The function of cryptography in data security is to protect sensitive information from unauthorized access and ensure data integrity. By converting plaintext into ciphertext through encryption methods, cryptography makes it difficult for unauthorized parties to decipher messages. Additionally, cryptography enables secure communication channels, preserving confidentiality during transmission over networks. It also employs techniques such as digital signatures to verify identity and authentication processes to ensure that only authorized users can access specific data. Overall, cryptography is fundamental in safeguarding data in various applications, from online banking to communication systems.