question: final byte [ ] compute ( byte type , byte buf [ ] , int offset , int len , boolean isSimulated ) { if ( macAlg . size == 0 ) { return nullMAC ; } if ( ! isSimulated ) { byte [ ] additional = acquireAuthenticationBytes ( type , len ) ; mac . update ( additional ) ; } mac . update ( buf , offset , len ) ; return mac . doFinal ( ) ; }
target:  Computes and returns the MAC for the data in this byte array.