What problem does public key cryptography address within Public Key Infrastructure (PKI)?

Public key cryptography is fundamentally designed to solve the challenge of secure key distribution within Public Key Infrastructure (PKI). In a conventional symmetric encryption system, parties must exchange shared keys securely before they can encrypt or decrypt messages. The risk of interception during this exchange can lead to compromised communications.

Public key cryptography eliminates this issue by utilizing a pair of keys: a public key, which can be shared openly, and a private key, which is kept secret. This asymmetrical approach means that anyone can use the recipient's public key to encrypt a message, but only the recipient, who holds the corresponding private key, is able to decrypt it. This ensures that even if the public key is widely distributed, the security of the communication is maintained because knowledge of the public key alone does not enable decryption of messages.

By providing a method to securely distribute keys without requiring a pre-existing shared secret, public key cryptography facilitates secure communication and authentication in digital transactions, thereby enhancing the overall security structure of PKI.