What is a PIN pad that performs message encryption and decryption known as?

The term for a PIN pad that performs message encryption and decryption is Encrypted PIN Pad (EPP). This type of device is specifically designed to securely process transaction data, such as personal identification numbers (PINs), by encrypting the information at the point of entry.

EPPs enhance security in payment processing by ensuring that sensitive information is protected from interception during transmission. This is critical in preventing fraud and unauthorized access to confidential data. By using encryption, an EPP helps maintain the integrity and confidentiality of transaction information, complying with industry standards for secure payment processing.

While there are other devices that might serve various functions within a payment system, such as access control or cryptographic functions, the specific role of an EPP focuses on the encryption and decryption of messages associated with payment transactions. This makes it the appropriate and correct answer to the question.