VB.NET

Convert a PuTTY Private Key (.ppk) to OpenSSH (.pem)

Demonstrates converting a PuTTY format private key to OpenSSH format. The .ppk is imported with FromPuttyPrivateKey and re-exported with ToOpenSshPrivateKey, both unencrypted and encrypted.

Note: The file paths are relative to the application's current working directory. Supply the paths to your own files.

Background: PuTTY and OpenSSH store the same underlying key material in different container formats, so converting between them is a re-encoding rather than a new key — the corresponding public key, and therefore the server-side authorized_keys entry, is unchanged. This matters when moving between Windows tooling built around PuTTY and Unix tooling that expects PEM. Note that the Password property serves double duty: it decrypts the key on import and encrypts it on export, so set it appropriately for each step.

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VB.NET

Dim success As Boolean = False

'  Demonstrates converting a PuTTY format private key (.ppk) to OpenSSH (.pem) format.

Dim key As New Chilkat.SshKey

'  Set the password before importing an encrypted PuTTY key.  If the key is not encrypted it
'  makes no difference whether Password is set.  This should come from a secure source rather
'  than being hard-coded.
key.Password = "myKeyPassword"

'  LoadText is a convenience method that reads any text file into a string.  It does not itself
'  load the key.
Dim keyStr As String = key.LoadText("qa_data/putty_private_key.ppk")
If (key.LastMethodSuccess = False) Then
    Debug.WriteLine(key.LastErrorText)
    Exit Sub
End If


success = key.FromPuttyPrivateKey(keyStr)
If (success = False) Then
    Debug.WriteLine(key.LastErrorText)
    Exit Sub
End If


'  Export to an unencrypted OpenSSH key.
Dim bEncrypt As Boolean = False
Dim unencryptedKeyStr As String = key.ToOpenSshPrivateKey(bEncrypt)
If (key.LastMethodSuccess = False) Then
    Debug.WriteLine(key.LastErrorText)
    Exit Sub
End If


success = key.SaveText(unencryptedKeyStr,"qa_output/unencrypted_openssh.pem")
If (success = False) Then
    Debug.WriteLine(key.LastErrorText)
    Exit Sub
End If


'  Export to an encrypted OpenSSH key.  The Password property supplies the passphrase used to
'  encrypt the output.
bEncrypt = True
key.Password = "myExportPassword"
Dim encryptedKeyStr As String = key.ToOpenSshPrivateKey(bEncrypt)
If (key.LastMethodSuccess = False) Then
    Debug.WriteLine(key.LastErrorText)
    Exit Sub
End If


success = key.SaveText(encryptedKeyStr,"qa_output/encrypted_openssh.pem")
If (success = False) Then
    Debug.WriteLine(key.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("Done!")