[Cryptography] Proposal of a fair contract signing protocol

Ray Dillinger bear at sonic.net
Tue Jun 14 11:59:29 EDT 2016

On 06/14/2016 12:03 AM, Ron Garret wrote:
> On Jun 13, 2016, at 11:24 PM, Ray Dillinger <bear at sonic.net> wrote:

>> Such antics and requirements for absolute mathematical purity do not
>> impress judges and juries, any more than a child's demand to know the
>> ultimate cause of the universe.

> Yes, I know that.  But this is not a discussion about the law, it’s a discussion about a proposed cryptographic protocol.

But protocols insofar as anyone cares about them are used for reasons
that people care about.  If the problem is signing a contract, the legal
binding that people are asking about is decided by a court.

If communications are unreliable, obviously there's a bottom case in
which communications don't exist at all and you can't make a contract no
matter what.  So what even was there to prove?  That missed messages
such as happen when communications don't exist at all can cause a
protocol to fail?  Was that a surprise to anyone?

Anyway, there are plenty of public, irrefutably timestamped venues where
neither participant controls the timestamp and neither participant can
rescind a message.  Usenet, bitcoin blockchain, etc.  Commitment or lack
thereof can be based on what appears on those channels within a time
limit, and there's no way either party can claim it's there when it's
not, or that it's not there when it is.

And if communications are unreliable, then maybe one party can't check
the venue on the first try.  But when they do check, they can see that
the terms were met and the contract is operational.

You can consider such a venue to be a third party, if that preserves
your proof of impossibility and you care about the proof.  But there's
no application your proof is meaningfully applicable to in the sense
that the practical application is impossible.  That would be like
claiming that the proof that the halting problem is insoluble in the
general case means nobody can prove that the specific case of "hello
world" terminates.


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