Issue #10924: Adding salt and Modular Crypt Format to crypt library.

Lib/crypt.py

@@ -0,0 +1,61 @@
+'''Wrapper to the POSIX crypt library call and associated functionality.
+'''
+
+import _crypt
+
+saltchars = 'abcdefghijklmnopqrstuvwxyz'
+saltchars += saltchars.upper()
+saltchars += '0123456789./'
+
+
+class _MethodClass:
+    '''Class representing a salt method per the Modular Crypt Format or the
+    legacy 2-character crypt method.'''
+    def __init__(self, name, ident, salt_chars, total_size):
+        self.name = name
+        self.ident = ident
+        self.salt_chars = salt_chars
+        self.total_size = total_size
+
+    def __repr__(self):
+        return '<crypt.METHOD_%s>' % self.name
+
+
+#  available salting/crypto methods
+METHOD_CRYPT = _MethodClass('CRYPT', None, 2, 13)
+METHOD_MD5 = _MethodClass('MD5', '1', 8, 34)
+METHOD_SHA256 = _MethodClass('SHA256', '5', 16, 63)
+METHOD_SHA512 = _MethodClass('SHA512', '6', 16, 106)
+
+
+def methods():
+    '''Return a list of methods that are available in the platform ``crypt()``
+    library, sorted from strongest to weakest.  This is guaranteed to always
+    return at least ``[METHOD_CRYPT]``'''
+    method_list = [ METHOD_SHA512, METHOD_SHA256, METHOD_MD5 ]
+    ret = [ method for method in method_list
+            if len(crypt('', method)) == method.total_size ]
+    ret.append(METHOD_CRYPT)
+    return ret
+
+
+def mksalt(method = None):
+    '''Generate a salt for the specified method.  If not specified, the
+    strongest available method will be used.'''
+    import random
+
+    if method == None: method = methods()[0]
+    s = '$%s$' % method.ident if method.ident else ''
+    s += ''.join([ random.choice(saltchars) for x in range(method.salt_chars) ])
+    return(s)
+
+
+def crypt(word, salt = None):
+    '''Return a string representing the one-way hash of a password, preturbed
+    by a salt.  If ``salt`` is not specified or is ``None``, the strongest
+    available method will be selected and a salt generated.  Otherwise,
+    ``salt`` may be one of the ``crypt.METHOD_*`` values, or a string as
+    returned by ``crypt.mksalt()``.'''
+    if salt == None: salt = mksalt()
+    elif isinstance(salt, _MethodClass): salt = mksalt(salt)
+    return(_crypt.crypt(word, salt))