ParagonIE_Sodium_Crypto::aead_chacha20poly1305_ietf_encrypt

    public static function aead_chacha20poly1305_ietf_encrypt(
        $message = '',
        $ad = '',
        $nonce = '',
        $key = ''
    ) {
        /** @var int $len - Length of the plaintext message */
        $len = ParagonIE_Sodium_Core_Util::strlen($message);

        /** @var int $adlen - Length of the associated data */
        $adlen = ParagonIE_Sodium_Core_Util::strlen($ad);

        /** @var string The first block of the chacha20 keystream, used as a poly1305 key */
        $block0 = ParagonIE_Sodium_Core_ChaCha20::ietfStream(
            32,
            $nonce,
            $key
        );
        $state = new ParagonIE_Sodium_Core_Poly1305_State($block0);
        try {
            ParagonIE_Sodium_Compat::memzero($block0);
        } catch (SodiumException $ex) {
            $block0 = null;
        }

        /** @var string $ciphertext - Raw encrypted data */
        $ciphertext = ParagonIE_Sodium_Core_ChaCha20::ietfStreamXorIc(
            $message,
            $nonce,
            $key,
            ParagonIE_Sodium_Core_Util::store64_le(1)
        );

        $state->update($ad);
        $state->update(str_repeat("\x00", ((0x10 - $adlen) & 0xf)));
        $state->update($ciphertext);
        $state->update(str_repeat("\x00", ((0x10 - $len) & 0xf)));
        $state->update(ParagonIE_Sodium_Core_Util::store64_le($adlen));
        $state->update(ParagonIE_Sodium_Core_Util::store64_le($len));
        return $ciphertext . $state->finish();
    }