From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, FSL_HELO_FAKE,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9DED6C433FF for ; Mon, 29 Jul 2019 20:30:02 +0000 (UTC) Received: from lists.sourceforge.net (lists.sourceforge.net [216.105.38.7]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6056920679; Mon, 29 Jul 2019 20:30:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=sourceforge.net header.i=@sourceforge.net header.b="A/0As5px"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=sf.net header.i=@sf.net header.b="Y4uAFJuj"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="DPew4TPf" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6056920679 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linux-f2fs-devel-bounces@lists.sourceforge.net Received: from [127.0.0.1] (helo=sfs-ml-4.v29.lw.sourceforge.com) by sfs-ml-4.v29.lw.sourceforge.com with esmtp (Exim 4.90_1) (envelope-from ) id 1hsCHS-0000Y4-0r; Mon, 29 Jul 2019 20:30:02 +0000 Received: from [172.30.20.202] (helo=mx.sourceforge.net) by sfs-ml-4.v29.lw.sourceforge.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1hsCHQ-0000Xl-VX for linux-f2fs-devel@lists.sourceforge.net; Mon, 29 Jul 2019 20:30:00 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sourceforge.net; s=x; h=In-Reply-To:Content-Type:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=ByJiHPJNYBI2ORziCi8B1eL/dGIYT86p+Gi5vc1wQEU=; b=A/0As5px+56Gyc38TCPLyj/yLS TiIs3GJqgR8elhP9UPhD3Yu+bOl3B+jJMheeASuRmD0pj2kHvI2wCUZkth66zOXogs8YE0AGB8tVc LmycSKabhStxiURcjotr5KF2lpw1BQAofjPCk0CKcarIkUZqllifweBCTJzcK82+oLKQ=; DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sf.net; s=x ; h=In-Reply-To:Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To :From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=ByJiHPJNYBI2ORziCi8B1eL/dGIYT86p+Gi5vc1wQEU=; b=Y4uAFJujJWD3PhRLb3OdCLw/8u RAUc/ort2fYWRWKspnAyVlp4kvAhPu6SxUbPTt/9qymiVSWem9Sl3QuF0GvjkjZre568jh4EOZWkV QsWySfCv2AKyJVq71dR+l026qGmus86Q0kx1M5FjO4iHFTekTW5pWLaAGnnUI+fD6X7I=; Received: from mail.kernel.org ([198.145.29.99]) by sfi-mx-1.v28.lw.sourceforge.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) id 1hsCHP-00FvJi-Jm for linux-f2fs-devel@lists.sourceforge.net; Mon, 29 Jul 2019 20:30:00 +0000 Received: from gmail.com (unknown [104.132.1.77]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B2FB620679; Mon, 29 Jul 2019 20:29:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564432194; bh=7LK4u/xXVtAq5xQMkemCjB4sBIVdQGteWvKYNQ+TBCY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DPew4TPf3PkKUXWtCLWWIQsryuZDmRsZW9HWBPCFmul6GOPKrMhWsOP2j0s6E1587 pPpWGjXg0oLEblY9YgIrbRyuoJDVlQC0LdMHo0X3YE5xtPBbo3Oz6TZzJnytmQbINO 1di8FZ/AmOwFvTEDEuqxMDphn/LIvGf9Grr0aIA8= Date: Mon, 29 Jul 2019 13:29:52 -0700 From: Eric Biggers To: "Theodore Y. Ts'o" Message-ID: <20190729202951.GG169027@gmail.com> Mail-Followup-To: "Theodore Y. Ts'o" , linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-mtd@lists.infradead.org, linux-api@vger.kernel.org, linux-crypto@vger.kernel.org, keyrings@vger.kernel.org, Paul Crowley , Satya Tangirala References: <20190726224141.14044-1-ebiggers@kernel.org> <20190726224141.14044-10-ebiggers@kernel.org> <20190728193949.GI6088@mit.edu> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190728193949.GI6088@mit.edu> User-Agent: Mutt/1.10.1 (2018-07-13) X-Headers-End: 1hsCHP-00FvJi-Jm Subject: Re: [f2fs-dev] [PATCH v7 09/16] fscrypt: add an HKDF-SHA512 implementation X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Satya Tangirala , linux-api@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-fscrypt@vger.kernel.org, keyrings@vger.kernel.org, linux-mtd@lists.infradead.org, linux-crypto@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, Paul Crowley Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On Sun, Jul 28, 2019 at 03:39:49PM -0400, Theodore Y. Ts'o wrote: > On Fri, Jul 26, 2019 at 03:41:34PM -0700, Eric Biggers wrote: > > From: Eric Biggers > > > > Add an implementation of HKDF (RFC 5869) to fscrypt, for the purpose of > > deriving additional key material from the fscrypt master keys for v2 > > encryption policies. HKDF is a key derivation function built on top of > > HMAC. We choose SHA-512 for the underlying unkeyed hash, and use an > > "hmac(sha512)" transform allocated from the crypto API. > > > > We'll be using this to replace the AES-ECB based KDF currently used to > > derive the per-file encryption keys. While the AES-ECB based KDF is > > believed to meet the original security requirements, it is nonstandard > > and has problems that don't exist in modern KDFs such as HKDF: > > > > 1. It's reversible. Given a derived key and nonce, an attacker can > > easily compute the master key. This is okay if the master key and > > derived keys are equally hard to compromise, but now we'd like to be > > more robust against threats such as a derived key being compromised > > through a timing attack, or a derived key for an in-use file being > > compromised after the master key has already been removed. > > > > 2. It doesn't evenly distribute the entropy from the master key; each 16 > > input bytes only affects the corresponding 16 output bytes. > > > > 3. It isn't easily extensible to deriving other values or keys, such as > > a public hash for securely identifying the key, or per-mode keys. > > Per-mode keys will be immediately useful for Adiantum encryption, for > > which fscrypt currently uses the master key directly, introducing > > unnecessary usage constraints. Per-mode keys will also be useful for > > hardware inline encryption, which is currently being worked on. > > > > HKDF solves all the above problems. > > > > Signed-off-by: Eric Biggers > > Unless I missed something there's nothing here which is fscrypt > specific. Granted that it's somewhat unlikely that someone would want > to implement (the very bloated) IKE from IPSEC in the kernel, I wonder > if there might be other users of HKDF, and whether this would be > better placed in lib/ or crypto/ instead of fs/crypto? > This is standard HKDF-SHA512; only the choice of parameters is fscrypt-specific. So it could indeed use a common implementation of HKDF if one were available. However, I don't think there are any other HKDF users in the kernel currently. Also, while there was a patch to support HKDF via the crypto_rng API, there was no consensus about whether this was actually the best way to add KDF support: https://lore.kernel.org/linux-crypto/2423373.Zd5ThvQH5g@positron.chronox.de So for now, to avoid unnecessarily blocking this patchset I think we should just go with this implementation in fs/crypto/. It can always be changed later, once we decide on the best way to add KDFs to the crypto API. [To be clear: this patch already uses "hmac(sha512)" from the crypto API. It's only the actual HKDF part that we're talking about here. Also, its correctness is tested by the ciphertext verification xfstests.] - Eric _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel