The purpose of a public key infrastructure (PKI) in data security is to manage digital certificates and encryption keys, ensuring secure communication over networks. PKI enables authentication, confidentiality, and integrity by providing a framework for issuing, renewing, and revoking digital certificates. This system is essential for establishing trust in online transactions, as it verifies the identities of parties involved. PKI plays a crucial role in securing data exchanges in e-commerce, email communication, and sensitive information transfer.