What is a cipher suite?

Short answer

A cipher suite is the named combination of the algorithms to be used together in a TLS connection: in TLS 1.2 and earlier, it defines the key exchange (e.g. ECDHE), authentication (RSA or ECDSA), data encryption (e.g. AES-GCM, CHACHA20) and hash algorithm together, for example ECDHE-RSA-AES128-GCM-SHA256. In the handshake, the client lists the cipher suites it supports, and the server selects one from its own allow list. In TR7, the allowed cipher suites are determined in the Cipher Algorithms field on the TLS Security Profiles screen from a ready-made set, or one by one with Algorithm List after Manual is selected; the Default Profile uses the Only Secure Ones (HIGH:!aNULL:!MD5) set.

Where It Is Used in TR7

Where	Field / label	What for
Certificates & PKI → TLS Security Profiles	Cipher Algorithms: ready-made sets (e.g. Only Secure Ones, General, Strict Secure, Strict Legacy Compatible, Strict Hardware Accelerated) or Manual	The cipher suites allowed on the vService and in the Backend Service connection
TLS Security Profiles → Cipher Algorithms = Manual	Algorithm List	Selecting the suites one by one or excluding them with !
TLS Security Profiles	Import Ciphers / Export Ciphers	Exporting the active list (a ready-made set or the Manual list) to a file; a list imported from a file switches the Cipher Algorithms field to Manual
Backend Service → SSL Service	Ciphers: Standard, Low	The cipher level used when connecting to the Backend Service
Load Balancer → Conditions (Policy Match)	SSL Cipher	A decision based on the cipher suite the client negotiated

How Does It Work?

• TLS 1.2 and earlier: The name contains four components. For ECDHE-RSA-AES128-GCM-SHA256, the key exchange is ECDHE, the authentication RSA, the encryption AES-128-GCM and the hash SHA-256.
• TLS 1.3: The key exchange and authentication are separated from the cipher suite; the name carries only the encryption and the hash (e.g. TLS_AES_128_GCM_SHA256), and all the defined suites are AEAD (RFC 8446).
• The suite names and codes are kept in IANA's TLS Cipher Suites registry.

Common Misconceptions

• "A cipher suite with a long key is the most secure." A key exchange that provides forward secrecy (ECDHE) and AEAD encryption (GCM, CHACHA20) are more decisive than the key length (What are Perfect Forward Secrecy (PFS) and ECDHE?).
• "The Cipher Algorithms field also selects the TLS 1.3 suites." The list in the field is applied as the suite list of TLS 1.2 and the earlier versions; in TLS 1.3 connections, the engine's default TLS 1.3 suites are used. The TLS v1.3 Compatible set contains only TLS 1.3 suite names and holds no suite that matches TLS 1.2; to limit the connection to TLS 1.3, Min. SSL Version = TLSv1.3 is selected instead of the set.
• "Narrowing the list is risk-free." Old clients that support none of the selected suites cannot connect; the client profile is evaluated before the change.

How it is done in the documentation

• TLS Security Profiles · Cipher Algorithms
• TLS Security Profiles · Algorithm List
• SSL Cipher

Related questions

• How do I disable weak ciphers?
• Can I import/export cipher lists?
• What do the "Low" and "Standard" cipher options mean for a Backend Service that uses SSL, and which should I choose?
• What are Perfect Forward Secrecy (PFS) and ECDHE?