code: protected PGPSecretKey findSecretKey(InputStream secretKey, KeyFilter<PGPSecretKey> keyFilter) throws IOException, PGPException {
      LOGGER.trace("findSecretKey(InputStream, KeyFilter<PGPSecretKey>)");
      PGPSecretKey result = null;
      LOGGER.debug("Wrapping secret key stream in ArmoredInputStream");
      try( InputStream armoredSecretKey = new ArmoredInputStream(secretKey) ) {
        LOGGER.debug("Creating PGPSecretKeyRingCollection");
        PGPSecretKeyRingCollection keyRingCollection = new PGPSecretKeyRingCollection(armoredSecretKey, new BcKeyFingerprintCalculator());
        result = retrieveSecretKey(keyRingCollection, keyFilter);
      }
      return result;
    }
docs: reads the given secret key and applies the provided key filter
  
  @param secretKey
  the secret key stream
  @param keyFilter
  the filter to apply on the stream
  @return the secret key or null if none matches the filter acceptance criteria
  @throws IOException
  @throws PGPException