When Bob Bought Some Vouchers For Carol, Trent and Faith
And Where Alice Can’t Trace Them Back to Bob
A demo of the method I will present is [here].
So how can Bob purchase 10 vouchers for presents for Carol, Trent and Faith, and then for Alice’s store to not be able to tell it was Bob who had bought them. For this, we can turn to obvious transfer, and zero-knowledge proof (ZPK) method. One of the best around uses the power of elliptic curve methods and is defined as EC-VOPRF (Elliptic Curve Verifiable Oblivious Pseudo-Random Function).
Now Bob wants to buy 10 vouchers from Alice, and he wants to give them to Carol, Trent and Faith. For this he generates 10 random numbers (x1, x2, … x10). He then matches these onto elliptic curve points (finding the nearest x-axis point). For these 10 vouchers, he then creates a random value for a blinding factor (b). Bob then multiplies each of the elliptic curve points with b, and hands these 10 elliptic curve points to Alice, and pays for 10 vouchers.
Alice then multiplies each of these points with her private key (k), and sends them back to Bob. When Bob receives these he now unblinds each voucher by dividing each of them by his blinding factor (b). The values he now has are k×X1, k×X2, … k×X10.Next, Bob gives Carol the values of X1 and k×X1, X2 and k×X2 to…
