[Cryptography] encrypting bcrypt hashes

[Robin Wood]

On Wed, 8 Mar 2017 at 16:53 Jonathan Thornburg <jthorn4242 at gmail.com> wrote:

> On Wed, Mar 08, 2017 at 10:45:41AM +0000, Robin Wood wrote:
> > The client is hashing 4-6 digit PINs (mostly 4 digit) with bcrypt, they
> > have the work factor set as high as the business will allow them but they
> > are worried that due to the small key space it will still be possible to
> > reverse individual PINs. They are now thinking of encrypting the hashes
> > before storing them to add an extra layer of protection. The encryption
> is
> > fast enough to not affect login times so my suggestion of using the
> > additional processing to increase the work factor instead was rejected.
>
> What about salting the hash?
>

I assumed bcrypt had to be salted so didn't mention it, yes, they have salt


> More generally, what's the threat model?
>

Someone grabbing just the database

Robin


> (Online attacks?  Offline attacks after someone steals the database of
> hashed PINs?  Something else?)
>
> ciao,
>
> --
> -- "Jonathan Thornburg [remove -animal to reply]" <
> jthorn at astro.indiana-zebra.edu>
>    Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA
>    "There was of course no way of knowing whether you were being watched
>     at any given moment.  How often, or on what system, the Thought Police
>     plugged in on any individual wire was guesswork.  It was even
> conceivable
>     that they watched everybody all the time."  -- George Orwell, "1984"
>
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