Re: [Teep] [Suit] Use of AES-CTR in TEEP?

[Hannes Tschofenig <[e-mail]>]

Hi Dave,

yes, at a minimum "GCM (or another AEAD cipher) should be used for any SUIT manifests for NON-constrained devices".

There are also cases where the use of GCM is fine for a constrained IoT device. For example, imagine a device that copies the binary first to RAM before executing it. Of course, you could argue whether this is still a constrained device when it has enough RAM to hold the firmware image...

Ciao
Hannes

PS: Using TEEP to manage firmware updates is, of course, possible. In my prior work LwM2M was used instead (with different properties than TEEP). I would be interested to hear from others who are planning to use TEEP in such a context. As more TEE-based IoT devices are out in the market, I could imagine that this becomes a viable strategy.

Am 11.10.2023 um 15:39 schrieb dthaler1968=[e-mail]:
> I think using TEEP to manage firmware updates on constrained devices is a
> perfectly valid use case.
>
> When I *think* you're arguing is that GCM should be used for any (not
> specific to TEEP)
> SUIT manifests for NON-constrained devices, and draft-suit-mti should say
> so.
> Is that what you're saying?
>
> Dave
>
>> -----Original Message-----
>> From: Suit <[e-mail]> On Behalf Of Tschofenig, Hannes
>> Sent: Wednesday, October 11, 2023 1:40 AM
>> To: Dave Thaler <dthaler=[e-mail]>;
>> [e-mail]; [e-mail]; [e-mail]
>> Subject: Re: [Suit] [Teep] Use of AES-CTR in TEEP?
>>
>> Hi Dave,
>>
>> in my view TAMs are not going to manage firmware updates on constrained
>> IoT devices, like microcontrollers, and hence they don't need to support
>> algorithms that are specifically designed to take issues of those
> constrained
>> IoT devices into account. Of course, I would be interested to hear whether
>> someone is planning to do this.
>>
>> I am wondering whether it is better to create a new draft that lists the
>> algorithms for use with TEEP (to avoid confusion with the classical SUIT
> use
>> cases). The algorithms in draft-ietf-suit-mti are fine for the IoT use
> case. I am
>> not arguing about that.
>>
>> I hope it is clear what I try to avoid. I dont' want developers to use
> AES-CTR
>> (or AES-CBC) for use cases it was not designed for. If you can use an AEAD
>> cipher, you should do it. Here is what RFC 9459 says on this topic:
>>
>> "
>>     This document specifies AES-CTR and AES-CBC for COSE, which are not
>>     AEAD ciphers.  The use of the ciphers is limited to special use
>>     cases, such as firmware encryption, where integrity and
>>     authentication is provided by another mechanism.
>> "
>>
>>
>> Ciao
>> Hannes
>>
>> -----Ursprüngliche Nachricht-----
>> Von: Suit <[e-mail]> Im Auftrag von Dave Thaler
>> Gesendet: Dienstag, 10. Oktober 2023 20:36
>> An: [e-mail]; [e-mail]; [e-mail]
>> Betreff: Re: [Suit] [Teep] Use of AES-CTR in TEEP?
>>
>> TEEP requires TAMs to support all MTI algorithms and allows Agents to pick
>> among MTI algorithms and may be constrained or not, support crypto offload
>> or not, etc. hence the allowing of choice.
>>
>> If I understand correctly, you're arguing that a TAM must support both CTR
>> and GCM, and an Agent can pick either one, and the suit-mti draft should
>> specify both profiles, did I get that right?
>>
>> Dave
>>
>>
>>> -----Original Message-----
>>> From: [e-mail] <[e-mail]>
>>> Sent: Tuesday, October 10, 2023 11:00 AM
>>> To: Dave Thaler <[e-mail]>; [e-mail]; [e-mail]
>>> Subject: RE: [Teep] Use of AES-CTR in TEEP?
>>>
>>> Sorry for the confusion, Dave. I have hit the "send" button a bit too
> fast.
>>> It should, of course, read "This adds no new requirements to
>>> constrained IoT devices."
>>>
>>> Ciao
>>> Hannes
>>>
>>> -----Original Message-----
>>> From: TEEP <[e-mail]> On Behalf Of Dave Thaler
>>> Sent: Dienstag, 10. Oktober 2023 19:41
>>> To: [e-mail]; [e-mail]; [e-mail]
>>> Subject: Re: [Teep] Use of AES-CTR in TEEP?
>>>
>>> Hannes wrote, regarding draft-suit-mti::
>>>> I would like to have a new profile added that defines
>>>> suit-sha256-es256-ecdh- a128gcm for use with TEEP.
>>>> This should be the default profile for use in TEEP.
>>>>
>>>> This adds new requirements to constrained IoT devices. Constrained
>>>> IoT devices should use one of the other 5 profiles already defined.
>>> Did I read that right, you want new requirements for _constrained_
> devices?
>>> Your last two sentences seem to contradict each other, so either
>>> there's a typo or I'm not understanding.
>>>
>>> Dave
>>>
>>> _______________________________________________
>>> TEEP mailing list
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>>> https://www/.
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