A cipher suite is a named combination of authentication

Authentication

Authentication is the act of confirming the truth of an attribute of a datum or entity...

, encryption

Encryption

In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...

, and message authentication code

Message authentication code

In cryptography, a message authentication code is a short piece of information used to authenticate a message.A MAC algorithm, sometimes called a keyed hash function, accepts as input a secret key and an arbitrary-length message to be authenticated, and outputs a MAC...

 (MAC) algorithm

Algorithm

In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...

s used to negotiate the security settings for a network connection using the Transport Layer Security

Transport Layer Security

Transport Layer Security and its predecessor, Secure Sockets Layer , are cryptographic protocols that provide communication security over the Internet...

 (TLS) or Secure Sockets Layer (SSL) network protocol.

The structure and use of the cipher suite concept is defined in the documents that define the protocol (RFC 5246 standard for TLS version 1.2). A reference for named cipher suites is provided in RFC 2434, the TLS Cipher Suite Registry.

Use

When a TLS connection is established, a handshaking

Handshaking

In information technology, telecommunications, and related fields, handshaking is an automated process of negotiation that dynamically sets parameters of a communications channel established between two entities before normal communication over the channel begins...

, known as the TLS Handshake Protocol, occurs. Within this handshake, a client hello (ClientHello) and a server hello (ServerHello) message is passed. (RFC 5246, p. 37) First, the client sends a cipher suite list, a list of the cipher suites that it supports, in order of preference. Then the server replies with the cipher suite that it has selected from the client cipher suite list. (RFC 5246, p. 40)
In order to test which TLS ciphers that a server supports an SSL/TLS Scanner may be used.

Detailed description

Each named cipher suite defines a key exchange algorithm, a bulk encryption algorithm, a message authentication code

Message authentication code

In cryptography, a message authentication code is a short piece of information used to authenticate a message.A MAC algorithm, sometimes called a keyed hash function, accepts as input a secret key and an arbitrary-length message to be authenticated, and outputs a MAC...

 (MAC) algorithm, and a pseudorandom function

Pseudorandom function

In cryptography, a pseudorandom function family, abbreviated PRF, is a collection of efficiently-computable functions which emulate a random oracle in the following way: no efficient algorithm can distinguish between a function chosen randomly from the PRF family and a random oracle...

 (PRF). (RFC 5246, p. 40)

• The key exchange algorithm is used to determine if and how the client and server will authenticate during the handshake. (RFC 5246, p. 47).
• The bulk encryption algorithm is used to encrypt the message stream. It also includes the key size and the lengths of explicit and implicit initialization vector
  Initialization vector
  In cryptography, an initialization vector is a fixed-size input to a cryptographic primitive that is typically required to be random or pseudorandom...
  
  s (cryptographic nonce
  Cryptographic nonce
  In security engineering, nonce is an arbitrary number used only once to sign a cryptographic communication. It is similar in spirit to a nonce word, hence the name. It is often a random or pseudo-random number issued in an authentication protocol to ensure that old communications cannot be reused...
  
  s). (RFC 5246, p. 17)
• The message authentication code (MAC) algorithm is used to create the message digest, a cryptographic hash of each block
  Block (telecommunications)
  In telecommunications a block is one of:* A group of bits or digits that is transmitted as a unit and that may be encoded for error-control purposes....
  
   of the message stream. (RFC 5246, p. 17)
• The pseudorandom function (PRF) is used to create the master secret, a 48-byte secret shared between the two peers in the connection. The master secret is used as a source of entropy when creating session keys, such as the one used to create the MAC. (RFC 5246, p. 16-17, 26)

Examples of algorithms used

key exchange: RSA, Diffie-Hellman, ECDH

Elliptic Curve Diffie-Hellman

Elliptic curve Diffie–Hellman is a key agreement protocol that allows two parties, each having an elliptic curve public-private key pair, to establish a shared secret over an insecure channel. This shared secret may be directly used as a key, or better yet, to derive another key which can then be...

, SRP

Secure remote password protocol

The Secure Remote Password protocol is a password-authenticated key agreement protocol.- Overview :The SRP protocol has a number of desirable properties: it allows a user to authenticate themselves to a server, it is resistant to dictionary attacks mounted by an eavesdropper, and it does not...

, PSK

Pre-shared key

In cryptography, a pre-shared key or PSK is a shared secret which was previously shared between the two parties using some secure channel before it needs to be used. To build a key from shared secret, the key derivation function should be used. Such systems almost always use symmetric key...

authentication: RSA, DSA

Digital Signature Algorithm

The Digital Signature Algorithm is a United States Federal Government standard or FIPS for digital signatures. It was proposed by the National Institute of Standards and Technology in August 1991 for use in their Digital Signature Standard , specified in FIPS 186, adopted in 1993. A minor...

, ECDSA

Elliptic Curve DSA

The Elliptic Curve Digital Signature Algorithm is a variant of the Digital Signature Algorithm which uses Elliptic curve cryptography.-Key and signature size comparison to DSA:...

bulk ciphers: RC4, Triple DES

Triple DES

In cryptography, Triple DES is the common name for the Triple Data Encryption Algorithm block cipher, which applies the Data Encryption Standard cipher algorithm three times to each data block....

, AES

Advanced Encryption Standard

Advanced Encryption Standard is a specification for the encryption of electronic data. It has been adopted by the U.S. government and is now used worldwide. It supersedes DES...

, IDEA

International Data Encryption Algorithm

In cryptography, the International Data Encryption Algorithm is a block cipher designed by James Massey of ETH Zurich and Xuejia Lai and was first described in 1991. As a block cipher, it is also symmetric. The algorithm was intended as a replacement for the Data Encryption Standard[DES]...

, DES

Data Encryption Standard

The Data Encryption Standard is a block cipher that uses shared secret encryption. It was selected by the National Bureau of Standards as an official Federal Information Processing Standard for the United States in 1976 and which has subsequently enjoyed widespread use internationally. It is...

, or Camellia

Camellia (cipher)

In cryptography, Camellia is a 128-bit block cipher jointly developed by Mitsubishi and NTT. The cipher has been approved for use by the ISO/IEC, the European Union's NESSIE project and the Japanese CRYPTREC project...

. In older versions of SSL, RC2

RC2

In cryptography, RC2 is a block cipher designed by Ron Rivest in 1987. "RC" stands for "Ron's Code" or "Rivest Cipher"; other ciphers designed by Rivest include RC4, RC5 and RC6....

 was also used.
message authentication: for TLS, a Hash-based Message Authentication Code

HMAC

In cryptography, HMAC is a specific construction for calculating a message authentication code involving a cryptographic hash function in combination with a secret key. As with any MAC, it may be used to simultaneously verify both the data integrity and the authenticity of a message...

 using MD5

MD5

The MD5 Message-Digest Algorithm is a widely used cryptographic hash function that produces a 128-bit hash value. Specified in RFC 1321, MD5 has been employed in a wide variety of security applications, and is also commonly used to check data integrity...

 or one of the SHA hash functions

SHA hash functions

In cryptography, SHA-1 is a cryptographic hash function designed by the United States National Security Agency and published by the United States NIST as a U.S. Federal Information Processing Standard. SHA stands for "secure hash algorithm". The three SHA algorithms are structured differently and...

 is used. For SSL, SHA

Sha

For other uses, see Sha .Sha is a letter of the Cyrillic alphabet. It commonly represents the voiceless postalveolar fricative , like the pronunciation of ⟨sh⟩ in "sheep", or the somewhat similar voiceless retroflex fricative . It is used in every variation of the Cyrillic alphabet, for Slavic and...

, MD5

MD5

The MD5 Message-Digest Algorithm is a widely used cryptographic hash function that produces a 128-bit hash value. Specified in RFC 1321, MD5 has been employed in a wide variety of security applications, and is also commonly used to check data integrity...

, MD4

MD4

The MD4 Message-Digest Algorithm is a cryptographic hash function developed by Ronald Rivest in 1990. The digest length is 128 bits. The algorithm has influenced later designs, such as the MD5, SHA-1 and RIPEMD algorithms....

, and MD2 are used.

Programming references

Programatically, a cipher suite is referred to as:
CipherSuite cipher_suites: a list of the cryptographic options supported by the client (RFC 5246, p. 41)
CipherSuite cipher_suite: the cipher suite selected by the server and revealed in the ServerHello message (RFC 5246, p. 42-43, 64)