Archived article · Original source date: 2024-08-03
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Validity proofs are most often discussed with zero-knowledge rollups and validiums. They are not ordinary validator signatures, transaction-format checks, or a universal digital stamp placed on every blockchain transaction.
What the proof establishes
A proving system expresses valid execution as a circuit or constraint system. The prover supplies private witness data and public inputs—such as the previous state root, new state root, and a batch commitment—and produces a succinct proof that the constraints were satisfied.
An on-chain verifier checks that proof. If it is valid and the public inputs match the expected state, the settlement contract can accept the new state root without reproducing the full off-chain computation.
SNARKs, STARKs, and zero knowledge
Implementations may use SNARKs, STARKs, or other proof systems. They differ in proof size, proving and verification cost, setup assumptions, hardware requirements, and cryptographic assumptions. A proof can establish computational validity without revealing all witness data, but that does not make every associated transaction or public input private.
Validity proof versus ordinary transaction validation
Base-layer nodes still validate ordinary transactions under their network's runtime and consensus rules. A rollup validity proof instead attests to a particular off-chain execution defined by its circuit. The proof is only as meaningful as the circuit, public inputs, verifier contract, implementation, and upgrade controls.
ZK-rollups and validiums
Both designs can use validity proofs for state-transition correctness. A ZK-rollup also publishes the data needed to reconstruct its state to the settlement layer, while a validium keeps that data elsewhere. This makes data availability—not proof validity—the defining difference and a major source of validium withdrawal risk.
What the proof does not guarantee
- That off-chain state data will remain available.
- That a sequencer will include a user's transaction or resist censorship.
- That the application logic, oracle inputs, governance, or upgrade authority is safe.
- That users understand or authorize the economic effect of a transaction.
- That the system provides legal compliance, confidentiality, or recovery.
Solana context
Validity proofs are not Solana's base-layer consensus mechanism. A Solana application may verify a proof or use zero-knowledge techniques for an application-specific protocol, but Solana validators still execute and confirm transactions according to Solana's runtime and proof-of-stake consensus rules.
For a detailed rollup example, see the Ethereum documentation on ZK-rollups and then verify the proof system, contracts, data-availability model, operator controls, audits, and upgrade process of the implementation being evaluated.