DATA ALTERATION DETECTION SYSTEM

摘要

PURPOSE:To detect that data is altered by decoding data so that the numbers of bits '0' and '1' can be constant without fail and detecting that the numbers of bits '0' and '1' are changed. CONSTITUTION:When data is encoded so that a bit (k) among n-bits can stand at '1', combinations that n-bits are encoded come to nCk. It means combinations when k-bits are selected among n-bits. An optical card records data by generating holes, and it is difficult to fill the holes. Therefore if data in said card is altered, the number of holes is larger than (k). As a result the fact of alteration and the altered part in the data can easily be detected.