Re: [Suit] COSE_Sign vs. COSE_Mac

[Koen Zandberg <[e-mail]>]

Hi Russ,

My 2 cents for this scenario: the device I'm currently developing for
(samr21-xplained pro) takes around 8 seconds for ed25519 signature
verification (TweetNaCl implementation). An HMAC based verification
would be a lot faster here (saving me battery power). If you like I can
provide you some numbers on flash requirements for both HMAC and
public-key implementations.

Thanks,
Koen


On 06/04/2018 05:52 PM, Russ Housley wrote:
> Brendan:
>
> That is a significant key management burden.  I would like to explore the assertion that hash-based signatures have too much data overhead.  Are you saying that they can buffer the firmware load, but not the signature value?
>
> Russ
>
>
>> On Jun 4, 2018, at 11:24 AM, Brendan Moran <[e-mail]> wrote:
>>
>> This is a solution that is intended to address a segment of devices that cannot use public-key due to code size or processing overhead, and cannot use hash-based signatures due to data overhead. Provided that every device has a unique PSK, COSE_Mac provides adequate security. However, it introduces significant key management overhead.
>>
>> Thanks,
>> Brendan
>>
>>> On 4 Jun 2018, at 16:16, Russ Housley <[e-mail]> wrote:
>>>
>>> I am struggling to see a case where COSE_Mac provides acceptable protection.  With a MAC, the sender and the recipient must use the same key.  This means that any recipient can make a modification and produce a valid MAC for the modified object.
>>>
>>> With a digital signature, the sender uses a private key, and the recipients use a public key, so the recipients cannot produce modified objects.
>>>
>>> Why accept this possibility?
>>>
>>> Russ
>>>
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