# 15.1 `hmac` -- Keyed-Hashing for Message Authentication

New in version 2.2.

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

`new`( | key[, msg[, digestmod]])

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

An HMAC object has the following methods:

`update`( | msg)

  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)`.

`digest`( | )

  Return the digest of the strings passed to the `update()` method so far. This is a 16-byte string (for `md5`) or a 20-byte string (for `sha`) which may contain non-ASCII characters, including NUL bytes.

`hexdigest`( | )

  Like `digest()` except the digest is returned as a string of length 32 for `md5` (40 for `sha`), containing only hexadecimal digits. This may be used to exchange the value safely in email or other non-binary environments.

`copy`( | )

  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.