Re: F30 Self-Contained Change proposal: krb5 crypto modernization

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> BC> == Detailed Description ==
> 
> 
> Is it just me or does this not actually say clearly what is changing?
> The first paragraph talks about two RFCs.  The second paragraph talks
> about how easy it is to break single DES.  The third paragraph talks
> about how disabled by default is undesirable.  The fourth paragraph
> talks about it not being possible to remove RC4.
> 
> But nothing says what is changing.  The release notes section says:
> 
> BC> krb5 removes support for several known-bad encryption types.
> BC> Hopefully users will see no changes.
> 
> but it doesn't really say what "removes support" means, or exactly which
> encryption types will no longer be supported.

Per your follow-up email, I'm not clear on whether you want changes here.  If you do, speak up, especially if you have suggestions.

> BC> == User Experience ==
> 
> BC> Ideally no change!  Worst case some users will see krb5 produce
> BC> error messages about bad enctypes not being able to be used (has no
> BC> enctype, could not fullfill enctype, etc.).  These pains are the
> BC> feeling of the world grinding forward security-wise.
> 
> I think this is an extremely optimistic description of the worst case
> behavior.

I really don't think that "it won't work and there'll be error messages" is an "extremely optimistic description".  If you have langauge changes, I'm happy to hear them out.

> There is a good document for migrating from old encryption types at
> https://web.mit.edu/kerberos/krb5-1.16/doc/admin/advanced/retiring-des.html
> Note that the last paragraph there mentions that single-DES is still
> basically OK for the K/M principal and it's not required to use
> allow_weak_crypto to access a database encrypted with single-DES.

That reading only applies to sites with a stash file nearby (though sites set up otherwise remain relatively uncommon in my impression, or are freeipa and will have AES keys).

> I
> can't tell if this change actually intends to remove all support for the
> single-DES algorithm, but if so then it is highly important to
> communicate the additional need to roll over the master key and stash
> files.

Session keys for sure, but ideally all of it.  I tried to state this in the Summary; if I was insufficiently clear I'm happy to make changes!  (Added rollover langauge to "Upgrade/Compatability Impact" section.)

> It would also be nice to document a way to find principals which do not
> have a sufficiently strong key.

This is good feedback.  I will explore and see if I can make something.

> I personally have a kerberos database which has existed for a very long
> time now and am still dealing with the 3DES deprecation (and the fact
> that the F29 crypto policies changed to remove it from
> supported_enctypes).

I'm sure you're aware, then, that there's only so much I can do as a packager here.  In particular, the KDC can't push keytab updates (because servers with keytabs are not required to be able to communicate with the KDC).  The UX on this is *going* to be bad for anyone with weak crypto in use - which is part of why I want to pull it all out at once, so we don't have to do this again for a while.

Please CC me on all future mails; I'm not subscribed to this list.

Thanks,
--Robbie
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