code: function (words, offset) {
                  // Shortcuts
                  var cipher = this._cipher;
                  var blockSize = cipher.blockSize;
  
                  // Remember this block to use with next block
                  var thisBlock = words.slice(offset, offset + blockSize);
  
                  // Decrypt and XOR
                  cipher.decryptBlock(words, offset);
                  xorBlock.call(this, words, offset, blockSize);
  
                  // This block becomes the previous block
                  this._prevBlock = thisBlock;
              }
docs: Processes the data block at offset.
  
  @param {Array} words The data words to operate on.
  @param {number} offset The offset where the block starts.
  
  @example
  
  mode.processBlock(data.words, offset);