core-concepts:zero-knowledge

Zero-knowledge proofs validate transactions by proving computational integrity through arithmetic circuits and witness inputs without exposing the underlying private state. Midnight uses this mechanism to verify transaction validity while keeping user data confidential.

Compact code compiles to arithmetic circuits by translating program logic into gate-level constraints, separating witness inputs from public inputs, and preparing the structure for PLONK-based proving. This process enables Zero-Knowledge SNARKs to generate verifiable proofs of private transactions.

Witness inputs are private values hidden during proof generation, while public inputs are visible data shared between the prover and verifier. In Midnight's Compact contracts, this distinction ensures that private state remains concealed while allowing necessary public validation.

Yes, PLONK uses a universal Structured Reference String (SRS) alongside per-circuit proving and verifying keys to secure private transactions. This setup allows multiple circuits to share the same trusted setup, reducing ceremony overhead while maintaining Zero-Knowledge proof integrity.

Performance tradeoffs in ZK proof generation involve balancing circuit size, gate-level constraint complexity, and disclose() boundaries with proof generation time. Larger circuits with more constraints increase proving time but enable richer private transaction validation logic within Midnight.

A Compact contract may fail to produce a valid PLONK-compatible proof due to incorrect witness and public input handling, malformed gate constraints, or improper disclose() boundary definitions. Debugging requires verifying circuit construction and ensuring constraint satisfaction across all witness values.