Advanced Placement (AP) Computer Science

What is a Public Key in cryptography?

1. A code that is available for anyone to use.

2. A code that must remain confidential to its respective owner.

3. A digital signature used for authentication.

4. A key that is used to delete encrypted files.

The correct answer is: A code that is available for anyone to use.

A Public Key in cryptography is indeed a code that is available for anyone to use. In public key cryptography, two keys are utilized: a public key and a private key. The public key can be shared openly and is used to encrypt data, allowing anyone to send secure messages. However, only the owner of the corresponding private key can decrypt these messages. This system enables secure communication over insecure channels, as anyone can send encrypted information using the public key, but only the designated recipient can decode it with their private key. This characteristic ensures that the public key can be widely disseminated without compromising security. In contrast, the other options describe different aspects of cryptography or security that do not accurately represent the function of a public key. The confidentiality of the private key, for example, is crucial in maintaining security, but it is not relevant to the public key itself. Similarly, digital signatures and file deletion do not pertain to the definition of a public key in the context of cryptography.