HTTP cookie
[1] They can also be used to save information that the user previously entered into form fields, such as names, addresses, passwords, and payment card numbers for subsequent use.
It was derived from the term magic cookie, which is a packet of data a program receives and sends back unchanged, used by Unix programmers.
Persistent cookies are also used for reasons such as keeping users logged into their accounts on websites, to avoid re-entering login credentials at every visit.
In 2016 Google Chrome version 51 introduced[27] a new kind of cookie with attribute SameSite with possible values of Strict, Lax or None.
[37] In a 2021 blog post, Mozilla used the term supercookie to refer to the use of browser cache as a means of tracking users across sites.
To keep track of which user is assigned to which shopping cart, the server sends a cookie to the client that contains a unique session identifier (typically, a long string of random letters and numbers).
When the user visits a website's login page, the web server typically sends the client a cookie containing a unique session identifier.
The browser then sends them back to the server with every request, introducing states (memory of previous events) into otherwise stateless HTTP transactions.
Below is an example of three Set-Cookie header fields that were received from a website after a user logged in: The first cookie, lu, is set to expire sometime on 15 January 2013.
This sort of cookie typically appears when web pages feature content from external websites, such as banner advertisements.
However, the newer standard, RFC 6265, explicitly allows user agents to implement whichever third-party cookie policy they wish.
Safari allows embedded sites to use Storage Access API to request permission to set first-party cookies.
In 2002, privacy activist Daniel Brandt found that the CIA had been leaving persistent cookies on computers that had visited its website.
On December 25, 2005, Brandt discovered that the National Security Agency (NSA) had been leaving two persistent cookies on visitors' computers due to a software upgrade.
In a case decided under the Data Protection Directive however, the Court of Justice of the European Union later confirmed however that the previous law implied the same strong quality of consent as the current instrument.
While not all data processing under the GDPR requires consent, the characteristics of behavioural advertising mean that it is difficult or impossible to justify under any other ground.
[81][82] The Court of Justice of the European Union has also ruled that consent must be 'efficient and timely', meaning that it must be gained before cookies are laid and data processing begins instead of afterwards.
Robert Bond of the law firm Speechly Bircham describes the effects as "far-reaching and incredibly onerous" for "all UK companies".
[84] However, scholars note that the onerous nature of cookie pop-ups stems from an attempt to continue to operate a business model through convoluted requests that may be incompatible with the GDPR.
[79] A study of 17,000 websites found that 84% of sites breached this criterion, finding additionally that many laid third party cookies with no notice at all.
[85] The UK regulator, the Information Commissioner's Office, stated in 2019 that the industry's 'Transparency and Consent Framework' from the advertising technology group the Interactive Advertising Bureau was 'insufficient to ensure transparency and fair processing of the personal data in question and therefore also insufficient to provide for free and informed consent, with attendant implications for PECR [e-Privacy] compliance.
'[81] Many companies that sell compliance solutions (Consent Management Platforms) permit them to be configured in manifestly illegal ways, which scholars have noted creates questions around the appropriate allocation of liability.
[86] A W3C specification called P3P was proposed for servers to communicate their privacy policy to browsers, allowing automatic, user-configurable handling.
[88] In 2020, the European Data Protection Board, composed of all EU data protection regulators, stated that cookie walls were illegal.In order for consent to be freely given, access to services and functionalities must not be made conditional on the consent of a user to the storing of information, or gaining of access to information already stored, in the terminal equipment of a user (so called cookie walls).
An attacker could use intercepted cookies to impersonate a user and perform a malicious task, such as transferring money out of the victim's bank account.
This occurs when an attacker takes advantage of a website that allows its users to post unfiltered HTML and JavaScript content.
In particular, they do not always accurately identify users, they can be used for security attacks, and they are often at odds with the Representational State Transfer (REST) software architectural style.
First, having the tracking information placed in the HTTP request body rather than in the URL means it will not be noticed by the average user.
All current web browsers can store a fairly large amount of data (2–32 MB) via JavaScript using the DOM property window.name.
Furthermore, some systems, such as Tor, are designed to retain Internet anonymity, rendering tracking by IP address impractical, impossible, or a security risk.
