What is the recommended way to encrypt user passwo

Question

In a web application written in Perl and using PostgreSQL the users have username and password. What would be the recommended way to store the passwords?

Encrypting them using the crypt() function of Perl and a random salt? That would limit the useful length of passswords to 8 characters and will require fetching the stored password in order to compare to the one given by the user when authenticating (to fetch the salt that was attached to it).

Is there a built-in way in PostgreSQL to do this?

Should I use Digest::MD5?

Answer 1

MD5 is commonly used, but SHA1/SHA256 is better. Still not the best, but better.

The problem with all of these general-purpose hashing algorithms is that they're optimized to be fast. When you're hashing your passwords for storage, though, fast is just what you don't want - if you can hash the password in a microsecond, then that means an attacker can try a million passwords every second if they get their hands on your password database.

But you want to slow an attacker down as much as possible, don't you? Wouldn't it be better to use an algorithm which takes a tenth of a second to hash the password instead? A tenth of a second is still fast enough that users won't generally notice, but an attacker who has a copy of your database will only be able to make 10 attempts per second - it will take them 100,000 times longer to find a working set of login credentials. Every hour that it would take them at a microsecond per attempt becomes 11 years at a tenth of a second per attempt.

So, how do you accomplish this? Some folks fake it by running several rounds of MD5/SHA digesting, but the bcrypt algorithm is designed specifically to address this issue. I don't fully understand the math behind it, but I'm told that it's based on the creation of Blowfish frames, which is inherently slow (unlike MD5 operations which can be heavily streamlined on properly-configured hardware), and it has a tunable "cost" parameter so that, as Moore's Law advances, all you need to do is adjust that "cost" to keep your password hashing just as slow in ten years as it is today.