openssl: how can i get public key from modulus

Question

I generate a pair of keys using openssl:

shell> ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/mike         


        

Answer 1

You can get the public key in a more standardized format using phpseclib, a pure PHP RSA implementation. eg.

<?php
include('Crypt/RSA.php');

$modulus = 'yEQs2LxSHBZgZCH0rRQQy9kmry8g2tNhQL1B9f5azNz9Ce9pXPgSRjVUo1B9Ggb/FK3jy41wWd2IfS6rse3vBzRsabMj29CVODM/19yZPmwEmjJHCgYd+AA2qweKZanDp4FLsSw/kyV5WoPN16GHEMLmLGkJFNIWtzzH5jV+S80=';
$exponent = 'AQAB';

$rsa = new Crypt_RSA();

$modulus = new Math_BigInteger(base64_decode($modulus), 256);
$exponent = new Math_BigInteger(base64_decode($exponent), 256);

$rsa->loadKey(array('n' => $modulus, 'e' => $exponent));
$rsa->setPublicKey();

echo $rsa->getPublicKey();