SFTP problem

[Yearling]

I tried connecting to SFTP (see attached image with configuration), but the connection failed (see log). The same configuration (without password) with the same certificat works in the WinSCP SFTP client (winscp.net/eng/). Where could the problem be?


2025-12-09 23:20:21 Codepage not set. Will try to auto-detect if UTF-8 is supported
2025-12-09 23:20:21 No text format conversions  will be done for text file transfers
2025-12-09 23:20:21 Connecting to sftp._______.cz:1222
2025-12-09 23:20:21 Connected
2025-12-09 23:20:22 Key exchange method : diffie-hellman-group-exchange-sha256
2025-12-09 23:20:22 Host key method : rsa-sha2-512
2025-12-09 23:20:22 Encryption method (both directions) : aes256-ctr
2025-12-09 23:20:22 MAC (message authentication code) method (both directions) : hmac-sha2-256
2025-12-09 23:20:22 Compression method (both directions) : none
2025-12-09 23:20:22 Fingerprint : 3E 0D 34 8A 0F 28 BD 24 8A FA F1 4E E3 03 18 F4
2025-12-09 23:20:22 Failed - Session not connected

[Mathias (Author)]

if you do not check the "Do not verify keyfiles" it will verify them..

If you upgrade to latest beta it will log move what is happening.

Might be that the keyfile format is not support. I know that the format it supports is the one that PuttyGen generates

[Yearling]

I am using version Multi Commander v15.6 (Build 3119) (64 bit). Is there any newer beta version (where)?

[Mathias (Author)]

That is latest Release,, In Core settings you enable you update to beta versions..

[Yearling]

OK, I have last beta version 64bit v.15.7 build 3123. Certificat (both) was generated by PUTTYgen, but results are the same as yesterday
I have tested both "Do not verify key file" checked and unchecked.
I have tested two certificates (first without password, second with password) - both in WinSCP SFTP client work flawlessly but in Multi Commander not :-(
There are log files in attachment - two from Multi Commnader (for both certificates) and one from WinSCP client for comparision.

2025-12-10 18:59:23 Windows Linebreak are used for text file transfers
2025-12-10 18:59:23 Connecting to sftp.______.cz:1222
2025-12-10 18:59:23 Connected
2025-12-10 18:59:24 Key exchange method : diffie-hellman-group-exchange-sha256
2025-12-10 18:59:24 Host key method : rsa-sha2-512
2025-12-10 18:59:24 Encryption method (both directions) : aes256-ctr
2025-12-10 18:59:24 MAC (message authentication code) method (both directions) : hmac-sha2-256
2025-12-10 18:59:24 Compression method (both directions) : none
2025-12-10 18:59:24 Fingerprint : 3E 0D 34 8A 0F 28 BD 24 8A FA F1 4E E3 03 18 F4
2025-12-10 18:59:24 Failed - Session not connected
2025-12-10 18:59:24 Disconnecting...
2025-12-10 18:59:24 Closing Session...
2025-12-10 18:59:25 Session closed

[Mathias (Author)]

Sorry. I don't know.
I use it daily. And it works for me. But the whole thing is messy. There are so many different algorithm and cryptos.  Maybe you using some that the SSH code used in MC does not support or something.
I actually does not know. MC is using libssh2 with WinCNG for the SSH access https://libssh2.org/ , There are information there on what crypto/algorithm it support on that page

Btw
Something is not correct with the logs..
There is no
"Auth via public key for user" that is shown when trying to login using public key.
And there is no error from the verify of the keyfile..

I see if I can add some more error logging with the login phase. that can give hits on why it does not want to login

[Mathias (Author)]

This is how I created keys

On Linux
1.  Generate keys on Linux

ssh-keygen -t rsa -b 4096

Specify names for the file : id_mc (example)
Specify password if wanted

Keys are generate with the name  id_mc  and  id_mc.pub

2. Add public Key to authorized keys on the linux server, so you can login
cat ~/id_mc.pub >> ~/.ssh/authorized_keys

3. Copy keys to host

4. in MC specify the Public Key (id_mc.pub) and Private Key (id_mc ) 
   Enter keypassword if you set any at #1

[Yearling]

Hello,
there is a description in the attachement,  how I generated the certificate. Unfortunately, I am currently unable to try a different method :-(
PuttyGen was installed and used on Windows, SFTP server is running on Linux.

[Mathias (Author)]

I think it is because that you use ECDSA keys

looks like libssh2 support that, but only if the code is build to minimal support Windows 10. (since it require Windows functions that does not exists on Windows 7/8)
Problem is that for now MC is built to run on Windows 7.

That might change soon.. More and more issues is poping up to support Win7/8