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TrueRNG – Hardware Random Number Generator


The True RNG provides a steady stream of random numbers through a USB CDC serial port. The random number data can then be used to fill the entropy pool of an operating system, or used directly in a custom application. The TrueRNG is ideal for Security related applications (SSH, SSL, GPG), Gaming (dice,cards), Statistical Sampling and simulations.

The Problem

An increasing number of computer software packages rely heavily on the availability of a source of random numbers. In some cases, these software packages require a large amount of random numbers for things such as SSH, SSL, GPG, etc. In the Linux operating system, the kernel keeps a small entropy pool (4 kiloBytes) that is used by applications. If this pool is depleted then the kernel will block causing a delay until the kernel can provide the requested random numbers. The Linux kernel can only slowly replenish the pool using keyboard timings, mouse movements, interrupt, and IDE timings because of the lack of a high-speed source of quality random numbers.

The Solution

A true hardware random number generator (HWRNG) will provide a high-speed source of entropy to the Linux kernel which minimizes blocking and delays while maintaining security. Most of the HWRNG that are available offer high security at a high cost. If you are a bank, financial institution, or run a huge e-commerce site, it may be worthwhile to invest several thousand dollars in a HWRNG, but this this not economical for most individuals and small enterprises. The TrueRNG is a low-cost USB Hardware Random Number Generator that provides more than 350 kilobits/second of true random numbers. This will refill the Linux entropy pool almost instantly and eliminate unnecessary blocking / delays.

Theory of Operation

The TrueRNG Hardware Random Number Generator uses the avalanche effect in a semiconductor junction to generate true random numbers. The avalanche effect has long been used for generation of random number / noise and is a time-tested and proven random noise source. The semiconductor junction is biased to 12 volts using a boost voltage regulator (since USB only supplies 5V), amplified, then digitized at high-speed. The digitized data is selected and whitened internal to the TrueRNG and sent over the USB port with more than 350 kilobits/second of throughput.

Without TrueRNG

Normal entropy level on an idle Linux machine, without TrueRNG This is what the normal entropy level looks like on a light use Linux server, without TrueRNG.

With TrueRNG

Entropy pool filled by TrueRNG + rng-tools on Linux Having the entropy pool filled on a Linux machine using a TrueRNG with the rng-tools package.  Notice the immediate gain in available entropy.

Entropy recovery rate on a normal Linux system Entropy recovery rate on a light use Linux server without TrueRNG while seeding an encryption job.
Instant entropy recovery with TrueRNG + rng-tools on Linux.  Entropy pool was artificially emptied to show recovery rate, Normal tasks such as SSH/Encryption didn't create enough visible notice to graph. Instant entropy recovery with TrueRNG + rng-tools on Linux. Entropy pool was artificially emptied to show recovery rate, Normal tasks such as SSH/Encryption didn’t create enough visible notice to graph.  This was with a 1s sampling resolution, but the recovery was much faster than that.


  • High Output Speed: >350 kilobits / second
  • Internal Whitening
  • Native Windows (XP/8/8.1) and Linux Support (CDC Virtual Serial Port)
  • Passes all the industry standard tests (Dieharder, ENT, Rngtest, etc.)
  • Low power <= 20 mA
  • Compatible with embedded environments such as Beaglebone, Raspberry PI, and UDOO


  • Security (SSH,SSL, GPG, etc).
  • Gaming Servers (Lottery, Dice Roller, Coin Flipper, Playing Cards)
  • Statistical Sampling
  • Simulations
  • Global Consciousness Project

Bitmap Analysis

Showing the random stream as a bitmap shows no visible patterns like a pseudo random number generator will

Character Distribution of 3 MB file


A Character distribution plot of a 3 MB stream captures shows that the min/max of character occurrences are between 0.38% and 0.40%

100 Mb File Entropy Analysis

Linux command: ent random.dat

(Results may vary between runs)

Entropy = 7.999998 bits per byte.

Optimum compression would reduce the size
 of this 106760304 byte file by 0 percent.

Chi square distribution for 106760304 samples is 260.12, and randomly
would exceed this value 50.00 percent of the times. 

Arithmetic mean value of data bytes is 127.4937 (127.5 = random). 
Monte Carlo value for Pi is 3.141909600 (error 0.01 percent). 
Serial correlation coefficient is 0.000026 (totally uncorrelated = 0.0).
* File captured in Linux using dd, entropy analysis done by package ent

What Not To Do

There have been some programmers who have developed software and techniques to quickly fill the entropy pool with pseudorandom numbers. Although this may solve the blocking issue, it unacceptably degrades security by causing applications to use potentially deducible random numbers. This may allow the “bad guy” to gain access to your protected information.


  • Linux — The USB Driver is included in most Linux Distributions. There is currently application support under rng-tools for Linux to fill the kernel’s entropy pool with data from TrueRNG.
  • Windows — We provide a signed driver which allows the device to be used in windows with custom applications.
  • OSX — Support is minimal, driver is included in OSX but a custom application or port of rngd would be needed to fill the system’s entropy pool
  • USB 2.0

Tools | App Notes | Code Samples

Documentation and Support