On Tue, Jun 19, 2012 at 2:30 AM, coderman <coder...@gmail.com> wrote: > ... > as for stating that it should never "run dry", or fail to not return > bits as long as the instruction is working...
i was incorrect; developers should expect this instruction to infrequently encounter transitory failures requiring retry: """ The RDRAND instruction returns with the carry flag set (CF = 1) to indicate valid data is returned. It is recommended that software using the RDRAND instruction to get random numbers retry for a limited number of iterations while RDRAND returns CF=0 and complete when valid data is returned... This will deal with transitory underflows. A retry limit should be employed to prevent a hard failure in the RNG (expected to be extremely rare) leading to a busy loop in software. """ in "Intel Advanced Vector Extensions Programming Reference" at http://software.intel.com/file/36945 i would be very curious to know what the distribution of these single or consecutive failures (CF=0) look like on a busy system or long run benchmark, and particularly if/how environmental factors* affect failure rates. *CPU temperature, voltage regulation, what else? _______________________________________________ cryptography mailing list cryptography@randombit.net http://lists.randombit.net/mailman/listinfo/cryptography
