What is the difference between a private key and a public key?

The distinction between a private key and a public key is fundamental to understanding asymmetric cryptography, which underpins secure communication solutions, including those used in the Army's PKI framework. The correct response highlights that a private key is designed to remain confidential and is known only to the user, while a public key can be shared broadly with anyone who wishes to send encrypted messages to the owner of that private key.

This asymmetric relationship allows individuals to communicate securely; a sender can encrypt a message using the recipient's public key, and only the recipient can decrypt it using their private key. The secrecy of the private key is essential for maintaining security, as anyone who possesses the private key can decrypt messages intended for that user. In contrast, the public key's role is strictly to allow others to encrypt data for the key owner or to verify signatures made with the owner's private key.

The other options misrepresent the functions of private and public keys. One, for instance, suggests that public keys are always encrypted, which is not the case, as public keys are accessible in an unencrypted format for the purpose of communication. Additionally, another option inaccurately states that a private key is used for encryption while the public key is for decryption, which is reversed.