Access protected chip card, data carrier

摘要

Security relevant operations are carried out with false secret data from which the genuine secret data cannot be derived without addition of further secret information. A function is determined with which the genuine secret data are falsified, e.g. with an EXOR operation of the secret data with a random number. The data is protected using an encryption operation whereby the data are falsified where possible by EXOR operation with a random number (Z). The falsification is possible with all functions (f) which have a linear behavior in EXOR operation. In the case of non- linear functions (g), the unfalsified data must be used. Hence before the use of the nonlinear function on the data, the falsification of the data by an EXOR operation is compensated by a function value (f(Z)). Nonlinear functions can only be used on unfalsified data, but nonlinear functions are difficult to intercept .