Perl

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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use strict;
use warnings;
use Chilkat2;

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

my $key = Chilkat2::SshKey->new;

# 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.
my $keyStr = $key->LoadText('qa_data/putty_private_key.ppk');
if (!$key->LastMethodSuccess) {
    print $key->LastErrorText, "\n";
    exit;
}

my $success = $key->FromPuttyPrivateKey($keyStr);
if (!$success) {
    print $key->LastErrorText, "\n";
    exit;
}

# Export to an unencrypted OpenSSH key.
my $bEncrypt = 0;
my $unencryptedKeyStr = $key->ToOpenSshPrivateKey($bEncrypt);
if (!$key->LastMethodSuccess) {
    print $key->LastErrorText, "\n";
    exit;
}

$success = $key->SaveText($unencryptedKeyStr, 'qa_output/unencrypted_openssh.pem');
if (!$success) {
    print $key->LastErrorText, "\n";
    exit;
}

# Export to an encrypted OpenSSH key.  The Password property supplies the passphrase used to
# encrypt the output.
$bEncrypt = 1;
$key->Password('myExportPassword');
my $encryptedKeyStr = $key->ToOpenSshPrivateKey($bEncrypt);
if (!$key->LastMethodSuccess) {
    print $key->LastErrorText, "\n";
    exit;
}

$success = $key->SaveText($encryptedKeyStr, 'qa_output/encrypted_openssh.pem');
if (!$success) {
    print $key->LastErrorText, "\n";
    exit;
}

print "Done!\n";