Common secret
90 points Hard

Here is the list of employees. https://mega.nz/#!PSBVFYwI!KxAhazVh9X-BP9SEfRRKb8yYHonPDJDU1FtQxO8OvMM Their task is to keep a vault safe. No one knows the key to open the vault, but each one of them has a secret key. In order to open the vault, any 3 of them have to meet and put their keys together. By doing so, they will get the key to open the vault. Given the secret key of each employee, can you figure out the key to open the vault? https://en.wikipedia.org/wiki/Lagrange_polynomial

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Rating 4.35
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Discussion

Yeah, this was quite challenging, but I got it in the end. When you get a 54-digit number ending in ...692 (in decimal representation), you most likely solved the first part right. The next part (that was quite challenging for me) is to find the flag from this number.

Maybe there should be a hint telling what to do from here, i really tried a few hours on that step.

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I just can't decode the secret to printable flag correctly. The polynomial and module p are 100% right with all the secret parts. Any decoding ways recommended?

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I am sure I found the correct module. How can I parse this answer. It can't be a regular conversion to ascii.

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Yeah, I solved it! If you're sure you found correct secret - you're right! Problem is algorithm hex->ascii, it's not same as to_bytes or Crypto's long_to_bytes - find correct algorithm and you'll get flag!

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did you use ssss-combine?

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how could there names make different

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Hi Basherru / Jagogo Id are not encoded. You both have close problem. Perhaps it come from the way you convert inputs keys.

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Thnx for the answer!

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Is the id the x co-ordinate, or is the secret split in two?

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