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To:     Stephan Mueller <smueller@chronox.de>,
        Christoph Hellwig <hch@lst.de>
Cc:     Sagi Grimberg <sagi@grimberg.me>,
        Keith Busch <keith.busch@wdc.com>,
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        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S . Miller" <davem@davemloft.net>,
        linux-crypto@vger.kernel.org
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 <463a191b9896dd708015645cfc125988cd5deaef.camel@chronox.de>
From:   Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH 09/11] nvmet: Implement basic In-Band Authentication
Message-ID: <2af95a8e-50d9-7e2d-a556-696e9404fee4@suse.de>
Date:   Mon, 19 Jul 2021 11:57:06 +0200
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On 7/19/21 10:51 AM, Stephan Mueller wrote:
> Am Montag, dem 19.07.2021 um 10:15 +0200 schrieb Hannes Reinecke:
>> On 7/18/21 2:56 PM, Stephan Müller wrote:
>>> Am Sonntag, 18. Juli 2021, 14:37:34 CEST schrieb Hannes Reinecke:
> 
>>>> The key is also used when using the ffdhe algorithm.
>>>> Note: I _think_ that I need to use this key for the ffdhe algorithm,
>>>> because the implementation I came up with is essentially plain DH with
>>>> pre-defined 'p', 'q' and 'g' values. But the DH implementation also
>>>> requires a 'key', and for that I'm using this key here.
>>>>
>>>> It might be that I'm completely off, and don't need to use a key for our
>>>> DH implementation. In that case you are correct.
>>>> (And that's why I said I'll need a review of the FFDHE implementation).
>>>> But for now I'll need the key for FFDHE.
>>>
>>> Do I understand you correctly that the dhchap_key is used as the input to
>>> the 
>>> DH - i.e. it is the remote public key then? It looks strange that this is
>>> used 
>>> for DH but then it is changed here by hashing it together with something
>>> else 
>>> to form a new dhchap_key. Maybe that is what the protocol says. But it
>>> sounds 
>>> strange to me, especially when you think that dhchap_key would be, say,
>>> 2048 
>>> bits if it is truly the remote public key and then after the hashing it is
>>> 256 
>>> this dhchap_key cannot be used for FFC-DH.
>>>
>>> Or are you using the dhchap_key for two different purposes?
>>>
>>> It seems I miss something here.
>>>
>> No, not entirely. It's me who buggered it up.
>> I got carried away by the fact that there is a crypto_dh_encode_key()
>> function, and thought I need to use it here.
> 
> Thank you for clarifying that. It sounds to me that there is no defined
> protocol (or if there, I would be wondering how the code would have worked
> with a different implementation). Would it make sense to first specify a
> protocol for authentication and have it discussed? I personally think it is a
> bit difficult to fully understand the protocol from the code and discuss
> protocol-level items based on the code.
> 
Oh, the protocol _is_ specified:

https://nvmexpress.org/wp-content/uploads/NVM-Express-Base-Specification-2_0-2021.06.02-Ratified-5.pdf

It's just that I have issues translating that spec onto what the kernel
provides.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@suse.de			                  +49 911 74053 688
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