Editorial for DMOJ Capture The Flag '20 C3 - Small AES - Olympiads Online Judge

Editorial for DMOJ Capture The Flag '20 C3 - Small AES

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Author: Ninjaclasher

This is a brute force problem. We can see that only 3 bytes of the SHA-256 hash are used towards encrypting the text, and that the os.urandom does absolutely nothing. Brute forcing all $256^3$ $256^{3}$ possible keys is enough to decrypt the text (just check which ones result in printable ASCII characters). The hardest part of this problem is probably reversing the encrypting method.

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