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Version: v3.x.x

Conditional Signing

Prerequisites​

Overview​

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 used 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.

note

toSign data is required to be in 32 byte format.

The ethers.utils.arrayify(ethers.utils.keccak256(...) can be used to convert the toSign data to the correct format.

Installed the latest client on cayenne

yarn install @lit-protocol/lit-node-client

Set up the Lit Action code to be run on the Lit nodes.

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;
  }

  const message = new Uint8Array(
    await crypto.subtle.digest('SHA-256', new TextEncoder().encode('Hello world'))
  );
  // this is the string "Hello World" for testing, hashed with sha-256 above.
  const toSign = message;
  // 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();
`;

Obtain an AuthSig

// 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",
};

Run the Lit Action code on the Lit nodes:


const runLitAction = async () => {

const litNodeClient = new LitJsSdk.LitNodeClient({
    litNetwork: "cayenne",
  });

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();