4 ms·

I don't know a whole lot about this area, but why would dictionary passwords be more vulnerable when considering a password hash? Couldn't you just salt the has

by rcfox 13y ago

I don't know a whole lot about this area, but why would dictionary passwords be more vulnerable when considering a password hash? Couldn't you just salt the hashes with enough characters to defeat rainbow tables?

dylangs1030 13y ago
You're right - dictionary attacks aren't more vulnerable using a password hash. As a rule, a hash will obviously only add complexity. Salting the hash in addition to that will prevent a list of common words, and corresponding hashes ("dictionary attack") from working because of the nonsense salt value. However, the real value of salting a hashed password is in defeating multiple password cracks. The salt is like a nonce added to a each individual password so that if you crack one, you can't formulaically crack them all. While en masse this is tedious, applied to a single password it's meaningless because the processing time for brute-forcing a salted hash and a non-salted hash will be trivial. It's mainly useful because you can't "recycle" computational power applied to one cracked password for another, assuming you have e.g. a database in front of you. To give a quick explanation of why a salt won't protect a single password, consider it this way - salting passwords allows each hash to come out differently, such that if you try to crack a list of passwords using a single algorithm it won't work because the salt randomizes each one. Repeating the computational steps for cracking one password will be null and void for finding additional passwords if they're salted - you'll have to start over.
bigiain 13y ago
There's a lot of modern password hash attacks like HashCat that don't use rainbow tables. There just aren't enough words in most people's vocabulary for a "dictionary word" to provide enough bits. Salts help, but HashCat on a decent GPU will test over 2million password/sec for salted MD5 hashes using phpass (the current WordPress password storage). That'll rip through the whole RockYou password list (32m words) in 15 seconds. Anecdotal evidence suggests something like 25% of typical passwords from publicly available dumped hashes fall to the RockYou list. Salts mean I ned to run each hash individually, but a 25% chance of revealing each hash's password in ~15secs isn't much of a challenge. (Oh, and the "journalist with a laptop" comment was about this: http://arstechnica.com/security/2013/03/how-i-became-a-password-cracker/ http://arstechnica.com/security/2013/03/how-i-became-a-passw... not a bad read if you're curious. See page 3, almost 5000 passwords out of a list of 17000 unsalted MD5 hashes in _one_ minute - on a laptop without using a GPU…)

by rcfox 13y ago

dylangs1030 13y ago

You're right - dictionary attacks aren't more vulnerable using a password hash. As a rule, a hash will obviously only add complexity. Salting the hash in addition to that will prevent a list of common words, and corresponding hashes ("dictionary attack") from working because of the nonsense salt value. However, the real value of salting a hashed password is in defeating multiple password cracks. The salt is like a nonce added to a each individual password so that if you crack one, you can't formulaically crack them all. While en masse this is tedious, applied to a single password it's meaningless because the processing time for brute-forcing a salted hash and a non-salted hash will be trivial. It's mainly useful because you can't "recycle" computational power applied to one cracked password for another, assuming you have e.g. a database in front of you. To give a quick explanation of why a salt won't protect a single password, consider it this way - salting passwords allows each hash to come out differently, such that if you try to crack a list of passwords using a single algorithm it won't work because the salt randomizes each one. Repeating the computational steps for cracking one password will be null and void for finding additional passwords if they're salted - you'll have to start over.

bigiain 13y ago

There's a lot of modern password hash attacks like HashCat that don't use rainbow tables. There just aren't enough words in most people's vocabulary for a "dictionary word" to provide enough bits. Salts help, but HashCat on a decent GPU will test over 2million password/sec for salted MD5 hashes using phpass (the current WordPress password storage). That'll rip through the whole RockYou password list (32m words) in 15 seconds. Anecdotal evidence suggests something like 25% of typical passwords from publicly available dumped hashes fall to the RockYou list. Salts mean I ned to run each hash individually, but a 25% chance of revealing each hash's password in ~15secs isn't much of a challenge. (Oh, and the "journalist with a laptop" comment was about this: http://arstechnica.com/security/2013/03/how-i-became-a-password-cracker/ http://arstechnica.com/security/2013/03/how-i-became-a-passw... not a bad read if you're curious. See page 3, almost 5000 passwords out of a list of 17000 unsalted MD5 hashes in _one_ minute - on a laptop without using a GPU…)