Worked Proof shown
A CTF flag checker solved
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A DownUnderCTF native binary checker turned into equations with REA, and the flag verified.
The full story
An REA showcase solving a capture-the-flag puzzle from DownUnderCTF: a 15 KB program that asks for a flag and prints "Correct!" or "Incorrect!". With the function names stripped, the agent finds the prompt string, follows the references to the checking function, extracts the masks it compares against and turns the checks into equations. It then solves them and confirms the recovered flag by running the original program.
How it was done
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Sources
From the maker's own write-up or code. We summarise what they report; we haven't tested it ourselves.
- Awesome REA list: Solve a CTF flag checker
The showcase with each REA query, the recovered checks and the verification step.