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Mon, 26 Oct 2026 04:25:41 -0700 (PDT) Received: from [10.0.0.48] ([71.69.222.122]) by smtp.gmail.com with ESMTPSA id 00721157ae682-8b166c5d605sm29719597b3.5.2026.10.26.04.25.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 26 Oct 2026 04:25:41 -0700 (PDT) Message-ID: Date: Mon, 26 Oct 2026 07:25:39 -0400 X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC net-next 1/5] tls: add HKDF-Expand-Label for the TLS 1.3 key schedule To: Hannes Reinecke , John Fastabend , Jakub Kicinski , Sabrina Dubroca , "David S. Miller" , Eric Dumazet , Paolo Abeni , Simon Horman , Jonathan Corbet , Shuah Khan , Randy Dunlap , Shuah Khan Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, Hannes Reinecke , Chuck Lever , kernel-tls-handshake@lists.linux.dev, linux-nvme@lists.infradead.org, Alistair Francis , Martin Belanger References: <20261025-keyupdate-rfc-v1-0-60b7756eccbd@gmail.com> <20261025-keyupdate-rfc-v1-1-60b7756eccbd@gmail.com> Content-Language: en-US From: Martin Belanger In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/26/26 03:27, Hannes Reinecke wrote: > On 10/26/26 1:36 AM, Martin Belanger via B4 Relay wrote: >> From: Martin Belanger >> >> A TLS 1.3 KeyUpdate derives the next traffic secret, key and IV with >> HKDF-Expand-Label (RFC 9846, section 7.2). Add the helper for the >> kernel to do this itself. >> >> Only the part of the key schedule after the handshake is needed. The >> input is a traffic secret, which is already a pseudorandom key, so >> HKDF-Extract is not needed. Each output is at most Hash.length bytes, >> so each derivation is a single HMAC with the library SHA-256 or SHA-384 >> functions. >> >> Assisted-by: LLM >> Signed-off-by: Martin Belanger >> --- >>   net/tls/Kconfig    |  2 ++ >>   net/tls/Makefile   |  2 +- >>   net/tls/tls.h      |  2 ++ >>   net/tls/tls_hkdf.c | 82 >> ++++++++++++++++++++++++++++++++++++++++++++++++++++++ >>   4 files changed, 87 insertions(+), 1 deletion(-) >> > And another HKDF implementation. Maybe it's time to split if off (again). > But anyway. > Yes. crypto/hkdf.c went away again in 6d888db2cfd9 ("crypto: remove HKDF library"), when fscrypt and nvme-auth moved to the HMAC library. tls_hkdf.c follows that pattern. It needs only HKDF-Expand-Label, which is one HMAC here. If a shared helper is wanted again, I would do it in a separate series. Thanks for the review. Martin > Reviewed-by: Hannes Reinecke > > Cheers, > > Hannes