8 .ds RF FORMFEED[Page %]
17 Network Working Group P. Riikonen
19 draft-riikonen-silc-pp-00.txt 28 June 2000
26 <draft-riikonen-silc-pp-00.txt>
31 This document is an Internet-Draft and is in full conformance with
32 all provisions of Section 10 of RFC 2026. Internet-Drafts are
33 working documents of the Internet Engineering Task Force (IETF), its
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37 Internet-Drafts are draft documents valid for a maximum of six months
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40 material or to cite them other than as "work in progress."
42 The list of current Internet-Drafts can be accessed at
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45 The list of Internet-Draft Shadow Directories can be accessed at
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48 The distribution of this memo is unlimited.
54 This memo describes a Packet Protocol used in the Secure Internet Live
55 Conferencing (SILC) protocol specified in the Secure Internet Live
56 Conferencing, Protocol Specification Internet Draft [SILC1]. This
57 protocol describes the packet types and packet payloads which defines
58 the contents of the packets. The protocol provides secure binary packet
59 protocol that assures that the contents of the packets are secured and
74 1 Introduction .................................................. 3
75 2 SILC Packet Protocol .......................................... 4
76 2.1 SILC Packet ............................................... 4
77 2.2 SILC Packet Header ........................................ 5
78 2.3 SILC Packet Types ......................................... 7
79 2.3.1 SILC Packet Payloads ................................ 15
80 2.3.2 Disconnect Payload .................................. 15
81 2.3.3 Success Payload ..................................... 16
82 2.3.4 Failure Payload ..................................... 16
83 2.3.5 Reject Payload ...................................... 17
84 2.3.6 Notify Payload ...................................... 17
85 2.3.7 Error Payload ....................................... 18
86 2.3.8 Channel Message Payload ............................. 19
87 2.3.9 Channel Key Payload ................................. 20
88 2.3.10 Private Message Payload ............................ 23
89 2.3.11 Private Message Key Payload ........................ 24
90 2.3.12 Command Payload .................................... 25
91 2.3.12.1 Command Argument Payload .................. 25
92 2.3.13 Command Reply Payload .............................. 26
93 2.3.14 Connection Auth Request Payload .................... 27
94 2.3.15 New ID Payload ..................................... 28
95 2.3.16 New ID List Payload ................................ 29
96 2.3.17 New Client Payload ................................. 29
97 2.3.18 New Server Payload ................................. 31
98 2.3.19 New Channel Payload ................................ 31
99 2.3.20 New Channel User Payload ........................... 32
100 2.3.21 New Channel List Payload ........................... 33
101 2.3.22 New Channel User List Payload ...................... 34
102 2.3.23 Replace ID Payload ................................. 34
103 2.3.24 Remove ID Payload .................................. 35
104 2.4 SILC ID Types ............................................. 36
105 2.5 Packet Encryption And Decryption .......................... 37
106 2.5.1 Normal Packet Encryption And Decryption ............. 37
107 2.5.2 Channel Message Encryption And Decryption ........... 37
108 2.5.3 Private Message Encryption And Decryption ........... 38
109 2.6 Packet MAC Generation ..................................... 39
110 2.7 Packet Padding Generation ................................. 39
111 2.8 Packet Compression ........................................ 40
112 2.9 Packet Sending ............................................ 40
113 2.10 Packet Reception ......................................... 41
114 2.11 Packet Routing ........................................... 42
115 2.12 Packet Forwarding ........................................
116 2.13 Packet Broadcasting ...................................... 41
117 2.14 Packet Tunneling ......................................... 42
118 3 Security Considerations ....................................... 43
119 4 References .................................................... 43
120 5 Author's Address .............................................. 44
126 Figure 1: Typical SILC Packet
127 Figure 2: SILC Packet Header
128 Figure 3: Disconnect Payload
129 Figure 4: Success Payload
130 Figure 5: Failure Payload
131 Figure 6: Reject Payload
132 Figure 7: Notify Payload
133 Figure 8: Error Payload
134 Figure 9: Channel Message Payload
135 Figure 10: Channel Key Payload
136 Figure 11: Private Message Payload
137 Figure 12: Private Message Key Payload
138 Figure 13: Command Payload
139 Figure 14: Command Argument Payload
140 Figure 15: Connection Auth Request Payload
141 Figure 16: New ID Payload
142 Figure 17: New Client Payload
143 Figure 18: New Server Payload
144 Figure 19: New Channel Payload
145 Figure 20: New Channel User Payload
146 Figure 21: Replace ID Payload
147 Figure 22: Remove ID Payload
148 Figure 23: Remove Channel User Payload
154 This document describes a Packet Protocol used in the Secure Internet
155 Live Conferencing (SILC) protocol specified in the Secure Internet Live
156 Conferencing, Protocol Specification Internet Draft [SILC1]. This
157 protocol describes the packet types and packet payloads which defines
158 the contents of the packets. The protocol provides secure binary packet
159 protocol that assures that the contents of the packets are secured and
162 The basis of SILC protocol relies in the SILC packets and it is with
163 out a doubt the most important part of the protocol. It is also probably
164 the most complicated part of the protocol. Packets are used all the
165 time in the SILC network to send messages, commands and other information.
166 All packets in SILC network are always encrypted and their integrity
167 is assured by computed MACs. The protocol defines several packet types
168 and packet payloads. Each packet type usually has a specific packet
169 payload that actually defines the contents of the packet. Each packet
170 also includes a default SILC Packet Header that provides sufficient
171 information about the origin of the packet and destination of the
176 2 SILC Packet Protocol
181 SILC packets deliver messages from sender to receiver securely by
182 encrypting important fields of the packet. The packet consists of
183 default SILC Packet Header, Padding, Packet Payload data, and, packet
186 The following diagram illustrates typical SILC packet.
191 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
192 | n bytes | 1 - n bytes | n bytes | n bytes
193 | SILC Header | Padding | Data Payload | MAC
194 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
198 Figure 1: Typical SILC Packet
201 SILC Header is always the first part of the packet and its purpose
202 is to provide information about the packet. It provides for example
203 the packet type, origin of the packet and the destination of the packet.
204 The header is variable in length and first two (2) bytes of the
205 header (thus first two bytes of the packet) are not encrypted. The
206 first two (2) bytes are the length of the packet which is not encrypted.
207 See following section for description of SILC Packet header. Packets
208 without SILC header or with malformed SILC header must be dropped.
210 Padding follows the packet header. The purpose of the padding is to
211 make the packet multiple by eight (8) or by the block size of the
212 cipher used in the encryption, which ever is larger. The maximum
213 length of padding is currently 16 bytes. The padding is always
216 Data payload area follows padding and it is the actual data of the
217 packet. The packet data is the packet payloads defined in this
218 protocol. The data payload area is always encrypted.
220 The last part of SILC packet is the packet MAC that assures the
221 integrity of the packet. The MAC is always computed from the packet
222 before the encryption is applied to the packet. If compression is used
223 in the packet the MAC is computed after the compression has been
224 applied. The compression, on the other hand, is always applied before
227 All fields in all packet payloads are always in MSB (most significant
232 2.2 SILC Packet Header
234 The default SILC packet header is applied to all SILC packets and it is
235 variable in length. The purpose of SILC Packet header is to provide
236 detailed information about the packet. The receiver of the packet uses
237 the packet header to parse the packet and gain other relevant parameters
240 Following diagram represents the default SILC header format.
241 (*) indicates that this field is never encrypted. Other fields are
248 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
249 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
250 | Payload Length * | Flags | Packet Type |
251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
252 | Source ID Length | Destination ID Length |
253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
269 Figure 2: SILC Packet Header
273 o Payload Length (2 bytes) - Is the length of the packet
274 not including the padding of the packet. This field must
275 not be encrypted but must always be authenticated.
277 o Flags (1 byte) - Indicates flags to be used in packet
278 processing. Several flags may be set by ORing the flags
281 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 desribtion 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
345 o Destination ID Length (2 bytes) - Indicates the length of the
346 Destination ID field in the header, not including this or
349 o Src ID Type (1 byte) - Indicates the type of ID in the
350 Source ID field. See section 2.4 SILC ID Types for
353 o Source ID (variable length) - The actual source ID that
354 indicates who is the original sender of the packet.
356 o Dst ID Type (1 byte) - Indicates the type of ID in the
357 Destination ID field. See section 2.4 SILC ID Types for
360 o Destination ID (variable length) - The actual source ID that
361 indicates who is the end receiver of the packet.
365 2.3 SILC Packet Types
367 SILC packet types defines the contents of the packet and it is used by
368 the receiver to parse the packet. The packet type is 8 bits, as a one
369 byte, in length. The range for the packet types are from 0 - 255,
370 where 0 is never sent and 255 is currently reserved for future
371 extensions and must not be defined to any other purpose. Every SILC
372 specification compliant implementation should support all of these packet
375 The below list of the SILC Packet types includes reference to the packet
376 payload as well. Packet payloads are the actual packet, that is, the data
377 that the packet consists of. Each packet type defines packet payload
378 which usually may only be sent with the specific packet type.
380 Most of the packets are packets that must be destined directly to entity
381 that is connected to the sender. It is not allowed, for example, for
382 router to send disconnect packet to client that is not directly connected
383 to the router. However, there are some special packet types that may
384 be destined to some entity that the sender has not direct connection
385 with. These packets are for example private message packets, channel
386 message packets, command packets and some other packets that may be
387 broadcasted in the SILC network. If the packet is allowed to be sent to
388 indirectly connected entity it is mentioned separately in the packet
389 description (unless it is obvious as in private and channel message
390 packets). Other packets must not be sent or accepted, if sent, to
391 indirectly connected entities.
393 List of SILC Packet types are defined as follows.
398 This type is reserved and it is never sent.
401 1 SILC_PACKET_DISCONNECT
403 This packet is sent to disconnect the remote end. Reason of
404 the disconnection is sent inside the packet payload. Client
405 usually does not send this packet.
407 Payload of the packet: See section 2.3.2 Disconnect Payload
410 2 SILC_PACKET_SUCCESS
412 This packet is sent upon successful execution of some protocol.
413 The status of the success is sent in the packet.
415 Payload of the packet: See section 2.3.3 Success Payload
418 3 SILC_PACKET_FAILURE
420 This packet is sent upon failure of some protocol. The status
421 of the failure is sent in the packet.
423 Payload of the packet: See section 2.3.4 Failure Payload
428 This packet may be sent upon rejection of some protocol.
429 The status of the rejection is sent in the packet.
431 Payload of the packet: See section 2.3.5 Reject Payload
436 This packet is used to send notify message, usually from
437 server to client, although it may be sent from server to another
438 server as well. Client never sends this packet. Server may
439 send this packet to channel as well when the packet is
440 distributed to all clients on the channel. Receiver of this
441 packet may ignore the packet if it chooses so. However, it
442 should not be ignored.
444 Payload of the packet: See section 2.3.6 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 Payload of the packet: See section 2.3.7 Error Payload.
458 7 SILC_PACKET_CHANNEL_MESSAGE
460 This packet is used to send messages to channels. The packet
461 includes Channel ID of the channel and the actual message to
462 the channel. Messages sent to the channel are always protected
463 by channel specific keys. Channel Keys are distributed by
464 SILC_PACKET_CHANNEL_KEY packet.
466 When client sends this packet the destination ID in the SILC
467 header must be the Channel ID of the channel the message is
468 destined to. If server sends this packet to a client the
469 destination ID in the SILC header must be the Client ID of
470 the client receiving the packet.
472 If server sends this packet to router or if router sends this
473 packet to server or another router the destination ID in the
474 SILC header must be the Channel ID of the channel. Server
475 (including router) distributes this packet only to its local
476 clients who are joined to the channel. Servers and routers
477 also determines who are on the channel and when this packet
478 needs to be sent, as described in section Client To Client
481 Payload of the packet: See section 2.3.8 Channel Message
485 8 SILC_PACKET_CHANNEL_KEY
487 This packet is used to distribute new key for particular
488 channel. Each channel has their own independent keys that
489 is used to protect the traffic on the channel. Only server
490 may send this packet. This packet may be sent to entity
491 that is indirectly connected to the sender.
493 Payload of the packet: See section 2.3.9 Channel Key Payload
496 9 SILC_PACKET_PRIVATE_MESSAGE
498 This packet is used to send private messages from client
499 to another client. By default, private messages are protected
500 by session keys established by normal key exchange protocol.
501 However, it is possible to use specific key to protect private
502 messages. SILC_PACKET_PRIVATE_MESSAGE_KEY packet is used to
503 agree the key with the remote client. Pre-shared key may be
504 used as well if both of the client knows it, however, it needs
505 to be agreed outside SILC. See more of this in [SILC1].
507 Payload of the packet: See section 2.3.10 Private Message
511 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
513 This packet is used to agree about a key to be used to protect
514 the private messages between two clients. If this is not sent
515 the normal session key is used to protect the private messages
516 inside SILC network. Agreeing to use specific key to protect
517 private messages adds security, as no server between the two
518 clients will be able to decrypt the private message. However,
519 servers inside SILC network are considered to be trusted, thus
520 using normal session key to protect private messages does not
521 degree security. Whether to agree to use specific keys by
522 default or to use normal session keys by default, is
523 implementation specific issue. See more of this in [SILC1].
525 Payload of the packet: See section 2.3.11 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 Payload of the packet: See section 2.3.12 Command Payload
541 12 SILC_PACKET_COMMAND_REPLY
543 This packet is send as reply to the SILC_PACKET_COMMAND packet.
544 The contents of this packet is command specific. This packet
545 maybe sent to entity that is indirectly connected to the sender.
547 Payload of the packet: See section 2.3.13 Command Reply
548 Payload and section 2.3.12 Command
552 13 SILC_PACKET_KEY_EXCHANGE
554 This packet is used to start SILC Key Exchange Protocol,
555 described in detail in [SILC3].
557 Payload of the packet: Payload of this packet is described
558 in the section SILC Key Exchange
559 Protocol and its sub sections in
563 14 SILC_PACKET_KEY_EXCHANGE_1
565 This packet is used as part of the SILC Key Exchange Protocol.
567 Payload of the packet: Payload of this packet is described
568 in the section SILC Key Exchange
569 Protocol and its sub sections in
573 15 SILC_PACKET_KEY_EXCHANGE_2
575 This packet is used as part of the SILC Key Exchange Protocol.
577 Payload of the packet: Payload of this packet is described
578 in the section SILC Key Exchange
579 Protocol and its sub sections in
583 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
585 This packet is used to request the authentication method to
586 be used in the SILC Connection Authentication Protocol. If
587 initiator of the protocol does not know the mandatory
588 authentication method this packet is used to determine it.
590 The party receiving this payload must respond with the same
591 packet including the mandatory authentication method.
593 Payload of the packet: See section 2.3.14 Connection Auth
597 17 SILC_PACKET_CONNECTION_AUTH
599 This packet is used to start and perform the SILC Connection
600 Authentication Protocol. This protocol is used to authenticate
601 the connecting party. The protocol is described in detail in
604 Payload of the packet: Payload of this packet is described
605 in the section SILC Authentication
606 Protocol and it sub sections in [SILC].
609 18 SILC_PACKET_NEW_ID
611 This packet is used to distribute new ID's from server to
612 router and from router to all routers in the SILC network.
613 This is used when for example new client is registered to
614 SILC network. The newly created ID's of these operations are
615 distributed by this packet. Only server may send this packet,
616 however, client must be able to receive this packet.
618 Payload of the packet: See section 2.3.15 New ID Payload
621 19 SILC_PACKET_NEW_ID_LIST
623 This packet is used to distribute list of new ID's from
624 server to routers. This is equivalent to previous packet
625 type except that it may include several ID's. Client must
626 not send this packet.
628 Payload of the packet: See section 2.3.16 New ID List
632 20 SILC_PACKET_NEW_CLIENT
634 This packet is used by client to register itself to the
635 SILC network. This is sent after key exchange and
636 authentication protocols has been completed. Client sends
637 various information about itself in this packet.
639 Payload of the packet: See section 2.3.17 New Client Payload
642 21 SILC_PACKET_NEW_SERVER
644 This packet is used by server to register itself to the
645 SILC network. This is sent after key exchange and
646 authentication protocols has been completed. Server sends
647 this to the router it connected to, or, if router was
648 connecting, to the connected router. Server sends
649 its Server ID and other information in this packet.
650 Client must not send or receive this packet.
652 Payload of the packet: See section 2.3.18 New Server Payload
655 22 SILC_PACKET_NEW_CHANNEL
657 This packet is used to notify routers about newly created
658 channel. Channels are always created by the router and it must
659 notify other routers about the created channel. Router sends
660 this packet to its primary route. Client must not send this
661 packet. This packet maybe sent to entity that is indirectly
662 connected to the sender.
664 Payload of the packet: See section 2.3.19 New Channel Payload
667 23 SILC_PACKET_NEW_CHANNEL_USER
669 This packet is used to notify routers about new user on channel.
670 The packet is sent after user has joined to the channel. Server
671 may send this packet to its router and router may send this to
672 its primary router. Client must not send this packet. This
673 packet maybe sent to entity that is indirectly connected to the
676 Payload of the packet: See section 2.3.20 New Channel User
680 24 SILC_PACKET_NEW_CHANNEL_LIST
682 This packet is used to distribute list of created channels
683 from server to routers. This is equivalent to the packet
684 SILC_PACKET_NEW_CHANNEL except that it may include several
685 payloads. Client must not send this packet.
687 Payload of the packet: See section 2.3.21 New Channel List
691 25 SILC_PACKET_NEW_CHANNEL_USER_LIST
693 This packet is used to distribute list of users on specific
694 channel from server to routers. This is equivalent to the
695 packet SILC_PACKET_NEW_CHANNEL_USER except that it may
696 include several payloads. Client must not send this packet.
698 Payload of the packet: See section 2.3.22 New Channel User
702 26 SILC_PACKET_REPLACE_ID
704 This packet is used to replace old ID with new ID sent in
705 the packet payload. For example, when client changes its
706 nickname new ID is created and this packet can be used to
707 distribute the new ID and the old ID is removed when it is
708 send in the packet. Client cannot send or receive this
709 packet. This packet maybe sent to entity that is indirectly
710 connected to the sender.
712 Payload of the packet: See section 2.3.23 Replace ID Payload
715 27 SILC_PACKET_REMOVE_ID
717 This packet is used to removed ID. For example, when client
718 exits SILC network its ID is removed. Client must not send
719 this packet. This packet maybe sent to entity that is
720 indirectly connected to the sender.
722 Payload of the packet: See section 2.3.24 Remove ID Payload
725 28 SILC_PACKET_REMOVE_CHANNEL_USER
727 This packet is used to remove user from a channel. This is
728 used by router to notify other routers in the network that a
729 client has leaved a channel. This packet maybe sent to entity
730 that is indirectly connected to the sender.
732 Payload of the packet: See section 2.3.25 Remove Channel User
738 This packet is used to indicate that re-key must be performed
739 for session keys. See section Session Key Regeneration in
740 [SILC1] for more information. This packet does not have
744 30 SILC_PACKET_REKEY_DONE
746 This packet is used to indicate that re-key is performed and
747 new keys must be used hereafter. This is sent only if re-key
748 was done without PFS option. If PFS is set, this is not sent
749 as SILC Key Exchange protocol is executed. This packet does
755 Currently undefined commands.
760 This type is reserved for future extensions and currently it
766 2.3.1 SILC Packet Payloads
768 All payloads resides in the main data area of the SILC packet. However
769 all payloads must be at the start of the data area after the default
770 SILC packet header and padding. All fields in the packet payload are
771 always encrypted, as, they reside in the data area of the packet which
774 Payloads described in this section are common payloads that must be
775 accepted anytime during SILC session. Most of the payloads may only
776 be sent with specific packet type which is defined in the description
779 There are a lot of other payloads in the SILC as well. However, they
780 are not common in the sense that they could be sent at any time.
781 These payloads are not described in this section. These are payloads
782 such as SILC Key Exchange payloads and so on. These are described
783 in [SILC1] and [SILC3].
787 2.3.2 Disconnect Payload
789 Disconnect payload is sent upon disconnection. The payload is simple;
790 reason of disconnection is sent to the disconnected party.
792 The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
793 must not be sent in any other packet type. Following diagram represents
794 the Disconnect 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
803 ~ Disconnect Message ~
805 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
809 Figure 3: Disconnect Payload
815 o Disconnect Message (variable length) - Human readable
816 reason of the disconnection.
821 2.3.3 Success Payload
823 Success payload is sent when some protocol execution is successfully
824 completed. The payload is simple; indication of the success is sent.
825 This maybe any data, including binary or human readable data.
830 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
831 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
833 ~ Success Indication ~
835 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
839 Figure 4: Success Payload
843 o Success Indication (variable length) - Indication of
844 the success. This maybe for example some flag that
845 indicates the protocol and the success status or human
846 readable success message. The true length of this
847 payload is available by calculating it from the SILC
853 2.3.4 Failure Payload
855 This is opposite of Success Payload. Indication of failure of
856 some protocol is sent in the payload.
862 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
863 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
865 ~ Failure Indication ~
867 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
871 Figure 5: Failure Payload
875 o Failure Indication (variable length) - Indication of
876 the failure. This maybe for example some flag that
877 indicates the protocol and the failure status or human
878 readable failure message. The true length of this
879 payload is available by calculating it from the SILC
887 This payload is sent when some protocol is rejected to be executed.
888 Other operations may send this as well that was rejected. The
889 indication of the rejection is sent in the payload. The indication
890 may be binary or human readable data.
896 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
897 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
899 ~ Reject Indication ~
901 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
905 Figure 6: Reject Payload
909 o Reject Indication (variable length) - Indication of
910 the rejection. This maybe for example some flag that
911 indicates the protocol and the rejection status or human
912 readable rejection message. The true length of this
913 payload is available by calculating it from the SILC
924 Notify payload is used to send notify messages. The payload is usually
925 sent from server to client, however, server may send it to another
926 server as well. Client must not send this payload. The receiver of
927 this payload may totally ignore the contents of the payload, however,
928 notify message should be noted and possibly logged.
930 The payload may only be sent with SILC_PACKET_NOTIFY packet. It must
931 not be sent in any other packet type. Following diagram represents the
937 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
938 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
942 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
946 Figure 7: Notify Payload
950 o Notify Message (variable length) - Human readable notify
958 Error payload is sent upon error. Error may occur in various
959 conditions when server sends this packet. Client may not send this
960 payload but must be able to accept it. However, client may
961 totally ignore the contents of the packet as server is going to
962 take action on the error anyway. However, it is recommended
963 that the client takes error packet seriously.
969 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
970 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
974 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
978 Figure 8: Error Payload
982 o Error Message (variable length) - Human readable error
988 2.3.8 Channel Message Payload
990 Channel messages are the most common messages sent in the SILC.
991 Channel Message Payload is used to send message to channels. These
992 messages can only be sent if client has joined to some channel.
993 Even though this packet is the most common in SILC it is still
994 special packet. Some special handling on sending and reception
995 of channel message is required.
997 Padding must be applied into this payload since the payload is
998 encrypted separately from other parts of the packet with the
999 channel specific key. Hence the requirement of the padding.
1000 The padding should be random data. The packet must be made
1001 multiple by eight (8) or by the block size of the cipher, which
1004 The SILC header in this packet is encrypted with the session key
1005 of the next receiver of the packet. Nothing else is encrypted
1006 with that key. Thus, the actual packet and padding to be
1007 encrypted with the session key is SILC Header plus padding to it
1008 to make it multiple by eight (8) or multiple by the block size
1009 of the cipher, which ever is larger.
1011 Receiver of the the channel message packet is able to determine
1012 the channel the message is destined to by checking the destination
1013 ID from the SILC Packet header which tells the destination channel.
1014 The original sender of the packet is also determined by checking
1015 the source ID from the header which tells the client who sent
1018 The payload may only be sent with SILC_PACKET_CHANNEL_MESSAGE packet.
1019 It must not be sent in any other packet type. Following diagram
1020 represents the Channel Message Payload.
1022 (*) indicates that the field is not encrypted.
1048 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
1049 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1050 | Nickname Length | |
1051 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1055 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1056 | Message Length | |
1057 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1061 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1062 | Padding Length | |
1063 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1067 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1069 ~ Initial Vector * ~
1071 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1075 Figure 9: Channel Message Payload
1079 o Nickname Length (2 bytes) - Indicates the length of the
1080 Nickname field, not including any other field.
1082 o Nickname (variable length) - Nickname of the sender of the
1083 channel message. This should not be trusted as a definite
1084 sender of the channel message. The SILC Packet Header in
1085 the packet indicates the true sender of the packet and
1086 client should verify that the nickname sent here belongs
1087 to the Client ID in the SILC Packet Header. This nickname
1088 is merely provided to be displayed by the client.
1090 If server is sending this packet this field is not included
1091 and zero (0) length must be set to the Nickname Length field.
1093 o Message Length (2 bytes) - Indicates the length of the
1094 the Message Data field in the payload, not including any
1098 o Message Data (variable length) - The actual message to
1101 o Padding Length (2 bytes) - Indicates the length of the
1102 Padding field in the payload, not including any other
1105 o Padding (variable length) - The padding that must be
1106 applied because this payload is encrypted separately from
1107 other parts of the packet.
1109 o Initial Vector (variable length) - The initial vector
1110 that has been used in packet encryption. It needs to be
1111 used in the packet decryption as well. What this field
1112 includes is implementation issue. However, it is
1113 recommended that it would be random data or, perhaps,
1114 a timestamp. It is not recommended to use zero (0) as
1115 initial vector. This field is not encrypted. This field
1116 is not included into the padding calculation. Length
1117 of this field equals the cipher's block size. This field
1118 is, however, authenticated.
1123 2.3.9 Channel Key Payload
1125 All traffic in channels are protected by channel specific keys.
1126 Channel Key Payload is used to distribute channel keys to all
1127 clients on the particular channel. Channel keys are sent when
1128 the channel is created, when new user joins to the channel and
1129 whenever a user leaves a channel. Server creates the new
1130 channel key and distributes it to the clients by encrypting this
1131 payload with the session key shared between the server and
1132 the client. After that, client starts using the key received
1133 in this payload to protect the traffic on the channel.
1135 Channel keys are cell specific thus every router in cell have
1136 to create a channel key and distribute it if any client in the
1137 cell has joined to a channel. Channel traffic between cell's
1138 are not encrypted using channel keys, they are encrypted using
1139 normal session keys between two routers. Inside a cell, all
1140 channel traffic is encrypted with the specified channel key.
1141 Channel key should expire peridiocally, say, in one hour, in
1142 which case new channel key is created and distributed.
1144 The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
1145 It must not be sent in any other packet type. Following diagram
1146 represents the Channel Key Payload.
1152 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
1153 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1154 | Channel ID Length | |
1155 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1159 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1160 | Cipher Name Length | |
1161 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1165 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1166 | Channel Key Length | |
1167 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1171 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1175 Figure 10: Channel Key Payload
1180 o Channel ID Length (2 bytes) - Indicates the length of the
1181 Channel ID field in the payload, not including any other
1184 o Channel ID (variable length) - The Channel ID of the
1185 channel this key is meant for.
1187 o Cipher Name Length (2 bytes) - Indicates the length of the
1188 Cipher name field in the payload, not including any other
1191 o Cipher Name (variable length) - Name of the cipher used
1192 in the protection of channel traffic. This name is
1193 initially decided by the creator of the channel but it
1194 may change during the life time of the channel as well.
1196 o Channel Key Length (2 bytes) - Indicates the length of the
1197 Channel Key field in the payload, not including any other
1200 o Channel Key (variable length) - The actual channel key
1201 material. This key is used as such as key material for
1202 encryption function.
1207 2.3.10 Private Message Payload
1209 Private Message Payload is used to send private message between
1210 two clients (or users for that matter). The messages are sent only
1211 to the specified user and no other user inside SILC network is
1212 able to see the message. The message is protected by the session
1213 key established by the SILC Key Exchange Protocol. However,
1214 it is also possible to agree to use specific keys to protect
1215 just the private messages. See section 2.3.11 Private Message
1216 Key Payload for detailed description of how to agree to use
1219 If normal session key is used to protect the message, every
1220 server between the sender client and the receiving client needs
1221 to decrypt the packet and always re-encrypt it with the session
1222 key of the next receiver of the packet. See section Client
1223 To Client in [SILC1].
1225 When specific key is used to protect the message, servers between
1226 the sender and the receiver needs not to decrypt/re-encrypt the
1227 packet. Section 4.8.2 Client To Client in [SILC1] gives example of
1228 this scheme as well.
1230 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE
1231 packet. It must not be sent in any other packet type. Following
1232 diagram represents the Private Message Payload.
1238 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
1239 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1240 | Nickname Length | |
1241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1249 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1253 Figure 11: Private Message Payload
1257 o Nickname Length (2 bytes) - Indicates the length of the
1258 Nickname field, not including any other field.
1260 o Nickname (variable length) - Nickname of the sender of the
1261 private message. This should not be trusted as a definite
1262 sender of the private message. The SILC Packet Header in
1263 the packet indicates the true sender of the packet and
1264 client should verify that the nickname sent here belongs
1265 to the Client ID in the SILC Packet Header. This nickname
1266 is merely provided to be displayed by the client.
1268 o Message Data (variable length) - The actual message to
1269 the client. Rest of the packet is reserved for the message
1275 2.3.11 Private Message Key Payload
1277 This payload is used to send key from client to another client that
1278 is going to be used to protect the private messages between these
1279 two clients. If this payload is not sent normal session key
1280 established by the SILC Key Exchange Protocol is used to protect
1281 the private messages.
1283 This payload may only be sent by client to another client. Server
1284 must not send this payload at any time. After sending this payload
1285 the sender of private messages must set the Private Message Key
1286 flag into SILC Packet Header.
1288 The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
1289 packet. It must not be sent in any other packet type. Following
1290 diagram represents the Private Message Key Payload.
1296 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
1297 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1298 | Private Message Key Length | |
1299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1301 ~ Private Message Key ~
1303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1307 Figure 12: Private Message Key Payload
1313 o Private Message Key Length (2 bytes) - Indicates the length
1314 of the Private Message Key field in the payload, not including
1317 o Private Message Key (variable length) - The actual private
1318 message key material. This key is used as such as key material
1319 for encryption function.
1324 2.3.12 Command Payload
1326 Command Payload is used to send SILC commands from client to server.
1327 Also server may send commands to other servers. Following diagram
1328 represents the Command Payload.
1334 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
1335 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1336 | Payload Length | SILC Command | Arguments Num |
1337 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1343 Figure 13: Command Payload
1347 o Payload Length (2 bytes) - Length of the entire command
1348 payload including any command argument payloads associated
1351 o SILC Command (1 byte) - SILC Command identifier. This must
1352 be set to non-zero value. If zero (0) value is found in this
1353 field the packet must be discarded.
1355 o Arguments Num (1 byte) - Indicates the number of arguments
1356 associated with the command. If there are no arguments this
1357 field is set to zero (0). The arguments must follow the
1360 o Command Unifier (2 bytes) - Unifies this command at the
1361 sender's end. The entity who replies to this command must
1362 set the value found from this field into the Command Payload
1363 used to send the reply to the sender. This way the sender
1364 can identify which command reply belongs to which originally
1365 sent command. What this field includes is implementation
1366 issue but it is recommended that wrapping counter value is
1370 See [SILC1] for detailed description of different SILC commands,
1371 their arguments and their reply messages.
1375 2.3.12.1 Command Argument Payload
1377 Command Argument Payload is used to set arguments for SILC commands.
1378 Number of arguments associated with a command are indicated by the
1379 Command Payload in the Arguments Num field. Command argument
1380 payloads may only be used with a command payload and they must
1381 always reside right after the command payload. Incorrect amount of
1382 argument payloads must cause rejection of the packet. Following
1383 diagram represents the Command Argument Payload.
1389 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
1390 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1391 | Argument Num | Argument Type | Payload Length |
1392 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1396 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1400 Figure 14: Command Argument Payload
1404 o Argument Num (1 byte) - Indicates the number of this argument.
1405 For first argument this is set to 1, for second argument this
1406 is set to 2, and so forth. If incorrect value is found
1407 in this field the packet must be discarded. Value is
1408 incorrect if it is zero (0) or, for example, a third argument
1409 does not include value 3.
1411 o Argument Type (1 byte) - Indicates the type of the argument.
1412 Every command specify a number for each argument that maybe
1413 associated with the command. By using this number the receiver
1414 of the packet knows what type of argument this is. The numbers
1415 are command specific and has been defined in section SILC
1416 Commands in [SILC1]. This field makes it possible to send
1417 arguments in free order as this field is used to identify
1418 the specific type of the argument.
1420 o Payload Length (2 bytes) - Length of the argument payload data
1421 area not including the length of any other fields in the
1424 o Argument Data (variable length) - Argument data.
1429 2.3.13 Command Reply Payload
1431 Command Reply Payload is used to send replies to the commands. The
1432 Command Reply Payload is identical to the Command Payload thus see the
1433 upper sections for Command Payload and for Command Argument Payload
1434 specifications. Command Reply message uses the Command Argument Payload
1437 The entity who sends the reply packet must set the Command Unifier
1438 field in the reply packet's Command Payload to the value it received
1439 in the original command packet.
1441 See SILC Commands in [SILC1] for detailed description of different
1442 SILC commands, their arguments and their reply messages.
1446 2.3.14 Connection Auth Request Payload
1448 Client may send this payload to server to request the authentication
1449 method that must be used in authentication protocol. If client knows
1450 this information beforehand this payload is not necessary to be sent.
1451 Server performing authentication with another server may also send
1452 this payload to request the authentication method. If the connecting
1453 server already knows this information this payload is not necessary
1456 Server receiving this request must reply with same payload sending
1457 the mandatory authentication method. Algorithms that may be required
1458 to be used by the authentication method are the ones already
1459 established by the SILC Key Exchange protocol. See section Key
1460 Exchange Start Payload in [SILC3] for detailed information.
1462 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
1463 packet. It must not be sent in any other packet type. Following
1464 diagram represents the Connection Auth Request Payload.
1470 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
1471 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1472 | Connection Type | Authentication Method |
1473 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1477 Figure 15: Connection Auth Request Payload
1481 o Connection Type (2 bytes) - Indicates the type of the ID.
1482 Following connection types are defined:
1488 If any other type is found in this field the packet must be
1489 discarded and the authentication must be failed.
1491 o Authentication Method (2 bytes) - Indicates the authentication
1492 method to be used in the authentication protocol. Following
1493 authentication methods are defined:
1498 1 password (mandatory)
1499 2 public key (mandatory)
1501 If any other type is found in this field the packet must be
1502 discarded and the authentication must be failed. If this
1503 payload is sent as request to receive the mandatory
1504 authentication method this field must be set to zero (0),
1505 indicating that receiver should send the mandatory
1506 authentication method. The receiver sending this payload
1507 to the requesting party, may also set this field to zero (0)
1508 to indicate that authentication is not required. In this
1509 case authentication protocol still must be started but
1510 server is most likely to respond with SILC_PACKET_SUCCESS
1516 2.3.15 New ID Payload
1518 New ID Payload is a multipurpose payload. It is used to send newly
1519 created ID's from clients and servers. When client connects to server
1520 and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
1521 packet, server replies with this packet by sending the created ID for
1522 the client. Server always creates the ID for the client.
1524 This payload is also used when server tells its router that new client
1525 has registered to the SILC network. In this case the server sends
1526 the Client ID of the client to the router. Similiary when router
1527 distributes information to other routers about the client in the SILC
1528 network this payload is used.
1530 Also, when server connects to router, router uses this payload to inform
1531 other routers about new server in the SILC network. However, every
1532 server (or router) creates their own ID's thus the ID distributed by
1533 this payload is not created by the distributor in this case. Servers
1534 create their own ID's. Server registers itself to the network by sending
1535 SILC_PACKET_NEW_SERVER to the router it connected to. The case is same
1536 when router connects to another router.
1538 Hence, this payload is very important and used every time when some
1539 new entity is registered to the SILC network. Client never sends this
1540 payload. Both client and server (and router) may receive this payload.
1542 The payload may only be sent with SILC_PACKET_NEW_ID packet. It must
1543 not be sent in any other packet type. Following diagram represents the
1550 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
1551 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1552 | ID Type | ID Length |
1553 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1557 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1561 Figure 16: New ID Payload
1565 o ID Type (2 bytes) - Indicates the type of the ID. See
1566 section 2.4 SILC ID Types for list of defined ID types.
1568 o ID Length (2 bytes) - Length of the ID Data area not
1569 including the length of any other fields in the payload.
1571 o ID Data (variable length) - The actual ID data.
1577 2.3.16 New ID List Payload
1579 New ID List Payload is used to distribute list of ID's usually from
1580 server to router but also from router to other routers in the network.
1581 This payload is used, for example, when server is connected to router
1582 and the server wants to distribute all of its locally connected clients
1583 and locally created channels to the router. It is convenient in this
1584 case to use this payload instead of sending all the information one
1585 by one using New ID Payload.
1587 There is no specific payload for this packet type. The packet type
1588 uses same payload as described in previous section. To form a list
1589 several payloads is put in the packet each after each. The payload
1590 is variable in length but can be calculated by calculating the ID
1591 Type field, Length field and the ID Data fields together. This forms
1592 one New ID Payload in the list.
1594 The list of payloads may only be sent with SILC_PACKET_NEW_ID_LIST
1595 packet. They must not be sent in any other packet type.
1599 2.3.17 New Client Payload
1601 When client is connected to the server, keys has been exchanged and
1602 connection has been authenticated client must register itself to the
1603 server. Clients first packet after key exchange and authentication
1604 protocols must be SILC_PACKET_NEW_CLIENT. This payload tells server all
1605 the relevant information about the connected user. Server creates a new
1606 client ID for the client when received this payload and sends it to the
1607 client in New ID Payload.
1609 This payload sends username and real name of the user on the remote host
1610 which is connected to the SILC server with SILC client. The server
1611 creates the client ID according the information sent in this payload.
1612 The nickname of the user becomes the username sent in this payload.
1613 However, client should call NICK command after sending this payload to
1614 set the real nickname of the user which is then used to create new
1617 The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
1618 must not be sent in any other packet type. Following diagram represents
1619 the New Client Payload.
1625 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
1626 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1627 | Username Length | |
1628 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1632 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1633 | Real Name Length | |
1634 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1638 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1642 Figure 17: New Client Payload
1646 o Username Length (2 bytes) - Length of the username.
1648 o Username (variable length) - The username of the user on
1649 the host where connecting to the SILC server.
1651 o Real Name Length (2 bytes) - Length of the Real Name.
1653 o Real Name (variable length) - The real name of the user
1654 on the host where connecting to the SILC server.
1659 2.3.18 New Server Payload
1661 This payload is sent by server when it has completed successfully both
1662 key exchange and connection authentication protocols. The server
1663 uses this payload to register itself to the SILC network. The
1664 first packet after these key exchange and authentication protocols
1665 is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
1666 of the server that it has created by itself. It also includes a
1667 name of the server that is associated to the Server ID.
1669 The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
1670 must not be sent in any other packet type. Following diagram represents
1671 the New Server Payload.
1677 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
1678 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1679 | Server ID Length | |
1680 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1685 | Server Name Length | |
1686 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1694 Figure 18: New Server Payload
1698 o Server ID Length (2 bytes) - Length of the ID Data area not
1699 including the length of any other fields in the payload.
1701 o Server ID Data (variable length) - The actual Server ID
1704 o Server Name Length (2 bytes) - Length of the server name.
1706 o Server Name (variable length) - The server name.
1711 2.3.19 New Channel Payload
1713 Information about newly created channel is broadcasted to all routers
1714 in the SILC network by sending this packet payload. Channels are
1715 created by router of the cell. Server never creates channels unless
1716 it is a standalone server and it does not have router connection,
1717 in this case server acts as router. Normal server forwards JOIN command
1718 to the router (after it has received JOIN command from client) which
1719 then processes the command and creates the channel. Client never sends
1722 The payload may only be sent with SILC_PACKET_NEW_CHANNEL packet.
1723 It must not be sent in any other packet type. Following diagram
1724 represents the New Channel Payload.
1730 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
1731 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1732 | Channel Name Length | |
1733 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1737 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1738 | Channel ID Length | |
1739 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1743 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1747 Figure 19: New Channel Payload
1752 o Channel Name Length (2 bytes) - Length of the channel name.
1754 o Channel Name (variable length) - The name of the created
1757 o Channel ID Length (2 bytes) - Length of the Channel ID.
1759 o Channel ID (variable length) - The created Channel ID.
1764 2.3.20 New Channel User Payload
1766 When client (user) joins to a channel, server must notify routers
1767 about the new user on the channel. Normal server sends this packet
1768 payload to its router which then broadcasts the packet further.
1769 Router sends this packet always to its primary router. Client must
1770 not send this packet payload. The mode of the user is NONE after
1771 user has joined to the channel.
1773 The payload may only be sent with SILC_PACKET_NEW_CHANNEL_USER
1774 packet. It must not be sent in any other packet type. Following
1775 diagram represents the New Channel User Payload.
1781 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
1782 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1783 | Channel ID Length | |
1784 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1788 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1789 | Client ID Length | |
1790 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1794 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1798 Figure 20: New Channel User Payload
1802 o Channel ID Length (2 bytes) - Length of the Channel ID.
1804 o Channel ID (variable length) - The Channel ID of the channel
1805 to which the client has joined.
1807 o Client ID Length (2 bytes) - Length of the Client ID.
1809 o Client ID (variable length) - The Client ID of the client
1810 who has joined the channel.
1815 2.3.21 New Channel List Payload
1817 This payload is used to distribute list of new channels from server
1818 to routers. It might convenient to send list of new channels when
1819 existing server connects to router, instead of sending them one
1822 There is no specific payload for this packet type. The packet type
1823 uses same payload as described in 2.3.19 New Channel Payload. To form
1824 a list several payloads is put in the packet each after each. The
1825 payload is variable in length but can be calculated by calculating
1826 the length of the fields together. This forms one New Channel Payload
1829 The list of payloads may only be sent with SILC_PACKET_NEW_CHANNEL_LIST
1830 packet. They must not be sent in any other packet type.
1834 2.3.22 New Channel User List Payload
1836 This payload is used to distribute list of channel users on specific
1837 channel from server to routers. It might convenient to send list of
1838 channel users when existing server connects to router, instead of
1839 sending them one by one.
1841 There is no specific payload for this packet type. The packet type
1842 uses same payload as described in 2.3.20 New Channel User Payload.
1843 To form a list several payloads is put in the packet each after each.
1844 The payload is variable in length but can be calculated by calculating
1845 the length of the fields together. This forms one New Channel User
1846 Payload in the list.
1848 The list of payloads may only be sent with packet
1849 SILC_PACKET_NEW_CHANNEL_USER_LIST. They must not be sent in any other
1854 2.3.23 Replace ID Payload
1856 This payload is used to replace old ID with new ID sent in the payload.
1857 When ID changes for some entity and the new ID is wanted to replace the
1858 old one this payload must be used. Client cannot send or receive this
1859 payload. Normal server and router server may send and receive this
1860 payload. After this packet has been sent the old ID must not be used
1863 The payload may only be sent with SILC_PACKET_REPLACE_ID packet. It must
1864 not be sent in any other packet type. Following diagram represents the
1865 Replace Payload Payload.
1878 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
1879 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1880 | Old ID Type | Old ID Length |
1881 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1885 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1886 | New ID Type | New ID Length |
1887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1891 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1895 Figure 21: Replace ID Payload
1899 o Old ID Type (2 bytes) - Indicates the type of the old ID. See
1900 section 2.4 SILC ID Types for list of defined ID types.
1902 o Old ID Length (2 bytes) - Length of the old ID Data area not
1903 including the length of any other fields in the payload.
1905 o Old ID Data (variable length) - The actual old ID data.
1907 o New ID Type (2 bytes) - Indicates the type of the new ID. See
1908 section 2.4 SILC ID Types for list of defined ID types.
1910 o New ID Length (2 bytes) - Length of the new ID Data area not
1911 including the length of any other fields in the payload.
1913 o New ID Data (variable length) - The actual new ID data.
1918 2.3.24 Remove ID Payload
1920 Remove ID payload is used to remove ID from SILC network. This is used
1921 for example when client exits SILC network. The server must in this
1922 case send this payload to notify that this ID is not valid anymore.
1923 After this has been send the old ID must not be used anymore. Client
1924 must not send this payload.
1926 The payload may only be sent with SILC_PACKET_REMOVE_ID packet. It must
1927 not be sent in any other packet type. Following diagram represents the
1928 Remove Payload Payload.
1934 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
1935 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1936 | ID Type | ID Length |
1937 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1941 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1945 Figure 22: Remove ID Payload
1949 o ID Type (2 bytes) - Indicates the type of the ID to be
1950 removed. See section 2.4 SILC ID Types for list of defined
1953 o ID Length (2 bytes) - Length of the ID Data area not including
1954 the length of any other fields in the payload.
1956 o ID Data (variable length) - The actual ID data to be removed.
1961 2.3.25 Remove Channel User Payload
1963 Remove Channel User payload is used to remove a user from a channel network
1964 wide. This is used by routers to notify other routers that a user has
1965 leaved a channel. As routers keep information about users on channels a
1966 user leaving channel must be removed from all routers. Normal server may
1967 send this payload as well. Client must not send this payload.
1969 The payload may only be sent with SILC_PACKET_REMOVE_CHANNEL USER packet.
1970 It must not be sent in any other packet type. Following diagram
1971 represents the Remove Payload Payload.
1977 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
1978 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1979 | Client ID Length | |
1980 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1984 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1985 | Channel ID Length | |
1986 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
1990 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1994 Figure 23: Remove Channel User Payload
1998 o Client ID Length (2 bytes) - Length of the Client ID Data area
1999 not including the length of any other fields in the payload.
2001 o Client ID Data (variable length) - The Client ID of the user
2002 that has left the channel.
2004 o Channel ID Length (2 bytes) - Length of the Channel ID Data area
2005 not including the length of any other fields in the payload.
2007 o Channel ID Data (variable length) - The Channel ID of the channel
2015 ID's are extensively used in the SILC network to associate different
2016 entities. Following ID's has been defined to be used in the SILC
2022 When ever specific ID cannot be used this is used.
2026 Server ID to associate servers. See the format of
2031 Client ID to associate clients. See the format of
2036 Channel ID to associate channels. See the format of
2042 2.5 Packet Encryption And Decryption
2044 SILC packets are encrypted almost entirely. Only small part of SILC
2045 header is not encrypted as described in section 5.2 SILC Packet Header.
2046 The SILC Packet header is the first part of a packet to be encrypted
2047 and it is always encrypted with the key of the next receiver of the
2048 packet. The data payload area of the packet is always entirely
2049 encrypted and it is usually encrypted with the next receiver's key.
2050 However, there are some special packet types and packet payloads
2051 that require special encryption process. These special cases are
2052 described in the next sections. First is described the normal packet
2057 2.5.1 Normal Packet Encryption And Decryption
2059 Normal SILC packets are encrypted with the session key of the next
2060 receiver of the packet. The entire SILC Packet header and the packet
2061 data payload is is also encrypted with the same key. Padding of the
2062 packet is also encrypted always with the session key, also in special
2063 cases. Computed MAC of the packet must not be encrypted.
2065 Decryption process in these cases are straightforward. The receiver
2066 of the packet must first decrypt the SILC Packet header, or some parts
2067 of it, usually first 16 bytes of it. Then the receiver checks the
2068 packet type from the decrypted part of the header and can determine
2069 how the rest of the packet must be decrypted. If the packet type is
2070 any of the special cases described in following sections the packet
2071 decryption is special. If the packet type is not among those special
2072 packet types rest of the packet may be decrypted with the same key.
2074 Also, note that two bytes of the SILC Packet header are not encrypted
2075 thus it must be noticed in the decryption process by starting the
2076 decryption from the second byte of the header. This sets some rules
2077 to padding generation as well, see the section 2.7 Packet Padding
2080 With out a doubt, this sort of decryption processing causes some
2081 overhead to packet decryption, but never the less, is required.
2085 2.5.2 Channel Message Encryption And Decryption
2087 Channel Messages (Channel Message Payload) are always encrypted with
2088 the channel specific key. However, the SILC Packet header is not
2089 encrypted with that key. As in normal case, the header is encrypted
2090 with the key of the next receiver of the packet, who ever that might
2091 be. Note that in this case the encrypted data area is not touched
2092 at all; it must not be re-encrypted with the session key.
2094 Receiver of a channel message, who ever that is, is required to decrypt
2095 the SILC Packet header to be able to even recognize the packet to be as
2096 channel message. This is same procedure as for normal SILC packets.
2097 As the receiver founds the packet to be channel message, rest of the
2098 packet processing is special. Rest of the SILC Packet header is
2099 decrypted with the same session key along with the padding of the
2100 packet. After that the packet is protected with the channel specific
2101 key and hence can be decrypted only if the receiver is the client on
2102 the channel. See section 2.7 Packet Padding Generation for more
2103 information about padding on special packets.
2105 If the receiver of the channel message is router who is routing the
2106 message to another router then it must decrypt the Channel Message
2107 payload. Between routers (that is, between cells) channel messages
2108 are protected with session keys shared between the routers. This
2109 causes another special packet processing for channel messages. If
2110 the channel message is received from another router then the entire
2111 packet, including Channel Message payload, is encrypted with the
2112 session key shared between the routers. In this case the packet
2113 decryption process is as with normal SILC packets. Hence, if the
2114 router is sending channel message to another router the Channel
2115 Message payload must have been decrypted and must be re-encrypted
2116 with the session key shared between the another router. In this
2117 case the packet encryption is as with any normal SILC packet.
2119 It must be noted that this is only when the channel messages are sent
2120 from router to another router. In all other cases the channel
2121 message encryption and decryption is as described above. This
2122 different processing of channel messages with router to router
2123 connection is because channel keys are cell specific. All cells has
2124 their own channel keys thus the channel message traveling from one
2125 cell to another must be protected as it would be any normal SILC
2130 2.5.3 Private Message Encryption And Decryption
2132 By default, private message in SILC are protected by session keys.
2133 In this case the private message encryption and decryption process is
2134 equivalent to normal packet encryption and decryption.
2136 However, private messages can be protected with private message key
2137 which causes the packet to be special packet. The procedure in this
2138 case is very much alike to channel packets. The actual private message
2139 is encrypted with the private message key and other parts of the
2140 packet is encrypted with the session key. See 2.7 Packet Padding
2141 Generation for more information about padding on special packets.
2143 The difference from channel message processing is that server or router
2144 en route never decrypts the actual private message, as it does not
2145 have the key to do that. Thus, when sending packets between router
2146 the processing is same as in any other case as well; the packet's header
2147 and padding is protected by the session key and the data area is not
2150 The true receiver of the private message, client, that is, is able
2151 to decrypt the private message as it shares the key with the sender
2156 2.6 Packet MAC Generation
2158 Data integrity of a packet is protected by including a message
2159 authentication code (MAC) at the end of the packet. The MAC is computed
2160 from shared secret MAC key, that is established by the SILC Key Exchange
2161 protocol, and from the original contents of the packet. The MAC is
2162 always computed before the packet is encrypted, although after it is
2163 compressed if compression is used.
2165 The MAC is computed from entire packet. Every bit of data in the packet,
2166 including SILC Packet Header is used in the MAC computing. This way
2167 the entire packet becomes authenticated.
2169 If the packet is special packet MAC is computed from the entire packet
2170 but part of the packet may be encrypted before the MAC is computed.
2171 This is case, for example, with channel messages where the message data
2172 is encrypted with key that server may not now. In this case the MAC
2173 has been computed from the encrypted data.
2175 See [SILC1] for defined and allowed MAC algorithms.
2179 2.7 Packet Padding Generation
2181 Padding is needed in the packet because the packet is encrypted. It
2182 must always be multiple by eight (8) or multiple by the size of the
2183 cipher's block size, which ever is larger. The padding is always
2186 For normal packets the padding is added after the SILC Packet Header
2187 and between the Data Payload area. The padding for normal packets
2188 are calculated as follows:
2191 padding length = 16 - ((packet length - 2) % 16)
2194 The 16 is the maximum padding allowed in SILC packet. Two (2) is
2195 subtracted from the true length of the packet because two (2) bytes
2196 is not encrypted in SILC Packet Header, see section 2.2 SILC Packet
2197 Header. Those two bytes that are not encrypted must not be calculated
2198 to the padding length.
2200 For special packets the padding calculation may be different as special
2201 packets may be encrypted differently. In these cases the encrypted
2202 data area must already be multiple by the block size thus in this case
2203 the padding is calculated only for SILC Packet Header, not for any
2204 other area of the packet. The same algorithm works in this case as
2205 well, except that the `packet length' is now the SILC Packet Header
2206 length. In this case, as well, two (2) is subtracted from the
2209 The padding must be random data, preferably, generated by
2210 cryptographically strong random number generator.
2214 2.8 Packet Compression
2216 SILC Packets may be compressed. In this case the data payload area
2217 is compressed and all other areas of the packet must remain as they
2218 are. After compression is performed for the data area, the length
2219 field of Packet Header must be set to the compressed length of the
2222 The compression must always be applied before encryption. When
2223 the packet is received and decrypted the data area must be decompressed.
2224 Note that the true sender of the packet must apply the compression and
2225 the true receiver of the packet must apply the decompression. Any
2226 server or router en route must not decompress the packet.
2232 The sender of the packet must assemble the SILC Packet Header with
2233 correct values. It must set the Source ID of the header as its own
2234 ID, unless it is forwarding the packet. It must also set the Destination
2235 ID of the header to the true destination. If the destination is client
2236 it will be Client ID, if it is server it will be Server ID and if it is
2237 channel it will be Channel ID.
2239 If the sender wants to compress the packet it must apply the
2240 compression now. Sender must also compute the padding as described
2241 in above sections. Then sender must compute the MAC of the packet.
2243 Then sender encrypts the packet as has been described in above
2244 sections according whether the packet is normal packet or special
2245 packet. The computed MAC must not be encrypted.
2249 2.10 Packet Reception
2251 On packet reception the receiver must check that all fields in the
2252 SILC Packet Header are valid sain. It must check the flags of the
2253 header and act accordingly. It must also check the MAC of the packet
2254 and if it is to be failed the packet must be discarded. Also if the
2255 header of the packet includes any bad fields the packet must be
2258 See above sections on the decryption process of the received packet.
2260 The receiver must also check that the ID's in the header are valid
2261 ID's. Unsupported ID types or malformed ID's must cause packet
2262 rejection. The padding on the reception is always ignored.
2264 The receiver must also check the packet type and start parsing the
2265 packet according to the type. However, note the above sections on
2266 special packet types and their parsing.
2272 Routers are the primary entities in the SILC network that takes care
2273 of packet routing. However, normal servers routes packets as well, for
2274 example, when they are routing channel message to the local clients.
2275 Routing is quite simple as every packet tells the true origin and the
2276 true destination of the packet.
2278 It is still recommended for routers that has several routing connections
2279 to create route cache for those destinations that has faster route than
2280 the router's primary route. This information is available for the router
2281 when other router connects to the router. The connecting party then
2282 sends all of its locally connected clients, server and channels. These
2283 informations helps to create the route cache. Also, when new channels
2284 are created to a cell its information is broadcasted to all routers
2285 in the network. Channel ID's are based on router's ID thus it is easy
2286 to create route cache based on these informations. If faster route for
2287 destination does not exist in router's route cache the packet must be
2288 routed to the primary route (default route).
2290 For server who receives a packet to be routed to its locally connected
2291 client the server must check whether the particular packet type is
2292 allowed to be routed to the client. Not all packets may be sent by
2293 some odd entity to client that is indirectly connected to the sender.
2294 See section 2.3 SILC Packet Types and paragraph about indirectly connected
2295 entities and sending packets to them. The section mentions the packets
2296 that may be sent to indirectly connected entities. It is clear that some
2297 server cannot send, for example, disconnect packet to client that is not
2298 directly connected to the server.
2302 2.12 Packet Forwarding
2304 Currently SILC command packets may be forwarded from one entity to another.
2305 Any other packet currently cannot be forwarded but support for more packet
2306 types may be added if needed. Forwarding is usually used by server to
2307 forward some command request coming from client to the router as the server
2308 may be incapable to handle the request. Forwarding may be only one hop
2309 long; the receiver of the packet with Forwarded flag set in the SILC
2310 Packet header must not forward the packet any further.
2312 The normal scenario is that client sends JOIN command to the server which
2313 is not able to create the channel as there are no local clients on the
2314 channel. Channels are created always by the router of the cell thus the
2315 packet must be forwarded to the router. The server forwards the original
2316 packet coming from client to the router after it has set the Forwarded
2317 flag to the SILC Packet header.
2319 Router receiving the packet knows that the packet has to be processed
2320 specially by checking the flags and the Forwarded flag in the SILC Packet
2321 header. After router has joined the client to the channel (and perhaps
2322 created a new channel) it sends normal command reply packet to the
2323 client. However, as the router doesn't have direct connection to the
2324 client the packet is sent through the server. Server detects that
2325 the command reply packet is destined to the client and sends it to
2330 2.13 Packet Broadcasting
2332 SILC packets may be broadcasted in SILC network. However, only router
2333 server may send or receive broadcast packets. Client and normal server
2334 must not send broadcast packets and they must ignore broadcast packets
2335 if they receive them. Broadcast packets are sent by setting Broadcast
2336 flag to the SILC packet header.
2338 Broadcasting packets means that the packet is sent to all routers in
2339 the SILC network, except to the router that sent the packet. The router
2340 receiving broadcast packet must send the packet to its primary route.
2341 The fact that SILC routers may have several router connections may
2342 cause problems, such as race conditions inside the SILC network, if
2343 care is not taken when broadcasting packets. Router must not send
2344 the broadcast packet to any other route except to its primary route.
2346 If the primary route of the router is the original sender of the packet
2347 the packet must not be sent to the primary route. This may happen
2348 if router has several router connections and some other router uses
2349 the router as its primary route.
2351 Routers use broadcast packets to broadcast for example information
2352 about newly registered clients, servers, channels etc. so that all the
2353 routers may keep these informations up to date.
2357 2.14 Packet Tunneling
2359 Tunneling is a feature that is available in SILC protocol. Tunneling
2360 means that extra SILC Packet Header is applied to the original packet
2361 and thus hiding the original packet entirely. There can be some
2362 interesting applications using tunneling, such as, using ID's based on
2363 private network IP addresses inside in the tunneled packet. This can
2364 open many interesting features relating to connecting to private network
2365 from the Internet with SILC and many more. However, this feature is
2366 optional currently in SILC as there does not exist thorough analysis of
2367 this feature. It is with out a doubt that there will be many more
2368 applications that has not yet been discovered. Thus, it is left
2369 to Internet Community to investigate the use of tunneling in SILC
2370 protocol. This document is updated according those investigations
2371 and additional documents on the issue may be written.
2375 3 Security Considerations
2377 Security is central to the design of this protocol, and these security
2378 considerations permeate the specification.
2384 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
2385 Protocol Specification", Internet Draft, June 2000.
2387 [SILC3] Riikonen, P., "SILC Key Exchange and Authentication
2388 Protocols", Internet Draft, June 2000.
2390 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
2393 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
2396 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
2399 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
2402 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
2403 Infrastructure, Certificate and CRL Profile", RFC 2459,
2406 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
2407 John Wiley & Sons, New York, NY, 1996.
2409 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
2412 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
2413 RFC 2412, November 1998.
2415 [ISAKMP] Maughan D., et al, "Internet Security Association and
2416 Key Management Protocol (ISAKMP)", RFC 2408, November
2419 [IKE] Harkins D., and Carrel D., "The Internet Key Exhange
2420 (IKE)", RFC 2409, November 1998.
2422 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
2423 Authentication", RFC 2104, February 1997.
2435 EMail: priikone@poseidon.pspt.fi
2437 This Internet-Draft expires 28 Jan 2001
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