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Fantastic and damming read. I had no idea they were so active and nefarious even in the 70s
by tetris11 3y ago
Fantastic and damming read. I had no idea they were so active and nefarious even in the 70s
- tptacek 3y agoAre you sure you read it carefully? NSA's role in DES was to make it resistant to linear and differential cryptanalysis.
- adrian_b 3y agoTrue, but they have also forced the reduction of the key size from 64 bits to 56 bits, making it much more vulnerable to brute force. So they have hardened DES towards attacks from those with much less money than NSA, while making it weaker against rich organizations like NSA.
- tetris11 3y agoThey made it resistant to differential attacks yes, but weakened it for their own attack surface
- tptacek 3y agoWhat does that mean?
- tetris11 3y agoThey made the S-blocks appear less deterministic when sampling their behaviour, but made sure that anyone with prohibitively expensive equipment (say, the NSA) could brute force them in a reasonable time frame.
- tptacek 3y agoThese are all words (mostly; "S-blocks" is not a thing, you mean "s-boxes"), but they're not coherent in a sentence. I think you're trying to point out that NSA shortened the key length from 64 to 56 bits, which has nothing to do with the DES s-boxes. NSA's interventions with the s-boxes made them more resilient to cryptanalysis, not less. The thing you're thinking is nefarious is not (unless you're a connoisseur of good bugs and believe that differential cryptanalysis, the most important fundamental technique in block cipher analysis, should have been public earlier). It is in fact the opposite of nefarious.
- tetris11 3y agoYou're right, I thought that the S-boxes were defined by the number of bits and that the NSA had deliberately shortened them, whilst obfuscating other attack techniques. Thanks for the clarification!