linux-kernel - Re: [PATCH v2 6/9] staging: ccree: add FIPS support

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Date:   Mon, 24 Apr 2017 09:06:09 +0300
From:   Gilad Ben-Yossef <gilad@...yossef.com>
To:     Stephan Müller <smueller@...onox.de>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devel@...verdev.osuosl.org, linux-crypto@...r.kernel.org,
        devicetree@...r.kernel.org,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>,
        Gilad Ben-Yossef <gilad.benyossef@....com>,
        Binoy Jayan <binoy.jayan@...aro.org>,
        Ofir Drang <ofir.drang@....com>,
        Stuart Yoder <stuart.yoder@....com>
Subject: Re: [PATCH v2 6/9] staging: ccree: add FIPS support

On Sun, Apr 23, 2017 at 12:48 PM, Gilad Ben-Yossef <gilad@...yossef.com> wrote:
> Hi,
>
> Thank you for the review.
>
> On Thu, Apr 20, 2017 at 4:39 PM, Stephan Müller <smueller@...onox.de> wrote:
>
>>> +/* The function verifies that tdes keys are not weak.*/
>>> +static int ssi_fips_verify_3des_keys(const u8 *key, unsigned int keylen)
>>> +{
>>> +#ifdef CCREE_FIPS_SUPPORT
>>> +        tdes_keys_t *tdes_key = (tdes_keys_t*)key;
>>> +
>>> +     /* verify key1 != key2 and key3 != key2*/
>>
>> I do not think that this check is necessary. There is no FIPS requirement or
>> IG that mandates this (unlike the XTS key check).
>>
>> If there would be such requirement, we would need a common service function
>> for all TDES implementations


Well, it turns out there is and we do :-)

This is from crypto/des_generic.c:

/*
 * RFC2451:
 *
 *   For DES-EDE3, there is no known need to reject weak or
 *   complementation keys.  Any weakness is obviated by the use of
 *   multiple keys.
 *
 *   However, if the first two or last two independent 64-bit keys are
 *   equal (k1 == k2 or k2 == k3), then the DES3 operation is simply the
 *   same as DES.  Implementers MUST reject keys that exhibit this
 *   property.
 *
 */
int __des3_ede_setkey(u32 *expkey, u32 *flags, const u8 *key,
                      unsigned int keylen)

However, this does not check that k1 == k3. In this case DES3
becomes 2DES (2-keys TDEA), the use of which was dropped post 2015
by NIST Special Publication 800-131A*.

Would it be acceptable if I offer a patch adding this check to
__des3_ede_setkey()
and use that in the ccree driver?

* http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-131Ar1.pdf


Many thanks,
Gilad

-- 
Gilad Ben-Yossef
Chief Coffee Drinker

"If you take a class in large-scale robotics, can you end up in a
situation where the homework eats your dog?"
 -- Jean-Baptiste Queru