4 ms·
> When we say that a random number has 78 bits of entropy, what we really mean is that an attacker has a 1 in 2⁷⁸ chance of guessing the random number. I don't
by thih9 6y ago
> When we say that a random number has 78 bits of entropy, what we really mean is that an attacker has a 1 in 2⁷⁸ chance of guessing the random number.
I don't have any experience with cryptographically secure randomness, I'm just curious. Assuming an attacker knows that a biased coin has been used and that a random number has 78 bits of entropy instead of 128; how in practice would the attacker use this knowledge to guess the random number?
- Taek 6y agoIf you know a coin is biased towards heads, the most likely outcome is all heads. So you'd start by guessing all heads, then guess all combinations with one head, all combinations with 2 heads, etc If you don't know the bias you can start with all heads, then do all tails, etc. Basically, anything you know about a bias allows you to sort the possible outcomes by how likely they are in your model and then try them in order from most likely to least likely.