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

[Dave Thaler <[e-mail]>]

So you argue that we need multiple crypto algorithms mandatory in constrained devices?
I can't comment on specific algorithms, but I'm curious to know why the extra code space
is required.   Do others in the WG agree?


> -----Original Message-----
> From: Hannes Tschofenig <[e-mail]>
> Sent: Monday, October 9, 2023 7:36 AM
> To: Dave Thaler <[e-mail]>; [e-mail]; [e-mail]
> Subject: Re: [Teep] Use of AES-CTR in TEEP?
> 
> We should create two algorithm profiles, one for firmware updates of IoT devices
> and another one for use with TA/config data update in TEEs.
> 
> 
> I believe these use cases are different enough to justify having two algorithm
> profiles.
> 
> 
> Ciao
> 
> Hannes
> 
> 
> 
> Am 06.10.2023 um 18:29 schrieb Dave Thaler:
> > In the TEEP WG, I believe we had consensus to reuse profiles from
> > draft-ietf-suit-mti in the TEEP protocol (not just for SUIT manifests).
> >
> > draft-ietf-suit-mti recently replaced the use of GCM with AES-CTR, and
> > Ken filed
> > https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgith
> > ub.com%2Fietf-teep%2Fteep-
> protocol%2Fissues%2F356&data=05%7C01%7Cdthal
> >
> er%40microsoft.com%7C626557262f6c4d7e0b6808dbc8d50831%7C72f988bf86f
> 141
> >
> af91ab2d7cd011db47%7C1%7C0%7C638324589530894110%7CUnknown%7CT
> WFpbGZsb3
> >
> d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D
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> >
> C3000%7C%7C%7C&sdata=lNxKlv26DY%2B8Drt%2BaXtkvEoKNiqiuK0m8xBGBM
> TS5SE%3
> > D&reserved=0 accordingly, proposing replacing GCM with AES-CTR in
> > TEEP, which we discussed at the interim last month.  The minutes say
> > at
> >
> https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdatatrack
> er.ietf.org%2Fmeeting%2Finterim-2023-suit-01%2Fmaterials%2Fminutes-interim-
> 2023-suit-01-202309111500-
> 00&data=05%7C01%7Cdthaler%40microsoft.com%7C626557262f6c4d7e0b6808
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> 85ycZ2pYo7r3Qfjtr7%2BOI0DOwunpe4SdNAoz4dCw%3D&reserved=0:
> >
> >> Noting: #356, there are no objections to replacing each of them.
> >> Brendan: for the use case of SUIT (TEEP+RATS), using AES-CTR makes
> >> sense, but in general, this is not the right mode.
> >> *
> >> https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmai
> >> larchive.ietf.org%2Farch%2Fmsg%2Fcose%2F9smwFXNpbd6Fci8-mIeaT2xPP-
> E%2
> >>
> F&data=05%7C01%7Cdthaler%40microsoft.com%7C626557262f6c4d7e0b6808d
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> >>
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> 9411
> >>
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> BTiI
> >>
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> W3GzsUtXI
> >> AR3UEf4xYTD2T2V77yHw%3D&reserved=0
> >> *
> >> https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmai
> >>
> larchive.ietf.org%2Farch%2Fmsg%2Fcose%2F0Dj5yp4mptZUBiw7FWb5PcXGJAg%
> 2
> >>
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> >>
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> 9411
> >>
> 0%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJ
> BTiI
> >>
> 6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=a5dVms2qZNcaowd
> xP0ulivW
> >> vPIeXS4xkABMxMuZ8fcw%3D&reserved=0
> >> RH: APIs are not supposed to return any plaintext if the integrity
> >> check fails, so the ability to break the image into chunks is an
> >> important aspect, so that's why it does not fit into AES-GCM.
> > However, in a discussion with Hannes this week, he said
> >> We should not use AES-CTR mode in TEEP. The registration of AES-CTR /
> >> AES-CBC in COSE was done to support low-end IoT devices that use
> >> flash memory. It is not an algorithm that should be used in other
> >> places where not needed. I don't see a use case for it in TEEP
> > I look to others to provide guidance here... should we
> > a) make TEEP and SUIT diverge so that a TEEP implementation has to
> > implement two different things
> > b) use AES-CTR in TEEP
> > c) add GCM back to suit-mti
> > d) something else because Dave is confused :)
> >
> > Dave
> >
> > _______________________________________________
> > TEEP mailing list
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> > https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.
> >
> ietf.org%2Fmailman%2Flistinfo%2Fteep&data=05%7C01%7Cdthaler%40microsof
> >
> t.com%7C626557262f6c4d7e0b6808dbc8d50831%7C72f988bf86f141af91ab2d7c
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> >
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> 7C%7
> >
> C&sdata=9h4QnUJfVSEgeAzR6PLcx%2BEG%2BzSirCfWpLU3WXBfJPs%3D&reserv
> ed=0