Step 1: Understand the question.
Digital signatures are based on which kind of key encryption?
Step 2: Recall how digital signatures work.
They use a pair of keys: a private key kept secret by the owner and a public key that anyone can see. This is called asymmetric or public-key cryptography.
Step 3: Follow the process.
The signer locks the message using their private key. The receiver checks it using the matching public key. This proves the message came from the signer and was not changed.
Step 4: Pick the right label.
Since the whole system is named after the public key infrastructure, the standard answer is public key encryption.
Step 5: Conclude.
Digital signatures are based on public key encryption.
Answer: Public