decrypt_ASCII_brute.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>


// Unknown keys.
const unsigned char cypher_text[] = {
   0xEC,0xDD,0xF3,0xB5,0xD9,0x9D,0xA6,  // l]s5Y.&
   0xAF,0xEF,0xC7,0x8F,0xDE,0x8F,0xCA,0xE7,  // /oG.^.Jg
   0xE5,0xB1,0xEF,0xEE,0xF0,0xB7,0xED,0xD6,  // e1onp7mV
   0xED,0xBF,0x9D,0xA4,0xBC,0xDB,0xC2,0xAF,  // m?.$<[B/
   0xE3,0xD6,0xC2,0xF0,0xBC,0xB9,0xEE,0xF5,  // cVBp<9nu
   0xE7,0xD4,0xDA,0xC3,0xE8,0xB8,0xA2,0xDF,  // gTZCh8"_
   0xC4,0x84,0xA6,0xF2,0xE6,0xED,0xC6,0xB1,  // D.&rfmF1
   0xD0,0xED,0xF7,0xDA,0xF4,0xB7,0xEB,0xE8,  // PmwZt7kh
   0xED,0xBA,0xC7,0xD0,0xAF,0xC2,0x8F,0xD9,  // m:GP/B.Y
   0xE3,0xF0,0xD1,0xF0,0xAC,0xEE,0xD9,0xB9,  // cpQp,nY9
   0xDE,0xE9,0xFA,0xDD,0xA0,0x22,0x0D,0x4F,  // ^iz] ".O
   0x55,0x2E  // U
};

// known keys: AB & BC
// const unsigned char cypher_text[] = {
//    0xD1,0xD4,0xDA,0xA5,0xCC,0xD8,0xA3,  // QTZ%LX#
//    0xD9,0xCB,0xCA,0xA3,0xD9,0xCC,0xD2,0xC8,  // YKJ#YLRH
// };

#define key_size 8

// Keyspace: A-Z * key_size characters

int a_length = 0;
int b_length = 0;

void increment_builder_a( char *i, int pos)
{
	if( pos == -1 )
	{
		a_length++;
		i[a_length] = 'A';
		return;
	}

	i[pos] += 1;

	if( i[pos] > 'Z' )
	{
		i[pos] = 'A';
		increment_builder_a( i, pos - 1);
	}
}

void increment_builder_b( char *i, int pos)
{
	if( pos == -1 )
	{
		b_length++;
		i[b_length] = 'A';
		return;
	}

	i[pos] += 1;

	if( i[pos] > 'Z' )
	{
		i[pos] = 'A';
		increment_builder_b( i, pos - 1);
	}
}

void print_key( char *key, int length )
{
	for( int i=0; i<=length; i++ )
	{
		printf( "%c", key[i] );
	}
}

int main(int argc, char *argv[] )
{
	unsigned long k=0;

	if( argc != 3 )
	{
		printf( "Key Checker\n");
		printf( "Key space A-Z\n");
		printf( "Built for key length: %d\n", key_size);
		printf( "usage: %s <start key 1> <start key 2>\n\n", argv[0]);
		return 0;
	}

	char a[key_size+1];
	char b[key_size+1];

	a_length = strlen(argv[1])-1;
	b_length = strlen(argv[2])-1;

	for( int i=0; i<strlen(argv[1]); i++ )
	{
		a[i] = toupper(argv[1][i]);

		if( a[i] < 'A' || a[i] > 'Z')
		{
			printf( "Character %c not in key space.\n", argv[1][i]);
			return 0;
		}
	}

	for( int i=0; i<strlen(argv[2]); i++ )
	{
		b[i] = toupper(argv[2][i]);

		if( b[i] < 'A' || b[i] > 'Z')
		{
			printf( "Character %c not in key space.\n", argv[2][i]);
			return 0;
		}
	}

	printf( "Starting with key: " );
	print_key( a, a_length );
	printf( " & ");
	print_key( b, b_length );
	printf("\n");

	int result[sizeof cypher_text];

	while( 1 )
	{

		// on my computer report key check ever 30 minutes
		if( ((k++) % (5470000 * 6 * 30)) == 0 )
		{
			printf( "k=%lu: ", k );

			print_key( a, a_length );
			printf( " & ");
			print_key( b, b_length );
			printf("\n");
		}

		int j=0, i=0, k=0;

		while( j < sizeof cypher_text)
		{
			result[j] = cypher_text[j] - a[i];

			if( result[j] < 0 ) result[j] += 255;

			result[j] = result[j] - b[k];

			if( result[j] < 0 ) result[j] += 255;

			j++;
			k++;
			i++;

			if( i==a_length+1) i=0;
			if( k==b_length+1) k=0;
		}

		for(int l=0; l<(sizeof cypher_text)-4; l++ )
		{
 			if( result[l] == 'T' && result[l+1] == 'H' && result[l+2] == 'E' && result[l+3] == ' ')
			{
				printf( "Find: " );
				print_key( a, a_length );
				printf( " & ");
				print_key( b, b_length );
				printf(": ");

				for( int m=0; m<(sizeof cypher_text); m++ )
				{
					printf( "%c", isprint(result[m]) ? result[m] : '.' );
				}

				printf( "\n" );
				break;
			}
		}

		increment_builder_a( a, a_length );

		if( a_length == key_size )
		{
			a_length = 0;
			increment_builder_b( b, b_length );

			if( b_length == key_size )
			{
				break;
			}
		}
	}

	printf(" last key searched: ");
	print_key( a, a_length );
	printf( " & ");
	print_key( b, b_length );
	printf("\n");

	return 0;
}