code: @Override
      protected long encryptBlock(long lPlainblock) {
  
  	// chain with the CBC IV
  
  	lPlainblock ^= m_lCBCIV;
  
  	// encrypt the block
  
  	lPlainblock = super.encryptBlock(lPlainblock);
  
  	// the encrypted block is the new CBC IV
  
  	return (m_lCBCIV = lPlainblock);
  
      }
docs: internal routine to encrypt a block in CBC mode