code: public static ByteString sha1(ByteString s) {
      try {
        MessageDigest messageDigest = MessageDigest.getInstance("SHA-1");
        byte[] sha1Bytes = messageDigest.digest(s.toByteArray());
        return ByteString.of(sha1Bytes);
      } catch (NoSuchAlgorithmException e) {
        throw new AssertionError(e);
      }
    }
docs: Returns a SHA-1 hash of {@code s}.