Comprehensive Explanation

verifier

Definition

A verifier in KERI is any entity or agent that performs cryptographic verification of data received from peers, specifically checking structure, signatures, and dates on event messages. In the KERI suite, a verifier cryptographically verifies signature(s) and digests on an event message. The verifier role is closely related to but distinct from a validator—while both terms are near-synonyms, a verifier focuses specifically on cryptographic verification operations, whereas a validator performs broader evaluation of statements and claims.

Key characteristics:

• Performs cryptographic signature verification using public keys
• Validates message integrity through digest checking
• Establishes control authority before signature verification
• Applies use-case-specific trust criteria beyond cryptographic checks

Context in KERI/ACDC

In KERI, the verifier plays a foundational role in the duplicity detection and trust establishment architecture. Before a verifier can validate a signature, they must first determine which key set was controlling an identifier at the time an event was issued—a process called establishing control authority.

Control Authority Establishment

The verification process differs based on identifier type:

For non-transferable identifiers: Control establishment requires only a copy of the inception event, as the controlling key set is fixed and cannot change.

: Verifiers must obtain and verify a complete sequence of , including the inception event and all subsequent , covering the period up to when the statement was issued.