SSH session sharing 

Session sharing is a useful feature of the SSH protocol. It's possible to share a single SSH connection between several instances of Ssh objects and Sftp/Scp objects (parts of Rebex SFTP) or to establish SSH tunnels. This makes it possible to transfer files, run SSH shell sessions, and tunnel TCP connections over a single SSH session.

To create a shared session, connect and authenticate an SshSession object. Then, instead of calling Connect and Login for each Ssh, Sftp or Scp object, use Bind to attach it to the shared SshSession.

// establish the shared SSH connection
var session = new Rebex.Net.SshSession();
session.Connect(hostname);
// check session.Fingerprint here

// authenticate
session.Authenticate(username, password);

// bind an SSH object to the SSH session
var ssh = new Rebex.Net.Ssh();
ssh.Bind(session);

// bind an SFTP object to the SSH session
Sftp sftp = new Sftp();
sftp.Bind(session);

' establish the shared SSH connection
Dim session = New Rebex.Net.SshSession()
session.Connect(hostname)
' check session.Fingerprint here

' authenticate
session.Authenticate(username, password)

' bind an SSH object to the SSH session
Dim ssh As New Ssh()
ssh.Bind(session)

' bind an SFTP object to the SSH session
Dim sftp As New Sftp()
sftp.Bind(session)

Changing password 

Some SSH servers make it possible to change user's password programmatically. This feature is accessible through SshSession object's ChangePassword method.

Please note that password can only be changed before the authentication has begun.

// connect to an SSH server but don't log in
var session = new SshSession();
session.Connect(hostname, port);

// try changing the password
SshPasswordChangeResult result
    = session.ChangePassword(username, password, newPassword);

// check the result
switch (result)
{
    case SshPasswordChangeResult.Success:
        // password changed;
        // now you are logged on using the new password
        break;
    case SshPasswordChangeResult.ChangedButNotAuthenticated:
        // password changed;
        // you should authenticate explicitly
        session.Authenticate(username, newPassword);
        break;
    case SshPasswordChangeResult.Failure:
        // password not changed
        throw new Exception("Password change failed.");
}

' connect to an SSH server but don't log in
Dim session = New SshSession()
session.Connect(hostname, port)

' try changing the password
Dim result As SshPasswordChangeResult = session.ChangePassword(username, password, newPassword)

' check the result
Select Case result
    Case SshPasswordChangeResult.Success
        ' password changed;
        ' now you are logged on using the new password
        Exit Select
    Case SshPasswordChangeResult.ChangedButNotAuthenticated
        ' password changed;
        ' you should authenticate explicitly
        session.Authenticate(username, newPassword)
        Exit Select
    Case SshPasswordChangeResult.Failure
        ' password not changed
        Throw New Exception("Password change failed.")
End Select

Keep-alive packet (pinging SSH server) 

Some firewall/router devices have a habit of dropping connections that have been inactive for a certain amount of time (such as 30 minutes). To prevent this, the client can send a special ignore packet periodically to keep the connection alive.

To send such packet, use SshSession.KeepAlive method. For a sample code to send the packet periodically, check out this forum post.

Key re-exchange 

SSH recommends changing encryption/decryption keys after each gigabyte of transmitted data or after each hour of connection time (whichever comes sooner). To achieve this, the client or server can initiate a key re-exchange process. This involves a public key operation that requires a fair amount of processing power; it is not initiated by Rebex Terminal Emulation automatically. To start a key re-exchange, simply call SshSession.Negotiate method.

Usually, however, it's the server that initiates the re-exchange. Rebex Terminal Emulation handles it transparently and there is no need to explicitly enable this feature.

SSH ciphers 

Rebex SSH Shell's SSH core supports a number of security algorithms. Use Ssh.Settings.SshParameters property to specify all kinds of SSH ciphers:

Key Exchange Ciphers

Use SshParameters.KeyExchangeAlgorithms property to enable/disable whole categories of key exchange ciphers. If you need more control over key exchange ciphers, use SshParameters.SetKeyExchangeAlgorithms(...) method to specify supported ciphers in order of preference. The following table lists supported key exchange ciphers:

Host Key Algorithms

Use SshParameters.HostKeyAlgorithms property to enable/disable whole categories of host key algorithms. If you need more control over host key algorithms, use SshParameters.SetHostKeyAlgorithms(...) method to specify supported algorithms in order of preference. The following table lists supported host key algorithms:

Encryption Ciphers

Use SshParameters.EncryptionAlgorithms and SshParameters.EncryptionModes properties to enable/disable whole categories of encryption ciphers. If you need more control over encryption ciphers, use SshParameters.SetEncryptionAlgorithms(...) method to specify supported ciphers in order of preference. The following table lists supported encryption ciphers:

MAC Ciphers

Use SshParameters.MacAlgorithms property to enable/disable whole categories of message authentication code (MAC) ciphers. If you need more control over MAC ciphers, use SshParameters.SetMacAlgorithms(...) method to specify supported ciphers in order of preference. The following table lists supported MAC ciphers:

* Might be very slow on legacy Windows CE platforms

** Windows 7 SP1 and higher, or Windows Embedded Compact 2013

Server ciphers information 

To retrieve lists of SSH ciphers supported by your SSH server, connect to it and inspect the Sftp.SshSession.ServerInfo property:

var ssh = new Ssh();
ssh.Connect("test.rebex.net");

SshServerInfo serverInfo = ssh.Session.ServerInfo;

Console.WriteLine("Key exchange algorithms: " + string.Join(", ", serverInfo.KeyExchangeAlgorithms));
Console.WriteLine("Host key algorithms: " + string.Join(", ", serverInfo.ServerHostKeyAlgorithms));

Console.WriteLine("MAC algorithms (server -> client): " + string.Join(", ", serverInfo.MacAlgorithmsServerToClient));
Console.WriteLine("MAC algorithms (client -> server): " + string.Join(", ", serverInfo.MacAlgorithmsClientToServer));

Console.WriteLine("Encryption algorithms (server -> client): " + string.Join(", ", serverInfo.EncryptionAlgorithmsServerToClient));
Console.WriteLine("Encryption algorithms (client -> server): " + string.Join(", ", serverInfo.EncryptionAlgorithmsClientToServer));

Console.WriteLine("Compression algorithms (server -> client): " + string.Join(", ", serverInfo.CompressionAlgorithmsServerToClient));
Console.WriteLine("Compression algorithms (client -> server): " + string.Join(", ", serverInfo.CompressionAlgorithmsClientToServer));

Dim ssh As New Ssh()
ssh.Connect("test.rebex.net")

Dim serverInfo As SshServerInfo = ssh.Session.ServerInfo

Console.WriteLine("Key exchange algorithms: " + String.Join(", ", serverInfo.KeyExchangeAlgorithms))
Console.WriteLine("Host key algorithms: " + String.Join(", ", serverInfo.ServerHostKeyAlgorithms))

Console.WriteLine("MAC algorithms (server -> client): " + String.Join(", ", serverInfo.MacAlgorithmsServerToClient))
Console.WriteLine("MAC algorithms (client -> server): " + String.Join(", ", serverInfo.MacAlgorithmsClientToServer))

Console.WriteLine("Encryption algorithms (server -> client): " + String.Join(", ", serverInfo.EncryptionAlgorithmsServerToClient))
Console.WriteLine("Encryption algorithms (client -> server): " + String.Join(", ", serverInfo.EncryptionAlgorithmsClientToServer))

Console.WriteLine("Compression algorithms (server -> client): " + String.Join(", ", serverInfo.CompressionAlgorithmsServerToClient))
Console.WriteLine("Compression algorithms (client -> server): " + String.Join(", ", serverInfo.CompressionAlgorithmsClientToServer))