From: Kamil Konieczny Subject: Re: [PATCH v2] X.509: unpack RSA signatureValue field from BIT STRING Date: Tue, 17 Apr 2018 17:07:37 +0200 Message-ID: References: <6f5cdb8a-809e-6651-0e32-711d415a8b38@maciej.szmigiero.name> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-2" Content-Transfer-Encoding: 7bit Cc: Herbert Xu , "David S. Miller" , Tom Lendacky , Gary Hook , James Morris , "Serge E. Hallyn" , keyrings@vger.kernel.org, linux-security-module@vger.kernel.org, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org To: "Maciej S. Szmigiero" , David Howells Return-path: In-reply-to: <6f5cdb8a-809e-6651-0e32-711d415a8b38@maciej.szmigiero.name> Content-language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org On 17.04.2018 15:39, Maciej S. Szmigiero wrote: > The signatureValue field of a X.509 certificate is encoded as a BIT STRING. > For RSA signatures this BIT STRING is of so-called primitive subtype, which > contains a u8 prefix indicating a count of unused bits in the encoding. > > We have to strip this prefix from signature data, just as we already do for > key data in x509_extract_key_data() function. > > This wasn't noticed earlier because this prefix byte is zero for RSA key > sizes divisible by 8. Since BIT STRING is a big-endian encoding adding zero > prefixes has no bearing on its value. > > The signature length, however was incorrect, which is a problem for RSA > implementations that need it to be exactly correct (like AMD CCP). > > Signed-off-by: Maciej S. Szmigiero your e-mail address looks incorrect [...] -- Best regards, Kamil Konieczny Samsung R&D Institute Poland