python-clinic / Doc / library / hashlib.rst

:mod:`hashlib` --- Secure hashes and message digests

Source code: :source:`Lib/`

This module implements a common interface to many different secure hash and message digest algorithms. Included are the FIPS secure hash algorithms SHA1, SHA224, SHA256, SHA384, and SHA512 (defined in FIPS 180-2) as well as RSA's MD5 algorithm (defined in Internet RFC 1321). The terms "secure hash" and "message digest" are interchangeable. Older algorithms were called message digests. The modern term is secure hash.


If you want the adler32 or crc32 hash functions they are available in the :mod:`zlib` module.


Some algorithms have known hash collision weaknesses, see the FAQ at the end.

There is one constructor method named for each type of :dfn:`hash`. All return a hash object with the same simple interface. For example: use :func:`sha1` to create a SHA1 hash object. You can now feed this object with objects conforming to the buffer interface (normally :class:`bytes` objects) using the :meth:`update` method. At any point you can ask it for the :dfn:`digest` of the concatenation of the data fed to it so far using the :meth:`digest` or :meth:`hexdigest` methods.


For better multithreading performance, the Python :term:`GIL` is released for strings of more than 2047 bytes at object creation or on update.


Feeding string objects into :meth:`update` is not supported, as hashes work on bytes, not on characters.

Constructors for hash algorithms that are always present in this module are :func:`md5`, :func:`sha1`, :func:`sha224`, :func:`sha256`, :func:`sha384`, :func:`sha512`, :func:`sha3_224`, :func:`sha3_256`, :func:`sha3_384`, and :func:`sha3_512`. Additional algorithms may also be available depending upon the OpenSSL library that Python uses on your platform.

For example, to obtain the digest of the byte string b'Nobody inspects the spammish repetition':

>>> import hashlib
>>> m = hashlib.md5()
>>> m.update(b"Nobody inspects")
>>> m.update(b" the spammish repetition")
>>> m.digest()
>>> m.digest_size
>>> m.block_size

More condensed:

>>> hashlib.sha224(b"Nobody inspects the spammish repetition").hexdigest()

Using :func:`new` with an algorithm provided by OpenSSL:

>>> h ='ripemd160')
>>> h.update(b"Nobody inspects the spammish repetition")
>>> h.hexdigest()

Hashlib provides the following constant attributes:

The following values are provided as constant attributes of the hash objects returned by the constructors:

A hash object has the following methods: