zk-REAL: A Zero-Knowledge-Based Protocol for Repeated Image Edit Authenticity Proof With Lattice Hashing

The rapid advancement of deepfake technology poses risks, including financial fraud and political misinforma tion, demanding robust methods for verifying image content authenticity. While C2PA and ZK-based methods provide mechanisms for authenticity, existing solutions struggle to efficiently support privacy-preserving edits and iterative modifications. We present zk-REAL, a system that combines lattice-based hashing (LHF) with a Halo2 circuit design to reduce constraint cost and to exploit LHF updatability for partial recomputation after local edits. To remain interoperable with standard toolchains, a SHA 256 hash is computed outside the circuit as a compatibility layer with C2PA. On 720p images, our implementation demonstrates reduced key-generation cost (2× faster) and proving time for complex transformations. For repeated edits we achieve up to 29% proving-time reduction relative to recomputing from scratch, and 48% for double-edit contrast. Trade-offs include larger proof sizes for simple operations (crop, resize) versus smaller proofs for complex operations (contrast), indicating suitability for computationally intensive multi-edit workflows.