hill_cpta.php

<?php

define ("ALLOWED_TIME", 600);
define ("NB_CHALLENGES", 5);
define ("NB_ALLOWED_PT", 32);

@session_start();

header("Content-Type: text/html; charset=utf-8");

/************************/
/*     FUNCTIONS        */
/************************/

// returns the determinant of a 3*3 matrix
function det33($matrix)
{
	if (count($matrix) != 3 or count($matrix[0]) != 3 or count($matrix[1]) != 3 or count($matrix[2]) != 3)
		return False;
	return $matrix[0][0] * ($matrix[1][1]*$matrix[2][2] - $matrix[1][2]*$matrix[2][1])
		+  $matrix[0][1] * ($matrix[1][2]*$matrix[2][0] - $matrix[1][0]*$matrix[2][2])
		+  $matrix[0][2] * ($matrix[1][0]*$matrix[2][1] - $matrix[1][1]*$matrix[2][0]) ;
}

// returns a random matrix (3*3, integer values in range 1..25)
function get_matrix()
{
	$matrix = array();
	for ($i = 0; $i < 3; $i++)
	{
		$vect = array();
		for ($j = 0; $j < 3; $j++)
			$vect[] = rand(1, 25);
		$matrix[] = $vect;
	}
	return $matrix;
}

// returns a matrix invertible modulo 26
function get_key_matrix()
{
	while (True)
	{
		$matrix = get_matrix();
		$det = det33($matrix);

		if ($det % 2 != 0 and $det % 13 != 0)
			return $matrix;
	}
}

// returns a random 3-letter text
function get_random_trigraph()
{
	$text = "";
	for ($i = 0; $i < 3; $i++)
		$text.= chr(rand(0, 25) + 0x41);
	return $text;
}

function get_permutation()
{
	$perm = range(0, 25);
	shuffle($perm);
	return $perm;
}


function hill($keymatrix, $permutation, $inputtext)
{