As per title, other than brute force, are there any attacks on Threefish-512 using only a single plaintext block? Are there any attacks like this in any other cipher?

  • 1
    $\begingroup$ A single plaintext/ciphertext pair is much too small a sample to do anything on modern ciphers. On older, or significantly broken ciphers, it may be enough for successful cryptanalysis though. For Threefish-512, there are none, to my knowledge. $\endgroup$
    – Thomas
    Jul 18 '12 at 0:34

According to Schneier, there is an attack on 42 rounds of ThreeFish-512, but if you check out the analysis, it relies on multiple plaintext values.

Wikipedia lists no singular known plaintext attack, only a boomerang attack, which also depends on multiple known plaintexts.

So given these sources, it would seem there is not a well known and effective attack on three fish 512 with only one plaintext block.

Generally speaking, given only an encryption of a single plaintext block it would be difficult to use cryptanalysis to break a cipher. Even block cipher modes of operation which are deprecated, such as ECB, will operate securely for single block-key encryptions.

The Known-Plaintext-Attack seems to utilize single blocks of plaintext in some situations. That wiki site lists its usage on a cipher used during WWII, so technically Yes, there do exist ciphers which have been susceptible to a single known plaintext block at some points in history. But for modern ciphers, No, it does not seem to be an effective means of attack

  • $\begingroup$ Both attacks only work on reduced round ThreeFish, and not on the full Threefish. The first one only works that well on older versions of Threefish. $\endgroup$ Jul 18 '12 at 15:49
  • $\begingroup$ yep all of that it correct. I'll edit to make it more clear $\endgroup$
    – crawfish
    Jul 18 '12 at 15:51

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.