@Override
  int nonceSizeInBytes() {
    return NONCE_SIZE_IN_BYTES;
  }
Constructs a new InsecureNonceXChaCha20 cipher with the supplied {@code key}.

@throws IllegalArgumentException when {@code key} length is not {@link
    ChaCha20Util#KEY_SIZE_IN_BYTES}.
java_src/src/main/java/com/google/crypto/tink/aead/internal/InsecureNonceXChaCha20.java