I want to generate a Chrome extension (Chrome theme) from PHP. My PHP script generates a zip file (download.zip). To convert it to a .crx package, it needs to add headers, including a public key and a signature.
I saw this answer, but you need a .pem file that generates a .pub file. I'm on a shared hosting so exec() won't work (to convert a .pem to a .pub). There is no need to have a .pem file, it only has to use it once downloading (no updating needed).
Then I saw this comment that explains you can generate the private and public keys. Combining the two scripts won't work (see code).
How can I generate a keypair and use it to sign a chrome .crx package with PHP?
This code fails (CRX_SIGNATURE_VERIFICATION_INITALIZATION_FAILED):
// Create the keypair
$res=openssl_pkey_new();
// Get private key
openssl_pkey_export($res, $pk);
// Get public key
$key=openssl_pkey_get_details($res);
$key=$key["key"];
# make a SHA1 signature using our private key
openssl_sign(file_get_contents('download.zip'), $signature, $pk, 'sha1');
# decode the public key
$key = base64_decode($key);
# .crx package format:
#
# magic number char(4)
# crx format ver byte(4)
# pub key lenth byte(4)
# signature length byte(4)
# public key string
# signature string
# package contents, zipped string
#
# see http://code.google.com/chrome/extensions/crx.html
#
$fh = fopen('extension.crx', 'wb');
fwrite($fh, 'Cr24'); // extension file magic number
fwrite($fh, pack('V', 2)); // crx format version
fwrite($fh, pack('V', strlen($key))); // public key length
fwrite($fh, pack('V', strlen($signature))); // signature length
fwrite($fh, $key); // public key
fwrite($fh, $signature); // signature
fwrite($fh, file_get_contents('download.zip')); // package contents, zipped
fclose($fh);
You were using openssl_pkey_export
wrong and you haven't removed
-----BEGIN PUBLIC KEY-----
...
-----END PUBLIC KEY-----
from public key string before decoding it. I figured this out by looking at length of public key and signature. First one should be 161 and second one should be 128 bytes long (source):
A2 00 00 00 # 162 -- length of public key in bytes
80 00 00 00 # 128 -- length of signature in bytes
Here is the fixed code (PHP 5.4):
$pk=file_get_contents('pk.pem');
$priv = openssl_pkey_get_private($pk);
$pub = openssl_pkey_get_details($priv)['key'];
# make a SHA1 signature using our private key
openssl_sign(file_get_contents('download.zip'), $signature, $priv, OPENSSL_ALGO_SHA1);
# geting rid of -----BEGIN/END PUBLIC KEY-----
# you can probably do it better using preg_match_all / explode(PHP_EOL, $pub) etc.
$pub = trim(explode('-----',$pub)[2]);
# decode the public key
$pub = base64_decode($pub);
# .crx package format:
#
# magic number char(4)
# crx format ver byte(4)
# pub key lenth byte(4)
# signature length byte(4)
# public key string
# signature string
# package contents, zipped string
#
# see http://code.google.com/chrome/extensions/crx.html
#
$fh = fopen('extension.crx', 'wb');
fwrite($fh, 'Cr24'); // extension file magic number
fwrite($fh, pack('V', 2)); // crx format version
fwrite($fh, pack('V', strlen($pub))); // public key length
fwrite($fh, pack('V', strlen($signature))); // signature length
fwrite($fh, $pub); // public key
fwrite($fh, $signature); // signature
fwrite($fh, file_get_contents('download.zip')); // package contents, zipped
fclose($fh);
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