From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-3.5 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI shortcircuit=no autolearn=ham autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id 7AA451F453 for ; Tue, 18 Sep 2018 15:32:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729932AbeIRVFT (ORCPT ); Tue, 18 Sep 2018 17:05:19 -0400 Received: from mail-pl1-f194.google.com ([209.85.214.194]:43259 "EHLO mail-pl1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728065AbeIRVFS (ORCPT ); Tue, 18 Sep 2018 17:05:18 -0400 Received: by mail-pl1-f194.google.com with SMTP id 38-v6so1174143plc.10 for ; Tue, 18 Sep 2018 08:32:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=GjKITQ5Jb5v4nmTUNv6ucoYP200wEXui1OW3qFyoV+w=; b=YKmKsORVEw0FNFwS5MrZSHtu3Kd51InJ0ISeseETMo8TlqUhtZ7PDD1tQvjgPLwcAD vNW28Rpt9bRwwUrqI7cYB/SD0czofvbIIZ1Z1vtO1cC+ENP7MVyhG60FSgLZdsd935HH OsFAGEolNazxRaFaZcDIWK8CzUWJitSKhvOb9V3C7Pifc/DYxpp2YvWxkXArPYQ5uVa+ qvQszV+ZwumOLLtXwitPOFWFQfwADm479hiR8yNZ8OnZ/ZZQkJMUg4ykXmBPkaas/8Vx BtoIZcOeedOueD/MMzqBQqRwVlRWH9vt6D+rQwfVLgP//Ivn8fNc2qZUeJC3a5TR3A1N SAug== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to:user-agent; bh=GjKITQ5Jb5v4nmTUNv6ucoYP200wEXui1OW3qFyoV+w=; b=b5Nzur4FDg/tpcW7pn955DUO6wsPuKiAkKg6hCrbVs/8rCewDapbs0gYVZUz/xiKqG pPL1fpWwjnQQYMjpIZftq3sjvkvrJvTpmKdwI28n3njMTptHtwdDZZ9XxKdYzyHhWlOG qtL5fl0/2JgpPLBAtk7YKgQWh7HOPJ4g9ifoR9Hkdsleu9aD2Xtw1sewVl1sQOYGGHqr dmxWemR2H7ZykW58UTUQViloEh6wxGGs/gGWK1e07lWpo5y2iTr7MjxtAmRVcXJcl3lP 2Rtid0IP7JWG7SCJenLpHQqlAiesVaTKrUDW/0bB8K32q9L+Kg6hIJq2Dlwz9Eow1gth 0PQQ== X-Gm-Message-State: APzg51Aoeg4+PUF6mK3+xqbovwbS7q4D8ODoXE4sohvlg9wUM39iSmrE UklFx6SGloTmqIUM3mqSM4M= X-Google-Smtp-Source: ANB0VdapJGygnilYh6Xosjq44Kr2llWfqdYQj9zoMYQJeVYHN88677oV/rREwmh/p/KQ2ulpKOmZYg== X-Received: by 2002:a17:902:1121:: with SMTP id d30-v6mr29288102pla.250.1537284733041; Tue, 18 Sep 2018 08:32:13 -0700 (PDT) Received: from aiede.svl.corp.google.com ([2620:0:100e:422:4187:1d6c:d3d6:9ce6]) by smtp.gmail.com with ESMTPSA id b73-v6sm32033064pfj.93.2018.09.18.08.32.12 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 18 Sep 2018 08:32:12 -0700 (PDT) Date: Tue, 18 Sep 2018 08:32:10 -0700 From: Jonathan Nieder To: Joan Daemen Cc: Dan Shumow , Johannes Schindelin , "brian m. carlson" , Junio C Hamano , Linus Torvalds , Edward Thomson , Git Mailing List , demerphq , Adam Langley Subject: Re: Hash algorithm analysis Message-ID: <20180918153210.GA133875@aiede.svl.corp.google.com> References: <20180609224913.GC38834@genre.crustytoothpaste.net> <20180611192942.GC20665@aiede.svl.corp.google.com> <20180720215220.GB18502@genre.crustytoothpaste.net> <20180724190136.GA5@0f3cdde9c159> <20180724221008.GI18502@genre.crustytoothpaste.net> <64c1fc82-8830-bd62-7cc6-ef76ad06f6d5@noekeon.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <64c1fc82-8830-bd62-7cc6-ef76ad06f6d5@noekeon.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Hi, A quick note. Joan Daemen wrote: > when going over my todo list I was confronted with the mail of Dan > Shumow on the successor of SHA-1 for git. I know the decision was > made and it is not my intention to change it, but please see below > some comments on Dan's arguments. When the time comes for the next hash change in Git, it will be useful to be able to look back over this discussion. Thanks for adding details. [...] > On 30/07/2018 22:01, Dan Shumow wrote: >> So, I also want to state my biases in favor of SHA2 as an employee >> of Microsoft. [...] As such, and reflecting this bias, in the >> internal discussions that Johannes alluded to, SHA2 and SHA3 were >> the primary suggestions. There was a slight preference for SHA2 >> because SHA3 is not exposed through the windows cryptographic APIs >> (though Git does not use those, so this is a nonissue for this >> discussion.) > > We find it cynical to bring up a Microsoft-internal argument that is > actually not relevant to Git. On the contrary, I am quite grateful that Dan was up front about where his preference comes from, *especially* when the reasons are not relevant to Git. It is useful background for better understanding his rationale and understanding the ramifications for some subset of users. In other words, consider someone active in the Git project that disagrees with the decision to use SHA2. This explanation by Dan can help such a person understand where the disagreement is coming from and whether we are making the decision for the wrong reasons (because Git on Windows does not even use those APIs). [...] > 3) The relatively large state in the sponge construction increases > the generic strength against attacks when the input contains > redundancy or has a certain form. For instance, if the input is > restricted to be text in ASCII (such as source code), then the > collision-resistance grows higher than the nominal 2^{c/2}. Such an > effect does not exist with narrow-pipe Merkle-Damgård. (This may be > what Linus had intuitively in mind.) Interesting. [...] > [2] Daniel J. Bernstein, Cost analysis of hash collisions: Will > quantum computers make SHARCS obsolete? Workshop Record of > SHARCS'09. I remember that paper! Thanks for the pointer. Sincerely, Jonathan