docs: public PGPSecretKeyRing getSigningKeyRing() throws IOException, PGPException {
          PGPSecretKeyRingCollection secretKeyRings = getSecretKeys();
          if (secretKeyRings == null) {
              return null;
          }
  
          PGPSecretKeyRing signingKeyRing = null;
          for (PGPSecretKeyRing ring : secretKeyRings) {
              if (signingKeyRing == null) {
                  signingKeyRing = ring;
                  continue;
              }
  
              if (ring.getPublicKey().getCreationTime().after(signingKeyRing.getPublicKey().getCreationTime())) {
                  signingKeyRing = ring;
              }
          }
  
          return signingKeyRing;
      }