Verifies that the supplied signature is a valid ECDSA
signature of the supplied hash value using the supplied public key.
\param dgst pointer to the hash value
\param dgst_len length of the hash value
\param sig ECDSA_SIG structure
\param eckey EC_KEY object containing a public EC key
\return 1 if the signature is valid, 0 if the signature is invalid
and -1 on error
Verifies that the supplied signature is a valid ECDSA signature of the supplied hash value using the supplied public key. \param dgst pointer to the hash value \param dgst_len length of the hash value \param sig ECDSA_SIG structure \param eckey EC_KEY object containing a public EC key \return 1 if the signature is valid, 0 if the signature is invalid and -1 on error