Author:

• Name: Aaron Grothe
  Location: US - United States of America (United States)

To build:

    make

NOTE: this entry requires the X11/Xlib.h header file and the X11 library to compile. For more information see the FAQ on “X11”.

To use:

    ./grothe carrier_freq pixelclock horizontal_total < some_input.txt

Try:

Put on your “electronic ears” and then try:

    ./try.sh

You may find using a tunable scanning electronic ear helps.

Judges’ remarks:

Most of the time, interference is annoying. This entry is the exception that proves the rule. What is a bug to some is a feature to this entry. :-)

Author’s remarks:

The program draws patterns on the screen that can be picked up by a shortwave radio. It emulates the frequencies for an old fashion touch tone phone, so old songs can be played by hitting 0-9,#, and *.

To be able to run the program you need to determine the following parameters:

• carrier_freq
  • base frequency used to host music
• pixelclock
  • refresh rate of the monitor
• horizontal_total
  • total scan along the horizontal axis

If you have xvidtune installed you can get the pixelclock and horizontal_total with the following command

    xvidtune -show | head -n 1 | awk '{ print "pixelclock " $2 * 1000000 " horizontal_total = " $6 }'

Example from my laptops:

    ./grothe 65000000 10000000 1344 < twinkle.txt

Even if the user gets a setting off, the sound will usually be able to be heard on AM at a multiple of the original frequency.

The core idea of using a machine to play music on AM radio goes all the way back to the Altair computers and Timex Sinclair ZX-81s.

Several example songs

Olympics Fanfare - from antang@phakt.usc.edu - Tony:

    4-9-91231,2222-321123123-9-91231,2222-32112321

Twinkle Twinkle Little Star - from fsufunkyb@aol.com - Ben Schmidt:

    1199##9-6633221-9966332-9966332-1199#9-6633221-

Generic Arabian Tune - from rdippold@qualcomm.com - Ron “Asbestos” Dippold:

    453,54,4569564459,9#95458,8987453 54

Others can be found by doing a search for “touch tone phone songs”.

Obfuscations

• Some numbers expressed in Octal, some in hex and some in decimal:

“A foolish consistency is the hobgoblin of little minds.” - Ralph Waldo Emerson.

• Funky scoping, looking at the nanosleep section and XsetWindowAttributes declares local variables.
• Algorithm is very weird, uses y dimension to draw carrier frequency and x dimension to draw audio frequency, based on Erik Thiele’s Tempest for Eliza.
• lack of #defines confuses many people :-)
• figuring out your pixelclock and horizontal_total and which carrier_freq to use can be an exercise in obfuscation for the user.
• use of commas in various places, confuses most C code beautifiers sometimes making the beautified code harder to read
• use of static to ensure initialization is EVIL and done in several places
• uses static declarations & void function returns we don’t care about making the code harder to read.
• does sound using only X11 libs, no other libs required.
• demonstrates tempest emissions in a fun/easy way.
• follows good programming practices of actually setting exit codes and giving usage when run with incorrect parameters.

References

Tempest for Eliza - Basis for Algorithms.

Tempest AM - Another early program in this field. See here for a bit more information on the program (search for Tempest-AM Radio Signal Transmitter).

The paper Soft Tempest: Hidden Data Transmission Using Electromagnetic Emanations by Markus G. Kuhn’s and Ross J. Anderson’s.

Primary files

• grothe.c - entry source code
• Makefile - entry Makefile
• grothe.orig.c - original source code
• arabian.txt - sample input
• olympic.txt - sample input
• test.txt - sample input
• try.sh - script to try entry
• twinkle.txt - sample input

Secondary files

• 2006_grothe.tar.bz2 - download entry tarball
• README.md - markdown source for this web page
• .entry.json - entry summary and manifest in JSON
• .gitignore - list of files that should not be committed under git
• .path - directory path from top level directory
• index.html - this web page

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