"Brute forcing all md5(x)=x means checking 2.410^38 values. My quick test implementation can test some 2.310^9 values per hour, meaning it would take almost exactly 10^29 hours to brute force it.
Let’s say I get a million people to help me out, then we’re down to 10^23 years.. And let’s say the algorithm gets a million times faster with some clever optimization, and we’re down to 10^17 years. And let’s pretend computers get a million times faster over night, and we’re down to 10^11 years, which is significantly longer than the universe has existed for."
See also: the MD5 Game, which keeps track of significant overlaps.
