# How can I calculate the probability of collisions of a hashing algorithm? [duplicate]

• You mean probability that collisions happen due to weaknesses in your design? Because generally (without cryptanalysis) the probability of finding one is good after $2^{-n/2}$ calls for digest length $n$. – SEJPM Aug 11 '15 at 17:42
• ... because of the birthday problem. I guess what SEJPM is saying is that the calculation of the probability of collisions that are happening because of the internal design depends on the internal design. $2^{-n/2}$ is just the lower bound (where $n$ is the output size). – Maarten Bodewes Aug 11 '15 at 18:11