On 7/19/21 1:19 PM, Stephan Mueller wrote:

Am Montag, dem 19.07.2021 um 11:57 +0200 schrieb Hannes Reinecke:

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On 7/19/21 10:51 AM, Stephan Mueller wrote:

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Am Montag, dem 19.07.2021 um 10:15 +0200 schrieb Hannes Reinecke:

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On 7/18/21 2:56 PM, Stephan Müller wrote:

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Am Sonntag, 18. Juli 2021, 14:37:34 CEST schrieb Hannes Reinecke:

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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.

according to the naming conventions there in figures 447 and following:

- x and y: DH private key (kernel calls it secret set with dh_set_secret or
encoded into param.key)

x and y are defined in Figure 444: "Random numbers used as exponents in
a DH exchange". Sections 8.13.5.3 "DH-HMAC-CHAP_Challenge Message" and
8.13.5.4 "DH-HMAC-CHAP_Reply Message" additionally specify that "x is a
random number selected by the controller that shall be at least 256 bits
long" and "y is a random number selected by the host that shall be at
least 256 bits long".

So, x and y are just random numbers, no need to overcomplicate their
generation in the way that is beyond of the standard scope.

Vlad

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