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Re: [Issue 4145] Master passphrase and encrypted credentials cache

From: Branko Čibej <brane_at_apache.org>
Date: Tue, 27 Mar 2012 05:29:59 +0200

On 27.03.2012 05:23, Greg Stein wrote:
> On Mon, Mar 26, 2012 at 21:05, Branko Čibej <brane_at_apache.org> wrote:
>> On 26.03.2012 17:45, Greg Hudson wrote:
>>> On 03/26/2012 09:00 AM, C. Michael Pilato wrote:
>>>> The on-disk cache will contain everything it does today where
>>>> plaintext caching is enabled, save that the password won't be
>>>> plaintext, and there will be a bit of known encrypted text (for
>>>> passphrase validation).
>>> Is it important to be able to locally validate the passphrase? That
>>> property intrinsically enables offline dictionary attacks.
>> I was going to say the same. When I read "known encrypted text" my hair
>> stood on end. :)
>>
>> You don't need passphrase validation. If the passphase is wrong, then
>> the recovered password will be wrong, too. It is bad practice to tell
>> people that they used the wrong passphrase, and it's even better if you
>> don't even know that it's wrong.
> While discussing this on IRC some, I did think of one case where you
> want to know they got the correct master passphrase: when they are
> updating a server's password. A mis-entry could completely garble the
> stored/encrypted contents.

I dunno, all the systems I've used rely on the user correctly typing in
the passphrase in this case (and usually that means
verification-by-repetition). I'm really not comfortable with giving
potential crackers such a leg up.

I think it's even better to give the user the option to echo the
passphrase in plain (on screen only, of course) rather than store any
passphrase-derived bits (except for encrypted passwords) on disk.

-- Brane
Received on 2012-03-27 05:30:10 CEST

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