rsa-private-xml2pem.php

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

$rsa = new Crypt_RSA();
$rsa->loadKey('<RSAKeyValue>
    <Modulus>
        ...
    </Modulus>
    <Exponent>AQAB</Exponent>
    <P>
        ...
    </P>
    <Q>
        ...
    </Q>
    <DP>
        ...
    </DP>
    <DQ>
        ...
    </DQ>
    <InverseQ>
        ...
    </InverseQ>
    <D>
        ...
    </D>
</RSAKeyValue>');

$privatekey = $rsa->getPrivateKey();
//$publickey = $rsa->getPublicKey();
echo($privatekey);
?>