SFTP plugin: can't connect to server

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Stoneboy
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SFTP plugin: can't connect to server

Post by *Stoneboy » 2019-05-11, 06:10 UTC

Hi,

first, thank you very much for Total Commander. I hope that I´ve changed some setting somewhere without realizing it, but since yesterday, I can´t connect to the remote server using the SFTP plugin. When I try using a different program (WinSCP) or on my laptop using the SFTP plugin, it works :(.

The connection isn´t established and is terminated with the error: Unable to exchange ssh keys.

I´ve tried reinstalling the plugin and the entire totalcmd, didn´t solve the issue. I use Windows 10 1903 (recently updated, but it worked on it before it just stopped yesterday morning).

Any help would be appreciated.

Thank you in advance.

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ghisler(Author)
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Re: SFTP plugin: can't connect to server

Post by *ghisler(Author) » 2019-05-13, 14:21 UTC

Sounds like the server side changed encryption algorithms to one not supported by the SFTP plugin. Try updating the plugin. If this doesn't help, you can try the one using OpenSSL dlls from here:
http://www.totalcommander.ch/win/fs/sftpplugxp.zip
and then install the latest OpenSSL dlls from here:
https://www.ghisler.com/openssl
Author of Total Commander
http://www.ghisler.com

Stoneboy
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Re: SFTP plugin: can't connect to server

Post by *Stoneboy » 2019-05-14, 13:12 UTC

Thank you VERY much, it works :).

Gab
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Re: SFTP plugin: can't connect to server

Post by *Gab » 2019-05-24, 07:09 UTC

Hi, I've had this problem, too and updating to the latest plugin and dlls fixed this for me, too. So thanks. :)

I'm very suspicous however, that the problem was caused by the latest Windows 10 1903 update. I am admin of several linux servers and before the update all of them connected without problem. After the update none of them. I experienced this with two Windows client machines.

Arminator
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Re: SFTP plugin: can't connect to server

Post by *Arminator » 2019-05-24, 11:27 UTC

I also suspect that the Windows 10 1903 update has to do with it.
I was using Total Commander with the SFTP Plugin fine yesterday, and updated my testing machine in the office to Windows 10 1903.
The regular work machine still on 1809 can connect to the same server fine, but the 1903 machine throws the error: Unable to exchange ssh keys.

I'll try to install the OpenSSL dlls and see if that resolves it as described by the other posters.

EDIT: Can confirm that by installing the XP Plugin and OpenSSL, it works under 1903.

Stoneboy
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Re: SFTP plugin: can't connect to server

Post by *Stoneboy » 2019-05-29, 04:11 UTC

I think so too (the problem started after I updated to 1903). The problem is that it worked for a time and then it stopped. If it stopped working right after the update, I could understand it better.

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Re: SFTP plugin: can't connect to server

Post by *ghisler(Author) » 2019-05-30, 09:09 UTC

Unfortunately it doesn't look good: The problem is a bug in the Windows function BCryptImportKeyPair:
It fails to import an RSA key where the public key exponent is as large as the modulus.
It works with a small 3 byte modulus 65537.

This function is used for the initial key exchange between client and server.
Unfortunately there is almost no chance to get this fixed, there is no way to contact anyone at Microsoft about it.
I will therefore try to find a solution via other functions, e.g. Microsoft Crypto API (although it is marked as deprecated by Microsoft).

So for now, please use the OpenSSL version of the plugin. Sorry for the inconvenience.
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