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The Kidekin TRNG Hardware Random Number Generator

Yesterday, I received my Kidekin TRNG hardware random number generator. I was eager to purchase this, because on the Tindie website, the first 2 people to purchase the RNG would get $50 off, making the device $30 total. I quickly ordered one. Hilariously enough, I received a letter from the supplier that I was their first customer! Hah!

Image of the Kidekin Digital TRNG

Upon opening the package, I noticed the size of the TRNG. It's roughly 10.5 cm from end-to-end which makes it somewhat awkward for a device sitting in your USB port on your laptop. It would work fine sitting in the back of a desktop or server, out of the way, but on my Thinkpad T61, it's a bit large to be sitting there 24/7 feeding my kernel CSPRNG.

Plugging the device in, the kernel actually sees two USB devices, not just one, and sets them up as /dev/ttyUSB0 and /dev/ttyUSB1. Curious. Downloading the software ZIP file from their webpage, and looking through it, the following UDEV rules are provided:


$ cat /etc/udev/rules.d/98-kidekin.rules 
#SYMLINK+= method works on more systems, if it does not on your system, please switch to the NAME= method.

#disable the unused port.
#SUBSYSTEM=="tty", ATTRS{interface}=="kidekin_trng", ATTRS{bInterfaceNumber}=="00", NAME="kidekin_dont_use", MODE="0000", ENV{ID_MM_DEVICE_IGNORE}="1", ENV{ID_MM_CANDIDATE}="0"
SUBSYSTEM=="tty", ATTRS{interface}=="kidekin_trng", ATTRS{bInterfaceNumber}=="00", SYMLINK+="kidekin_dont_use", MODE="0000", ENV{ID_MM_DEVICE_IGNORE}="1", ENV{ID_MM_CANDIDATE}="0"

#connect kidekin TRNG to /dev/random
#SUBSYSTEM=="tty", ATTRS{interface}=="kidekin_trng", ATTRS{bInterfaceNumber}=="01", NAME="kidekin_trng", MODE="0777", RUN+="/bin/stty raw -echo -crtscts -F /dev/kidekin_trng speed 3000000", ENV{ID_MM_DEVICE_IGNORE}="1", ENV{ID_MM_CANDIDATE}="0"
SUBSYSTEM=="tty", ATTRS{interface}=="kidekin_trng", ATTRS{bInterfaceNumber}=="01", SYMLINK+="kidekin_trng", MODE="0777", RUN+="/bin/stty raw -echo -crtscts -F /dev/kidekin_trng speed 3000000", ENV{ID_MM_DEVICE_IGNORE}="1", ENV{ID_MM_CANDIDATE}="0"
SUBSYSTEM=="tty", ATTRS{interface}=="kidekin_trng", ATTRS{bInterfaceNumber}=="01", RUN+="/etc/init.d/rng-tools restart"

This is a bit assuming, and a bit overdoing it IMO, so I simplified it, and setup the following:

SUBSYSTEM=="tty", ATTRS{interface}=="kidekin_trng", ATTRS{bInterfaceNumber}=="01", SYMLINK+="kidekin", MODE="0777", RUN+="/bin/stty raw -echo -crtscts -F /dev/kidekin speed 3000000", ENV{ID_MM_DEVICE_IGNORE}="1", ENV{ID_MM_CANDIDATE}="0"

This avoids setting up a "do not use" symlink for the unnecessary USB device, and changes the symlink of the usable USB device to /dev/kidekin. This also doesn't restart rngd(8), as I'll administer that on my own. At this point, I am ready for testing.

First and foremost, I wanted to test its throughput:

$ dd if=/dev/kidekin count=1G | pv -a > /dev/null
[ 282KiB/s]

The device held stable at 282 KBps or roughly 2.2 Mbps. This is 75.2 KBps per dollar for my $30 purchase. Not bad.

The Kidekin is based on astable free running oscillators, or multivibrators. Unfortunately, a security proof does not accompany the device. So, while this may hold up to the suite of randomness tests, the output may not be cryptographically secure, and could also potentially be backdoored, as verifying the hardware is not easily doable. So, let's see if it at least holds up to the randomness tests. I created a 256 MB file, and ran the standard suites of tests:

$ dd if=/dev/kidekin of=entropy.kidekin bs=1M count=256 iflag=fullblock
256+0 records in
256+0 records out
268435456 bytes (268 MB) copied, 928.326 s, 289 kB/s

At this point, I can start my testing. First, let's quantify the amount of entropy per byte, as well as some basic tests with ent(1):

$ ent entropy.kidekin
Entropy = 7.999999 bits per byte.

Optimum compression would reduce the size
of this 268435456 byte file by 0 percent.

Chi square distribution for 268435456 samples is 248.92, and randomly
would exceed this value 59.56 percent of the times.

Arithmetic mean value of data bytes is 127.4924 (127.5 = random).
Monte Carlo value for Pi is 3.141825693 (error 0.01 percent).
Serial correlation coefficient is -0.000003 (totally uncorrelated = 0.0).

Everything good so far. How about the FIPS 140-2 tests for randomness:

$ rngtest < entropy.kidekin
rngtest 2-unofficial-mt.14
Copyright (c) 2004 by Henrique de Moraes Holschuh
This is free software; see the source for copying conditions.  There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

rngtest: starting FIPS tests...
rngtest: entropy source exhausted!
rngtest: bits received from input: 2147483648
rngtest: FIPS 140-2 successes: 107292
rngtest: FIPS 140-2 failures: 82
rngtest: FIPS 140-2(2001-10-10) Monobit: 14
rngtest: FIPS 140-2(2001-10-10) Poker: 13
rngtest: FIPS 140-2(2001-10-10) Runs: 26
rngtest: FIPS 140-2(2001-10-10) Long run: 30
rngtest: FIPS 140-2(2001-10-10) Continuous run: 0
rngtest: input channel speed: (min=317.891; avg=7386.982; max=19073.486)Mibits/s
rngtest: FIPS tests speed: (min=6.563; avg=109.376; max=114.901)Mibits/s
rngtest: Program run time: 19261018 microseconds
$ echo $?
1

Again, so far so good. Some failures are expected with random input of this size. 82 failures versus 107292 successes is right on par with the tests. Now the Dieharder battery of tests:

$ dieharder -a < entropy.kidekin
#=============================================================================#
#            dieharder version 3.31.1 Copyright 2003 Robert G. Brown          #
#=============================================================================#
   rng_name    |rands/second|   Seed   |
        mt19937|  8.99e+07  | 722892634|
#=============================================================================#
        test_name   |ntup| tsamples |psamples|  p-value |Assessment
#=============================================================================#
   diehard_birthdays|   0|       100|     100|0.87388974|  PASSED  
      diehard_operm5|   0|   1000000|     100|0.25081726|  PASSED  
  diehard_rank_32x32|   0|     40000|     100|0.80329585|  PASSED  
    diehard_rank_6x8|   0|    100000|     100|0.87234234|  PASSED  
   diehard_bitstream|   0|   2097152|     100|0.27873738|  PASSED  
        diehard_opso|   0|   2097152|     100|0.05958924|  PASSED  
        diehard_oqso|   0|   2097152|     100|0.10540020|  PASSED  
         diehard_dna|   0|   2097152|     100|0.30006047|  PASSED  
diehard_count_1s_str|   0|    256000|     100|0.43809130|  PASSED  
diehard_count_1s_byt|   0|    256000|     100|0.29758303|  PASSED  
 diehard_parking_lot|   0|     12000|     100|0.78081639|  PASSED  
    diehard_2dsphere|   2|      8000|     100|0.58294587|  PASSED  
    diehard_3dsphere|   3|      4000|     100|0.04012616|  PASSED  
     diehard_squeeze|   0|    100000|     100|0.97651988|  PASSED  
        diehard_sums|   0|       100|     100|0.01875349|  PASSED  
        diehard_runs|   0|    100000|     100|0.17566659|  PASSED  
        diehard_runs|   0|    100000|     100|0.78887310|  PASSED  
       diehard_craps|   0|    200000|     100|0.16369886|  PASSED  
       diehard_craps|   0|    200000|     100|0.42148915|  PASSED  
 marsaglia_tsang_gcd|   0|  10000000|     100|0.27534860|  PASSED  
 marsaglia_tsang_gcd|   0|  10000000|     100|0.45190499|  PASSED  
         sts_monobit|   1|    100000|     100|0.88204376|  PASSED  
            sts_runs|   2|    100000|     100|0.15277754|  PASSED  
          sts_serial|   1|    100000|     100|0.71489026|  PASSED  
          sts_serial|   2|    100000|     100|0.85005457|  PASSED  
          sts_serial|   3|    100000|     100|0.77631916|  PASSED  
          sts_serial|   3|    100000|     100|0.81111751|  PASSED  
          sts_serial|   4|    100000|     100|0.72512842|  PASSED  
          sts_serial|   4|    100000|     100|0.68758000|  PASSED  
          sts_serial|   5|    100000|     100|0.69083583|  PASSED  
          sts_serial|   5|    100000|     100|0.09706031|  PASSED  
          sts_serial|   6|    100000|     100|0.52758972|  PASSED  
          sts_serial|   6|    100000|     100|0.27970465|  PASSED  
          sts_serial|   7|    100000|     100|0.07925569|  PASSED  
          sts_serial|   7|    100000|     100|0.25874891|  PASSED  
          sts_serial|   8|    100000|     100|0.33647659|  PASSED  
          sts_serial|   8|    100000|     100|0.80952471|  PASSED  
          sts_serial|   9|    100000|     100|0.99948911|   WEAK   
          sts_serial|   9|    100000|     100|0.32461849|  PASSED  
          sts_serial|  10|    100000|     100|0.69360795|  PASSED  
          sts_serial|  10|    100000|     100|0.96022345|  PASSED  
          sts_serial|  11|    100000|     100|0.91349333|  PASSED  
          sts_serial|  11|    100000|     100|0.95918606|  PASSED  
          sts_serial|  12|    100000|     100|0.69821905|  PASSED  
          sts_serial|  12|    100000|     100|0.57652285|  PASSED  
          sts_serial|  13|    100000|     100|0.28393582|  PASSED  
          sts_serial|  13|    100000|     100|0.45849491|  PASSED  
          sts_serial|  14|    100000|     100|0.30832853|  PASSED  
          sts_serial|  14|    100000|     100|0.89099315|  PASSED  
          sts_serial|  15|    100000|     100|0.87022105|  PASSED  
          sts_serial|  15|    100000|     100|0.06938123|  PASSED  
          sts_serial|  16|    100000|     100|0.79568629|  PASSED  
          sts_serial|  16|    100000|     100|0.53218489|  PASSED  
         rgb_bitdist|   1|    100000|     100|0.38552808|  PASSED  
         rgb_bitdist|   2|    100000|     100|0.79403454|  PASSED  
         rgb_bitdist|   3|    100000|     100|0.66811643|  PASSED  
         rgb_bitdist|   4|    100000|     100|0.84954470|  PASSED  
         rgb_bitdist|   5|    100000|     100|0.90198903|  PASSED  
         rgb_bitdist|   6|    100000|     100|0.98808244|  PASSED  
         rgb_bitdist|   7|    100000|     100|0.25730860|  PASSED  
         rgb_bitdist|   8|    100000|     100|0.43237015|  PASSED  
         rgb_bitdist|   9|    100000|     100|0.90916135|  PASSED  
         rgb_bitdist|  10|    100000|     100|0.81131338|  PASSED  
         rgb_bitdist|  11|    100000|     100|0.31361128|  PASSED  
         rgb_bitdist|  12|    100000|     100|0.40786889|  PASSED  
rgb_minimum_distance|   2|     10000|    1000|0.03358258|  PASSED  
rgb_minimum_distance|   3|     10000|    1000|0.99298827|  PASSED  
rgb_minimum_distance|   4|     10000|    1000|0.47721533|  PASSED  
rgb_minimum_distance|   5|     10000|    1000|0.86641982|  PASSED  
    rgb_permutations|   2|    100000|     100|0.10084049|  PASSED  
    rgb_permutations|   3|    100000|     100|0.99560585|   WEAK   
    rgb_permutations|   4|    100000|     100|0.42217190|  PASSED  
    rgb_permutations|   5|    100000|     100|0.95466090|  PASSED  
      rgb_lagged_sum|   0|   1000000|     100|0.64120688|  PASSED  
      rgb_lagged_sum|   1|   1000000|     100|0.22106106|  PASSED  
      rgb_lagged_sum|   2|   1000000|     100|0.41244281|  PASSED  
      rgb_lagged_sum|   3|   1000000|     100|0.98880097|  PASSED  
      rgb_lagged_sum|   4|   1000000|     100|0.78380177|  PASSED  
      rgb_lagged_sum|   5|   1000000|     100|0.25533777|  PASSED  
      rgb_lagged_sum|   6|   1000000|     100|0.78150371|  PASSED  
      rgb_lagged_sum|   7|   1000000|     100|0.53903267|  PASSED  
      rgb_lagged_sum|   8|   1000000|     100|0.04436257|  PASSED  
      rgb_lagged_sum|   9|   1000000|     100|0.77174302|  PASSED  
      rgb_lagged_sum|  10|   1000000|     100|0.54862612|  PASSED  
      rgb_lagged_sum|  11|   1000000|     100|0.48691334|  PASSED  
      rgb_lagged_sum|  12|   1000000|     100|0.06308057|  PASSED  
      rgb_lagged_sum|  13|   1000000|     100|0.42530804|  PASSED  
      rgb_lagged_sum|  14|   1000000|     100|0.86907366|  PASSED  
      rgb_lagged_sum|  15|   1000000|     100|0.66262930|  PASSED  
      rgb_lagged_sum|  16|   1000000|     100|0.85485044|  PASSED  
      rgb_lagged_sum|  17|   1000000|     100|0.39817394|  PASSED  
      rgb_lagged_sum|  18|   1000000|     100|0.90608610|  PASSED  
      rgb_lagged_sum|  19|   1000000|     100|0.94996515|  PASSED  
      rgb_lagged_sum|  20|   1000000|     100|0.78715690|  PASSED  
      rgb_lagged_sum|  21|   1000000|     100|0.93364519|  PASSED  
      rgb_lagged_sum|  22|   1000000|     100|0.84438533|  PASSED  
      rgb_lagged_sum|  23|   1000000|     100|0.77439531|  PASSED  
      rgb_lagged_sum|  24|   1000000|     100|0.12530311|  PASSED  
      rgb_lagged_sum|  25|   1000000|     100|0.79035917|  PASSED  
      rgb_lagged_sum|  26|   1000000|     100|0.93286961|  PASSED  
      rgb_lagged_sum|  27|   1000000|     100|0.32567247|  PASSED  
      rgb_lagged_sum|  28|   1000000|     100|0.39563718|  PASSED  
      rgb_lagged_sum|  29|   1000000|     100|0.15628693|  PASSED  
      rgb_lagged_sum|  30|   1000000|     100|0.69368810|  PASSED  
      rgb_lagged_sum|  31|   1000000|     100|0.00197963|   WEAK   
      rgb_lagged_sum|  32|   1000000|     100|0.23325783|  PASSED  
     rgb_kstest_test|   0|     10000|    1000|0.18940877|  PASSED  
     dab_bytedistrib|   0|  51200000|       1|0.57007834|  PASSED  
             dab_dct| 256|     50000|       1|0.76567665|  PASSED  
Preparing to run test 207.  ntuple = 0
        dab_filltree|  32|  15000000|       1|0.60537852|  PASSED  
        dab_filltree|  32|  15000000|       1|0.78894908|  PASSED  
Preparing to run test 208.  ntuple = 0
       dab_filltree2|   0|   5000000|       1|0.11775507|  PASSED  
       dab_filltree2|   1|   5000000|       1|0.34799105|  PASSED  
Preparing to run test 209.  ntuple = 0
        dab_monobit2|  12|  65000000|       1|0.69182598|  PASSED  

Finally, a visual check on the data, even though it's safe to assume that it's "true random" given the previous testing:

$ dd if=white.bmp of=entropy.kidekin bs=1 count=54 conv=notrunc
54+0 records in
54+0 records out
54 bytes (54 B) copied, 0.000547208 s, 98.7 kB/s
$ gimp entropy.kidekin # convert to grayscale, export as "entropy.png"
$ optipng entropy.png
** Processing: entropy.png
512x512 pixels, 8 bits/pixel, grayscale
Input IDAT size = 250107 bytes
Input file size = 250564 bytes

Trying:
  zc = 9  zm = 8  zs = 0  f = 0		IDAT size = 215319
  zc = 9  zm = 8  zs = 1  f = 0		IDAT size = 214467
  zc = 1  zm = 8  zs = 2  f = 0		IDAT size = 214467
  zc = 9  zm = 8  zs = 3  f = 0		IDAT size = 214467
                               
Selecting parameters:
  zc = 1  zm = 8  zs = 2  f = 0		IDAT size = 214467

Output IDAT size = 214467 bytes (35640 bytes decrease)
Output file size = 214564 bytes (36000 bytes = 14.37% decrease)

And the result is:

RNG visual output of the Kidekin TRNG

My conclusion of the Kidekin TRNG is positive. I love the throughput of the device, loved the price, and aside from the UDEV rule, it is plug-and-play. Unfortunately, the TRNG is a bit on the big side for a physical device, and because it doesn't come with a security proof, and the hardware design is closed, I would be skeptical to trust it for your random numbers directly. Instead, I would recommend adding it the Linux kernel's CSPRNG, and rely on /dev/urandom instead. This is trivial with rngd(8). But, overall, I am very pleased with the device, and which I had actually purchased a second one.

{ 9 } Comments

  1. Kidekin | June 21, 2015 at 4:53 am | Permalink

    Hi,
    Thanks for the review, glad you like it 🙂

    About "The Kidekin is based on astable free running oscillators, or multivibrators"
    I guess you have read that on wikipedia. I don't know why they think so. I had originally described it as "array of register less LFSR oscillators" and I still think that the clearest description. I added a little schematic to the Tindie product page. (it will make its way in the user manual too at some point).
    Cheers,
    Kidekin TRNG maker

  2. Aaron Toponce | June 21, 2015 at 8:44 am | Permalink

    I updated the Wikipedia page.

  3. Xavier | July 2, 2015 at 8:03 am | Permalink

    "the hardware design is closed"
    Hm... what's the point of buying this ? Is it really better than builtin RNG devices in motherboard ?

  4. Kenneth | August 6, 2015 at 1:30 pm | Permalink

    Probably not, Xavier. However, not everyone *has* one on the motherboard. For them, this is a good way to get real random numbers. There are two or three others like the Kidekin out there as well. I use one something like this, for instance.

  5. William Heimbigner | September 30, 2015 at 1:36 pm | Permalink

    As this product appears to no longer be for sale, do you have a different one you would recommend?

  6. Adam Elteto | October 5, 2015 at 10:13 am | Permalink

    William, you might check out http://ubld.it/products/truerngpro , or its cheaper (and of course, slower) sibling http://ubld.it/products/truerng-hardware-random-number-generator/

  7. Adam Elteto | October 5, 2015 at 10:19 am | Permalink

    Aaron, what an excellent article! Quick note, you may try also running ent with the -b option, it will give you slightly different readings; probably because the random data generated by a TRNG is a stream of debiased bits as opposed to random bytes (characters).

  8. Vitalie Ciubotaru | July 11, 2017 at 10:39 am | Permalink

    I guess, in this command

    $ dd if=white.bmp of=entropy.kidekin bs=1 count=54 conv=notrunc

    'if' and 'of' parameters need to be swapped.

  9. Vitalie Ciubotaru | July 11, 2017 at 10:41 am | Permalink

    Oops, I was wrong. Please disregard my previous comment.

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