Security Settings

All security settings are located in the CDN resource card on the Settings tab.

Key Access

When using the Key Access option, the content can be downloaded only by requests containing a hash key. This option protects the content from potentially unwanted downloads. Temporary links to protected content will look as follows:

  • CDN Selectel: <cdn_selectel-domain>/123.jpg?md5=DMF1ucDxtHCxwYQ&expires=2147483647
  • CDN Akamai: <akamai-domain>/123.jpg?sel-token=exp=1592563853~hmac=0851b56b74c47120565024a6c6532dc77dff809b0eeeb6fc1e01c86090a1bccd

Follow these steps to enable Key Access:

  1. Go to the Settings tab in the CDN resource card and activate this function.
  2. Click Generate key in the new window or enter the desired signature key.

Key requirements:

  • CDN Selectel

    • numbers and Latin characters;
    • length from 6 to 32 symbols;

  • CDN Akamai

    • hexadecimal number;
    • length from 6 to 64 bits;
    • even number of bits.

By default, the following 4 parameters are taken into account when generating a token:

  • link expiration time;
  • original link to the file;
  • IP addresses for which the file access is open;
  • key.

You can configure the token so that file access is open to any IP addresses. To do this, uncheck the Add client’s IP to the token box and configure the token on the source server so that the IP parameter is ignored.

Configuration on the Source Server for Selectel CDN

Organize the website so that the users access protected files in the CDN using temporary links. When accessing CDN servers, the content should be returned regardless of whether the key is available. Hash key is the result of calculating the one-way MD5 hash function (String), where String is a parameter obtained by merging the following elements (in the specified sequence): <expires><path><ip> <key>

Element Description
expires Link expiration time. Specified in the UNIX Timestamp format.
path Original link to the file
key Key
IP IP addresses for which the file access is open (this parameter may not be taken into account).

To generate Unix Timestamp on Linux: date +%s -d "10min" (current time + 10 minutes). CDN servers validate every request on their side. They have the same input data (<expires><path><ip> <key>) and use it to generate a hash key.

If the computed signature does not match and/or has expired, the CDN content delivery server sends the 403 Forbidden error.

If the computed signature matches and the link has not expired, the G-core CDN content delivery server sends the requested file to the user.

Options for Generating a Token at the Source

PHP script with the IP parameter

<?php
$secret = 'secret_key';
$ip = '1.2.3.4';
$path = '/live/133529_2/chunklist.m3u8';
$expires = time() + 10000;
$link = "$expires$path$ip $secret";
$md5 = md5($link, true);
$md5 = base64_encode($md5);
$md5 = strtr($md5, '+/', '-_');
$md5 = str_replace('=', '', $md5);
$url = "http://cdn.site.com{$path}?md5={$md5}&expires={$expires}";
echo $url;
echo "\n";

PHP script without the IP parameter

<?php
$secret = 'secret_key';
$path = '/live/133529_2/chunklist.m3u8';
$expires = time() + 10000;
$link = "$expires$path $secret";
$md5 = md5($link, true);
$md5 = base64_encode($md5);
$md5 = strtr($md5, '+/', '-_');
$md5 = str_replace('=', '', $md5);
$url = "http://cdn.site.com{$path}?md5={$md5}&expires={$expires}";
echo $url;
echo "\n";

Where:

  • secret is the secret key;
  • path is the path to the file;
  • ip is the IP address that is allowed to receive content;
  • expires is the link lifetime (in seconds);
  • link is the string for generating a token with the necessary parameters of the hash key;
  • url is the link to the file.

Python script with the IP parameter

import base64
from hashlib import md5
from time import time
secret = 'secret_key'
path = "/images/1.jpg"
ip = '1.2.3.4'
expires = int(time()) + 1800
token = base64.encodestring(
     md5(
     "%s%s%s %s" % (expires, path, ip, secret)
      ).digest()
  ).replace("\n", "").replace("+", "-").replace("/", "_").replace("=", "")
secured_url = "http://cdn.site.com%s?md5=%s&expires=%s" % (path, token, expires)
print secured_url

Python script without the IP parameter

import base64
from hashlib import md5
from time import time
secret = 'secret_key'
path = "/images/1.jpg"
expires = int(time()) + 100000
token = base64.encodestring(
md5(
"%s%s %s" % (expires, path, secret)
).digest()
).replace("\n", "").replace("+", "-").replace("/", "_").replace("=", "")
secured_url = "http://cdn.site.com%s?md5=%s&expires=%s" % (path, token, expires)
print secured_url

Where:

  • secret is the secret key;
  • path is the path to the file;
  • ip is the IP address that is allowed to receive content;
  • expires is the link lifetime (in seconds);
  • token is token generation;
  • secured_url is the link to the file.

Using openssl

As a result, you will only get a token. You must use it in links and additionally specify the link expiration time in the UNIX Timestamp format.

With the IP parameter::

echo -n '2147483647/images/1.jpg1.2.3.4 secret_key' | openssl md5 -binary | openssl base64 | tr +/ -_ | tr -d =
'2147483647/images/1.jpg1.2.3.4 secret_key' = '{expires}{path}{ip} {secret_key}'

Without the IP parameter:

echo -n '2147483647/images/1.jpg secret_key' | openssl md5 -binary | openssl base64 | tr +/ -_ | tr -d =
'2147483647/images/1.jpg secret_key' = '{expires}{path} {secret_key}'

Configuration on the Source Server for CDN Akamai

Use the following libraries to generate Akamai tokens:

You need to generate the url parameter query string when using these libraries. Use the following required values:

token_name = "sel-token"
escape_early = true

Python script without the IP parameter

from akamai.edgeauth import EdgeAuth, EdgeAuthError
ET_HOSTNAME = '<resourceID>.akamaized.net'
ET_ENCRYPTION_KEY = 'deadbeef'
DEFAULT_WINDOW_SECONDS = 500 # seconds
et = EdgeAuth(**{'key': ET_ENCRYPTION_KEY,
                  'window_seconds': DEFAULT_WINDOW_SECONDS})
et.token_name = "sel-token"
et.escape_early = "true"
token = et.generate_url_token("/123.jpg")
url = "http://{0}{1}?{2}={3}".format(ET_HOSTNAME, "/123.jpg", et.token_name, token)

Python script with the IP parameter and time

from akamai.edgeauth import EdgeAuth, EdgeAuthError
from time import time
ET_HOSTNAME = '<resourceID>.akamaized.net'
ET_ENCRYPTION_KEY = 'deadbeef'
START_TIME = time() + 60000 # seconds
END_TIME = time() + 660000 # seconds
IP = "1.1.1.1"

et = EdgeAuth(**{'key': ET_ENCRYPTION_KEY})
et.start_time = START_TIME
et.end_time = END_TIME
et.ip = IP
et.token_name = "sel-token"
et.escape_early = "true"
token = et.generate_url_token("/123.jpg")
url = "http://{0}{1}?{2}={3}".format(ET_HOSTNAME, "/123.jpg", et.token_name, token)
print(url)

Where:

  • ET_HOSTNAME is the hostname;
  • ET_ENCRYPTION_KEY is the secret key;
  • DEFAULT_WINDOW_SECONDS is the token lifetime in seconds starting from the moment of generation;
  • START_TIME is the token start time;
  • END_TIME is the token expiration time;
  • IP is the IP address for the request from which this token will be valid.

To set the token lifetime, you can choose either DEFAULT_WINDOW_SECONDS, and then the token lifetime will be equal to time (), or a pair of START_TIME and END_TIME values.

Examples in other languages are available in the repositories with the libraries.

The use/non-use of the client’s IP address in the token in CDN Akamai is configured when the token is generated and, accordingly, may differ in links to different files and even in links to the same file for different clients.

Domain Access Policy

This option is necessary to prohibit posting links to your content on other websites. By default, no domain restrictions are applied to the resource. You can set a permissive or prohibitive policy.

Permissive Policy

Specify the domains you want to deny access to in the new window. When accessing from the entered domains, the user will be denied access.

Prohibitive Policy

Specify the domains you want to allow access to in the new window. When accessing from the entered domains, the user will be allowed access.

IP Access Policy

This option is necessary to restrict access to the CDN content from specific IP addresses. By default, no IP access restrictions are applied to the resource. You can set a permissive or prohibitive policy.

Permissive Policy

Access to the resource is allowed to all IP addresses, except for those specified in the field.

Prohibitive Policy

Access to the resource is prohibited to all IP addresses, except for those specified in the field.

Access Policy by Countries

You can allow or deny access to the content from specific countries. By default, no country-specific access restrictions are applied to the resource. You can set a permissive or prohibitive policy. Please note that this feature is not available in Akamai.

Permissive Policy

Access to the resource is allowed for all countries except for those specified in the field.

Prohibitive Policy

Access to the resource is denied for all countries except for those specified in the field.

Access Policies by Client Applications

You can limit access to the content from the CDN by client applications (User Agent), for example, for a specific browser, set-top box, or device. By default, all client applications are allowed to access the resource. You can set a permissive or prohibitive policy.

Permissive Policy

Access to the resource is allowed for all client applications except for those specified in the field.

Prohibitive Policy

Access to the resource is denied for all client applications except for those specified in the field.

Unique HTTP Headers

You can set your own HTTP headers that the CDN server will add to the request when accessing the source. Valid characters for the fields are as follows:

  • Header name: Latin characters (A-Z, a-z), numbers (0-9), underscore (_), and dash (-);
  • Meaning: Latin characters (A-Z, a-z), numbers (0-9), underscore (_), dot mark (.), slash (/), colon (:), dash (-), equal mark (=), and space.

Spaces can only be added in the middle of the value. The value cannot begin or end with spaces. You can also add only one space in the middle between words.

Access-Control-Allow-Origin Header

You can protect the content from downloading on the third-party sites or in the third-party applications by adding the Access-Control-Allow-Origin header. This option applies to all files transmitted through the CDN.

How Does CORS Work?

For example, a user at http://domain1.com opens the image that is located on your website at http://cdn-domain.com/image.jpg.

In this case, the user’s browser sends a http://cdn-domain.com/image.jpg request to the domain server, for example:

GET /image HTTP/1.1
Host: domain2.com
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.1b3pre) Gecko/20081130 Minefield/3.1b3pre
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Connection: keep-alive
Referer: http://domain1.com/examples/access-control/test.html
Origin: http://domain1.com

The Origin header is important in the request. It informs the server that the request has been sent from the http://domain1.com domain.

The http://cdn-domain.com/image.jpg domain server takes into account the Origin header of the request and accepts the request or refuses to process it.

If the server accepts the request, the Access-Control-Allow-Origin header will be sent to the browser in response, which will allow the browser to display the image for the user of the http://domain1.com website.

If the server refuses to process the request, the response will be sent to the browser without the Access-Control-Allow-Origin header and the browser will not display the image to the user.

Configuration in the Control Panel

There are three configuration options:

  1. *, for all domains — content display is allowed for all websites.
  2. For specified domains only — when receiving a request, CDN checks the Origin header value against the domains specified for the Access-Control-Allow-Origin HTTP header. If the Origin header value matches one of the specified domains, CDN adds the Access-Control-Allow-Origin header to the response with the domain that the request came from. If the Origin header value does not match the specified domains, the Access-Control-Allow-Origin header is not added. The client’s browser only serves content if the Access-Control-Allow-Origin header is present in the response.
  3. For all domains — all websites are allowed to display content. When a request is received, the CDN server adds the Access-Control header to the response that the request came from.

Redirecting to HTTPS

This option redirects all requests from HTTP to HTTPS.

If you are using a personal CNAME, make sure it is accessible over HTTPS.