Shifted Bits Blog

/**
 * Encodes a plaintext message using the given key, and polybius square
 */
void	ADFGVX::encode( )
{
	//Local Variables to help encoding.
	string	coordinates = "";
 
	//Create polybius square coordinates for each letter in the phrase.
	for( unsigned int i = 0; i < plaintext.length(); i++ )
	{
		char c = plaintext.at( i );
		for( int y = 0; y < 6; y++ )
		{
			for( int x = 0; x < 6; x++ )
			{
				if( polybius.at(y).at(x) == c )
				{
					coordinates.append( 1, squaremap.at( x ) );
					coordinates.append( 1, squaremap.at( y ) );
				}
			}
		}
	}
 
	//Create Sorted key character, and index pairs.
	//Maps are auto sorted, so we need the index as the second half of the
	//pair to make a successful mapping.
	map< char, int > m;
	for( unsigned int i = 0; i < key.length(); i++ )
	{
		pair<char, int> p( key.at( i ), i );
		m.insert( p );
	}
 
	//Preparing the table to be filled with "coordinates".
	vector< string > v;
	for( unsigned int i = 0; i < key.length(); i++ )
		v.push_back( "" );
 
	//Fill it with coordinates
	for( unsigned int i = 0; i < coordinates.length(); i++ )
		v.at( i % key.length() ).append( 1, coordinates.at( i ) );
 
	//Generate The Cipher Text
	ciphertext = ""; //Clear it out first, in case there's one already there.
	map< char, int >::iterator k; //Iterator through the key map.
 
	//Loop through the map, using the vector to get the proper values to append
	//to the cipher text.
	for( k = m.begin(); k != m.end(); k++ )
	{
		ciphertext.append( v.at( k->second ) );
		ciphertext.append( " " );
	}
}

/**
 * Decodes a cipher text using the given key, and polybius square.
 */
void	ADFGVX::decode( )
{
	//Temporary variables to help with the decoding.
	vector< string > v, v1;
	string	s;
 
	//Separate each piece into bits in the vector to un-map.
	for( unsigned int i = 0; i < ciphertext.length(); i++ )
	{
		char c = ciphertext.at( i );
		//If we hit a space, we're at the end of a piece, so push it onto the vector.
		if( c == ' ' )
		{
			v.push_back( s );
			s = "";
		}
		else
		{
			s.append( 1, ciphertext.at( i ) );
		}
	}
	//Since the end isn't blocked by a space, we need to push it
	//as it wasn't detected.
	v.push_back( s );
 
	//Re-map the key to get the coordinates in their proper places.
	map< char, int > m;
	for( unsigned int i = 0; i < key.length(); i++ )
	{
		pair<char, int> p( key.at( i ), i );
		m.insert( p );
	}
 
	//Go through the key to get the correct mappings.
	map< char, int >::iterator k;
	for( unsigned int i = 0; i < key.length(); i++ )
	{
		//k is an iterator, and we can't get it's relative position while 
		//looping through, so we have j to keep track of that for us.
		int j = 0; 
		for( k = m.begin(); k != m.end(); k++ )
		{
			if( k->first == key.at( i ) )
				v1.push_back( v.at( j ) );
			j++;
		}
	}
 
	//Peel off the letters to recreate the non-mapped version
	//of the cipher text.
	s = "";
	for( unsigned int i = 0; i < ciphertext.length(); i++ )
	{
		int location = i % v.size();
		string at = v1.at( location );
 
		//This is to make sure we're not dealing with any strings that are
		//already translated and are shorter than other strings being
		//translated.
		if( at.length() > 0 )
		{
			char c = at.at( 0 );
			s.append( 1, c );
			string n_at = at.substr( 1 ); //Chop off the first character
			v1.at( location ) = n_at; //And reset the string to the new value.
		}
	}
 
	//Decode the resulting text from the polybius square.
	plaintext = "";
	for( unsigned int i = 0; i < s.length(); i += 2 )
	{
		int x, y;
		char cx = s.at( i );
		char cy = s.at( i + 1 );
 
		//We need the numerical positions of the coordinate letters.
		for( int k = 0; k < 6; k++ )
			if( cx == squaremap.at( k ) )
				x = k;
		for( int k = 0; k < 6; k++ )
			if( cy == squaremap.at( k ) )
				y = k;
 
		plaintext.append( 1, polybius.at(y).at(x) );
	}
}