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

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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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#include <C_CkSshKey.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkSshKey key;
    const char *keyStr;
    BOOL bEncrypt;
    const char *unencryptedKeyStr;
    const char *encryptedKeyStr;

    success = FALSE;

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

    key = CkSshKey_Create();

    //  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.
    CkSshKey_putPassword(key,"myKeyPassword");

    //  LoadText is a convenience method that reads any text file into a string.  It does not itself
    //  load the key.
    keyStr = CkSshKey_loadText(key,"qa_data/putty_private_key.ppk");
    if (CkSshKey_getLastMethodSuccess(key) == FALSE) {
        printf("%s\n",CkSshKey_lastErrorText(key));
        CkSshKey_Dispose(key);
        return;
    }

    success = CkSshKey_FromPuttyPrivateKey(key,keyStr);
    if (success == FALSE) {
        printf("%s\n",CkSshKey_lastErrorText(key));
        CkSshKey_Dispose(key);
        return;
    }

    //  Export to an unencrypted OpenSSH key.
    bEncrypt = FALSE;
    unencryptedKeyStr = CkSshKey_toOpenSshPrivateKey(key,bEncrypt);
    if (CkSshKey_getLastMethodSuccess(key) == FALSE) {
        printf("%s\n",CkSshKey_lastErrorText(key));
        CkSshKey_Dispose(key);
        return;
    }

    success = CkSshKey_SaveText(key,unencryptedKeyStr,"qa_output/unencrypted_openssh.pem");
    if (success == FALSE) {
        printf("%s\n",CkSshKey_lastErrorText(key));
        CkSshKey_Dispose(key);
        return;
    }

    //  Export to an encrypted OpenSSH key.  The Password property supplies the passphrase used to
    //  encrypt the output.
    bEncrypt = TRUE;
    CkSshKey_putPassword(key,"myExportPassword");
    encryptedKeyStr = CkSshKey_toOpenSshPrivateKey(key,bEncrypt);
    if (CkSshKey_getLastMethodSuccess(key) == FALSE) {
        printf("%s\n",CkSshKey_lastErrorText(key));
        CkSshKey_Dispose(key);
        return;
    }

    success = CkSshKey_SaveText(key,encryptedKeyStr,"qa_output/encrypted_openssh.pem");
    if (success == FALSE) {
        printf("%s\n",CkSshKey_lastErrorText(key));
        CkSshKey_Dispose(key);
        return;
    }

    printf("Done!\n");


    CkSshKey_Dispose(key);

    }