{"id":8508,"date":"2013-06-07T22:06:40","date_gmt":"2013-06-08T02:06:40","guid":{"rendered":"http:\/\/scruss.com\/blog\/?p=8508"},"modified":"2024-05-17T19:43:30","modified_gmt":"2024-05-17T23:43:30","slug":"well-that-was-unexpected-the-raspberry-pis-hardware-random-number-generator","status":"publish","type":"post","link":"https:\/\/scruss.com\/blog\/2013\/06\/07\/well-that-was-unexpected-the-raspberry-pis-hardware-random-number-generator\/","title":{"rendered":"\u201cWell, that was unexpected\u00a0\u2026\u201d\u009d: The Raspberry Pi’s Hardware Random Number Generator"},"content":{"rendered":"

Hey! This is a bit old! Things may have changed and I haven’t necessarily fixed them.<\/strong><\/span><\/p>\n

Most computers can’t create true random numbers. They use a formula which makes a very long stream of pseudo-random<\/a> numbers, but real randomness comes from thermal noise in analogue components. The Raspberry Pi has such a circuit in its SoC, as it helps making the seed data for secure transactions. It was only recently<\/a> that a driver for this circuit was supplied. To enable it (on Raspbian):<\/del> I think the module is enabled by default now for the different versions of the SoC.<\/p>\n

    \n
  1. Make sure your system is up to date with
    sudo apt-get update<\/span>
    sudo apt -y upgrade<\/span><\/li>\n
  2. Install the module:<\/del>
    sudo modprobe bcm2708-rng<\/span><\/del><\/li>\n
  3. To make sure it’s always loaded, add the following line to \/etc\/modules (editing as root):<\/del>
    bcm2708-rng<\/span><\/del><\/li>\n
  4. For some RNG-related stuff, install rng-tools:
    sudo apt-get install rng-tools<\/code><\/span><\/li>\n<\/ol>\n

    The \/dev\/hwrng device should now be available, but can only be read by the root user.<\/p>\n

    Nico <\/a>pointed out that you also need to:<\/p>\n

      \n
    1. Edit \/etc\/default\/rng-tools, and remove the # at the start of the line
      HRNGDEVICE=\/dev\/hwrng<\/span><\/li>\n
    2. Restart rng-tools with
      sudo service rng-tools restart<\/span><\/li>\n<\/ol>\n

      What random looks like<\/h2>\n

      \"random20130606210642\"\"random20130606210630\"<\/p>\n

      Random data look pretty dull. Here are random RGB values made with:<\/p>\n

      sudo cat \/dev\/hwrng\u00a0 | rawtoppm -rgb 256 256 | pnmtopng > random$(date +%Y%m%d%H%M%S).png<\/span><\/pre>\n
      (you’ll need to install the netpbm toolkit to do this.)<\/p>\n
      What random sounds like<\/h2>\n
      Two short WAV samples of, well, noise<\/em>:<\/p>\n