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Re: [Suit] CBOR and Firmware Word Alignment

Rønningstad, Øyvind <Oyvind.Ronningstad@nordicsemi.no> Thu, 28 June 2018 06:59 UTC

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From: "Rønningstad, Øyvind" <Oyvind.Ronningstad@nordicsemi.no>
To: Carsten Bormann <cabo@tzi.org>
CC: Michael Richardson <mcr+ietf@sandelman.ca>, suit <suit@ietf.org>
Thread-Topic: [Suit] CBOR and Firmware Word Alignment
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Date: Thu, 28 Jun 2018 06:59:06 +0000
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Subject: Re: [Suit] CBOR and Firmware Word Alignment
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Definitely. I’m not entirely convinced we need a container format though. The order of blobs in the stream could be implicit, and size information is already present in the manifests.

From: Carsten Bormann [mailto:cabo@tzi.org]
Sent: 27. juni 2018 10:27
To: Rønningstad, Øyvind <Oyvind.Ronningstad@nordicsemi.no>
Cc: Michael Richardson <mcr+ietf@sandelman.ca>; suit <suit@ietf.org>
Subject: Re: [Suit] CBOR and Firmware Word Alignment

So what is the container format for delivering manifest and image?  You could solve the problem there. (eg, round up before spending the next thing.)
Sent from mobile

On 27. Jun 2018, at 08:46, Rønningstad, Øyvind <Oyvind.Ronningstad@nordicsemi.no<mailto:Oyvind.Ronningstad@nordicsemi.no>> wrote:



-----Original Message-----
From: Suit [mailto:suit-bounces@ietf.org] On Behalf Of Michael
Richardson
Sent: 27. juni 2018 01:33
To: suit <suit@ietf.org<mailto:suit@ietf.org>>
Subject: Re: [Suit] CBOR and Firmware Word Alignment


Paul Lambert <paul.lambert@intrinsic-id.com<mailto:paul.lambert@intrinsic-id.com>> wrote:
Has any thought gone into word alignment issues?

Many platforms require firmware or other data objects to be word
aligned. It waould be especially desirable to have large objects (like
the firmware) be packaged such that the data does not have to be
copied
to a new location just to ensure word alignment. Word alignment
would
also facilitate in-place decryption of the firmeare.

AFAIK, the firmware image is not *in* the manifest, so the actual
firmware alignment does not depend upon any feature of the manifest.
The firmware image can be put anywhere one likes.
I find it unlikely that the manifest contents will need any specific
alignment for a bulk operation.  If so, it's small enough to copy around
the place.

Over on the mcuboot list, it seems that they currently putting their image
TLV at the end of the firmware image, and they will place the manifest
there.  That would seem to align the firmware image nicely.


In some cases it makes sense to concatenate the payload after the manifest to simplify delivery, In which case I think it would be useful to have the option of padding. There could be a bstr padding entry at the end of the manifest, or maybe a padding extension.

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