15.2. hmac — Keyed-Hashing for Message Authentication

New in version 2.2.

This module implements the HMAC algorithm as described by RFC 2104.

hmac.new(key[, msg[, digestmod]])

Return a new hmac object. If msg is present, the method call update(msg) is made. digestmod is the digest constructor or module for the HMAC object to use. It defaults to the hashlib.md5() constructor.


The md5 hash has known weaknesses but remains the default for backwards compatibility. Choose a better one for your application.

An HMAC object has the following methods:

Update the hmac object with the string msg. Repeated calls are equivalent to a single call with the concatenation of all the arguments: m.update(a); m.update(b) is equivalent to m.update(a + b).
Return the digest of the strings passed to the update() method so far. This string will be the same length as the digest_size of the digest given to the constructor. It may contain non-ASCII characters, including NUL bytes.
Like digest() except the digest is returned as a string twice the length containing only hexadecimal digits. This may be used to exchange the value safely in email or other non-binary environments.
Return a copy (“clone”) of the hmac object. This can be used to efficiently compute the digests of strings that share a common initial substring.

See also

Module hashlib
The python module providing secure hash functions.

Previous topic

15.1. hashlib — Secure hashes and message digests

Next topic

15.3. md5 — MD5 message digest algorithm

This Page