Most surreptitious
Don Yang
omoikane@uguu.org
http://uguu.org/
Judges' comments:
To build:
make nyaruko
To run:
./nyaruko [seed.txt] < original.bin > output.c
bash output.c > key.c
perl output.c > data.c
cat key.c data.c > output.c
gcc output.c -o output
./output > regenerated.bin
Try:
echo "A quick brown fox jumps over the lazy dog" | ./nyaruko > output.c
perl output.c > data.c
gcc -o data data.c
./data
gcc -o output output.c
./output
Selected Judges Remarks:
The judges have nothing to add that has not already been written about in the spoiler.html.gz file! :-)
Author's comments:
Usage
Nyaruko is a binary to text filter. Given some input on stdin, Nyaruko will produce C code that reproduces this input on stdout:
./nyaruko < original.bin > output.c
gcc output.c -o output
./output > regenerated.bin
Output is encrypted, but both key and data are included in the output. To separate the key from the data, run these commands:
bash output.c > key.c
perl output.c > data.c
The key-less data.c still compiles, but produces a different message on stdout instead of the original input. This message is a hint to why the code is formatted the way it is.
To combine the key and data, concatenate them together in either order:
cat key.c data.c > output.c
cat data.c key.c > output.c
By default, Nyaruko generates a unique random key for every message, using /dev/urandom as the seed. If given an extra command line argument, Nyaruko will seed using that file instead of /dev/urandom:
./nyaruko seed.txt < input.bin > output.c
This makes the output key deterministic, allowing the same key to be shared across different files. On operating systems that do not have /dev/urandom, users should always specify this extra seed argument to avoid deterministic keys.
Features
Implementation details that makes Nyaruko more obfuscated than usual programs:
- Nyaruko recycles variables and buffers to reduce internal state. The variable names are also carefully chosen for mixed-case madness.
- Nyaruko employs some preprocessor magic to share much of the same code and state between the encoder and decoder, and to increase occurrences of smileys ;)
Output code has these features:
- Fits nicely under 80 columns, and does not contain any trigraphs.
- Uses a fairly efficient encoding scheme, better than uuencode for files larger than ~13K, and better than base64 for files larger than 20K.
- Encryption with ISAAC, a cryptographically secure pseudorandom number generator.
- Trivial 3 language polyglot.
Code layout is meant to resemble Nyaruko, also known as Nyarlathotep, the Crawling Chaos. The most obvious thing to do with chaos is to make a random number generator, and the most obvious thing to do with a random number generator is to make one-time-pads for encryption.
Compatibility
Nyaruko has these environment dependencies:
- Requires ASCII character set.
- Assumes sizeof(unsigned int) == 4.
- Best viewed with tab stops set to 8 spaces.
Output code has the same dependencies, with the additional requirement that the compiler must support arbitrarily long string literals. Maximum input size that can be encoded while still producing standard-compliant output is ~276 bytes for C89, and ~3168 bytes for C99.
Nyaruko has been to verified to work with these compiler/OS combinations:
- gcc 4.4.5 on Linux (32bit and 64bit)
- clang 3.1 on Windows (Cygwin)
- gcc 4.5.3 on Windows (Cygwin)
- gcc 4.5.3 on Windows (MingW)
- gcc 4.3.5 on JSLinux
- tcc 0.9.25 on JSLinux
Note that on MingW, stdin and stdout are not opened in binary mode by default, this means Nyaruko may not faithfully encode files on MingW.
Extra files
spoiler.html.gz - Contains full recording of how the code went from blank state to an obfuscated program, gzipped to fit under 1MB.