I didn't suggest hashing, I suggested forcing random state jumps of a pseudo-random sequence. Done at a rate comparable to (or even higher than) the clock rate, none of the sequential states of the shift register would be detectable, and any asymmetry or autocorrelations of the analog noise source would be obliterated. It's a nice way to clean up an analog noise generator, which usually have nasties.
John
Any pseudorandom generator is inherently limited by the number of states -- in 168 or so bits, an attacker can fully determine the state of said generator. It's nice that it's a simple linear feedback shift register -- real easy to solve for. Whatever processing goes after it might mix it up, but as a linear combination of few other states, that's apparently trivial...
The Mersenne Twister is claimed to be one of the best, although of course it's limited by the amount of state data it keeps. It's fairly bulky, so has a bit going for it.
Tim
its not being used for any cryptographic purpose. Attacks on the state of the generator are irrelevant.
I'm not an expert, but I understand that many of the obvious and commonly-used hardware methods of making noise, while they might cycle through the maximum length before repeating, have quite poor short-term spectral characteristics. Please do read the literature and choose an appropriate method, or use suitable whitening techniques. Especially since spectral purity seems to be important in this application...
Clifford Heath.
If an LFSR isn't "pure" enough for you, then simply pass the output of one through an encryption algorithm with a constant key.
Sure, this is probably the way to go. However, for prototyping, I would also like to explore the possibility of what happens when each source signal used for a single measurement is statistically independent of the signal used for another measurement.
Please do read
Of course, the literature will be important when attempting to work with this.
Of course, there are a number of "black-box" devices offered by manufacturers which can easily generate random numbers:
(1) True random number generator IC (RPG100):
(2) Random number generator module (R300A):
These can be simply placed into a system, and this is an attractive way to place random number functionality into the circuit. However, it is impossible to know the complete theory behind such devices.
Nicholas
IIRC LFSR are excellent in this regard. Much hardware falls down because its noise is a uniform distribution but this is not the case here.
Many years ago (80's) ETI did a project using an 11 stage LFSR as a white noise generator - I forget the chip used.
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