Re: [Rats] Age Claim in EAT

Henk Birkholz <henk.birkholz@sit.fraunhofer.de> Wed, 29 July 2020 09:11 UTC

Return-Path: <henk.birkholz@sit.fraunhofer.de>
X-Original-To: rats@ietfa.amsl.com
Delivered-To: rats@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id C863A3A0ABE for <rats@ietfa.amsl.com>; Wed, 29 Jul 2020 02:11:52 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.9
X-Spam-Level:
X-Spam-Status: No, score=-1.9 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, NICE_REPLY_A=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id ZJNma03GfugJ for <rats@ietfa.amsl.com>; Wed, 29 Jul 2020 02:11:49 -0700 (PDT)
Received: from mail-edgeKA27.fraunhofer.de (mail-edgeka27.fraunhofer.de [153.96.1.27]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 135E43A0D48 for <rats@ietf.org>; Wed, 29 Jul 2020 02:11:21 -0700 (PDT)
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: =?us-ascii?q?A2E2CwDNOyFf/xoHYZlgHgE8DAILFYF?= =?us-ascii?q?KAoFzBoEegTMKhCuQcSWBAZkOFIFgCQsBAQEBAQEBAQEGAQEYCwoCBAEBAoR?= =?us-ascii?q?KAoIjASQ2Bw4CEAEBBgEBAQEBBgQCAoZFDEMWAYJ5gQMBAQEBAQEBAQEBAQE?= =?us-ascii?q?BAQEBAQEBFgJDVRIBHgEBAQECAQEBIQ8BBTYCBAoLCQISBgICERUCAicgAg4?= =?us-ascii?q?GAQwGAgEBgldLAYJcHwULkwybBHaBMoVSg1qBOgaBDioBhkiFIIEPDw+BTD8?= =?us-ascii?q?maycMA4FcSTU+glwBAQIBgRUSARIBTROCV4JgBI83TIJpohNcKQeBWoEIgQg?= =?us-ascii?q?EC4dEi0CFVgUKHoJ7NokVhH8GjimSIIoylGwCBAIJAhWBWgWBFnBNJE+CaVA?= =?us-ascii?q?XAg2OKQEXgQIBAoddhURyNwIGAQcBAQMJfIxpgXIBgRABAQ?=
X-IPAS-Result: =?us-ascii?q?A2E2CwDNOyFf/xoHYZlgHgE8DAILFYFKAoFzBoEegTMKh?= =?us-ascii?q?CuQcSWBAZkOFIFgCQsBAQEBAQEBAQEGAQEYCwoCBAEBAoRKAoIjASQ2Bw4CE?= =?us-ascii?q?AEBBgEBAQEBBgQCAoZFDEMWAYJ5gQMBAQEBAQEBAQEBAQEBAQEBAQEBFgJDV?= =?us-ascii?q?RIBHgEBAQECAQEBIQ8BBTYCBAoLCQISBgICERUCAicgAg4GAQwGAgEBgldLA?= =?us-ascii?q?YJcHwULkwybBHaBMoVSg1qBOgaBDioBhkiFIIEPDw+BTD8maycMA4FcSTU+g?= =?us-ascii?q?lwBAQIBgRUSARIBTROCV4JgBI83TIJpohNcKQeBWoEIgQgEC4dEi0CFVgUKH?= =?us-ascii?q?oJ7NokVhH8GjimSIIoylGwCBAIJAhWBWgWBFnBNJE+CaVAXAg2OKQEXgQIBA?= =?us-ascii?q?oddhURyNwIGAQcBAQMJfIxpgXIBgRABAQ?=
X-IronPort-AV: E=Sophos;i="5.75,409,1589234400"; d="scan'208";a="23370391"
Received: from mail-mtas26.fraunhofer.de ([153.97.7.26]) by mail-edgeKA27.fraunhofer.de with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 29 Jul 2020 11:11:18 +0200
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: =?us-ascii?q?A0AmDgC2PCFf/1lIDI1ggQmBSgKBcwY?= =?us-ascii?q?vbwNUMCwKhCuQcSWBAZkOFIFpCwEDAQEBAQEGAQEYCwoCBAEBhEwCgiECJDY?= =?us-ascii?q?HDgIQAQEFAQEBAgEGBG2FXAxDFgGFFwEBAQMBAQEhDwEFNgIECgsJAhIGAgI?= =?us-ascii?q?RFQICJyACDgYBDAYCAQGCV0sBglwkC5MMmwR2gTKFUoNVgToGgQ4qAYZIhSC?= =?us-ascii?q?BDw8PgUw/JmsnDAOBXEk1PoJcAQECAYEVEgESAU0TgleCYASPN0yCaaITXCk?= =?us-ascii?q?HgVqBCIEIBAuHRItAhVYFCh6CezaJFYR/Bo4pkiCKMpRsAgQCCQIVgVoFLmd?= =?us-ascii?q?wTSRPgmlQFwINjikBF4ECAQKHXYVEQTE3AgYBBwEBAwl8jGmBcgGBEAEB?=
X-IronPort-AV: E=Sophos;i="5.75,409,1589234400"; d="scan'208";a="118570394"
Received: from mailext.sit.fraunhofer.de ([141.12.72.89]) by mail-mtaS26.fraunhofer.de with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 29 Jul 2020 11:11:16 +0200
Received: from mail.sit.fraunhofer.de (mail.sit.fraunhofer.de [141.12.84.171]) by mailext.sit.fraunhofer.de (8.15.2/8.15.2/Debian-10) with ESMTPS id 06T9BFfl002589 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-SHA256 bits=128 verify=NOT); Wed, 29 Jul 2020 11:11:15 +0200
Received: from [192.168.16.50] (79.206.156.41) by mail.sit.fraunhofer.de (141.12.84.171) with Microsoft SMTP Server (TLS) id 14.3.487.0; Wed, 29 Jul 2020 11:11:10 +0200
To: Hannes Tschofenig <Hannes.Tschofenig@arm.com>, "rats@ietf.org" <rats@ietf.org>
References: <AM0PR08MB371633B5B66CCC34BD38DB4BFA700@AM0PR08MB3716.eurprd08.prod.outlook.com>
From: Henk Birkholz <henk.birkholz@sit.fraunhofer.de>
Message-ID: <b467f730-5000-0aad-9c2c-3bd3d92321e5@sit.fraunhofer.de>
Date: Wed, 29 Jul 2020 11:11:08 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <AM0PR08MB371633B5B66CCC34BD38DB4BFA700@AM0PR08MB3716.eurprd08.prod.outlook.com>
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 8bit
X-Originating-IP: [79.206.156.41]
Archived-At: <https://mailarchive.ietf.org/arch/msg/rats/K9zdvZi5tPLVTBqXRQqmVdCHizA>
Subject: Re: [Rats] Age Claim in EAT
X-BeenThere: rats@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Remote ATtestation procedureS <rats.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/rats>, <mailto:rats-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/rats/>
List-Post: <mailto:rats@ietf.org>
List-Help: <mailto:rats-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/rats>, <mailto:rats-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 29 Jul 2020 09:11:53 -0000

Hi Hannes,

in the scope of Evidence:

Signing a CWT structure is creating an EAT. This event is defined as 
time(EG) here: 
https://tools.ietf.org/html/draft-ietf-rats-architecture-05#appendix-A

"Creating a token" would mean "Evidence Generation", for example.

Age also is a time interval based on a time unit (units that apply to 
Henk are years, I claim that Henk's age is 21, of course. Trust in 
Henk's Claims can be established via Endorsements). Age is a time 
interval expressed as a duration. That means that the beginning of that 
time interval is set as zero (an epoch) and then counts the time units.

The semantics of age in EAT are:

the epoch is time(EG) and the unit is seconds.
This only works, if time sources for relative time-counters are 
available, of course.

Collection of Claims - time(CC) was proposed to the architecture, but 
did not find consensus yet (we are working on time(AA), though, the time 
at which the Attester becomes aware of a changes value in the Target 
Environment right now).

But! there is time(VG), the Value Generation. This time can often only 
be inferred or approximated (in contrast to time(AA)), but it is the 
best we have defined right now in the context of:

> If that's the case, I wonder whether it would also make sense to take into account that different information may be collected at a different point in time and hence the age indication would better go (somehow) with specific claims where the time difference between the collection of the data and the signature generation matters.

As a note: We have not talked at all before about the common concept of 
"latches" or stage transitions... this is an important concept that does 
capture the "this event has happened" (before/after a defined event) and 
represents strong security implications that are not included in the 
RATS architecture today. Would that maybe help in your context?

Viele Grüße,

Henk


On 29.07.20 10:37, Hannes Tschofenig wrote:
> Hi Laurence, Hi all,
> 
> How does the age claim work?
> 
> The spec says "represents the number of seconds that have elapsed since the token was created".
> 
> By creating a token you also protect the claims with a signature and hence you cannot change the content of the claims anymore (without breaking the signature).
> 
> Hence, here "creating a token" must mean something different. I suspect it means when certain values have been collected from the device and before the token with the signature was put together. Correct?
> 
> If that's the case, I wonder whether it would also make sense to take into account that different information may be collected at a different point in time and hence the age indication would better go (somehow) with specific claims where the time difference between the collection of the data and the signature generation matters. I also wonder whether the number of seconds matter and whether you really want to communicate something more abstract, such as "I created a hash over the firmware during boot time" rather than "I created the hash over the firmware in real-time when I was asked".
> 
> Ciao
> Hannes
> 
> IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.
> 
> _______________________________________________
> RATS mailing list
> RATS@ietf.org
> https://www.ietf.org/mailman/listinfo/rats
>