The purpose of a digital certificate in network security is to establish the identity of parties involved in online communications, ensuring secure data exchanges. Digital certificates use cryptographic techniques to validate the authenticity of an entity, such as a website or individual, and facilitate secure connections through protocols like SSL/TLS. By providing assurance that a sender is who they claim to be, digital certificates help prevent man-in-the-middle attacks and other malicious activities, fostering trust in digital transactions.