Human Server

Server implements ECDSA, and allows us to send what we want to Alice and Bob. We can also control a nonce, which gets xored with the private key at the end. The server only does one check, and that is that the private keys match at the end of the transfer. We can send the generator point to both Alice and Bob, as we know what the generator multiplied by their private keys are, and then we create a pair of nonces so that they xor to give the same private key. We then just decrypt the flag by using AliceX ^ BobNonce as the shared secret