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Date:   Tue, 16 Feb 2021 11:04:43 -0800
From:   Eric Biggers <ebiggers@kernel.org>
To:     Simo Sorce <simo@redhat.com>
Cc:     Thibaud Ecarot <thibaud.ecarot@gmail.com>,
        Jeff Layton <jlayton@redhat.com>,
        linux-fscrypt <linux-fscrypt@vger.kernel.org>
Subject: Re: fscrypt and FIPS
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On Tue, Feb 16, 2021 at 12:47:05PM -0500, Simo Sorce wrote:
> Some more info, sorry for the delay.
> 
> Currently, as epxlained eralier, the HKDF is approved only in specific
> cases (from SP.800-56C rev 2), which is why I asked Jeff to inquire if
> KDF agility was possible for fscrypt.
> 
> That said, we are also trying to get NIST to approve HKDF for use in
> SP800-133 covered scenarios (Symmetric Keys Derived from Pre-Existing
> Key), which is the case applicable to fscrypt (afaict).
> 
> SP.800-133 currently only allows KDFs as defined in SP.800-108, but
> there is hope that SP.800-56C rev 2 KDFs can be alloed also, after all
> they are already allowed for key-agreement schemes.
> 
> Hope this clears a bit why we inquired, it is just in case, for
> whatever reason, NIST decided not to approve or delays a decision; to
> be clear, there is nothing wrong in HKDF itself that we know of.
> 

Just getting HKDF properly approved seems like a much better approach than doing
a lot of work for nothing.  Not just for fscrypt but also for everything else
using HKDF.

- Eric