From: Keith Busch <kbusch@kernel.org>
To: Chris Leech <cleech@redhat.com>
Cc: linux-nvme@lists.infradead.org, Hannes Reinecke <hare@suse.de>,
Christoph Hellwig <hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>,
Chaitanya Kulkarni <kch@nvidia.com>,
Eric Biggers <ebiggers@kernel.org>
Subject: Re: [PATCH v2 REPOST] nvme-auth: Hash DH shared secret to create session key
Date: Wed, 22 Apr 2026 14:04:25 -0600 [thread overview]
Message-ID: <aekpyfAzqqIN6oKU@kbusch-mbp> (raw)
In-Reply-To: <20260422190636.2651992-1-cleech@redhat.com>
On Wed, Apr 22, 2026 at 12:06:36PM -0700, Chris Leech wrote:
> The NVMe Base Specification 8.3.5.5.9 states that the session key Ks
> shall be computed from the ephemeral DH key by applying the hash
> function selected by the HashID parameter.
>
> The current implementation stores the raw DH shared secret as the
> session key without hashing it. This causes redundant hash operations:
>
> 1. Augmented challenge computation (section 8.3.5.5.4) requires
> Ca = HMAC(H(g^xy mod p), C). The code compensates by hashing the
> unhashed session key in nvme_auth_augmented_challenge() to produce
> the correct result.
>
> 2. PSK generation (section 8.3.5.5.9) requires PSK = HMAC(Ks, C1 || C2)
> where Ks should already be H(g^xy mod p). As the DH shared secret
> is always larger than the HMAC block size, HMAC internally hashes
> it before use, accidentally producing the correct result.
Thanks, applied to nvme-7.1.
prev parent reply other threads:[~2026-04-22 20:04 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-22 19:06 [PATCH v2 REPOST] nvme-auth: Hash DH shared secret to create session key Chris Leech
2026-04-22 20:04 ` Keith Busch [this message]
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