Definition
A validity proof is a succinct cryptographic object that mathematically certifies that a given computation, such as a set of blockchain transactions or state transitions, was executed according to the protocol’s rules. Instead of re-executing all underlying operations, a verifier checks the proof to be convinced that the resulting state is correct. This concept underpins systems where correctness is enforced by cryptography rather than by every participant redundantly recomputing all activity.
In blockchain scalability designs, validity proofs are typically generated off-chain and then verified on a base layer, allowing the base chain to accept new state as correct based solely on the proof. Constructions such as zk-SNARK and zk-STARK are concrete zero-knowledge proof systems that can be used to implement validity proofs. These proofs can optionally be zero-knowledge, meaning they reveal only the correctness of the computation while hiding private inputs.
Context and Usage
Validity proofs are central to certain Rollup architectures on Layer 2, where large batches of transactions are processed off-chain and a single proof is submitted on-chain to attest to their correctness. In this context, the base layer acts as a minimal verification engine, checking the proof rather than replaying all transactions. This enables higher throughput while preserving strong security guarantees anchored in the underlying chain.
When instantiated with zero-knowledge properties, validity proofs are a specialized form of Zero-Knowledge Proof, ensuring that only the validity of the computation is exposed to verifiers. Different proof systems, such as zk-SNARK and zk-STARK, offer alternative trade-offs in proof size, verification cost, and security assumptions while serving the same core role of certifying valid state transitions for Rollup and other Layer 2 designs.