Password Hashing Competition winner and special recognitions • Hacker News Board

Re: Password Hashing Competition winner and special recognitions

#21

Post by kijin » Tue, Jul 21, 2015, 2:15 AM UTC

riquito wrote: post #17

nly wrote: post #14

Earlier quoted context omitted.

This is trivial to achieve with any hash function.

AFAIK you store the hash along the algorithm/parameters you used to generate it. To update the hash you wait for the user to log in and... 1. check if the stored hash is identical to the hash you generate on fly using the old algorithm 2. create a new hash using the new algorithm and substitute both the old hash and the old informations about the algorithm/parameters What's the trivial way to achieve it without the u…

GP might be thinking of cases where the Nth iteration of the hash is only based on the salt and the result of the N-1st iteration, rather than on the original passphrase.

I'm not aware of any currently recommended algorithm that does this, though. The original passphrase usually goes into each and every iteration, not just the first round.

Re: Password Hashing Competition winner and special recognitions

#22

Post by nly » Tue, Jul 21, 2015, 2:22 AM UTC

mankyd wrote: post #20

riquito wrote: post #17

Earlier quoted context omitted.

AFAIK you store the hash along the algorithm/parameters you used to generate it. To update the hash you wait for the user to log in and... 1. check if the stored hash is identical to the hash you generate on fly using the old algorithm 2. create a new hash using the new algorithm and substitute both the old hash and the old informations about the algorithm/parameters What's the trivial way to achieve it without the u…

Hash your existing hash with a more powerful algorithm.

Exactly, it's hacky, but Scrypt'ing your ancient MD5 databases is better than sitting on your ass and being caught with your pants down when your database gets dumped on pastebin or a Russian forum

Re: Password Hashing Competition winner and special recognitions

#23

Post by AngrySkillzz » Tue, Jul 21, 2015, 5:12 PM UTC

baby wrote: post #15

tyho wrote: post #7

Impressive stuff. One of the features of the winner is that you can offload the expensive computation to a client and still maintain the security you would have if it were done on the server. This should hopefully persuade people to use slow hash functions where they otherwise would not due to performance concerns.

> One of the features of the winner is that you can offload the expensive computation to a client and still maintain the security you would have if it were done on the server Can't you do that with any password hashing alg?

Yeah, I've heard it called "server relief." Slow password hash is computed on the client, then transmitted to the server and run through a fast hash before being stored.