phc-discussions - Re: [PHC] Do we need a common password hashing API?

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Date: Mon, 14 Apr 2014 11:20:41 +0400
From: Solar Designer <solar@...nwall.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Do we need a common password hashing API?

Hi Alec,

It's very nice to see you in here!

On Sun, Apr 13, 2014 at 04:53:45PM +0100, Alec Muffett wrote:
> Some of this was the original intention behind the Solaris Pluggable Crypt
> Framework. [statement of interest: I am a co-author]
> 
> tl;dr: make it ASCII and let the DLL sort out the details.
> http://dropsafe.crypticide.com/article/1389

Where's the huge warning that Sun/Oracle has patented this stuff, making
it unsuitable for the PHC community? ;-(  While there's prior art for most
or all of it (including my crypt_gensalt() on Owl), I think we should
stay away from the dynamic linking because of the patent, until it expires.

http://dropsafe.crypticide.com/aboutalecm

"Patents

Method and apparatus for implementing a pluggable password obscuring mechanism -
Inventors: Darren J. Moffat, Casper H. Dik, Alec Muffett."

http://www.google.com/patents/US20050005173

Bill, here's a description of my crypt_gensalt(), etc., introduced into
Owl slightly earlier than Solaris' use of the same function name (year
2000 vs. slightly later):

http://www.openwall.com/crypt/openwall-crypt.3.pdf

Besides the different function prototype and several other differences,
the major difference is in that my crypt_gensalt() accepts prefix
(requesting a particular hashing scheme) and iteration count as an
arguments, whereas Solaris' crypt_gensalt() reads the equivalents of
these (and possibly more) from a system-wide configuration file.  In
practice, the iteration count for my crypt_gensalt() is passed via
pam_tcb's command line found in system configuration files anyway, but
other uses are possible as well.

So these differ in the kind of flexibility they provide.  In my case,
it's no dependence of this interface on system-wide configuration.
In Solaris' case, it's no dependence on there being just these two
parameters, so it's easier (or rather more consistent) to add m_cost and
any hashing scheme specific parameters.  These can be added via a
configuration file with my crypt_gensalt() too, but it becomes
inconsistent (t_cost is passed to the function, but m_cost, etc. is
somehow read by the function from files).

Maybe yet another interface is desirable, where crypt_gensalt() would
accept an arbitrary set of parameters for the hashing scheme, and if
those are not provided then read them from a configuration file.

As to the name=value encoding in salt strings (which I dislike), I think
it's orthogonal in this context.  Whether the encoding is verbose and
human-readable (such as the name=value stuff) or compact and
machine-focused (such as what I intend to use for yescrypt), there's a
need for an interface to produce those strings from the individual
parameter values.  e.g. yescrypt_gensalt() does that, and it accepts a
yescrypt-specific set of parameters.  This is fine for any particular
hashing scheme, but for a more generic crypt_gensalt() function the set
of possible parameters would need to vary by the requested hashing scheme.

Alexander