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Couldn't agree a key host algorithm (available rsa-sha2-512, rsa-sha2-256)

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Piscator
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Couldn't agree a key host algorithm (available rsa-sha2-512, rsa-sha2-256)

I am using the latest version (5.19.6) and WinSCP is giving me this error. I use the key via Pageant (ssh-rsa 2048) and connecting via PuTTY (0.76.0.20220214) works fine. Suggestions?

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ogbonnaebuka@...
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Re: Cannot upgrade WinSCP

I am having the same issue with error text "Couldn't agree a host key algorithm (available: ecdsa-sha2-nistp256)". I am at version 5.7.7, but unfortunately I cannot upgrade as WinSCP is running on a remote Windows server which is not allowed to access the internet.

What would you advise in my case?

Thanks in advance.

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martin◆
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Re: Cannot upgrade WinSCP

@ogbonnaebuka: Well, you need to upgrade. There has to be a way to update software on the remote machine, right? Only other option to reconfigure your SFTP server to allow older deprecated algorithms (obviously, not a good solution).

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Sivakumar
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Even in latest version same issue occurs

I am using WinSCP version 6.3.6, In this version also I am getting the "Couldn't agree a key host algorithm (available rsa-sha2-512, rsa-sha2-256)" issue.

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martin◆
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Re: Even in latest version same issue occurs

@Sivakumar: Please attach a full session log file showing the problem (using the latest version of WinSCP).

To generate the session log file, enable logging, log in to your server and do the operation and only the operation that causes the error. Submit the log with your post as an attachment. Note that passwords and passphrases not stored in the log. You may want to remove other data you consider sensitive though, such as host names, IP addresses, account names or file names (unless they are relevant to the problem). If you do not want to post the log publicly, you can mark the attachment as private.

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steph_og
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Thanks for your response. I appreciate it. I have upgraded already but not sure why the logs still shows that version? I have also generated a new PuTTY using the newest version but still have the same error as below: 
2025-03-20 14:53:36.854 Connecting to 13.54.5.193 port 22000
. 2025-03-20 14:53:36.854 We claim version: SSH-2.0-WinSCP_release_5.17.9
. 2025-03-20 14:53:36.870 Remote version: SSH-2.0-AWS_SFTP_1.1
. 2025-03-20 14:53:36.870 Using SSH protocol version 2
. 2025-03-20 14:53:36.870 Have a known host key of type rsa2
. 2025-03-20 14:53:36.886 Couldn't agree a host key algorithm (available: rsa-sha2-512,rsa-sha2-256)
. 2025-03-20 14:53:36.886 Attempt to close connection due to fatal exception:
* 2025-03-20 14:53:36.886 Couldn't agree a host key algorithm (available: rsa-sha2-512,rsa-sha2-256)
. 2025-03-20 14:53:36.886 Closing connection.
I am just a newbie trying to support the client and would appreciate any help and insights. thank you!

2025-03-20_12-29-41.png

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martin◆
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@steph_og: You probably have more copies of WinSCP on the machine. Possibly one installed and other just a copy of a binary (or portable package). You have upgraded the installed copy, but you are actually using other copy. How are you starting WinSCP?

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martin◆
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What is "normal startup from the Menu"? Do you mean Windows "Start" menu? Did you check where does the menu shortcut point to? (right-click "WinSCP" menu entry and select "Open file location")

Did you verify that the installer is installing the new version to the same location? You can see the target path here:
https://winscp.net/eng/docs/ui_installer_ready

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steph_og
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Hi @martin,

Here is the location from the Start Menu: 
C:\ProgramData\Microsoft\Windows\Start Menu\Programs
Here is from the Desktop Shortcut: 
C:\Program Files (x86)\WinSCP
They point me to the same screen and application

and the installer says here: 
This PC > Windows (C:) > Program Files (x86) > WinSCP
Should I just upgrade to 6.3.7?
Please feel free to reach out where I can contact you

Thanks.

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martin◆
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What do you mean by "installer says here"? I do not think that installer says "This PC" anywhere. Can you post a screenshot?

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martin◆
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Ok, so you have 6.3.7 installed. And you obviously can run it (as earlier screenshots show). So how did you obtain the log from 5.17.9? You must have run it another way that time.

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steph_og
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We are doing the transfer by batch file program and here is how it looks like. (attachment 1)
What i do is to just replace the host key from the new connection in winscp when generating a new URL Code session.

One thing I noticed in the new version is it has this extra data in the connection string which we don't have in the other server which I have done the configuration successfully without that error in the logfile. (attachment 2)

2.png

1.png

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martin◆
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@steph_og: You've never mentioned "batch file" so far. You've kept posting GUI screenshots only.

So does your batch file run C:\Program Files (x86)\WinSCP\WinSCP.com? I guess it does not. If you believe it does, please post complete session logs both from batch and the GUI.

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