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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, which is safer than the basic access authentication, which uses the easily reversible Base64 encoding instead of encryption. Technically, digest authentication is an application of MD5 cryptographic hashing with usage of nonce values to prevent replay attacks. It uses the HTTP protocol. == Overview == 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 ''nonce value''. 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. If the algorithm directive's value is "MD5" or unspecified, then HA1 is : If the algorithm directive's value is "MD5-sess", then HA1 is : If the qop directive's value is "auth" or is unspecified, then HA2 is : If the qop directive's value is "auth-int", then HA2 is : If the qop directive's value is "auth" or "auth-int", then compute the response as follows: : If the qop directive is unspecified, then compute the response as follows: : The above shows that when qop is not specified, the simpler RFC 2069 standard is followed. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「digest access authentication」の詳細全文を読む スポンサード リンク
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