Tim Smith <email@example.com> writes:
> 2. If you want to keep your method secret for some reason, you could > implement it yourself, and use it to factor some large numbers, chosen > by others. If you are worried someone might use this to trick you into > factoring an important RSA key for them, that's easy to get around. > Here's how: > > A. Someone posts a challenge number for you. > > B. You factor it, and then post a hash of each factor, but > not the factors themselves. > > C. The challenger posts the factors. > > D. The rest of us verify the factors, and verify the hashes match > what you posted. > > Note that you never have to reveal the factors this way. >
Even better, just RSA-encrypt a message with the secret key based on the factors of a two-factor composite number. Anybody can decrypt this message using the public key based on the composite number.