Re: Phone Flip Over the Phone...

On Dec 20, 10:31 am, The Translucent Amoebae <transamoe...@xxxxxxxxxx>
wrote:

Instead; Suggest Ways to make it more Functional...!

Yes, there is a way to flip a coin over the phone that is similar to
what you are thinking of, and not too difficult.

You are just missing one ingredient. A "one-way" function is needed.
That does not mean you need to use the really complicated mathematics
of public-key cryptography, though.

In addition to a telephone, both people need copies of the same phone
book.

Each person does this:

1) He picks a random spot in the phone book - its randomness is to his
own advantage. However, you do have to watch for, and avoid, spots
where the same phone number repeats.

2) The two phone numbers at the spot each one picks are added to form
the number that is either odd or even.

3) Each person gives the phone number *five places down* in the phone
book from the number he picked.

4) After both people have done that, they then tell each other the
name of the person with that phone number. So each one can then verify
that, yes, the phone number the other person committed to belonged to
that name.

5) Then, they count five places up to get the phone number to be added
for the odd or even.

This is, I think, as simple as what you're looking for.

You could do it with a hash function too, but even a half-decent hash
function is too complicated to do on a pocket calculator.

But assuming your steps of doing things with digits are a good hash
function, then you just have to do it backwards.

Each person picks his own row of digits, and does the operations that
correspond to them. They give the other person the *result*, but what
gets added for odd or even are the digits used to get the result.

John Savard
.

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