10 Channel Key Payload ................................ 24
91 2.3.11 Private Message Payload ............................ 26
92 2.3.12 Private Message Key Payload ........................ 27
93 2.3.13 Command Payload .................................... 28
94 2.3.14 Command Reply Payload .............................. 29
95 2.3.15 Connection Auth Request Payload .................... 29
96 2.3.16 New ID Payload ..................................... 30
97 2.3.17 New ID List Payload ................................ 31
98 2.3.18 New Client Payload ................................. 31
99 2.3.19 New Server Payload ................................. 32
100 2.3.20 New Channel Payload ................................ 33
101 2.3.21 New Channel User Payload ........................... 34
102 2.3.22 New Channel List Payload ........................... 35
103 2.3.23 New Channel User List Payload ...................... 36
104 2.3.24 Replace ID Payload ................................. 36
105 2.3.25 Remove ID Payload .................................. 37
106 2.3.26 Remove Channel User Payload ........................ 38
107 2.4 SILC ID Types ............................................. 39
108 2.5 Packet Encryption And Decryption .......................... 39
109 2.5.1 Normal Packet Encryption And Decryption ............. 39
110 2.5.2 Channel Message Encryption And Decryption ........... 40
111 2.5.3 Private Message Encryption And Decryption ........... 41
112 2.6 Packet MAC Generation ..................................... 41
113 2.7 Packet Padding Generation ................................. 42
114 2.8 Packet Compression ........................................ 42
115 2.9 Packet Sending ............................................ 43
116 2.10 Packet Reception ......................................... 43
117 2.11 Packet Routing ........................................... 44
118 2.12 Packet Forwarding ........................................ 44
119 2.13 Packet Broadcasting ...................................... 45
120 2.14 Packet Tunneling ......................................... 45
121 3 Security Considerations ....................................... 46
122 4 References .................................................... 46
123 5 Author's Address .............................................. 47
129 Figure 1: Typical SILC Packet
130 Figure 2: SILC Packet Header
132 Figure 4: Argument Payload
133 Figure 5: Disconnect Payload
134 Figure 6: Success Payload
135 Figure 7: Failure Payload
136 Figure 8: Reject Payload
137 Figure 9: Notify Payload
138 Figure 10: Error Payload
139 Figure 11: Channel Message Payload
140 Figure 12: Channel Key Payload
141 Figure 13: Private Message Payload
142 Figure 14: Private Message Key Payload
143 Figure 15: Command Payload
144 Figure 16: Connection Auth Request Payload
145 Figure 17: New Client Payload
146 Figure 18: New Server Payload
147 Figure 19: New Channel Payload
148 Figure 20: New Channel User Payload
149 Figure 21: Replace ID Payload
150 Figure 22: Remove Channel User Payload
156 This document describes a Packet Protocol used in the Secure Internet
157 Live Conferencing (SILC) protocol specified in the Secure Internet Live
158 Conferencing, Protocol Specification Internet Draft [SILC1]. This
159 protocol describes the packet types and packet payloads which defines
160 the contents of the packets. The protocol provides secure binary packet
161 protocol that assures that the contents of the packets are secured and
164 The basis of SILC protocol relies in the SILC packets and it is with
165 out a doubt the most important part of the protocol. It is also probably
166 the most complicated part of the protocol. Packets are used all the
167 time in the SILC network to send messages, commands and other information.
168 All packets in SILC network are always encrypted and their integrity
169 is assured by computed MACs. The protocol defines several packet types
170 and packet payloads. Each packet type usually has a specific packet
171 payload that actually defines the contents of the packet. Each packet
172 also includes a default SILC Packet Header that provides sufficient
173 information about the origin of the packet and destination of the
178 2 SILC Packet Protocol
183 SILC packets deliver messages from sender to receiver securely by
184 encrypting important fields of the packet. The packet consists of
185 default SILC Packet Header, Padding, Packet Payload data, and, packet
188 The following diagram illustrates typical SILC packet.
193 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
194 | n bytes | 1 - n bytes | n bytes | n bytes
195 | SILC Header | Padding | Data Payload | MAC
196 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
200 Figure 1: Typical SILC Packet
203 SILC Header is always the first part of the packet and its purpose
204 is to provide information about the packet. It provides for example
205 the packet type, origin of the packet and the destination of the packet.
206 The header is variable in length and first two (2) bytes of the
207 header (thus first two bytes of the packet) are not encrypted. The
208 first two (2) bytes are the length of the packet which is not encrypted.
209 See following section for description of SILC Packet header. Packets
210 without SILC header or with malformed SILC header must be dropped.
212 Padding follows the packet header. The purpose of the padding is to
213 make the packet multiple by eight (8) or by the block size of the
214 cipher used in the encryption, which ever is larger. The maximum
215 length of padding is currently 16 bytes. The padding is always
218 Data payload area follows padding and it is the actual data of the
219 packet. The packet data is the packet payloads defined in this
220 protocol. The data payload area is always encrypted.
222 The last part of SILC packet is the packet MAC that assures the
223 integrity of the packet. The MAC is always computed from the packet
224 before the encryption is applied to the packet. If compression is used
225 in the packet the MAC is computed after the compression has been
226 applied. The compression, on the other hand, is always applied before
229 All fields in all packet payloads are always in MSB (most significant
234 2.2 SILC Packet Header
236 The default SILC packet header is applied to all SILC packets and it is
237 variable in length. The purpose of SILC Packet header is to provide
238 detailed information about the packet. The receiver of the packet uses
239 the packet header to parse the packet and gain other relevant parameters
242 Following diagram represents the default SILC header format.
243 (*) indicates that this field is never encrypted. Other fields are
250 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
252 | Payload Length * | Flags | Packet Type |
253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
254 | Source ID Length | Destination ID Length |
255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
271 Figure 2: SILC Packet Header
275 o Payload Length (2 bytes) - Is the length of the packet
276 not including the padding of the packet. This field must
277 not be encrypted but must always be authenticated.
279 o Flags (1 byte) - Indicates flags to be used in packet
280 processing. Several flags may be set by ORing the flags
283 Following flags are reserved for this field:
288 In this case the field is ignored.
291 Private Message Key 0x01
293 Indicates that the packet must include private
294 message that is encrypted using private key set by
295 client. Servers does not know anything about this
296 key and this causes that the private message is
297 not handled by the server at all, it is just
298 passed along. See section 2.5.3 Private Message
299 Encryption And Decryption for more information.
304 Marks the packet to be forwarded. Some specific
305 packet types may be forwarded. Receiver of packet
306 with this flag set must not forward the packet any
307 further. See section 2.12 Packet Forwarding for
308 description of packet forwarding.
313 Marks the packet to be broadcasted. Client cannot
314 send broadcast packet and normal server cannot send
315 broadcast packet. Only router server may send broadcast
316 packet. The router receiving of packet with this flag
317 set must send (broadcast) the packet to its primary
318 route. If router has several router connections the
319 packet may be sent only to the primary route. See
320 section 2.13 Packet Broadcasting for description of
326 Marks that the packet is tunneled. Tunneling means
327 that extra SILC Packet Header has been applied to the
328 original packet. The outer header has this flag
329 set. See section 2.14 Packet Tunneling for more
335 o Packet Type (1 byte) - Is the type of the packet. Receiver
336 uses this field to parse the packet. See section 2.3
337 SILC Packets for list of defined packet types.
339 o Source ID Length (2 bytes) - Indicates the length of the
340 Source ID field in the header, not including this or any
343 o Destination ID Length (2 bytes) - Indicates the length of the
344 Destination ID field in the header, not including this or
347 o Src ID Type (1 byte) - Indicates the type of ID in the
348 Source ID field. See section 2.4 SILC ID Types for
351 o Source ID (variable length) - The actual source ID that
352 indicates who is the original sender of the packet.
354 o Dst ID Type (1 byte) - Indicates the type of ID in the
355 Destination ID field. See section 2.4 SILC ID Types for
358 o Destination ID (variable length) - The actual source ID that
359 indicates who is the end receiver of the packet.
363 2.3 SILC Packet Types
365 SILC packet types defines the contents of the packet and it is used by
366 the receiver to parse the packet. The packet type is 8 bits, as a one
367 byte, in length. The range for the packet types are from 0 - 255,
368 where 0 is never sent and 255 is currently reserved for future
369 extensions and must not be defined to any other purpose. Every SILC
370 specification compliant implementation should support all of these packet
373 The below list of the SILC Packet types includes reference to the packet
374 payload as well. Packet payloads are the actual packet, that is, the data
375 that the packet consists of. Each packet type defines packet payload
376 which usually may only be sent with the specific packet type.
378 Most of the packets are packets that must be destined directly to entity
379 that is connected to the sender. It is not allowed, for example, for
380 router to send disconnect packet to client that is not directly connected
381 to the router. However, there are some special packet types that may
382 be destined to some entity that the sender has not direct connection
383 with. These packets are for example private message packets, channel
384 message packets, command packets and some other packets that may be
385 broadcasted in the SILC network. If the packet is allowed to be sent to
386 indirectly connected entity it is mentioned separately in the packet
387 description (unless it is obvious as in private and channel message
388 packets). Other packets must not be sent or accepted, if sent, to
389 indirectly connected entities.
391 List of SILC Packet types are defined as follows.
396 This type is reserved and it is never sent.
399 1 SILC_PACKET_DISCONNECT
401 This packet is sent to disconnect the remote end. Reason of
402 the disconnection is sent inside the packet payload. Client
403 usually does not send this packet.
405 Payload of the packet: See section 2.3.3 Disconnect Payload
408 2 SILC_PACKET_SUCCESS
410 This packet is sent upon successful execution of some protocol.
411 The status of the success is sent in the packet.
413 Payload of the packet: See section 2.3.4 Success Payload
416 3 SILC_PACKET_FAILURE
418 This packet is sent upon failure of some protocol. The status
419 of the failure is sent in the packet.
421 Payload of the packet: See section 2.3.5 Failure Payload
426 This packet may be sent upon rejection of some protocol.
427 The status of the rejection is sent in the packet.
429 Payload of the packet: See section 2.3.6 Reject Payload
434 This packet is used to send notify message, usually from
435 server to client, although it may be sent from server to another
436 server as well. Client never sends this packet. Server may
437 send this packet to channel as well when the packet is
438 distributed to all clients on the channel.
440 Payload of the packet: See section 2.3.7 Notify Payload.
445 This packet is sent when an error occurs. Server may
446 send this packet. Client never sends this packet. The
447 client may entirely ignore the packet, however, server is
448 most likely to take action anyway. This packet may be sent
449 to entity that is indirectly connected to the sender.
451 Payload of the packet: See section 2.3.8 Error Payload.
454 7 SILC_PACKET_CHANNEL_MESSAGE
456 This packet is used to send messages to channels. The packet
457 includes Channel ID of the channel and the actual message to
458 the channel. Messages sent to the channel are always protected
459 by channel specific keys. Channel Keys are distributed by
460 SILC_PACKET_CHANNEL_KEY packet.
462 Payload of the packet: See section 2.3.9 Channel Message
466 8 SILC_PACKET_CHANNEL_KEY
468 This packet is used to distribute new key for particular
469 channel. Each channel has their own independent keys that
470 is used to protect the traffic on the channel. Only server
471 may send this packet. This packet may be sent to entity
472 that is indirectly connected to the sender.
474 Payload of the packet: See section 2.3.10 Channel Key Payload
477 9 SILC_PACKET_PRIVATE_MESSAGE
479 This packet is used to send private messages from client
480 to another client. By default, private messages are protected
481 by session keys established by normal key exchange protocol.
482 However, it is possible to use specific key to protect private
483 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
484 agree the key with the remote client. Pre-shared key may be
485 used as well if both of the client knows it, however, it needs
486 to be agreed outside SILC. See more of this in [SILC1].
488 Payload of the packet: See section 2.3.11 Private Message
492 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
494 This packet is used to agree about a key to be used to protect
495 the private messages between two clients. If this is not sent
496 the normal session key is used to protect the private messages
497 inside SILC network. Agreeing to use specific key to protect
498 private messages adds security, as no server between the two
499 clients will be able to decrypt the private message. However,
500 servers inside SILC network are considered to be trusted, thus
501 using normal session key to protect private messages does not
502 degree security. Whether to agree to use specific keys by
503 default or to use normal session keys by default, is
504 implementation specific issue. See more of this in [SILC1].
506 Payload of the packet: See section 2.3.12 Private Message
510 11 SILC_PACKET_COMMAND
512 This packet is used to send commands from client to server.
513 Server may send this packet to other servers as well. All
514 commands are listed in their own section SILC Command Types
515 in [SILC1]. The contents of this packet is command specific.
516 This packet may be sent to entity that is indirectly connected
519 Payload of the packet: See section 2.3.13 Command Payload
522 12 SILC_PACKET_COMMAND_REPLY
524 This packet is send as reply to the SILC_PACKET_COMMAND packet.
525 The contents of this packet is command specific. This packet
526 maybe sent to entity that is indirectly connected to the sender.
528 Payload of the packet: See section 2.3.14 Command Reply
529 Payload and section 2.3.13 Command
533 13 SILC_PACKET_KEY_EXCHANGE
535 This packet is used to start SILC Key Exchange Protocol,
536 described in detail in [SILC3].
538 Payload of the packet: Payload of this packet is described
539 in the section SILC Key Exchange
540 Protocol and its sub sections in
544 14 SILC_PACKET_KEY_EXCHANGE_1
546 This packet is used as part of the SILC Key Exchange Protocol.
548 Payload of the packet: Payload of this packet is described
549 in the section SILC Key Exchange
550 Protocol and its sub sections in
554 15 SILC_PACKET_KEY_EXCHANGE_2
556 This packet is used as part of the SILC Key Exchange Protocol.
558 Payload of the packet: Payload of this packet is described
559 in the section SILC Key Exchange
560 Protocol and its sub sections in
564 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
566 This packet is used to request the authentication method to
567 be used in the SILC Connection Authentication Protocol. If
568 initiator of the protocol does not know the mandatory
569 authentication method this packet is used to determine it.
571 The party receiving this payload must respond with the same
572 packet including the mandatory authentication method.
574 Payload of the packet: See section 2.3.15 Connection Auth
578 17 SILC_PACKET_CONNECTION_AUTH
580 This packet is used to start and perform the SILC Connection
581 Authentication Protocol. This protocol is used to authenticate
582 the connecting party. The protocol is described in detail in
585 Payload of the packet: Payload of this packet is described
586 in the section SILC Authentication
587 Protocol and it sub sections in [SILC].
590 18 SILC_PACKET_NEW_ID
592 This packet is used to distribute new ID's from server to
593 router and from router to all routers in the SILC network.
594 This is used when for example new client is registered to
595 SILC network. The newly created ID's of these operations are
596 distributed by this packet. Only server may send this packet,
597 however, client must be able to receive this packet.
599 Payload of the packet: See section 2.3.16 New ID Payload
602 19 SILC_PACKET_NEW_ID_LIST
604 This packet is used to distribute list of new ID's from
605 server to routers. This is equivalent to previous packet
606 type except that it may include several ID's. Client must
607 not send this packet.
609 Payload of the packet: See section 2.3.17 New ID List
613 20 SILC_PACKET_NEW_CLIENT
615 This packet is used by client to register itself to the
616 SILC network. This is sent after key exchange and
617 authentication protocols has been completed. Client sends
618 various information about itself in this packet.
620 Payload of the packet: See section 2.3.18 New Client Payload
623 21 SILC_PACKET_NEW_SERVER
625 This packet is used by server to register itself to the
626 SILC network. This is sent after key exchange and
627 authentication protocols has been completed. Server sends
628 this to the router it connected to, or, if router was
629 connecting, to the connected router. Server sends
630 its Server ID and other information in this packet.
631 Client must not send or receive this packet.
633 Payload of the packet: See section 2.3.19 New Server Payload
636 22 SILC_PACKET_NEW_CHANNEL
638 This packet is used to notify routers about newly created
639 channel. Channels are always created by the router and it must
640 notify other routers about the created channel. Router sends
641 this packet to its primary route. Client must not send this
642 packet. This packet maybe sent to entity that is indirectly
643 connected to the sender.
645 Payload of the packet: See section 2.3.20 New Channel Payload
648 23 SILC_PACKET_NEW_CHANNEL_USER
650 This packet is used to notify routers about new user on channel.
651 The packet is sent after user has joined to the channel. Server
652 may send this packet to its router and router may send this to
653 its primary router. Client must not send this packet. This
654 packet maybe sent to entity that is indirectly connected to
657 When received, the server or router must distribute
658 SILC_NOTIFY_TYPE_JOIN to local clients on the channel.
660 Payload of the packet: See section 2.3.21 New Channel User
664 24 SILC_PACKET_NEW_CHANNEL_LIST
666 This packet is used to distribute list of created channels
667 from server to routers. This is equivalent to the packet
668 SILC_PACKET_NEW_CHANNEL except that it may include several
669 payloads. Client must not send this packet.
671 Payload of the packet: See section 2.3.22 New Channel List
675 25 SILC_PACKET_NEW_CHANNEL_USER_LIST
677 This packet is used to distribute list of users on specific
678 channel from server to routers. This is equivalent to the
679 packet SILC_PACKET_NEW_CHANNEL_USER except that it may
680 include several payloads. Client must not send this packet.
682 When received, the server or router must distribute
683 SILC_NOTIFY_TYPE_JOIN to local clients on the channel.
685 Payload of the packet: See section 2.3.23 New Channel User
689 26 SILC_PACKET_REPLACE_ID
691 This packet is used to replace old ID with new ID sent in
692 the packet payload. For example, when client changes its
693 nickname new ID is created and this packet can be used to
694 distribute the new ID and the old ID is removed when it is
695 send in the packet. Client cannot send or receive this
696 packet. This packet maybe sent to entity that is indirectly
697 connected to the sender.
699 When received and the replaced ID is Client ID the server or
700 router must distribute SILC_NOTIFY_TYPE_NICK_CHANGE to the
701 local clients on the channels (if any) of the client whose
702 ID was changed. However, the notify type must be sent only
705 Payload of the packet: See section 2.3.24 Replace ID Payload
708 27 SILC_PACKET_REMOVE_ID
710 This packet is used to removed ID. For example, when client
711 exits SILC network its ID is removed. Client must not send
712 this packet. This packet maybe sent to entity that is
713 indirectly connected to the sender.
715 When received and the replaced ID is Client ID the server or
716 router must distribute SILC_NOTIFY_TYPE_SIGNOFF to the
717 local clients on the channels (if any) of the client whose
718 ID was changed. However, the notify type must be sent only
721 Payload of the packet: See section 2.3.25 Remove ID Payload
724 28 SILC_PACKET_REMOVE_CHANNEL_USER
726 This packet is used to remove user from a channel. This is
727 used by router to notify other routers in the network that a
728 client has left a channel. This packet maybe sent to entity
729 that is indirectly connected to the sender.
731 When received, the server or router must distribute
732 SILC_NOTIFY_TYPE_LEAVEW to local clients on the channel.
734 Payload of the packet: See section 2.3.26 Remove Channel User
740 This packet is used to indicate that re-key must be performed
741 for session keys. See section Session Key Regeneration in
742 [SILC1] for more information. This packet does not have
746 30 SILC_PACKET_REKEY_DONE
748 This packet is used to indicate that re-key is performed and
749 new keys must be used hereafter. This is sent only if re-key
750 was done without PFS option. If PFS is set, this is not sent
751 as SILC Key Exchange protocol is executed. This packet does
757 Currently undefined commands.
762 These packet types are reserved for private use and they will not
763 be defined by this document.
768 This type is reserved for future extensions and currently it
774 2.3.1 SILC Packet Payloads
776 All payloads resides in the main data area of the SILC packet. However
777 all payloads must be at the start of the data area after the default
778 SILC packet header and padding. All fields in the packet payload are
779 always encrypted, as, they reside in the data area of the packet which
782 Payloads described in this section are common payloads that must be
783 accepted anytime during SILC session. Most of the payloads may only
784 be sent with specific packet type which is defined in the description
787 There are a lot of other payloads in the SILC as well. However, they
788 are not common in the sense that they could be sent at any time.
789 These payloads are not described in this section. These are payloads
790 such as SILC Key Exchange payloads and so on. These are described
791 in [SILC1] and [SILC3].
795 2.3.2 Generic payloads
797 This section describes generic payloads that are not associated to any
798 specific packet type. They can be used for example inside some other
805 This payload can be used to send an ID. ID's are variable length thus
806 this payload provides a way to send variable length ID's.
808 Following diagram represents the ID Payload.
813 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
814 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
815 | ID Type | ID Length |
816 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
820 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
828 o ID Type (2 bytes) - Indicates the type of the ID. See
829 section 2.4 SILC ID Types for list of defined ID types.
831 o ID Length (2 bytes) - Length of the ID Data area not
832 including the length of any other fields in the payload.
834 o ID Data (variable length) - The actual ID data.
839 2.3.2.2 Argument Payload
841 Argument Payload is used to set arguments for any packet payload that
842 needs and supports arguments, such as commands. Number of arguments
843 associated with a packet must be indicated by the packet payload who
844 needs the arguments. Argument Payloads must always reside right after
845 the packet payload needing the arguments. Incorrect amount of argument
846 payloads must cause rejection of the packet. Following diagram represents
847 the Argument Payload.
853 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
854 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
855 | Payload Length | Argument Type | |
856 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
860 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
864 Figure 4: Argument Payload
868 o Payload Length (2 bytes) - Length of the argument payload data
869 area not including the length of any other fields in the
872 o Argument Type (1 byte) - Indicates the type of the argument.
873 Every argument may have a specific type that must be defined
874 by the packet payload needing the argument. For example
875 every command specify a number for each argument that maybe
876 associated with the command. By using this number the receiver
877 of the packet knows what type of argument this is. If there is
878 no specific argument type this field is set to zero (0).
880 o Argument Data (variable length) - Argument data.
885 2.3.3 Disconnect Payload
887 Disconnect payload is sent upon disconnection. The payload is simple;
888 reason of disconnection is sent to the disconnected party.
890 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
891 must not be sent in any other packet type. Following diagram represents
892 the Disconnect Payload.
903 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
904 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
906 ~ Disconnect Message ~
908 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
912 Figure 5: Disconnect Payload
918 o Disconnect Message (variable length) - Human readable
919 reason of the disconnection.
924 2.3.4 Success Payload
926 Success payload is sent when some protocol execution is successfully
927 completed. The payload is simple; indication of the success is sent.
928 This maybe any data, including binary or human readable data.
933 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
934 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
936 ~ Success Indication ~
938 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
942 Figure 6: Success Payload
946 o Success Indication (variable length) - Indication of
947 the success. This maybe for example some flag that
948 indicates the protocol and the success status or human
949 readable success message. The true length of this
950 payload is available by calculating it from the SILC
956 2.3.5 Failure Payload
958 This is opposite of Success Payload. Indication of failure of
959 some protocol is sent in the payload.
965 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
966 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
968 ~ Failure Indication ~
970 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
974 Figure 7: Failure Payload
978 o Failure Indication (variable length) - Indication of
979 the failure. This maybe for example some flag that
980 indicates the protocol and the failure status or human
981 readable failure message. The true length of this
982 payload is available by calculating it from the SILC
990 This payload is sent when some protocol is rejected to be executed.
991 Other operations may send this as well that was rejected. The
992 indication of the rejection is sent in the payload. The indication
993 may be binary or human readable data.
999 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
1000 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1002 ~ Reject Indication ~
1004 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1008 Figure 8: Reject Payload
1012 o Reject Indication (variable length) - Indication of
1013 the rejection. This maybe for example some flag that
1014 indicates the protocol and the rejection status or human
1015 readable rejection message. The true length of this
1016 payload is available by calculating it from the SILC
1025 2.3.7 Notify Payload
1027 Notify payload is used to send notify messages. The payload is usually
1028 sent from server to client, however, server may send it to another
1029 server as well. This payload may also be sent to a channel. Client must
1030 not send this payload. The receiver of this payload may totally ignore the
1031 contents of the payload, however, notify message should be noted and
1034 The payload may only be sent with SILC_PACKET_NOTIFY packet. It must
1035 not be sent in any other packet type. Following diagram represents the
1041 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
1042 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1043 | Notify Type | Payload Length |
1044 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1050 Figure 9: Notify Payload
1054 o Notify Type (2 bytes) - Indicates the type of the notify
1057 o Payload Length (2 bytes) - Length of the entire Notify Payload
1058 including any associated Argument Payloads.
1060 o Argument Nums (2 bytes) - Indicates the number of Argument
1061 Payloads associated to this payload. Notify types may define
1062 arguments to be send along the notify message.
1065 Following list of currently defined notify types. The format for notify
1066 arguments is same as in SILC commands described in [SILC1]. Also, all
1067 ID's sent in arguments are sent inside ID Payload.
1070 0 SILC_NOTIFY_TYPE_NONE
1072 If no specific notify type apply for the notify message this type
1076 Arguments: (1) <message>
1078 The <message> is implementation specific free text string. Receiver
1079 may ignore this message.
1082 1 SILC_NOTIFY_TYPE_INVITE
1084 Sent when receiver has been invited to a channel. This type must be
1085 sent directly to the invited client.
1088 Arguments: (1) <Client ID> (2) <Channel ID>
1090 The <Client ID> is the client who invites the receiver of this type
1091 to channel indicated by <Channel ID>.
1094 2 SILC_NOTIFY_TYPE_JOIN
1096 Sent when client has joined to a channel. The server must distribute
1097 this type only to the local clients on the channel and then send
1098 SILC_PACKET_NEW_CHANNEL_USER packet to its primary route. The router
1099 or server receiving the packet distributes this type to the local
1100 clients on the channel. See description of SILC_PACKET_NEW_CHANNEL_USER
1101 packet for more information.
1104 Arguments: (1) <Client ID>
1106 The <Client ID> is the client that joined to the channel.
1109 3 SILC_NOTIFY_TYPE_LEAVE
1111 Sent when client has left a channel. The server must distribute
1112 this type only to the local clients on the channel and then send
1113 SILC_PACKET_REMOVE_CHANNEL_USER packet to its primary route. The
1114 router or server receiving the packet distributes this type to the
1115 local clients on the channel. See description of
1116 SILC_PACKET_REMOVE_CHANNEL_USER packet for more information.
1119 Arguments: (1) <Client ID>
1121 The <Client ID> is the client who left the channel.
1124 4 SILC_NOTIFY_TYPE_SIGNOFF
1126 Sent when client signoffs from SILC network. This type is sent only
1127 if the client was joined to any channel. This type is sent by server
1128 or router when SILC_PACKET_REMOVE_ID packet has been received. See
1129 detailed information from description of SILC_PACKET_REMOVE_ID packet.
1132 Arguments: (1) <Client ID>
1134 The <Client ID> is the client who left SILC network.
1137 5 SILC_NOTIFY_TYPE_TOPIC_SET
1139 Sent when topic is set/changed on a channel. This type must be sent
1140 only to the clients who is joined on the channel whose topic was
1144 Arguments: (1) <Client ID> (2) <topic>
1146 The <Client ID> is the client who set or changed the <topic>.
1149 6 SILC_NOTIFY_TYPE_NICK_CHANGE
1151 Sent when client changes nick on a channel. This type is sent only if
1152 the client has joined to any channel. This type is sent by server or
1153 router when SILC_PACKET_REPLACE_ID packet has been received. See
1154 detailed information from description of SILC_PACKET_REPLACE_ID packet.
1157 Arguments: (1) <Old Client ID> (2) <New Client ID>
1159 The <Old Client ID> is the old ID of the client who changed the
1160 nickname. The <New Client ID> is the new ID generated by the change
1164 7 SILC_NOTIFY_TYPE_CMODE_CHANGE
1166 Sent when channel mode has changed. This type must be sent only to
1167 the clients who is joined on the channel whose mode was changed.
1170 Arguments: (1) <Client ID> (2) <mode mask>
1172 The <Client ID> is the client who changed the mode. The <mode mask>
1173 is the new mode mask of the channel.
1176 8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
1178 Sent when user mode on channel has changed. This type must be sent
1179 only to the clients who is joined on the channel where the target
1183 Arguments: (1) <Client ID> (2) <mode mask>
1184 (3) <Target Client ID>
1186 The <Client ID> is the client who changed the mode. The <mode mask>
1187 is the new mode mask of the channel. The <Target Client ID> is the
1188 client whose mode was changed.
1191 9 SILC_NOTIFY_TYPE_MOTD
1193 Sent when Message of the Day (motd) is sent to client.
1196 Arguments: (1) <motd>
1198 The <motd> is the Message of the Day.
1201 Notify types starting from 16384 are reserved for private notify
1208 Error payload is sent upon error. Error may occur in various
1209 conditions when server sends this packet. Client may not send this
1210 payload but must be able to accept it. However, client may
1211 totally ignore the contents of the packet as server is going to
1212 take action on the error anyway. However, it is recommended
1213 that the client takes error packet seriously.
1219 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
1220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1228 Figure 10: Error Payload
1232 o Error Message (variable length) - Human readable error
1238 2.3.9 Channel Message Payload
1240 Channel messages are the most common messages sent in the SILC.
1241 Channel Message Payload is used to send message to channels. These
1242 messages can only be sent if client has joined to some channel.
1243 Even though this packet is the most common in SILC it is still
1244 special packet. Some special handling on sending and reception
1245 of channel message is required.
1247 Padding must be applied into this payload since the payload is
1248 encrypted separately from other parts of the packet with the
1249 channel specific key. Hence the requirement of the padding.
1250 The padding should be random data. The packet must be made
1251 multiple by eight (8) or by the block size of the cipher, which
1254 The SILC header in this packet is encrypted with the session key
1255 of the next receiver of the packet. Nothing else is encrypted
1256 with that key. Thus, the actual packet and padding to be
1257 encrypted with the session key is SILC Header plus padding to it
1258 to make it multiple by eight (8) or multiple by the block size
1259 of the cipher, which ever is larger.
1261 Receiver of the the channel message packet is able to determine
1262 the channel the message is destined to by checking the destination
1263 ID from the SILC Packet header which tells the destination channel.
1264 The original sender of the packet is also determined by checking
1265 the source ID from the header which tells the client who sent
1268 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1269 It must not be sent in any other packet type. Following diagram
1270 represents the Channel Message Payload.
1272 (*) indicates that the field is not encrypted.
1278 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
1279 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1280 | Message Length | |
1281 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1285 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1286 | Padding Length | |
1287 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1291 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1293 ~ Initial Vector * ~
1295 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1299 Figure 11: Channel Message Payload
1303 o Message Length (2 bytes) - Indicates the length of the
1304 the Message Data field in the payload, not including any
1307 o Message Data (variable length) - The actual message to
1310 o Padding Length (2 bytes) - Indicates the length of the
1311 Padding field in the payload, not including any other
1314 o Padding (variable length) - The padding that must be
1315 applied because this payload is encrypted separately from
1316 other parts of the packet.
1318 o Initial Vector (variable length) - The initial vector
1319 that has been used in packet encryption. It needs to be
1320 used in the packet decryption as well. What this field
1321 includes is implementation issue. However, it is
1322 recommended that it would be random data or, perhaps,
1323 a timestamp. It is not recommended to use zero (0) as
1324 initial vector. This field is not encrypted. This field
1325 is not included into the padding calculation. Length
1326 of this field equals the cipher's block size. This field
1327 is, however, authenticated.
1332 2.3.10 Channel Key Payload
1334 All traffic in channels are protected by channel specific keys.
1335 Channel Key Payload is used to distribute channel keys to all
1336 clients on the particular channel. Channel keys are sent when
1337 the channel is created, when new user joins to the channel and
1338 whenever a user has left a channel. Server creates the new
1339 channel key and distributes it to the clients by encrypting this
1340 payload with the session key shared between the server and
1341 the client. After that, client starts using the key received
1342 in this payload to protect the traffic on the channel.
1344 Channel keys are cell specific thus every router in cell have
1345 to create a channel key and distribute it if any client in the
1346 cell has joined to a channel. Channel traffic between cell's
1347 are not encrypted using channel keys, they are encrypted using
1348 normal session keys between two routers. Inside a cell, all
1349 channel traffic is encrypted with the specified channel key.
1350 Channel key should expire periodically, say, in one hour, in
1351 which case new channel key is created and distributed.
1353 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1354 It must not be sent in any other packet type. Following diagram
1355 represents the Channel Key Payload.
1372 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
1373 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1374 | Channel ID Length | |
1375 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1379 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1380 | Cipher Name Length | |
1381 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1385 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1386 | Channel Key Length | |
1387 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1391 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1395 Figure 12: Channel Key Payload
1400 o Channel ID Length (2 bytes) - Indicates the length of the
1401 Channel ID field in the payload, not including any other
1404 o Channel ID (variable length) - The Channel ID of the
1405 channel this key is meant for.
1407 o Cipher Name Length (2 bytes) - Indicates the length of the
1408 Cipher name field in the payload, not including any other
1411 o Cipher Name (variable length) - Name of the cipher used
1412 in the protection of channel traffic. This name is
1413 initially decided by the creator of the channel but it
1414 may change during the life time of the channel as well.
1416 o Channel Key Length (2 bytes) - Indicates the length of the
1417 Channel Key field in the payload, not including any other
1420 o Channel Key (variable length) - The actual channel key
1421 material. This key is used as such as key material for
1422 encryption function.
1427 2.3.11 Private Message Payload
1429 Private Message Payload is used to send private message between
1430 two clients (or users for that matter). The messages are sent only
1431 to the specified user and no other user inside SILC network is
1432 able to see the message. The message is protected by the session
1433 key established by the SILC Key Exchange Protocol. However,
1434 it is also possible to agree to use specific keys to protect
1435 just the private messages. See section 2.3.11 Private Message
1436 Key Payload for detailed description of how to agree to use
1439 If normal session key is used to protect the message, every
1440 server between the sender client and the receiving client needs
1441 to decrypt the packet and always re-encrypt it with the session
1442 key of the next receiver of the packet. See section Client
1443 To Client in [SILC1].
1445 When specific key is used to protect the message, servers between
1446 the sender and the receiver needs not to decrypt/re-encrypt the
1447 packet. Section 4.8.2 Client To Client in [SILC1] gives example of
1448 this scheme as well.
1450 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1451 packet. It must not be sent in any other packet type. Following
1452 diagram represents the Private Message Payload.
1458 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
1459 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1460 | Nickname Length | |
1461 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1465 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1469 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1473 Figure 13: Private Message Payload
1477 o Nickname Length (2 bytes) - Indicates the length of the
1478 Nickname field, not including any other field.
1480 o Nickname (variable length) - Nickname of the sender of the
1481 private message. This should not be trusted as a definite
1482 sender of the private message. The SILC Packet Header in
1483 the packet indicates the true sender of the packet and
1484 client should verify that the nickname sent here belongs
1485 to the Client ID in the SILC Packet Header. This nickname
1486 is merely provided to be displayed by the client.
1488 o Message Data (variable length) - The actual message to
1489 the client. Rest of the packet is reserved for the message
1495 2.3.12 Private Message Key Payload
1497 This payload is used to send key from client to another client that
1498 is going to be used to protect the private messages between these
1499 two clients. If this payload is not sent normal session key
1500 established by the SILC Key Exchange Protocol is used to protect
1501 the private messages.
1503 This payload may only be sent by client to another client. Server
1504 must not send this payload at any time. After sending this payload
1505 the sender of private messages must set the Private Message Key
1506 flag into SILC Packet Header.
1508 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1509 packet. It must not be sent in any other packet type. Following
1510 diagram represents the Private Message Key Payload.
1516 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
1517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1518 | Private Message Key Length | |
1519 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1521 ~ Private Message Key ~
1523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1527 Figure 14: Private Message Key Payload
1533 o Private Message Key Length (2 bytes) - Indicates the length
1534 of the Private Message Key field in the payload, not including
1537 o Private Message Key (variable length) - The actual private
1538 message key material. This key is used as such as key material
1539 for encryption function.
1544 2.3.13 Command Payload
1546 Command Payload is used to send SILC commands from client to server.
1547 Also server may send commands to other servers. Following diagram
1548 represents the Command Payload.
1554 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
1555 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1556 | Payload Length | SILC Command | Arguments Num |
1557 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1559 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1563 Figure 15: Command Payload
1567 o Payload Length (2 bytes) - Length of the entire command
1568 payload including any command argument payloads associated
1571 o SILC Command (1 byte) - SILC Command identifier. This must
1572 be set to non-zero value. If zero (0) value is found in this
1573 field the packet must be discarded.
1575 o Arguments Num (1 byte) - Indicates the number of arguments
1576 associated with the command. If there are no arguments this
1577 field is set to zero (0). The arguments must follow the
1578 command payload. See section 2.3.2.2 for definition of the
1581 o Command Unifier (2 bytes) - Unifies this command at the
1582 sender's end. The entity who replies to this command must
1583 set the value found from this field into the Command Payload
1584 used to send the reply to the sender. This way the sender
1585 can identify which command reply belongs to which originally
1586 sent command. What this field includes is implementation
1587 issue but it is recommended that wrapping counter value is
1591 See [SILC1] for detailed description of different SILC commands,
1592 their arguments and their reply messages.
1596 2.3.14 Command Reply Payload
1598 Command Reply Payload is used to send replies to the commands. The
1599 Command Reply Payload is identical to the Command Payload thus see the
1600 upper sections for Command Payload and for Command Argument Payload
1601 specifications. Command Reply message uses the Command Argument Payload
1604 The entity who sends the reply packet must set the Command Unifier
1605 field in the reply packet's Command Payload to the value it received
1606 in the original command packet.
1608 See SILC Commands in [SILC1] for detailed description of different
1609 SILC commands, their arguments and their reply messages.
1613 2.3.15 Connection Auth Request Payload
1615 Client may send this payload to server to request the authentication
1616 method that must be used in authentication protocol. If client knows
1617 this information beforehand this payload is not necessary to be sent.
1618 Server performing authentication with another server may also send
1619 this payload to request the authentication method. If the connecting
1620 server already knows this information this payload is not necessary
1623 Server receiving this request must reply with same payload sending
1624 the mandatory authentication method. Algorithms that may be required
1625 to be used by the authentication method are the ones already
1626 established by the SILC Key Exchange protocol. See section Key
1627 Exchange Start Payload in [SILC3] for detailed information.
1629 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1630 packet. It must not be sent in any other packet type. Following
1631 diagram represents the Connection Auth Request Payload.
1637 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
1638 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1639 | Connection Type | Authentication Method |
1640 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1644 Figure 16: Connection Auth Request Payload
1648 o Connection Type (2 bytes) - Indicates the type of the ID.
1649 Following connection types are defined:
1655 If any other type is found in this field the packet must be
1656 discarded and the authentication must be failed.
1658 o Authentication Method (2 bytes) - Indicates the authentication
1659 method to be used in the authentication protocol. Following
1660 authentication methods are defined:
1665 1 password (mandatory)
1666 2 public key (mandatory)
1668 If any other type is found in this field the packet must be
1669 discarded and the authentication must be failed. If this
1670 payload is sent as request to receive the mandatory
1671 authentication method this field must be set to zero (0),
1672 indicating that receiver should send the mandatory
1673 authentication method. The receiver sending this payload
1674 to the requesting party, may also set this field to zero (0)
1675 to indicate that authentication is not required. In this
1676 case authentication protocol still must be started but
1677 server is most likely to respond with SILC_PACKET_SUCCESS
1683 2.3.16 New ID Payload
1685 New ID Payload is a multipurpose payload. It is used to send newly
1686 created ID's from clients and servers. When client connects to server
1687 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
1688 packet, server replies with this packet by sending the created ID for
1689 the client. Server always creates the ID for the client.
1691 This payload is also used when server tells its router that new client
1692 has registered to the SILC network. In this case the server sends
1693 the Client ID of the client to the router. Similary when router
1694 distributes information to other routers about the client in the SILC
1695 network this payload is used.
1697 Also, when server connects to router, router uses this payload to inform
1698 other routers about new server in the SILC network. However, every
1699 server (or router) creates their own ID's thus the ID distributed by
1700 this payload is not created by the distributor in this case. Servers
1701 create their own ID's. Server registers itself to the network by sending
1702 SILC_PACKET_NEW_SERVER to the router it connected to. The case is same
1703 when router connects to another router.
1705 Hence, this payload is very important and used every time when some
1706 new entity is registered to the SILC network. Client never sends this
1707 payload. Both client and server (and router) may receive this payload.
1709 The packet uses generic ID Payload as New ID Payload. See section
1710 2.3.2.1 for generic ID Payload.
1714 2.3.17 New ID List Payload
1716 New ID List Payload is used to distribute list of ID's usually from
1717 server to router but also from router to other routers in the network.
1718 This payload is used, for example, when server is connected to router
1719 and the server wants to distribute all of its locally connected clients
1720 and locally created channels to the router. It is convenient in this
1721 case to use this payload instead of sending all the information one
1722 by one using New ID Payload.
1724 There is no specific payload for this packet type. The packet type
1725 uses same payload as described in previous section. To form a list
1726 several payloads is put in the packet each after each. The payload
1727 is variable in length but can be calculated by calculating the ID
1728 Type field, Length field and the ID Data fields together. This forms
1729 one New ID Payload in the list.
1731 The list of payloads may only be sent with SILC_PACKET_NEW_ID_LIST
1732 packet. They must not be sent in any other packet type.
1736 2.3.18 New Client Payload
1738 When client is connected to the server, keys has been exchanged and
1739 connection has been authenticated client must register itself to the
1740 server. Clients first packet after key exchange and authentication
1741 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
1742 the relevant information about the connected user. Server creates a new
1743 client ID for the client when received this payload and sends it to the
1744 client in New ID Payload.
1746 This payload sends username and real name of the user on the remote host
1747 which is connected to the SILC server with SILC client. The server
1748 creates the client ID according the information sent in this payload.
1749 The nickname of the user becomes the username sent in this payload.
1750 However, client should call NICK command after sending this payload to
1751 set the real nickname of the user which is then used to create new
1754 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
1755 must not be sent in any other packet type. Following diagram represents
1756 the New Client Payload.
1763 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
1764 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1765 | Username Length | |
1766 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1770 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1771 | Real Name Length | |
1772 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1776 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1780 Figure 17: New Client Payload
1784 o Username Length (2 bytes) - Length of the username.
1786 o Username (variable length) - The username of the user on
1787 the host where connecting to the SILC server.
1789 o Real Name Length (2 bytes) - Length of the Real Name.
1791 o Real Name (variable length) - The real name of the user
1792 on the host where connecting to the SILC server.
1797 2.3.19 New Server Payload
1799 This payload is sent by server when it has completed successfully both
1800 key exchange and connection authentication protocols. The server
1801 uses this payload to register itself to the SILC network. The
1802 first packet after these key exchange and authentication protocols
1803 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
1804 of the server that it has created by itself. It also includes a
1805 name of the server that is associated to the Server ID.
1807 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
1808 must not be sent in any other packet type. Following diagram represents
1809 the New Server Payload.
1818 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
1819 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1820 | Server ID Length | |
1821 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1825 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1826 | Server Name Length | |
1827 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1831 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1835 Figure 18: New Server Payload
1839 o Server ID Length (2 bytes) - Length of the ID Data area not
1840 including the length of any other fields in the payload.
1842 o Server ID Data (variable length) - The actual Server ID
1845 o Server Name Length (2 bytes) - Length of the server name.
1847 o Server Name (variable length) - The server name.
1852 2.3.20 New Channel Payload
1854 Information about newly created channel is broadcasted to all routers
1855 in the SILC network by sending this packet payload. Channels are
1856 created by router of the cell. Server never creates channels unless
1857 it is a standalone server and it does not have router connection,
1858 in this case server acts as router. Normal server forwards JOIN command
1859 to the router (after it has received JOIN command from client) which
1860 then processes the command and creates the channel. Client never sends
1863 The payload may only be sent with SILC_PACKET_NEW_CHANNEL packet.
1864 It must not be sent in any other packet type. Following diagram
1865 represents the New Channel Payload.
1873 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
1874 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1875 | Channel Name Length | |
1876 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1880 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1881 | Channel ID Length | |
1882 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1886 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1890 Figure 19: New Channel Payload
1895 o Channel Name Length (2 bytes) - Length of the channel name.
1897 o Channel Name (variable length) - The name of the created
1900 o Channel ID Length (2 bytes) - Length of the Channel ID.
1902 o Channel ID (variable length) - The created Channel ID.
1907 2.3.21 New Channel User Payload
1909 When client (user) joins to a channel, server must notify routers
1910 about the new user on the channel. Normal server sends this packet
1911 payload to its router which then broadcasts the packet further.
1912 Router sends this packet always to its primary router. Client must
1913 not send this packet payload. The mode of the user is NONE after
1914 user has joined to the channel.
1916 The payload may only be sent with SILC_PACKET_NEW_CHANNEL_USER
1917 packet. It must not be sent in any other packet type. Following
1918 diagram represents the New Channel User Payload.
1928 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
1929 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1930 | Channel ID Length | |
1931 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1935 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1936 | Client ID Length | |
1937 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1941 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1945 Figure 20: New Channel User Payload
1949 o Channel ID Length (2 bytes) - Length of the Channel ID.
1951 o Channel ID (variable length) - The Channel ID of the channel
1952 to which the client has joined.
1954 o Client ID Length (2 bytes) - Length of the Client ID.
1956 o Client ID (variable length) - The Client ID of the client
1957 who has joined the channel.
1962 2.3.22 New Channel List Payload
1964 This payload is used to distribute list of new channels from server
1965 to routers. It might convenient to send list of new channels when
1966 existing server connects to router, instead of sending them one
1969 There is no specific payload for this packet type. The packet type
1970 uses same payload as described in 2.3.19 New Channel Payload. To form
1971 a list several payloads is put in the packet each after each. The
1972 payload is variable in length but can be calculated by calculating
1973 the length of the fields together. This forms one New Channel Payload
1976 The list of payloads may only be sent with SILC_PACKET_NEW_CHANNEL_LIST
1977 packet. They must not be sent in any other packet type.
1981 2.3.23 New Channel User List Payload
1983 This payload is used to distribute list of channel users on specific
1984 channel from server to routers. It might convenient to send list of
1985 channel users when existing server connects to router, instead of
1986 sending them one by one.
1988 There is no specific payload for this packet type. The packet type
1989 uses same payload as described in 2.3.20 New Channel User Payload.
1990 To form a list several payloads is put in the packet each after each.
1991 The payload is variable in length but can be calculated by calculating
1992 the length of the fields together. This forms one New Channel User
1993 Payload in the list.
1995 The list of payloads may only be sent with packet
1996 SILC_PACKET_NEW_CHANNEL_USER_LIST. They must not be sent in any other
2001 2.3.24 Replace ID Payload
2003 This payload is used to replace old ID with new ID sent in the payload.
2004 When ID changes for some entity and the new ID is wanted to replace the
2005 old one this payload must be used. Client cannot send or receive this
2006 payload. Normal server and router server may send and receive this
2007 payload. After this packet has been sent the old ID must not be used
2010 The payload may only be sent with SILC_PACKET_REPLACE_ID packet. It must
2011 not be sent in any other packet type. Following diagram represents the
2012 Replace Payload Payload.
2019 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
2020 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2021 | Old ID Type | Old ID Length |
2022 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2026 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2027 | New ID Type | New ID Length |
2028 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2032 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2036 Figure 21: Replace ID Payload
2040 o Old ID Type (2 bytes) - Indicates the type of the old ID. See
2041 section 2.4 SILC ID Types for list of defined ID types.
2043 o Old ID Length (2 bytes) - Length of the old ID Data area not
2044 including the length of any other fields in the payload.
2046 o Old ID Data (variable length) - The actual old ID data.
2048 o New ID Type (2 bytes) - Indicates the type of the new ID. See
2049 section 2.4 SILC ID Types for list of defined ID types.
2051 o New ID Length (2 bytes) - Length of the new ID Data area not
2052 including the length of any other fields in the payload.
2054 o New ID Data (variable length) - The actual new ID data.
2059 2.3.25 Remove ID Payload
2061 Remove ID payload is used to remove ID from SILC network. This is used
2062 for example when client exits SILC network. The server must in this
2063 case send this payload to notify that this ID is not valid anymore.
2064 After this has been send the old ID must not be used anymore. Client
2065 must not send this payload.
2067 The packet uses generic ID Payload as New ID Payload. See section
2068 2.3.2.1 for generic ID Payload.
2072 2.3.26 Remove Channel User Payload
2074 Remove Channel User payload is used to remove a user from a channel network
2075 wide. This is used by routers to notify other routers that a user has
2076 left a channel. As routers keep information about users on channels a
2077 user leaving channel must be removed from all routers. Normal server may
2078 send this payload as well. Client must not send this payload.
2080 The payload may only be sent with SILC_PACKET_REMOVE_CHANNEL USER packet.
2081 It must not be sent in any other packet type. Following diagram
2082 represents the Remove Payload Payload.
2091 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
2092 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2093 | Client ID Length | |
2094 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2098 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2099 | Channel ID Length | |
2100 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
2104 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2108 Figure 22: Remove Channel User Payload
2112 o Client ID Length (2 bytes) - Length of the Client ID Data area
2113 not including the length of any other fields in the payload.
2115 o Client ID Data (variable length) - The Client ID of the user
2116 that has left the channel.
2118 o Channel ID Length (2 bytes) - Length of the Channel ID Data area
2119 not including the length of any other fields in the payload.
2121 o Channel ID Data (variable length) - The Channel ID of the channel
2130 ID's are extensively used in the SILC network to associate different
2131 entities. Following ID's has been defined to be used in the SILC
2137 When ever specific ID cannot be used this is used.
2141 Server ID to associate servers. See the format of
2146 Client ID to associate clients. See the format of
2151 Channel ID to associate channels. See the format of
2157 2.5 Packet Encryption And Decryption
2159 SILC packets are encrypted almost entirely. Only small part of SILC
2160 header is not encrypted as described in section 5.2 SILC Packet Header.
2161 The SILC Packet header is the first part of a packet to be encrypted
2162 and it is always encrypted with the key of the next receiver of the
2163 packet. The data payload area of the packet is always entirely
2164 encrypted and it is usually encrypted with the next receiver's key.
2165 However, there are some special packet types and packet payloads
2166 that require special encryption process. These special cases are
2167 described in the next sections. First is described the normal packet
2172 2.5.1 Normal Packet Encryption And Decryption
2174 Normal SILC packets are encrypted with the session key of the next
2175 receiver of the packet. The entire SILC Packet header and the packet
2176 data payload is is also encrypted with the same key. Padding of the
2177 packet is also encrypted always with the session key, also in special
2178 cases. Computed MAC of the packet must not be encrypted.
2180 Decryption process in these cases are straightforward. The receiver
2181 of the packet must first decrypt the SILC Packet header, or some parts
2182 of it, usually first 16 bytes of it. Then the receiver checks the
2183 packet type from the decrypted part of the header and can determine
2184 how the rest of the packet must be decrypted. If the packet type is
2185 any of the special cases described in following sections the packet
2186 decryption is special. If the packet type is not among those special
2187 packet types rest of the packet may be decrypted with the same key.
2189 Also, note that two bytes of the SILC Packet header are not encrypted
2190 thus it must be noticed in the decryption process by starting the
2191 decryption from the second byte of the header. This sets some rules
2192 to padding generation as well, see the section 2.7 Packet Padding
2195 With out a doubt, this sort of decryption processing causes some
2196 overhead to packet decryption, but never the less, is required.
2200 2.5.2 Channel Message Encryption And Decryption
2202 Channel Messages (Channel Message Payload) are always encrypted with
2203 the channel specific key. However, the SILC Packet header is not
2204 encrypted with that key. As in normal case, the header is encrypted
2205 with the key of the next receiver of the packet, who ever that might
2206 be. Note that in this case the encrypted data area is not touched
2207 at all; it must not be re-encrypted with the session key.
2209 Receiver of a channel message, who ever that is, is required to decrypt
2210 the SILC Packet header to be able to even recognize the packet to be as
2211 channel message. This is same procedure as for normal SILC packets.
2212 As the receiver founds the packet to be channel message, rest of the
2213 packet processing is special. Rest of the SILC Packet header is
2214 decrypted with the same session key along with the padding of the
2215 packet. After that the packet is protected with the channel specific
2216 key and hence can be decrypted only if the receiver is the client on
2217 the channel. See section 2.7 Packet Padding Generation for more
2218 information about padding on special packets.
2220 If the receiver of the channel message is router who is routing the
2221 message to another router then it must decrypt the Channel Message
2222 payload. Between routers (that is, between cells) channel messages
2223 are protected with session keys shared between the routers. This
2224 causes another special packet processing for channel messages. If
2225 the channel message is received from another router then the entire
2226 packet, including Channel Message payload, is encrypted with the
2227 session key shared between the routers. In this case the packet
2228 decryption process is as with normal SILC packets. Hence, if the
2229 router is sending channel message to another router the Channel
2230 Message payload must have been decrypted and must be re-encrypted
2231 with the session key shared between the another router. In this
2232 case the packet encryption is as with any normal SILC packet.
2234 It must be noted that this is only when the channel messages are sent
2235 from router to another router. In all other cases the channel
2236 message encryption and decryption is as described above. This
2237 different processing of channel messages with router to router
2238 connection is because channel keys are cell specific. All cells has
2239 their own channel keys thus the channel message traveling from one
2240 cell to another must be protected as it would be any normal SILC
2245 2.5.3 Private Message Encryption And Decryption
2247 By default, private message in SILC are protected by session keys.
2248 In this case the private message encryption and decryption process is
2249 equivalent to normal packet encryption and decryption.
2251 However, private messages can be protected with private message key
2252 which causes the packet to be special packet. The procedure in this
2253 case is very much alike to channel packets. The actual private message
2254 is encrypted with the private message key and other parts of the
2255 packet is encrypted with the session key. See 2.7 Packet Padding
2256 Generation for more information about padding on special packets.
2258 The difference from channel message processing is that server or router
2259 en route never decrypts the actual private message, as it does not
2260 have the key to do that. Thus, when sending packets between router
2261 the processing is same as in any other case as well; the packet's header
2262 and padding is protected by the session key and the data area is not
2265 The true receiver of the private message, client, that is, is able
2266 to decrypt the private message as it shares the key with the sender
2271 2.6 Packet MAC Generation
2273 Data integrity of a packet is protected by including a message
2274 authentication code (MAC) at the end of the packet. The MAC is computed
2275 from shared secret MAC key, that is established by the SILC Key Exchange
2276 protocol, and from the original contents of the packet. The MAC is
2277 always computed before the packet is encrypted, although after it is
2278 compressed if compression is used.
2280 The MAC is computed from entire packet. Every bit of data in the packet,
2281 including SILC Packet Header is used in the MAC computing. This way
2282 the entire packet becomes authenticated.
2284 If the packet is special packet MAC is computed from the entire packet
2285 but part of the packet may be encrypted before the MAC is computed.
2286 This is case, for example, with channel messages where the message data
2287 is encrypted with key that server may not now. In this case the MAC
2288 has been computed from the encrypted data.
2290 See [SILC1] for defined and allowed MAC algorithms.
2294 2.7 Packet Padding Generation
2296 Padding is needed in the packet because the packet is encrypted. It
2297 must always be multiple by eight (8) or multiple by the size of the
2298 cipher's block size, which ever is larger. The padding is always
2301 For normal packets the padding is added after the SILC Packet Header
2302 and between the Data Payload area. The padding for normal packets
2303 are calculated as follows:
2306 padding length = 16 - ((packet length - 2) % 16)
2309 The 16 is the maximum padding allowed in SILC packet. Two (2) is
2310 subtracted from the true length of the packet because two (2) bytes
2311 is not encrypted in SILC Packet Header, see section 2.2 SILC Packet
2312 Header. Those two bytes that are not encrypted must not be calculated
2313 to the padding length.
2315 For special packets the padding calculation may be different as special
2316 packets may be encrypted differently. In these cases the encrypted
2317 data area must already be multiple by the block size thus in this case
2318 the padding is calculated only for SILC Packet Header, not for any
2319 other area of the packet. The same algorithm works in this case as
2320 well, except that the `packet length' is now the SILC Packet Header
2321 length. In this case, as well, two (2) is subtracted from the
2324 The padding must be random data, preferably, generated by
2325 cryptographically strong random number generator.
2329 2.8 Packet Compression
2331 SILC Packets may be compressed. In this case the data payload area
2332 is compressed and all other areas of the packet must remain as they
2333 are. After compression is performed for the data area, the length
2334 field of Packet Header must be set to the compressed length of the
2337 The compression must always be applied before encryption. When
2338 the packet is received and decrypted the data area must be decompressed.
2339 Note that the true sender of the packet must apply the compression and
2340 the true receiver of the packet must apply the decompression. Any
2341 server or router en route must not decompress the packet.
2348 The sender of the packet must assemble the SILC Packet Header with
2349 correct values. It must set the Source ID of the header as its own
2350 ID, unless it is forwarding the packet. It must also set the Destination
2351 ID of the header to the true destination. If the destination is client
2352 it will be Client ID, if it is server it will be Server ID and if it is
2353 channel it will be Channel ID.
2355 If the sender wants to compress the packet it must apply the
2356 compression now. Sender must also compute the padding as described
2357 in above sections. Then sender must compute the MAC of the packet.
2359 Then sender encrypts the packet as has been described in above
2360 sections according whether the packet is normal packet or special
2361 packet. The computed MAC must not be encrypted.
2365 2.10 Packet Reception
2367 On packet reception the receiver must check that all fields in the
2368 SILC Packet Header are valid. It must check the flags of the
2369 header and act accordingly. It must also check the MAC of the packet
2370 and if it is to be failed the packet must be discarded. Also if the
2371 header of the packet includes any bad fields the packet must be
2374 See above sections on the decryption process of the received packet.
2376 The receiver must also check that the ID's in the header are valid
2377 ID's. Unsupported ID types or malformed ID's must cause packet
2378 rejection. The padding on the reception is always ignored.
2380 The receiver must also check the packet type and start parsing the
2381 packet according to the type. However, note the above sections on
2382 special packet types and their parsing.
2388 Routers are the primary entities in the SILC network that takes care
2389 of packet routing. However, normal servers routes packets as well, for
2390 example, when they are routing channel message to the local clients.
2391 Routing is quite simple as every packet tells the true origin and the
2392 true destination of the packet.
2394 It is still recommended for routers that has several routing connections
2395 to create route cache for those destinations that has faster route than
2396 the router's primary route. This information is available for the router
2397 when other router connects to the router. The connecting party then
2398 sends all of its locally connected clients, server and channels. These
2399 informations helps to create the route cache. Also, when new channels
2400 are created to a cell its information is broadcasted to all routers
2401 in the network. Channel ID's are based on router's ID thus it is easy
2402 to create route cache based on these informations. If faster route for
2403 destination does not exist in router's route cache the packet must be
2404 routed to the primary route (default route).
2406 For server who receives a packet to be routed to its locally connected
2407 client the server must check whether the particular packet type is
2408 allowed to be routed to the client. Not all packets may be sent by
2409 some odd entity to client that is indirectly connected to the sender.
2410 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2411 entities and sending packets to them. The section mentions the packets
2412 that may be sent to indirectly connected entities. It is clear that some
2413 server cannot send, for example, disconnect packet to client that is not
2414 directly connected to the server.
2418 2.12 Packet Forwarding
2420 Currently SILC command packets may be forwarded from one entity to another.
2421 Any other packet currently cannot be forwarded but support for more packet
2422 types may be added if needed. Forwarding is usually used by server to
2423 forward some command request coming from client to the router as the server
2424 may be incapable to handle the request. Forwarding may be only one hop
2425 long; the receiver of the packet with Forwarded flag set in the SILC
2426 Packet header must not forward the packet any further.
2428 The normal scenario is that client sends JOIN command to the server which
2429 is not able to create the channel as there are no local clients on the
2430 channel. Channels are created always by the router of the cell thus the
2431 packet must be forwarded to the router. The server forwards the original
2432 packet coming from client to the router after it has set the Forwarded
2433 flag to the SILC Packet header.
2435 Router receiving the packet knows that the packet has to be processed
2436 specially by checking the flags and the Forwarded flag in the SILC Packet
2437 header. After router has joined the client to the channel (and perhaps
2438 created a new channel) it sends normal command reply packet to the
2439 client. However, as the router doesn't have direct connection to the
2440 client the packet is sent through the server. Server detects that
2441 the command reply packet is destined to the client and sends it to
2446 2.13 Packet Broadcasting
2448 SILC packets may be broadcasted in SILC network. However, only router
2449 server may send or receive broadcast packets. Client and normal server
2450 must not send broadcast packets and they must ignore broadcast packets
2451 if they receive them. Broadcast packets are sent by setting Broadcast
2452 flag to the SILC packet header.
2454 Broadcasting packets means that the packet is sent to all routers in
2455 the SILC network, except to the router that sent the packet. The router
2456 receiving broadcast packet must send the packet to its primary route.
2457 The fact that SILC routers may have several router connections may
2458 cause problems, such as race conditions inside the SILC network, if
2459 care is not taken when broadcasting packets. Router must not send
2460 the broadcast packet to any other route except to its primary route.
2462 If the primary route of the router is the original sender of the packet
2463 the packet must not be sent to the primary route. This may happen
2464 if router has several router connections and some other router uses
2465 the router as its primary route.
2467 Routers use broadcast packets to broadcast for example information
2468 about newly registered clients, servers, channels etc. so that all the
2469 routers may keep these informations up to date.
2473 2.14 Packet Tunneling
2475 Tunneling is a feature that is available in SILC protocol. Tunneling
2476 means that extra SILC Packet Header is applied to the original packet
2477 and thus hiding the original packet entirely. There can be some
2478 interesting applications using tunneling, such as, using ID's based on
2479 private network IP addresses inside in the tunneled packet. This can
2480 open many interesting features relating to connecting to private network
2481 from the Internet with SILC and many more. However, this feature is
2482 optional currently in SILC as there does not exist thorough analysis of
2483 this feature. It is with out a doubt that there will be many more
2484 applications that has not yet been discovered. Thus, it is left
2485 to Internet Community to investigate the use of tunneling in SILC
2486 protocol. This document is updated according those investigations
2487 and additional documents on the issue may be written.
2491 3 Security Considerations
2493 Security is central to the design of this protocol, and these security
2494 considerations permeate the specification.
2500 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2501 Protocol Specification", Internet Draft, June 2000.
2503 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2504 Protocols", Internet Draft, June 2000.
2506 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2509 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2512 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2515 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2518 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2519 Infrastructure, Certificate and CRL Profile", RFC 2459,
2522 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2523 John Wiley & Sons, New York, NY, 1996.
2525 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2528 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2529 RFC 2412, November 1998.
2531 [ISAKMP] Maughan D., et al, "Internet Security Association and
2532 Key Management Protocol (ISAKMP)", RFC 2408, November
2535 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
2536 (IKE)", RFC 2409, November 1998.
2538 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2539 Authentication", RFC 2104, February 1997.
2555 EMail: priikone@poseidon.pspt.fi
2557 This Internet-Draft expires 6 Jun 2001
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