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Subject: Re: [PATCH v2 6/6] KEYS: trusted: Introduce support for NXP
 CAAM-based trusted keys
To:     Richard Weinberger <richard@nod.at>
Cc:     Jonathan Corbet <corbet@lwn.net>,
        David Howells <dhowells@redhat.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        James Bottomley <jejb@linux.ibm.com>,
        Mimi Zohar <zohar@linux.ibm.com>,
        kernel <kernel@pengutronix.de>, James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        horia geanta <horia.geanta@nxp.com>,
        aymen sghaier <aymen.sghaier@nxp.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        davem <davem@davemloft.net>, Udit Agarwal <udit.agarwal@nxp.com>,
        Eric Biggers <ebiggers@kernel.org>,
        Jan Luebbe <j.luebbe@pengutronix.de>,
        david <david@sigma-star.at>,
        Franck Lenormand <franck.lenormand@nxp.com>,
        Sumit Garg <sumit.garg@linaro.org>,
        "open list, ASYMMETRIC KEYS" <keyrings@vger.kernel.org>,
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From:   Ahmad Fatoum <a.fatoum@pengutronix.de>
Message-ID: <ac8ef66f-4d57-ead0-d1b3-e97220463241@pengutronix.de>
Date:   Fri, 2 Jul 2021 14:33:52 +0200
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On 02.07.21 12:53, Richard Weinberger wrote:
> Ahmad,
> 
> ----- Ursprüngliche Mail -----
>> Von: "Ahmad Fatoum" <a.fatoum@pengutronix.de>
>>> I'm still think that hard coding the key modifier is not wise.
>>> As I said[0], there are folks out there that want to provide their own modifier,
>>> so it is not only about being binary compatible with other CAAM blob patches in
>>> the wild.
>>
>> I don't think the characterization as a salt is accurate. AFAIU it's more
>> of a namespace, so blobs being loaded are "type-checked" against the modifier.
> 
> Well, the CAAM programmer's reference manual states that the blob key is a 128 bit modifier
> and has two purposes:
> 1. It can be used as tag to provide separation between blobs to detect accidental replacement of blobs.
> 2. But it can also be treated as secret to provide additional protection. Because the blob encryption
> key derivation includes the key modifier.
> 
> While you have case 1 in mind, I care about case 2. :-)

Ah, using the key modifier as a passphrase didn't occur to me.

>>> I'll happily implement that feature after your patches got merged but IMHO we
>>> should first agree on an interface.
>>> How about allowing another optional parameter to Opt_new and Opt_load
>>
>> Sound good to me. pcrlock for TPM trusted keys has the same interface.
>>
>> I'd prefer the new option to accept strings, not hex though.
> 
> Both is possible. If the string starts with "0x" it needs to be decoded to a
> 128 bit key. Otherwise it has to be a up to 16 byte string.

Fine by me. Looking forward to your patches. :-)


Cheers,
Ahmad

> 
> Thanks,
> //richard
> 

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