useSignVrf

useSignVrf produces an sr25519 VRF signature with a product account. Call sign(transcriptLabel, items): the host builds a Merlin transcript from the label and replays each { label, value } item as append_message, signs it with the account's key and resolves a VrfSignature with the preOutput and its DLEQ proof. The output is deterministic for the same transcript and key, which is the property lotteries, leader election and commit-reveal schemes rely on.

Four things stay on the caller: domain separation (a label borrowed from another protocol makes the output replayable there), freshness (per-round values belong in items), transcript size (hosts cap it at 32 items / 8 KiB) and authorization (an AutoSigning allowance makes these calls silent; it covers other signing by the same account too). Without the allowance the host prompts the user per call, so trigger it from a user gesture.

The account defaults to the runtime's product account (index 0 of the configured or host-derived product id); pass a ProductAccountLookup to sign with another index. Host-only: standalone sign rejects with HostUnavailableError.

Usage

import { useSignVrf } from "@use-truapi/react";

const enc = (s: string) => new TextEncoder().encode(s);

function DrawTicket({ round }: { round: number }) {
  const { sign, data, isPending, error } = useSignVrf();

  async function onDraw() {
    const { preOutput } = await sign(enc("my-app/lottery/v1"), [
      { label: enc("round"), value: enc(String(round)) },
    ]);
    console.log("ticket", preOutput);
  }

  return (
    <>
      <button type="button" onClick={onDraw} disabled={isPending}>Draw</button>
      {data && <code>{data.preOutput.length} byte pre-output</code>}
      {error && <p role="alert">{error.message}</p>}
    </>
  );
}

<script setup lang="ts">
import { useSignVrf } from "@use-truapi/vue";

const props = defineProps<{ round: number }>();
const enc = (s: string) => new TextEncoder().encode(s);
const { sign, data, isPending, error } = useSignVrf();

async function onDraw() {
  await sign(enc("my-app/lottery/v1"), [{ label: enc("round"), value: enc(String(props.round)) }]);
}
</script>

<template>
  <button type="button" :disabled="isPending" @click="onDraw">Draw</button>
  <code v-if="data">{{ data.preOutput.length }} byte pre-output</code>
  <p v-if="error" role="alert">{{ error.message }}</p>
</template>

See also

• useSignRaw is the plain signature over arbitrary bytes.
• useResourceAllocation requests the AutoSigning allowance that makes repeated VRF calls prompt-free.
• useRingVrfSign signs with a registered ring-VRF key instead.

API reference

React

function useSignVrf(options?): NamedMutation<VrfSignature, SignVrfVariables> & object;

RFC-0023 sr25519 VRF signature from a product account: sign(label, items). Deterministic for the same transcript, so put per-round values in items. Host-only; standalone the call rejects with HostUnavailableError.

Parameters

Returns

NamedMutation<VrfSignature, SignVrfVariables> & object

Vue

function useSignVrf(options?): NamedMutation<VrfSignature, SignVrfVariables> & object;

RFC-0023 sr25519 VRF signature from a product account: sign(label, items). Deterministic for the same transcript, so put per-round values in items. Host-only; standalone the call rejects with HostUnavailableError.

Parameters

Returns

NamedMutation<VrfSignature, SignVrfVariables> & object