Thank you very much! I'll download and let you know if we have further questions.

You have taken the host key from a new version of WinSCP that supports Ed25519 host keys and you are trying to use it with an old version of WinSCP .NET assembly that does not support it.

Upgrade your WinSCP .NET assembly. Or use the same old version of WinSCP to obtain the host key. The first option is better, obviously.

See https://winscp.net/eng/docs/message_key_fingerprint_does_not_match

Hello,

We have historically connected to UNIX using winscpnet.dll. Here is an example of the host key parameter we are currently passing to connect to UNIX:

When we try to connect to a new LINUX box we are not able to. Here is the host key parameter we are currently trying to use to connect to LINUX:

We obtain the algorithm and host key via the WinSCP GUI.

Here is the error message we receive when trying to connect to LINUX:

"SSH host key fingerprint "ssh-ed25519 255 0a:36:1f:27:f8:dd:f8:f8:59:4a:a9:e8:d5:f1:c4:3c" does not match pattern /((ssh-rsa|ssh-dss)( |-))?(\d+ )?([0-9a-f]{2}(:|-)){15}[0-9a-f]{2}(;((ssh-rsa|ssh-dss)( |-))?(\d+ )?([0-9a-f]{2}(:|-)){15}[0-9a-f]{2})*/".

Please let me know if you need further information, we greatly appreciate your time!