Which of the following accurately describes a public key?

• A. It is a key known only to the owner
• B. It is a shared key for all users
• C. It can be openly distributed and used for encryption
• D. It is only used for decryption

Answer: (C)

A public key is specifically designed for a cryptographic system where it can be openly distributed without compromising the security of the communication. It is used in asymmetric encryption, where it serves the purpose of allowing anyone to encrypt a message that can only be decrypted by the corresponding private key, which is kept secret by the owner. This open distribution is essential for facilitating secure communication over networks, as it allows individuals to send confidential information without needing to exchange a secure key in advance.

In this context, the other options do not fit the definition of a public key. The notion that it is known only to the owner refers to a private key, which is the opposite of a public key. A shared key for all users relates to symmetric encryption but does not apply to public key cryptography. Lastly, the assertion that it is only used for decryption misrepresents its function; public keys are primarily used for encryption, whereas private keys are used to decrypt messages. Thus, the ability of a public key to be openly shared and utilized for encryption is what makes this answer accurate.