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Tue, 11 Nov 2025 08:15:01 -0800 (PST) Received: from m8.users.ipa.redhat.com ([2603:7000:9400:fe80::318]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8b29aa25791sm9814985a.52.2025.11.11.08.15.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Nov 2025 08:15:00 -0800 (PST) Message-ID: <1ce413b202ca7c008e077a6f1cfa88f94a3a7cbd.camel@redhat.com> Subject: Re: Module signing and post-quantum crypto public key algorithms From: Simo Sorce To: "Elliott, Robert (Servers)" , David Howells Cc: James Bottomley , Ignat Korchagin , Herbert Xu , Stephan Mueller , "torvalds@linux-foundation.org" , Paul Moore , Lukas Wunner , Clemens Lang , David Bohannon , Roberto Sassu , "keyrings@vger.kernel.org" , "linux-crypto@vger.kernel.org" , "linux-security-module@vger.kernel.org" , "linux-kernel@vger.kernel.org" Date: Tue, 11 Nov 2025 11:14:59 -0500 In-Reply-To: References: <501216.1749826470@warthog.procyon.org.uk> <3081793dc1d846dccef07984520fc544f709ca84.camel@HansenPartnership.com> <7ad6d5f61d6cd602241966476252599800c6a304.camel@redhat.com> <69775877d04b8ee9f072adfd2c595187997e59fb.camel@HansenPartnership.com> <3d650cc9ff07462e5c55cc3d9c0da72a3f2c5df2.camel@redhat.com> <534145.1762588015@warthog.procyon.org.uk> Organization: Red Hat Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: linux-crypto@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sun, 2025-11-09 at 19:30 +0000, Elliott, Robert (Servers) wrote: > The composite motivation is to provide some protection if someone > discovers a basic flaw in the PQC algorithm. If quantum computers > haven't arrived yet to break the traditional algorithm, the > composite still proves validity. Given you quoted me wrt composite signatures, I'd like to make clear I do *not* necessarily favor it. Unlike regular software or firmware, kernel modules are generally tied to a specific version of the kernel, therefore there is no real need for long term resistance (unless you plan to never upgrade a kernel). If a defect in a signing algorithm is found you can simply distribute a new kernel with modules resigned with a different algorithm. The problem of using composite algorithms are many: - You need composite keys (or at least two keys, depending on the implementation). - You will pay a higher price in terms of CPU/time for verification for each signature.=20 - You will pay a higher price in terms of disk/ram space to store multiple signatures. It is generally not worth paying this price when the remediation is easy. --=20 Simo Sorce Distinguished Engineer RHEL Crypto Team Red Hat, Inc