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ALT Unifying Zero-Knowledge Proofs of Knowledge Ueli Maurer Department of Computer Science ETH Zurich CH-8092 Zurich, Switzerland [email protected] Abstract. We present a simple zero-knowledge proof of knowledge pro- tocol of which many protocols in the literature are instantiations. These include Schnorr’s protocol for proving knowledge of a discrete logarithm, the Fiat-Shamir and Guillou-Quisquater protocols for proving knowl- edge of a modular root, protocols for proving knowledge of representa- tions (like Okamoto’s protocol), protocols for proving equality of secret values, a protocol for proving the correctness of a Diffie-Hellman key, protocols for proving the multiplicative relation of three commitments (as required in secure multi-party computation), and protocols used in credential systems. This shows that a single simple treatment (and proof), at a high level of abstraction, can replace the individual previous treatments. Moreover, one can devise new instantiations of the proto