code: public static String getDigest(String oid) {
          String ret = (String)digestNames.get(oid);
          if (ret == null)
              return oid;
          else
              return ret;
      }
docs: Gets the digest name for a certain id
  @param oid	an id (for instance "1.2.840.113549.2.5")
  @return	a digest name (for instance "MD5")
  @since	2.1.6