Which of the following best describes a public key?

A public key is designed to be shared openly and is a fundamental component of asymmetric encryption systems. In these systems, individuals generate a public-private key pair, where the public key can be freely distributed to anyone who wishes to communicate securely. When someone wants to send an encrypted message, they use the recipient's public key to encrypt the message. Only the corresponding private key, which is kept secret by the recipient, can decrypt this message, ensuring that only the intended recipient can read it.

This framework is crucial for establishing secure communication channels, allowing for data protection and integrity while maintaining accessibility for those who need to encrypt messages for the key holder. The openness of the public key is essential for the functioning of public-key infrastructures, enabling wide networked trust without requiring secure channels for initial key exchange.

In contrast, keys that must be kept secret or are used exclusively for specific functions, such as decryption or hashing, do not define the characteristics of a public key. These other options describe different aspects of cryptography but do not align with the nature and function of the public key.