Which cryptographic method uses two keys, a public key and a private key?

• A. Asymmetric encryption
• B. Symmetric Encryption
• C. One Time Pad
• D. Dictionary Attack

Answer: (A)

Two-key systems with a public key and a private key are the signature feature of asymmetric encryption. In this approach, a public key can be shared openly to encrypt data, while the private key remains secret and is used to decrypt it. This also enables digital signatures, where a message is signed with the private key and verified with the corresponding public key. This contrasts with symmetric encryption, which relies on a single shared secret for both encryption and decryption, requiring secure key exchange. The One Time Pad is a theoretically perfect method that uses a key as long as the message and must be shared securely in advance, not a general two-key scheme. A dictionary attack is a method for guessing passwords or keys, not a cryptographic method that uses two keys.