I know that block ciphers encrypts data in the shape of specified blocks and DES also belong to block cipher family. I totally understand the procedure of DES, but I am confused that is DES take all the blocks of 64 bits of any plaint text and apply the process to all of blocks at a time or it encrypts first blocks then 2nd and 3rd and so on.. can anyone explain it Please??

  • $\begingroup$ This depends in the implementation and the mode of operation $\endgroup$
    – SEJPM
    Nov 28, 2016 at 16:46
  • $\begingroup$ Cross-posted from Security Stack Exchange. $\endgroup$
    – Xander
    Nov 28, 2016 at 16:55

1 Answer 1


Guess what: in counter mode DES doesn't encrypt blocks of plaintext at all. In counter (CTR) mode DES encrypts a counter which is XOR-ed with the plaintext.

DES itself doesn't do anything with multiple blocks. DES is an algorithm called a block cipher which handles one block of input and permutes it to a block of output. The chosen permutation depends on the key.

To encrypt anything that is not precisely a block with DES (or any other block cipher) you need a block cipher mode of operation . There are many modes of operation in which a block cipher can be configured as underlying primitive.

How many bytes are actually encrypted by the mode of operation depends on the mode and implementation. One instance of DES - the block cipher - will only handle one 64 bit / 8 byte block at a time.


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