question: public byte [ ] wrap ( byte [ ] outgoing , int start , int len ) throws SaslException { if ( len == 0 ) { return EMPTY_BYTE_ARRAY ; } byte [ ] wrapped = new byte [ len + 10 + 2 + 4 ] ; System . arraycopy ( outgoing , start , wrapped , 0 , len ) ; incrementSeqNum ( ) ; byte [ ] mac = getHMAC ( myKi , sequenceNum , outgoing , start , len ) ; if ( logger . isLoggable ( Level . FINEST ) ) { traceOutput ( DI_CLASS_NAME , "wrap" , "DIGEST14:outgoing: " , outgoing , start , len ) ; traceOutput ( DI_CLASS_NAME , "wrap" , "DIGEST15:seqNum: " , sequenceNum ) ; traceOutput ( DI_CLASS_NAME , "wrap" , "DIGEST16:MAC: " , mac ) ; } System . arraycopy ( mac , 0 , wrapped , len , 10 ) ; System . arraycopy ( messageType , 0 , wrapped , len + 10 , 2 ) ; System . arraycopy ( sequenceNum , 0 , wrapped , len + 12 , 4 ) ; if ( logger . isLoggable ( Level . FINEST ) ) { traceOutput ( DI_CLASS_NAME , "wrap" , "DIGEST17:wrapped: " , wrapped ) ; } return wrapped ; }
target:  Append MAC onto outgoing message.