Verifier

A verifier is an entity that checks whether something is true, valid, or meets a defined criterion. Verifiers can be people, software modules, or hardware devices. They stand in contrast to the prover, which provides claims or data to be checked.

In cryptography, verifiers validate digital signatures, certificates, or cryptographic proofs. A signature verifier confirms that a message was signed with the corresponding private key and has not been altered. Certificate verifiers check the trust chain and validity of digital certificates. Verifiers are also used in protocols such as zero-knowledge proofs, where a verifier decides whether a proof or claim is credible without learning the underlying secret.

In data integrity, verifiers compare data against reference values such as cryptographic hashes or checksums to detect corruption or tampering. They are used in software updates, file transfers, backups, and storage systems to ensure data remains unchanged.

In software engineering and formal methods, a verifier checks that a program or model satisfies a formal specification. This includes static type checkers, model checkers, and proof assistants. Bytecode or runtime verifiers ensure that code complies with safety and security rules during execution or loading.

In identity and authentication, verifiers validate claims about a person, organization, or device, often through credentials, biometrics, or challenge-response mechanisms. Verifiers play a key role in access control, online commerce, and regulatory compliance.

Limitations and trust models: the reliability of a verifier depends on its design, the integrity of verification data, and the security of the verification environment. False positives and negatives can occur, and multiple layers of verification are common in high-assurance systems.