Concept for true random number generators

designrandom number

I have an idea. Lets say we have an unpowered TTL set-reset flip flop with both inputs tied to 5v(logic high). When we apply power to the flip flop, it goes into a quiescent state, so there is no telling what the output would be. Basically, we have a one bit random number generator.

Now for my question. Modern processors and microcontrollers have the ability to generate pseudo-random numbers. Of course, these aren't truly random. But if my flip flop scenario generates true-random numbers, then why don't designers use this concept, but with more flip flops?

Best Answer

They don't use that concept because, unfortunately, it doesn't work-- the start-up state of a FF won't be very random at all.

Quoting from "Cryptographic Hardware and Embedded Systems -- CHES 2003: 5th International Workshop Volume 5"

enter image description here

Making a truly random number generator is not easy.

Related Solutions

Electronic – arduino – Is Arduino ideal for making a HRNG (hardware random number generator)

I think you'll want to go down the path busz suggests. Search for the concept "diode noise". The PN junctions in diodes and transistors can produce close to perfect Gaussian white noise. Sampling that should be a source of entropy that's better than any environmental source.

The problem with most environmental/ambient data is the values just don't change that much over time: temperature, humidity, light and sound all have less than an order-of-magnitude of variability with really strong modes. An accelerometer to measure motion might be a good source of variability if mounted on a person, but you'd likely have to do a bit of signal processing to remove the normal modes of oscillation that are present in how humans move. An ambient light & sound source might have some pretty high variability if placed in an high-density urban space, but again I think there would be a lot of repetition. I still think the best source of entropy would be going down towards fundamental physical properties of materials like diode noise than going up in scale and looking at environmental factors capable of being read by a microcontroller.

Electronic – AVR Random Number Generator

How bad do you to use the XMega? If the crypto and random number generation are a big part of your project, Atmel's SecureAVR series has a hardware random number built in, and is designed for cryptographic applications.

Regardless, I doubt that you'll find a random seed source that has a good distribution. You'll want to run it through a pseudo random number generator a few times As long as you start with a different seed every time, this will give you a nice set of random numbers. An LGC is a quick and easy pseudo random generator:

static unsigned long Seed; 

/* Call before first use of NextVal */
unsigned long InitSeed()
{
   //Your code for random seed here

   // Correct distribution errors in seed
   NextVal();
   NextVal();
   NextVal();
   return NextVal();
}

 /* Linear Congruential Generator 
  * Constants from  
  * "Numerical Recipes in C" 
  * by way of 
   * <http://en.wikipedia.org/wiki/Linear_congruential_generator#LCGs_in_common_use>
   * Note: Secure implementations may want to get uncommon/new LCG values
  */
unsigned long NextVal()
{
  Seed=Seed*1664525L+1013904223L;
  return Seed;
}

Best Answer

Related Solutions

Electronic – arduino – Is Arduino ideal for making a HRNG (hardware random number generator)

Electronic – AVR Random Number Generator

Related Topic