ParagonIE_Sodium_Crypto::box_seal

    public static function box_seal($message, $publicKey)
    {
        /** @var string $ephemeralKeypair */
        $ephemeralKeypair = self::box_keypair();

        /** @var string $ephemeralSK */
        $ephemeralSK = self::box_secretkey($ephemeralKeypair);

        /** @var string $ephemeralPK */
        $ephemeralPK = self::box_publickey($ephemeralKeypair);

        /** @var string $nonce */
        $nonce = self::generichash(
            $ephemeralPK . $publicKey,
            '',
            24
        );

        /** @var string $keypair - The combined keypair used in crypto_box() */
        $keypair = self::box_keypair_from_secretkey_and_publickey($ephemeralSK, $publicKey);

        /** @var string $ciphertext Ciphertext + MAC from crypto_box */
        $ciphertext = self::box($message, $nonce, $keypair);
        try {
            ParagonIE_Sodium_Compat::memzero($ephemeralKeypair);
            ParagonIE_Sodium_Compat::memzero($ephemeralSK);
            ParagonIE_Sodium_Compat::memzero($nonce);
        } catch (SodiumException $ex) {
            $ephemeralKeypair = null;
            $ephemeralSK = null;
            $nonce = null;
        }
        return $ephemeralPK . $ciphertext;
    }