Digest access authentication

Digest access authentication is one of the agreed-upon methods a web server can use to negotiate credentials, such as username or password, with a user's web browser. This can be used to confirm the identity of a user before sending sensitive information, such as online banking transaction history. It applies a hash function to the username and password before sending them over the network. In contrast, basic access authentication uses the easily reversible Base64 encoding instead of encryption, making it non-secure unless used in conjunction with SSL.

Technically, digest authentication is an application of MD5 cryptographic hashing with usage of nonce values to prevent replay attacks. It uses the protocol.

Digest access authentication was originally specified by RFC 2069 (An Extension to HTTP: Digest Access Authentication). RFC 2069 specifies roughly a traditional digest authentication scheme with security maintained by a server-generated noncevalue. The authentication response is formed as follows (where HA1 and HA2 are names of string variables):

RFC 2069 was later replaced by RFC 2617 (HTTP Authentication: Basic and Digest Access Authentication). RFC 2617 introduced a number of optional security enhancements to digest authentication; "quality of protection" (qop), nonce counter incremented by client, and a client-generated random nonce. These enhancements are designed to protect against, for example, chosen-plaintext attack cryptanalysis.

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