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211 lines
7.2 KiB
211 lines
7.2 KiB
:mod:`hashlib` --- Secure hashes and message digests
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====================================================
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.. module:: hashlib
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:synopsis: Secure hash and message digest algorithms.
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.. moduleauthor:: Gregory P. Smith <greg@krypto.org>
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.. sectionauthor:: Gregory P. Smith <greg@krypto.org>
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.. versionadded:: 2.5
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.. index::
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single: message digest, MD5
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single: secure hash algorithm, SHA1, SHA224, SHA256, SHA384, SHA512
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**Source code:** :source:`Lib/hashlib.py`
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--------------
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This module implements a common interface to many different secure hash and
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message digest algorithms. Included are the FIPS secure hash algorithms SHA1,
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SHA224, SHA256, SHA384, and SHA512 (defined in FIPS 180-2) as well as RSA's MD5
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algorithm (defined in Internet :rfc:`1321`). The terms secure hash and message
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digest are interchangeable. Older algorithms were called message digests. The
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modern term is secure hash.
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.. note::
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If you want the adler32 or crc32 hash functions, they are available in
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the :mod:`zlib` module.
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.. warning::
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Some algorithms have known hash collision weaknesses, refer to the "See
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also" section at the end.
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There is one constructor method named for each type of :dfn:`hash`. All return
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a hash object with the same simple interface. For example: use :func:`sha1` to
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create a SHA1 hash object. You can now feed this object with arbitrary strings
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using the :meth:`update` method. At any point you can ask it for the
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:dfn:`digest` of the concatenation of the strings fed to it so far using the
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:meth:`digest` or :meth:`hexdigest` methods.
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.. index:: single: OpenSSL; (use in module hashlib)
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Constructors for hash algorithms that are always present in this module are
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:func:`md5`, :func:`sha1`, :func:`sha224`, :func:`sha256`, :func:`sha384`, and
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:func:`sha512`. Additional algorithms may also be available depending upon the
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OpenSSL library that Python uses on your platform.
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For example, to obtain the digest of the string ``'Nobody inspects the spammish
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repetition'``:
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>>> import hashlib
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>>> m = hashlib.md5()
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>>> m.update("Nobody inspects")
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>>> m.update(" the spammish repetition")
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>>> m.digest()
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'\xbbd\x9c\x83\xdd\x1e\xa5\xc9\xd9\xde\xc9\xa1\x8d\xf0\xff\xe9'
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>>> m.digest_size
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16
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>>> m.block_size
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64
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More condensed:
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>>> hashlib.sha224("Nobody inspects the spammish repetition").hexdigest()
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'a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2'
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A generic :func:`new` constructor that takes the string name of the desired
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algorithm as its first parameter also exists to allow access to the above listed
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hashes as well as any other algorithms that your OpenSSL library may offer. The
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named constructors are much faster than :func:`new` and should be preferred.
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Using :func:`new` with an algorithm provided by OpenSSL:
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>>> h = hashlib.new('ripemd160')
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>>> h.update("Nobody inspects the spammish repetition")
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>>> h.hexdigest()
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'cc4a5ce1b3df48aec5d22d1f16b894a0b894eccc'
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This module provides the following constant attribute:
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.. data:: hashlib.algorithms
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A tuple providing the names of the hash algorithms guaranteed to be
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supported by this module.
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.. versionadded:: 2.7
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.. data:: algorithms_guaranteed
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A set containing the names of the hash algorithms guaranteed to be supported
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by this module on all platforms.
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.. versionadded:: 2.7.9
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.. data:: algorithms_available
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A set containing the names of the hash algorithms that are available in the
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running Python interpreter. These names will be recognized when passed to
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:func:`new`. :attr:`algorithms_guaranteed` will always be a subset. The
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same algorithm may appear multiple times in this set under different names
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(thanks to OpenSSL).
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.. versionadded:: 2.7.9
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The following values are provided as constant attributes of the hash objects
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returned by the constructors:
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.. data:: hash.digest_size
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The size of the resulting hash in bytes.
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.. data:: hash.block_size
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The internal block size of the hash algorithm in bytes.
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A hash object has the following methods:
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.. method:: hash.update(arg)
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Update the hash object with the string *arg*. Repeated calls are equivalent to
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a single call with the concatenation of all the arguments: ``m.update(a);
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m.update(b)`` is equivalent to ``m.update(a+b)``.
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.. versionchanged:: 2.7
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The Python GIL is released to allow other threads to run while
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hash updates on data larger than 2048 bytes is taking place when
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using hash algorithms supplied by OpenSSL.
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.. method:: hash.digest()
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Return the digest of the strings passed to the :meth:`update` method so far.
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This is a string of :attr:`digest_size` bytes which may contain non-ASCII
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characters, including null bytes.
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.. method:: hash.hexdigest()
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Like :meth:`digest` except the digest is returned as a string of double length,
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containing only hexadecimal digits. This may be used to exchange the value
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safely in email or other non-binary environments.
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.. method:: hash.copy()
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Return a copy ("clone") of the hash object. This can be used to efficiently
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compute the digests of strings that share a common initial substring.
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Key derivation
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--------------
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Key derivation and key stretching algorithms are designed for secure password
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hashing. Naive algorithms such as ``sha1(password)`` are not resistant against
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brute-force attacks. A good password hashing function must be tunable, slow, and
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include a `salt <https://en.wikipedia.org/wiki/Salt_%28cryptography%29>`_.
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.. function:: pbkdf2_hmac(name, password, salt, rounds, dklen=None)
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The function provides PKCS#5 password-based key derivation function 2. It
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uses HMAC as pseudorandom function.
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The string *name* is the desired name of the hash digest algorithm for
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HMAC, e.g. 'sha1' or 'sha256'. *password* and *salt* are interpreted as
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buffers of bytes. Applications and libraries should limit *password* to
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a sensible value (e.g. 1024). *salt* should be about 16 or more bytes from
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a proper source, e.g. :func:`os.urandom`.
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The number of *rounds* should be chosen based on the hash algorithm and
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computing power. As of 2013, at least 100,000 rounds of SHA-256 is suggested.
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*dklen* is the length of the derived key. If *dklen* is ``None`` then the
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digest size of the hash algorithm *name* is used, e.g. 64 for SHA-512.
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>>> import hashlib, binascii
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>>> dk = hashlib.pbkdf2_hmac('sha256', b'password', b'salt', 100000)
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>>> binascii.hexlify(dk)
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b'0394a2ede332c9a13eb82e9b24631604c31df978b4e2f0fbd2c549944f9d79a5'
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.. versionadded:: 2.7.8
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.. note::
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A fast implementation of *pbkdf2_hmac* is available with OpenSSL. The
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Python implementation uses an inline version of :mod:`hmac`. It is about
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three times slower and doesn't release the GIL.
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.. seealso::
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Module :mod:`hmac`
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A module to generate message authentication codes using hashes.
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Module :mod:`base64`
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Another way to encode binary hashes for non-binary environments.
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http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf
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The FIPS 180-2 publication on Secure Hash Algorithms.
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https://en.wikipedia.org/wiki/Cryptographic_hash_function#Cryptographic_hash_algorithms
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Wikipedia article with information on which algorithms have known issues and
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what that means regarding their use.
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