Abstract: A system for securely transmitting data between two devices is disclosed. Each device comprises an interface, an encryption module, a decryption module and a message authentication code (MAC) generator. The encryption and decryption modules may utilize a stream cipher, while the MAC generator utilizes a hashing algorithm. A MAC is transmitted after a predetermined amount of time, regardless of the amount of activity on the interface. The device receiving the MAC compares it to the MAC that it generated to ensure that they match. This guarantees that a breach of integrity can be detected in a reasonable amount of time and addressed accordingly. This system may utilize an interface having bidirectional data signals or unidirectional data signals.