How to connect via :ssh module using an id_ed25519 private key string

Questions / Help
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1

I spent more than a day trying to figure out how to connect via ssh using a private key but without a result… all languages some to have an example when it comes to ssh except erlang/elixir which I don’t know why it’s that hard.

The only example I can find is using username/password, but I want to ssh to another machine using username and private ssh key (id_ed25519),

Any idea?

2

If you are using OTP, it’s always worth checking out the official documentation. Here is how to configure custom keypairs for servers and the next paragraph is for clients: ssh — ssh v5.2.1

The parameters that can be sent to the client/daemon are also clearly documented, take a look through them: ssh — ssh v5.2.1

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3

Ok I believe this is so easy for you so please just add that one line or 2 missing lines where I have put a placeholder for completion (my private key is located in /home/me/.ssh/id_ed25519)

ssh_options = [
      {:user, user},
      {:silently_accept_hosts, true},
      {:user_interaction, false},
      # ====== please just fill in here those easy missing lines ======
    ]

{:ok, conn} <- :ssh.connect(ip, port, ssh_options, 5000)

BTW I am really newbie to OTP, but I am sure you an experienced on these stuff.

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4

I am still waiting for the “it’s easy to do” guy to answer, but unfortunately the easy things are not easy. Said is always easier than Done. Anyway!

5

You can PM me and I’ll hand you the consulting prices, then you won’t have to wait anymore :slight_smile: .

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6

For the record, I re-read the comment you are referring to three times and hereby I admit it does not have wording “it is easy to do.”

It suggests reading docs. Which is the great advice, btw. You might also read something about SSH in a nutshell, because your attempt to pass the username alongside with the file hints you are not quite familiar with it.

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7

As far as I can tell the only way to do this is to implement a ssh_client_key_api callback.
The default is to look for the key files in the .ssh folder, this you can override with user_dir option.

I have never used it myself, but saw a reference to a package called librarian that seems to support it.
If you want to write it yourself, you can look at how they do it.

8

A good starting point IMO is the example in the :ssh user guide.

That shows the general shape of things (connect/session_channel/exec) but doesn’t really use the messages, or answer your original question.

For the “using the messages” part, take a look at how SSHEx does it - the whole file is worth reading, but this is where the actual {:ssh_cm, ...} messages get handled:

For the second half, there are two behaviours that :ssh depends on but the one we care about is :ssh_client_key_api. That’s implemented by two modules supplied with :ssh, :ssh_file and :ssh_agent which use either files or the SSH agent. :ssh_file is the default, but you can pass an alternative implementation via the :key_cb option to :ssh.connect.

HOWEVER

:ssh_client_key_api has more moving parts than just “here is a key”, it also deals with known hosts. SSHEx includes an implementation you could use / model after:

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