[Freeipa-users] Using FreeIPA OTP in a PAM module

[Sumit Bose]

On Tue, Jun 30, 2015 at 09:31:55AM +0200, Jakub Hrozek wrote:
> On Tue, Jun 30, 2015 at 09:22:13AM +0200, Sumit Bose wrote:
> > On Tue, Jun 30, 2015 at 09:09:19AM +0200, Jakub Hrozek wrote:
> > > On Tue, Jun 30, 2015 at 11:34:55AM +0530, Prashant Bapat wrote:
> > > > Hi,
> > > > 
> > > > I was able to set this up in a Fedora instance with SSSD and it works as
> > > > expected. SSHD first uses the public key and then prompts for password
> > > > which is ofcourse password+OTP.
> > > > 
> > > > However, having a user enter the password+OTP every time he logs in during
> > > > the day is kind of inconvenient. Is it possible to make sure the user has
> > > > to login once and the credentials are cached for say 12/24 hours. I know
> > > > this is possible just using the password. Question is, is this possible
> > > > using password+OTP?
> > > 
> > > We have an SSSD feature under review now that would help you:
> > >     https://fedorahosted.org/sssd/ticket/1807
> > > 
> > > But to be honest, I'm not sure if we tested the patches with 2FA yet. We
> > > should!
> > 
> > hm, I agree we should, but I guess we should test that cached
> > authentication does _not_ work with 2FA/OTP. Because it is expected that
> > the OTP token only works once, so that e.g. it can be used in an
> > insecure environment to set up a secure tunnel.
> 
> Sure, the second factor must not be reused :-) but couldn't we use the
> cached auth to support cases like this where the second factor is to be
> used only once per some time and use only the first factor in the
> meantime?

I'm a bit reluctant here. If the two factors are intercepted in an
insecure environment the attacker will still have a valid password which
can be used for some time. Additionally, iirc cached authentication is
not aware of the service used. If e.g. OTP was used to just get a
response from some unprotected and unprivileged service the intercepted
password can be used to log in with ssh as well. So I guess we need a
careful discussion here.

bye,
Sumit

> 
> > 
> > Maybe it would make sense to add a paragraph to
> > https://fedorahosted.org/sssd/wiki/DesignDocs/CachedAuthentication and
> > discuss OTP/2FA usage here or on sssd-devel.
> 
> Yes, whatever the result it, it should be documented, also in the man
> pages, because currently it's not clear what happens.