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Date: Thu, 24 May 2012 12:43:53 -0600
From: Stephen John Smoogen <>
Subject: Re: Can Excessive Rounds make Password cracking Infeasable

On 24 May 2012 12:30, Brad Tilley <> wrote:

> 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?

Yes people will. To many people, a password is a puzzle. You know that
something hidden is inside it and you want to see what is inside it. I
have dealt with more than enough breakins where the person didn't do
anything with the site they had but just wanted the hashes to "play"
with.  Other people will go to any length if the prize is high enough
for them (money, top billing rights, leak something great to
anonymous, etc.)

> 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 <>
>> To:
>> 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

Stephen J Smoogen.
"The core skill of innovators is error recovery, not failure avoidance."
Randy Nelson, President of Pixar University.
"Years ago my mother used to say to me,... Elwood, you must be oh
so smart or oh so pleasant. Well, for years I was smart. I
recommend pleasant. You may quote me."  —James Stewart as Elwood P. Dowd

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