Conditional Signing

Lit Actions inherit the powerful condition checking that Lit Protocol utilizes for Access Control. This means that you can easily check any on-chain condition inside a Lit Action, which can be useful for generating proofs. This system can be harnessed to uphold the integrity of data on the open web, in its function as a decentralized notary.

The below example will check if the user has at least 1 Wei on Ethereum, only returning a signature if they do.

import * as LitJsSdk from "@lit-protocol/lit-node-client@serrano";

// this code will be run on the node
const litActionCode = `
const go = async () => {
  // test an access control condition
  const testResult = await Lit.Actions.checkConditions({conditions, authSig, chain})

  console.log('testResult', testResult)

  // only sign if the access condition is true
  if (!testResult){
    return;
  }

  // this is the string "Hello World" for testing
  const toSign = [72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100];
  // this requests a signature share from the Lit Node
  // the signature share will be automatically returned in the HTTP response from the node
  const sigShare = await LitActions.signEcdsa({ toSign, publicKey: "0x02e5896d70c1bc4b4844458748fe0f936c7919d7968341e391fb6d82c258192e64", sigName: "sig1" });
};



go();
`;

// you need an AuthSig to auth with the nodes
// normally you would obtain an AuthSig by calling LitJsSdk.checkAndSignAuthMessage({chain})
const authSig = {
  sig: "0x2bdede6164f56a601fc17a8a78327d28b54e87cf3fa20373fca1d73b804566736d76efe2dd79a4627870a50e66e1a9050ca333b6f98d9415d8bca424980611ca1c",
  derivedVia: "web3.eth.personal.sign",
  signedMessage:
    "localhost wants you to sign in with your Ethereum account:\n0x9D1a5EC58232A894eBFcB5e466E3075b23101B89\n\nThis is a key for Partiful\n\nURI: https://localhost/login\nVersion: 1\nChain ID: 1\nNonce: 1LF00rraLO4f7ZSIt\nIssued At: 2022-06-03T05:59:09.959Z",
  address: "0x9D1a5EC58232A894eBFcB5e466E3075b23101B89",
};

const runLitAction = async () => {
  const litNodeClient = new LitJsSdk.LitNodeClient({
    litNetwork: "serrano",
  });
  await litNodeClient.connect();
  const signatures = await litNodeClient.executeJs({
    code: litActionCode,
    authSig,
    jsParams: {
      conditions: [
        {
          conditionType: "evmBasic",
          contractAddress: "",
          standardContractType: "",
          chain: "ethereum",
          method: "eth_getBalance",
          parameters: [":userAddress", "latest"],
          returnValueTest: {
            comparator: ">=",
            value: "1",
          },
        },
      ],
      authSig: {
        sig: "0x2bdede6164f56a601fc17a8a78327d28b54e87cf3fa20373fca1d73b804566736d76efe2dd79a4627870a50e66e1a9050ca333b6f98d9415d8bca424980611ca1c",
        derivedVia: "web3.eth.personal.sign",
        signedMessage:
          "localhost wants you to sign in with your Ethereum account:\n0x9D1a5EC58232A894eBFcB5e466E3075b23101B89\n\nThis is a key for Partiful\n\nURI: https://localhost/login\nVersion: 1\nChain ID: 1\nNonce: 1LF00rraLO4f7ZSIt\nIssued At: 2022-06-03T05:59:09.959Z",
        address: "0x9D1a5EC58232A894eBFcB5e466E3075b23101B89",
      },
      chain: "ethereum",
    },
  });
  console.log("signatures: ", signatures);
};

runLitAction();

Example Project: Conditional Signing

Below is an example project demonstrating how to program a conditionally signed response using Lit Actions.

The app will display the returned JSON if Ether balance >= Min balance entered AND if you signed the transaction within 2 mins of the set time.

Here is the complete React project.