Why can't someone create a valid digital signature without knowing your private key?
Why can't someone create a valid digital signature without knowing your private key? I understand from the following two posts that private keys are not displayed by the sender when getting their transaction validated by the bitcoin miners: What happens to Private Key on Payment How can transactions be verified without the private key? Instead a digital signature is provided that is based on the Private Key, and, as far as I understand, that digital signature is verifiable when "compared" to the Public Key. Why then can't someone generate a verifiable digital signature using only someone else's public key? Or put another way, quoting an answer from the first post listed above: "A valid signature cannot be created without access to the private key" - why not? http://ift.tt/2m6vDfM