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Re: CVE request: crypt_blowfish 8-bit character mishandling
From: Solar Designer <solar () openwall com>
Date: Mon, 11 Jul 2011 20:22:54 +0400

On Mon, Jul 11, 2011 at 04:39:08PM +0200, Ludwig Nussel wrote:
Solar Designer wrote:
[...]
Also, it brings up the question: why merely use $2a$ running the new
code rather than fully emulate the bug even for newly set passwords,
which would make all passwords work, even on other networked machines?
Sure, that would be even nastier for security, so maybe you managed to
strike a balance well.  But nevertheless the question is there.  One of
your options results in full backwards compatibility at a security cost
(for the local system), but the other somehow chooses to strike a
balance between compatibility and security without achieving either of
these fully (for a network of systems).

Maybe you can afford to drop BLOWFISH_2y to avoid those inconsistencies?
I imagine that people won't know to enable this option unless/until they
have already run into an issue anyway (that is, someone is already
unable to log in).  At this point, they could likely upgrade the rest of
their networked systems as well... or downgrade this one. ;-(

I'm not sure I understand what you are suggesting.

I am not exactly suggesting anything specific as I don't know your
priorities, but I point out the inconsistency.

My preference would be that you don't implement that BLOWFISH_2y option -
always have new hashes generated as 2y, even though this means that
networked systems need to be upgraded to new package versions in sync.

Keep using the buggy
algorithm for new passwords and keep storing them as 2a

I'd be unhappy about that, but it's a valid option to provide if you
want to minimize user annoyance, including for networked systems that
are not upgraded in sync (but are manually configured for this...)

as long as BLOWFISH_2a2x is turned on?

No, you'd need a separate option (or a tri-state option) such that
there's a way for non-networked systems to gradually migrate to 2y
hashes without annoying any users.

Alexander


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