# What are the differences between collision attack and birthday attack?

From my understanding both types of attack, collision and birthday, are based on the principle of two randomly/pseudo-randomly chosen plaintext to hash to the same value. I don't want to launch any biased supposition, but aren't they the same?

From Collision attack wikipedia article I learned that every cryptographic hash function is inherently vulnerable to collisions using a birthday attack but in the Birthday attack article it is stated that the attack depends on the higher likelihood of collisions found between random attack attempts and a fixed degree of permutations, thus birthday attack only has this permutation plus?

• The quote from the second Wikipedia page is not very well-written. I'm not sure what it is trying to say. – bmm6o Jun 18 '15 at 14:32
• That was my point, I can't tell the difference from available online sources. – Rares Sabin Rusu Jun 18 '15 at 15:12

• @HeatfanJohn: Yes. In crypto we often use the approximation that a birthday attack on a fair hash of $n$ bits succeeds with odds near $1/2$ after $2^{n/2}$ hashes (if we are able to detect any collision that might occur). $2^{64}$ is 19% lower that the more precise estimate that you quote. – fgrieu Jun 22 '15 at 20:36