.ds RF FORMFEED[Page %]
.ds CF
.ds LH Internet Draft
-.ds RH XXX
+.ds RH 15 May 2002
.ds CH
.na
.hy 0
.nf
Network Working Group P. Riikonen
Internet-Draft
-draft-riikonen-silc-spec-05.txt XXX
-Expires: XXX
+draft-riikonen-silc-spec-05.txt 15 May 2002
+Expires: 15 November 2002
.in 3
3.2.2 Server ID ........................................... 11
3.2.3 SILC Server Ports ................................... 12
3.3 Router .................................................... 12
- 3.3.1 Router's Local ID List .............................. 12
+ 3.3.1 Router's Local ID List .............................. 13
3.3.2 Router's Global ID List ............................. 13
3.3.3 Router's Server ID .................................. 14
3.4 Channels .................................................. 14
- 3.4.1 Channel ID .......................................... 16
+ 3.4.1 Channel ID .......................................... 15
3.5 Operators ................................................. 16
3.6 SILC Commands ............................................. 16
3.7 SILC Packets .............................................. 17
3.8 Packet Encryption ......................................... 17
- 3.8.1 Determination of the Source and the Destination ..... 17
+ 3.8.1 Determination of the Source and the Destination ..... 18
3.8.2 Client To Client .................................... 18
- 3.8.3 Client To Channel ................................... 19
+ 3.8.3 Client To Channel ................................... 20
3.8.4 Server To Server .................................... 20
3.9 Key Exchange And Authentication ........................... 20
- 3.9.1 Authentication Payload .............................. 20
- 3.10 Algorithms ............................................... 22
- 3.10.1 Ciphers ............................................ 22
- 3.10.2 Public Key Algorithms .............................. 23
+ 3.9.1 Authentication Payload .............................. 21
+ 3.10 Algorithms ............................................... 23
+ 3.10.1 Ciphers ............................................ 23
+ 3.10.2 Public Key Algorithms .............................. 24
3.10.3 Hash Functions ..................................... 24
- 3.10.4 MAC Algorithms ..................................... 24
+ 3.10.4 MAC Algorithms ..................................... 25
3.10.5 Compression Algorithms ............................. 25
- 3.11 SILC Public Key .......................................... 25
- 3.12 SILC Version Detection ................................... 27
+ 3.11 SILC Public Key .......................................... 26
+ 3.12 SILC Version Detection ................................... 28
3.13 Backup Routers ........................................... 28
- 3.13.1 Switching to Backup Router ......................... 29
- 3.13.2 Resuming Primary Router ............................ 30
- 3.13.3 Discussion on Backup Router Scheme ................. 32
-4 SILC Procedures ............................................... 33
- 4.1 Creating Client Connection ................................ 33
- 4.2 Creating Server Connection ................................ 34
- 4.2.1 Announcing Clients, Channels and Servers ............ 35
- 4.3 Joining to a Channel ...................................... 36
- 4.4 Channel Key Generation .................................... 37
- 4.5 Private Message Sending and Reception ..................... 38
- 4.6 Private Message Key Generation ............................ 38
- 4.7 Channel Message Sending and Reception ..................... 39
- 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
+ 3.13.1 Switching to Backup Router ......................... 30
+ 3.13.2 Resuming Primary Router ............................ 31
+ 3.13.3 Discussion on Backup Router Scheme ................. 33
+4 SILC Procedures ............................................... 34
+ 4.1 Creating Client Connection ................................ 34
+ 4.2 Creating Server Connection ................................ 35
+ 4.2.1 Announcing Clients, Channels and Servers ............ 36
+ 4.3 Joining to a Channel ...................................... 37
+ 4.4 Channel Key Generation .................................... 38
+ 4.5 Private Message Sending and Reception ..................... 39
+ 4.6 Private Message Key Generation ............................ 39
+ 4.7 Channel Message Sending and Reception ..................... 40
+ 4.8 Session Key Regeneration .................................. 40
+ 4.9 Command Sending and Reception ............................. 41
+ 4.10 Closing Connection ....................................... 42
+ 4.11 Detaching and Resuming a Session ......................... 42
+5 Security Considerations ....................................... 44
+6 References .................................................... 45
+7 Author's Address .............................................. 47
This document describes a Secure Internet Live Conferencing (SILC)
protocol which provides secure conferencing services over insecure
network channel. SILC is IRC [IRC] like protocol, however, it is
-not equivalent to IRC and does not support IRC.
+not equivalent to IRC and does not support IRC. Some of the SILC's
+features are not found in IRC but in traditional Instant Message (IM)
+protocols. SILC combines features from both of these chat protocol
+styles, and SILC can be implemented as either IRC-like system or
+IM-like system.
Strong cryptographic methods are used to protect SILC packets inside
the SILC network. Three other Internet Drafts relates very closely
requires message and command sending. The SILC Packet Protocol is
described in [SILC2] and should be read to fully comprehend this
document and protocol. [SILC2] also describes the packet encryption
-and decryption in detail.
+and decryption in detail. The SILC Packet Protocol provides secured
+and authenticated packets, and the protocol is designed to be compact.
+This makes SILC also suitable in environment of low bandwidth
+requirements such as mobile networks. All packet payloads in SILC
+can be also compressed.
The security of SILC protocol, and for any security protocol for that
matter, is based on strong and secure key exchange protocol. The SILC
are in the center of the cell and servers are connected to the router.
-
-
-
-
-
The following diagram represents SILC network topology.
.in 8
represents message sending between cells.
+
+
+
.in 16
.nf
1 --- S1 S4 --- 5 S2 --- 1
must not routers use each other as their primary routes. The router
connections in the network must form a ring.
-
-
-
-
-
-
Example with three routers in the network:
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
messages addressed to that channel. The channel is created when first
client requests JOIN command to the channel, and the channel ceases to
exist when the last client has left it. When channel exists, any client
-can reference it using the name of the channel.
+can reference it using the name of the channel. If the channel has
+a founder mode set and last client leaves the channel the channel does
+not cease to exist. The founder mode can be used to make permanent
+channels in the network. The founder of the channel can regain the
+channel founder privileges on the channel later when he joins the
+channel.
Channel names are unique although the real uniqueness comes from 64 bit
Channel ID. However, channel names are still unique and no two global
-channels with same name may exist. The Channel name is a string of
+channels with same name may exist. The channel name is a string of
maximum length of 256 bytes. Channel names MUST NOT contain any
-spaces (` '), any non-printable ASCII characters, commas (`,') and
-wildcard characters.
+whitespaces (` '), any non-printable ASCII characters, commas (`,')
+and wildcard characters.
Channels can have operators that can administrate the channel and
operate all of its modes. The following operators on channel exist on
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
Authentication Data = sign(HASH);
The hash() and the sign() are the hash function and the public key
-cryptography function selected in the SKE protocol. The public key
+cryptography function selected in the SKE protocol, unless otherwise
+stated in the context where this payload is used. 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 encoding is described in [SILC2]. The random bytes are non-zero
Additional public key algorithms MAY be defined to be used in SILC.
+When signatures are computed in SILC the computing of the signature is
+represented as sign(). The signature computing procedure is dependent
+of the public key algorithm, and the public key or certificate encoding.
+When using SILC public key the signature is computed as described in
+previous section for RSA and DSS keys. When using SSH2 public keys
+the signature is computed as described in [SSH-TRANS]. When using
+X.509 version 3 certificates the signature is computed as described
+in [PKCS7]. When using OpenPGP certificates the signature is computed
+as described in [PGP].
+
.ti 0
3.10.3 Hash Functions
.in 3
All fields in the public key are in MSB (most significant byte first)
-order.
+order. All strings in the public key are UTF-8 encoded.
.ti 0
Also, if any other router in the network is using the cell's primary
router as its own primary router, it must also have passive connection
to the cell's backup router. It too is prepared to switch to use the
-backup router as its new primary router as soon as the orignal primary
+backup router as its new primary router as soon as the original primary
router becomes unresponsive.
All of the parties of this protocol knows which one is the backup router
backup router. The backup router usually needs to do local modifications
to its database in order to update all the information needed to maintain
working routes. The backup router must understand that clients that
-were orignated from the primary router are now originated from some of
+were originated from the primary router are now originated from some of
the existing server connections and must update them accordingly. It
must also remove those clients that were owned by the primary router
since those connections were lost when the primary router became
3.13.2 Resuming Primary Router
Usually the primary router is unresponsive only a short period of time
-and it is intended that the original router of the cell will reassume
+and it is intended that the original router of the cell will resume
its position as primary router when it comes back online. The backup
router that is now acting as primary router of the cell must constantly
try to connect to the original primary router of the cell. It is
3.13.3 Discussion on Backup Router Scheme
It is clear that this backup router support is not able to handle all
-possible situations arrising in unreliable network environment. This
+possible situations arising in unreliable network environment. This
scheme for example does not handle situation when the router actually
does not go offline but the network link goes down temporarily. It would
require some intelligence to figure out when it is best time to switch
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_NOTIFY_TYPE_ERROR
-notify to the client with error status indicating that such ID does
-not exist to the client.
+destination 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
+destination 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 message 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
are running the service. It is recommended that some form of registration
is required by the server and router administrator prior acceptance to
the SILC Network. Even though, the SILC protocol is secure in a network
-of mutual distrust between clients, servers, routers and adminstrators
+of mutual distrust between clients, servers, routers and administrators
of the servers, the client should be able to trust the servers they are
-using if they whish to do so.
+using if they wish to do so.
It however must be noted that if the client requires absolute security
by not trusting any of the servers or routers in the SILC Network, it can
messages, private messages and channel messages.
It is important to note that SILC, like any other security protocol is
-not full proof system and cannot secure from insecure environment; the
-SILC servers and routers could very well be compromised. However, to
-provide acceptable level of security and usability for end user the
-protocol use many times session keys or other keys generated by the
-servers to secure the messages. This is intentional design feature to
-allow ease of use for end user. This way the network is still usable,
-and remains encrypted even if the external means of distributing the
-keys is not working. The implementation, however, may like to not
-follow this design feature, and always negotiate the keys outside SILC
-network. This is acceptable solution and many times recommended. The
-implementation still must be able to work with the server generated keys.
+not full proof system; the SILC servers and routers could very well be
+compromised. However, to provide acceptable level of security and
+usability for end user the protocol use many times session keys or other
+keys generated by the servers to secure the messages. This is
+intentional design feature to allow ease of use for end user. This way
+the network is still usable, and remains encrypted even if the external
+means of distributing the keys is not working. The implementation,
+however, may like to not follow this design feature, and always negotiate
+the keys outside SILC network. This is acceptable solution and many times
+recommended. The implementation still must be able to work with the
+server generated keys.
If this is unacceptable for the client or end user, the private keys
-negotiatied outside the SILC Network should always be used. In the end
+negotiated outside the SILC Network should always be used. In the end
it is always implementor's choice whether to negotiate private keys by
default or whether to use the keys generated by the servers.
6 References
[SILC2] Riikonen, P., "SILC Packet Protocol", Internet Draft,
- April 2001.
+ May 2002.
[SILC3] Riikonen, P., "SILC Key Exchange and Authentication
- Protocols", Internet Draft, April 2001.
+ Protocols", Internet Draft, May 2002.
-[SILC4] Riikonen, P., "SILC Commands", Internet Draft, April 2001.
+[SILC4] Riikonen, P., "SILC Commands", Internet Draft, May 2002.
[IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
RFC 1459, May 1993.
[RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 2279, January 1998.
+[PKCS7] Kalinski, B., "PKCS #7: Cryptographic Message Syntax,
+ Version 1.5", RFC 2315, March 1998.
.ti 0
.nf
Pekka Riikonen
-Snellmanninkatu 34 A 15
+Snellmaninkatu 34 A 15
70100 Kuopio
Finland
EMail: priikone@iki.fi
-This Internet-Draft expires XXX
+This Internet-Draft expires 15 November 2002
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