/**
* Creates a message authentication code (MAC) for the given input.
*
* @param msg input
* @param k secret key
* @param a encryption algorithm
* @param enc encoding
* @return MAC
* @throws QueryException query exception
*/
Item hmac(final byte[] msg, final byte[] k, final byte[] a, final byte[] enc)
throws QueryException {
// create hash value from input message
final Key key = new SecretKeySpec(k, string(a));
final byte[] aa = a.length == 0 ? DEFA : a;
if (!ALGHMAC.contains(lc(aa))) throw CX_INVHASH.get(info, aa);
final boolean b64 = eq(lc(enc), BASE64) || enc.length == 0;
if (!b64 && !eq(lc(enc), HEX)) throw CX_ENC.get(info, enc);
try {
final Mac mac = Mac.getInstance(string(ALGHMAC.get(lc(aa))));
mac.init(key);
final byte[] hash = mac.doFinal(msg);
// convert to specified encoding, base64 as a standard, else use hex
return Str.get(b64 ? org.basex.util.Base64.encode(hash) : hex(hash, true));
} catch (final NoSuchAlgorithmException e) {
throw CX_INVHASH.get(info, e);
} catch (final InvalidKeyException e) {
throw CX_KEYINV.get(info, e);
}
}
