Key pair auth issue with Windows 11 [SOLVED]

[alienjon]

I have both a desktop (192.168.1.139) and laptop (192.168.1.13) trying to connect to server (192.168.1.4). I've tried a few methods and seem to get the same results. For the sake of consistency I'll use putty for the example. I use putty's key-gen to create an ecdsa pub/priv keypair. I copy the pub into authorized_keys and set the private key to load when loading putty. I've done this for both the desktop and laptop (laptop first and desktop second). I find that using this method I can login just fine on the laptop (which I setup first) but it fails with the desktop (which I setup second) and requires a username/password to be set explicitly. Now, I had cleared the authorized_keys file and redid all this in the manner described, but previously I had done it in reverse (desktop setup first and laptop second) and in that scenario the desktop loaded fine, but the laptop required the username/password.

My /var/messages mentions:

[alienjon]

So... progress. I had been looking at debug on the server side, but not the client side. When running ssh {host} -vv I noticed:

[Banana]

You can name your key what every you want. If so, you need to specify the file everytime you want to use it. If you do not specify the file the defaults will be used.

[sMueggli]

The default names are what SSH is looking for out of the box. But this is not very comfortable in the long term. There are at least two possibilities to work with keys:

One way is to use an SSH agent such as ssh-agent or pageant (for putty).

The other way is to write a SSH config and specify the identity file (the key) for the different servers (I hope you have different keys for different servers); see also "man 5 ssh_config" for more details.

[alienjon]

[Banana]

As default it does work with the .ssh folder and does use the default files.
If you do not want it, as sMueggli already said, you need to specify which. Either with a tool or with custom config, like described here: https://unix.stackexchange.com/questions/494483/specifying-an-identityfile-with-ssh
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[sMueggli]

From "man 1 ssh-agent":

[alienjon]

Thanks both! This is exactly what I needed. Is there a benefit to an ssh-agent vs changing the configuration? In Windows the agent seems to be an easier choice.

[sMueggli]

Hard to tell. And you can combine both together. So the usage of one or the other is not mutually exclusive.

If you have a static setup you could use the config. That way you just "ssh foobar" and it works. It is easier to debug: ssh client works? if yes, is config correct? if yes, the fun begins...
The config is also self-documenting. If you read the config you will know, where default values are used and where you set specific values.

On the other hand I just start the ssh-agent with a systemd user unit at login. And whenever I need access to a server I load the key (and need to figure out the specific password) and start working. In case of failure you need to check more parts.

And on Windows I like MobaXterm for SSH and RDP.

[alienjon]

Thanks for the insight! It's just a home network, so pretty small and a config would likely make sense. I'll have to check out those SSH clients as well. Thanks for the recommendation!