Learn more about the Public Suffix List
The Public Suffix List is a cross-vendor initiative to provide an accurate list of domain name suffixes.
The usefulness of this can be seen if we take the example of cookies. Currently, browsers use an algorithm which basically only denies setting wide-ranging cookies for top-level domains with no dots (e.g. com or org). However, this does not work for top-level domains where only third-level registrations are allowed (e.g. .co.uk). In these cases, websites can set a cookie for .co.uk which will be passed onto every website registered under co.uk.
Since there is no algorithmic method of finding the highest level at which a domain may be registered for a particular top-level domain (the policies differ with each registry), the only method is to create a list. This is the aim of the Public Suffix List.
Software using the Public Suffix List will be able to detemine where cookies may and may not be set, protecting the user's data from theft.
As well as this, the Public Suffix List can also be used to support features such as site grouping in browsers. By knowing where the user-controlled section of the domain name begins and ends, browsers can group cookies and history entries by site in a way that couldn't easily be done before.
To take an example, the list of things for which Public Suffixes are used in Firefox 3 is:
- Restricting cookie-setting (as explained above)
- Restricting the setting of the document.domain property
- Sorting in the download manager
- Sorting in the cookie manager
- Searching in history
- "Responsible domain" display for some SSL certificates (not enabled by default)
In the future it may be used for, for example, restricting DOM Storage allowances on a per-domain basis.