Too Long; Didn't Read
Zero-Knowledge Proof, or Zero-Knowledge Protocol, is a probabilistic-based verification method that includes “fact-like statements” and “statements about personal knowledge”. The verifier asks the prover based on certain randomness. If the correct answer is given, the prover has a high probability of possessing what he claims to be “knowledge.” Zero-Knowledge Proof can verify that you did spend the money without revealing which currency was spent.