5 ms·

I would really love to submit this encryption method to the PCI auditors.... "uses encryption extensively". Edit: seriously? The first example is a shift ciphe

by rnovak 12y ago

I would really love to submit this encryption method to the PCI auditors.... "uses encryption extensively". Edit: seriously? The first example is a shift cipher and a one time pad of all 'M'.

isomorphic 12y ago
Perhaps you'd be happier with the term "obfuscation." But the code does meet the textbook definition of "encryption." Maybe not strong encryption...
- rnovak 12y ago
  Where did I say it wasn't encryption? I said I'd like to submit it to my PCI auditor as _my_ method of encryption, much easier than proper applied crypto.
KMag 12y ago
It's more accurate to call it a Caesar cipher in GF2(8) instead of a one-time pad.
- rnovak 12y ago
  Caeser cipher _is_ a shift cipher, which is exactly what I said it was...
  - KMag 12y ago
    I was referring to "and a one time pad of all 'M'".
    - rnovak 12y ago
      Yeah, sorry, I'm not good enough with the math behind crypto enough to have recognized that :( learn something new every day.
      - KMag 12y ago
        Perhaps my notation was a bit too terse. GF2(8) is a Galois field of order Pow(2, 8). The xor operation is addition in a Galois field, so 8-bit xor with 'M' is the same thing as a constant additive shift by 'M' in a Galois field of order Pow(2, 8). So, it's a Caesar shift cipher using the GF2(8) definition of byte addition rather than the standard modulo 256 definition.
swatkat 12y ago
And, the key 'MZ' used in DecryptStrings() seems to be a "tribute" to DOS executable header :)
AlyssaRowan 12y ago
Yes: the term the VX scene uses is "crypter". Code size and unusualness/uniqueness are goals here, as they're for obfuscation, not strong encryption - the code needs to be small, hard for an AV to recognise with a heuristic (so tables and baked constants are bad) and ideally amenable to being passed through a polymorphic/metamorphic mutation engine.

5 ms·

I would really love to submit this encryption method to the PCI auditors.... "uses encryption extensively". Edit: seriously? The first example is a shift ciphe

by rnovak 12y ago

I would really love to submit this encryption method to the PCI auditors.... "uses encryption extensively". Edit: seriously? The first example is a shift cipher and a one time pad of all 'M'.

isomorphic 12y ago
Perhaps you'd be happier with the term "obfuscation." But the code does meet the textbook definition of "encryption." Maybe not strong encryption...
- rnovak 12y ago
  Where did I say it wasn't encryption? I said I'd like to submit it to my PCI auditor as _my_ method of encryption, much easier than proper applied crypto.
KMag 12y ago
It's more accurate to call it a Caesar cipher in GF2(8) instead of a one-time pad.
- rnovak 12y ago
  Caeser cipher _is_ a shift cipher, which is exactly what I said it was...
  - KMag 12y ago
    I was referring to "and a one time pad of all 'M'".
    - rnovak 12y ago
      Yeah, sorry, I'm not good enough with the math behind crypto enough to have recognized that :( learn something new every day.
      - KMag 12y ago
        Perhaps my notation was a bit too terse. GF2(8) is a Galois field of order Pow(2, 8). The xor operation is addition in a Galois field, so 8-bit xor with 'M' is the same thing as a constant additive shift by 'M' in a Galois field of order Pow(2, 8). So, it's a Caesar shift cipher using the GF2(8) definition of byte addition rather than the standard modulo 256 definition.
swatkat 12y ago
And, the key 'MZ' used in DecryptStrings() seems to be a "tribute" to DOS executable header :)
AlyssaRowan 12y ago
Yes: the term the VX scene uses is "crypter". Code size and unusualness/uniqueness are goals here, as they're for obfuscation, not strong encryption - the code needs to be small, hard for an AV to recognise with a heuristic (so tables and baked constants are bad) and ideally amenable to being passed through a polymorphic/metamorphic mutation engine.