How do I convert an XML RSA key to a PEM file?

Question

I have two XML files, structured as follows:

My Key

<RSAKeyValue>
  <Modulus> ... </Modulus>
  <Exponent> ... </Exponent>
  <P> ... </P>
  <Q> ... </Q>
  <DP> ... </DP>
  <DQ> ... </DQ>
  <InverseQ> ... </InverseQ>
  <D> ... </D>
</RSAKeyValue>

A Public Key

<RSAKeyValue>
   <Modulus> ... </Modulus>
   <Exponent> ... </Exponent>
</RSAKeyValue>

I am using the xmlseclibs library by Robert Richards which requires a .PEM representation of the key in order to encrypt and decrypt things.

As an encryption novice, I'm not sure where to begin, and a cursory Google search did not reveal anything particularly obvious...

Thanks!

Answer 1

I have found a Java utility that can do it.

Answer 2

For those who want the resulting PEM to be readable by BouncyCastle:

1. use XMLSec2PEM tool to get a pem file
2. convert pem to pkcs8 and back (!)

The final solution I am happy with:

1. java XMLSec2PEM my.xml > my.pem
2. edit my.pem manually a bit
3. org.bouncycastle.openssl.PEMReader.readObject() returns null :-(
4. openssl pkcs8 -topk8 -inform pem -in my.pem -outform pem -nocrypt -out my.pkcs8
5. openssl pkcs8 -inform pem -nocrypt -in my.pkcs8 -out my.pkcs8.pem
6. now my.pkcs8.pem is readable with the PEMReader

Answer 3

I was searching for hours for exactly the same problem. This Java tool did the job :)

But the link has changed, it is now available from here

Answer 4

Found this useful online tool RSA Key Converter, which supports

• XML -> PEM
• PEM -> XML

Answer 5

Since xmlseclibs is PHP it seems like another PHP solution might be desirable. Here's how:

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

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

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

phpseclib has built in support for XML keys, PuTTY keys and PKCS1 keys. It'll auto detect the format and load it and getPrivateKey / getPublicKey will output PKCS1 formatted keys by default if no parameters are provided. More info:

http://phpseclib.sourceforge.net/rsa/examples.html#convert