Yep, I did catch that you're seeding multiple PRNGs. My criticism of the method is based on the notion that, since most users will let it run for about the same amount of time each time you do this 'press a key to seed next PRNG' process, you'll end up with a set of seeds which is more predictable than the output of rand. e.g., If the average user has a 0.1 second variance in their response times, then an attacker would only have a range of about 10,000 seeds (based on your "about 100K iterations per second") to check, with those near the middle of the range being much more likely to occur. Granted, each user may have a different range of likely response times, but many users would probably have similar enough ranges that the set of likely seeds would still be smaller than the set of possible results from a mere 16-bit PRNG.