From: rjq@phys.ksu.edu (Rob Quinn)
Newsgroups: alt.security
Subject: Crack and exabyte libraries
Date: 22 Jul 1992 22:04:44 GMT
Organization: Kansas State University
NNTP-Posting-Host: bohr.phys.ksu.edu


 I've made the assumption that the encrypted password contains the
same range of characters as the salt - is this true? (ie 64 different
letters).
 If I've made any mistakes, please correct me. (Like you wouldn't have
if I hadn't asked?)

>So let's assume there are 100,000 entries in /usr/dict/words - for each of
>those words, Crack generates a "perversion" based on (for example) replacing
>'o' with '0', that is, changing 'cool' to 'c00l'.  For each word there are
>probably at least 20 different rules that Crack applies to each word:
>so you would have to have 100,000 * 4096 * 20 different encrypted
>results - that's about 8 billion.  Now assume 10 (or is it 12?  I'm too
>lazy to check :-) characters per encrypted password, and we get almost
>100 gigabytes of storage required :-)

 From a crackers point of view: If you increase the size of the password
file, you can decrease the size of your crack database. For a large system,
the cracker only needs to break one account. In my small experience, there's
always at least one trivial password. I would bet that if a cracker had an
exabyte collection of ONLY common names, with no wierd Crack permutations,
they could almost always break into the average computer.
 My common names file has 22426 uniq names. An encrypted password (without
salt) takes 11  6 bit letters,  or 66 bits each.
 22426 words *4096 salts * 66/8 bytes=7.57^^8 bytes ~ 740 meg.
Is that right?
 Now, for me, if I could use all 13 of our machines, I could encrypt
22426*4096 words in less than 2 hours, and on a real password file
I wouldn't have to use all 4096 salts, so the exabyte tape wouldn't
be an incredible gain, but for Joe Cracker sitting on a small computer
it might be "of use."


>too, that Crack has several different ways of deriving possible passwords
>from each user's full name, telephone number, etc - and this kind of
>thing you could never store ahead of time.

 Yep.

>
>	Now I have *heard* (emphasize the unreliability of this story
>here :-) of attacks just like you were talking about with an Exabyte
>tape

 I've always wanted to try it. I'm very security paranoid, and I've been
wondering how feasable it would be.

>- I would assume the attackers simply left out Crack's 20 different

 20? Crack4.1 comes with over 240 rules in the dicts.rules file.


 Regarding the question of multiple passwords encrypting to the same thing,
if people were trusting enough to share F.merged files we might find out.
Any ideas on how to do that anonymously and safely? Didn't think so.


 Asuming passwords only take 66 bits, how many words could I put on a
5gig tape?
5000meg *1024K/meg *1024bytes/K=5.233e+09 bytes=63550060 words.


-- 
|                                                                Rob Quinn |
|                                                         rjq@phys.ksu.edu |
|                                                    QuinnBob@KSUVM.BITNET |
--
|                                                                Rob Quinn |
|                                                         rjq@phys.ksu.edu |
|                                                    QuinnBob@KSUVM.BITNET |
Newsgroups: alt.security