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Date: Tue, 28 Oct 2014 10:57:30 -0400
From: Dave Kalaluhi <>
Subject: Re: passwdqc min= and enforce= should be quick questions

Thanks for the information Alexander!

On Mon, Oct 27, 2014 at 5:10 PM, Solar Designer <> wrote:

> On Mon, Oct 27, 2014 at 04:18:23PM -0400, Dave Kalaluhi wrote:
> > So on some newer systems we are using passwdqc via pam.d.
> >
> > The (not actual) settings are:
> > min=5,5,5,5,5 similar=deny enforce=everyone
> >
> > Based on the man pages: with the above min settings, a password like
> > passw should work. (unless I'm reading the man pages wrong).
> You're probably not reading descriptions of options that you're not
> using.  The match=N option by default (that is, when it is not
> specified) implies additional checks:
>      match=N
>              (default: match=4) The length of common substring required to
>              conclude that a password is at least partially based on
> informa-
>              tion found in a character string, or 0 to disable the
> substring
>              search.  Note that the password will not be rejected once a
> weak
>              substring is found; it will instead be subjected to the usual
>              strength requirements with the weak substring partially dis-
>              counted.
>              The substring search is case-insensitive and is able to detect
>              and remove a common substring spelled backwards.
> Observe:
> $ echo passw | pwqcheck -1 min=5,5,5,5,5
> Bad passphrase (based on a dictionary word and not a passphrase)
> $ echo passw | pwqcheck -1 min=5,5,5,5,5 match=0
> OK
> > pam/passwdqc doesn't allow that, and I'm assuming that's because of
> > the enforce=everyone directive.
> No, the enforce=everyone option only affects for whom the policy is
> enforced, whereas your question is about the policy itself (whether a
> password is considered weak or not).
> > My question is, HOW passwdqc enforces passw is NOT a strong password.
> I assume you mean how it "infers" that, not how it "enforces" anything.
> (As I mentioned above, enforcement is a separate thing.)
> It finds that "passw" has a 4-character common substring with the word
> "pass", which is on its internal wordlist.  The default for substring
> matching is match=4, which means that a 4-character match is considered
> long enough to trigger this behavior.  The length of this substring is
> then assumed to be one less than the minimum required for a match, thus
> making it 3 characters, plus the "w" character.  That's an effective
> password length of 3 + 1 = 4, which is less than your minimum of 5.
> The reported reason is nevertheless what originally caused this sort of
> checking, "based on a dictionary word and not a passphrase".
> I strongly recommend that you don't alter passwdqc's default policy
> unless you have a very important reason to do so.
> Alexander

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