Authentication with PPK key in SSH.NET

Question

I'm creating a window service for downloading files from an SFTP server. For that I'm using Renci.SshNet , Renci.SshNet.Common and Renci.SshNet.Sftp .

I have this code:

String Host = "HostName";
int Port = 22;
String RemoteFileDirectory =
    Convert.ToString(ConfigurationManager.AppSettings["SourcePath"]);
String Username = "UserName";
String Password = "*******";

var KeybasedMethod = new KeyboardInteractiveAuthenticationMethod(Username);
KeybasedMethod.AuthenticationPrompt +=
    (sender, e) => { e.Prompts.First().Response = password; };

AuthenticationMethod[] methods = new AuthenticationMethod[] 
{
    new PrivateKeyAuthenticationMethod(Username, new PrivateKeyFile(@"Z:\SFTP SETUP\CJ22")),
    KeybasedMethod
};
ConnectionInfo connectionInfo = new ConnectionInfo(hostname, username, methods);

using (var sftp = new SftpClient(connectionInfo))
{
    sftp.Connect();
    // ...
}

I get exception.

Invalid private key file.

I can't figure it out that what I'm missing in my code.

Below is the log file I'm getting at the time when I login to server from my client machine using FileZilla.

2017-04-03 16:25:19 8120 3 Status: Connecting to abc.domainname.com... 
2017-04-03 16:25:19 8120 3 Trace: Going to execute "C:\Program Files\FileZilla FTP Client\fzsftp.exe" 
2017-04-03 16:25:19 8120 3 Response: fzSftp started 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::ConnectParseResponse(fzSftp started) 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::SendNextCommand() 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::ConnectSend() 
2017-04-03 16:25:19 8120 3 Command: keyfile "Z:\SFTP SETUP\CJ21_PVT.ppk" 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::ConnectParseResponse() 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::SendNextCommand() 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::ConnectSend() 
2017-04-03 16:25:19 8120 3 Command: keyfile "Z:\SFTP SETUP\CJ22_PVT.ppk" 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::ConnectParseResponse() 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::SendNextCommand() 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::ConnectSend() 
2017-04-03 16:25:19 8120 3 Command: keyfile "Z:\SFTP SETUP\CJ24_PVT.ppk" 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::ConnectParseResponse() 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::SendNextCommand() 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::ConnectSend() 
2017-04-03 16:25:19 8120 3 Command: keyfile "Z:\SFTP SETUP\CJ90_PVT.ppk" 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::ConnectParseResponse() 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::SendNextCommand() 
2017-04-03 16:25:19 8120 3 Trace: CSftpControlSocket::ConnectSend() 
2017-04-03 16:25:19 8120 3 Command: open "[email protected]" 22 
2017-04-03 16:25:19 8120 3 Trace: Looking up host "abc.domainname.com" 
2017-04-03 16:25:19 8120 3 Trace: Connecting to xxx.xxx.163.74 port 22 
2017-04-03 16:25:23 8120 3 Trace: Server version: SSH-2.0-1.82_sshlib Globalscape 
2017-04-03 16:25:23 8120 3 Trace: Using SSH protocol version 2 
2017-04-03 16:25:23 8120 3 Trace: We claim version: SSH-2.0-PuTTY_Local:_Mar_28_2014_10:34:48 
2017-04-03 16:25:24 8120 3 Trace: Doing Diffie-Hellman group exchange 
2017-04-03 16:25:24 8120 3 Trace: Doing Diffie-Hellman key exchange with hash SHA-1 
2017-04-03 16:25:25 8120 3 Trace: Host key fingerprint is: 
2017-04-03 16:25:25 8120 3 Trace: ssh-rsa 2048 6b:80:2c:5e:af:3f:2c:c7:f7:ef:4b:dd:85:55:32:fe 
2017-04-03 16:25:25 8120 3 Trace: Initialised AES-256 SDCTR client->server encryption 
2017-04-03 16:25:25 8120 3 Trace: Initialised HMAC-SHA1 client->server MAC algorithm 
2017-04-03 16:25:25 8120 3 Trace: Initialised AES-256 SDCTR server->client encryption 
2017-04-03 16:25:25 8120 3 Trace: Initialised HMAC-SHA1 server->client MAC algorithm 
2017-04-03 16:25:25 8120 3 Trace: Successfully loaded 4 key pairs from file 
2017-04-03 16:25:26 8120 3 Trace: Offered public key from "Z:\SFTP SETUP\CJ21_PVT.ppk" 
2017-04-03 16:25:26 8120 3 Trace: Server refused public key 
2017-04-03 16:25:26 8120 3 Trace: Offered public key from "Z:\SFTP SETUP\CJ22_PVT.ppk" 
2017-04-03 16:25:26 8120 3 Trace: Offer of public key accepted, trying to authenticate using it. 
2017-04-03 16:25:29 8120 3 Trace: Further authentication required 
2017-04-03 16:25:30 8120 3 Trace: Using keyboard-interactive authentication. inst_len: 0, num_prompts: 1 
2017-04-03 16:25:30 8120 3 Command: Pass: ********* 
2017-04-03 16:25:30 8120 3 Trace: Access granted 
2017-04-03 16:25:30 8120 3 Trace: Opened channel for session 
2017-04-03 16:25:31 8120 3 Trace: Started a shell/command 
2017-04-03 16:25:31 8120 3 Status: Connected to abc.domainname.com 
2017-04-03 16:25:33 8120 3 Trace: CSftpControlSocket::ConnectParseResponse() 
2017-04-03 16:25:33 8120 3 Trace: CSftpControlSocket::ResetOperation(0) 
2017-04-03 16:25:33 8120 3 Trace: CControlSocket::ResetOperation(0) 
2017-04-03 16:25:33 8120 3 Trace: CFileZillaEnginePrivate::ResetOperation(0) 
2017-04-03 16:25:33 8120 3 Status: Retrieving directory listing... 
2017-04-03 16:25:33 8120 3 Trace: CSftpControlSocket::SendNextCommand() 
2017-04-03 16:25:33 8120 3 Trace: CSftpControlSocket::ChangeDirSend() 
2017-04-03 16:25:33 8120 3 Command: cd "/" 
2017-04-03 16:25:34 8120 3 Response: New directory is: "/" 
2017-04-03 16:25:34 8120 3 Trace: CSftpControlSocket::ResetOperation(0) 
2017-04-03 16:25:34 8120 3 Trace: CControlSocket::ResetOperation(0) 
2017-04-03 16:25:34 8120 3 Trace: CSftpControlSocket::ParseSubcommandResult(0) 
2017-04-03 16:25:34 8120 3 Trace: CSftpControlSocket::ListSubcommandResult() 
2017-04-03 16:25:34 8120 3 Trace: state = 1 
2017-04-03 16:25:34 8120 3 Trace: CSftpControlSocket::SendNextCommand() 
2017-04-03 16:25:34 8120 3 Trace: CSftpControlSocket::ListSend() 
2017-04-03 16:25:34 8120 3 Trace: state = 2 
2017-04-03 16:25:34 8120 3 Command: ls 
2017-04-03 16:25:34 8120 3 Status: Listing directory / 
2017-04-03 16:25:36 8120 3 Listing: drwxrw-rw- 1 user group 0 Mar 24 2015 JKOB1 
2017-04-03 16:25:36 8120 3 Listing: drwxrw-rw- 1 user group 0 Apr 3 10:40 JKOB 
2017-04-03 16:25:36 8120 3 Trace: CSftpControlSocket::ListParseResponse() 
2017-04-03 16:25:36 8120 3 Trace: CSftpControlSocket::SendNextCommand() 
2017-04-03 16:25:36 8120 3 Trace: CSftpControlSocket::ListSend() 
2017-04-03 16:25:36 8120 3 Trace: state = 3 
2017-04-03 16:25:36 8120 3 Status: Calculating timezone offset of server... 
2017-04-03 16:25:36 8120 3 Command: mtime "JKOB" 
2017-04-03 16:25:37 8120 3 Response: 1491216040 
2017-04-03 16:25:37 8120 3 Trace: CSftpControlSocket::ListParseResponse(1491216040) 
2017-04-03 16:25:37 8120 3 Status: Timezone offsets: Server: 0 seconds. Local: 19800 seconds. Difference: 19800 seconds. 
2017-04-03 16:25:37 8120 3 Trace: CSftpControlSocket::ResetOperation(0) 
2017-04-03 16:25:37 8120 3 Trace: CControlSocket::ResetOperation(0) 
2017-04-03 16:25:37 8120 3 Status: Directory listing successful 
2017-04-03 16:25:37 8120 3 Trace: CFileZillaEnginePrivate::ResetOperation(0) 
2017-04-03 16:27:24 8120 3 Status: Disconnected from server 
2017-04-03 16:27:24 8120 3 Trace: CControlSocket::DoClose(64) 
2017-04-03 16:27:24 8120 3 Trace: CSftpControlSocket::ResetOperation(66) 
2017-04-03 16:27:24 8120 3 Trace: CControlSocket::ResetOperation(66) 
2017-04-03 16:27:24 8120 3 Trace: CFileZillaEnginePrivate::ResetOperation(66) 
2017-04-03 16:27:24 8120 3 Trace: CControlSocket::DoClose(64) 
2017-04-03 16:27:24 8120 3 Trace: CControlSocket::DoClose(64) 
2017-04-03 16:27:24 8120 3 Trace: CFileZillaEnginePrivate::ResetOperation(0)

I've tried multiple solution from here and from other sources one after another but none of them worked. If you've any suggestion then it's more than welcome.

Solution

SSH.NET does not support .ppk key files. You have to use PuTTYgen to convert the .ppk key to OpenSSH format.

See How to convert SSH keypairs generated using PuTTYgen (Windows) into key-pairs used by ssh-agent and Keychain (Linux).

---

Original answer, before the question was edited:

You are using multifactor private key and keyboard interactive authentication in FileZilla:

2017-04-03 16:25:26 8120 3 Trace: Offered public key from "Z:\SFTP SETUP\CJ22_PVT.ppk"
2017-04-03 16:25:26 8120 3 Trace: Offer of public key accepted, trying to authenticate using it.
2017-04-03 16:25:29 8120 3 Trace: Further authentication required
2017-04-03 16:25:30 8120 3 Trace: Using keyboard-interactive authentication. inst_len: 0, num_prompts: 1
2017-04-03 16:25:30 8120 3 Command: Pass: *********
2017-04-03 16:25:30 8120 3 Trace: Access granted

While, you are using simple password authentication in your code:

using (var sftp = new SftpClient(Host, Port, Username, Password))

How can you even expect this to work?

---

To implement multifactor authentication, you have to use ConnectionInfo.

var keybInterMethod = new KeyboardInteractiveAuthenticationMethod(username);
keybInterMethod.AuthenticationPrompt +=
    (sender, e) => { e.Prompts.First().Response = password; };

AuthenticationMethod[] methods = new AuthenticationMethod[] {
    new PrivateKeyAuthenticationMethod(username, new PrivateKeyFile(privateKey)),
    keybInterMethod
};
ConnectionInfo connectionInfo = new ConnectionInfo(hostname, username, methods);

using (var sftp = new SftpClient(connectionInfo))
{
    sftp.Connect();

    // ...
}