It is very hard to find system that has CPU powerful enough for doing any kind of cryptography while not having any usable entropy source, there is always somet

It is very hard to find system that has CPU powerful enough for doing any kind of cryptography while not having any usable entropy source, there is always something non-deterministic that you can measure (hash contents of memory at start of boot, time accesses to EEPROM, ADC noise, timing of events, the actual data that your system processes...).