:mod:`hashlib` --- Secure hashes and message digests ==================================================== .. module:: hashlib :synopsis: Secure hash and message digest algorithms. .. moduleauthor:: Gregory P. Smith .. sectionauthor:: Gregory P. Smith **Source code:** :source:`Lib/hashlib.py` .. index:: single: message digest, MD5 single: secure hash algorithm, SHA1, SHA224, SHA256, SHA384, SHA512 .. testsetup:: import hashlib -------------- 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. .. note:: If you want the adler32 or crc32 hash functions, they are available in the :mod:`zlib` module. .. warning:: Some algorithms have known hash collision weaknesses, refer to the "See also" section at the end. .. _hash-algorithms: Hash algorithms --------------- 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:`sha256` to create a SHA-256 hash object. You can now feed this object with :term:`bytes-like objects ` (normally :class:`bytes`) 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. .. note:: For better multithreading performance, the Python :term:`GIL` is released for data larger than 2047 bytes at object creation or on update. .. note:: Feeding string objects into :meth:`update` is not supported, as hashes work on bytes, not on characters. .. index:: single: OpenSSL; (use in module hashlib) Constructors for hash algorithms that are always present in this module are :func:`sha1`, :func:`sha224`, :func:`sha256`, :func:`sha384`, :func:`sha512`, :func:`blake2b`, and :func:`blake2s`. :func:`md5` is normally available as well, though it may be missing if you are using a rare "FIPS compliant" build of Python. Additional algorithms may also be available depending upon the OpenSSL library that Python uses on your platform. .. versionadded:: 3.6 :func:`blake2b` and :func:`blake2s` were added. For example, to obtain the digest of the byte string ``b'Nobody inspects the spammish repetition'``:: >>> import hashlib >>> m = hashlib.sha256() >>> m.update(b"Nobody inspects") >>> m.update(b" the spammish repetition") >>> m.digest() b'\x03\x1e\xdd}Ae\x15\x93\xc5\xfe\\\x00o\xa5u+7\xfd\xdf\xf7\xbcN\x84:\xa6\xaf\x0c\x95\x0fK\x94\x06' >>> m.digest_size 32 >>> m.block_size 64 More condensed: >>> hashlib.sha224(b"Nobody inspects the spammish repetition").hexdigest() 'a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2' .. function:: new(name[, data]) Is a generic constructor that takes the string name of the desired algorithm as its first parameter. It also exists to allow access to the above listed hashes as well as any other algorithms that your OpenSSL library may offer. The named constructors are much faster than :func:`new` and should be preferred. Using :func:`new` with an algorithm provided by OpenSSL: >>> h = hashlib.new('ripemd160') >>> h.update(b"Nobody inspects the spammish repetition") >>> h.hexdigest() 'cc4a5ce1b3df48aec5d22d1f16b894a0b894eccc' Hashlib provides the following constant attributes: .. data:: algorithms_guaranteed A set containing the names of the hash algorithms guaranteed to be supported by this module on all platforms. Note that 'md5' is in this list despite some upstream vendors offering an odd "FIPS compliant" Python build that excludes it. .. versionadded:: 3.2 .. data:: algorithms_available A set containing the names of the hash algorithms that are available in the running Python interpreter. These names will be recognized when passed to :func:`new`. :attr:`algorithms_guaranteed` will always be a subset. The same algorithm may appear multiple times in this set under different names (thanks to OpenSSL). .. versionadded:: 3.2 The following values are provided as constant attributes of the hash objects returned by the constructors: .. data:: hash.digest_size The size of the resulting hash in bytes. .. data:: hash.block_size The internal block size of the hash algorithm in bytes. A hash object has the following attributes: .. attribute:: hash.name The canonical name of this hash, always lowercase and always suitable as a parameter to :func:`new` to create another hash of this type. .. versionchanged:: 3.4 The name attribute has been present in CPython since its inception, but until Python 3.4 was not formally specified, so may not exist on some platforms. A hash object has the following methods: .. method:: hash.update(arg) Update the hash object with the object *arg*, which must be interpretable as a buffer of bytes. 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)``. .. versionchanged:: 3.1 The Python GIL is released to allow other threads to run while hash updates on data larger than 2047 bytes is taking place when using hash algorithms supplied by OpenSSL. .. method:: hash.digest() Return the digest of the data passed to the :meth:`update` method so far. This is a bytes object of size :attr:`digest_size` which may contain bytes in the whole range from 0 to 255. .. method:: hash.hexdigest() Like :meth:`digest` except the digest is returned as a string object of double length, containing only hexadecimal digits. This may be used to exchange the value safely in email or other non-binary environments. .. method:: hash.copy() Return a copy ("clone") of the hash object. This can be used to efficiently compute the digests of data sharing a common initial substring. Key derivation -------------- Key derivation and key stretching algorithms are designed for secure password hashing. Naive algorithms such as ``sha1(password)`` are not resistant against brute-force attacks. A good password hashing function must be tunable, slow, and include a `salt `_. .. function:: pbkdf2_hmac(hash_name, password, salt, iterations, dklen=None) The function provides PKCS#5 password-based key derivation function 2. It uses HMAC as pseudorandom function. The string *hash_name* is the desired name of the hash digest algorithm for HMAC, e.g. 'sha1' or 'sha256'. *password* and *salt* are interpreted as buffers of bytes. Applications and libraries should limit *password* to a sensible length (e.g. 1024). *salt* should be about 16 or more bytes from a proper source, e.g. :func:`os.urandom`. The number of *iterations* should be chosen based on the hash algorithm and computing power. As of 2013, at least 100,000 iterations of SHA-256 are suggested. *dklen* is the length of the derived key. If *dklen* is ``None`` then the digest size of the hash algorithm *hash_name* is used, e.g. 64 for SHA-512. >>> import hashlib, binascii >>> dk = hashlib.pbkdf2_hmac('sha256', b'password', b'salt', 100000) >>> binascii.hexlify(dk) b'0394a2ede332c9a13eb82e9b24631604c31df978b4e2f0fbd2c549944f9d79a5' .. versionadded:: 3.4 .. note:: A fast implementation of *pbkdf2_hmac* is available with OpenSSL. The Python implementation uses an inline version of :mod:`hmac`. It is about three times slower and doesn't release the GIL. .. function:: scrypt(password, *, salt, n, r, p, maxmem=0, dklen=64) The function provides scrypt password-based key derivation function as defined in :rfc:`7914`. *password* and *salt* must be bytes-like objects. Applications and libraries should limit *password* to a sensible length (e.g. 1024). *salt* should be about 16 or more bytes from a proper source, e.g. :func:`os.urandom`. *n* is the CPU/Memory cost factor, *r* the block size, *p* parallelization factor and *maxmem* limits memory (OpenSSL 1.1.0 defaults to 32 MB). *dklen* is the length of the derived key. Availability: OpenSSL 1.1+ .. versionadded:: 3.6 BLAKE2 ------ BLAKE2 takes additional arguments, see :ref:`hashlib-blake2`. .. seealso:: Module :mod:`hmac` A module to generate message authentication codes using hashes. Module :mod:`base64` Another way to encode binary hashes for non-binary environments. See :ref:`hashlib-blake2`. http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf The FIPS 180-2 publication on Secure Hash Algorithms. https://en.wikipedia.org/wiki/Cryptographic_hash_function#Cryptographic_hash_algorithms Wikipedia article with information on which algorithms have known issues and what that means regarding their use. https://www.ietf.org/rfc/rfc2898.txt PKCS #5: Password-Based Cryptography Specification Version 2.0