Re: [Taler] repurchase detection

[Christian Grothoff]

On 02/22/2016 11:59 AM, Marcello Stanisci wrote:
>> If it's just the correlation ID, what if it clashes for two merchants?
>>
>> Should we use the hostname of the fulfillment URL?  The hostname of the
>> site that offered the contract (with taler-confirm-contract) in the
>> first place?  What if the merchant's hostname changes?
> 
> There is also a field in the contract that encompasses the triple
> (address, name, jurisdiction) associated with a merchant. This value
> is less likely to change than keys and hostnames, and should not make
> any clash happen. So just use its hash?
> 

I think that might be dangerous, as it is most easily faked.  I can put
a fake address, name and jurisdiction trivially, a fake DNS name is
harder; in contrast, if we tie this to the EdDSA public key (ideally
X.509-certified) it becomes nearly impossible to fake (assuming it is
combined with an EdDSA signature in the right spot...).  So
security-wise, not supporting key rotation is a really minor issue
compared to using insecure information.

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