W3C home > Mailing lists > Public > public-credentials@w3.org > November 2015

Re: Solutions to the NASCAR problem?

From: David Chadwick <d.w.chadwick@kent.ac.uk>
Date: Mon, 23 Nov 2015 17:10:30 +0000
To: Dave Longley <dlongley@digitalbazaar.com>, Anders Rundgren <anders.rundgren.net@gmail.com>, public-credentials@w3.org
Message-ID: <56534886.20909@kent.ac.uk>


On 22/11/2015 22:14, Dave Longley wrote:
> On 11/22/2015 12:53 PM, David Chadwick wrote:
>>
>>
>> On 22/11/2015 16:33, Anders Rundgren wrote:
>>> On 2015-11-22 17:10, David Chadwick wrote:
>>>> Hi Anders
>>>
>>> Hi David,
>>>
>>> <snip>
>>>
>>>>>> The user sends the consumer SOP public key to the issuer and
>>>>>> the issuer assigns the attribute to that.
>>>>>
>>>>> I think you lost me here, at least with respect to the NASCAR
>>>>> problem.
>>>>
>>>> This is because the user does not go to any third party to
>>>> authenticate to a site. A new key pair is generated for the site,
>>>> and this authenticates the user each time he calls. Note however
>>>> that FIDO does not provide any identity or authz information,
>>>> just an authn key, which is why we need to add this functionality
>>>> using issuers.
>>>
>>> It is this sending of the consumer public key to issuer by the user
>>> which I don't quite understand :(
>>
>> The user can prove possession of all the public keys his device has 
>> issued. This is how he authenticates. The consumer only knows it is
>> the user at the other end of the connection because a challenge from
>> the consumer was signed by the private key corresponding to the
>> user's consumer public key.
>>
>> Now if the consumer receives an attribute signed by an issuer, it
>> proves that the issuer issued it, but not who it belongs it. By using
>> the consumer public key as the ID of the user, the consumer now knows
>> that the user it has authenticated is the righful owner of the
>> attributes.
> 
> It may be difficult to do, but is there a danger that the user will
> present the public key ID for a user other than themselves and receive a
> credential that is signed for that other person?

Yes they could hack the system to do this. But that would be the
equivalent of giving your credit card away to someone else to spend for
you. Of course, if you have say, a store discount attribute for 10%, and
you give that to all your friends public keys, the issuer might become
rather suspicious.

> How does the issuer
> authenticate the user's ownership of the public key ID?

He doesnt. He trusts the user, just as credit card companies and all
other plastic card issuers do today. Legal agreements will help to
ensure user compliance with sole use.

regards

David
> 
> 
Received on Monday, 23 November 2015 17:10:38 UTC

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