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What are Cookies?

Cookies are small pieces of data that websites send to a user's web browser, where they are stored locally. These data fragments are then sent back to the web server with subsequent requests, allowing websites to remember information about the user's interactions and preferences, enhance user experience, and perform various functions on the internet.

Dissecting Cookies

Cookies, as a concept, were first introduced in 1994 by a web browser engineer named Lou Montulli while he was working at Netscape Communications Corporation. The term "cookie" is derived from "magic cookie," a computer science term that refers to a piece of data shared between different software programs.

The primary motivation behind creating cookies was to solve a problem related to state management in web applications. In the early days of the internet, web servers had no way of retaining information about a user's previous interactions with a website. This posed a challenge for e-commerce and other dynamic web applications that required some form of user session management.

How Cookies works

In order for cookies to enable a web server to transmit small data fragments to a user's web browser, where the browser stores information locally, they need to perform the following actions:

  1. Cookie Creation: When a user visits a website, the web server can generate and send cookies to the user's web browser as part of the HTTP response. Cookies are typically represented as key-value pairs, such as "username=JohnDoe" or "sessionID=123456."
  2. Storage on the User's Device: Once received, the user's web browser stores these cookies locally on the user's device. This storage can vary depending on the type of cookie.
  3. Sending Cookies with Requests: When the user makes subsequent requests to the same website (e.g., clicking on links or submitting forms), the web browser automatically includes the relevant cookies in the HTTP request headers.
  4. Server-Side Handling: The web server, upon receiving a request, can read the cookies from the request headers. This allows the server to access the data stored in the cookies and use it to customize the response.
  5. Usage Scenarios:
  6. Authentication: Cookies are commonly used for user authentication. When a user logs in, a session cookie is often created, storing a session ID. Subsequent requests include this session ID, allowing the server to identify the user.
  7. Personalization: Cookies can store user preferences, such as language settings, theme choices, or shopping cart contents. This information is retrieved from cookies to personalize the user's experience.
  8. Tracking: Advertisers and website owners use cookies to track user behavior. Information about visited pages, click-through rates, and user interests can be stored in cookies for analytics and advertising targeting.
  9. Cookie Attributes: Cookies can have various attributes that control their behavior:
  10. Domain: Specifies which domains can access the cookie. For example, a cookie set for "" can be accessed by subdomains like "" and ""
  11. Path: Defines the URL path for which the cookie is valid. A cookie with the path "/account" will only be sent for requests to URLs starting with "/account."
  12. Secure: Secure cookies are only transmitted over HTTPS connections, enhancing security.
  13. HttpOnly: HttpOnly cookies cannot be accessed or manipulated by JavaScript, providing protection against cross-site scripting (XSS) attacks.

Types of Cookies

There are several types of cookies used in web technology, each serving a specific purpose. The main types of cookies are:

  • Session Cookies: These temporary cookies reside in the browser's memory for the duration of a single browsing session. They play a crucial role in maintaining session-specific information, such as a user's login status or the items in a shopping cart. Once the user closes their browser, session cookies are automatically deleted, ensuring that the information is only relevant for the current session.
  • Persistent Cookies: Persistent cookies, in contrast, have a predefined expiration date set by the web server when they are created. These cookies are stored as files on the user's device and remain there until they reach their expiration date or until the user manually deletes them. They are commonly utilized for tasks such as remembering login credentials or storing user preferences, making them valuable for personalization and user convenience across multiple sessions.
  • Secure Cookies: Secure cookies are specifically designed to be transmitted exclusively over secure and encrypted connections, typically HTTPS. They serve a critical role in enhancing security by ensuring that sensitive data, such as login information or financial transactions, is not exposed to potential attackers during transmission.
  • HttpOnly Cookies: HttpOnly cookies are primarily focused on security. They possess the attribute that prevents them from being accessed or manipulated by client-side scripts, like JavaScript. This attribute is instrumental in safeguarding cookies from cross-site scripting (XSS) attacks, where malicious scripts attempt to steal or manipulate cookie data.
  • First-Party Cookies: These cookies are set by the website that the user is actively visiting and are associated with the domain displayed in the browser's address bar. First-party cookies are commonly employed for legitimate website functions such as session management, personalization, and tracking user preferences.
  • Third-Party Cookies: In contrast, third-party cookies are established by domains other than the one the user is presently visiting. They often serve tracking and advertising purposes, allowing third-party advertisers to monitor user behavior across various websites. However, their usage has raised privacy concerns as they contribute to user tracking across the internet.
  • Same-Site Cookies: These cookies are designed to mitigate the risk of cross-site request forgery (CSRF) attacks. By specifying the same-site attribute in the cookie, their scope is restricted to the originating site, reducing vulnerability to cross-origin attacks.
  • Cross-Origin Cookies: Cross-origin cookies are set by one website but can be accessed by others under specific conditions, typically adhering to the same-origin policy. Subdomain sharing can also be configured through the cookie's domain attribute, enabling controlled sharing of cookie data.
  • Supercookies and Evercookies: These persistent cookies are notoriously difficult to delete and can be employed for extensive user tracking across websites. They employ various techniques to store redundant copies of data, making them highly resistant to user attempts at removal.
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