Proving authenticity and integrity with asymmetric cryptography
Digital signatures provide three security guarantees:
1. Authentication: Proves the message came from the claimed sender (only they have the private key)
2. Integrity: Any modification to the message invalidates the signature
3. Non-repudiation: The signer cannot deny having signed the message
The process: Alice hashes the message and encrypts the hash with her private key (creating the signature). Bob decrypts the signature with Alice's public key to get the hash, then compares it to his own hash of the message. If they match, the signature is valid.