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Message-ID: <50962.128.173.192.90.1337884234.squirrel@webmail.tuffmail.net>
Date: Thu, 24 May 2012 14:30:34 -0400 (EDT)
From: "Brad Tilley" <brad@...ystems.com>
To: john-users@...ts.openwall.com
Subject: Re: Can Excessive Rounds make Password cracking
Infeasable
> Hello Brad,
>
> You have started a good discussion. I believe, by number of rounds you
> mean number of iterations?
Yes, in general, it has been my experience that those terms are used
interchangeably and have the same meaning. glibc's sha512-crypt.c uses the
term 'rounds' and the pam configuration files do as well, but iterations
is often used by OpenBSD devs, etc.
> If so, yes, by increasing the number of iterations in a hashing algorithm,
> the resultant hash becomes stronger. However, the function performed by
> the hashing algorithm in each iteration need not be the same.
I understand this and the other points you make. My question is about the
feasibility of cracking such hashes. In my mind, outside of a simple word
list or two to check for the top 1000 most commonly used passwords or so,
I don't think I would bother attempting to crack these much more than
that.
That's what I was hoping to discuss in this thread. Would others take time
and resources to attempt to crack these sort of hashes beyond the very
basic tests or not?
Thanks again,
Brad
> For instance, in the case of MD5-crypt, of the 1000 iterations that take
> place, during each iteration the function performed by the hashing
> algorithm is different based on the iteration counter.
>
> Blowfish hashes provide you a way to decide the number of iterations as
> well.
>
> $2a$<logarithm 2 of the number of iterations>$.........
>
> However, what you state below, the number of iterations look extremely
> high (391939).
>
> While implementing a cryptographic hashing algorithm, besides its strength
> the computational feasibility also needs to be kept in mind.
>
> May I ask you, what is the distro of Linux you are using?
>
> I hope other experienced people on this mailing list would share their
> ideas as well.
>
> Thanks.
>
>
>
> ________________________________
> From: Brad Tilley <brad@...ystems.com>
> To: john-users@...ts.openwall.com
> Sent: Thursday, May 24, 2012 11:36 PM
> Subject: [john-users] Can Excessive Rounds make Password cracking
> Infeasable
>
> This is slightly off-topic as it does not specifically relate to John use,
> but I wanted to ask the opinions of others here. When do rounds make
> password cracking infeasible, or do they? For example, the hash below is a
> SHA-512 hash with 391939 rounds applied. You can actually feel the delay
> at logon (about 2 seconds on newer machines):
>
> test:$6$rounds=391939$UqhsyLSZ$F/K1CGpBf9yefYXCRbY5uK/LW1HzW8EiPCzdq8PMVvZ4JLhb4F464ps87MX/YwYEI0s62KIsnZBuCt45a.A4I0:1002:1002::/home/test:/bin/sh
>
> The source code of sha512-crypt.c sets this as the maximum number of
> rounds so Linux sys admins could configure this number even higher:
>
> /* Maximum number of rounds. */
> #define ROUNDS_MAX 999999999
>
> So long as the passwords are sufficiently complex and users can't select
> simple words such as 'password' for their password, I would think that
> these hashes are close to un-crackable (certainly not in a reasonable time
> period anyway). What do other John users think?
>
> Thanks,
>
> Brad
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