From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 4FFDA39A7E8 for ; Wed, 14 Jan 2026 13:19:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768396746; cv=none; b=PxKzovpcSVXRnd2i7zXIhKqiXmB/3NgLOWFrRlUIlr1HAd/PWzbgnS+NuiH0LLOG3QPPtetoNTxEHYhOLYbpR171zVtrBhly2ab6gwMWWJeqglYMos6xjWGZgIhpGtKDb202+1Z+2hQ/DdMM/Ki0+D88zwtAGFvmgFkXV5H9YP4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768396746; c=relaxed/simple; bh=hAL4+xS8CMGErHmtD78CZ18h+3sR2NdXWMCPH5tghVA=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=QyeOEGxqhdZhW70KPuOYo6rw2Hj2gdhFyU1EMzAU7G3+JmuKPwTX8veekwewFK7YP2epC/QrhJS+yyh5H2cad4HwPZGq+xlZtNiK55AIMXKYIIGagQcZtCaHEIVqDgZIOuoX5kgHtNP7oufHlJ2Pi/lDV3pdIMEvxEGpBJVUOtI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AeFVlyrv; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="AeFVlyrv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 600BCC4CEF7; Wed, 14 Jan 2026 13:19:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768396746; bh=hAL4+xS8CMGErHmtD78CZ18h+3sR2NdXWMCPH5tghVA=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=AeFVlyrvfRTDuCbGAEI6uS248bFcvwVnLMEQYyYOEnaBDS8l6NiUKIqO3yF9SsLB6 Ws4I9FlgxXEBnyqm5ZU3cax2aHIbI6I6pmC1L91IZWcoQBp00W/sz3iPDtDcGxG1VX iaNpuLN1biOCcH/WrkmzZKAQH+ZLEpi3gwiHtEM4R5jQoj9etBDLicIbRIjcAznC+X tHKaB9BfPg+u9G7qLt8JEUBLeTwt3NXxCVSvdYCH0DdEmgDUmTitV05hHC/eD5GpK3 H95bi6yebYVAUt43ZhtRjJNZy02Tl2q0tC6fqotDczvMqMxuZ96eRY0Ng7OD/vDTui VaXA3dqTU1OJA== Message-ID: Subject: Re: [PATCH v1 0/7] kNFSD Encrypted Filehandles From: Jeff Layton To: Benjamin Coddington , Eric Biggers Cc: Chuck Lever , Chuck Lever , NeilBrown , Trond Myklebust , Anna Schumaker , linux-nfs@vger.kernel.org Date: Wed, 14 Jan 2026 08:19:04 -0500 In-Reply-To: <834DBCBA-1CD8-4BA9-81E8-09E621B3F176@hammerspace.com> References: <1e92e144-d436-44dd-956f-3125403dfdc8@kernel.org> <1c5569bd-fcac-4b55-8e84-3fbc096cdff3@kernel.org> <86B6E978-C67B-4C78-9E5F-6F171FD62F3E@hammerspace.com> <20260114004205.GC2178@quark> <834DBCBA-1CD8-4BA9-81E8-09E621B3F176@hammerspace.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv 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linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2026-01-14 at 07:39 -0500, Benjamin Coddington wrote: > On 13 Jan 2026, at 19:42, Eric Biggers wrote: >=20 > > On Tue, Jan 13, 2026 at 05:33:37PM -0500, Benjamin Coddington wrote: > > > > - Individual filehandles are small, on the order of 32- or 64-bytes > > > >=20 > > > > - But there are a lot of filehandles, perhaps billions, that would > > > > be encrypted or signed by the same key > > > >=20 > > > > - The filehandle plaintext is predictable > > >=20 > > > Mostly, yes. I think a strength of the AES-CBC implementation is tha= t each > > > 16-byte block is hashed with the results of the previous block. So, = by > > > starting with the fileid (unique per-file) and then proceeding to the= less > > > unique block (fsid + fileid again), the total entropy for each encryp= ted > > > filehandle is increased. > >=20 > > This sort of comment shows that the choice of AES-CBC still isn't well > > motivated. AES-CBC is an unauthenticated encryption algorithm that > > protects a message's confidentiality. It isn't a hash function, it > > isn't a MAC, and it doesn't protect a message's authenticity. AES-CBC > > will successfully decrypt any ciphertext, even one tampered with by an > > attacker, into some plaintext. You may be confusing AES-CBC with > > AES-CBC-MAC. >=20 > I'm not confusing them, and you're absolutely correct - if an encrypted > filehandle were tampered with we'd be relying on the decoded filehandle > being garbage - the routines to decode the fsid and fileid would return > errors, because a filehandle's data is meaningful and well-structured. >=20 > That's a big difference from what using a MAC would provide - immediate > knowledge the filehandle had been modified. >=20 I think a MAC is a better idea here too: One thing that people keep pointing out is that you could potentially sniff traffic and just nab the encrypted filehandles, and match them with inode numbers, etc. If you append a MAC though and check it on the server, you could give out filehandles that are limited-use. For instance, with v4, you could salt the hash with the long-form clientid and ensure that that filehandle is only usable by that client. Anyone else gets back NFS4ERR_STALE. Couple that with TLS and you'd have a pretty decent guard against sniffing and filehandle guessing attacks. --=20 Jeff Layton