hashlib里因为会有类似Crypto的数字计算，如果纯用python做的话，速度很慢，达不到要求，因此这个具体的实现是放在_hashlib.pyd，对于Python2.7, 路径位于C:\Python27\DLLs_hashlib.pyd，采用C实现的这个动态库里

import hashlib print help(hashlib.md5) import _hashlib print help(_hashlib.openssl_md5) # 生成的MD5值一样 S = "this is a demo for md5" assert hashlib.md5(S).hexdigest() == _hashlib.openssl_md5(S).hexdigest()

加载过程为：

try: import _hashlib new = __hash_new __get_hash = __get_openssl_constructor algorithms_available = algorithms_available.union( _hashlib.openssl_md_meth_names) except ImportError: new = __py_new __get_hash = __get_builtin_constructor for __func_name in __always_supported: # try them all, some may not work due to the OpenSSL # version not supporting that algorithm. try: globals()[__func_name] = __get_hash(__func_name) except ValueError: import logging logging.exception('code for hash %s was not found.', __func_name) try: # OpenSSL's PKCS5_PBKDF2_HMAC requires OpenSSL 1.0+ with HMAC and SHA from _hashlib import pbkdf2_hmac except ImportError: import binascii import struct _trans_5C = b"".join(chr(x ^ 0x5C) for x in range(256)) _trans_36 = b"".join(chr(x ^ 0x36) for x in range(256)) def pbkdf2_hmac(hash_name, password, salt, iterations, dklen=None): """Password based key derivation function 2 (PKCS #5 v2.0) This Python implementations based on the hmac module about as fast as OpenSSL's PKCS5_PBKDF2_HMAC for short passwords and much faster for long passwords. """ if not isinstance(hash_name, str): raise TypeError(hash_name) if not isinstance(password, (bytes, bytearray)): password = bytes(buffer(password)) if not isinstance(salt, (bytes, bytearray)): salt = bytes(buffer(salt)) # Fast inline HMAC implementation inner = new(hash_name) outer = new(hash_name) blocksize = getattr(inner, 'block_size', 64) if len(password) > blocksize: password = new(hash_name, password).digest() password = password + b'\x00' * (blocksize - len(password)) inner.update(password.translate(_trans_36)) outer.update(password.translate(_trans_5C)) def prf(msg, inner=inner, outer=outer): # PBKDF2_HMAC uses the password as key. We can re-use the same # digest objects and just update copies to skip initialization. icpy = inner.copy() ocpy = outer.copy() icpy.update(msg) ocpy.update(icpy.digest()) return ocpy.digest() if iterations < 1: raise ValueError(iterations) if dklen is None: dklen = outer.digest_size if dklen < 1: raise ValueError(dklen) hex_format_string = "%%0%ix" % (new(hash_name).digest_size * 2) dkey = b'' loop = 1 while len(dkey) < dklen: prev = prf(salt + struct.pack(b'>I', loop)) rkey = int(binascii.hexlify(prev), 16) for i in xrange(iterations - 1): prev = prf(prev) rkey ^= int(binascii.hexlify(prev), 16) loop += 1 dkey += binascii.unhexlify(hex_format_string % rkey) return dkey[:dklen] # Cleanup locals() del __always_supported, __func_name, __get_hash del __py_new, __hash_new, __get_openssl_constructor