How to use SFTP connection with key file using C# and .NET

Question

I have a C# .NET project, where am trying to open an SFTP connection to a server and put a file to the server.

I have SFTP hostname, username and key file (.pem file).
I do not have a password here.

Please help me with something to use SFTP in C# and .Net.

Answer 1

Probably every SFTP/SSH library supports public key authentication.

For example:

• SSH.NET (NuGet package):

  var privateKey = new PrivateKeyFile(@"C:\some\path\key.pem");
  var client = new SftpClient("example.com", "username", new[] { privateKey });
  client.Connect();
  

  If the private key is encrypted:

  var privateKey = new PrivateKeyFile(@"C:\some\path\key.pem", "passphrase");
  

• WinSCP .NET assembly (NuGet package):

  SessionOptions sessionOptions = new SessionOptions
  {
      Protocol = Protocol.Sftp,
      HostName = "example.com",
      UserName = "username",
      SshHostKeyFingerprint = "ssh-rsa 2048 ...=",
      SshPrivateKeyPath = @"C:\some\path\key.ppk",
  };
  
  using (Session session = new Session())
  {
      session.Open(sessionOptions);
  
      // Your code
  }
  

  WinSCP needs the key converted to PPK format (You can use WinSCP GUI for that, or PuTTYgen). Also note that WinSCP verifies the SSH host key (SshHostKeyFingerprint). SSH.NET fails to do that by default, what is a security flaw.

  If the private key is encrypted, add PrivateKeyPassphrase or SecurePrivateKeyPassphrase.

  WinSCP GUI can generate a code template for you.

  (I'm the author of the library)