# Tag Info

When you use a PRF to derive a key, there is the potential for collisions. If you derived a 128-bit key from each possible 128-bit number, you'd expect some of them to collide. Specifically, you'd expect only about 63% of all the inputs ($1-e^{-1}$) to appear as outputs. That means you lose less than a bit of entropy even if the original key had the full ...