Low cost encryption transponder

Abstract

Novel means of achieving increased security while still obtaining a low cost, manufacturable device are disclosed and claimed. The first mode of operation is the learn mode which provides means for initial checkout with no security. In the learn mode of operation, the interrogator and transponder may be switched to a predetermined error detection algorithm, i.e. CCITT(Start Mask, CCITT Mask), and certain information is programmed into the transponder memory. During programming, all the bits received from the interrogator are shifted through the preintialized CRC generator. In addition, once the transponder response is sent back to the interrogator, the response is also shifted through a preinitialized CRC generator within the interrogator(which could be a software implementation). Because neither the Cypher Key nor the Function Key are directly readable once programmed, an encryption must be performed to verify the proper Cypher Key and Function Key were programmed into the transponder's memory. In the second and encryption mode of operation, after a special Command/Address is transmitted, a Random Number (which may vary in length but which has a minimum length) is transmitted from the interrogator to the transponder which in turn generates the Signature by shifting the Random Number through the CRC Encryption Generator (initialized with the Cypher and Function Key). The Signature along with data, status and address are transmitted back to the interrogator which in the meantime has predetermined the awaited Signature using the same Cypher and Function Key. If the received Signature and calculated Signature are equal validation is positive and then the programmed data must be locked(especially the Cypher Key and Function Key) to protect them against reprogramming in the future.