make
To create a shared secret shared among M
people with N+1
needed to reconstruct:
./grothe -secret 1-/dev/urandom 2-/dev/urandom ... \
N-/dev/urandom 1+shared1 2+shared2 ... M+sharedM
To reconstruct the original (an arbitrary combination of N+1
or
more shared files with their proper numbers):
./grothe I-sharedI J-sharedJ K-sharedK ... +reconstructed
./try.sh
Also known as ‘Best abuse of the judging process’.
The IOCCC 2012 submission page didn’t enforce the 2048 meaningful character limit. This entry, as submitted, weighed in at 2222 chars but lucky for it, it was extremely easy to bring down below the limit. There were a number of strings that when concatenated allowed the program to slide under the limit.
It was clear to the judges that the extra size was an entry beautification step. Had it not been, this entry would have been rejected in round 0.
The judges also took some liberty obfuscating this entry a little more.
How does this entry work? The only place multiplication is used is
to perform the atoi(3)
conversion.
This program implements a version of Shamir’s Secret
Sharing. Shamir’s Secret
Sharing allows you to encrypt a file into N
parts where it will take M
parts to
recreate the original file. E.g. you can split the secret recipe for Crystal Pepsi
into 3 parts and require two of them be available to extract the original recipe.
Actually surprisingly useful for an IOCCC entry :-)
To share a secret. For example:
To split a secret into 4 pieces of which at least 3 will be needed to get it (in this case the cookie recipe) back:
./grothe \
-cookie_recipe.txt\
\
1-/dev/urandom 2-/dev/urandom 1+cookie_piece1.dat 2+cookie_piece2.dat 3+cookie_piece3.dat 4+cookie_piece4.dat
To put the recipe back together using the first, second and fourth pieces:
./grothe \
1-cookie_piece1.dat 2-cookie_piece2.dat 4-cookie_piece4.dat+cookie_recipe_restore.txt
The program is limited to 256 input and output files and will slow down dramatically when you get past 20-50 inputs and outputs.
Nothing is done consistently throughout the program E.g i+=1
, i=i+1
, i++
and ++i
are all used in the program. The mark of true code buggery: “A
foolish consistency is the hobgoblin of little minds.” - Ralph Waldo
Emerson
Uses the most powerful obfuscation of all “Math”. “Any sufficiently advanced cryptography is indistinguishable from magic.” - Apologies to Arthur C. Clarke
Shadows variables by using brackets in main program to create local copies of
variables that are the same as global scope variables. -Wshadow
should
probably be a part of -Wall
in gcc.
Uses array_index[array_name]
instead of array_name[array_index]
in several
places. Still don’t know why C continues to allow this (error strings are
encoded with offsets that are also used to select them in the case statement.
All strings are located in one function for easy localization).
Liberal use of octal numbers, hexadecimal numbers and regular decimal numbers throughout the program.
Variables and function names are semi-random and upper and lower case characters are used.
Use of #define
s from stdio.h
, stdlib.h
for values _STDIO_H
and
EXIT_SUCCESS
used to represent 1 and 0 respectively in the program.
Arrays only need to be 256x256 but most are set to greater values than they need to be so trying to figure it out can be a bit tough.