公开 EVP_MD_CTX 的 _hashlib.pyd 内部结构吗？

Question

有人知道如何使用 ctypes 公开 python 2.x _hashlib.pyd 内部结构吗？我特别需要提取 EVP_MD_CTX 结构来序列化 python HASH 对象。

Answer 1

从头文件（在您的例子中是 openssl/evp.h 和 _hashopenssl.c）映射 C 结构很简单，但并不总是可以跨不同版本移植。这是针对我的环境的：

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),
    ]

下面是如何使用它来保存的示例并恢复哈希对象的状态：

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()