Introduction:

This project permits the creation of RNG generators based on nuclear decay, interfacing a Geiger counter with audio exit to a MC. It's an evolution of my previous project you find here:

NuclearRNG

Theoretically it permits the conversion of any Geiger with audio feedback to an RNG in fact, differently from its predecessor, this appliance doesn't use exotic hardware but standard Geiger counters. A Raspberry Pico W is employed as microcontroller platform.

Hardware:

• A Raspberry Pico (RP2040) is employed as microcontroller platform;
• An OpAmp based circuit raises the audio signal level of the Geiger "pulses" captured using the audio jack:

Algorithm and Features:

• Two thread are in execution : one for Geiger pulses sampling, another to provide RNGs via socket;
• In the main loop, a register is cyclically increased from 0 to 15, when it reaches 15 is reset to 0. When a particle is detected, the current value is stored in queue ready to be deployed on request;
• Default queue length is 10240 bytes.

Protocol:

• When a socket connects to the appliance via WIFI, a message with the following format is given as response:

ready\n

where '\n' is "newline" character

• You require a RN sending the message:

req

• Then you'll receive a RN in an answer with the following format:

<random_number><separator><generator_number><separator><available_numbers><newline>

where:

• the first field is a random number in the range 0-15 or the number 16 if an error was generated or no number is available yet;
• the chosen range is 0-15 is convenient because the union of two generated random numbers represent a full random byte;
• the second field represent the original value of the register incremented in loop to extract the random number using module operator of integer division by the specific range (0-15), it's provided as safeguard to verify that the loop cover every possible value for a given event frequency;
• the separator is the character ':';
• then a field with an integer telling you how many RNs are available in the appliance buffer, ready to be requested;
• a newline ( '\n' ) ends the message.

• Example:

52:3473460:1384\n

• You can terminate the connection with the command:

end

• At the moment, concurrent access is not supported (aka I don't need it for now), so, closing the connection also permits different client to connect;

Dependencies:

• Raspberry Pi Pico SDK
• Cmake

Detailed instruction for dependencies installation are available on Raspberry website.

Configuration:

• Before compiling, is required to edit wifi_credential.hpp inserting Wifi SSID and password.

Installation and Use:

• compile the program as follow (set -DPICO_SDK_PATH using real pico-sdk path):

  cd build
  make -f makefile.srv all

• deploy the generated binary file named:

geiger_gen2.uf2 

putting the Pico in "deploy mode" pushing the white button before connecting USB cable and releasing the same button a second after the connection.

• A trivial Python client example is present in "test" directory in the present software distribution.
• The number can be requested from any program able to create Berkeley sockets using the described protocol.

Tests:

• 'test' directory contains test results and tools to perform the tests themselves;
• Python3 and some dependencies are required;
• Ent suit is required:

apt-get install ent

• A makefile is present, to perform the test use the following:

make -f makefile clean all

• A file with 250'000 and RNs and another file with 10'000 RNs extracted from the bigger one are provided.

Results:

• Preliminary tests gave good results:

• Ent suite:

Entropy = 7.998604 bits per byte.

Optimum compression would reduce the size
of this 125000 byte file by 0 percent.

Chi square distribution for 125000 samples is 241.57, and randomly
would exceed this value 71.76 percent of the times.

Arithmetic mean value of data bytes is 127.6767 (127.5 = random).
Monte Carlo value for Pi is 3.135794173 (error 0.18 percent).
Serial correlation coefficient is 0.002606 (totally uncorrelated = 0.0).

Important Note:

• Not all Geiger counters could be suitable for this application: some cheap devices could produce a programmed audio feedback, a software routine written so the device sound "good". So, if you looking for a device to make your RNG, do not purchase blindlyr: do your research;

• Be sure alarm and other audio feedbacks other than the pulses are disabled or they will be translate in a sequence of non-random numbers.