Voting Verifier

Not used on the XRPL side. XRPL messages are verified by the XRPL Voting Verifier, which handles XRPL's union message type with five variants (InterchainTransferMessage, CallContractMessage, AddGasMessage, AddReservesMessage, ProverMessage). The generic voting-verifier documented here is the template deployed for most other connected amplifier chains.

The voting verifier verifies batches of messages via RPC voting. Polls are created and votes are cast via a generic voting module, which the voting verifier uses. The generic voting module does not know the meaning of the polls, and simply returns a Poll ID to the voting verifier. The voting verifier internally maps a Poll ID to the messages in the poll, storing the results in storage. The gateway can then query the voting verifier to check message verification status.

There are two types of polls: messages polls and verifier set polls. Messages polls are used to verify incoming messages, while verifier set polls are used to verify that the external gateway has updated its stored verifier set. Verifier set polls are a necessary component of the verifier set update flow. See update and confirm VerifierSet sequence diagram for more details.

Interface

pub enum ExecuteMsg {
    // Computes the results of a poll. For all verified messages, marks them as verified
    // in storage so the gateway can later query their status. Permission: Any.
    EndPoll { poll_id: PollId },

    // Casts votes for the specified poll. Permission: Any (only active verifiers count
    // toward quorum).
    Vote { poll_id: PollId, votes: Vec<Vote> },

    // Returns a vector indicating current verification status for each message; starts a
    // poll for any not yet verified messages. Permission: Any.
    VerifyMessages(Vec<Message>),

    // Starts a poll to confirm a verifier set update on the external gateway. Permission: Any.
    VerifyVerifierSet {
        message_id: nonempty::String,
        new_verifier_set: VerifierSet,
    },

    // Update the threshold used for new polls. Permission: Governance.
    UpdateVotingThreshold {
        new_voting_threshold: MajorityThreshold,
    },
}

pub enum QueryMsg {
    // Returns a PollResponse for the given poll id.
    Poll { poll_id: PollId },

    // Returns the verification status of each message in the input.
    MessagesStatus(Vec<Message>),

    // Returns the verification status of the given verifier set.
    VerifierSetStatus(VerifierSet),

    // Returns the currently configured voting threshold.
    CurrentThreshold,
}

Verifier graph

flowchart TD
subgraph Axelar
    G{"Gateway"}
    Vr{"Voting Verifier"}
    R{"Service Registry"}
end
OC{"Verifiers"}

G--"VerifyMessages([M, M', M''])"-->Vr
Vr--"ActiveVerifiers"-->R
OC--"Vote(poll_id, votes)"-->Vr
OC--"EndPoll(poll_id)"-->Vr

Message Verification Sequence Diagram

sequenceDiagram
participant Gateway
participant Voting Verifier
participant Service Registry
participant OC as Verifiers


Gateway->>Voting Verifier: VerifyMessages([M,M',M''])

Voting Verifier->>Service Registry: ActiveVerifiers
Service Registry-->>Voting Verifier: list of verifiers and stake
Voting Verifier->>OC: emit event with poll_id and messages
Voting Verifier-->>Gateway: [false,false,false]

OC->>Voting Verifier: Vote(poll_id, votes)
OC->>Voting Verifier: Vote(poll_id, votes)

OC->>Voting Verifier: EndPoll(poll_id)
note right of Voting Verifier: Poll results are now stored.

opt After poll has ended
    Gateway->>Voting Verifier: query MessagesStatus([M,M',M''])
    Voting Verifier-->>Gateway: return [MessageStatus, ...]
end