ParagonIE_Sodium_File::box_seal_open

    public static function box_seal_open($inputFile, $outputFile, $ecdhKeypair)
    {
        /* Type checks: */
        if (!is_string($inputFile)) {
            throw new TypeError('Argument 1 must be a string, ' . gettype($inputFile) . ' given.');
        }
        if (!is_string($outputFile)) {
            throw new TypeError('Argument 2 must be a string, ' . gettype($outputFile) . ' given.');
        }
        if (!is_string($ecdhKeypair)) {
            throw new TypeError('Argument 3 must be a string, ' . gettype($ecdhKeypair) . ' given.');
        }

        /* Input validation: */
        if (self::strlen($ecdhKeypair) !== ParagonIE_Sodium_Compat::CRYPTO_BOX_KEYPAIRBYTES) {
            throw new TypeError('Argument 3 must be CRYPTO_BOX_KEYPAIRBYTES bytes');
        }

        $publicKey = ParagonIE_Sodium_Compat::crypto_box_publickey($ecdhKeypair);

        /** @var int $size */
        $size = filesize($inputFile);
        if (!is_int($size)) {
            throw new SodiumException('Could not obtain the file size');
        }

        /** @var resource $ifp */
        $ifp = fopen($inputFile, 'rb');
        if (!is_resource($ifp)) {
            throw new SodiumException('Could not open input file for reading');
        }

        /** @var resource $ofp */
        $ofp = fopen($outputFile, 'wb');
        if (!is_resource($ofp)) {
            fclose($ifp);
            throw new SodiumException('Could not open output file for writing');
        }

        $ephemeralPK = fread($ifp, ParagonIE_Sodium_Compat::CRYPTO_BOX_PUBLICKEYBYTES);
        if (!is_string($ephemeralPK)) {
            throw new SodiumException('Could not read input file');
        }
        if (self::strlen($ephemeralPK) !== ParagonIE_Sodium_Compat::CRYPTO_BOX_PUBLICKEYBYTES) {
            fclose($ifp);
            fclose($ofp);
            throw new SodiumException('Could not read public key from sealed file');
        }

        $nonce = ParagonIE_Sodium_Compat::crypto_generichash(
            $ephemeralPK . $publicKey,
            '',
            24
        );
        $msgKeypair = ParagonIE_Sodium_Compat::crypto_box_keypair_from_secretkey_and_publickey(
            ParagonIE_Sodium_Compat::crypto_box_secretkey($ecdhKeypair),
            $ephemeralPK
        );

        $res = self::box_decrypt($ifp, $ofp, $size, $nonce, $msgKeypair);
        fclose($ifp);
        fclose($ofp);
        try {
            ParagonIE_Sodium_Compat::memzero($nonce);
            ParagonIE_Sodium_Compat::memzero($ephKeypair);
        } catch (SodiumException $ex) {
            unset($ephKeypair);
        }
        return $res;
    }