Digital Signature

Problem

You receive: Transfer €10,000 to Alice Encryption can hide the message. But how can you verify that the message was really authorized by the claimed sender and wasn't modified?

Solution — Digital Signature

The sender signs using their private key. Others verify using the corresponding public key.

Message + private key
        ↓
     signature

Message + signature + public key
        ↓
      verify

Core idea: digital signatures provide integrity and proof that the signer possessed the private key.