Re: [TLS] Should we support static RSA in TLS 1.3?

Eric Rescorla <ekr@rtfm.com> Sun, 17 November 2013 05:30 UTC

Return-Path: <ekr@rtfm.com>
X-Original-To: tls@ietfa.amsl.com
Delivered-To: tls@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 5C8D111E85C0 for <tls@ietfa.amsl.com>; Sat, 16 Nov 2013 21:30:22 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -102.976
X-Spam-Level:
X-Spam-Status: No, score=-102.976 tagged_above=-999 required=5 tests=[BAYES_00=-2.599, FM_FORGED_GMAIL=0.622, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_LOW=-1, USER_IN_WHITELIST=-100]
Received: from mail.ietf.org ([12.22.58.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Hpl8FaVMH+35 for <tls@ietfa.amsl.com>; Sat, 16 Nov 2013 21:30:16 -0800 (PST)
Received: from mail-wi0-f177.google.com (mail-wi0-f177.google.com [209.85.212.177]) by ietfa.amsl.com (Postfix) with ESMTP id 9178511E8120 for <tls@ietf.org>; Sat, 16 Nov 2013 21:30:15 -0800 (PST)
Received: by mail-wi0-f177.google.com with SMTP id hq4so2560125wib.4 for <tls@ietf.org>; Sat, 16 Nov 2013 21:30:13 -0800 (PST)
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:content-type; bh=2tCt+iMkUKnN3gRow2OYDPrWrdK/16/MhLNO7cXCIhY=; b=EDrDgtLPtmZpOg8dNO5Ir0L/4zdPikygs29+P0NB0q+YW/1ptG4obClBJ8Ljmb7BrD HPVnadFveI2cU2mcSbrEXOZVlQUrYLAxGHJ6djyDZq9jgbgtzoLi0yWpoIaJ9QjFkD57 MHruTgmBVT4oera4ZyxgYA/AsYhe//J3q78/LPL6wQEjesi9s1q+hhIRf5aen/o2ymMG S4tbXj0gj+pAznnoEyFraFqcbfF512qLNYmHAH4Nya2ukT9Xoq7szsqexBANZbPd+ZYj +BKthL4bvhhOcjhCxK4Nh4UYhgrRW/+X01/zXtXHmkBThehgtGQSd/KCUBLDc9xGhqy0 cIqw==
X-Gm-Message-State: ALoCoQli0HzjgFvlfVqgBxSDubx05mWZeAzfRFoZq3CDnkhtacAayvc84A4U3YL5ZDqk+LftPZra
X-Received: by 10.180.24.137 with SMTP id u9mr12547087wif.5.1384666213916; Sat, 16 Nov 2013 21:30:13 -0800 (PST)
MIME-Version: 1.0
Received: by 10.216.152.137 with HTTP; Sat, 16 Nov 2013 21:29:33 -0800 (PST)
X-Originating-IP: [74.95.2.168]
In-Reply-To: <m238mv1wkq.fsf@localhost.localdomain>
References: <CABcZeBN3WPigLn-ggm2YGTcPEwn8G-1ecRAxdCtK3ueuUPF09Q@mail.gmail.com> <m238mv1wkq.fsf@localhost.localdomain>
From: Eric Rescorla <ekr@rtfm.com>
Date: Sat, 16 Nov 2013 21:29:33 -0800
Message-ID: <CABcZeBPzYi3rztRv7-mNWf7BwTJ83-Sc1c_=j4kN8nJhh2FCjA@mail.gmail.com>
To: Geoffrey Keating <geoffk@geoffk.org>
Content-Type: multipart/alternative; boundary=f46d04447f67d0363404eb58b955
Cc: "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] Should we support static RSA in TLS 1.3?
X-BeenThere: tls@ietf.org
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: "This is the mailing list for the Transport Layer Security working group of the IETF." <tls.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/tls>, <mailto:tls-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/tls>
List-Post: <mailto:tls@ietf.org>
List-Help: <mailto:tls-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/tls>, <mailto:tls-request@ietf.org?subject=subscribe>
X-List-Received-Date: Sun, 17 Nov 2013 05:30:22 -0000

On Sat, Nov 16, 2013 at 8:28 PM, Geoffrey Keating <geoffk@geoffk.org> wrote:
>
> Then, if people want a key agreement where one side generates a random
> master key, encrypts it with RSA, and sends it to the other, we can do
> that.  The RSA key can be ephemeral (or, at least, changed much more
> often than today's typical "once every two years"), which gives
> forward secrecy, or the RSA key can be fixed, if forward secrecy is
> explicitly not wanted
>

Oops, yeah, forgot to mention this.

As you say, it's possible to generate a short-term RSA key and use it
for multiple connections. This gives some level of forward security.

-Ekr