A communication system includes communication devices which communicate during a communication session. During communication session establishment, the devices exchange a session key in an encrypted manner for privacy. When one device has information to transfer to the other device, the one device will append the session key to the information and apply a hash function thereto to generate a hash value, and generate a message packet for transfer to the other device that includes an information portion containing the information and a hash value portion containing the hash value. When the other device receives the message packet, it will append the session key to the information from the information portion of the packet that it receives, and generate a hash value therefrom. If the receiving device determines that the generated hash value corresponds to the hash value received in the message packet, properties of the hash function that is used to generate the hash values enable it to conclude that the message packet was not tampered with during the transfer and that it originated from the one device. The system avoids the necessity of computation-intensive encryption and decryption for message packet transfer during a communication session.