US Patent 7984320 Silent time tampering detection

Computers and other electronic devices typically include a timing operation such as a clock in an operating system. It is anticipated that hackers may tamper with this clock. This tampering might be especially advantage in the context of systems which provide for rental of audio and video content, such as movies. Tampering with the system clock on the playing device would allow an extension of the rental period to the detriment of the provider of the rental content. Hence the present method is directed to detecting clock modifications both in terms of time shifting and clock rate tampering. This detection is done using digital signal processing.