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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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llSuccess = .F.

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

loKey = createobject("CkSshKey")

//  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.
loKey.Password = "myKeyPassword"

//  LoadText is a convenience method that reads any text file into a string.  It does not itself
//  load the key.
lcKeyStr = loKey.LoadText("qa_data/putty_private_key.ppk")
if (loKey.LastMethodSuccess = .F.) then
    ? loKey.LastErrorText
    release loKey
    return
endif

llSuccess = loKey.FromPuttyPrivateKey(lcKeyStr)
if (llSuccess = .F.) then
    ? loKey.LastErrorText
    release loKey
    return
endif

//  Export to an unencrypted OpenSSH key.
llBEncrypt = .F.
lcUnencryptedKeyStr = loKey.ToOpenSshPrivateKey(llBEncrypt)
if (loKey.LastMethodSuccess = .F.) then
    ? loKey.LastErrorText
    release loKey
    return
endif

llSuccess = loKey.SaveText(lcUnencryptedKeyStr,"qa_output/unencrypted_openssh.pem")
if (llSuccess = .F.) then
    ? loKey.LastErrorText
    release loKey
    return
endif

//  Export to an encrypted OpenSSH key.  The Password property supplies the passphrase used to
//  encrypt the output.
llBEncrypt = .T.
loKey.Password = "myExportPassword"
lcEncryptedKeyStr = loKey.ToOpenSshPrivateKey(llBEncrypt)
if (loKey.LastMethodSuccess = .F.) then
    ? loKey.LastErrorText
    release loKey
    return
endif

llSuccess = loKey.SaveText(lcEncryptedKeyStr,"qa_output/encrypted_openssh.pem")
if (llSuccess = .F.) then
    ? loKey.LastErrorText
    release loKey
    return
endif

? "Done!"


release loKey