Ethereum Ðapp Development - Video 18 | Signing Arbitrary Messages

script.js

// Private Key
var pKey = "..."
var pKeyx = new Buffer(pKey, "hex")

// Shared Message
var message = "..."
var messageHash = web3.sha3(message)
var messageHashx = new Buffer(messageHash.replace("0x", ""), "hex")

// Signed Hash
var signedMessage = EthUtil.ecsign(messageHashx, pKeyx)
var signedHash = EthUtil.toRpcSig(signedMessage.v, signedMessage.r, signedMessage.s).toString("hex")

// Recover Address
var sigDecoded = EthUtil.fromRpcSig(signedHash)
var recoveredPub = EthUtil.ecrecover(messageHashx, sigDecoded.v, sigDecoded.r, sigDecoded.s)
var recoveredAddress = EthUtil.pubToAddress(recoveredPub).toString("hex")