How do I encrypt text using phpseclib and RSA with only the modulus and exponent?

Question

I tried the answer to this question, but it did not work:

$rsa = new \Crypt_RSA();
$rsa->loadKey(
    array(
        'e' => new \Math_BigInteger($exponent),
        'n' => new \Math_BigInteger($modulus)
    )
);
$cipher = $rsa->encrypt($text, CRYPT_RSA_PRIVATE_FORMAT_PKCS1);

My modulus is a 512-character hexadecimal number and my exponent is 10001. I've tried many different solutions, but I haven't found one that made this work. I'm receiving this error:

Notice: Uninitialized string offset: 0 in BigInteger.php on line 547

Answer 1

As you are using strings representing hexadecimal numbers you should tell that to Math_BigInteger

$rsa = new Crypt_RSA();
$rsa->loadKey(
    array(
        'e' => new Math_BigInteger($exponent, 16),
        'n' => new Math_BigInteger($modulus, 16)
    )
);