| 摘要 |
<p>In an electronic funds transfer system, in which a HOST transfers cash amounts between accounts which it maintains, as a result of transmission messages sent to it, a retailer (R) has a point of sale terminal (POST), and each potential customer (P) has a portable terminal (XATR), and a data storage and transfer card (DSTC), forming a XATR/DSTC sub-assembly which can be selectively coupled to the POST. The POST and XATR/DSTC have respective block-cipher encryption units (28, 11) with respective keys (KR, Kp), keyboards (24, 14) displays (20, 10), and electronic switches (S5 to 8, S1 to 4) operable under control from the keyboards. The system including the switches is operated to form a transmission message comprising (1) R's Business Number in clear, which identifies KR to H (2) transaction data TM1 encrypted under KR (3) Person's card number, which identifies Kp to H, encrypted under KR (4) and transaction data Tm2 encrypted under Kp first and KR second. HOST on receiving the message first decrypts it using KR, and then retrieves Kp and decrypts TM2 using Kp. HOST acts on the message if it finds TM1 and TM2 identical. Neither R nor P can validly change the information content represented by the other's TM2 or TM1, since neither knows the other's key.</p> |
