Messages in this thread | | | From | Robin Getz <> | Subject | Re: IRQF_SAMPLE_RANDOM question... | Date | Thu, 9 Apr 2009 00:24:42 -0400 |
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On Wed 8 Apr 2009 19:16, Chris Friesen pondered: > Gilles Espinasse wrote: > > > Readme say : > > "This daemon attempts to collect real randomness from fluctuations of > > high-frequency clocks on a PC's mainboard. The basic assumption is that > > mainboard and CPU are clocked by two separate physical clocks." > > > How large is this basic assumption true, on x86, on other arch? > > Isn't the cpu frequency normally a phase-locked multiple of the > mainboard bus frequency?
Yes - typically they are the same.
However - I have tested clrngd out on a Blackfin, and found it gave an excessively high load - but it did give ok results. 77% of the time (659/848 times) it provided results that passed it's built in FIPS test. It did die a few times (if the FIPS tests fails 5 times in a row clrngd aborts).
I was going to write my own (based on a similar architecture) - but use the RTC clock and the main clock - since those actually would be different physical crystals - and the accuracy of low cost 32kHz crystals is crappy (typically measureable with a high enough core clock).
But I think delays of cache misses/flushes will dominate things anyway - which is why clrngd works today on systems which are using the same clock source. (but since it will be RTC interrupt driven, vs while(1){} like clrngd - the load will be much lower).
-Robin
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