I want to use gpg with a symmetric password for encrypting a message. How to do this is explained here in the forum itself, but also in the internet. I'm aware that a symmetric key has the general problem of key exchange. A possible solution is to make a quiz test. The idea is to take 20 questions from an exam test, which can be answered with a, b, c or d. And this will be the password for encrypting the message. The entropy of the password is 4^20, which is high enough for a little fun exam.
The problem is, that the PGP software needs a 100% correct password. But in reality no student will be able to answer all questions correct. What i need is something which is a bit error tolerant. What is the algorithm to generate a password, which is also correct if only 90% of the questions are answered correct? Can this be done with some kind of hash-function or salt?
The idea from educational perspective is, that the students are first attending a quiz, and if they have done all right, they can read the secret message which contains music. Only the student which were successful can hear the song.