1 

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

     3 ====================================================

     4 

     5 .. module:: hashlib

     6    :synopsis: Secure hash and message digest algorithms.

     7 .. moduleauthor:: Gregory P. Smith <greg@users.sourceforge.net>

     8 .. sectionauthor:: Gregory P. Smith <greg@users.sourceforge.net>

     9 

    10 

    11 .. versionadded:: 2.5

    12 

    13 .. index::

    14    single: message digest, MD5

    15    single: secure hash algorithm, SHA1, SHA224, SHA256, SHA384, SHA512

    16 

    17 This module implements a common interface to many different secure hash and

    18 message digest algorithms.  Included are the FIPS secure hash algorithms SHA1,

    19 SHA224, SHA256, SHA384, and SHA512 (defined in FIPS 180-2) as well as RSA's MD5

    20 algorithm (defined in Internet :rfc:`1321`). The terms secure hash and message

    21 digest are interchangeable.  Older algorithms were called message digests.  The

    22 modern term is secure hash.

    23 

    24 .. note::

    25    If you want the adler32 or crc32 hash functions they are available in

    26    the :mod:`zlib` module.

    27 

    28 .. warning::

    29 

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

    31 

    32 There is one constructor method named for each type of :dfn:`hash`.  All return

    33 a hash object with the same simple interface. For example: use :func:`sha1` to

    34 create a SHA1 hash object. You can now feed this object with arbitrary strings

    35 using the :meth:`update` method.  At any point you can ask it for the

    36 :dfn:`digest` of the concatenation of the strings fed to it so far using the

    37 :meth:`digest` or :meth:`hexdigest` methods.

    38 

    39 .. index:: single: OpenSSL; (use in module hashlib)

    40 

    41 Constructors for hash algorithms that are always present in this module are

    42 :func:`md5`, :func:`sha1`, :func:`sha224`, :func:`sha256`, :func:`sha384`, and

    43 :func:`sha512`.  Additional algorithms may also be available depending upon the

    44 OpenSSL library that Python uses on your platform.

    45 

    46 For example, to obtain the digest of the string ``'Nobody inspects the spammish

    47 repetition'``:

    48 

    49    >>> import hashlib

    50    >>> m = hashlib.md5()

    51    >>> m.update("Nobody inspects")

    52    >>> m.update(" the spammish repetition")

    53    >>> m.digest()

    54    '\xbbd\x9c\x83\xdd\x1e\xa5\xc9\xd9\xde\xc9\xa1\x8d\xf0\xff\xe9'

    55    >>> m.digest_size

    56    16

    57    >>> m.block_size

    58    64

    59 

    60 More condensed:

    61 

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

    63    'a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2'

    64 

    65 A generic :func:`new` constructor that takes the string name of the desired

    66 algorithm as its first parameter also exists to allow access to the above listed

    67 hashes as well as any other algorithms that your OpenSSL library may offer.  The

    68 named constructors are much faster than :func:`new` and should be preferred.

    69 

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

    71 

    72    >>> h = hashlib.new('ripemd160')

    73    >>> h.update("Nobody inspects the spammish repetition")

    74    >>> h.hexdigest()

    75    'cc4a5ce1b3df48aec5d22d1f16b894a0b894eccc'

    76 

    77 The following values are provided as constant attributes of the hash objects

    78 returned by the constructors:

    79 

    80 

    81 .. data:: digest_size

    82 

    83    The size of the resulting hash in bytes.

    84 

    85 .. data:: block_size

    86 

    87    The internal block size of the hash algorithm in bytes.

    88 

    89 A hash object has the following methods:

    90 

    91 

    92 .. method:: hash.update(arg)

    93 

    94    Update the hash object with the string *arg*.  Repeated calls are equivalent to

    95    a single call with the concatenation of all the arguments: ``m.update(a);

    96    m.update(b)`` is equivalent to ``m.update(a+b)``.

    97 

    98 

    99 .. method:: hash.digest()

   100 

   101    Return the digest of the strings passed to the :meth:`update` method so far.

   102    This is a string of :attr:`digest_size` bytes which may contain non-ASCII

   103    characters, including null bytes.

   104 

   105 

   106 .. method:: hash.hexdigest()

   107 

   108    Like :meth:`digest` except the digest is returned as a string of double length,

   109    containing only hexadecimal digits.  This may  be used to exchange the value

   110    safely in email or other non-binary environments.

   111 

   112 

   113 .. method:: hash.copy()

   114 

   115    Return a copy ("clone") of the hash object.  This can be used to efficiently

   116    compute the digests of strings that share a common initial substring.

   117 

   118 

   119 .. seealso::

   120 

   121    Module :mod:`hmac`

   122       A module to generate message authentication codes using hashes.

   123 

   124    Module :mod:`base64`

   125       Another way to encode binary hashes for non-binary environments.

   126 

   127    http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf

   128       The FIPS 180-2 publication on Secure Hash Algorithms.

   129 

   130    http://www.cryptography.com/cnews/hash.html

   131       Hash Collision FAQ with information on which algorithms have known issues and

   132       what that means regarding their use.

   133