question: public int unpad ( byte [ ] in , int off , int len ) { if ( ( in == null ) || ( len == 0 ) ) { return 0 ; } byte lastByte = in [ off + len - 1 ] ; int padValue = ( int ) lastByte & 0x0ff ; if ( ( padValue < 0x01 ) || ( padValue > blockSize ) ) { return - 1 ; } int start = off + len - ( ( int ) lastByte & 0x0ff ) ; if ( start < off ) { return - 1 ; } return start ; }
target:  Returns the index where the padding starts. <p>Given a buffer with padded data, this method returns the index where the padding starts.