I'm working on a challenge at school on Internet, to learn programming and all security issue: "An api request is protected by checksum" and we have to bypass this. The checksum format is really weird; I've never something like it before. I think it convert all the string in an array of bytes, after that I don't know.

I search the algorithm to calculate the checksum.

Input : "a" --> "868969713355645187"
Input : "b" --> "208175330546845762"
Input : "example" --> "15743641371246298"
Input : "example1234" --> "1019540279168570200"
Input : "example1234778293782" --> "201687914436075516"

Length is 18-19 characters, only decimal

  • 1
    $\begingroup$ In general, such questions consisting mostly of ciphertext are off-topic (see Can I get data analysed here?). Possibly related Q with a general technique. I suggest to rewrite the question asking what techniques to use in such case, and giving a link to a pastebin or similar with more data, like 1-character messages for 0-9a-zA-z. Also check if twice the same message yields twice the same code. $\endgroup$
    – fgrieu
    Jun 24, 2021 at 15:35
  • $\begingroup$ I will do that ! Thanks $\endgroup$ Jun 24, 2021 at 15:44
  • 2
    $\begingroup$ Requests for analyzing ciphertext only (or similar) without a description of the system are off-topic here. Do you have any other info about the problem? You mention it's online, is it something where you are supposed to look at the JS and reverse-engineer it (in which case this belongs on reverse-engineering SE, not here)? $\endgroup$ Jun 24, 2021 at 15:46


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