[Cryptography] Proposal of a fair contract signing protocol

mok-kong shen mok-kong.shen at t-online.de
Sat Jun 25 02:22:52 EDT 2016

Am 25.06.2016 um 02:44 schrieb Sidney Markowitz:
> mok-kong shen wrote on 25/06/16 10:56 AM:
>>> Therefore, the creation of
>>> the valid contract is completely under Alice's control at this point,
>>> and completely out of Bob's control.
>> Did you read what in step 1 Alice promises to do if Bob commits? If Bob
>> commits in step 2 and Alice doesn't do step 3 then she breaks her
>> promise and Bob could suit her. Note once again that if a contract
>> doesn't come into being for technical or human reasons, my definition
>> of unfairness is never touched upon, for the definition assumes a
>> valid document, i.e. step 3 is completed.
> If you say that because of Alice's promise in Step 1 that it is not true that
> in Step 3 "the valid contract is completely under Alice's control at this
> point, and completely out of Bob's control" then you are asserting that the
> promise has the force of taking it out of Alice's control after Step 1. In
> which case the validity of the contract is completely under Bob's control in
> Step 2. Either the "promise" falls under the definition of "commitment" and
> Bob has unfair control in step 2, or it is not, in which case Alice has unfair
> control in Step 3.

Sorry that I don't yet fully understand your point. Let me sketch
my scheme in a way that IMHO would be easier for you to exactly
pinpoint in order to provide your corresponding critiques, if any:

In step 1 Alice proposes a contract C (in terms of X and Y of visual
cryptography) but she signs "only" X which (alone) has no significance
in the sense of a commitment. (Note that X could be combined with a
different Y' to result in a C' that is different from C.) She promises
that "if" in future Bob fully commits in step 2 via signing X and Y
"then" she would (and is responsible to) sign Y in step 3, thus
completing the formality of the proposed contract C. Of course step 2
is under the control of Bob, since step 2 is to be done by him in case
he considers Alice's C is acceptable. If he chooses not to do that,
i.e. he deems C to be not acceptable, then the protocol fails to
complete. I don't care scenarios where the protocol fails due to this
reason or other akin causes. What I do care is a scenario where the
protocol succeeds, i.e. a valid contract C comes into being, but the
signing processing is unfair according to my definition of fairness.
I attempt/hope to convince everybody that such a valid contract C
can never come out from my protocol. (This is my goal, nothing more,
nor less.)

M. K. Shen

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