爲EVP_MD_CTX公開_hashlib.pyd內部函數？

Question

任何人都知道如何使用ctypes公開python 2.x _hashlib.pyd內部？我特別需要提取EVP_MD_CTX結構以便序列化python HASH對象。

Answer 1

從頭文件（openssl/evp.h和_hashopenssl.c）映射C結構很簡單，但並不總是可以跨不同版本移植。這是我的環境：

from ctypes import * 

PyObject_HEAD = [ 
    ('ob_refcnt', c_size_t), 
    ('ob_type', c_void_p), 
] 

class EVP_MD(Structure): 
    _fields_ = [ 
     ('type', c_int), 
     ('pkey_type', c_int), 
     ('md_size', c_int), 
     ('flags', c_ulong), 
     ('init', c_void_p), 
     ('update', c_void_p), 
     ('final', c_void_p), 
     ('copy', c_void_p), 
     ('cleanup', c_void_p), 
     ('sign', c_void_p), 
     ('verify', c_void_p), 
     ('required_pkey_type', c_int*5), 
     ('block_size', c_int), 
     ('ctx_size', c_int), 
    ] 

class EVP_MD_CTX(Structure): 
    _fields_ = [ 
     ('digest', POINTER(EVP_MD)), 
     ('engine', c_void_p), 
     ('flags', c_ulong), 
     ('md_data', POINTER(c_char)), 
    ] 

class EVPobject(Structure): 
    _fields_ = PyObject_HEAD + [ 
     ('name', py_object), 
     ('ctx', EVP_MD_CTX), 
    ] 

下面是關於如何用它來save and restore state of hash object一個例子：我需要

import hashlib 

hash = hashlib.md5('test') 
print hash.hexdigest() 

c_evp_obj = cast(c_void_p(id(hash)), POINTER(EVPobject)).contents 
ctx = c_evp_obj.ctx 
digest = ctx.digest.contents 
state = ctx.md_data[:digest.ctx_size] 

hash2 = hashlib.md5() 
c_evp_obj = cast(c_void_p(id(hash2)), POINTER(EVPobject)).contents 
ctx = c_evp_obj.ctx 
digest = ctx.digest.contents 
memmove(ctx.md_data, state, digest.ctx_size) 
print hash2.hexdigest()