Computes ECDSA signature of a given hash value using the supplied
private key (note: sig must point to ECDSA_size(eckey) bytes of memory).
\param dgst pointer to the hash value to sign
\param dgstlen length of the hash value
\param kinv BIGNUM with a pre-computed inverse k (optional)
\param rp BIGNUM with a pre-computed rp value (optioanl),
see ECDSA_sign_setup
\param eckey EC_KEY object containing a private EC key
\return pointer to a ECDSA_SIG structure or NULL if an error occurred
Computes ECDSA signature of a given hash value using the supplied private key (note: sig must point to ECDSA_size(eckey) bytes of memory). \param dgst pointer to the hash value to sign \param dgstlen length of the hash value \param kinv BIGNUM with a pre-computed inverse k (optional) \param rp BIGNUM with a pre-computed rp value (optioanl), see ECDSA_sign_setup \param eckey EC_KEY object containing a private EC key \return pointer to a ECDSA_SIG structure or NULL if an error occurred