Proving You Have a Positive Value Without Revealing It
Our data world needs to change, and for it not to reveal our most precious of secrets. This results in proving proofs of knowledge, and where we do not reveal our data, but a proof of it. One thing we might do, is to prove that we have a positive value, without revealing the value. This might relate to our bank balance, and a proof that it is in a positive state. So, let’s look at a method that does a proof of knowledge that a value is greater than zero.
With the Damgard-Fujisaki method, Peggy proves to Victor that she has a positive integer value, and using the secp256k1 curve. In this case we will use the Damgard-Fujisaki method defined [here], and where Peggy has to prove to Victor that she has a positive value:
First Victor and Peggy agree on two bases for their calculations (g and h) and a prime number (n). Victor then sends Peggy using a random number (r) as a challenge. Every positive value can be represented in the form:
For example:
