Hacker News Reader

> you won't know what usernames they go with

But if you've got a list of all usernames (probably a relatively small number) and access to a running system, isn't it easy to just try each password against each user until you find a match?

The common practice of limiting logins from a single username wouldn't help with that either.

View on HN

Yes, but we currently have 2.1 million users, so that's still no small burden. And don't forget that's only after you brute forced the passwords.

So you basically increased the cracker's workload by six orders of magnitude, which is equivalent to increasing bcrypt's work factor by 20. Cool!

If you increase bcrypt's workfactor then legitimate requests take longer.

It's not the security of the passwords I'm thinking about, it's whether or not you've really enhanced it much by obfuscating the relationship between password and username. I'm sure you've thought about this more than me, but I'm a bit skeptical, since if you have a lot of users, you probably have had to create systems to make the log in process extremely efficient. If all of your users wanted to log into your system within a 24hr period, could they? Maybe a week? If they could, then an attacker can attempt to log in with each username over the same period of time.

Reply on news.ycombinator.com