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RE: ADS Password Storage Protection
From: Harold Winshel <winshel () camden rutgers edu>
Date: Fri, 21 Jul 2006 06:46:06 -0400

Roger,

Thanks for the great detailed answer.

Regarding the shorter complex passwords, my understanding is that the reason many organizations recommend a complex password but only up to 8 characters long is because many unix systems don't support a password longer than that. And the organizations don't want to tell the users to use an 8-character password for their unix systems but to use 15 characters for their Windows systems. So they keep it simple and just one have short (8 character) password policy.

And if the password is only going to be 8 characters, it needs to be complex for dictionary attack and other similar reasons.

For purposes of a password policy for windows users - if I understand your comments - we would suggest a 15-character minimum password, and it can be a passphrase, but we should try to make it something that wouldn't appear in some body of work that would be a candidate for digitizing for purposes of a password attack.

I'm not suggesting that it needs to be a phrase that never appeared in any book or newspaper or magazine or any periodical in the history of the world. But if I wanted to pick out two or three books that I would not want the passphrase to appear in, I would exclude a popular book of quotes (such as Bartlet's Book of Quotations).

Given that, would you think that changing just one or two characters of a passphrase would make it a strong passphrase. For instance:

Frankly, my dear, I don't give a damn.

Frankly, my d*ar, I don't give a damn.

For protection against a passphrase attack, I would hope that the second passphrase would make it a much stronger passphrase.

A passphrase that is a real phrase would make it easier for users to remember their password, but if it could be made much stronger by changing only one character it would be less of a burden on the users to remember.

I appreciate your thoughts.

Thanks,

Harold


08:49 PM 7/20/2006, Roger A. Grimes wrote:
There isn't any publicly domain software that specifically attacks
passphrases that I know of, but creating a tool like that should be
almost trivial for a regular programmer. It could be scripted with a few
dozen lines of code. The program would use a password dictionary and
treat each word as character, and apply varying combinations of those
words, in different forms, in varying cases, along with spaces and other
symbols to create one longer password that is then hashed and compared.

But if one was created, mathematically, a passphrase only using words
would suddenly become much weaker than bruteforcing each character
alone. Several researchers and thinkers have concluded that a typical
passphrase containing only whole words would be less secure than a much
shorter, more complex password. And I support this idea completely.

But there aren't tools like this in the public domain, and there is no
way to guarantee real complexity on shorter passwords. Since the vast
majority of people will use a much smaller character set than is
available for them to use, the effective security of a shorter password
becomes equivalent to how smart the brute force/dictionary cracker is in
its hybrid attack.  My my experience, John the Ripper and Cain can both
be configured to guess on much smaller character sets than the password
administrators think users are availing themselves of, and hence their
shorter password aren't that much complex, just shorter.

I hate that if I want to use a 30 character long password/passphrase,
which would be much more difficult to break than a 6 character "complex"
password, that nearly every system requires that I input "complexity"
into my already uncrackable password.

-----Original Message-----
From: Harold Winshel [mailto:winshel () camden rutgers edu]
Sent: Thursday, July 20, 2006 8:08 PM
To: Roger A. Grimes; Depp, Dennis M.; security-basics () securityfocus com
Subject: RE: ADS Password Storage Protection

Roger,

Just to clarify, when I mention password cracking, I'm strictly
referring to passwored cracking software.

You make good points but, for purposes of discussion I'm excluding
protection against shoulder surfing or people trying to manually guess a
password.

So, if I understand your answer - strictly in terms of a brute force
attack - any given 15-character password would be just as strong as any
other 15-character password.

If that's the case, then I go back to one of my original questions,
which is whether there is such a thing as a passphrase attack.  I am not
knowledgeable about password cracking software but it strikes me as
something that should be easy to include in a password cracking program.

Harold


At 09:14 AM 7/20/2006, Roger A. Grimes wrote:
>Yes, as long as I didn't know that was your password.
>
>To second my yes, most password crackers don't guess sequentially, they

>guess randomly (birthday attack theory), so it's not even like
>aaaaaaaaaaaaa would come be guaranteed to up first before
>5adf,nasa73 () #$  A dictionary attack would fail, so only brute force or
>luck could find it.
>
>I think it would be a strange logon, easy to recreate, for someone
>shoulder surfing though.
>
>-----Original Message-----
>From: Harold Winshel [mailto:winshel () camden rutgers edu]
>Sent: Thursday, July 20, 2006 6:17 AM
>To: Roger A. Grimes; Depp, Dennis M.; security-basics () securityfocus com
>Subject: RE: ADS Password Storage Protection
>
>Please correct me if I'm wrong.  If length is the tool for a secure
>windows passphrase then, in theory, a password of "aaaaaaaaaaaaaaa"
>should be just as strong as a 15-character password consisting of
>random characters?
>
>Thanks,
>
>
>
>At 02:55 PM 7/18/2006, Roger A. Grimes wrote:
> >My conjecture is that franklyidon'tgiveadamn is pretty uncrackable as

> >well. No complexity, but length prevents it from being easily
> >broken...non-trivial.  Pull out the complexity and the length is
> >still insurmountable in most cases.
> >
> >If you don't believe that then break my 123456789012345 length, no
> >complexity challenges.
> >
> >-----Original Message-----
> >From: Depp, Dennis M. [mailto:deppdm () ornl gov]
> >Sent: Tuesday, July 18, 2006 8:36 AM
> >To: winshel () camden rutgers edu; security-basics () securityfocus com
> >Subject: RE: ADS Password Storage Protection
> >
> >The phrase you gave, "frankly, my dear, I don't give a damn" meets
> >most
>
> >definitions of complexity.  I has upper and lower case letters and
> >special characters.
> >
> >Dennis
> >
> >-----Original Message-----
> >From: winshel () camden rutgers edu [mailto:winshel () camden rutgers edu]
> >Sent: Saturday, July 15, 2006 12:25 AM
> >To: security-basics () securityfocus com
> >Subject: Re: RE: ADS Password Storage Protection
> >
> >I've read and heard many sources say this same thing, i.e., that, for

> >windows systems, length is stronger than short and complex.  And that

> >a
> >15 character or longer password can be a real phrase and it will be a

> >secure password.
> >
> >
> >I can see why a long password that consists of a real phrase - such
> >as "frankly, my dear, I don't give a damn" - would be just as secure
> >as an
>
> >equally long complex password, in terms of protection against a brute

> >force attack.
> >
> >
> >I don't know much about password cracking programs but am surprised
> >that, while they would be working  on a brute force attack, they
> >wouldn't be able to try a lot of commonly-used phrases at the same
>time.
> >
> >
> >If some password cracking programs can use a dictionary attack,
> >couldn't there also be something called a passphrase attack?  Would
> >it be difficult for a password cracker to digitize Bartlett's Book of

> >Quotations and include that in an attack on a password?
> >
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> >
> >
> >---------------------------------------------------------------------
> >--
> >-
> >---
> >This list is sponsored by: SensePost
> >
> >Hacking, like any art, will take years of dedicated study and
> >practice to master. We can't teach you to hack. But we can teach you
> >what we've learned so far. Our courses are honest, real, technical
and practical.
> >SensePost willl be at Black Hat Vegas in July. To see what we're
> >about,
>
> >visit us at:
> >
> >http://www.sensepost.com/training.html
> >---------------------------------------------------------------------
> >--
> >-
> >---
>
>Harold Winshel
>Computing and Instructional Technologies Faculty of Arts & Sciences
>Rutgers University, Camden Campus
>311 N. 5th Street, Room B36 Armitage Hall Camden NJ 08102
>(856) 225-6669 (O)

Harold Winshel
Computing and Instructional Technologies Faculty of Arts & Sciences
Rutgers University, Camden Campus
311 N. 5th Street, Room B36 Armitage Hall Camden NJ 08102
(856) 225-6669 (O)

Harold Winshel
Computing and Instructional Technologies
Faculty of Arts & Sciences
Rutgers University, Camden Campus
311 N. 5th Street, Room B36 Armitage Hall
Camden NJ 08102
(856) 225-6669 (O)


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