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Date: Thu, 13 Oct 2022 15:55:32 +0200
From: Matthias Apitz <>
Subject: Re: using john to decrypt DES hashes

El día jueves, octubre 13, 2022 a las 02:29:57p. m. +0200, Solar Designer escribió:

> Hello Matthias,
> On Thu, Oct 13, 2022 at 11:18:59AM +0200, Matthias Apitz wrote:
> > Me and my company are managing large databases wherein the PIN of users
> > are hashed with UNIX crypt(3) in the old DES form and a fixed salt "xX".
> > With large I mean some thousands. For data security reasons we want to
> > move to a better algorithm, "yescrypt", and when the user provides the
> > PIN in clear, it is checked against the old DES hash, and when correct
> > the field in the database is updated to "yescrypt" by our software. So
> > far so good. I also want to update the (remaining) old hashes to "yescrypt"
> > before some hacker is using them, if he got access to the DES strings.
> This makes sense, but you can instead use the existing DES-based hashes
> as input to yescrypt.  That way, you can upgrade all of your hashes to
> yescrypt-of-descrypt at once, without needing to wait for users to log
> in nor cracking any hashes.
> yescrypt-of-descrypt has subtly different security properties from
> direct application of yescrypt, but it's certainly a major upgrade
> compared to descrypt alone.

Hello Alexander,

Thanks for your feedback.

Do I understand you correct: I yescrypt all DES strings in the database
and when the user presents the PIN 4711 I first crypt the with DES and
the old salt 'xX' and the result with yescrypt and the stored "$y$...."  
salt and when this match the user is authenticated, correct?

What would be the security problem with this compared with direct
application of yescrypt?



Matthias Apitz, ✉, +49-176-38902045
Public GnuPG key:

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