Re: Hardware-random-bits interface
At 3:17 PM 11/15/95, David K. Merriman wrote:
At 02:31 PM 11/14/95 -0800, you wrote:
I've been thinking about physically random bits recently, so I'd like to offer a simple, easily implementable interface to a source of such bits, along with a design sketch using a common radio receiver chip as the noise source.
It sounds like a fairly decent idea, _as long as you shield the bejeebers (technical term :-) out of it_. Otherwise, anybody with a signal generator could skew your numbers however they saw fit: any component lead can act as an antenna, no matter now small that lead is.
But if you "shield the bejeebers out of it," then all the radio receiver generates is whatever signal manages to sneak through--which, ironically, would make it _easier_ for an outside attacker to drive--and some amount of internal receiver/amplifier noise, such as the Johnson noise talked about here. (Every receiver has an "equivalent noise temperature," recall.) And if one is left with only internal noise, why not simply use a nice clean source like a Zener diode? --Tim May Views here are not the views of my Internet Service Provider or Government. ---------:---------:---------:---------:---------:---------:---------:---- Timothy C. May | Crypto Anarchy: encryption, digital money, tcmay@got.net 408-728-0152 | anonymous networks, digital pseudonyms, zero Corralitos, CA | knowledge, reputations, information markets, Higher Power: 2^756839 | black markets, collapse of governments. "National borders are just speed bumps on the information superhighway."
Timothy C. May writes:
But if you "shield the bejeebers out of it," then all the radio receiver generates is whatever signal manages to sneak through--which, ironically, would make it _easier_ for an outside attacker to drive--and some amount of internal receiver/amplifier noise, such as the Johnson noise talked about here. (Every receiver has an "equivalent noise temperature," recall.)
And if one is left with only internal noise, why not simply use a nice clean source like a Zener diode?
Quite solidly agreed. Internal noise beats external noise, and there is no point in using a radio receiver when what you want is internal noise. .pm
And if one is left with only internal noise, why not simply use a nice clean source like a Zener diode?
Quite solidly agreed. Internal noise beats external noise, and there is no point in using a radio receiver when what you want is internal noise.
It may have been misleading to refer to a radio receiver chip: the noise generated by the chip will be entirely internal. It doesn't depend on any external signal "sneaking in"; the noise comes from the effective resistance of the first amplifier stage. Nothing is being "received", in some sense; it's just a big hunk 'o gain. A Zener diode would be fine, but the design is a bit more complex, especially for wide bandwidths---you need to mess with biasing voltages, speedy op-amps, interface to CMOS, and all that jazz. You'd need external power (or a DC-DC converter). I wanted a super-simple design that people could just plonk down on a PC board. Two chips and some bypass capacitors. Peter
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