linux-kernel - Re: [PATCH 5/6] crypto: hkdf

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Message-ID: <2750733.sbdFDJOICv@positron.chronox.de>
Date:   Mon, 14 Jan 2019 10:25:16 +0100
From:   Stephan Müller <smueller@...onox.de>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Andy Lutomirski <luto@...capital.net>,
        "Lee, Chun-Yi" <joeyli.kernel@...il.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, keyrings@...r.kernel.org,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Chen Yu <yu.c.chen@...el.com>,
        Oliver Neukum <oneukum@...e.com>,
        Ryan Chen <yu.chen.surf@...il.com>,
        David Howells <dhowells@...hat.com>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        Randy Dunlap <rdunlap@...radead.org>,
        Jann Horn <jannh@...gle.com>,
        Andy Lutomirski <luto@...nel.org>, linux-crypto@...r.kernel.org
Subject: Re: [PATCH 5/6] crypto: hkdf - add known answer tests

Am Samstag, 12. Januar 2019, 06:19:15 CET schrieb Eric Biggers:

Hi Eric,

[...]
> 
> > +			}
> > +		}
> > +	}, {
> > +		.alg = "hkdf(hmac(sha224))",
> > +		.test = alg_test_null,
> > +		.fips_allowed = 1,
> 
> I think it is dumb to add algorithms to the testmgr with no tests just so
> the 'fips_allowed' flag can be set. 

Currently it is the only way. But I agree that it could be done better.

> And doesn't FIPS sometimes require
> tests anyway?  I don't think the "null test" should count as a test :-)

Yes, it DOES count as a test (as strange as it may sound)! :-)

The FIPS requirements are as follows:

- raw ciphers must be subject to a FIPS test with one block chaining mode to 
cover that cipher with all block chaining modes (e.g. you can test ecb(aes) to 
cover AES with *all* existing block chaining modes).

- for compound crypto algorithm (like RSA with respect to hashes, KDF with 
respect to the keyed message digest, HMAC with respect to hashes), the 
wrapping crypto algorithm needs to be tested with *one* wrapped cipher at 
least (but also not more. E.g. if you have a self test for, say, all SHA-1 and 
SHA-2, you only need one HMAC SHA test or one KDF HMAC SHA test.

- in some circumstances, it is even permissible to test wrapping crypto 
algorithms where the underlying algo is implicitly tested. E.g. if you have a 
HMAC SHA-256 test, you do not need an individual SHA-256 test.


> 
> Perhaps just include sha256 and sha512, and have tests for them?

Do you happen to have an official SHA-512 HKDF test vector? RFC5869 only has 
SHA-1 and SHA-256 tests.
> 

[...]
> > 
> > +/* Test vectors from RFC 5869 appendix A */
> > +static struct kdf_testvec hkdf_hmac_sha256_tv_template[] = {
> 
> const
> 
> Likewise for all other kdf_testvecs.

const does not work with __VECS :-(

I leave it without const at the moment. I think the __VECS should be updated 
along with all test vectors.

[...]

Ciao
Stephan