Syntax:
ASYMMETRIC_VERIFY(algorithm, digest_str, sig_str, pub_key_str,
digest_type)

Verifies whether the signature string matches the digest string, and
returns 1 or 0 to indicate whether verification succeeded or failed.

digest_str is the digest string. It can be generated by calling
CREATE_DIGEST(). digest_type indicates the digest algorithm used to
generate the digest string.

sig_str is the signature string. It can be generated by calling
ASYMMETRIC_SIGN().

pub_key_str is the public key string of the signer. It corresponds to
the private key passed to ASYMMETRIC_SIGN() to generate the signature
string and must be a valid key string in PEM format. algorithm
indicates the encryption algorithm used to create the key.

Supported algorithm values: 'RSA', 'DSA'

Supported digest_type values: 'SHA224', 'SHA256', 'SHA384', 'SHA512'

URL: http://dev.mysql.com/doc/refman/5.7/en/enterprise-encryption-functions.html

