here is the how bitcoin works under the hood article http://www.imponderablethings.com/2013/07/how-bitcoin-works-under-hood.html i did not got this why message is needed when using this verify function ? 1 =? v(message, public key, signature)
Say you see a check for "$50,000 to Bob" that needs to be signed by Ed. What you want to know is whether the signature on the check came from Ed and signs the message "$50,000 to Bob". So the question a signature checker answers is, does the given signature attach the given credential to the given message. How would it check that without the message?
Checking a signature detached from a message would serve no purpose. Say you see that check for $50,000 to Bob. If Ed actually signed "$50 to Alice", the the signature check must fail -- since Ed didn't sign that message. So you can't check the signature without knowing the message.