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copied!<p>Mapping C structures from header files (openssl/evp.h and _hashopenssl.c in your case) is straightforward, but is not always portable across different versions. Here it is for my environment:</p> <pre><code>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), ] </code></pre> <p>Below is an example on how to use it to <a href="https://stackoverflow.com/questions/5865824/hash-algorithm-for-dynamic-growing-streaming-data">save and restore state of hash object</a>:</p> <pre><code>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() </code></pre>

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