case MACAlgorithm._null:
return null;
case MACAlgorithm.hmac_md5:
return new MD5Digest();
case MACAlgorithm.hmac_sha1:
return new SHA1Digest();
case MACAlgorithm.hmac_sha256:
return new SHA256Digest();
case MACAlgorithm.hmac_sha384:
return new SHA384Digest();
case MACAlgorithm.hmac_sha512: