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World ID is built for easy integration, but here are a few core concepts that are helpful to understand before you start.

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World ID

A user’s self-custodial identity which lives in their Authenticator. When referring to the protocol, it’s usually written as the World ID Protocol.

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Relying Party (RP)

A third-party application that wants to verify a user’s credential. This is probably you.

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Credential

A signed attestation about a subject used to generate proofs. It includes issuer, subject, validity window, and claim commitments as defined in the Credential’s World ID 4.0 specs

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Issuer

An entity that issues credentials to users. In World ID, issuers are responsible for verifying a user’s identity and signing their credential. Issuers must be registered in the CredentialSchemaIssuerRegistry to be recognized by the protocol.

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Proof Concepts

  • Action: A developer-facing primitive that lets you put any app operation behind a unique-human gate. An app can have one or more actions depending on your use case.
  • Zero-Knowledge Proof (ZKP): A cryptographic method to prove that a statement is true without revealing any information about the statement itself. World ID uses ZKPs to prove that a user is verified without revealing the user’s identity.
  • Nullifier Hash: A component of the World ID ZKP; a unique identifier for a combination of a user, app_id, and action.
  • Signal: A component of the World ID ZKP; data attached to the proof that cannot be tampered with. An example may be a user’s choice for an election.

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Legacy Concepts (World ID 3.0)

  • Identity Commitment: A hash of a user’s secret identity nullifier and trapdoor, which is inserted into the Merkle Tree. This is no longer used in World ID 4.0, but you may see it referenced in older documentation.
  • App ID: The ID of your app that is assigned in our Developer Portal. In World ID 4.0, this is now referred to as RP ID.
  • Merkle Root: A component of the World ID ZKP; The root of the Merkle Tree that identity commitments are inserted to. While 4.0 still uses Merkle Trees, the root is now encoded within the received ZKP, so you don’t need to worry about handling it.