It seems like many recommendations are to use at least 75-100, or even 128. Being fairly conservative, if you had 10k hosts hashing 1B passwords a second, it would take 7.5 years worst case to crack [1]. If a particular site neglects to use a slow hash function and salting, it's easy to imagine bad actors precomputing rainbow tables that would make attacks relatively easy.
You can rebut that that's still a crazy amount of computation needed, but since it's reusable, I find it easy to believe it's already being done. For comparison, if the passwords have 100 bits of entropy, it would take those same 10k servers over 4 billion years to crack the password.
It seems like many recommendations are to use at least 75-100, or even 128. Being fairly conservative, if you had 10k hosts hashing 1B passwords a second, it would take 7.5 years worst case to crack [1]. If a particular site neglects to use a slow hash function and salting, it's easy to imagine bad actors precomputing rainbow tables that would make attacks relatively easy.
You can rebut that that's still a crazy amount of computation needed, but since it's reusable, I find it easy to believe it's already being done. For comparison, if the passwords have 100 bits of entropy, it would take those same 10k servers over 4 billion years to crack the password.
[1]: (2*71 / 1e9 / 10000 / (606024*365)) ≈ 7.5