Re: Jointly calculating the sum

From: Peter Pearson (ppearson_at_nowhere.invalid)
Date: 07/28/05 

Date: Thu, 28 Jul 2005 09:52:18 -0700

Ann Brandon wrote:

> assume we have 3 partys Alice, Bob and Carol. Each party chooses a
> random value r_A, r_B, r_C \in Z_p (where p is prime). Now the partys
> want to calculate the sum r=r_A + r_B + r_C, so that each party only
> knows its own value and the sum r.

If you don't require detection of cheating, you can do the
sum-of-ages-at-the-lunch-table trick: Alice picks a random X
and passes X+A to Bob, who adds his number and passes X+A+B
to Carol, who passes X+A+B+C to Alice, who subtracts X and
announces A+B+C. 

-- 
Peter Pearson
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