The Public Suffix List (PSL) is a catalog of certain Internet

domain name A domain name is a string that identifies a realm of administrative autonomy, authority or control within the Internet. Domain names are often used to identify services provided through the Internet, such as websites, email services and more. As ...

s. Entries on the list are also referred to as effective top-level domains (eTLD). The

Mozilla Foundation The Mozilla Foundation (stylized as moz://a) is an American non-profit organization that exists to support and collectively lead the open source Mozilla project. Founded in July 2003, the organization sets the policies that govern development, ...

initiated the suffix list for the security and privacy policies of its

Firefox Mozilla Firefox, or simply Firefox, is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. It uses the Gecko rendering engine to display web pages, which implements current ...

web browser, but it is widely applied, with varying success, to a variety of other purposes under the

Mozilla Public License The Mozilla Public License (MPL) is a free and open-source weak copyleft license for most Mozilla Foundation software such as Firefox and Thunderbird The MPL license is developed and maintained by Mozilla, which seeks to balance the concerns ...

(MPL).

List

The list is used by

Mozilla Mozilla (stylized as moz://a) is a free software community founded in 1998 by members of Netscape. The Mozilla community uses, develops, spreads and supports Mozilla products, thereby promoting exclusively free software and open standards, w ...

browsers (Firefox), by Google in Chrome and Chromium projects on certain platforms, and by

Opera Opera is a form of theatre in which music is a fundamental component and dramatic roles are taken by singers. Such a "work" (the literal translation of the Italian word "opera") is typically a collaboration between a composer and a libr ...

. According to Mozilla, While ''com'', ''uk'', and ''us'' are

top-level domain A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System of the Internet after the root domain. The top-level domain names are installed in the root zone of the name space. For all domains in ...

s (TLDs), Internet users cannot always register the next level of domain, such as "co.uk" or "wy.us", because these may be controlled by

domain registrars A domain name registrar is a company that manages the reservation of Internet domain names. A domain name registrar must be accredited by a generic top-level domain (gTLD) registry or a country code top-level domain (ccTLD) registry. A registra ...

. By contrast, users can register second level domains within ''com'', such as ''example.com'', because registrars control only the top level. The Public Suffix List is intended to enumerate all domain suffixes controlled by registrars. An internet ''site'' consists of the online resources which can be controlled by the registrant of a domain name. That includes resources available via the domain and all its sub-domains. Two domains are ''related'' if they are in the same ''site,'' i.e. they share a suffix that is not included in the Public Suffix List. Security issues like a same-site attack can arise if the Public Suffix List is incorrect, or if browsers or sites are not properly configured. Some uses for the list are: * Avoiding " supercookies", HTTP cookies set by related-domain attackers for high-level domain name suffixes. In other words, a page at foo.example.co.uk might normally have access to cookies at bar.example2.co.uk, but example.co.uk should be walled off from cookies at example2.co.uk, to prevent a same-site attack, since the latter two domains could be registered by different owners. * Finding

DMARC Domain-based Message Authentication, Reporting and Conformance (DMARC) is an email authentication protocol. It is designed to give email domain owners the ability to protect their domain from unauthorized use, commonly known as email spoofing. Th ...

policy records for email subdomains. * Highlighting the most important part of a domain name in the

user interface In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine f ...

. * Improving the sorting of browser history entries by site.

Issues

The PSL has been seen as a tool for a variety of goals related to security, privacy, usability and resource management which can be in tension with each other, leading to maintenance difficulties and operational challenges. Ideas for effective approaches such as dbound, HTTP Stake Tokens and First Party Sets have been explored without consensus yet on good alternatives. In 2021, privacy enhancements in

iOS iOS (formerly iPhone OS) is a mobile operating system created and developed by Apple Inc. exclusively for its hardware. It is the operating system that powers many of the company's mobile devices, including the iPhone; the term also include ...

14.5 related to Apple's

Identifier for Advertisers Apple's Identifier for Advertisers (IDFA) is a unique random device identifier Apple generates and assigns to every device. It is intended to be used by advertisers to deliver personalized ads and attribute ad interactions for ad retargeting. Use ...

and unclear guidance from Facebook led to a flood of inappropriate requests for domains to be added to the Public Suffix List.

References

External links

*{{official Domain Name System Mozilla