ParagonIE_Sodium_Crypto::box_seal_open

    public static function box_seal_open($message, $keypair)
    {
        /** @var string $ephemeralPK */
        $ephemeralPK = ParagonIE_Sodium_Core_Util::substr($message, 0, 32);

        /** @var string $ciphertext (ciphertext + MAC) */
        $ciphertext = ParagonIE_Sodium_Core_Util::substr($message, 32);

        /** @var string $secretKey */
        $secretKey = self::box_secretkey($keypair);

        /** @var string $publicKey */
        $publicKey = self::box_publickey($keypair);

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

        /** @var string $keypair */
        $keypair = self::box_keypair_from_secretkey_and_publickey($secretKey, $ephemeralPK);

        /** @var string $m */
        $m = self::box_open($ciphertext, $nonce, $keypair);
        try {
            ParagonIE_Sodium_Compat::memzero($secretKey);
            ParagonIE_Sodium_Compat::memzero($ephemeralPK);
            ParagonIE_Sodium_Compat::memzero($nonce);
        } catch (SodiumException $ex) {
            $secretKey = null;
            $ephemeralPK = null;
            $nonce = null;
        }
        return $m;
    }