new ubuntu server / no auth possible

[stereomouse]

Hi everyone, maybe someone can help. We generate XML data on an SFTP server. Unfortunately, our server crashed, and we had to move it. On the new Ubuntu server, we can’t establish a connection to edit the XML files. I’ve checked everything thoroughly. Now I got this message from the IA:

--> 3. The server no longer accepts this key type (Very common with modern servers)
Newer Linux servers (e.g., with OpenSSH version 8.8 or later) have disabled the old ssh-rsa algorithm (which your key uses) by default for security reasons, as it is considered obsolete. Since Oxygen uses an older Java library in the background, it stubbornly tries to log in using this old method, which the server rejects with “Rejected” (Auth cancel).
The quickest solution (generate a new key):
Create a more modern key of type ED25519, which Oxygen supports in newer versions and which is accepted by every modern server.
Open your terminal (command prompt) and type:
ssh-keygen -t ed25519
Upload the new public key (.pub) to your server.
Enter the new private key into Oxygen."


Is that right? Thanks and best regards

[adrian]

Hello,

Unfortunately no, that's not quite right.
Oxygen uses an old library for SSH support, JSch 0.1.54, and relies mostly on RSA keys which are currently disabled by default in recent versions of OpenSSH (mind you, they can still be reactivated). Your realistic options are:
1. Allow ssh-rsa on the server, scoped to your user only, with something like this in sshd_config:

Code: Select all

   Match User yourname
       PubkeyAcceptedAlgorithms +ssh-rsa

Then use an RSA key in PEM (ssh-keygen -t rsa -b 4096 -m PEM) or PPK format for Oxygen.

2. Try an ECDSA key (ssh-keygen -t ecdsa -b 256 -m PEM). OpenSSH still accepts ECDSA signatures by default, and I believe the 0.1.54 JSch can authenticate with ECDSA keys. However, I'd point out that Oxygen’s docs only mention RSA, so this is untested and undocumented. It’s worth a quick try before changing things on the server.

Regards,
Adrian

[stereomouse]

Thank you very much—we'll give that a try!