From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-4.6 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD shortcircuit=no autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id BEF952018B for ; Mon, 18 Jul 2016 16:51:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751451AbcGRQvq (ORCPT ); Mon, 18 Jul 2016 12:51:46 -0400 Received: from mail-qt0-f181.google.com ([209.85.216.181]:35039 "EHLO mail-qt0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750965AbcGRQvp (ORCPT ); Mon, 18 Jul 2016 12:51:45 -0400 Received: by mail-qt0-f181.google.com with SMTP id x25so14869387qtx.2 for ; Mon, 18 Jul 2016 09:51:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=pTA+Zs6/jkZLIMo4ePWd7ioes/yuioAZycTVln4jy28=; b=dJWdM+aLFNNT2MHiotwCFfQ+qP9qTQ1pEdxrXHlk4MIPKrE9qeAi1yf7hXWnbryrDv t+tO32Et+sq7znD3PB+IPuq6zudoa7G9Fr7ncCeY9TTvoDIMcy/HrKufhnb1SDQXgqU2 +2oNRmT7KWEPEDEW/q+CDElKLtm4zG9nTynjqCzt2e1ChndcEo5fRtncQvbZvfjhedr/ e8Y0ogm5sgs5fnludi1aWVGQUGOYsopr6CIBI6z389Fzw7KR6UmNPSd+l1f5fvEEL7Lq MqjwbdZJMuBl7TBk6ciJQpXus+nc1V4WKO0DBHfX1Y+BV0EKSYuMxM3hXrRbeU/s1jkr yPFA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=pTA+Zs6/jkZLIMo4ePWd7ioes/yuioAZycTVln4jy28=; b=cV+6hP015g8tXSMPAiWpyqYXs85BAO4oBjYHnaeXj4OulLo7NkruoYk29OBSlfLxLX p1YZOMMiiScJafs4dZRYp6rHxRfLSgulEp4pvrfiyTaSSx7SRW5sT6gxnZzfGIpwP+s1 b2xJXv8LybBrs2buA3vyLi+Ixa8uZF5R7Th1bR9+LpO3jGQyRHQPzS6i4+ZnPVsS3HCv mlgs+FXEqyOhurhJfWge/x/Nu8c/pPiJ6CFjbuIF4kJwDDWj+LiEoskSrIuW2T9vYOAR fUaAflBSnYiWxst352choTKa+ojAuFK0TYgdJSLNy+ICdUEUzXeSUmUu0Y7e2bzj8C3I DI0w== X-Gm-Message-State: ALyK8tJ7FjMluhGwZHk+gEKabJHM9W2jAFI4sBUwl6F1/6UkT3AN4Q/iBGAjD5U9g2zN93fcKAKLC086YVvW6g== X-Received: by 10.237.36.38 with SMTP id r35mr54201772qtc.3.1468860703241; Mon, 18 Jul 2016 09:51:43 -0700 (PDT) MIME-Version: 1.0 Received: by 10.55.36.77 with HTTP; Mon, 18 Jul 2016 09:51:23 -0700 (PDT) In-Reply-To: References: From: =?UTF-8?B?w4Z2YXIgQXJuZmrDtnLDsCBCamFybWFzb24=?= Date: Mon, 18 Jul 2016 18:51:23 +0200 Message-ID: Subject: Re: Git and SHA-1 security (again) To: Herczeg Zsolt Cc: Git , "Theodore Ts'o" Content-Type: text/plain; charset=UTF-8 Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Sat, Jul 16, 2016 at 3:48 PM, Herczeg Zsolt wrote: > I would like to discuss an old topic from 2006. I understand it was > already discussed. The only reason i'm sending this e-mail is to talk > about a possible solution which didn't show up on this list before. You mention the 2006 discussion, but I wonder if you've read the more recent discussion from April on the subject. > I think we all understand that SHA-1 is broken. It still works perfect > as a storage key, but it's not cryptographically secure anymore. Git > is not moving away from SHA-1 because it would break too many > projects, and cryptographic security is not needed but git if you have > your own repository. > > However I would like to show some big problems caused by SHA-1: > - Git signed tags and signed commits are cryptographically insecure, > they're useless at the moment. > - Git Torrent (https://github.com/cjb/GitTorrent) is also > cryptographically broken, however it would be an awesome experiment. > - Linus said: "You only need to know the SHA-1 of the top of your > tree, and if you know that, you can trust your tree." That's not true > anymore. You have to trust your computer, you servers, your git > provider in a way that no-one can maliciously modify your data. In particular, as far as I know and as Theodore Ts'o's post describes better than I could[1], you seem to be confusing preimage attacks with collision attacks, and then concluding that because SHA1 is vulnerable to collision attacks that use-cases that would need a preimage attack to be compromised (which as far is I can tell, includes all your examples) are also "broken". 1. http://thread.gmane.org/gmane.comp.version-control.git/291305/focus=291511