The sun.security.x509.X509CRLEntryImpl.getExtensionValue(String) method is difficult to use. It returns the OCTET STRING representing the X509 Extension
extnValue field, which encapsulates encoding of the actual extension class.
The uses for getExtensionValue are:
1. to create a class for the extension so that values in the extension
   may be retrieved: this can't be done directly with the returned value
2. to compare two extension values for equality: this could be done with
   either the existing value or with the class-compatible value.