In public key cryptography, what is the function of public keys?

In public key cryptography, public keys primarily function to encrypt messages. The essence of public key infrastructure is that each user has a pair of keys: a public key and a private key. The public key can be distributed widely and is used by senders to encrypt data intended for the key owner.

When a message is encrypted with a public key, only the corresponding private key can decrypt it. This ensures that even if the public key is known to anyone (since it is meant to be shared), only the individual who holds the private key can access the encrypted messages. This method enables secure, confidential communication over insecure channels, such as the internet, without pre-shared secrets.

In this context, other options represent functions that do not align with the role of public keys. Public keys are not used for decrypting messages, as that function is reserved for private keys. Signing messages is another function typically associated with a private key, which creates a digital signature that can verify the authenticity and integrity of a message when verified using the corresponding public key. Generating symmetric keys is a different process not directly related to public key operations, as symmetric keys are usually shared secrets between parties for encryption and decryption purposes. Thus, the correct understanding of public