John Larkin wrote:


There are lots of digital chips, including some Intel processors, that
have cryptographic-grade random number generators on-chip.

One of the main features of the cryptography grade RNG is the self test
subsystem that continuously monitors that 1) RNG is in the good health
2) RNG had not been tampered with. If there is no such subsystem, the
RNG is consumer or amateur grade, not cryptography grade.

One common
technique is to use a bunch of asynchronous ring oscillators to
scramble pseudo-random shift registers. Lots of references on the web.

Just to remember that a deterministic function over the random number
don't add to the randomness. So the output hash should not generate more
of the scrambled bits then the true entropy of the random source.

I have a technique that uses an i/o pin as a noisy/chaotic RC ramp
generator. Fun, but essentially useless.

I used to measure the timing of self charge/discharge of the uncommited
MCU input to set up the seed for the PRNG for the rolling code.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com