Re: [TUHS] Recovered /etc/passwd files

[Arthur Krewat <krewat@kilonet.net>]

I cracked a root password for a certain system, back in the ARPANET days.

If memory serves, it was 5 characters.

I was able to get my hands on the crypt() source, and figure out that 
the first part of it was intentionally "lengthy" and it just 
pre-computed a bunch of stuff on purpose. At least, that's my memory of 
it at the time.

I was able to separate that precompute part, and then loop through all 
combinations further down the crypt() function. Made it a lot faster.

Was able to crack a 5-character password in less than a week (or maybe 
it was a few days) on a VAX-11/750. Of course, it was a simple password 
consisting of lower-case alpha and no numerics.

I think the first letter of the password was "b" which helped a lot ;)

Nowadays, run hashcat on an HPC cluster and you can break a lot of stuff...

art k.


On 10/5/2019 1:29 PM, Michael Kjörling wrote:
> On 3 Oct 2019 18:51 +0000, from finnoleary@inventati.org (Finn O'Leary):
>> password was something interesting like './,..,/' (it was entirely
>> punctuation characters, was around three different characters in total, and
>> was pretty damn short).
> I'm a bit late to the party here (it's been a crazy week for me and
> I'm only just now starting to catch up), but don't forget that hashed
> Unix passwords back then were limited to eight bytes (actually I
> believe the hard limit was 64 bits' worth of password, so if your
> system used less than 8 bits per character, you could theoretically
> cram more _characters_ into the password, but not more _entropy_,
> which topped out at 2^64 no matter what you did, and in practice a
> fair bit less because you wanted to be able to type it in).
>
> Of course, this wasn't a problem in practice when even just hashing a
> single candidate password took noticable fractions of a second. At 100
> ms per hash, while you could exhaustively search the lower
> alphanumerics four characters space within about two days (my
> calculator says 1.944 * 86400 seconds for that) if you could hog the
> computer for everyone, by the time you got to six characters the same
> search would take almost 7 years, and eight characters the better part
> of 9000 years (assuming you kept running it on the same hardware for
> the duration).
>
> Adding uppercase A-Z alongside lowercase a-z and 0-9 increases the
> exhaustive search time even for the four characters password space to
> about 17 days at 100 ms per hash. So with no additional information
> for an attacker, even a [a-zA-Z0-9]{4} password was tolerably secure,
> and a [a-zA-Z0-9]{5} one was more than good enough if you changed it
> once a year (would take about three years to crack at 100 ms/hash).
>
> William Cheswick mentioned 8e9 hashes per second. While that sounds
> low for good ol' Unix crypt() to me, at that rate, an exhaustive
> search of [a-z0-9]{8} would take about 353 days, again according to my
> calculator. [a-z0-9]{4} would finish in about 18 seconds. My _guess_,
> without having looked up current numbers, is that these figures are at
> least some two orders of magnitude too high given modern hardware.
> Just look at EFF's good ol' Deep Crack.
>
> I wasn't really around much at the time, but if _The Cuckoo's Egg_ is
> to be believed, the bigger problem was that people in general weren't
> any better at choosing good passwords (or keeping them secret) back
> then than they are today. That honestly wouldn't particularly surprise
> me. Technology advances, but people remain largely the same?
>