Cannot connect any more using FTPS (WiFi FTP Server)

[manitz]

I used to run FFS (10.16 to 10.25 Donation Edition) on Windows 10 to sync files
between Windows and two Android devices:

Samsung Galaxy Tab S5e
Huawei P30 lite New Edition

Both devices ran Android 9 and on both I used the App WiFi FTP Server with the option FTPS/SSL mode explicit. FFS worked flawless as did WinSCP with the corresponding protocoll and encryption mode.

Since I updated both devices to Android 10 WinSCP still connects to both but FFS fails to connect. I had to fall back to an unencrypted connection between FFS and the Andoid devices to get a sync done. The error message reads (translated from German):

The following folder was not found:
ftp://p30-manfred/Dokumente
---------------------------
The time limit for searching folder "ftp://p30-manfred/Dokumente" has been exceeded. [15 sec]

Is there anything I can do to again have an encrypted FTP connection between FFS
and Android? Remenber please, that WinSCP has no such problems connecting to the
WiFi FTP Server on both Androids using encryption.

Thank you very much for the great program which I use to also sync one desktop
PC and two notebooks running Windows.

Manfred

[ryang]

I am having the exact same issue. I confirmed that I can connect using FileZilla with no issues. I am running version 11 though.
Were you able to figure this out?

Update: I was able to get this working by enabling plain unencrypted traffic. For me it's not that big of a deal as it isn't connecting to a publicly accessible FTP.

[manitz]

@ryang
Thank you for your comment. Unfortunately, I didn't find a secure solution. FFS version 11 has the same issue as version 10.x has. As I mentioned in my first post, reverting to an unencrypted connection makes syncing possible. But having an encrypted ftp connection to android 10 like to android 9 in the past would be a security gain.

[Zenju]

FreeFileSync is using the libcurl library. There is also a command line tool named "curl" available which also implements the lib. You could tests with this tool to see if the problem is curl or FreeFileSync:
https://curl.haxx.se/docs/manpage.html

[manitz]

I downloaded curl-7.71.1-win64-mingw.zip from https://curl.haxx.se/windows/ and unzipped the file.
Then I tried

curl --ftp-ssl --user myusername:mypasswd ftp://p30-manfred:12345/test.txt

and got

curl: (60) SSL certificate problem: self signed certificate
More details here: https://curl.haxx.se/docs/sslcerts.html

curl failed to verify the legitimacy of the server and therefore could not
establish a secure connection to it. To learn more about this situation and
how to fix it, please visit the web page mentioned above.

So I used the option --insecure:

curl --ftp-ssl --insecure --user myusername:mypasswd ftp://p30-manfred:12345/test.txt

But curl hangs and has to be interupted with ^C. I don't know if I had used the right options. But maybe you are right that curl is the problem.

I don't understand that the connection problem occured with the update from Android 9 to 10 without changing anything else. And WinSCP still works with an explicit FTPS connection.

[Zenju]

I was able to reproduce the problem: It turns out WiFi FTP Server is using (the deprecated) *implicit* FTPS encryption by default, thous a hang in all tested tools WinSCP, FileZilla, FreeFileSync when set to "explicit FTPS". WinSCP and FileZilla can manually be set to "implicit" FTPS and will then connect, while FreeFileSync currently only supports explicit.

PS: WiFi FTP Server allows to set "SSL mode" to "excplicit" under options, in which case connection with FreeFileSync will work.

[manitz]

PS: WiFi FTP Server allows to set "SSL mode" to "excplicit" under options, in which case connection with FreeFileSync will work.

Right, FreeFileSync used to work running WiFi FTP Server with mode "explicit" on Android 9. Unfortunately, it does not work anymore running WiFi FTP Server on Android 10, tested with two different devices (Samsung and Huawei). WinSCP does connect in mode "explicit" while FileZilla does not (times out like FFS).

For me it is impossible to decide which side is responsible for the problem WiFi FTP Server on one hand or FFS/Curl/FileZilla on the other.

Anyway, thank you for your support.

[manitz]

The Author of WiFi FTP Server released a new version 1.9.4. This solved the problem using SSL mode explicit on Android 10. Now FreeFileSync, Curl, and FileZilla can connect to the server.