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ziq wrote

I think this would work better with invites by mods, not passwords. Passwords could be shared indiscriminately.

4

tlckl OP wrote

Okay, here's my idea:

When you get an invite, a random number is generated. This random number corresponds to the key used to encrypt the forum.

From this secret key, a small hex value that the user has to remember is generated, through XOR'ing the user's salt and the random number.

When the user enters the forum, they give the generated key, which is then used to decrypt the forum (by XORing with the salt, and then using that as key to a chiper).

To have multiple keys (so that they can't be shared), one uses a hash-based multi-key scheme (this works by having a normal cipher and a SHA256 fingerprint based dictionary, which maps h(k) (where k is a key) to C(K, k), where C is the cipher and K is the key used to the cipher).

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tlckl OP wrote

Actually, I think above scheme can be simplified a bit:

Each encrypted subforum are asigned a random key, which is used to encrypt them. This key is never stored on the server, it is only given to the moderators after creation.

To generate keys to users, the moderator sends the key, and the server encrypts this key with the user's salt (or maybe another random number assigned to every user upon creation).

The generated key is the secret value only known to the user. When the subforum is visited, the user enters this key, and the server decrypts it to the real one by using the user's salt.

Sharing the key is only possible if two users has the same salt, which won't happen before the heat death of the universe.

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tlckl OP wrote

Hmm. But we'd need a way to encrypt. Let me come up with something.

2