/**
* Generates prime number with length $bits_cnt
* using $random_generator as random generator function.
*
* @param int $bits_cnt
* @param string $rnd_generator
* @access public
*/
function getPrime($bits_cnt, $random_generator)
{
$bytes_n = intval($bits_cnt / 8);
$bits_n = $bits_cnt % 8;
do {
$str = '';
for ($i = 0; $i < $bytes_n; $i++) {
$str .= chr(call_user_func($random_generator) & 0xff);
}
$n = call_user_func($random_generator) & 0xff;
$n |= 0x80;
$n >>= 8 - $bits_n;
$str .= chr($n);
$num = $this->bin2int($str);
// search for the next closest prime number after [$num]
$num = bi_next_prime($num);
} while ($this->bitLen($num) != $bits_cnt);
return $num;
}
Returns pseudorandom number with $bit_len bit length.
Attention: do not use this function in cryptographic
or security applications! The function can be used only
for educational purposes :)
*/
$c = bi_rand(100);
echo 'rand(100) = ', bi_to_str($c), "<br/>\n";
$c = bi_rand(100, 'mt_rand');
// use mt_rand() as random generator
echo 'rand(100, "mt_rand") = ', bi_to_str($c), "<br/>\n";
/*
functions for modular arithmetic calculations
*/
echo '<h3>modular arithmetic functions</h3>' . "\n";
// find next pseudoprime number after $c
$modulus = bi_next_prime($c);
echo '$modulus = next_prime($c) = [', bi_to_str($modulus), "]<br/>\n";
$c = bi_addmod($a, $b, $modulus);
echo '$a + $b (mod $modulus) = [', bi_to_str($c), "]<br/>\n";
$c = bi_submod($a, $b, $modulus);
echo '$a - $b (mod $modulus) = [', bi_to_str($c), "]<br/>\n";
$c = bi_mulmod($a, $b, $modulus);
echo '$a * $b (mod $modulus) = [', bi_to_str($c), "]<br/>\n";
$c = bi_divmod($a, $b, $modulus);
echo '$a / $b (mod $modulus) = [', bi_to_str($c), "]<br/>\n";
$c = bi_powmod($a, $b, $modulus);
echo 'pow($a, $b) (mod $modulus) = [', bi_to_str($c), "]<br/>\n";
$c = bi_factmod(1000, $modulus);
echo '1000! (mod $modulus) = [', bi_to_str($c), "]<br/>\n";
$c = bi_absmod(-1, $modulus);
echo '-1 (mod $modulus) = [', bi_to_str($c), "]<br/>\n";
/**
* Finds next strong pseudoprime number, following after $num
*
* @param big_int resource $num
* @return big_int resource
* @access public
*/
function nextPrime($num)
{
return bi_next_prime($num);
}
/**
returns a "good" prime $a with length $bit_len with
resrtiction:
$a - 1 != 0 (mod $e)
*/
function get_prime($bit_len)
{
return bi_next_prime(bi_set_bit(bi_rand($bit_len, 'microtime_generator'), $bit_len - 1));
}
