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Re: [TLS] Should CCM_8 CSs be Recommended?

Russ Housley <housley@vigilsec.com> Wed, 04 October 2017 13:56 UTC

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From: Russ Housley <housley@vigilsec.com>
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Date: Wed, 04 Oct 2017 09:56:51 -0400
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To: Yoav Nir <ynir.ietf@gmail.com>
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Subject: Re: [TLS] Should CCM_8 CSs be Recommended?
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> On Oct 4, 2017, at 9:48 AM, Yoav Nir <ynir.ietf@gmail.com> wrote:
> 
> 
>> On 4 Oct 2017, at 16:29, Russ Housley <housley@vigilsec.com <mailto:housley@vigilsec.com>> wrote:
>> 
>> 
>>> On Oct 4, 2017, at 3:30 AM, Yoav Nir <ynir.ietf@gmail.com <mailto:ynir.ietf@gmail.com>> wrote:
>>> 
>>>    (IoT) - This requirement is for interoperability with IoT.  Only
>>>    128-bit keys are at the given level.
>> If the IoT environment is willing to accept lower integrity protection in order to save a few bits on the wire/ether, I do not see why the specification also forces them from using a larger key size.
> 
> Maybe to save a few cycles in addition to the few bits?  They claimed that the one AEAD cipher they needed was AES_CCM_8 with a 128-bit key, because that was all that their hardware supports.
> 
> What we are saying is that if you want your (in that case IPsec, but it’s no different for TLS) to work with IoT devices, you need that AEAD cipher.

Right, but is there any reason to restrict CCM_8 to 128-bit keys in the IANA registry entry?  I can't see one.

Russ

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