Cipher suite
Lua error in package.lua at line 80: module 'strict' not found. A cipher suite is a named combination of authentication, encryption, message authentication code (MAC) and key exchange algorithms used to negotiate the security settings for a network connection using the Transport Layer Security (TLS) / Secure Sockets Layer (SSL) network protocol.
The structure and use of the cipher suite concept is defined in the documents that define the protocol.[1] A reference for named cipher suites is provided in the TLS Cipher Suite Registry.[2]
Contents
Use
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When a TLS connection is established, a handshaking, known as the TLS Handshake Protocol, occurs. Within this handshake, a client hello (ClientHello) and a server hello (ServerHello) message are passed.[3] 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.[4] In order to test which TLS ciphers that a server supports an SSL/TLS Scanner may be used.
Detailed description
Each named cipher suite, e.g. TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256, defines a key exchange algorithm, a bulk encryption algorithm, a message authentication code (MAC) algorithm, and a pseudorandom function (PRF).[5][6][4]
- The key exchange algorithm, e.g. ECDHE_RSA, is used to determine if and how the client and server will authenticate during the handshake.[7]
- The bulk encryption algorithm, e.g. AES_128_GCM, is used to encrypt the message stream. It also includes the key size and the lengths of explicit and implicit initialization vectors (cryptographic nonces).[8]
- The message authentication code (MAC) algorithm, e.g. SHA256, is used to create the message digest, a cryptographic hash of each block of the message stream.[8]
- The pseudorandom function (PRF), e.g. TLS 1.2's PRF using the MAC-algorithm's hash function, 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.[9]
Examples of algorithms used
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- key exchange/agreement
- RSA, Diffie-Hellman, ECDH, SRP, PSK
- authentication
- RSA, DSA, ECDSA
- bulk ciphers
- RC4, Triple DES, AES, IDEA, DES, or Camellia. In older versions of SSL, RC2 was also used.
- message authentication
- for TLS, a Hash-based Message Authentication Code using MD5 or one of the SHA hash functions is used. For SSL, SHA, MD5, MD4, 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[10]
- CipherSuite cipher_suite
- the cipher suite selected by the server from the client's cipher_suites and revealed in the ServerHello message[11]
References
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<references />, or <references group="..." />- ↑ RFC 5246
- ↑ TLS Cipher Suite Registry
- ↑ RFC 5246, p. 37
- ↑ 4.0 4.1 RFC 5246, p. 40
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ RFC 5246, p. 47
- ↑ 8.0 8.1 RFC 5246, p. 17
- ↑ RFC 5246, p. 16-17, 26
- ↑ RFC 5246, p. 41
- ↑ RFC 5246, p. 42-43, 64
