Sign message twice with web3

Question

a quick beginner's question... is it possible to sign a message twice with web3? For example Alice creates a message and signs it. Then it is sent to Bob. Can Bob sign the message before he executes the transaction to make sure that the message was accepted by both of them?

Thanks a lot!

Answer 1

Just take the signed message of Alice and use it as a message to sign by Bob

var alice_signature;
var message = "Some Text ";
web3.personal.sign( web3.fromUtf8( message), <Alice> , function( err, signature ) {
      alice_signature = signature;
      send_to_bob(signature,message);
})

And then, for example

var message = message_from_alice + signature_from alice
web3.personal.sign( web3.fromUtf8( message ), <Bob> , function( err, signature ) {
      console.log(signature);
})

Answer 2

        {
            const message = "Hello, world!"
            const messageHash = ethers.utils.solidityKeccak256(["string"], [message])
            const messageHashBinary = ethers.utils.arrayify(messageHash)
            const signature = await signer.signMessage(messageHashBinary)
            const verified = ethers.utils.verifyMessage(messageHashBinary, signature)

            console.log("Signer: ", signer.address)
            console.log("Original MSGHash: \n", messageHash, "Binary: \n", messageHashBinary)
            console.log("Original signature: \n", signature)
            console.log("Verified with signer: \n", verified, "\n")

            const newmessage = signature + message
            const newMessageHash = ethers.utils.solidityKeccak256(["string"], [newmessage])
            const newMessageHashBinary = ethers.utils.arrayify(newMessageHash)
            const newSignature = await wrongSigner.signMessage(newMessageHashBinary)
            const newVerified = ethers.utils.verifyMessage(newMessageHashBinary, newSignature)

            console.log("Wrong Signer: ", wrongSigner.address)
            console.log("New MSGHash: \n", newMessageHash, "Binary: \n", newMessageHashBinary)
            console.log("New signature: \n", newSignature)
            console.log("Verified with wrongSigner: \n", newVerified, "\n")
        }