[Cryptography] Proposal of a fair contract signing protocol

mok-kong shen mok-kong.shen at t-online.de
Sat Jun 25 00:23:44 EDT 2016

Am 25.06.2016 um 05:05 schrieb Adrian McCullagh:
> Dear MK Shen,
> I do not understand your terminology “against the law”.  If you mean
> criminally illegal then no it is not against the law ibut f you mean not
> legally enforceable under civil law then I see your protocol as being
> unnecessary and frankly overly complicated from a commercial perspective.

In case both partners are honest and trust each other, exact protocols
would be unnecessary. But otherwise a protocol ensuring that, in case
a contract comes into being, then there is no unfairness in the signing
process would be desirable/necessary. Since there are even previously
published papers claiming that such protocols would be impossible, I
designed a protocol that apparently contradicts that. My discussions
with some other persons who sent in comments are intended to settle the
issue whether I am right or wrong.

Could you say whether you agree to what I wrote above?

> If Alice does to receive the acceptance communication (excluding the
> postal rule which I doubt would apply) even though Bob may have sent his
> acceptance there is no contract.  Further the Uniform Electronic
> Transactions Act (1999) deals with receipt of communications from a
> legal perspective (section 15).  My understanding is that this law has
> been enacted in more than 46 US States (though I have not recently checked).

I am interested to know a bit more details of how the law deals with
receipt of electronic messages with respect to time and actual arrival
at the site of the recipient. Could you kindly give a short sketch
showing how the sender could legally claim that he has sent something
in time to a recipient over the Internet?

> In my law practice I advise my clients that if the acceptance is
> important then telephone the other side to satisfy themselves that the
> acceptance has been received.  Further take a diary note of the call and
> ask the otherside to send an acknowledgement.  Basically a three way
> handshake with an out of bounds communication.

You scheme may work, though I personally doubt that it could work in
all conceivable cases in practice. I don't like to argue with you here.
On the other hand, the existence of your scheme doesn't constitute a
ground to "prove" that my scheme is wrong or doesn't work, do you agree?

M. K. Shen

> If the acknowledgement is not received within a reasonable time then
> call again.  The whole exercise is to obtain as best as possible some
> evidence to support the acceptance being received by Alice.
> Again, I do not see how your proposed protocol provides the evidence
> that a court will need.  Further, are we talking about minor contracts
> (less than $500) or contracts required by law to be in writing (statute
> of Frauds).
> It is the value of implementing this that also needs to be taken into
> consideration.
> Kind Regards
> Dr. Adrian McCullagh
> Ph.D. LL.B. (Hons) B.App. Sc. (Computing)
> ODMOB Lawyers
> Email: ajmccullagh57 at gmail.com
> Email: amccullagh at live.com
> MOB: +61 401 646 486
> SKYPE: admac57
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> *From: *mok-kong shen <mailto:mok-kong.shen at t-online.de>
> *Sent: *Saturday, 25 June 2016 9:31 AM
> *To: *Adrian McCullagh <mailto:amccullagh at live.com>; Salz, Rich
> <mailto:rsalz at akamai.com>; cryptography at metzdowd.com
> <mailto:cryptography at metzdowd.com>
> *Subject: *Re: [Cryptography] Proposal of a fair contract signing protocol
> You are entirely right that "Bob is under no legal obligation to do
> anything with Alices Offer". The issue in the present thread assumes
> however that Bob considers Alice's offer to be acceptable and does
> step 2 and the protocol comes to an end with Alice doing step 3,
> producing the contract document C and showing that it is signed by
> both Alice and Bob. Now the question is whether the contract signing
> process is fair. My argumentation is that it is indeed fair according
> to the fairness definition I have given.
> Is the matter now clear to you?
> I don't fully understand your last paragraph: (1) If Alice and Bob
> choose to do as desribed in my protocol, is that against the law??
> (2) If you don't see any unfairness in what is done in the protocol,
> then all the better for me, isn't it?
> M. K. Shen

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