title: How can I determine a valid OID to use to extend an X.509-compliant digital signature?
body: <p>I need an OID to use to add a custom extension (already ASN1.encoded) to an X.509v3/PKCS#7 digital signature.  I don't care if it's interoperable;  this is a private proprietary application (actually, a research project).  Right now I actually don't even care if it's an OID that's in use in some proprietary application, although obviously I couldn't use that OID for long.</p>
  
  <p>Currently I've been using 1.2.3.4.5, which is in the test code for the crypto library I'm using (cryptlib).  However, signature creation is crashing and I don't know if this might be why.  I do know that the library rejects at least some invalid OID's when checking inputs.</p>