HP Open Source Security for OpenVMS Volume 2: HP SSL for OpenVMS > Chapter 2 Overview of SSL

Cipher Suite

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Integral to the SSL protocol is its use of cryptographic algorithms, generally called ciphers. Ciphers are required to authenticate the server and client to each other, transmit certificates, and establish session keys. Clients and servers can support different cipher suites, or sets of ciphers, depending on factors such as the version of SSL they support, company policies regarding acceptable encryption strength, and government restrictions on the export of SSL-enabled software.

Among its other functions, the SSL handshake protocol determines how the server and client negotiate which cipher suites they will use to authenticate each other, to transmit certificates, and to establish session keys. Key exchange algorithms such as RSA and DH key exchange govern the way the server and client determine the symmetric keys they will both use during an SSL session. The most commonly used SSL cipher suites use RSA key exchange.

The SSL 2.0 and SSL 3.0 protocols support overlapping sets of cipher suites. Administrators can enable or disable any of the supported cipher suites for both clients and servers. When a particular client and server exchange information during the SSL handshake, they identify the strongest enabled cipher suites they have in common and use those for the SSL session.

Decisions about which cipher suites a particular organization decides to enable depend on trade-offs among the sensitivity of the data involved, the speed of the cipher, and the applicability of export rules.