Sismo Connect Server: Verify Offchain

Verify proofs from your users

The Sismo Connect Server is a back-end package built on top of the Hydra-S2 Verifier to easily verify proofs from your users offchain.

The Sismo Connect Server is


Install Sismo Connect server package in your backend with npm or yarn:

# with npm
npm i @sismo-core/sismo-connect-server
# with yarn
yarn add @sismo-core/sismo-connect-server

Make sure to have at least v18.15.0 as Node version. You can encounter issues with ethers dependencies if not.



The first step for integrating Sismo Connect in your back end is to create a sismoConnectServerConfig. This config will require an appId and can be customized with optional fields. You can go to the Sismo Factory to register an appId (here is a tutorial).

This config is then used to create a SismoConnect instance that will be used to verify proofs.

import { SismoConnect, SismoConnectConfig } from "@sismo-core/sismo-connect-server";

const config: SismoConnectConfig = {
  // you will need to register an appId in the Factory
  appId: "0x8f347ca31790557391cec39b06f02dc2",

// create a new Sismo Connect instance with the server configuration
const sismoConnect = SismoConnect({ config });

Verify proofs from your users

Proofs need to be sent from your front end to your back end with a SismoConnectResponse. The verify function takes the SismoConnectResponseas inputs but also requests to verify that proofs held in the response are cryptographically valid with respect to these requests.

import { SismoConnectVerifiedResult, AuthType } from "@sismo-core/sismo-connect-server";

async function verifyResponse(sismoConnectResponse: SismoConnectResponse) {
  // verifies the proofs contained in the sismoConnectResponse
  // with respect to the different auths
  // and the group(s) in the claim(s)
  // i.e. user prove they own a Vault, a Twitter account
  // and they are member of the group with id "0x42c768bb8ae79e4c5c05d3b51a4ec74a"
  const result: SismoConnectVerifiedResult = await sismoConnect.verify(
      // proofs in the sismoConnectResponse should be valid
      // with respect to a Vault and Twitter account ownership
      auths: [
        { authType: AuthType.VAULT }, 
        { authType: AuthType.TWITTER }
      // proofs in the sismoConnectResponse should be valid
      // with respect to a specific group membership
      // here the group with id 0x42c768bb8ae79e4c5c05d3b51a4ec74a
      claims: [{ groupId: "0x42c768bb8ae79e4c5c05d3b51a4ec74a"}],

  // vaultId = hash(userVaultSecret, appId).
  // the vaultId is an app-specific, anonymous identifier of a vault
  const vaultId = result.getUserId(AuthType.VAULT)
  // you can also get the twitterId of the user
  const twitterId = result.getUserId(AuthType.TWITTER)

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