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Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <2366240.1767794004@warthog.procyon.org.uk> References: <2366240.1767794004@warthog.procyon.org.uk> <20260105152145.1801972-1-dhowells@redhat.com> <20260105152145.1801972-3-dhowells@redhat.com> To: Ignat Korchagin Cc: dhowells@redhat.com, Lukas Wunner , Jarkko Sakkinen , Herbert Xu , Eric Biggers , Luis Chamberlain , Petr Pavlu , Daniel Gomez , Sami Tolvanen , "Jason A . Donenfeld" , Ard Biesheuvel , Stephan Mueller , linux-crypto@vger.kernel.org, keyrings@vger.kernel.org, linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v11 2/8] pkcs7: Allow the signing algo to calculate the digest itself Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <2727728.1767877161.1@warthog.procyon.org.uk> Date: Thu, 08 Jan 2026 12:59:21 +0000 Message-ID: <2727729.1767877161@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 David Howells wrote: > Also, we probably don't actually need to copy the authattrs, just retain a > pointer into the source buffer and the length since we don't intend to keep > the digest around beyond the verification procedure. So I might be able to > get away with just a flag saying I don't need to free it. Actually, we probably do need to copy it. The problem is that we have to modify the tag on the authenticatedAttributes (PKCS#7)/signedAttrs (CMS) blob before we digest it, e.g. in pkcs7_digest(): memcpy(sig->digest, sinfo->authattrs, sinfo->authattrs_len); ((u8 *)sig->digest)[0] = ASN1_CONS_BIT | ASN1_SET; as specified in RFC9882 and other places: 3.2. Signature Generation and Verification ... When signed attributes are included, ML-DSA (pure mode) signatures are computed over the complete DER encoding of the SignedAttrs value contained in the SignerInfo's signedAttrs field. As described in Section 5.4 of [RFC5652], this encoding includes the tag and length octets, but an EXPLICIT SET OF tag is used rather than the IMPLICIT [0] tag that appears in the final message. ... We might be able to get away with modifying it in place - but I don't know that that's true for all users. David