verifyData.js

async function verifyData(data) {

    // return false if the object has no signature
    if (!data.sig) {
        return false;
    }
    else {

        // save the signature and delite it from the object
        const signature = data.sig;
        delete data.sig;
        
        // converts the object to a string
        const json = JSON.stringify(data);

        // loads to public key as a file
        const publicKey = await util.promisify(fs.readFile)(path.join(pubKeyFile));

        // Creates and returns a Verify object that uses RSA-SHA256
        //https://en.wikipedia.org/wiki/RSA_(cryptosystem)

        // https://en.wikipedia.org/wiki/RSA_(cryptosystem)
        // https://en.wikipedia.org/wiki/Secure_Hash_Algorithms
        const verifier = crypto.createVerify("RSA-SHA256");

        // Updates the Verify content with the given data as json string
        verifier.update(json);

        // Verifies the provided json with the public key as a string and the saved signature
        // Returns true or false depending on the validity of the signature for the data and public key.
        // https://nodejs.org/api/crypto.html#crypto_verify_verify_object_signature_signatureformat
        return verifier.verify(publicKey.toString(), signature, "hex");
    }
  }