Sunday, April 10, 2016

Python hashlib algorithms

It's very interesting that some algorithms from Python hashlib module are not documented, for example SHA which is SHA-0.

>>> import hashlib
>>> h ='sha')
>>> h.update(b'')
>>> h.hexdigest()

The reason of such behavior is loading of these algorithms using _hashlib module, which is based on OpenSSL library available on your platform. Therefore, these additional algorithms may vary.

Here is how hashlib new() constructor is assigned based on _hashlib (OpenSSL) module availability (from

    import _hashlib
    new = __hash_new
    __get_hash = __get_openssl_constructor
    algorithms_available = algorithms_available.union(
except ImportError:
    new = __py_new
    __get_hash = __get_builtin_constructor

By default only several hash algorithms are always available in hashlib module.
You can check all of them using hashlib.algorithms_available (was added in version 2.7.9):
>>> hashlib.algorithms
('md5', 'sha1', 'sha224', 'sha256', 'sha384', 'sha512')

Additional algorithms available by hashlib.algorithms_available (was added in version 2.7.9):
>>> hashlib.algorithms_available
{'SHA384', 'MD5', 'sha512', 'MD4', 'RIPEMD160', 'dsaEncryption', 'SHA224', 'SHA', 'sha', 'ecdsa-with-SHA1', 'md5', 'whirlpool', 'dsaWithSHA', 'SHA1', 'sha1', 'sha384', '
DSA', 'sha224', 'md4', 'ripemd160', 'DSA-SHA', 'SHA512', 'SHA256', 'sha256'}

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