cdef extern from "openssl/evp.h":
    ctypedef struct EVP_MD_CTX:
        pass
    ctypedef struct EVP_MD:
        pass
    EVP_MD_CTX *EVP_MD_CTX_new()
    void EVP_MD_CTX_free(EVP_MD_CTX *)
    const EVP_MD *EVP_sha256()
    int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, void *impl)
    int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt)
    int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md,
                           unsigned int *s)
    int EVP_MD_size(const EVP_MD *md)
    int EVP_MD_CTX_reset(EVP_MD_CTX *ctx)