Visual Basic 6.0

SSH Keyboard-Interactive Authentication

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.

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Visual Basic 6.0

Dim success As Long
success = 0

'  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.

Dim ssh As New ChilkatSsh

ssh.ConnectTimeoutMs = 5000
ssh.ReadTimeoutMs = 15000

Dim hostname As String
hostname = "ssh.example.com"
Dim port As Long
port = 22
success = ssh.Connect(hostname,port)
If (success = 0) Then
    Debug.Print ssh.LastErrorText
    Exit Sub
End If

'  Begin keyboard-interactive authentication.  The returned XML describes the server's prompts.
Dim xmlResponse As String
xmlResponse = ssh.StartKeyboardAuth("mySshLogin")
If (ssh.LastMethodSuccess = 0) Then
    Debug.Print ssh.LastErrorText
    Exit Sub
End If

'  If the server sent a user authentication banner, an application may display it before
'  prompting.
Debug.Print "UserAuthBanner: " & ssh.UserAuthBanner

Dim xml As New ChilkatXml
success = xml.LoadXml(xmlResponse)
If (success = 0) Then
    Debug.Print xml.LastErrorText
    Exit Sub
End If

'  Authentication is complete when the XML contains either a "success" or an "error" node.
If (xml.HasChildWithTag("success")) Then
    Debug.Print "No password required, already authenticated."
    Exit Sub
End If

If (xml.HasChildWithTag("error")) Then
    Debug.Print "Authentication failed."
    Exit Sub
End If

'  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.
Dim password As 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 = 0) Then
    Debug.Print ssh.LastErrorText
    Exit Sub
End If

success = xml.LoadXml(xmlResponse)
If (success = 0) Then
    Debug.Print xml.LastErrorText
    Exit Sub
End If

If (xml.HasChildWithTag("success")) Then
    Debug.Print "SSH keyboard-interactive authentication successful."
    Exit Sub
End If

If (xml.HasChildWithTag("error")) Then
    Debug.Print "Authentication failed."
End If