4 ms·

I'm curious how these password cracking techniques work. I have almost no background in cryptography, so pardon the basic question: is this basically just runni

I'm curious how these password cracking techniques work. I have almost no background in cryptography, so pardon the basic question: is this basically just running billions of text passwords through the md5 algorithm and comparing the results with the unknown string? I assume that the hash would have been salted, so how would this work exactly (unless they obtained the salt too)?

jacobparker 12y ago
You store the salts with the hashes. The basic idea is that salts force attackers to actually do a hash ("slow") instead of pre-computing hashes for common passwords and doing a dictionary lookup ("fast".) All that is to say that if you (the attacker) have the hash you probably also have the salt.
- mirkules 12y ago
  That makes sense. Since md5 can have collisions, is it also safe to assume that the cracked username is not guaranteed to be 100% accurate? In reading about it some more (particularly the md5 collision demo based on Patrick Stach's implementation), it looks like it would be trivial to create an md5 hash that resolved to a "fake" username while the real username remained uncracked. Although that would mean that both the fake username and the real one would be exempt from the exploit, so there would really be no point to it.
  - laxatives 12y ago
    Given this context, it seems like the cracked username is accurate (both usernames are "unregistered" in different languages).
shangxiao 12y ago
> is this basically just running billions of text passwords through the md5 algorithm and comparing the results with the unknown string? Yes: "using a computer that tried more than 300 billion plaintext guesses every second" The Arabic version was obtained by doing an educated guess based on the English version
huhtenberg 12y ago
Straight (unsalted) hashes are typically reversed with the help of a rainbow table - http://en.wikipedia.org/wiki/Rainbow_table http://en.wikipedia.org/wiki/Rainbow_table

jacobparker 12y ago

You store the salts with the hashes. The basic idea is that salts force attackers to actually do a hash ("slow") instead of pre-computing hashes for common passwords and doing a dictionary lookup ("fast".) All that is to say that if you (the attacker) have the hash you probably also have the salt.

mirkules 12y ago
That makes sense. Since md5 can have collisions, is it also safe to assume that the cracked username is not guaranteed to be 100% accurate? In reading about it some more (particularly the md5 collision demo based on Patrick Stach's implementation), it looks like it would be trivial to create an md5 hash that resolved to a "fake" username while the real username remained uncracked. Although that would mean that both the fake username and the real one would be exempt from the exploit, so there would really be no point to it.
- laxatives 12y ago
  Given this context, it seems like the cracked username is accurate (both usernames are "unregistered" in different languages).

shangxiao 12y ago

> is this basically just running billions of text passwords through the md5 algorithm and comparing the results with the unknown string? Yes: "using a computer that tried more than 300 billion plaintext guesses every second" The Arabic version was obtained by doing an educated guess based on the English version

huhtenberg 12y ago

Straight (unsalted) hashes are typically reversed with the help of a rainbow table - http://en.wikipedia.org/wiki/Rainbow_table http://en.wikipedia.org/wiki/Rainbow_table