BECAUSE DATA CAN NOW BE ENCRYPTED IN A PRACTICAL AND COST-EFFICIENT FORM, COMMERCIAL-GRADE ALARM SYSTEMS CAN BE MADE VIRTUALLY IMMUNE TO SPOOFING ATTEMPTS. PERHAPS THE MOST SIGNIFICANT IMPROVEMENT IN INTRUSION PROTECTION WOULD RESULT FROM A COMBINATION OF TWO PRODUCTS DEVELOPED TO SERVE DIFFERENT MARKET DEMANDS. A DATA ENCRYPTION STANDARD (DES), ADOPTED BY THE U.S. NATIONAL BUREAU OF STANDARDS, HAS BEEN DEVELOPED IN RESPONSE TO THE NEED FOR SECURE DATA HANDLING IN ELECTRONIC FUNDS TRANSFER SYSTEMS AND COMPUTER-BASED DATA BANKS. CONCURRENTLY, NEW ALARM SYSTEMS CONTROLLED BY MICROPROCESSORS ARE COMING ONTO THE MARKET IN RESPONSE TO THE NEED TO REDUCE WIRING BY MULTIPLEXING TECHNIQUES. THESE MICROPROCESSOR-CONTROLLED SYSTEMS EASILY INTERFACE WITH DES CIRCUITRY TO PROTECT ALARM MESSAGES. THE DES IS STRONGLY RESISTANT TO SOPHISTICATED ATTACK. IT OPERATES ON DATA IN BLOCK FORM INSTEAD OF THE USUAL BIT-BY-BIT ENCIPHERMENT. A FIELD OF VARYING DATA CAN BE MIXED WITH THE STATIC ALARM DATA TO INTERACT WITH THE DES KEY AND PRODUCE CIPHERTEXT THAT COMPLETELY MASKS THE ALARM STATUS CONDITIONS. (AUTHOR ABSTRACT)