question: public int decryptBlock ( byte [ ] in , int inOff , byte [ ] out , int outOff ) throws DataLengthException , IllegalStateException { if ( ( inOff + blockSize ) > in . length ) { throw new DataLengthException ( "input buffer too short" ) ; } if ( ( outOff + blockSize ) > out . length ) { throw new DataLengthException ( "output buffer too short" ) ; } cipher . processBlock ( cfbV , 0 , cfbOutV , 0 ) ; System . arraycopy ( cfbV , blockSize , cfbV , 0 , cfbV . length - blockSize ) ; System . arraycopy ( in , inOff , cfbV , cfbV . length - blockSize , blockSize ) ; for ( int i = 0 ; i < blockSize ; i ++ ) { out [ outOff + i ] = ( byte ) ( cfbOutV [ i ] ^ in [ inOff + i ] ) ; } return blockSize ; }
target:  Do the appropriate processing for CFB mode decryption.