An executing device for conducting playback is high during the playback of
contents. The executing device is equipped with a highly efficient
processor and reduces the processing load involved in verification by
using, for the verification, only a predetermined number of encrypted
units selected randomly from multiple encrypted units constituting
encrypted contents recorded on a DVD. In addition, the executing device
is capable of improving the accuracy of detecting unauthorized contents
by randomly selecting a predetermined number of encrypted units every
time the verification is performed.