Can not connect to the Debian 8 servers with CuteFTP

[tfetfe]

Just installed a new server with Debian8 (jessie) system. Many years use CuteFTP to upload/synchronize files on home computer and server using SFTP connection. Unfortunately, CuteFTP can not connect to Deabian8 servers:

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Disconnect: key exchange failed.
ERROR:>     [22/06/2016 15:10:03] Check security settings; make sure that the username and password are correct, and that the chosen encryption algorithms are supported by server.

Opened a ticket and the only answer was:

I was following up to see if you have any information related to Debian 8 for you host authentication method.

On Globalscape forum I saw a thread with the same problem but now the forum is closed for some reason. CuteFTP is not a free software but no support at all.

I installed WinSCP and there is no problem to connect to the server. Just CuteFTP acn not connect. But I want to use CuteFTP because it has scheduled synchronization, multiple simultaneous upload/download possibility etc.

Any ideas why CuteFTP can not connect to the Debian8 servers?

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*** CuteFTP 9.0 - build Jun 25 2013 ***

STATUS:>  	[22/06/2016 15:10:02] Getting listing ""...
STATUS:>  	[22/06/2016 15:10:02] Connecting to SFTP server... XXX.XXX.XXX.XXX:1641 (ip = XXX.XXX.XXX.XXX)...
ERROR:>   	[22/06/2016 15:10:03] Disconnect: key exchange failed.
ERROR:>   	[22/06/2016 15:10:03] Check security settings; make sure that the username and password are correct, and that the chosen encryption algorithms are supported by server.
STATUS:>  	[22/06/2016 15:10:03] Can't connect to XXX.XXX.XXX.XXX:1641.
STATUS:>  	[22/06/2016 15:10:03] SFTP connection closed.

[sgosnell]

You're trying to use sftp, not ftp. Secure ftp (sftp) requires a password. The Debian servers don't use use sftp, AFAIK. Check your Cuteftp settings. I'm not sure why you want to access the Debian servers from Windows, but it's not my business.

[gradinaruvasile]

Umm, what are we talking about here, FTPS or SFTP?

sftp = file transfer over ssh - it is not even THE ftp because it only uses the 22 port compared to ftp's dynamic allocation (ftp uses a port for command and others for data)
ftps = ftp with slapped on ssl encryption - this is standard ftp but with added encryption

Most distribution's ssh servers have sftp enabled by default, including Debian's.

[reinob]

.. Disconnect: key exchange failed ..

You need to:

1) find out which key exchange algorithms your version of cuteftp supports,
2) find out which key exchange algorithms your version of sftp (openssh) supports.

your client (cuteftp) should be able to give you that information. Saying "key exchange failed" is very unhelpful, as it knows what it has tried and what has failed.

Alternatively, could check the server log (assuming you have control over it).