Syntax:
asymmetric_sign(algorithm, digest_str, priv_key_str, digest_type)

Signs a digest string using a private key string, and returns the
signature as a binary string. If signing fails, the result is NULL.

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.

priv_key_str is the private key string to use for signing the digest
string. It 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'

For a usage example, see the description of asymmetric_verify().

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

