--- /dev/null
+.pl 10.0i
+.po 0
+.ll 7.2i
+.lt 7.2i
+.nr LL 7.2i
+.nr LT 7.2i
+.ds LF Riikonen
+.ds RF FORMFEED[Page %]
+.ds CF
+.ds LH Internet Draft
+.ds RH XXX
+.ds CH
+.na
+.hy 0
+.in 0
+.nf
+Network Working Group P. Riikonen
+Internet-Draft
+draft-riikonen-silc-pp-08.txt XXX
+Expires: XXX
+
+.in 3
+
+.ce 2
+SILC Packet Protocol
+<draft-riikonen-silc-pp-09.txt>
+
+.ti 0
+Status of this Memo
+
+This document is an Internet-Draft and is in full conformance with
+all provisions of Section 10 of RFC 2026. Internet-Drafts are
+working documents of the Internet Engineering Task Force (IETF), its
+areas, and its working groups. Note that other groups may also
+distribute working documents as Internet-Drafts.
+
+Internet-Drafts are draft documents valid for a maximum of six months
+and may be updated, replaced, or obsoleted by other documents at any
+time. It is inappropriate to use Internet-Drafts as reference
+material or to cite them other than as "work in progress."
+
+The list of current Internet-Drafts can be accessed at
+http://www.ietf.org/ietf/1id-abstracts.txt
+
+The list of Internet-Draft Shadow Directories can be accessed at
+http://www.ietf.org/shadow.html
+
+The distribution of this memo is unlimited.
+
+
+.ti 0
+Abstract
+
+This memo describes a Packet Protocol used in the Secure Internet Live
+Conferencing (SILC) protocol, specified in the Secure Internet Live
+Conferencing, Protocol Specification [SILC1]. This protocol describes
+the packet types and packet payloads which defines the contents of the
+packets. The protocol provides secure binary packet protocol that
+assures that the contents of the packets are secured and authenticated.
+
+
+
+
+
+
+
+
+
+.ti 0
+Table of Contents
+
+.nf
+1 Introduction .................................................. 3
+ 1.1 Requirements Terminology .................................. 4
+2 SILC Packet Protocol .......................................... 4
+ 2.1 SILC Packet ............................................... 4
+ 2.2 SILC Packet Header ........................................ 5
+ 2.3 SILC Packet Types ......................................... 7
+ 2.3.1 SILC Packet Payloads ................................ 15
+ 2.3.2 Generic payloads .................................... 15
+ 2.3.2.1 ID Payload .................................. 15
+ 2.3.2.2 Argument Payload ............................ 16
+ 2.3.2.3 Argument List Payload ....................... 17
+ 2.3.2.4 Channel Payload ............................. 18
+ 2.3.2.5 Public Key Payload .......................... 19
+ 2.3.2.6 Message Payload ............................. 19
+ 2.3.3 Disconnect Payload .................................. 23
+ 2.3.4 Success Payload ..................................... 23
+ 2.3.5 Failure Payload ..................................... 24
+ 2.3.6 Reject Payload ...................................... 25
+ 2.3.7 Notify Payload ...................................... 25
+ 2.3.8 Error Payload ....................................... 34
+ 2.3.9 Channel Message Payload ............................. 35
+ 2.3.10 Channel Key Payload ................................ 35
+ 2.3.11 Private Message Payload ............................ 37
+ 2.3.12 Private Message Key Payload ........................ 37
+ 2.3.13 Command Payload .................................... 39
+ 2.3.14 Command Reply Payload .............................. 40
+ 2.3.15 Connection Auth Request Payload .................... 40
+ 2.3.16 New ID Payload ..................................... 42
+ 2.3.17 New Client Payload ................................. 42
+ 2.3.18 New Server Payload ................................. 43
+ 2.3.19 New Channel Payload ................................ 44
+ 2.3.20 Key Agreement Payload .............................. 45
+ 2.3.21 Resume Router Payload .............................. 46
+ 2.3.22 File Transfer Payload .............................. 47
+ 2.3.23 Resume Client Payload .............................. 48
+ 2.4 SILC ID Types ............................................. 49
+ 2.5 Packet Encryption And Decryption .......................... 49
+ 2.5.1 Normal Packet Encryption And Decryption ............. 50
+ 2.5.2 Channel Message Encryption And Decryption ........... 50
+ 2.5.3 Private Message Encryption And Decryption ........... 51
+ 2.6 Packet MAC Generation ..................................... 52
+ 2.7 Packet Padding Generation ................................. 53
+ 2.8 Packet Compression ........................................ 53
+ 2.9 Packet Sending ............................................ 54
+ 2.10 Packet Reception ......................................... 54
+ 2.11 Packet Routing ........................................... 54
+ 2.12 Packet Broadcasting ...................................... 56
+3 Security Considerations ....................................... 56
+4 References .................................................... 56
+5 Author's Address .............................................. 58
+6 Full Copyright Statement ...................................... 58
+
+.ti 0
+List of Figures
+
+.nf
+Figure 1: Typical SILC Packet
+Figure 2: SILC Packet Header
+Figure 3: ID Payload
+Figure 4: Argument Payload
+Figure 5: Argument List Payload
+Figure 6: Channel Payload
+Figure 7: Public Key Payload
+Figure 8: Message Payload
+Figure 9: Disconnect Payload
+Figure 10: Success Payload
+Figure 11: Failure Payload
+Figure 12: Reject Payload
+Figure 13: Notify Payload
+Figure 14: Error Payload
+Figure 15: Channel Key Payload
+Figure 16: Private Message Key Payload
+Figure 17: Command Payload
+Figure 18: Connection Auth Request Payload
+Figure 19: New Client Payload
+Figure 20: New Server Payload
+Figure 21: Key Agreement Payload
+Figure 22: Resume Router Payload
+Figure 23: File Transfer Payload
+Figure 24: Resume Client Payload
+
+
+.ti 0
+1. Introduction
+
+This document describes a Packet Protocol used in the Secure Internet
+Live Conferencing (SILC) protocol specified in the Secure Internet Live
+Conferencing, Protocol Specification [SILC1]. This protocol describes
+the packet types and packet payloads which defines the contents of the
+packets. The protocol provides secure binary packet protocol that
+assures that the contents of the packets are secured and authenticated.
+The packet protocol is designed to be compact to avoid unnecessary
+overhead as much as possible. This makes the SILC suitable also in
+environment of low bandwidth requirements such as mobile networks. All
+packet payloads can also be compressed to further reduce the size of
+the packets.
+
+All packets in SILC network are always encrypted and their integrity
+is assured by computed MACs. The protocol defines several packet types
+and packet payloads. Each packet type usually has a specific packet
+payload that actually defines the contents of the packet. Each packet
+also includes a default SILC Packet Header that provides sufficient
+information about the origin and the destination of the packet.
+
+
+.ti 0
+1.1 Requirements Terminology
+
+The keywords MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED,
+MAY, and OPTIONAL, when they appear in this document, are to be
+interpreted as described in [RFC2119].
+
+
+.ti 0
+2 SILC Packet Protocol
+
+.ti 0
+2.1 SILC Packet
+
+SILC packets deliver messages from sender to receiver securely by
+encrypting important fields of the packet. The packet consists of
+default SILC Packet Header, Padding, Packet Payload data, and, packet
+MAC.
+
+The following diagram illustrates typical SILC packet.
+
+.in 5
+.nf
+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+| n bytes | 1 - n bytes | n bytes | n bytes
+| SILC Header | Padding | Data Payload | MAC
+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+.in 3
+
+.ce
+Figure 1: Typical SILC Packet
+
+
+SILC Header is always the first part of the packet and its purpose
+is to provide information about the packet. It provides for example
+the packet type, origin of the packet and the destination of the packet.
+The header is variable in length. See the following section for
+description of SILC Packet header. Packets without SILC header or
+with malformed SILC header MUST be dropped.
+
+Padding follows the packet header. The purpose of the padding is to
+make the packet multiple by eight (8) or by the block size of the
+cipher used in the encryption, which ever is larger. The maximum
+length of padding is currently 128 bytes. The padding is always
+encrypted. The padding is applied always, even if the packet is
+not encrypted. See the section 2.7 Padding Generation for more
+detailed information.
+
+Data payload area follows padding and it is the actual data of the
+packet. The packet data is the packet payloads defined in this
+protocol. The data payload area is always encrypted.
+
+The last part of SILC packet is the packet MAC that assures the
+integrity of the packet. See the section 2.6 Packet MAC Generation
+for more information. If compression is used the compression is
+always applied before encryption.
+
+All fields in all packet payloads are always in MSB (most significant
+byte first) order.
+
+
+.ti 0
+2.2 SILC Packet Header
+
+The SILC packet header is applied to all SILC packets and it is
+variable in length. The purpose of SILC Packet header is to provide
+detailed information about the packet. The receiver of the packet
+uses the packet header to parse the packet and gain other relevant
+parameters of the packet.
+
+The following diagram represents the SILC packet header.
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Payload Length | Flags | Packet Type |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Pad Length | RESERVED | Source ID Len | Dest ID Len |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Src ID Type | |
++-+-+-+-+-+-+-+-+ +
+| |
+~ Source ID ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Dst ID Type | |
++-+-+-+-+-+-+-+-+ +
+| |
+~ Destination ID ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 2: SILC Packet Header
+
+.in 6
+o Payload Length (2 bytes) - Indicates the length of the
+ packet not including the padding of the packet.
+
+o Flags (1 byte) - Indicates flags to be used in packet
+ processing. Several flags may be set by ORing the flags
+ together.
+
+ The following flags are reserved for this field:
+
+
+ No flags 0x00
+
+ In this case the field is ignored.
+
+
+ Private Message Key 0x01
+
+ Indicates that the packet data MUST include private
+ message that is encrypted using private key set by
+ client. Servers does not know this key and cannot
+ handle the packet, but passes it along. See section
+ 2.5.3 Private Message Encryption And Decryption for
+ more information.
+
+
+ List 0x02
+
+ Indicates that the packet consists of list of
+ packet payloads indicated by the Packet Type field.
+ The payloads are added one after the other. Note that
+ there are packet types that must not be used as
+ list. Parsing of list packet is done by calculating
+ the length of each payload and parsing them one by
+ one.
+
+
+ Broadcast 0x04
+
+ Marks the packet to be broadcasted. Client and normal
+ server cannot send broadcast packets. Only router server
+ may send broadcast packet. The router receiving of packet
+ with this flag set MUST send (broadcast) the packet to
+ its primary route. If router has several router connections
+ the packet may be sent only to the primary route. See
+ section 2.12 Packet Broadcasting for description of
+ packet broadcasting.
+
+
+ Compressed 0x08
+
+ Marks that the payload of the packet is compressed.
+ The sender of the packet marks this flag when it
+ compresses the payload, and any server or router
+ en route to the recipient MUST NOT unset this flag.
+ See section 2.8 Packet Compression for description of
+ packet compressing.
+
+.in 3
+
+o Packet Type (1 byte) - Indicates the type of the packet.
+ Receiver uses this field to parse the packet. See section
+ 2.3 SILC Packets for list of defined packet types.
+
+o Pad Length (1 byte) - Indicates the length of the padding
+ applied after the SILC Packet header. Maximum length for
+ padding is 128 bytes.
+
+o RESERVED (1 byte) - Reserved field and must include a
+ zero (0) value.
+
+o Source ID Length (1 byte) - Indicates the length of the
+ Source ID field in the header, not including this or any
+ other fields.
+
+o Destination ID Length (1 byte) - Indicates the length of the
+ Destination ID field in the header, not including this or
+ any other fields.
+
+o Src ID Type (1 byte) - Indicates the type of ID in the
+ Source ID field. See section 2.4 SILC ID Types for
+ defined ID types.
+
+o Source ID (variable length) - The actual source ID that
+ indicates which is the original sender of the packet.
+
+o Dst ID Type (1 byte) - Indicates the type of ID in the
+ Destination ID field. See section 2.4 SILC ID Types for
+ defined ID types.
+
+o Destination ID (variable length) - The actual destination
+ ID that indicates which is the end receiver of the packet.
+
+
+
+.ti 0
+2.3 SILC Packet Types
+
+SILC packet types defines the contents of the packet and it is used by
+the receiver to parse the packet. The packet type is 8 bits in length.
+The range for the packet types are from 0 - 255, where 0 is never sent and
+255 is currently reserved for future extensions and MUST NOT be defined to
+any other purpose. Every SILC specification compliant implementation
+SHOULD support all the following packet types.
+
+The below list of the SILC Packet types includes reference to the packet
+payload as well. Packet payloads are the actual packet data area. Each
+packet type defines packet payload which usually may only be sent with
+the specific packet type.
+
+Most of the packets are packets that must be destined directly to entity
+that is connected to the sender. It is not allowed, for example, for a
+router to send SILC_PACKET_DISCONNECT packet to client that is not
+directly connected to the router. However, there are some special packet
+types that may be destined to some entity that the sender does not have
+direct connection with. These packets are for example private message
+packets, channel message packets, command packets and some other packets
+that may be broadcasted in the SILC network. The following packet
+desription list will define it separately if a packet is allowed to be
+sent to indirectly connected entity. Other packets MUST NOT be sent or
+accepted, if sent, to indirectly connected entities.
+
+Some packets MAY be sent as lists by adding the List flag to the Packet
+Header and constructing multiple packet payloads one after the other.
+When this is allowed it is separately defined in the following list.
+Other packets MUST NOT be sent as list and the List flag MUST NOT be set.
+
+
+List of SILC Packet types are defined as follows.
+
+.in 1
+ 0 SILC_PACKET_NONE
+
+ This type is reserved and it is never sent.
+
+
+ 1 SILC_PACKET_DISCONNECT
+
+ This packet is sent to disconnect the remote end. Reason of
+ the disconnection is sent inside the packet payload.
+
+ Payload of the packet: See section 2.3.3 Disconnect Payload
+
+
+ 2 SILC_PACKET_SUCCESS
+
+ This packet is sent upon successful execution of a protocol.
+ The status of the success is sent in the packet payload.
+
+ Payload of the packet: See section 2.3.4 Success Payload
+
+
+ 3 SILC_PACKET_FAILURE
+
+ This packet is sent upon failure of a protocol. The status
+ of the failure is sent in the packet payload.
+
+ Payload of the packet: See section 2.3.5 Failure Payload
+
+
+ 4 SILC_PACKET_REJECT
+
+ This packet MAY be sent upon rejection of a protocol. The
+ status of the rejection is sent in the packet payload.
+
+ Payload of the packet: See section 2.3.6 Reject Payload
+
+
+ 5 SILC_PACKET_NOTIFY
+
+ This packet is used to send notify message. The packet is
+ usually sent between server and client, but also between
+ server and router. Client MUST NOT send this packet. Server
+ MAY destine this packet to channel as well when the packet is
+ distributed to all clients on the channel. This packet MAY
+ be sent as list.
+
+ Payload of the packet: See section 2.3.7 Notify Payload.
+
+
+ 6 SILC_PACKET_ERROR
+
+ This packet is sent when an error occurs. Server MAY
+ send this packet. Client MUST NOT send this packet. The
+ client MAY entirely ignore the packet, however, server is
+ most likely to take action anyway. This packet MAY be sent
+ to entity that is indirectly connected to the sender.
+
+ Payload of the packet: See section 2.3.8 Error Payload.
+
+
+ 7 SILC_PACKET_CHANNEL_MESSAGE
+
+ This packet is used to send messages to channels. The packet
+ includes Channel ID of the channel and the actual message to
+ the channel. Messages sent to the channel are always protected
+ by channel specific keys. This packet MAY be sent to entity
+ that is indirectly connected to the sender.
+
+ Payload of the packet: See section 2.3.9 Channel Message
+ Payload
+
+
+ 8 SILC_PACKET_CHANNEL_KEY
+
+ This packet is used to distribute new key for particular
+ channel when server generates it. Each channel has their own
+ independent keys that is used to protect the traffic on the
+ channel. It is also possible to use channel private keys that
+ are not server generated. In this case this packet is not used.
+ Client MUST NOT send this packet. This packet MAY be sent to
+ entity that is indirectly connected to the sender.
+
+ Payload of the packet: See section 2.3.10 Channel Key Payload
+
+
+ 9 SILC_PACKET_PRIVATE_MESSAGE
+
+ This packet is used to send private messages from client
+ to another client. By default, private messages are protected
+ by session keys established by normal key exchange protocol.
+ However, it is possible to use specific key to protect private
+ messages. See [SILC1] for private message key generation.
+ This packet MAY be sent to entity that is indirectly connected
+ to the sender.
+
+ Payload of the packet: See section 2.3.11 Private Message
+ Payload
+
+
+ 10 SILC_PACKET_PRIVATE_MESSAGE_KEY
+
+ This packet is OPTIONAL and sender of the packet can indicate
+ that a private message key should be used in private message
+ communication. The actual key material is not sent in this
+ packet but must be either static or pre-shared key. The
+ receiver of the packet is considered to be the responder
+ when processing the static or pre-shared key material as
+ defined in [SILC1] and [SILC3] for private message keys.
+ This packet MAY be sent to entity that is indirectly connected
+ to the sender.
+
+ Payload of the packet: See section 2.3.12 Private Message
+ Key Payload
+
+
+ 11 SILC_PACKET_COMMAND
+
+ This packet is used to send commands from client to server.
+ Server MAY send this packet to other servers as well. All
+ commands are listed in their own section SILC Command Types
+ in [SILC4]. The contents of this packet is command specific.
+ This packet MAY be sent to entity that is indirectly connected
+ to the sender.
+
+ Payload of the packet: See section 2.3.13 Command Payload
+
+
+ 12 SILC_PACKET_COMMAND_REPLY
+
+ This packet is sent as reply to the SILC_PACKET_COMMAND packet.
+ The contents of this packet is command specific. This packet
+ MAY be sent to entity that is indirectly connected to the
+ sender. This packet MAY be sent as list.
+
+ Payload of the packet: See section 2.3.14 Command Reply
+ Payload and section 2.3.13 Command
+ Payload
+
+
+ 13 SILC_PACKET_KEY_EXCHANGE
+
+ This packet is used to start SILC Key Exchange Protocol,
+ described in detail in [SILC3].
+
+ Payload of the packet: Payload of this packet is described
+ in the section SILC Key Exchange
+ Protocol and its sub sections in
+ [SILC3].
+
+
+ 14 SILC_PACKET_KEY_EXCHANGE_1
+
+ This packet is used as part of the SILC Key Exchange Protocol.
+
+ Payload of the packet: Payload of this packet is described
+ in the section SILC Key Exchange
+ Protocol and its sub sections in
+ [SILC3].
+
+
+ 15 SILC_PACKET_KEY_EXCHANGE_2
+
+ This packet is used as part of the SILC Key Exchange Protocol.
+
+ Payload of the packet: Payload of this packet is described
+ in the section SILC Key Exchange
+ Protocol and its sub sections in
+ [SILC3].
+
+
+ 16 SILC_PACKET_CONNECTION_AUTH_REQUEST
+
+ This packet is used to request an authentication method to
+ be used in the SILC Connection Authentication Protocol. If
+ initiator of the protocol does not know the mandatory
+ authentication method this packet MAY be used to determine it.
+ The party receiving this payload SHOULD respond with the same
+ packet including the mandatory authentication method.
+
+ Payload of the packet: See section 2.3.15 Connection Auth
+ Request Payload
+
+
+ 17 SILC_PACKET_CONNECTION_AUTH
+
+ This packet is used to start and perform the SILC Connection
+ Authentication Protocol. This protocol is used to authenticate
+ the connecting party. The protocol is described in detail in
+ [SILC3].
+
+ Payload of the packet: Payload of this packet is described
+ in the section SILC Authentication
+ Protocol and it sub sections in [SILC].
+
+
+ 18 SILC_PACKET_NEW_ID
+
+ This packet is used to distribute new IDs from server to
+ router and from router to all other routers in SILC network.
+ This is used when for example new client is registered to
+ SILC network. The newly created IDs of these operations are
+ distributed by this packet. Only server may send this packet,
+ however, client MUST be able to receive this packet. This
+ packet MAY be sent to entity that is indirectly connected
+ to the sender. This packet MAY be sent as list.
+
+ Payload of the packet: See section 2.3.16 New ID Payload
+
+
+ 19 SILC_PACKET_NEW_CLIENT
+
+ This packet is used by client to register itself to the
+ SILC network. This is sent after key exchange and
+ authentication protocols has been completed. Client sends
+ various information about itself in this packet to the server.
+
+ Payload of the packet: See section 2.3.17 New Client Payload
+
+
+ 20 SILC_PACKET_NEW_SERVER
+
+ This packet is used by server to register itself to the
+ SILC network. This is sent after key exchange and
+ authentication protocols has been completed. Server sends
+ this to the router it connected to, or, if router was
+ connecting, to the connected router. Server sends its
+ Server ID and other information in this packet. The client
+ MUST NOT send or receive this packet.
+
+ Payload of the packet: See section 2.3.18 New Server Payload
+
+
+ 21 SILC_PACKET_NEW_CHANNEL
+
+ This packet is used to notify routers about newly created
+ channel. Channels are always created by the router and it MUST
+ notify other routers about the created channel. Router sends
+ this packet to its primary route. Client MUST NOT send this
+ packet. This packet MAY be sent to entity that is indirectly
+ connected to the sender. This packet MAY be sent as list.
+
+ Payload of the packet: See section 2.3.19 New Channel Payload
+
+
+ 22 SILC_PACKET_REKEY
+
+ This packet is used to indicate that re-key must be performed
+ for session keys. See section Session Key Regeneration in
+ [SILC1] for more information. This packet does not have
+ a payload.
+
+
+ 23 SILC_PACKET_REKEY_DONE
+
+ This packet is used to indicate that re-key is performed and
+ new keys must be used hereafter. This packet does not have a
+ payload.
+
+
+ 24 SILC_PACKET_HEARTBEAT
+
+ This packet is used by clients, servers and routers to keep the
+ connection alive. It is RECOMMENDED that all servers implement
+ keepalive actions and perform it to both direction in a link.
+ This packet does not have a payload.
+
+
+ 25 SILC_PACKET_KEY_AGREEMENT
+
+ This packet is used by clients to request key negotiation
+ between another client in the SILC network. If the negotiation
+ is started it is performed using the SKE protocol. The result of
+ the negotiation, the secret key material, can be used for
+ example as private message key. The server and router MUST NOT
+ send this packet.
+
+ Payload of the packet: See section 2.3.20 Key Agreement Payload
+
+
+ 26 SILC_PACKET_RESUME_ROUTER
+
+ This packet is used during backup router protocol when the
+ original primary router of the cell comes back online and wishes
+ to resume the position as being the primary router of the cell.
+
+ Payload of the packet: See section 2.3.21 Resume Router Payload
+
+
+ 27 SILC_PACKET_FTP
+
+ This packet is used to perform an file transfer protocol in the
+ SILC session with some entity in the network. The packet is
+ multi purpose. The packet is used to tell other entity in the
+ network that the sender wishes to perform an file transfer
+ protocol. The packet is also used to actually tunnel the
+ file transfer protocol stream. The file transfer protocol
+ stream is always protected with the SILC binary packet protocol.
+
+ Payload of the packet: See section 2.3.22 File Transfer Payload
+
+
+ 28 SILC_PACKET_RESUME_CLIENT
+
+ This packet is used to resume a client back to the network
+ after it has been detached. A client is able to detach from
+ the network but the client is still valid client in the network.
+ The client may then later resume its session back by sending
+ this packet to a server. Routers also use this packet to notify
+ other routers in the network that the detached client has resumed.
+
+ Payload of the packet: See section 2.3.23 Resume Client Payload
+
+
+ 29 - 199
+
+ Currently undefined commands.
+
+
+ 200 - 254
+
+ These packet types are reserved for private use and they will
+ not be defined by this document.
+
+
+ 255 SILC_PACKET_MAX
+
+ This type is reserved for future extensions and currently it
+ MUST NOT be sent.
+.in 3
+
+
+.ti 0
+2.3.1 SILC Packet Payloads
+
+All payloads resides in the main data area of the SILC packet. However
+all payloads MUST be at the start of the data area after the SILC
+packet header and padding. All fields in the packet payload are always
+encrypted, as they reside in the data area of the packet which is
+always encrypted. Most of the payloads may only be sent with specific
+packet type which is defined in the description of the payload.
+
+There are some other payloads in SILC as well. However, they are not
+common in the sense that they could be sent at any time. These payloads
+are not described in this section. These are payloads such as SILC
+Key Exchange payloads and so on. These are described in [SILC1],
+[SILC3] and [SILC4].
+
+
+.ti 0
+2.3.2 Generic payloads
+
+This section describes generic payloads that are not associated to any
+specific packet type. They can be used for example inside some other
+packet payload.
+
+
+.ti 0
+2.3.2.1 ID Payload
+
+This payload can be used to send an ID. ID's are variable in length
+thus this payload provides a way to send variable length ID.
+
+The following diagram represents the ID Payload.
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| ID Type | ID Length |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| |
+~ ID Data ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 3: ID Payload
+
+
+.in 6
+o ID Type (2 bytes) - Indicates the type of the ID. See
+ section 2.4 SILC ID Types for list of defined ID types.
+
+o ID Length (2 bytes) - Length of the ID Data area not
+ including the length of any other fields in the payload.
+
+o ID Data (variable length) - The actual ID data. The encoding
+ of the ID data is defined in section 2.4 SILC ID Types.
+.in 3
+
+
+.ti 0
+2.3.2.2 Argument Payload
+
+Argument Payload is used to set arguments for any packet payload that
+need and support arguments, such as commands. Number of arguments
+associated with a packet MUST be indicated by the packet payload which
+need the arguments. Argument Payloads MUST always reside right after
+the packet payload needing the arguments. Incorrect amount of argument
+payloads MUST cause rejection of the packet.
+
+The following diagram represents the Argument Payload.
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Data Length | Argument Type | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Argument Data ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 4: Argument Payload
+
+
+.in 6
+o Data Length (2 bytes) - Length of the Argument Data field
+ not including the length of any other field in the payload.
+
+o Argument Type (1 byte) - Indicates the type of the argument.
+ Every argument can have a specific type that are defined
+ by the packet payload needing the argument. For example
+ every command specify a number for each argument that may be
+ associated with the command. By using this number the receiver
+ of the packet knows what type of argument this is. If there is
+ no specific argument type this field is set to zero (0) value.
+
+o Argument Data (variable length) - Argument data.
+.in 3
+
+
+.ti 0
+2.3.2.3 Argument List Payload
+
+Argument List Payload is a list of Argument Payloads appended one
+after the other. The number of arguments is indicated in the
+payload.
+
+The following diagram represents the Argument List Payload.
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Argument Nums | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Argument Payloads ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 5: Argument List Payload
+
+
+.in 6
+o Argument Nums (2 bytes) - Indicates the number of Argument
+ Payloads. If zero (0) value is found in this field no
+ arguments are present.
+
+o Argument Payloads (variable length) - The Argument Payloads
+ appended one after the other. The payloads can be decoded
+ since the length of the payload is indicated in each of
+ the Argument Payload.
+.in 3
+
+
+
+
+
+.ti 0
+2.3.2.4 Channel Payload
+
+Generic Channel Payload may be used to send information about a channel,
+its name, the Channel ID and a mode.
+
+The following diagram represents the Channel Payload.
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Channel Name Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Channel Name ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Channel ID Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Channel ID ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Mode Mask |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 6: New Channel Payload
+
+
+.in 6
+o Channel Name Length (2 bytes) - Length of the Channel Name
+ field.
+
+o Channel Name (variable length) - The name of the channel.
+
+o Channel ID Length (2 bytes) - Length of the Channel ID field.
+
+o Channel ID (variable length) - The encoded Channel ID.
+
+o Mode Mask (4 bytes) - A mode. This can be the mode of the
+ channel but it can also be the mode of a client on the
+ channel. The contents of this field is dependent of the
+ usage of this payload. The usage is defined separately
+ when this payload is used. This is a 32 bit MSB first value.
+.in 3
+
+
+
+
+
+
+.ti 0
+2.3.2.5 Public Key Payload
+
+Generic Public Key Payload may be used to send different type of
+public keys and certificates.
+
+The following diagram represents the Public Key Payload.
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Public Key Length | Public Key Type |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| |
+~ Public Key (or certificate) ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 7: Public Key Payload
+
+
+.in 6
+o Public Key Length (2 bytes) - The length of the Public Key
+ (or certificate) field, not including any other field.
+
+o Public Key Type (2 bytes) - The public key (or certificate)
+ type. This field indicates the type of the public key in
+ the packet. See the [SILC3] for defined public key types.
+
+o Public Key (or certificate) (variable length) - The
+ encoded public key or certificate data.
+.in 3
+
+
+.ti 0
+2.3.2.6 Message Payload
+
+Generic Message Payload can be used to send messages in SILC. It
+is used to send channel messages and private messages.
+
+The following diagram represents the Message Payload.
+
+(*) indicates that the field is not encrypted.
+
+
+
+
+
+
+
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Message Flags | Message Length |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| |
+~ Message Data ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Padding Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Padding ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| |
+~ Initialization Vector * ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| |
+~ MAC * ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 8: Message Payload
+
+
+.in 6
+o Message Flags (2 bytes) - Includes the Message Flags of the
+ message. The flags can indicate a reason or a purpose for
+ the message. The following Message Flags are defined:
+
+ 0x0000 SILC_MESSAGE_FLAG_NONE
+
+ No specific flags set.
+
+ 0x0001 SILC_MESSAGE_FLAG_AUTOREPLY
+
+ This message is an automatic reply to an earlier
+ received message.
+
+ 0x0002 SILC_MESSAGE_FLAG_NOREPLY
+
+ There should not be reply messages to this
+ message.
+
+ 0x0004 SILC_MESSAGE_FLAG_ACTION
+
+ The sender is performing an action and the message
+ is the indication of the action.
+
+ 0x0008 SILC_MESSAGE_FLAG_NOTICE
+
+ The message is for example an informational notice
+ type message.
+
+ 0x0010 SILC_MESSAGE_FLAG_REQUEST
+
+ This is a generic request flag to send request
+ messages. A separate document should define any
+ payloads associated to this flag.
+
+ 0x0020 SILC_MESSAGE_FLAG_SIGNED
+
+ This flag indicates that the message is signed
+ with sender's private key and thus can be verified
+ by the receiver using the sender's public key. A
+ separate document should define the detailed procedure
+ of the signing process and any associated payloads
+ for this flag.
+
+ 0x0040 SILC_MESSAGE_FLAG_REPLY
+
+ This is a generic reply flag to send a reply to
+ previously received request. A separate document
+ should define any payloads associated to this flag.
+
+ 0x0080 SILC_MESSAGE_FLAG_DATA
+
+ This is a generic data flag, indicating that the
+ message includes some data which can be interpreted
+ in a specific way. Using this flag any kind of data
+ can be delivered inside message payload. A separate
+ document should define how this flag is interpreted
+ and define any associated payloads.
+
+ 0x0100 SILC_MESSAGE_FLAG_UTF8
+
+ This flag indicates that the message is UTF-8 encoded
+ textual message. When sending text messages in SILC
+ this flag SHOULD be used. When this flag is used the
+ text sent as message MUST be UTF-8 encoded.
+
+ 0x0200 SILC_MESSAGE_FLAG_ACK
+
+ This flag indicates the sender requires the recpipient
+ to acknowledge the received message. This same flag
+ is used in the acknowledgement. A separate document
+ should define how the acknowledgement is performed.
+
+ 0x0400 - 0x1000 RESERVED
+
+ Reserved for future flags.
+
+ 0x2000 - 0x8000 PRIVATE RANGE
+
+ Private range for free use.
+
+o Message Length (2 bytes) - Indicates the length of the
+ Message Data field in the payload, not including any
+ other field.
+
+o Message Data (variable length) - The actual message data.
+
+o Padding Length (2 bytes) - Indicates the length of the
+ Padding field in the payload, not including any other
+ field.
+
+o Padding (variable length) - If this payload is used as
+ channel messages, the padding MUST be applied because
+ this payload is encrypted separately from other parts
+ of the packet. If this payload is used as private
+ messages, the padding is present only when the payload
+ is encrypted with private message key. If encrypted
+ with session keys this field MUST NOT be present and the
+ Padding Length field includes a zero (0) value. The
+ padding SHOULD be random data.
+
+o Initialization Vector (variable length) - This field MUST
+ be present when this payload is used as channel messages.
+ The IV SHOULD be random data for each channel message.
+
+ When encrypting private messages with session keys this
+ field MUST NOT be present. For private messages this
+ field is present only when encrypting with a static
+ private message key (pre-shared key). If randomly
+ generated key material is used this field MUST NOT be
+ present. Also, If Key Agreement (SKE) was used to
+ negotiate fresh key material for private message key
+ this field MUST NOT be present. See the section 4.6
+ in [SILC1] for more information about IVs when
+ encrypting private messages.
+
+ This field includes the initialization vector used in message
+ encryption. It need to be used in the packet decryption
+ as well. Contents of this field depends on the encryption
+ algorithm and encryption mode. This field is not encrypted,
+ is not included in padding calculation and its length
+ equals to cipher's block size. This field is authenticated
+ by the message MAC.
+
+o MAC (variable length) - The MAC computed from the
+ Message Flags, Message Length, Message Data, Padding Length,
+ Padding and Initialization Vector fields in that order.
+ The MAC is computed after the payload is encrypted. This
+ is so called Encrypt-Then-MAC order; first encrypt, then
+ compute MAC from ciphertext. The MAC protects the integrity
+ of the Message Payload. Also, when used as channel messages
+ it is possible to have multiple private channel keys set,
+ and receiver can use the MAC to verify which of the keys
+ must be used in decryption. This field is not present
+ when encrypting private messages with session key. This
+ field is not encrypted. This field is authenticated by
+ the SILC packet MAC.
+.in 3
+
+
+.ti 0
+2.3.3 Disconnect Payload
+
+Disconnect payload is sent upon disconnection. Reason of the
+disconnection is sent to the disconnected party in the payload.
+
+The payload may only be sent with SILC_PACKET_DISCONNECT packet. It
+MUST NOT be sent in any other packet type. The following diagram
+represents the Disconnect Payload.
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Status | |
++-+-+-+-+-+-+-+-+ +
+| |
+~ Disconnect Message ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 9: Disconnect Payload
+
+.in 6
+o Status (1 byte) - Indicates the Status Type, defined in [SILC3]
+ for the reason of disconnection.
+
+o Disconnect Message (variable length) - Human readable UTF-8
+ encoded string indicating reason of the disconnection. This
+ field MAY be omitted.
+.in 3
+
+
+.ti 0
+2.3.4 Success Payload
+
+Success payload is sent when some protocol execution is successfully
+completed. The payload is simple; indication of the success is sent.
+This may be any data, including binary or human readable data, and
+it is protocol dependent.
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| |
+~ Success Indication ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 10: Success Payload
+
+
+.in 6
+o Success Indication (variable length) - Indication of
+ the success. This may be for example some flag that
+ indicates the protocol and the success status or human
+ readable success message. The true length of this
+ payload is available by calculating it from the SILC
+ Packet Header.
+.in 3
+
+
+.ti 0
+2.3.5 Failure Payload
+
+This is opposite of Success Payload. Indication of failure of
+some protocol is sent in the payload.
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| |
+~ Failure Indication ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 11: Failure Payload
+
+
+.in 6
+o Failure Indication (variable length) - Indication of
+ the failure. This may be for example some flag that
+ indicates the protocol and the failure status or human
+ readable failure message. The true length of this
+ payload is available by calculating it from the SILC
+ Packet Header.
+.in 3
+
+
+.ti 0
+2.3.6 Reject Payload
+
+This payload is sent when some protocol is rejected to be executed.
+Other operations MAY send this as well that was rejected. The
+indication of the rejection is sent in the payload. The indication
+may be binary or human readable data and is protocol dependent.
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| |
+~ Reject Indication ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 12: Reject Payload
+
+
+.in 6
+o Reject Indication (variable length) - Indication of
+ the rejection. This maybe for example some flag that
+ indicates the protocol and the rejection status or human
+ readable rejection message. The true length of this
+ payload is available by calculating it from the SILC
+ Packet Header.
+.in 3
+
+
+
+.ti 0
+2.3.7 Notify Payload
+
+Notify payload is used to send notify messages. The payload is usually
+sent from server to client and from server to router. It is also used
+by routers to notify other routers in the network. This payload MAY also
+be sent to a channel. Client MUST NOT send this payload. When this
+packet is received by client it SHOULD process it. Servers and routers
+MUST process notify packets.
+
+The payload may only be sent with SILC_PACKET_NOTIFY packet. It MUST
+NOT be sent in any other packet type. The following diagram represents
+the Notify Payload.
+
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Notify Type | Payload Length |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Argument Nums |
++-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 13: Notify Payload
+
+
+.in 6
+o Notify Type (2 bytes) - Indicates the type of the notify
+ message.
+
+o Payload Length (2 bytes) - Length of the entire Notify Payload
+ including any associated Argument Payloads.
+
+o Argument Nums (1 byte) - Indicates the number of Argument
+ Payloads associated to this payload. Notify types may define
+ arguments to be sent along the notify message.
+.in 3
+
+Following the list of currently defined notify types. The format for
+notify arguments is same as in SILC commands described in [SILC4].
+Note that all IDs sent in arguments are sent inside ID Payload. Also
+note that all strings sent as arguments MUST be UTF-8 [RFC3629] encoded,
+unless otherwise defined. Also note that all public keys or
+certificates sent inside arguments are actually Public Key Payloads.
+
+
+.in 6
+0 SILC_NOTIFY_TYPE_NONE
+
+ If no specific notify type apply for the notify message this type
+ MAY be used.
+
+ Max Arguments: 1
+ Arguments: (1) <message>
+
+ The <message> is implementation specific free text string.
+ Receiver MAY ignore this message.
+
+
+1 SILC_NOTIFY_TYPE_INVITE
+
+ Sent when an client is invited to a channel. This is also sent
+ when the invite list of the channel is changed. This notify type
+ is sent to local servers on the channel, but MUST NOT be sent
+ to clients on the channel. Router MUST broadcast this to its
+ primary router and to local servers on the channel. When a client
+ was directly invited to the channel this is also sent to that
+ client. In this case the packet is destined to the client.
+
+ Max Arguments: 5
+ Arguments: (1) <Channel ID> (2) <channel name>
+ (3) [<sender Client ID>] (4) [<add | del>]
+ (5) [<invite list>]
+
+ The <Channel ID> is the channel. The <channel name> is the name
+ of the channel and is provided because the client which receives
+ this notify packet may not have a way to resolve the name of the
+ channel from the <Channel ID>. The <sender Client ID> is the
+ Client ID which invited the client to the channel. The
+ <add | del> is an argument of size of 1 byte where 0x00 means
+ adding a client to invite list, and 0x01 means deleting a client
+ from invite list. The <invite list>, if present, indicates the
+ information to be added to or removed from the invite list.
+ The <invite list> format is defined in [SILC4] with
+ SILC_COMMAND_INVITE command. When this notify is destined to
+ a client the <add | del> and <invite list> MUST NOT be sent.
+ When <add | del> is used to announce information during server
+ connecting phase the argument type MUST be 0x03. See section
+ 4.2.1 in [SILC1] for more information.
+
+
+2 SILC_NOTIFY_TYPE_JOIN
+
+ Sent when client has joined to a channel. The server MUST
+ distribute this type to the local clients on the channel and then
+ send it to its primary router. Note that, when router is joining
+ the client on behalf of normal server then router MUST send this
+ notify type locally and globally. The router or server receiving
+ the packet distributes this type to the local clients on the
+ channel and broadcast it to the network. This notify is sent
+ also to the client that joined the channel.
+
+ Max Arguments: 2
+ Arguments: (1) [<Client ID>] (2) <Channel ID>
+
+ The <Client ID> is the client that joined to the channel
+ indicated by the <Channel ID>.
+
+
+3 SILC_NOTIFY_TYPE_LEAVE
+
+ Sent when client has left a channel. The server must distribute
+ this type to the local clients on the channel and then send it
+ to its primary router. The router or server receiving the
+ packet distributes this type to the local clients on the channel
+ and broadcast it to the network. This notify MUST NOT be sent to
+ the leaving client.
+
+ Max Arguments: 1
+ Arguments: (1) <Client ID>
+
+ The <Client ID> is the client which left the channel.
+
+
+4 SILC_NOTIFY_TYPE_SIGNOFF
+
+ Sent when client signoff from SILC network. The server MUST
+ distribute this type to the local clients on the channel and
+ then send it to its primary router. The router or server
+ receiving the packet distributes this type to the local clients
+ on the channel and broadcast it to the network. This notify
+ MUST NOT be sent to the quitting client.
+
+ Max Arguments: 2
+ Arguments: (1) <Client ID> (2) <message>
+
+ The <Client ID> is the client which left SILC network. The
+ <message> is free text string indicating the reason of the
+ signoff.
+
+
+5 SILC_NOTIFY_TYPE_TOPIC_SET
+
+ Sent when topic is set/changed on a channel. This type may be
+ sent only to the clients which are joined on the channel which
+ topic was just set or changed. The packet is destined to the
+ channel.
+
+ Max Arguments: 2
+ Arguments: (1) <ID Payload> (2) <topic>
+
+ The <ID Payload> is the ID of the entity who set the topic.
+ It usually is Client ID but it can be Server ID and Channel ID
+ as well.
+
+
+6 SILC_NOTIFY_TYPE_NICK_CHANGE
+
+ Sent when client changes nick on a channel. The server MUST
+ distribute this type only to the local clients on the channel
+ and then send it to its primary router. The router or server
+ receiving the packet distributes this type to the local clients
+ on the channel and broadcast it to the network. This packet is
+ destined directly to the sent entity. This MUST be sent to those
+ clients that are joined on same channels as the client that
+ changed the nickname. This notify MUST NOT be sent multiple
+ times to the same recipient. This notify MUST be sent also to
+ the client that changed the nickname.
+
+ Max Arguments: 3
+ Arguments: (1) <Old Client ID> (2) <New Client ID>
+ (3) <nickname>
+
+ The <Old Client ID> is the old ID of the client which changed
+ the nickname. The <New Client ID> is the new ID generated by
+ the change of the nickname. The <nickname> is the new nickname.
+ Note that it is possible to send this notify even if the
+ nickname has not changed, but client ID was changed.
+
+
+7 SILC_NOTIFY_TYPE_CMODE_CHANGE
+
+ Sent when channel mode has changed. This type MUST be sent only
+ to the clients which are joined on the channel which mode was
+ changed. This packet is destined to the channel.
+
+ Max Arguments: 8
+ Arguments: (1) <ID Payload> (2) <mode mask>
+ (3) [<cipher>] (4) <[hmac>]
+ (5) [<passphrase>] (6) [<founder public key>]
+ (7) [<channel pubkey>] (8) [<user limit>]
+
+ The <ID Payload> is the ID (usually Client ID but it can be
+ Server ID as well when the router is enforcing channel mode
+ change) of the entity which changed the mode. The <mode mask>
+ is the new mode mask of the channel. The client can safely
+ ignore the <cipher> argument since the SILC_PACKET_CHANNEL_KEY
+ packet will force the new channel key change anyway. The <hmac>
+ argument is important since the client is responsible of setting
+ the new HMAC and the hmac key into use. The <passphrase> is
+ the passphrase of the channel, if it was now set. The <founder
+ public key> argument is sent when the founder mode on the
+ channel was set. All routers and servers that receive the packet
+ MUST save the founder's public key so that the founder can
+ reclaim the channel founder rights back for the channel on any
+ server in the network. The <user limit> argument is present when
+ the user limit was set or changed on the channel.
+
+ The <channel pubkey> is an Argument List Payload and it is used
+ to add and/or remove channel public keys from the channel. Also,
+ when announcing channel information between servers and routers
+ during connecting phase this argument includes the list of channel
+ public keys. To add a public key to channel public key list the
+ SILC_CMODE_CHANNEL_AUTH mode is set and the argument type is 0x00,
+ and the argument is the public key. To remove a public key from
+ the channel public key list the argument type is 0x01, and the
+ argument is the public key to be removed. If the mode
+ SILC_CMODE_CHANNEL_AUTH is unset (and was set earlier) all public
+ keys are removed at once. Implementation MAY add and remove
+ multiple public keys at the same time by including multiple
+ arguments to the <channel pubkey> Argument List Payload where each
+ argument is one Public Key Payload. When <channel pubkey> is used
+ to announce information during server connecting phase the
+ argument type MUST be 0x03. See section 4.2.1 in [SILC1] for
+ more information.
+
+
+8 SILC_NOTIFY_TYPE_CUMODE_CHANGE
+
+ Sent when user mode on channel has changed. This type MUST be
+ sent only to the clients which are joined on the channel where
+ the target client is on. This packet is destined to the channel.
+
+ Max Arguments: 4
+ Arguments: (1) <ID Payload> (2) <mode mask>
+ (3) <Target Client ID> (4) [<founder pubkey>]
+
+ The <ID Payload> is the ID (usually Client ID but it can be
+ Server ID as well when the router is enforcing user's mode
+ change) of the entity which changed the mode. The <mode mask>
+ is the new mode mask of the channel. The <Target Client ID>
+ is the client which mode was changed. The <founder pubkey>
+ is the public key of the channel founder and may be sent only
+ when first time setting the channel founder mode using the
+ SILC_COMMAND_CUMODE command, and when sending this notify.
+
+
+9 SILC_NOTIFY_TYPE_MOTD
+
+ Sent when Message of the Day (motd) is sent to a client.
+
+ Max Arguments: 1
+ Arguments: (1) <motd>
+
+ The <motd> is the Message of the Day. This notify MAY be
+ ignored and is OPTIONAL.
+
+
+10 SILC_NOTIFY_TYPE_CHANNEL_CHANGE
+
+ Sent when channel's ID has changed for a reason or another.
+ This is sent by normal server to the client. This can also be
+ sent by router to other server to force the Channel ID change.
+ The Channel ID MUST be changed to use the new one. When sent
+ to clients, this type MUST be sent only to the clients which are
+ joined on the channel. This packet is destined to the sent
+ entity.
+
+ Max Arguments: 2
+ Arguments: (1) <Old Channel ID> (2) <New Channel ID>
+
+ The <Old Channel ID> is the channel's old ID and the <New
+ Channel ID> is the new one that MUST replace the old one.
+ Server which receives this from router MUST re-announce the
+ channel to the router by sending SILC_PACKET_NEW_CHANNEL packet
+ with the new Channel ID.
+
+
+11 SILC_NOTIFY_TYPE_SERVER_SIGNOFF
+
+ Sent when server quits SILC network. Those clients from this
+ server that are on channels must be removed from the channel.
+ This packet is destined to the sent entity.
+
+ Max Arguments: 256
+ Arguments: (1) <Server ID> (n) [<Client ID>] [...]
+
+ The <Server ID> is the server's ID. The rest of the arguments
+ are the Client IDs of the clients which are coming from this
+ server and are thus quitting the SILC network also. If the
+ maximum number of arguments are reached another
+ SILC_NOTIFY_TYPE_SERVER_SIGNOFF notify packet MUST be sent.
+ When this notify packet is sent between routers the Client ID's
+ MAY be omitted. Server receiving the Client ID's in the payload
+ may use them directly to remove the client.
+
+
+12 SILC_NOTIFY_TYPE_KICKED
+
+ Sent when a client has been kicked from a channel. This MUST
+ also be sent to the client which was kicked from the channel.
+ The client which was kicked from the channel MUST be removed
+ from the channel. The client MUST also be removed from channel's
+ invite list if it is explicitly added in the list. This packet
+ is destined to the channel. The router or server receiving the
+ packet distributes this type to the local clients on the channel
+ and broadcast it to the network.
+
+ Max Arguments: 3
+ Arguments: (1) <Client ID> (2) [<comment>]
+ (3) <Kicker's Client ID>
+
+ The <Client ID> is the client which was kicked from the channel.
+ The kicker may have set the <comment> string to indicate the
+ reason for the kicking. The <Kicker's Client ID> is the kicker.
+
+
+13 SILC_NOTIFY_TYPE_KILLED
+
+ Sent when a client has been killed from the network. This MUST
+ also be sent to the client which was killed from the network.
+ This notify MUST be sent to those clients which are joined on
+ same channels as the killed client. The client which was killed
+ MUST be removed from the network. This packet is destined
+ directly to the sent entity. The router or server receiving
+ the packet distributes this type to the local clients on the
+ channel and broadcast it to the network. The client MUST also
+ be removed from joined channels invite list if it is explicitly
+ added in the lists. This notify MUST NOT be sent multiple
+ times to same recipient.
+
+ Max Arguments: 3
+ Arguments: (1) <Client ID> (2) [<comment>]
+ (3) <Killer's ID>
+
+ The <Client ID> is the client which was killed from the network.
+ The killer may have set the <comment> string to indicate the
+ reason for the killing. The <Killer's ID> is the killer, which
+ may be client but also router server.
+
+
+14 SILC_NOTIFY_TYPE_UMODE_CHANGE
+
+ Sent when user's mode in the SILC changes. This type is sent
+ only between routers as broadcast packet.
+
+ Max Arguments: 2
+ Arguments: (1) <Client ID> (2) <mode mask>
+
+ The <Client ID> is the client which mode was changed. The
+ <mode mask> is the new mode mask.
+
+
+15 SILC_NOTIFY_TYPE_BAN
+
+ Sent when the ban list of the channel is changed. This notify
+ type is sent to local servers on the channel, but MUST NOT be
+ sent to clients on the channel. Router MUST broadcast this to
+ its primary router and to local servers on the channel.
+
+ Max Arguments: 3
+ Arguments: (1) <Channel ID> (2) [<add | del>]
+ (3) [<ban list>]
+
+ The <Channel ID> is the channel which ban list was changed.
+ The <add | del> is an argument of size of 1 byte where 0x00 means
+ adding a client to ban list, and 0x01 means deleting a client
+ from ban list. The <ban list> indicates the information to be
+ added to or removed from the ban list. The <ban list> format
+ format is defined in [SILC4] with SILC_COMMAND_BAN command.
+ When <add | del> is used to announce information during server
+ connecting phase the argument type MUST be 0x03. See section
+ 4.2.1 in [SILC1] for more information.
+
+
+16 SILC_NOTIFY_TYPE_ERROR
+
+ Sent when an error occurs during processing some SILC procedure.
+ This is not used when error occurs during command processing, see
+ [SILC4] for more information about commands and command replies.
+ This type is sent directly to the sender of the packet whose
+ packet caused the error. See [SILC1] for definition when this
+ type can be sent.
+
+ Max Arguments: 256
+ Arguments: (1) <Status Type> (n) [...]
+
+ The <Status Type> is the error type defined in [SILC4]. Note
+ that same types are also used with command replies to indicate
+ the status of a command. Both commands and this notify type
+ share same status types. Rest of the arguments are status type
+ dependent and are specified with those status types that can be
+ sent currently inside this notify type in [SILC4]. The <Status
+ Type> is size of 1 byte.
+
+
+17 SILC_NOTIFY_TYPE_WATCH
+
+ Sent to indicate change in a watched user. Client can set
+ nicknames to be watched with SILC_COMMAND_WATCH command, and
+ receive notifications when they login to network, signoff from
+ the network or their user mode is changed. This notify type
+ is used to deliver these notifications. The notify type is
+ sent directly to the watching client.
+
+ Max Arguments: 5
+ Arguments: (1) <Client ID> (2) [<nickname>]
+ (3) <user mode> (4) [<Notify Type>]
+ (5) [<public key>]
+
+ The <Client ID> is the user's Client ID which is being watched,
+ and the <nickname> is its nickname. If the client just
+ changed the nickname, then <nickname> is the new nickname, but
+ the <Client ID> is the old client ID. The <user mode> is the
+ user's current user mode. The <Notify Type> can be same as the
+ Notify Payload's Notify Type, and is 16 bit MSB first order
+ value. If provided it may indicate the notify that occurred
+ for the client. If client logged in to the network the
+ <Notify Type> MUST NOT be present. The <public key> MAY be
+ present, and it is the public key of the client being watched.
+.in 3
+
+Notify types starting from 16384 are reserved for private notify
+message types.
+
+Router server which receives SILC_NOTIFY_TYPE_SIGNOFF,
+SILC_NOTIFY_TYPE_SERVER_SIGNOFF, SILC_NOTIFY_TYPE_KILLED,
+SILC_NOTIFY_TYPE_NICK_CHANGE and SILC_NOTIFY_TYPE_UMODE_CHANGE
+MUST check whether someone in the local cell is watching the nickname
+the client has, and send the SILC_NOTIFY_TYPE_WATCH notify to the
+watcher, unless the watched client in case has the user mode
+SILC_UMODE_REJECT_WATCHING set. If the watcher client and the client
+that was watched is same the notify SHOULD NOT be sent.
+
+
+.ti 0
+2.3.8 Error Payload
+
+Error payload is sent upon error in protocol. Error may occur in
+various conditions when server sends this packet. Client MUST NOT
+send this payload but MUST be able to accept it. However, client
+MAY ignore the contents of the packet as server is going to take
+action on the error anyway. However, it is recommended that the
+client takes error packet seriously.
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| |
+~ Error Message ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 14: Error Payload
+
+
+.in 6
+o Error Message (variable length) - Human readable error
+ message.
+.in 3
+
+
+.ti 0
+2.3.9 Channel Message Payload
+
+Channel Message Payload is used to send message to channels, a group
+of users. These messages can only be sent if client has joined to
+some channel. Even though this packet is very common in SILC it
+is still special packet. Some special handling on sending and
+reception of channel message is required.
+
+Padding MUST be applied into this payload since the payload is
+encrypted separately from other parts of the packet with the
+channel specific key. Hence the requirement of the padding.
+The packet MUST be made multiple by eight (8) or by the block
+size of the cipher, which ever is larger.
+
+The SILC header in this packet is encrypted with the session key
+of the next receiver of the packet. Nothing else is encrypted
+with that key. Thus, the actual packet and padding to be
+encrypted with the session key is SILC Header plus padding to it.
+
+Receiver of the the channel message packet is able to determine
+the channel the message is destined to by checking the Destination
+ID from the SILC Packet header which tells the destination channel.
+The original sender of the packet is also determined by checking
+the source ID from the header which tells the client which sent
+the message. The Destination ID MUST be Channel ID in the SILC
+Packet header.
+
+This packet use generic Message Payload as Channel Message Payload.
+See section 2.3.2.6 for generic Message Payload.
+
+
+.ti 0
+2.3.10 Channel Key Payload
+
+All traffic in channels are protected by channel specific keys.
+Channel Key Payload is used to distribute channel keys to all
+clients on the particular channel. Channel keys are sent when
+the channel is created, when new user joins to the channel and
+whenever a user has left a channel. Server creates the new
+channel key and distributes it to the clients by encrypting this
+payload with the session key shared between the server and
+the client. After that, client MUST start using the key received
+in this payload to protect the traffic on the channel.
+
+The client which is joining to the channel receives its key in the
+SILC_COMMAND_JOIN command reply message thus it is not necessary to
+send this payload to the entity which sent the SILC_COMMAND_JOIN
+command.
+
+Channel keys are cell specific thus every router in the cell have
+to create a channel key and distribute it if any client in the
+cell has joined to a channel. Channel traffic between cell's
+are not encrypted using channel keys, they are encrypted using
+normal session keys between two routers. Inside a cell, all
+channel traffic is encrypted with the specified channel key.
+Channel key SHOULD expire periodically, say, in one hour, in
+which case new channel key is created and distributed.
+
+Note that, this packet is not used if SILC_CMODE_PRIVKEY mode is set
+on channel. This means that channel uses channel private keys which
+are not server generated. For this reason server cannot send this
+packet as it does not know the key.
+
+The payload may only be sent with SILC_PACKET_CHANNEL_KEY packet.
+It MUST NOT be sent in any other packet type. The following diagram
+represents the Channel Key Payload.
+
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Channel ID Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Channel ID ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Cipher Name Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Cipher Name ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Channel Key Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Channel Key ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 15: Channel Key Payload
+
+
+
+.in 6
+o Channel ID Length (2 bytes) - Indicates the length of the
+ Channel ID field in the payload, not including any other
+ field.
+
+o Channel ID (variable length) - The Channel ID of the
+ channel.
+
+o Cipher Name Length (2 bytes) - Indicates the length of the
+ Cipher name field in the payload, not including any other
+ field.
+
+o Cipher Name (variable length) - Name of the cipher used
+ in the protection of channel traffic. This name is
+ initially decided by the creator of the channel but it
+ may change during the life time of the channel as well.
+
+o Channel Key Length (2 bytes) - Indicates the length of the
+ Channel Key field in the payload, not including any other
+ field.
+
+o Channel Key (variable length) - The actual channel key
+ material.
+.in 3
+
+
+.ti 0
+2.3.11 Private Message Payload
+
+Private Message Payload is used to send private message between
+two clients. The messages are sent only to the specified user
+and no other user inside SILC network is able to see the message.
+
+The message can be protected by the session key established by the
+SILC Key Exchange Protocol. However, it is also possible to agree
+to use a private key to protect just the private messages. It is
+for example possible to perform Key Agreement between two clients.
+See section 2.3.20 Key Agreement Payload how to perform key
+agreement. It is also possible to use static or pre-shared keys
+to protect private messages. See the 2.3.12 Private Message Key
+Payload and [SILC1] section 4.6 for detailed description for private
+message key generation.
+
+If normal session key is used to protect the message, every server
+between the sender client and the receiving client MUST decrypt the
+packet and always re-encrypt it with the session key of the next
+receiver of the packet. See section Client To Client in [SILC1].
+
+When the private message key is used, and the Private Message Key
+flag was set in the SILC Packet header no server or router en route
+is able to decrypt or re-encrypt the packet. In this case only the
+SILC Packet header is processed by the servers and routers en route.
+Section Client To Client in [SILC1] gives example of this scheme.
+
+This packet use generic Message Payload as Private Message Payload.
+See section 2.3.2.6 for generic Message Payload.
+
+
+.ti 0
+2.3.12 Private Message Key Payload
+
+This payload is OPTIONAL and can be used to indicate that a static
+or pre-shared key should be used in the private message communication
+to protect the messages. The actual key material has to be sent
+outside the SILC network, or it has to be a static or pre-shared key.
+The sender of this packet is considered to be the initiator and the
+receiver the responder when processing the raw key material as
+described in the section 4.6 in [SILC1] and in the section 2.3 in
+[SILC3].
+
+Note that it is also possible to use static or pre-shared keys in
+client implementations without sending this packet. Clients may
+naturally agree to use a key without sending any kind of indication
+to each other. The key may be for example a long-living static key
+that the clients has agreed to use at all times. Note that it is
+also possible to agree to use private message key by performing
+a Key Agreement. See the section 2.3.20 Key Agreement Payload.
+
+This payload may only be sent by client to another client. Server
+MUST NOT send this payload. After sending this payload and setting the
+key into use this payload the sender of private messages MUST set the
+Private Message Key flag into the SILC Packet Header.
+
+The payload may only be sent with SILC_PACKET_PRIVATE_MESSAGE_KEY
+packet. It MUST NOT be sent in any other packet type. The following
+diagram represents the Private Message Key Payload.
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Cipher Name Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Cipher Name ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| HMAC Name Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ HMAC Name ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 16: Private Message Key Payload
+
+
+
+.in 6
+o Cipher Name Length (2 bytes) - Indicates the length of the
+ Cipher Name field in the payload, not including any other
+ field.
+
+o Cipher Name (variable length) - Name of the cipher to use
+ in the private message encryption. If this field does not
+ exist then the default cipher of the SILC protocol is used.
+ See the [SILC1] for defined ciphers.
+
+o HMAC Name Length (2 bytes) - Indicates the length of the
+ HMAC Name field in the payload, not including any other
+ field.
+
+o HMAC Name (variable length) - Name of the HMAC to use
+ in the private message MAC computation. If this field does
+ not exist then the default HMAC of the SILC protocol is used.
+ See the [SILC1] for defined HMACs.
+.in 3
+
+
+.ti 0
+2.3.13 Command Payload
+
+Command Payload is used to send SILC commands from client to server.
+Also server MAY send commands to other servers. The following diagram
+represents the Command Payload.
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Payload Length | SILC Command | Arguments Num |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Command Identifier |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 17: Command Payload
+
+
+.in 6
+o Payload Length (2 bytes) - Length of the entire command
+ payload including any command argument payloads associated
+ with this payload.
+
+o SILC Command (1 byte) - Indicates the SILC command. This MUST
+ be set to non-zero value. If zero (0) value is found in this
+ field the packet MUST be discarded.
+
+o Arguments Num (1 byte) - Indicates the number of arguments
+ associated with the command. If there are no arguments this
+ field is set to zero (0). The arguments MUST follow the
+ Command Payload. See section 2.3.2.2 for definition of the
+ Argument Payload.
+
+o Command Identifier (2 bytes) - Identifies this command at the
+ sender's end. The entity which replies to this command MUST
+ set the value found from this field into the Command Payload
+ used to send the reply to the sender. This way the sender
+ can identify which command reply belongs to which originally
+ sent command. What this field includes is implementation
+ issue but it is RECOMMENDED that wrapping counter value is
+ used in the field.
+.in 3
+
+See [SILC4] for detailed description of different SILC commands,
+their arguments and their reply messages.
+
+
+.ti 0
+2.3.14 Command Reply Payload
+
+Command Reply Payload is used to send replies to the commands. The
+Command Reply Payload is identical to the Command Payload thus see
+the 2.3.13 section for the payload specification.
+
+The entity which sends the reply packet MUST set the Command Identifier
+field in the reply packet's Command Payload to the value it received
+in the original command packet.
+
+See SILC Commands in [SILC4] for detailed description of different
+SILC commands, their arguments and their reply messages.
+
+
+.ti 0
+2.3.15 Connection Auth Request Payload
+
+Client MAY send this payload to server to request the authentication
+method that must be used in authentication protocol. If client knows
+this information beforehand this payload is not necessary to be sent.
+Server performing authentication with another server MAY also send
+this payload to request the authentication method. If the connecting
+server already knows this information this payload is not necessary
+to be sent.
+
+Server receiving this request SHOULD reply with same payload sending
+the mandatory authentication method. Algorithms that may be required
+to be used by the authentication method are the ones already
+established by the SILC Key Exchange protocol. See section Key
+Exchange Start Payload in [SILC3] for detailed information.
+
+The payload may only be sent with SILC_PACKET_CONNECTION_AUTH_REQUEST
+packet. It MUST NOT be sent in any other packet type. The following
+diagram represents the Connection Auth Request Payload.
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Connection Type | Authentication Method |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 18: Connection Auth Request Payload
+
+
+.in 6
+o Connection Type (2 bytes) - Indicates the type of the
+ connection. The following connection types are defined:
+
+
+ 1 Client connection
+ 2 Server connection
+ 3 Router connection
+
+ If any other type is found in this field the packet MUST be
+ discarded and the authentication MUST be failed.
+
+o Authentication Method (2 bytes) - Indicates the authentication
+ method to be used in the authentication protocol. The following
+ authentication methods are defined:
+
+ 0 NONE (mandatory)
+ 1 password (mandatory)
+ 2 public key (mandatory)
+
+ If any other type is found in this field the packet MUST be
+ discarded and the authentication MUST be failed. If this
+ payload is sent as request to receive the mandatory
+ authentication method this field MUST be set to zero (0),
+ indicating that receiver should send the mandatory
+ authentication method. The receiver sending this payload
+ to the requesting party, MAY also set this field to zero (0)
+ to indicate that authentication is not required. In this
+ case authentication protocol still MUST be started but
+ server is most likely to respond with SILC_PACKET_SUCCESS
+ immediately.
+.in 3
+
+
+.ti 0
+2.3.16 New ID Payload
+
+New ID Payload is a multipurpose payload. It is used to send newly
+created ID's from clients and servers. When client connects to server
+and registers itself to the server by sending SILC_PACKET_NEW_CLIENT
+packet, server replies with this packet by sending the created ID for
+the client. Server always creates the ID for the client.
+
+This payload is also used when server tells its router that new client
+has registered to the SILC network. In this case the server sends
+the Client ID of the client to the router. Similarly when router
+distributes information to other routers about the client in the SILC
+network this payload is used.
+
+Also, when server connects to router, router use this payload to inform
+other routers about new server in the SILC network. However, every
+server (or router) creates their own ID's thus the ID distributed by
+this payload is not created by the distributor in this case. Servers
+create their own ID's. Server registers itself to the network by
+sending SILC_PACKET_NEW_SERVER to the router it connected to. The case
+is same when router connects to another router.
+
+This payload MUST NOT be used to send information about new channels.
+New channels are always distributed by sending the dedicated
+SILC_PACKET_NEW_CHANNEL packet. Client MUST NOT send this payload.
+Both client and server (and router) MAY receive this payload.
+
+The packet use generic ID Payload as New ID Payload. See section
+2.3.2.1 for generic ID Payload.
+
+
+.ti 0
+2.3.17 New Client Payload
+
+When client is connected to the server, keys has been exchanged and
+connection has been authenticated, client MUST register itself to the
+server. Client's first packet after key exchange and authentication
+protocols MUST be SILC_PACKET_NEW_CLIENT. This payload tells server all
+the relevant information about the connected user. Server creates a new
+client ID for the client when received this payload and sends it to the
+client in New ID Payload.
+
+This payload sends username and real name of the user on the remote host
+which is connected to the SILC server with SILC client. The server
+creates the client ID according the information sent in this payload.
+The nickname of the user becomes the nickname sent in this payload.
+
+The payload may only be sent with SILC_PACKET_NEW_CLIENT packet. It
+MUST NOT be sent in any other packet type. The following diagram
+represents the New Client Payload.
+
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Username Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Username ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Real Name Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Real Name ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 19: New Client Payload
+
+
+.in 6
+o Username Length (2 bytes) - Length of the Username field.
+
+o Username (variable length) - The username of the user on
+ the host where connecting to the SILC server.
+
+o Real Name Length (2 bytes) - Length of the Real Name field.
+
+o Real Name (variable length) - The real name of the user
+ on the host where connecting to the SILC server.
+.in 3
+
+
+.ti 0
+2.3.18 New Server Payload
+
+This payload is sent by server when it has completed successfully both
+key exchange and connection authentication protocols. The server
+MUST register itself to the SILC Network by sending this payload.
+The first packet after these key exchange and authentication protocols
+is SILC_PACKET_NEW_SERVER packet. The payload includes the Server ID
+of the server that it has created by itself. It also includes a
+name of the server that is associated to the Server ID.
+
+The payload may only be sent with SILC_PACKET_NEW_SERVER packet. It
+MUST NOT be sent in any other packet type. The following diagram
+represents the New Server Payload.
+
+
+
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Server ID Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Server ID Data ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Server Name Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Server Name ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 20: New Server Payload
+
+
+.in 6
+o Server ID Length (2 bytes) - Length of the Server ID Data
+ field.
+
+o Server ID Data (variable length) - The encoded Server ID
+ data.
+
+o Server Name Length (2 bytes) - Length of the server name
+ field.
+
+o Server Name (variable length) - The server name string.
+.in 3
+
+
+.ti 0
+2.3.19 New Channel Payload
+
+Information about newly created channel is broadcasted to all routers
+in the SILC network by sending this packet payload. Channels are
+created by router of the cell. Server never creates channels unless
+it is a standalone server and it does not have router connection,
+in this case server acts as router. Normal server send JOIN command
+to the router (after it has received JOIN command from client) which
+then processes the command and creates the channel. Client MUST NOT
+send this packet. Server MAY send this packet to a router when it is
+announcing its existing channels to the router after it has connected
+to the router.
+
+The packet use generic Channel Payload as New Channel Payload. See
+section 2.3.2.3 for generic Channel Payload. The Mode Mask field in the
+Channel Payload is the mode of the channel.
+
+
+.ti 0
+2.3.20 Key Agreement Payload
+
+This payload is used by clients to request key negotiation between
+another client in the SILC Network. The key agreement protocol used
+is the SKE protocol. The result of the protocol, the secret key
+material, can be used for example as private message key between the
+two clients. This significantly adds security as the clients agree
+about the key without any server interaction. The protocol is executed
+peer to peer. The server and router MUST NOT send this payload.
+
+The sender MAY tell the receiver of this payload the hostname and the
+port where the SKE protocol is running in the sender's end. The
+receiver MAY then initiate the SKE negotiation with the sender. The
+sender MAY also optionally not to include the hostname and the port
+of its SKE protocol. In this case the receiver MAY reply to the
+request by sending the same payload filled with the receiver's hostname
+and the port where the SKE protocol is running. The sender MAY then
+initiate the SKE negotiation with the receiver.
+
+This payload may be sent with SILC_PACKET_KEY_AGREEMENT and
+SILC_PACKET_FTP packet types. It MUST NOT be sent in any other packet
+types. The following diagram represents the Key Agreement Payload.
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Hostname Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Hostname ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Port |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 21: Key Agreement Payload
+
+
+.in 6
+o Hostname Length (2 bytes) - Indicates the length of the
+ Hostname field.
+
+o Hostname (variable length) - The hostname or IP address where
+ the SKE protocol is running, as UTF-8 encoded string. The sender
+ MAY fill this field when sending the payload. If the receiver
+ sends this payload as reply to the request it MUST fill this field.
+
+o Port (4 bytes) - The port where the SKE protocol is bound.
+ The sender MAY fill this field when sending the payload. If
+ the receiver sends this payload as reply to the request it
+ MUST fill this field. This is a 32 bit MSB first order value.
+.in 3
+
+
+After the key material has been received from the SKE protocol it is
+processed as the [SILC3] describes. If the key material is used as
+channel private key then the Sending Encryption Key, as defined in
+[SILC3] is used as the channel private key. Other key material must
+be discarded. The [SILC1] in section 4.6 defines the way to use the
+key material if it is intended to be used as private message keys.
+Any other use for the key material is undefined.
+
+
+.ti 0
+2.3.21 Resume Router Payload
+
+See the [SILC1] for Resume Router protocol where this payload is
+used. The payload may only be sent with SILC_PACKET_RESUME_ROUTER
+packet. It MUST NOT be sent in any other packet type. The following
+diagram represents the Resume Router Payload.
+
+
+.in 21
+.nf
+ 1
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Type | Session ID |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 22: Resume Router Payload
+
+
+.in 6
+o Type (1 byte) - Indicates the type of the backup resume
+ protocol packet. The type values are defined in [SILC1].
+
+o Session ID (1 bytes) - Indicates the session ID for the
+ backup resume protocol. The sender of the packet sets this
+ value and the receiver MUST set the same value in subsequent
+ reply packet.
+.in 3
+
+
+
+
+.ti 0
+2.3.22 File Transfer Payload
+
+File Transfer Payload is used to perform file transfer protocol between
+two entities in the network. The actual file transfer protocol is always
+encapsulated inside the SILC Packet. The actual data stream is also sent
+peer to peer outside SILC network.
+
+When an entity, usually a client wishes to perform file transfer protocol
+with another client in the network, they perform Key Agreement protocol
+as described in the section 2.3.20 Key Agreement Payload and in [SILC3],
+inside File Transfer Payload. After the Key Agreement protocol has been
+performed the subsequent packets in the data stream will be protected
+using the new key material. The actual file transfer protocol is also
+initialized in this stage. All file transfer protocol packets are always
+encapsulated in the File Transfer Payload and protected with the
+negotiated key material.
+
+The payload may only be sent with SILC_PACKET_FTP packet. It MUST NOT
+be sent in any other packet type. The following diagram represents the
+File Transfer Payload.
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Type | |
++-+-+-+-+-+-+-+-+ +
+| |
+~ Data ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 23: File Transfer Payload
+
+
+.in 6
+o Type (1 byte) - Indicates the type of the file transfer
+ protocol. The following file transfer protocols has been
+ defined:
+
+ 1 Secure File Transfer Protocol (SFTP) (mandatory)
+
+ If zero (0) value or any unsupported file transfer protocol
+ type is found in this field the packet MUST be discarded.
+ The currently mandatory file transfer protocol is SFTP.
+ The SFTP protocol is defined in [SFTP].
+
+o Data (variable length) - Arbitrary file transfer data. The
+ contents and encoding of this field is dependent of the usage
+ of this payload and the type of the file transfer protocol.
+ When this payload is used to perform the Key Agreement
+ protocol, this field include the Key Agreement Payload,
+ as defined in the section 2.3.20 Key Agreement Payload.
+ When this payload is used to send the actual file transfer
+ protocol data, the encoding is defined in the corresponding
+ file transfer protocol.
+.in 3
+
+
+.ti 0
+2.3.23 Resume Client Payload
+
+This payload is used by client to resume its detached session in the
+SILC Network. A client is able to detach itself from the network by
+sending SILC_COMMAND_DETACH command to its server. The network
+connection to the client is lost but the client remains as valid
+client in the network. The client is able to resume the session back
+by sending this packet and including the old Client ID, and an
+Authentication Payload [SILC1] which the server use to verify with
+the detached client's public key. This also implies that the
+mandatory authentication method is public key authentication.
+
+Server or router that receives this from the client also sends this,
+without the Authentication Payload, to routers in the network so that
+they know the detached client has resumed. Refer to the [SILC1] for
+detailed description how the detaching and resuming procedure is
+performed.
+
+The payload may only be sent with SILC_PACKET_RESUME CLIENT packet. It
+MUST NOT be sent in any other packet type. The following diagram
+represents the Resume Client Payload.
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Client ID Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Client ID ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| |
+~ Authentication Payload ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 24: Resume Client Payload
+
+
+.in 6
+o Client ID Length (1 byte) - The length of the Client ID
+ field not including any other field.
+
+o Client ID (variable length) - The detached client's Client
+ ID. The client that sends this payload must know the Client
+ ID.
+
+o Authentication Payload (variable length) - The authentication
+ payload that the server will verify with the detached client's
+ public key. If the server doesn't know the public key, it must
+ retrieve it for example with SILC_COMMAND_GETKEY command.
+.in 3
+
+
+
+.ti 0
+2.4 SILC ID Types
+
+ID's are used in the SILC network to associate different entities.
+The following ID's has been defined to be used in the SILC network.
+
+.in 6
+0 No ID
+
+ This is used when other ID type is available at the time.
+
+1 Server ID
+
+ Server ID to associate servers. See the format of
+ this ID in [SILC1].
+
+2 Client ID
+
+ Client ID to associate clients. See the format of
+ this ID in [SILC1].
+
+3 Channel ID
+
+ Channel ID to associate channels. See the format of
+ this ID in [SILC1].
+.in 3
+
+When encoding different IDs into the ID Payload, all fields are always
+in MSB first order. The IP address, port, and/or the random number
+are encoded in the MSB first order.
+
+
+.ti 0
+2.5 Packet Encryption And Decryption
+
+SILC packets are encrypted almost entirely. Only the MAC at the end
+of the packet is never encrypted. The SILC Packet header is the first
+part of a packet to be encrypted and it is always encrypted with the
+key of the next receiver of the packet. The data payload area of the
+packet is always entirely encrypted and it is usually encrypted with
+the next receiver's key. However, there are some special packet types
+and packet payloads that require special encryption process. These
+special cases are described in the next sections. First is described
+the normal packet encryption process.
+
+
+
+.ti 0
+2.5.1 Normal Packet Encryption And Decryption
+
+Normal SILC packets are encrypted with the session key of the next
+receiver of the packet. The entire SILC Packet header and the packet
+data payload is is encrypted with the same key. Padding of the packet
+is also encrypted always with the session key, also in special cases.
+Computed MAC of the packet MUST NOT be encrypted.
+
+Decryption process in these cases are straightforward. The receiver
+of the packet MUST first decrypt the SILC Packet header, or some parts
+of it, usually first 16 bytes of it. Then the receiver checks the
+packet type from the decrypted part of the header and can determine
+how the rest of the packet must be decrypted. If the packet type is
+any of the special cases described in the following sections the packet
+decryption is special. If the packet type is not among those special
+packet types rest of the packet can be decrypted with the same key.
+At this point the receiver is also able to determine the length of the
+packet.
+
+With out a doubt, this sort of decryption processing causes some
+overhead to packet decryption, but never the less, is required.
+
+The MAC of the packet is also verified at this point. The MAC is
+computed from the ciphertext of the packet so it can be verified
+at this stage. The length of the packet need to be known to be able
+to verify the MAC from the ciphertext so the first 16 bytes need to
+be decrypted to determine the packet length. However, the MAC MUST
+be verified from the entire ciphertext.
+
+
+.ti 0
+2.5.2 Channel Message Encryption And Decryption
+
+Channel Messages (Channel Message Payload) are always encrypted with
+the channel specific key. However, the SILC Packet header is not
+encrypted with that key. As in normal case, the header is encrypted
+with the key of the next receiver of the packet. Note that, in this
+case the encrypted data area is not touched at all; it MUST NOT be
+re-encrypted with the session key.
+
+Receiver of a channel message, who ever that is, is REQUIRED to decrypt
+the SILC Packet header to be able to recognize the packet to be as
+channel message. This is same procedure as for normal SILC packets.
+As the receiver founds the packet to be channel message, rest of the
+packet processing is special. Rest of the SILC Packet header is
+decrypted with the same session key along with the padding of the
+packet. After that the packet is protected with the channel specific
+key and thus can be decrypted only if the receiver is the client on
+the channel. See section 2.7 Packet Padding Generation for more
+information about padding on special packets.
+
+If the receiver of the channel message is router which is routing the
+message to another router then it MUST decrypt the Channel Message
+payload too. Between routers (that is, between cells) channel messages
+are protected with session keys shared between the routers. This
+causes another special packet processing for channel messages. If
+the channel message is received from another router then the entire
+packet, including Channel Message payload, MUST be encrypted with the
+session key shared between the routers. In this case the packet
+decryption process is as with normal SILC packets. Hence, if the
+router is sending channel message to another router the Channel
+Message payload MUST have been decrypted and MUST be re-encrypted
+with the session key shared between the another router. In this
+case the packet encryption is as with any normal SILC packet.
+
+It must be noted that this is only when the channel messages are sent
+from router to another router. In all other cases the channel
+message encryption and decryption is as described before. This
+different processing of channel messages with router to router
+connection is because channel keys are cell specific. All cells have
+their own channel keys thus the channel message traveling from one
+cell to another MUST be protected as it would be any normal SILC
+packet.
+
+If the SILC_CMODE_PRIVKEY channel mode has been set for the channel
+then the router cannot decrypt the packet as it does not know the
+private key. In this case the entire packet MUST be encrypted with
+the session key and sent to the router. The router receiving the
+packet MUST check the channel mode and decrypt the packet accordingly.
+
+
+.ti 0
+2.5.3 Private Message Encryption And Decryption
+
+By default, private message in SILC are protected by session keys.
+In this case the private message encryption and decryption process is
+equivalent to normal packet encryption and decryption.
+
+However, private messages MAY be protected with private message key
+which causes the packet to be special packet. The procedure in this
+case is very much alike to channel packets. The actual private message
+is encrypted with the private message key and other parts of the
+packet is encrypted with the session key. See 2.7 Packet Padding
+Generation for more information about padding on special packets.
+
+The difference from channel message processing is that server or router
+en route never decrypts the actual private message, as it does not
+have the key to do that. Thus, when sending packets between router
+the processing is same as in any other case as well; the packet's header
+and padding is protected by the session key and the data area is not
+touched and is not re-encrypted.
+
+The true receiver of the private message is able to decrypt the private
+message as it shares the key with the sender of the message.
+
+
+.ti 0
+2.6 Packet MAC Generation
+
+Data integrity of a packet is protected by including a message
+authentication code (MAC) at the end of the packet. The MAC is computed
+from shared secret MAC key, that is established by the SILC Key Exchange
+protocol, from packet sequence number, and from the encrypted packet
+data. The MAC is always computed after packet is encrypted. This is
+so called Encrypt-Then-MAC order; packet is first encrypted, then MAC
+is computed from the encrypted data.
+
+The MAC is computed from entire packet. Every bit of data in the packet,
+including SILC Packet Header is used in the MAC computing. This way
+the entire packet becomes authenticated.
+
+Hence, packet's MAC generation is as follows:
+
+ mac = MAC(key, sequence number | Encrypted SILC packet)
+
+The MAC key is negotiated during the SKE protocol. The sequence number
+is a 32 bit MSB first value starting from zero for first packet and
+increasing for subsequent packets, finally wrapping after 2^32 packets.
+The value is never reset, not even after rekey has been performed.
+However, rekey MUST be performed before the sequence number wraps
+and repeats from zero. Note that the sequence number is incremented only
+when MAC is computed for a packet. If packet is not encrypted and MAC is
+not computed then the sequence number is not incremented. Hence, the
+sequence number is zero for the very first encrypted packet.
+
+See [SILC1] for defined and allowed MAC algorithms.
+
+
+.ti 0
+2.7 Packet Padding Generation
+
+Padding is needed in the packet because the packet is encrypted. It
+always MUST be multiple by eight (8) or multiple by the block size
+of the cipher, which ever is larger. The padding is always encrypted.
+
+For normal packets the padding is added after the SILC Packet Header
+and between the Data Payload area. The padding for normal packets
+may be calculated as follows:
+
+.in 6
+padding_length = 16 - (packet_length mod block_size)
+if (padding_length < 8)
+ padding_length += block_size
+.in 3
+
+The `block_size' is the block size of the cipher. The maximum padding
+length is 128 bytes, and minimum is 8 bytes. For example, packets that
+include a passphrase or a password for authentication purposes SHOULD
+pad the packet up to the maximum padding length. The maximum padding
+is calculated as follows:
+
+.in 6
+padding_length = 128 - (packet_length mod block_size)
+.in 3
+
+For special packets the padding calculation is different as special
+packets may be encrypted differently. In these cases the encrypted
+data area MUST already be multiple by the block size thus in this case
+the padding is calculated only for SILC Packet Header, not for any
+other area of the packet. The same algorithm works in this case as
+well, except that the `packet length' is now the SILC Packet Header
+length.
+
+The padding MUST be random data, preferably, generated by
+cryptographically strong random number generator for each packet
+separately.
+
+
+.ti 0
+2.8 Packet Compression
+
+SILC Packets MAY be compressed. In this case the data payload area
+is compressed and all other areas of the packet MUST remain as they
+are. After compression is performed for the data area, the length
+field of Packet Header MUST be set to the compressed length of the
+data.
+
+The compression MUST always be applied before encryption. When
+the packet is received and decrypted the data area MUST be decompressed.
+Note that the true sender of the packet MUST apply the compression and
+the true receiver of the packet MUST apply the decompression. Any
+server or router en route SHOULD NOT decompress the packet.
+
+
+.ti 0
+2.9 Packet Sending
+
+The sender of the packet MUST assemble the SILC Packet Header with
+correct values. It MUST set the Source ID of the header as its own
+ID, unless it is forwarding the packet. It MUST also set the Destination
+ID of the header to the true destination. If the destination is client
+it will be Client ID, if it is server it will be Server ID and if it is
+channel it will be Channel ID.
+
+If the sender wants to compress the packet it MUST apply the
+compression now. Sender MUST also compute the padding as described
+in above sections. Then sender MUST encrypt the packet as has been
+described in above sections according whether the packet is normal
+packet or special packet. Then sender MUST compute the MAC of the
+packet. The computed MAC MUST NOT be encrypted.
+
+
+.ti 0
+2.10 Packet Reception
+
+On packet reception the receiver MUST check that all fields in the
+SILC Packet Header are valid. It MUST check the flags of the
+header and act accordingly. It MUST also check the MAC of the packet
+and if it is to be failed the packet MUST be discarded. Also if the
+header of the packet includes any bad fields the packet MUST be
+discarded.
+
+See above sections on the decryption process of the received packet.
+
+The receiver MUST also check that the ID's in the header are valid
+ID's. Unsupported ID types or malformed ID's MUST cause packet
+rejection. The padding on the reception is always ignored.
+
+The receiver MUST also check the packet type and start parsing the
+packet according to the type. However, note the above sections on
+special packet types and their parsing.
+
+
+.ti 0
+2.11 Packet Routing
+
+Routers are the primary entities in the SILC network that takes care
+of packet routing. However, normal servers routes packets as well, for
+example, when they are routing channel message to the local clients.
+Routing is quite simple as every packet tells the true origin and the
+true destination of the packet.
+
+It is still RECOMMENDED for routers that has several routing connections
+to create route cache for those destinations that has faster route than
+the router's primary route. This information is available for the router
+when other router connects to the router. The connecting party then
+sends all of its locally connected clients, servers and channels. These
+informations helps to create the route cache. Also, when new channels
+are created to a cell its information is broadcasted to all routers
+in the network. Channel ID's are based on router's ID thus it is easy
+to create route cache based on these informations. If faster route for
+destination does not exist in router's route cache the packet MUST be
+routed to the primary route (default route).
+
+However, there are some issues when routing channel messages to group
+of users. Routers are responsible of routing the channel message to
+other routers, local servers and local clients as well. Routers MUST
+send the channel message to only one router in the network, preferably
+to the shortest route to reach the channel users. The message can be
+routed into either upstream or downstream. After the message is sent
+to a router in the network it MUST NOT be sent to any other router in
+either same route or other route. The message MUST NOT be routed to
+the router it came from.
+
+When routing for example private messages they should be routed to the
+shortest route always to reach the destination client as fast as possible.
+
+For server which receives a packet to be routed to an entity that is
+indirectly connected to the sender, the server MUST check whether that
+particular packet type is allowed to be routed to that destination. Not
+all packets may be sent by some odd entity to for example a local client,
+or to some remote server or router, that is indirectly connected to the
+sender. See section 2.3 SILC Packet Types and paragraph about indirectly
+connected entities and sending packets to them. That section defines the
+packets that may be sent to indirectly connected entities. When a server
+or a router receives a packet that may be sent to indirectly connected
+entity and it is destined to other entity except that server, it MUST
+route it further either to shortest route or to the primary route to reach
+that destination.
+
+Routers form a ring in the SILC network. However, routers may have other
+direct connections to other routers in the network too. This can cause
+interesting routing problems in the network. Since the network is a ring,
+the packets usually should be routed into clock-wise direction, or if it
+cannot be used then always counter clock-wise (primary route) direction.
+Problems may arise when a faster direct route exists and router is routing
+a channel message. Currently channel messages must be routed either
+in upstream or downstream, they cannot be routed to other direct routes.
+The SILC protocol should have a shortest path discovery protocol, and some
+existing routing protocol, that can handle a ring network with other
+direct routes inside the ring (so called hybrid ring-mesh topology),
+MAY be defined to be used with the SILC protocol. Additional
+specifications MAY be written on the subject to permeate this
+specification.
+
+
+.ti 0
+2.12 Packet Broadcasting
+
+SILC packets MAY be broadcasted in SILC network. However, only router
+server may send or receive broadcast packets. Client and normal server
+MUST NOT send broadcast packets and they MUST ignore broadcast packets
+if they receive them. Broadcast packets are sent by setting Broadcast
+flag to the SILC packet header.
+
+Broadcasting packets means that the packet is sent to all routers in
+the SILC network, except to the router that sent the packet. The router
+receiving broadcast packet MUST send the packet to its primary route.
+The fact that SILC routers may have several router connections can
+cause problems, such as race conditions inside the SILC network, if
+care is not taken when broadcasting packets. Router MUST NOT send
+the broadcast packet to any other route except to its primary route.
+
+If the primary route of the router is the original sender of the packet
+the packet MUST NOT be sent to the primary route. This may happen
+if router has several router connections and some other router uses
+the router as its primary route.
+
+Routers use broadcast packets to broadcast for example information
+about newly registered clients, servers, channels etc. so that all the
+routers may keep these informations up to date.
+
+
+.ti 0
+3 Security Considerations
+
+Security is central to the design of this protocol, and these security
+considerations permeate the specification. Common security considerations
+such as keeping private keys truly private and using adequate lengths for
+symmetric and asymmetric keys must be followed in order to maintain the
+security of this protocol.
+
+
+.ti 0
+4 References
+
+[SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
+ Protocol Specification", Internet Draft, May 2002.
+
+[SILC3] Riikonen, P., "SILC Key Exchange and Authentication
+ Protocols", Internet Draft, May 2002.
+
+[SILC4] Riikonen, P., "SILC Commands", Internet Draft, May 2002.
+
+[IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
+ RFC 1459, May 1993.
+
+[IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
+ April 2000.
+
+[IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
+ 2811, April 2000.
+
+[IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
+ 2812, April 2000.
+
+[IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
+ 2813, April 2000.
+
+[SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
+ Internet Draft.
+
+[PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
+ November 1998.
+
+[SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
+ September 1999.
+
+[PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
+ Infrastructure, Certificate and CRL Profile", RFC 2459,
+ January 1999.
+
+[Schneier] Schneier, B., "Applied Cryptography Second Edition",
+ John Wiley & Sons, New York, NY, 1996.
+
+[Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
+ CRC Press 1997.
+
+[OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
+ RFC 2412, November 1998.
+
+[ISAKMP] Maughan D., et al, "Internet Security Association and
+ Key Management Protocol (ISAKMP)", RFC 2408, November
+ 1998.
+
+[IKE] Harkins D., and Carrel D., "The Internet Key Exchange
+ (IKE)", RFC 2409, November 1998.
+
+[HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
+ Authentication", RFC 2104, February 1997.
+
+[PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
+ Specifications, Version 2.0", RFC 2437, October 1998.
+
+[RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate
+ Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+[SFTP] Ylonen T., and Lehtinen S., "Secure Shell File Transfer
+ Protocol", Internet Draft, March 2001.
+
+[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
+ 10646", RFC 3629, November 2003.
+
+
+.ti 0
+5 Author's Address
+
+.nf
+Pekka Riikonen
+Snellmaninkatu 34 A 15
+70100 Kuopio
+Finland
+
+EMail: priikone@iki.fi
+
+
+.ti 0
+6 Full Copyright Statement
+
+Copyright (C) The Internet Society (2003). All Rights Reserved.
+
+This document and translations of it may be copied and furnished to
+others, and derivative works that comment on or otherwise explain it
+or assist in its implementation may be prepared, copied, published
+and distributed, in whole or in part, without restriction of any
+kind, provided that the above copyright notice and this paragraph are
+included on all such copies and derivative works. However, this
+document itself may not be modified in any way, such as by removing
+the copyright notice or references to the Internet Society or other
+Internet organizations, except as needed for the purpose of
+developing Internet standards in which case the procedures for
+copyrights defined in the Internet Standards process must be
+followed, or as required to translate it into languages other than
+English.
+
+The limited permissions granted above are perpetual and will not be
+revoked by the Internet Society or its successors or assigns.
+
+This document and the information contained herein is provided on an
+"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
+TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
+BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
+HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
+MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
projects / silc.git / commitdiff