ParagonIE_Sodium_Crypto::secretstream_xchacha20poly1305_init_pull

    public static function secretstream_xchacha20poly1305_init_pull($key, $header)
    {
        # crypto_core_hchacha20(state->k, in, k, NULL);
        $subkey = ParagonIE_Sodium_Core_HChaCha20::hChaCha20(
            ParagonIE_Sodium_Core_Util::substr($header, 0, 16),
            $key
        );
        $state = new ParagonIE_Sodium_Core_SecretStream_State(
            $subkey,
            ParagonIE_Sodium_Core_Util::substr($header, 16)
        );
        $state->counterReset();
        # memcpy(STATE_INONCE(state), in + crypto_core_hchacha20_INPUTBYTES,
        #     crypto_secretstream_xchacha20poly1305_INONCEBYTES);
        # memset(state->_pad, 0, sizeof state->_pad);
        # return 0;
        return $state->toString();
    }