code: public boolean isOK(PublicKey key) {
          try {
              final var digester = MessageDigest.getInstance(get(DIGEST_KEY).getString());
              final var ser = unsigned();
              final var digestValue = digester.digest(ser);
              final var cipher = Cipher.getInstance(key.getAlgorithm());
              cipher.init(Cipher.DECRYPT_MODE, key);
              final var sigDigest = cipher.doFinal(getSignature());
              return Arrays.equals(digestValue, sigDigest);
          } catch (Exception e) {
              return false;
          }
      }
docs: Returns true if the license is signed and the authenticity of the signature can be checked successfully
  using the key.
  
  @param key encryption key to check the authenticity of the license signature
  @return {@code true} if the license was properly signed and is intact. In any other cases it returns
  {@code false}.