I'm trying to connect to a postgres db through an ssh tunnel.

I'm using the following code:

var key = @"-----BEGIN OPENSSH PRIVATE KEY-----
b3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtzc2gtZW
QyNTUxOQAAACCXh/hzgihW+MyThoACSVPrcyxq2mR3X07BINeo0EAxRQAAAJgzheTNM4Xk
zQAAAAtzc2gtZWQyNTUxOQAAACCXh/hzgihW+MyThoACSVPrcyxq2mR3X07BINeo0EAxRQ
AAAECyv5JGjoNs6lPe8gdUjlSaOddVNJ4z3sF9ErOQpfcXwZeH+HOCKFb4zJOGgAJJU+tz
LGraZHdfTsEg16jQQDFFAAAAFW1yb3NhQE1ST1NBLUNMT1NFUi1QQw==
-----END OPENSSH PRIVATE KEY-----";

MemoryStream keyStream = new MemoryStream(Encoding.UTF8.GetBytes(key));

Renci.SshNet.ConnectionInfo connn = new Renci.SshNet.ConnectionInfo(
           "141.147.35.80", "tml",
           new AuthenticationMethod[]
               {
                   new PrivateKeyAuthenticationMethod("tml", new PrivateKeyFile[] { new PrivateKeyFile(keyStream, ""), }),
               });

SshClient client = new SshClient(connn);

client.Connect();

if (!client.IsConnected)
{
    // Display error
    Console.WriteLine("Client not connected!");
}
else
{
    Console.WriteLine("Client connected!");
}

var port = new ForwardedPortLocal("10.5.10.43", 8080, "141.147.35.80", 22);
client.AddForwardedPort(port);

port.Start();

using (var conn = new NpgsqlConnection("Server=10.5.10.43;Database=trino;Port=8080;User Id=admin;Password=;"))
{
    conn.Open();
}

port.Stop();
client.Disconnect();

But I'm always getting an error

Invalid private key

I've already used putty gen load key ->

Export open ssh key but I always got the same key format and the same error (Invalid private key).

How to get the right key to connect correctly through the tunnel?