SILC (Secure Internet Live Conferencing protocol) is a

protocol Protocol may refer to: Sociology and politics * Protocol (politics), a formal agreement between nation states * Protocol (diplomacy), the etiquette of diplomacy and affairs of state * Etiquette, a code of personal behavior Science and technolog ...

that provides secure

synchronous conferencing Synchronous conferencing is the formal term used in computing, in particular in computer-mediated communication, collaboration and learning, to describe technologies informally known as online chat. It is sometimes extended to include audio/vid ...

services (very much like IRC) over the

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...

Components

The SILC protocol can be divided in three main parts: SILC Key Exchange (SKE) protocol, SILC Authentication protocol and SILC Packet protocol. SILC protocol additionally defines SILC Commands that are used to manage the SILC session. SILC provides channels (groups), nicknames, private messages, and other common features. However, SILC nicknames, in contrast to many other protocols (''e.g.''

IRC Internet Relay Chat (IRC) is a text-based chat system for instant messaging. IRC is designed for group communication in discussion forums, called '' channels'', but also allows one-on-one communication via private messages as well as chat an ...

), are not unique; a user is able to use any nickname, even if one is already in use. The real identification in the protocol is performed by unique Client ID. The SILC protocol uses this to overcome nickname collision, a problem present in many other protocols. All messages sent in a SILC network are binary, allowing them to contain any type of data, including text, video, audio, and other

multimedia Multimedia is a form of communication that uses a combination of different content forms such as text, audio, images, animations, or video into a single interactive presentation, in contrast to tradition ...

data. The SKE protocol is used to establish

session key A session key is a single-use symmetric key used for encrypting all messages in one communication session. A closely related term is content encryption key (CEK), traffic encryption key (TEK), or multicast key which refers to any key used for en ...

and other security parameters for protecting the SILC Packet protocol. The SKE itself is based on the

Diffie–Hellman key exchange Diffie–Hellman key exchangeSynonyms of Diffie–Hellman key exchange include: * Diffie–Hellman–Merkle key exchange * Diffie–Hellman key agreement * Diffie–Hellman key establishment * Diffie–Hellman key negotiation * Exponential key exc ...

algorithm (a form of

asymmetric cryptography Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic alg ...

) and the exchange is protected with

digital signatures A digital signature is a mathematical scheme for verifying the authenticity of digital messages or documents. A valid digital signature, where the prerequisites are satisfied, gives a recipient very high confidence that the message was created b ...

. The SILC Authentication protocol is performed after successful SKE protocol execution to authenticate a client and/or a server. The authentication may be based on

passphrase A passphrase is a sequence of words or other text used to control access to a computer system, program or data. It is similar to a password in usage, but a passphrase is generally longer for added security. Passphrases are often used to control ...

or on

, and if successful gives access to the relevant SILC network. The SILC Packet protocol is intended to be a secure binary packet protocol, assuring that the content of each

packet Packet may refer to: * A small container or pouch ** Packet (container), a small single use container ** Cigarette packet ** Sugar packet * Network packet, a formatted unit of data carried by a packet-mode computer network * Packet radio, a form ...

(consisting of a packet header and packet payload) is secured and authenticated. The packets are secured using algorithms based on symmetric cryptography and authenticated by using

Message Authentication Code In cryptography, a message authentication code (MAC), sometimes known as a ''tag'', is a short piece of information used for authenticating a message. In other words, to confirm that the message came from the stated sender (its authenticity) and ...

algorithm, HMAC. SILC channels (groups) are protected by using symmetric channel keys. It is optionally possible to digitally sign all channel messages. It is also possible to protect messages with a privately generated channel key that has been previously agreed upon by channel members. Private messages between users in a SILC network are protected with session keys. It is, however, possible to execute SKE protocol between two users and use the generated key to protect private messages. Private messages may be optionally digitally signed. When messages are secured with key material generated with the SKE protocol or previously agreed upon key material (for example,

s) SILC provides security even when the SILC server may be compromised.

History

SILC was designed by Pekka Riikonen between 1996 and 1999 and first released in public in summer 2000. A

client Client(s) or The Client may refer to: * Client (business) * Client (computing), hardware or software that accesses a remote service on another computer * Customer or client, a recipient of goods or services in return for monetary or other valuabl ...

and a

server Server may refer to: Computing *Server (computing), a computer program or a device that provides functionality for other programs or devices, called clients Role * Waiting staff, those who work at a restaurant or a bar attending customers and su ...

were written. Protocol specifications were proposed, but ultimately request for publication was denied in June 2004 by

IESG The Internet Engineering Task Force (IETF) is a standards organization for the Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster or requirements and a ...

and no RFC has been published to date. At present time, there are several clients, the most advanced being the official SILC client and an

irssi Irssi ( ) is an IRC client program for Linux, FreeBSD, macOS and Microsoft Windows. It was originally written by Timo Sirainen, and released under the terms of the GNU GPL-2.0-or-later in January 1999. Features Irssi is written in the C progr ...

plugin. SILC protocol is also integrated to the popular

Pidgin A pidgin , or pidgin language, is a grammatically simplified means of communication that develops between two or more groups of people that do not have a language in common: typically, its vocabulary and grammar are limited and often drawn from s ...

instant messaging client. Other

GUI The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inste ...

clients are Silky and Colloquy. The Silky client was put on hold and abandoned on the 18th of July 2007, due to inactivity for several years. The latest news on the Silky website was that the client was to be completely rewritten. As of 2008, three SILC protocol implementations have been written. Most SILC clients use libsilc, part of the SILC Toolkit. The SILC Toolkit is dual-licensed and distributed under both the GNU General Public License (GPL) and the revised BSD license.

Security

As described in the SILC FAQ, chats are secured through the generation of symmetric encryption keys. These keys have to be generated somewhere, and this occurs on the server. This means that chats might be compromised, if the server itself is compromised. This is just a version of the

man-in-the-middle attack In cryptography and computer security, a man-in-the-middle, monster-in-the-middle, machine-in-the-middle, monkey-in-the-middle, meddler-in-the-middle, manipulator-in-the-middle (MITM), person-in-the-middle (PITM) or adversary-in-the-middle (AiTM) ...

. The solution offered is that chat members generate their own public-private keypair for

asymmetric encryption Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic al ...

. The private key is shared only by the chat members, and this is done out of band. The public key is used to encrypt messages into the channel. This approach is still open to compromise, if one of the members of the chat should have their private key compromised, or if they should share the key with another, without agreement of the group.

Networks

SILC uses a similar pattern to IRC, in that there is no global "SILC network" but many small independent networks consisting of one or several servers each, although it is claimed that SILC can scale better with many servers in a single network. The "original" network is called SILCNet, at the round-robin. However, as of May 2014, it has only one active (though unstable) server out of four. Most SILC networks have shut down due to declining popularity of SILC.

References

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External links