For example, if a 128-bit key was bring used, the computer first divides the document or file into 128-bit-long blocks and then combines each block and the key in the manner specified by the algorithm (for example, by adding them). This produces a ciphertext version of the document or file, equal in size to the original. To reproduce the original document, the computer first divides the ciphertext into 128-bitblocks and then applies the decryption key to each block.