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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 49E49C433EF for ; Wed, 22 Dec 2021 06:31:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242757AbhLVGbD (ORCPT ); Wed, 22 Dec 2021 01:31:03 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38014 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233175AbhLVGbC (ORCPT ); Wed, 22 Dec 2021 01:31:02 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 52200C061574 for ; Tue, 21 Dec 2021 22:31:02 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id DBD7C618BF for ; Wed, 22 Dec 2021 06:31:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5B83FC36AE5; Wed, 22 Dec 2021 06:31:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1640154661; bh=kOC4wWHNwotDFufgc5qAmoRfDRS0MtG/Ry58g//qJNs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Flhc3hMIuoPFhMzcN6pCAvjrTONovn+Ke8Dip1zDqYJ+jOtaHvAoF1u0+r20dTRUG iAsxEv2XH3FkRX9s4hHYKlimA3yjPIh19uVEVexjmlJTCqPGWgvGObO2ORnMmjqdbc pTgmoRulAbGk1Q0TP62/77ZCO7hM4j20sZ5wOC6k= Date: Wed, 22 Dec 2021 07:30:57 +0100 From: Greg KH To: "Jason A. Donenfeld" Cc: linux-kernel@vger.kernel.org, tytso@mit.edu, Jean-Philippe Aumasson Subject: Re: [PATCH] random: use BLAKE2s instead of SHA1 in extraction Message-ID: References: <20211221175047.341782-1-Jason@zx2c4.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211221175047.341782-1-Jason@zx2c4.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 21, 2021 at 06:50:47PM +0100, Jason A. Donenfeld wrote: > This commit addresses one of the lower hanging fruits of the RNG: its > usage of SHA1. > > BLAKE2s is generally faster, and certainly more secure, than SHA1, which > has [1] been [2] really [3] very [4] broken [5]. Additionally, the > current construction in the RNG doesn't use the full SHA1 function, as > specified, and allows overwriting the IV with RDRAND output in an > undocumented way, even in the case when RDRAND isn't set to "trusted", > which means potential malicious IV choices. And its short length means > that keeping only half of it secret when feeding back into the mixer > gives us only 2^80 bits of forward secrecy. In other words, not only is > the choice of hash function dated, but the use of it isn't really great > either. > > This commit aims to fix both of these issues while also keeping the > general structure and semantics as close to the original as possible. > Specifically: > > a) Rather than overwriting the hash IV with RDRAND, we put it into > BLAKE2's documented "salt" and "personal" fields, which were > specifically created for this type of usage. > b) Since this function feeds the full hash result back into the > entropy collector, we only return from it half the length of the > hash, just as it was done before. This increases the > construction's forward secrecy from 2^80 to a much more > comfortable 2^128. > c) Rather than using the raw "sha1_transform" function alone, we > instead use the full proper BLAKE2s function, with finalization. > > This also has the advantage of supplying 16 bytes at a time rather than > SHA1's 10 bytes, which, in addition to having a faster compression > function to begin with, means faster extraction in general. On an Intel > i7-11850H, this commit makes calls to RNDRESEEDCRNG around 28% faster. > > BLAKE2s itself has the nice property of internally being based on the > ChaCha permutation, which the RNG is already using for expansion, so > there shouldn't be any issue with newness, funkiness, or surprising CPU > behavior, since it's based on something already in use. > > [1] https://eprint.iacr.org/2005/010.pdf > [2] https://www.iacr.org/archive/crypto2005/36210017/36210017.pdf > [3] https://eprint.iacr.org/2015/967.pdf > [4] https://shattered.io/static/shattered.pdf > [5] https://www.usenix.org/system/files/sec20-leurent.pdf > > Reviewed-by: Jean-Philippe Aumasson > Signed-off-by: Jason A. Donenfeld 0-day build issues asside, this looks sane to me, nice work: Reviewed-by: Greg Kroah-Hartman