Lib/hashlib.py

   1 # $Id$
   2 #
   3 #  Copyright (C) 2005   Gregory P. Smith (greg@krypto.org)
   4 #  Licensed to PSF under a Contributor Agreement.
   5 #
   6
   7 __doc__ = """hashlib module - A common interface to many hash functions.
   8
   9 new(name, string='') - returns a new hash object implementing the
  10                        given hash function; initializing the hash
  11                        using the given string data.
  12
  13 Named constructor functions are also available, these are much faster
  14 than using new():
  15
  16 md5(), sha1(), sha224(), sha256(), sha384(), and sha512()
  17
  18 More algorithms may be available on your platform but the above are
  19 guaranteed to exist.
  20
  21 NOTE: If you want the adler32 or crc32 hash functions they are available in
  22 the zlib module.
  23
  24 Choose your hash function wisely.  Some have known collision weaknesses.
  25 sha384 and sha512 will be slow on 32 bit platforms.
  26
  27 Hash objects have these methods:
  28  - update(arg): Update the hash object with the string arg. Repeated calls
  29                 are equivalent to a single call with the concatenation of all
  30                 the arguments.
  31  - digest():    Return the digest of the strings passed to the update() method
  32                 so far. This may contain non-ASCII characters, including
  33                 NUL bytes.
  34  - hexdigest(): Like digest() except the digest is returned as a string of
  35                 double length, containing only hexadecimal digits.
  36  - copy():      Return a copy (clone) of the hash object. This can be used to
  37                 efficiently compute the digests of strings that share a common
  38                 initial substring.
  39
  40 For example, to obtain the digest of the string 'Nobody inspects the
  41 spammish repetition':
  42
  43     >>> import hashlib
  44     >>> m = hashlib.md5()
  45     >>> m.update("Nobody inspects")
  46     >>> m.update(" the spammish repetition")
  47     >>> m.digest()
  48     '\\xbbd\\x9c\\x83\\xdd\\x1e\\xa5\\xc9\\xd9\\xde\\xc9\\xa1\\x8d\\xf0\\xff\\xe9'
  49
  50 More condensed:
  51
  52     >>> hashlib.sha224("Nobody inspects the spammish repetition").hexdigest()
  53     'a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2'
  54
  55 """
  56
  57 # This tuple and __get_builtin_constructor() must be modified if a new
  58 # always available algorithm is added.
  59 __always_supported = ('md5', 'sha1', 'sha224', 'sha256', 'sha384', 'sha512')
  60
  61 algorithms = __always_supported
  62
  63 __all__ = __always_supported + ('new', 'algorithms')
  64
  65
  66 def __get_builtin_constructor(name):
  67     if name in ('SHA1', 'sha1'):
  68         import _sha
  69         return _sha.new
  70     elif name in ('MD5', 'md5'):
  71         import _md5
  72         return _md5.new
  73     elif name in ('SHA256', 'sha256', 'SHA224', 'sha224'):
  74         import _sha256
  75         bs = name[3:]
  76         if bs == '256':
  77             return _sha256.sha256
  78         elif bs == '224':
  79             return _sha256.sha224
  80     elif name in ('SHA512', 'sha512', 'SHA384', 'sha384'):
  81         import _sha512
  82         bs = name[3:]
  83         if bs == '512':
  84             return _sha512.sha512
  85         elif bs == '384':
  86             return _sha512.sha384
  87
  88     raise ValueError('unsupported hash type %s' % name)
  89
  90
  91 def __get_openssl_constructor(name):
  92     try:
  93         f = getattr(_hashlib, 'openssl_' + name)
  94         # Allow the C module to raise ValueError.  The function will be
  95         # defined but the hash not actually available thanks to OpenSSL.
  96         f()
  97         # Use the C function directly (very fast)
  98         return f
  99     except (AttributeError, ValueError):
 100         return __get_builtin_constructor(name)
 101
 102
 103 def __py_new(name, string=''):
 104     """new(name, string='') - Return a new hashing object using the named algorithm;
 105     optionally initialized with a string.
 106     """
 107     return __get_builtin_constructor(name)(string)
 108
 109
 110 def __hash_new(name, string=''):
 111     """new(name, string='') - Return a new hashing object using the named algorithm;
 112     optionally initialized with a string.
 113     """
 114     try:
 115         return _hashlib.new(name, string)
 116     except ValueError:
 117         # If the _hashlib module (OpenSSL) doesn't support the named
 118         # hash, try using our builtin implementations.
 119         # This allows for SHA224/256 and SHA384/512 support even though
 120         # the OpenSSL library prior to 0.9.8 doesn't provide them.
 121         return __get_builtin_constructor(name)(string)
 122
 123
 124 try:
 125     import _hashlib
 126     new = __hash_new
 127     __get_hash = __get_openssl_constructor
 128 except ImportError:
 129     new = __py_new
 130     __get_hash = __get_builtin_constructor
 131
 132 for __func_name in __always_supported:
 133     # try them all, some may not work due to the OpenSSL
 134     # version not supporting that algorithm.
 135     try:
 136         globals()[__func_name] = __get_hash(__func_name)
 137     except ValueError:
 138         import logging
 139         logging.exception('code for hash %s was not found.', __func_name)
 140
 141 # Cleanup locals()
 142 del __always_supported, __func_name, __get_hash
 143 del __py_new, __hash_new, __get_openssl_constructor