I use getEncoded() on X509Certificate, store it in LDAP, and convert it
back. Should work the same way, here some code. Note that LDAP
ctx.lookup returns Object, in my case 'bin' and I just convert back to
byte array, as I store it.

X509Certificate cert = null;
   try
   {
     // retrieve as binary object
     Object bin = doLookup(results, "userCertificate;binary");
     if (null==bin)
     {
       throw new IllegalStateException("Search results do not contain
X509 Certificate");
     }
     // convert to byte array
     byte[] buf = (byte[])bin;
     if (1 >= buf.length)
     {
       throw new IllegalStateException("Illegal certificate size");
     }
     // convert to X.509 class
     CertificateFactory cf = CertificateFactory.getInstance( "X.509"
);
     ByteArrayInputStream bais = new ByteArrayInputStream(buf);
     while (bais.available() > 0)
     {
       cert = (X509Certificate) cf.generateCertificate( bais );
     }
   }//end try

HTH,
iksrazal
http://www.braziloutsource.com/

I think you should use the KeyFactory class. Look at its Javadoc, there
is an example for a DSA public key encoded using X509.
In your case, the code should probably look like (provided you encoded
your key using PKCS8)

PKCS8EncodedKeySpec privateKeySpec = new PKCS8EncodedKeySpec(bytes);
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
PrivateKey privateKey = keyFactory.generatePrivate(privateKeySpec);

JB.