3 ms·

They had me until this part . . . Authentication requires that you play a round of the game — but this time, your 30-letter sequence is interspersed wi

• Dove 14y ago
  Their discussion of that attack, from the paper itself: If the attacker is allowed multiple authentication attempts — iterating the extraction and test phases, alternating between the two — then the protocol may become insecure. The reason is that during an authentication attempt the attacker sees the three sequences k0; k1; k2 and could memorize one of them (30 symbols). He would then train offline on that sequence so that at the next authentication attempt he would have a 1/3 chance in succeeding. If the attacker could memorize all three sequences (90 symbols), he could offline subject a trained user to all three sequences and reliably determine which is the correct one and then train himself on that sequence. He is then guaranteed success at the next authentication trial. We note that this attack is non-trivial to pull off since it can be difficult for a human attacker to memorize an entire sequence at the speed the game is played. . . . which isn't all that reassuring, given that if I were trying to break in using this technique, I wouldn't be memorizing, I'd be recording. But it sounds like the system is designed to only give an attacker one trial (notionally opening a trap door under his feet if he fails even once), and it does seem much more secure in that context.