Verify MAC

To verify a MAC:

1. Obtain a [previously calculated MAC value]. Put that value in a byte array.

2. Get an instance of a Mac object. Pass the algorithm as an argument.

3. Obtain an instance of the key that was used to create the MAC.

4. Initialize the Mac object and pass the previously calculated MAC value by encapsulating the byte array in a MACValue object.

5. Convert the original plaintext to a byte array and invoke the doFinal method of the Mac object to verify the previously calculated MAC.

Code sample

The following code sample compares the value of prevMac with a newly calculated MAC of the string password.

byte[] prevMac = ... /* get previously calculated MAC */
Mac mac = Mac.getInstance("HmacSHA1Verify", "IngrianProvider");
SecretKey key = NAEKey.getSecretKey("mackey");
mac.init(key, new MACValue(prevMac));
byte[] result = mac.doFinal("password".getBytes());
boolean verified = (result[0] == 1);