A digital signature is the following process: - Use message - Hash it (giving digest), encrypt digest with private key. - Append encrypted digest to the message.
- Why not just encrypt the message with private key?
I assume that then attacker could just change something, we would be able to decode, but we would get different message than the sent one. We also wouldn't be able to recognize that the message was changed.
- Why not just encrypt the message and append the encrypted one to the original message?
I assume the message would be twice the size which is inconvenient for large messages. Also public-private keys have the restriction on message length, which would lead to the need of breaking message into parts.
Are my reasons correct? Something else that I missed?