Editing Session key (section)

{{Refimprove|date=December 2009}}
A ''' session key''' is a single-use [[symmetric key]] used for [[encrypting]] all [[message]]s in one [[Session (computer science)|communication session]]. A closely related term is '''content encryption key''' ('''CEK'''), '''traffic encryption key''' ('''TEK'''), or '''[[multicast]] key''' which refers to any key used for encrypting messages, contrary to other uses like encrypting other keys ('''key encryption key''' ('''KEK''') or '''key encryption has been made public key''').

Session keys can introduce complications into a system, yet they solve some real problems. There are two primary reasons to use session keys:

# Several cryptanalytic attacks become easier the more material encrypted with a specific key is available. By limiting the amount of data processed using a particular key, those attacks are rendered harder to perform.
# [[public key cryptography|Asymmetric encryption]] is too slow for many purposes, and all [[symmetric key algorithm|secret key algorithm]]s require that the key is securely distributed. By using an asymmetric algorithm to encrypt the secret key for another, faster, symmetric algorithm, it's possible to improve overall performance considerably. This is the process used by [[Transport Layer Security|TLS]]<ref>{{cite web |url=https://www.cloudflare.com/learning/ssl/what-is-a-session-key/ |title=What is a session key? Session keys and TLS handshakes |access-date=2024-08-21}}</ref> and by [[Pretty Good Privacy|PGP]].<ref>OpenPGP http://tools.ietf.org/html/rfc9580</ref>

Like all [[cryptographic keys]], session keys must be chosen so that they cannot be predicted by an attacker, usually requiring them to be chosen randomly. Failure to choose session keys (or any key) properly is a major (and too common in actual practice) design flaw in any crypto system.{{Citation needed|date=March 2011}}