5 kyu

Break Caesar cipher variation : PNG image

32tchai2
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Cryptography
Fundamentals
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  • avermakov Avatar

    Thank you very much! I enjoyed this a lot, just a few years ago I used to do similar things at work :)

  • Blind4Basics Avatar

    For the Test you don't pass, a debug helper is provided.

    Where???

    What are we supposed to do about the CRC part of each chunk? It's not explained anywhere how it's calculated, while it apparently needs to be (ie, just applying the shift of the chunck doesn't lead me to the expected CRC value...)

    edit: ok, got it... I just forgot what the underlying task was... (ie. ceasar...)

  • lechevalier Avatar

    I'm looking at test cases and what's going on here? You added the whole png module to test cases. Is it really needed to generate random test cases? Simple byte comprehension seems enough.

    Otherwise you can use preloaded section to import png module and keep only relevant test generator in kata test cases section.

  • lechevalier Avatar

    Interesting kata & clear description

    To ease debugging, can you add shortest sample tests from 1x1 pixel png please?

    • tchai2 Avatar

      Done I have put a 1x1 pixel png as first test. And I have put more information on png file with this 1 pixel png example.

      Suggestion marked resolved by tchai2 3 years ago
  • anter69 Avatar
    • What is the shift key?
    • CRC has to be recalculated? How?
    • Could we have shorter sample tests?
    • tchai2 Avatar
      • You have to find the shift key.
      • CRC don't need to be recalculated.
      • Sample test are 3x3 pixels png. Hard to make shorter.
      • For the Test you don't pass, a debug helper is provided.
      Issue marked resolved by tchai2 3 years ago
    • anter69 Avatar

      You have to find the shift key.

      So this is a puzzle?

    • lechevalier Avatar

      Not really. Description states:

      Each chunk is encrypted with cesar code with its own key (amount of shift)

      When you read it carefully, there is a block slightly less changing than the others that contains shift key for the whole chunk.

    • anter69 Avatar

      Then indeed it is a puzzle: you have to find something, somewhere, without explanation...

    • lechevalier Avatar

      Are you considering deciphering as a puzzle? In opposition to some kata where you have literally to guess what is the answer by looking at test cases, this description gives enough hints to figure what is the weaker block and how to decipher it to obtain the key. That's why I think cryptography tag is enough.

      Tag puzzle is somewhat negatively connoted on CW and that would be unfair for this kata to label it as such as enough hints are given.

  • Voile Avatar

    PLTE tag aren't tested.