Abstract: A data processing system method and program are disclosed for limiting a book reading program for softcopy books, to be capable of reading only softcopy books published by a selected publisher. The method includes the step of generating with a data processor, a customized polynomial expression to be associated with a selected softcopy book publisher. The method continues by merging with a data processor, the customized polynomial expression with a first shell program, forming a stamping tool program for stamping a key value onto a softcopy book published by the selected publisher. The key value results from the polynomial, using the product of an integer times a hash value of the publisher's identity, as the value of the independent variable. Then the method continues by generating with a data processor, a customized inverse polynomial expression to the customized polynomial expression, to be associated with the selected softcopy book publisher.