CODEWITHSUNDEEP
php
Lukas Mittun Alexander Guldstv
Lukas Mittun Alexander Guldstv

Reputation: 602

Working with large numbers in php is outputing 0

I am trying to do some Diffie-Hellman which works fine with smaller generator, mod and private keys. But when the numbers get to large it just outputs zero. I've looked at other posts with no real solution. Could it be configured in php.ini?

$gen = 877;
$mod = 80182923;

$saltA = 517;
$saltB = 1517;


echo "calculation of Ga og Gb<br>";
echo "<br>user A shareable value<br>";
$calculatedSecretKeyA =  ($gen**$saltA) % $mod;
echo $gen . "^" . $saltA . " mod " . $mod . " = " . $calculatedSecretKeyA;

echo "<br>user B shareable value<br>";
$calculatedSecretKeyB = ($gen**$saltB) % $mod;
echo $gen . "^" . $saltB . " mod " . $mod . " = " . $calculatedSecretKeyB;


echo "<br>user As calc of secret key <br>";
$calcKeyA =  ($calculatedSecretKeyB**$saltA) % $mod;
echo $calculatedSecretKeyB . "^" . $saltA . "" . " mod " . $mod . " = " . $calcKeyA;


echo "<br><br>user Bs calc of secret key <br>";
$calcKeyB =  ($calculatedSecretKeyA**$saltB) % $mod;
echo $calculatedSecretKeyA . "^" . $saltB . "" . " mod " . $mod . " = " . $calcKeyB;



echo "<br><br>bruteforcer A calc of secret key <br>";
$calcKeyB =  ($calculatedSecretKeyA**7) % $mod;
echo $calculatedSecretKeyA . "^" . 7 . "" . " mod " . $mod . " = " . $calcKeyB;

Upvotes: 1

Views: 57

Answers (1)

Felippe Duarte
Felippe Duarte

Reputation: 15131

You can use GMP library for this (https://www.php.net/manual/en/ref.gmp.php):

echo "calculation of Ga og Gb<br>";
echo "<br>user A shareable value<br>";
$calculatedSecretKeyA = gmp_mod ( gmp_pow ($gen, $saltA), $mod);
echo $gen . "^" . $saltA . " mod " . $mod . " = " . $calculatedSecretKeyA;

Output:

calculation of Ga og Gb

user A shareable value
877^517 mod 80182923 = 79127908

Upvotes: 3

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