'Permission denied (publickey).' but terminal ssh connection works fine

[JPVenson]

Hey,

Maybe i am missing the obvious here, but i see no reason why my connection should not work.

The Key is already converted into something SSH.net usable:

-----BEGIN RSA PRIVATE KEY-----
Proc-Type: 4,ENCRYPTED
DEK-Info: AES-128-CBC,

...

-----END RSA PRIVATE KEY-----

and a corresponding ssh call shows the public key is registered on the server correctly:

ssh DOMAIN -l root -i C:\Users\XXXX\.ssh\id_XXXX
-> Works

Then why does this code throws an exception on connect?

var connectionInfo = new ConnectionInfo(uploadTargetHost,
    sshUser,
    new PrivateKeyAuthenticationMethod(sshUser, new PrivateKeyFile(@"C:\Users\XXXX\.ssh\id_XXXX", keyPassword)));

using var client = new SftpClient(connectionInfo);
EventHandler<HostKeyEventArgs> clientOnHostKeyReceived = (sender, e) =>
{
    e.CanTrust = true;
};
client.HostKeyReceived += clientOnHostKeyReceived;
client.Connect();

Renci.SshNet.Common.SshAuthenticationException: 'Permission denied (publickey).'

[Zananok]

After upgrading the host of my 3 servers to Debian 12, I had the same issue. Works from the terminal, but not from SshNet
Removed the symlink and create an "original" clean authorized_keys with 600. No success.

All vms that are debian 11, ubuntu and arch, works fine, just the debian 12 which I get:
Renci.SshNet.Common.SshAuthenticationException: 'Permission denied (publickey).'

The solution is to just add PubkeyAcceptedAlgorithms +ssh-rsa on the server config.

Seems like SshNet's default algo to send is becoming deprecated or at least by default unaccepted by new ssh servers.

Edit:

Further research shows that ssh-rsa is using SHA-1 which is not secure, thus the default rejection from ssh servers.
One ahs to change the sending algo to use SHA-256 and SHA-512 to be accepted without changing the server config to allow a less secure algo.

Edit2: #825

[WojciechNagorski]

Version 2023.0.0 has been published https://www.nuget.org/packages/SSH.NET/2023.0.0