密钥哈希消息鉴别码（英语：Keyed-hash message authentication code，缩写为HMAC），又称哈希消息鉴别码（Hash-based message authentication code），是一种通过特别计算方式之后产生的消息鉴别码（MAC），使用密码哈希函数，同时结合一个加密密钥。它可以用来保证数据的完整性，同时可以用来作某个消息的身份验证。

In cryptography, a keyed-hash message authentication code (HMAC) is a specific type of message authentication code (MAC) involving a cryptographic hash function (hence the 'H') in combination with a secret cryptographic key. As with any MAC, it may be used to simultaneously verify both the data integrity and the authentication of a message. Any cryptographic hash function, such as MD5 or SHA-1, may be used in the calculation of an HMAC; the resulting MAC algorithm is termed HMAC-MD5 or HMAC-SHA1 accordingly. The cryptographic strength of the HMAC depends upon the cryptographic strength of the underlying hash function, the size of its hash output, and on the size and quality of the key.