I'm trying to create a signature for a privately stored file in Google Cloud Storage; so that I can distribute a time-limited link.
Currently doing this and it makes a signature that's too short ... where am I going wrong?
var crypto = require("crypto");
var ttl = new Date().getTime() + 3600;
var id = 'the_target_file.txt';
var bucketName = 'bucket_name';
var POLICY_JSON = "GET\n" + "\n" + "\n" + ttl + "\n" + '/' + bucketName + '/' + id;
// stringify and encode the policy
var stringPolicy = JSON.stringify(POLICY_JSON);
var base64Policy = Buffer(stringPolicy, "utf-8").toString("base64");
// sign the base64 encoded policy
var privateKey = "MY_PRIVATE_KEY";
var sha256 = crypto.createHmac("sha256", privateKey);
var signature = sha256.update(new Buffer(base64Policy, "utf-8")).digest("base64");
console.log ( signature );
Options for generating a signed URL Simply specify Cloud Storage resources, point to the host storage.googleapis.com , and use Google HMAC credentials in the process of generating the signed URL.
To create a valid pre-signed URL for your object, you must provide your security credentials, specify a bucket name, an object key, specify the HTTP method (for instance the method is "GET" to download the object) and expiration date and time. Anyone who receives the pre-signed URL can then access the object.
There is an API/module for getting signed URLs now.
module: https://www.npmjs.com/package/@google-cloud/storage
API docs: https://googleapis.dev/nodejs/storage/latest/File.html#getSignedUrl
Example
var storage = require('@google-cloud/storage')();
var myBucket = storage.bucket('my-bucket');
var file = myBucket.file('my-file');
//-
// Generate a URL that allows temporary access to download your file.
//-
var request = require('request');
var config = {
action: 'read',
expires: '03-17-2025' // this could also include time (MM-DD-YYYYTHH:MM:SSZ)
};
file.getSignedUrl(config, function(err, url) {
if (err) {
console.error(err);
return;
}
// The file is now available to read from this URL.
request(url, function(err, resp) {
// resp.statusCode = 200
});
});
Realised what I was doing wrong ... I was hashing the policy string instead of signing it. The below code now gives me the correct output.
var crypto = require("crypto");
var fs = require("fs");
var expiry = new Date().getTime() + 3600;
var key = 'the_target_file';
var bucketName = 'bucket_name';
var accessId = 'my_access_id';
var stringPolicy = "GET\n" + "\n" + "\n" + expiry + "\n" + '/' + bucketName + '/' + key;
var privateKey = fs.readFileSync("gcs.pem","utf8");
var signature = encodeURIComponent(crypto.createSign('sha256').update(stringPolicy).sign(privateKey,"base64"));
var signedUrl = "https://" + bucketName + ".commondatastorage.googleapis.com/" + key +"?GoogleAccessId=" + accessId + "&Expires=" + expiry + "&Signature=" + signature;
console.log(signedUrl);
For completeness ... here is a PHP version that does the same thing, which I used to check my results
$expiry = time() + 3600;
$key = 'the_target_file';
$bucketName = 'bucket_name';
$accessId = 'my_access_id';
$stringPolicy = "GET\n\n\n".$expiry."\n/".$bucketName."/".$key;
$fp = fopen('gcs.pem', 'r');
$priv_key = fread($fp, 8192);
fclose($fp);
$pkeyid = openssl_get_privatekey($priv_key,"password");
if (openssl_sign( $stringPolicy, $signature, $pkeyid, 'sha256' )) {
$signature = urlencode( base64_encode( $signature ) );
echo 'https://'.$bucketName.'.commondatastorage.googleapis.com/'.
$key.'?GoogleAccessId='.$accessId.'&Expires='.$expiry.'&Signature='.$signature;
}
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