SSH Keyboard-Interactive Authentication

See more SSH Examples

Demonstrates keyboard-interactive authentication with an SSH server. StartKeyboardAuth returns XML describing the server's prompts, and ContinueKeyboardAuth submits each response. Authentication is complete when the returned XML contains either a success or an error node.

Background: Keyboard-interactive is SSH's flexible, prompt-driven method: rather than assuming a single password, the server asks one or more questions — a password, a one-time code, a security question — and the client answers each. This is how SSH supports two-factor and other challenge-response schemes. The prompt XML also indicates whether each response should be echoed, so a client knows when to mask input. A server may issue several rounds, so a robust implementation loops until it sees success or error rather than assuming one exchange is enough.

Chilkat C# Downloads

Download Chilkat for C#

bool success = false;

//  This example requires the Chilkat API to have been previously unlocked.
//  See Global Unlock Sample for sample code.

//  Demonstrates keyboard-interactive authentication with an SSH server.  The server sends one or
//  more prompts as XML, and the application answers each with ContinueKeyboardAuth.

Chilkat.Ssh ssh = new Chilkat.Ssh();

ssh.ConnectTimeoutMs = 5000;
ssh.ReadTimeoutMs = 15000;

string hostname = "ssh.example.com";
int port = 22;
success = ssh.Connect(hostname,port);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  Begin keyboard-interactive authentication.  The returned XML describes the server's prompts.
string xmlResponse = ssh.StartKeyboardAuth("mySshLogin");
if (ssh.LastMethodSuccess == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  If the server sent a user authentication banner, an application may display it before
//  prompting.
Debug.WriteLine("UserAuthBanner: " + ssh.UserAuthBanner);

Chilkat.Xml xml = new Chilkat.Xml();
success = xml.LoadXml(xmlResponse);
if (success == false) {
    Debug.WriteLine(xml.LastErrorText);
    return;
}

//  Authentication is complete when the XML contains either a "success" or an "error" node.
if (xml.HasChildWithTag("success")) {
    Debug.WriteLine("No password required, already authenticated.");
    return;
}

if (xml.HasChildWithTag("error")) {
    Debug.WriteLine("Authentication failed.");
    return;
}

//  Normally you would not hard-code the password in source.  You should instead obtain it
//  from an interactive prompt, environment variable, or a secrets vault.
string password = "mySshPassword";

//  Answer the prompt.  Typically one call is enough, but a server may issue several rounds of
//  prompts, so a robust client loops until it sees "success" or "error".
xmlResponse = ssh.ContinueKeyboardAuth(password);
if (ssh.LastMethodSuccess == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

success = xml.LoadXml(xmlResponse);
if (success == false) {
    Debug.WriteLine(xml.LastErrorText);
    return;
}

if (xml.HasChildWithTag("success")) {
    Debug.WriteLine("SSH keyboard-interactive authentication successful.");
    return;
}

if (xml.HasChildWithTag("error")) {
    Debug.WriteLine("Authentication failed.");
}