From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lamorak.hansenpartnership.com (lamorak.hansenpartnership.com [198.37.111.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8454A4A04; Fri, 1 Aug 2025 19:20:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.37.111.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754076056; cv=none; b=JoDyuj82dR/gMz+iyImNV/mYBDSSCopyJMI1VCYYhyG0WtjturGMxSqoDIwVRul36C5P1qOLKHQnsASvOBrv24fi124T0Mo/bfXMD4RglI+e/W5CNMJ+e5Puw4CVZW6aY7/gu4JTs8EMauDLXul/wnlhwQ0PqA6bPIixFMi9KTI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754076056; c=relaxed/simple; bh=/OhmmueiM+PBzyqYNxwzAhMVDfVEDoowF1MB6aWN5jI=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; 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linux-kernel@vger.kernel.org, stable@vger.kernel.org Date: Fri, 01 Aug 2025 15:20:52 -0400 In-Reply-To: <20250801190331.GC1274@sol> References: <20250731215255.113897-1-ebiggers@kernel.org> <20250731215255.113897-2-ebiggers@kernel.org> <3ed1ae7e7f52afe53ce2ff00f362ed153b3eec20.camel@HansenPartnership.com> <20250801030210.GA1495@sol> <20250801171125.GA1274@sol> <2da3f6d36dccb86f19292015ea48e5d7a89e3171.camel@HansenPartnership.com> <20250801184026.GB1274@sol> <321c09c7cb2edb113ce9a829d37c0ae5c835e17f.camel@HansenPartnership.com> <20250801190331.GC1274@sol> Autocrypt: addr=James.Bottomley@HansenPartnership.com; prefer-encrypt=mutual; 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 8mT2Eh9SkH+YVOmaKsajgZgrBxA7fWmGoxXswEVxJIFj3vW7yNc0C5HaUdYa5iGOMs4kg2ht4s7yy7NRQuh7BifWjo6BQ6k4S1H+6axZucxhSV1L6zN9d+lr3Xo/vy1unzA== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.3 Precedence: bulk X-Mailing-List: linux-crypto@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2025-08-01 at 12:03 -0700, Eric Biggers wrote: > On Fri, Aug 01, 2025 at 02:53:09PM -0400, James Bottomley wrote: > > On Fri, 2025-08-01 at 11:40 -0700, Eric Biggers wrote: > > > On Fri, Aug 01, 2025 at 02:03:47PM -0400, James Bottomley wrote: > > > > On Fri, 2025-08-01 at 10:11 -0700, Eric Biggers wrote: > > [...] > > > > > It's true that such attacks don't work with one-time keys.=C2=A0 > > > > > But here it's not necessarily a one-time key.=C2=A0 E.g., > > > > > tpm2_get_random() sets a key, then authenticates multiple > > > > > messages using that key. > > > >=20 > > > > The nonces come one from us and one from the TPM.=C2=A0 I think our= s > > > > doesn't change if the session is continued although it could, > > > > whereas the TPM one does, so the HMAC key is different for > > > > every communication of a continued session. > > >=20 > > > Again, tpm2_get_random() sets a HMAC key once and then uses it > > > multiple times. > >=20 > > No it doesn't.=C2=A0 If you actually read the code, you'd find it does > > what I say above.=C2=A0 Specifically=C2=A0 tpm_buf_fill_hmac_session() = which > > is called inside that loop recalculates the hmac key from the > > nonces.=C2=A0 This recalculated key is what is used in > > tpm_buf_check_hmac_response(), and which is where the new tpm nonce > > is collected for the next > > iteration. >=20 > tpm_buf_fill_hmac_session() computes a HMAC value, but it doesn't > modify the HMAC key.=C2=A0 tpm2_parse_start_auth_session() is the only > place where the HMAC key is changed.=C2=A0 You may be confusing HMAC > values with keys. Is this simply a semantic quibble about what gets called a key? For each TPM command we compute a cphash across all the command parameters (and for each return a rphash). This hash then forms a hmac(session_key, cphash | our_nonce | tpm_nonce | attrs). The point being that although session_key is fixed across the session, the our_nonce and tpm_nonce can change with every iteration. Since the cphash is over the ciphertext, it's the only bit you get to vary with a chosen ciphertext attack, so the other parameters effectively key the hmac. Regards, James