Cipher Suite
A cipher suite is the combination of algorithms negotiated during a TLS handshake: key exchange (ECDHE), authentication (RSA/ECDSA), bulk encryption (AES-256-GCM), and integrity (SHA-384). TLS 1.3 simplified suites to just AEAD cipher + hash, removing key exchange from the suite name since ECDHE is mandatory.
Definition
A TLS cipher suite specifies four algorithms that protect the connection. In TLS 1.2, the suite name encodes all four: TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 means ECDHE key exchange, RSA authentication, AES-256-GCM encryption, SHA-384 for PRF. TLS 1.3 reduced suites to three options (TLS_AES_256_GCM_SHA384, TLS_CHACHA20_POLY1305_SHA256, TLS_AES_128_GCM_SHA256) because key exchange and authentication are negotiated separately. Cipher suite ordering determines preference – servers should prefer ECDHE (forward secrecy) over static RSA, AEAD ciphers (GCM, ChaCha20) over CBC, and modern hashes (SHA-256+) over SHA-1. Misconfigured cipher suites enabling 3DES, RC4, or export ciphers create vulnerabilities exploitable by SWEET32, BEAST, or FREAK attacks.
Examples
- –openssl s_client -connect host:443 -cipher 'ECDHE+AESGCM'
- –ssl_ciphers 'TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256'; (Nginx TLS 1.3)
- –nmap --script ssl-enum-ciphers -p 443 target
Related Protocols
Related Terms
Key Exchange
Key exchange is the process of establishing a shared secret between client and server over an insecure channel. TLS uses ephemeral Diffie-Hellman (DHE/ECDHE) – both parties contribute randomness, and eavesdroppers cannot derive the shared key. ECDHE with Curve25519 or P-256 is the modern standard. Static RSA key exchange has no forward secrecy.
Perfect Forward Secrecy (PFS)
Perfect Forward Secrecy guarantees that compromise of long-term keys does not decrypt past sessions. PFS requires ephemeral key exchange (DHE/ECDHE) – each session uses unique keys that are destroyed after use. If the server's private key is stolen tomorrow, previously captured traffic remains encrypted. TLS 1.3 mandates PFS.