| 摘要 |
PROBLEM TO BE SOLVED: To accurately detect a prepaid card medium altered or forged by the copy of stored information. SOLUTION: When a prepaid card is set, a reading/writing device 1 detects the gradation distribution of bar code printing sites, and quantizes the detected information by different prescribed quantization systems, and decodes variable information (a) and (b) read from information areas A and B of the prepaid card by using quantized data Ra and Rb as cryptographic keys, and checks the validity/invalidity of decoding. When they are both decoded, it is judged that the prepaid card is normal, and when it is judged that at least one of them is not made correspond as the result of collation, it is judged that the prepaid card is abnormal and an illegal card. |
