I already know AES produces a "random" output.
Its cipher-text doesn't follow a pattern and is indistinguishable from noise.

Is this common in most cipher-texts?
What are some other (specifically fast) examples of ciphers?

  • 1
    Is your last sentence asking us to just list out fast encryption algorithms or are you looking for something else? – Neil Smithline Jan 16 '16 at 0:10
  • I would like to know which ciphers are both fast and have a random output. – 54 69 6D Jan 16 '16 at 2:07
  • I'm not an expert, but I believe any successful cipher is going to produce output that's reasonably random. Consider as a counter-example ECB, which now "is not recommended for use in cryptographic protocols at all." (See also the caveat, "Note that the random appearance of the image on the right does not ensure that the image has been securely encrypted; many kinds of insecure encryption have been developed which would produce output just as 'random-looking'.") – gowenfawr Jan 16 '16 at 4:45
  • Why do you ask, though? Is it just curiosity or are you looking for a random-number generator? Because there are MUCH better random number generators out there than abusing ciphers for that purpose. – Ben Jan 16 '16 at 5:15
  • FYI: cross-posted on crypto.se – SEJPM Jan 16 '16 at 19:38

All modern ciphers aim to produce what looks like random data - it's one of the core principles of information theory.

Ciphers that don't produce apparently random looking data tend to have fairly serious flaws, since this provides an avenue for attack - going back to pre-computer ciphers, enigma had this issue, and fell, in part, due to pattern recognition (specifically, someone spotted that A could never map to A, reducing the search space significantly, among other issues).

Any reasonable modern block cipher should be both fast and generate apparently random data, if used properly.

  • Well, in theory it would be possible to communicate securely with the text of the full works of Shakespeare repeated as needed with spelling errors. Then the spelling errors are the real data and that should be random looking. – bjb568 Jan 16 '16 at 10:27
  • "Any reasonable modern block cipher should be both fast" - some more than others, especially fast are (X)Salsa20, ChaCha20 and AES (if you have hardware support for AES). – SEJPM Jan 16 '16 at 11:51

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