Hi all,
Thanks for your attention to the matter/threads. I have thought
a bit about this, and I hope I can add some value to the current
conversation, below:
On 03/07/2014 07:36 PM, Xin Li wrote:
On 03/07/14 14:50, A.J. Kehoe IV (Nanoman) wrote:
Xin Li wrote:
On 03/07/14 13:52, A.J. Kehoe IV (Nanoman) wrote:
Allan Jude wrote:
On 2014-03-07 11:13, A.J. Kehoe IV (Nanoman) wrote:
Allan Jude wrote:
[...]
Honestly, my use case is just silently upgrading the
strength of the hashing algorithm (when combined with my
other feature request). Updating my bcrypt hashes from
$2a$04$ to $2b$12$ or something. Same applies for the
default sha512, maybe I want to update to rounds=15000
Like this?
http://www.freebsd.org/cgi/query-pr.cgi?pr=182518
Request for comments:
http://docs.freebsd.org/cgi/mid.cgi?20140106205156.GD4903
[...]
Speaking for adding rounds, the only problem that needs to be
fixed is that the proposed patch makes it possible to create
conflicting configuration (passwd_format and passwd_modular can
use different hashing algorithms) and need to be fixed and
polished. I like the idea of making it possible to use more
rounds though.
This was deliberate for backward compatibility. passwd_format will
be used by default if passwd_modular isn't defined. If
passwd_modular is defined as "disabled", then passwd_format will be
used.
Well, my point is that the two shouldn't be allowed to exist together
if they can mean something conflicting. Allowing passwd_format=sha512
AND passwd_modular=$2a$08$ in the same configuration creates confusion
and it's not good.
Agreed. My original intention was to create a patch that didn't
touch a lot of code.
My reasons for this were first to see if there was any interest
from a committer to take this further. Much more likely to have
a 15 or so line patch looked at, than one that touches stuff all
over the place - I think.
We are now at least having a conversation about it.
It seemed to be a lot of work to specify rounds via
login_setcryptfmt, with a bunch of changes also required in
libcrypt.
I don't have the resources to test for regressions in libcrypt,
beyond the scope of whether login.conf works as expected
(specifically, the ports tree, yp, ldap, or any other areas that
I don't know about).
If other developers were willing to work together on the api/abi
changes, I would feel a lot better about spending my time there
and doing it right. Without support from other, more
knowledgeable people (as far as what will break if we do XYZ),
who will eventually merge productive changes, I would be wasting
my time.
I don't want to be the libcrypt api changing pixie, scattering
patches into /dev/null. :)
My suggestion is that we either have:
a) passwd_format and passwd_round (so that they don't conflict), or
I recommend against this. By example, based on current scrypt
modular crypt RFCs, there are multiple tunable parameters. It's
conceivable that other future algorithms will have different
functional and named parameters.
Additionally, I think having all the parsing code for this
scattered about actually makes things less clear. For example,
$2a$08$ means a lot more to people (across different *nix
backgrounds) than blf, is concise, and is/already should be well
documented in crypt(3). Likewise with sha512. Looking at
login.conf, you can't tell exactly what it means.
Modular crypt is something that developers are working to stay
compatible with (e.g. $5$, $6$, $2y$, etc), is understood outside
of the context of FreeBSD system administration, and would be
understood by people who are knowledgeable enough to seek to
change this aspect of their system.
b) extend passwd_format in a compatible manner to allow specifying a
round, or,
c) make passwd_format and passwd_modular conflict so we don't silently
accept it and instead bail out when doing pwd_mkdb.
As jmg suggested, by supplying the modular format for
passwd_format, we eliminate this conflict, and make it obvious.
I definitely support this notion.
That means touching login_setcryptfmt and friends, I think.
What do you think of the idea of putting this into libcrypt instead
of pam_unix.c, and then patching pam_unix.c and pw_user.c to
reference libcrypt?
Which part of the idea? I think it's a bad idea to make libcrypt to
depend on libutil (for login_cap(3)) but we should probably provide
new wrappers in login_cap(3) to do the common things when requested
for various password manipulating tools to reduce duplicated code.
Specifically:
The makesalt aspect can/should be put into libcrypt, refined
appropriately, and exposed publicly. It is a terrible little
piece of code as it is now, twice (or more!), and it could be
cleaned up considerably. This could be a nice little api.
Secondly, since the digests are used externally, I think it would
be good to push the custom base64 code out to a library
somewhere, so there is the standard way to do it, documented.
Maybe libcrypt is the right place for this function too, since
that is the context in which I have seen it. I forget for sure
now, but I think each algorithm is also responsible for base64
encoding their output. Not that I'm saying we should just rip it
out, but it might be worthwhile to look case by case, if it's
appropriate.
As far as autotuning the work-factor, I think that just being
able to set it at all is a huge improvement, and autotuning is
Just Details. We can see that this will be fraught with problems
establishing consensus, and could stall making progress with the
other good work. Even if every couple of years, the default in
login.conf gets bumped to whatever. When people run mergemaster,
it'll show, and the admin can decide then. As it is right now,
rounds are fixed, that's not appropriate for any use-case, small
or large.
Finally, I agree the ability to auto-update existing digests is
desirable. That and the other policy stuff can happen totally
separate from the discussion around exposing the tunables.
Thanks for considering my input,
- Derek
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