Mistake number 1: The cryptographic algorithm is a proprietary 40-bit cipher (
Schneier).
The encryption algorithm used in the TI DST tags is an unpublished, proprietary cipher that uses a 40-bit key. The algorithm was designed in the early 1990's by engineers at Texas Intruments, but is still being deploying in current systems. By today's standards, a 40-bit key is unacceptably short: advances in computing power have made such keys succeptable to brute-force key guessing attacks. Therefore, the actual security of the DST system rests with the secrecy of the proprietary algorithm used in the tags.