An HTTP cookie, a diminutive data fragment produced by a web server and stored on a user’s device via a web browser, serves to retain information and monitor a user’s online behavior. These cookies come in a variety of forms, such as authentication and tracking cookies. The concept of HTTP cookies was first introduced by Lou Montulli, who drew inspiration from Unix’s ‘magic cookie’, and the original blueprint was crafted by Netscape in 1994. Cookies may be short-lived (session cookies), enduring (persistent cookies), secure, or impervious to client-side APIs (Http-only cookies). They play a crucial role in managing online sessions, tailoring user experiences, and tracing online behavior. However, they carry potential security threats, including the generation of Supercookies and Zombie cookies. The communication between a web browser and a server involves the exchange of these cookies, adhering to specific rules and specifications to ensure safe and efficient functionality.
HTTP cookies (also called web cookies, Internet cookies, browser cookies, or simply cookies) are small blocks of data created by a web server while a user is browsing a website and placed on the user's computer or other device by the user's web browser. Cookies are placed on the device used to access a website, and more than one cookie may be placed on a user's device during a session.
Cookies serve useful and sometimes essential functions on the web. They enable web servers to store stateful information (such as items added in the shopping cart in an online store) on the user's device or to track the user's browsing activity (including clicking particular buttons, logging in, or recording which pages were visited in the past). 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.
Authentication cookies are commonly used by web servers to authenticate that a user is logged in, and with which account they are logged in. Without the cookie, users would need to authenticate themselves by logging in on each page containing sensitive information that they wish to access. The security of an authentication cookie generally depends on the security of the issuing website and the user's web browser, and on whether the cookie data is encrypted. Security vulnerabilities may allow a cookie's data to be read by an attacker, used to gain access to user data, or used to gain access (with the user's credentials) to the website to which the cookie belongs (see cross-site scripting and cross-site request forgery for examples).
Tracking cookies, and especially third-party tracking cookies, are commonly used as ways to compile long-term records of individuals' browsing histories — a potential privacy concern that prompted European and U.S. lawmakers to take action in 2011. European law requires that all websites targeting European Union member states gain "informed consent" from users before storing non-essential cookies on their device.
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