4.8 Session Key Regeneration .................................. 39
4.9 Command Sending and Reception ............................. 40
4.10 Closing Connection ....................................... 41
+ 4.11 Detaching and Resuming a Session ......................... XXXXX
5 Security Considerations ....................................... 41
6 References .................................................... 42
7 Author's Address .............................................. 44
possible to have 2^8 same nicknames from the same
server IP address.
-o MD5 hash - MD5 hash value of the nickname is truncated
- taking 88 bits from the start of the hash value. This
- hash value is used to search the user's Client ID from
- the ID lists.
+o MD5 hash - MD5 hash value of the lowercase nickname is
+ truncated taking 88 bits from the start of the hash value.
+ This hash value is used to search the user's Client ID
+ from the ID lists. Note that the nickname MUST be in
+ lowercase format.
.in 3
Collisions could occur when more than 2^8 clients using same nickname
Client usually sends the commands and server replies by sending a reply
packet to the command. Server MAY also send commands usually to serve
-the original client's request. However, server MUST NOT send commands
-to client and there are some commands that server must not send.
+the original client's request. Usually server cannot send commands to
+clients, however there MAY be commands that allow the server to send
+commands to client. By default servers MAY send commands only to other
+servers and routers.
Note that the command reply is usually sent only after client has sent
the command request but server is allowed to send command reply packet
-to client even if client has not requested the command. Client MAY,
+to client even if client has not requested the command. Client MAY
choose to ignore the command reply.
It is expected that some of the commands may be miss-used by clients
Every packet sent from client to server, with exception of packets for
channels, are encrypted with this session key.
-Channels has their own key that are shared by every client on the channel.
+Channels has a channel key that are shared by every client on the channel.
However, the channel keys are cell specific thus one cell does not know
the channel key of the other cell, even if that key is for same channel.
Channel key is also known by the routers and all servers that has clients
The header in the packet MUST NOT change during the routing of the
packet. The original sender, for example client, assembles the packet
and the packet header and server or router between the sender and the
-receiver MUST NOT change the packet header.
+receiver MUST NOT change the packet header. Note however, that some
+packets such as commands may resent by a server to serve the client's
+original command. In this case the command packet send by the server
+includes the server's IDs.
Note that the packet and the packet header may be encrypted with
different keys. For example, packets to channels are encrypted with
message delivery key with each other and that is used in
the message encryption.
-o Client 1. sends encrypted packet to its server. The packet is
- encrypted with the private message delivery key shared between
- clients.
+o Client 1. sends encrypted packet to its server. The packet header
+ is encrypted with the session key shared between the client and
+ server, and the private message is encrypted with the private
+ message delivery key shared between clients.
o Server determines the destination of the packet and sends the
packet to the router.
client connecting to the server. However, usually clients are accepted
to connect to server without explicit authentication. Servers are
required use authentication protocol when connecting. The authentication
-may be based on passphrase (pre-shared-secret) or public key. The
-connection authentication protocol is described in detail in [SILC3].
+may be based on passphrase (pre-shared-secret) or public key. All
+passphrases sent in SILC protocol MUST be UTF-8 [RFC2279] encoded.
+The connection authentication protocol is described in detail in [SILC3].
.ti 0
3.9.1 Authentication Payload
Authentication payload is used separately from the SKE and the Connection
-Authentication protocol. It is used during the session to authenticate
+Authentication protocol. It can be used during the session to authenticate
with the remote. For example, the client can authenticate itself to the
server to become server operator. In this case, Authentication Payload is
used.
.in 6
o Payload Length (2 bytes) - Length of the entire payload.
-o Authentication Method (2) - The method of the authentication.
- The authentication methods are defined in [SILC2] in the
- Connection Auth Request Payload. The NONE authentication
- method SHOULD NOT be used.
+o Authentication Method (2 bytes) - The method of the
+ authentication. The authentication methods are defined
+ in [SILC2] in the Connection Auth Request Payload. The NONE
+ authentication method SHOULD NOT be used.
o Public Data Length (2 bytes) - Indicates the length of
the Public Data field.
the signature process, described subsequently.
o Authentication Data Length (2 bytes) - Indicates the
- length of the Authentication Data field.
+ length of the Authentication Data field. If zero (0)
+ value is found in this field the payload MUST be
+ discarded.
o Authentication Data (variable length) - Authentication
method dependent authentication data.
If the authentication method is password based, the Authentication
-Data field includes the plaintext password. It is safe to send
-plaintext password since the entire payload is encrypted. In this
-case the Public Data Length is set to zero (0), but MAY also include
+Data field includes the plaintext UTF-8 encoded password. It is safe
+to send plaintext password since the entire payload is encrypted. In
+this case the Public Data Length is set to zero (0), but MAY also include
random data for padding purposes. It is also RECOMMENDED that maximum
amount of padding is applied to SILC packet when using password based
authentication. This way it is not possible to approximate the length
cryptography function selected in the SKE protocol. The public key
is SILC style public key unless certificates are used. The ID is the
entity's ID (Client or Server ID) which is authenticating itself. The
-ID is raw ID data. The random bytes are non-zero random bytes of
-length between 128 and 4096 bytes, and will be included into the
-Public Data field as is.
+ID encoding is described in [SILC2]. The random bytes are non-zero
+random bytes of length between 128 and 4096 bytes, and will be included
+into the Public Data field as is.
The receiver will compute the signature using the random data received
in the payload, the ID associated to the connection and the public key
(or certificate) received in the SKE protocol. After computing the
-receiver MUST verify the signature. In this case also, the entire
-payload is encrypted.
+receiver MUST verify the signature. In case of public key authentication
+this payload is also encrypted.
.ti 0
.in 3
Protocol version MAY provide both major and minor version. Currently
-implementations MUST set the protocol version and accept the protocol
-version as SILC-1.1-<software version>. If new protocol version causes
-in compatibilities with older version the the <minor> versio number MUST
-be incremented. The <major> is incremented if new protocol version is
-fully incompatible.
+implementations MUST set the protocol version and accept at least the
+protocol version as SILC-1.1-<software version>. If new protocol version
+causes incompatibilities with older version the <minor> version number
+MUST be incremented. The <major> is incremented if new protocol version
+is fully incompatible.
-Software version MAY provide major, minor and build version. The
-software version MAY be freely set and accepted.
+Software version MAY provide major, minor and build (vendor) version.
+The software version MAY be freely set and accepted. The version string
+MUST consist of printable US-ASCII characters.
Thus, the version strings could be, for example:
SILC-1.1-2.0.2
SILC-1.0-1.2
SILC-1.1-1.0.VendorXYZ
+SILC-1.1-2.4.5 Vendor Limited
.in 3
client to its router (or if the server is router, to all routers in
the SILC network). More information about this in [SILC2].
+Router server MUST also check whether some client in the local cell
+is watching for the nickname this new client has, and send the
+SILC_NOTIFY_TYPE_WATCH to the watcher.
+
.ti 0
4.2 Creating Server Connection
it should have cached the Client ID from the SILC Packet Header.
If server receives a private message packet which includes invalid
-destionation Client ID the server MUST send SILC_COMMAND_IDENTIFY
-command reply packet destined to the client with error status.
+destionation Client ID the server MUST send SILC_NOTIFY_TYPE_ERROR
+notify to the client with error status indicating that such Client ID
+does not exist.
See [SILC2] for description of private message encryption and decryption
process.
in [SILC3], however, the HMAC key material MUST be discarded.
If the key is pre-shared-key or randomly generated the implementations
-should use the SILC protocol's mandatory cipher as the cipher. If the
-SKE was used to negotiate key material the cipher was negotiated as well.
+SHOULD use the SILC protocol's mandatory cipher as the cipher. If the
+SKE was used to negotiate key material the cipher was negotiated as well,
+and may be different from default cipher.
+
.ti 0
4.7 Channel Message Sending and Reception
distribute the message to all clients on the channel by sending the
channel message destined explicitly to a client on the channel.
-See the [SILC2] for description of channel messege routing for router
-servers.
+If server receives a channel message packet which includes invalid
+destionation Channel ID the server MUST send SILC_NOTIFY_TYPE_ERROR
+notify to the sender with error status indicating that such Channel ID
+does not exist.
-See [SILC2] for description of channel message encryption and decryption
-process.
+See the [SILC2] for description of channel messege routing for router
+servers, and channel message encryption and decryption process.
.ti 0
Client usually sends the commands in the SILC network. In this case
the client simply sends the command packet to server and the server
-processes it and replies with command reply packet.
+processes it and replies with command reply packet. See the [SILC3]
+for detailed description of all commands.
However, if the server is not able to process the command, it is sent
to the server's router. This is case for example with commands such
local clients that are joined on the same channels with the remote
server's or router's clients.
+Router server MUST also check whether some client in the local cell
+is watching for the nickname this client has, and send the
+SILC_NOTIFY_TYPE_WATCH to the watcher, unless the client which left
+the network has the SILC_UMODE_REJECT_WATCHING user mode set.
+
+
+.ti 0
+4.11 Detaching and Resuming a Session
+
+SILC protocol provides a possibility for a client to detach itself from
+the network without actually signing off from the network. The client
+connection to the server is closed but the client remains as valid client
+in the network. The client may then later resume its session back from
+any server in the network.
+
+When client wishes to detach from the network it MUST send the
+SILC_COMMAND_DETACH command to its server. The server then MUST set
+SILC_UMODE_DETACHED mode to the client and send SILC_NOTIFY_UMODE_CHANGE
+notify to its primary router, which will then MUST broadcast it further
+to other routers in the network. This user mode indicates that the
+client is detached from the network. Implementations MUST NOT use
+the SILC_UMODE_DETACHED flag to determine whether a packet can be sent
+to the client. All packets MUST still be sent to the client even if
+client is detached from the network. Only the server that originally
+had the active client connection is able to make the decision after it
+notices that the network connection is not active. In this case the
+default case is to discard the packet.
+
+The SILC_UMODE_DETACHED flag cannot be set by client itself directly
+with SILC_COMMAND_UMODE command, but only implicitly by sending the
+SILC_COMMAND_DETACH command. The flag also cannot be unset by the
+client, server or router with SILC_COMMAND_UMODE command, but only
+implicitly by sending and receiving the SILC_PACKET_RESUME_CLIENT
+packet.
+
+When the client wishes to resume its session in the SILC Network it
+connects to a server in the network, which MAY also be a different
+from the original server, and performs normal procedures regarding
+creating a connection as described in section 4.1. After the SKE
+and the Connection Authentication protocols has been successfully
+completed the client MUST NOT send SILC_PACKET_NEW_CLIENT packet, but
+MUST send SILC_PACKET_RESUME_CLIENT packet. This packet is used to
+perform the resuming procedure. The packet MUST include the detached
+client's Client ID, which the client must know. It also includes
+Authentication Payload which includes signature made with the client's
+private key. The signature is computed as defined in the section
+3.9.1. Thus, the authentication method MUST be based in public key
+authentication.
+
+When server receives the SILC_PACKET_RESUME_CLIENT packet it MUST
+do the following: Server checks that the Client ID is valid client
+and that it has the SILC_UMODE_DETACHED mode set. Then it verifies
+the Authentication Payload with the detached client's public key.
+If it does not have the public key it retrieves it by sending
+SILC_COMMAND_GETKEY command to the server that has the public key from
+the original client connection. The server MUST NOT use the public
+key received in the SKE protocol for this connection. If the
+signature is valid the server unsets the SILC_UMODE_DETACHED flag,
+and sends the SILC_PACKET_RESUME_CLIENT packet to its primary router.
+The routers MUST broadcast the packet and unset the SILC_UMODE_DETACHED
+flag when the packet is received. If the server is router server it
+also MUST send the SILC_PACKET_RESUME_CLIENT packet to the original
+server whom owned the detached client.
+
+The servers and routers that receives the SILC_PACKET_RESUME_CLIENT
+packet MUST know whether the packet already has been received for
+the client. It is protocol error to attempt to resume the client
+session from more than one server. The implementations could set
+internal flag that indicates that the client is resumed. If router
+receive SILC_PACKET_RESUME_CLIENT packet for client that is already
+resumed the client MUST be killed from the network. This would
+indicate that the client is attempting to resume the session more
+than once which is protocol error. In this case the router sends
+SILC_NOTIFY_TYPE_KILLED to the client. All routers that detect
+the same situation MUST also send the notify for the client.
+
+The servers and routers that receive the SILC_PACKET_RESUME_CLIENT
+must also understand that the client may not be found behind the
+same server that it originally came from. They must update their
+caches according this. The server that now owns the client session
+MUST check whether the Client ID of the resumed client is based
+on the server's Server ID. If it is not it creates a new Client
+ID and send SILC_NOTIFY_TYPE_NICK_CHANGE to the network. It MUST
+also send the channel keys of all channels that the client is
+joined to the client since it does not have them. Whether the
+Client ID was changed or not the server MUST send SILC_PACKET_NEW_ID
+packet to the client. Only after this the client is resumed back
+to the network and may start sending packets and messages.
+
+It is also possible that the server does not know about the channels
+that the client has joined. In this case it join the client internally
+to the channels, generate new channel keys and distribute the keys
+to the channels as described in section 4.4.
+
+It is implementation issue for how long servers keep detached client
+sessions. It is RECOMMENDED that the detached sessions would be
+persistent as long as the server is running.
+
.ti 0
5 Security Considerations
[RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
-
-
+[RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO
+ 10646", RFC 2279, January 1998.
projects / silc.git / blobdiff