HTTP

What is HTTP?

HyperText Transfer Protocol is the most widely used network protocol on the Internet. All web browsers (such as Chrome, Firefox, Safari) use the HTTP protocol to retrieve web pages. HTTP defines the rules for requests and responses between clients (usually web browsers) and servers, and is the foundation for data transmission on the World Wide Web (WWW).

In simple terms, HTTP is like the language used for communication between web browsers and Web servers. When you type a web address and press Enter, the browser sends an HTTP request to the server, and the server returns an HTTP response, which contains the web page content you requested.

How HTTP Works: Request-Response Model

HTTP is a protocol based on the client-server model, and its basic working principle follows a simple request-response model:

1. Client Initiates a Request:

   • The client (usually a web browser) sends an HTTP request to the server. The request typically includes the following parts:
     • Request Method: Such as GET, POST, which indicates the action the server is to perform.
     • Request URI: Usually a Uniform Resource Identifier (URI) pointing to a specific resource, i.e., the web address you are visiting.
     • Version Number: Such as HTTP/1.1 or HTTP/2, indicating the protocol version being used.
     • Header Information: Contains additional information, such as client type, accepted encoding, Cookies, etc.
     • Request Body: Some requests (such as POST) include data to be sent to the server.

2. Server Processes Request:

   • After receiving the request, the server processes it according to the request method, URI, and other information.
   • Processing may include finding files, executing scripts, accessing databases, etc.

3. Server Sends Response:

   • After processing is complete, the server sends an HTTP response to the client. The response also includes the following parts:
     • Status Code: Such as 200 (Success), 404 (Resource Not Found), 301 (Permanent Redirect), etc., indicating the result of the request processing.
     • Status Message: Text description corresponding to the status code, such as “OK”, “Not Found”, “Moved Permanently”.
     • Header Information: Contains additional information, such as content type (Content-Type), content length (Content-Length), cache control directives, etc.
     • Response Body: Contains the actual data, such as web page content (HTML), images, videos, JSON data, etc. For ordinary web page visits using GET requests, the response body is usually HTML.

4. Client Receives Response:

   • After receiving the response, the client parses the status code and header information. If the status code is in the 2xx series (Success), the client parses the response body (usually HTML) and renders it into a user-visible web page.

This process is constantly repeated, forming the underlying basis for all Web activities such as browsing web pages, submitting forms, and loading images that we do on a daily basis.

What Security Issues Does HTTP Face?

Although HTTP is the foundation of the World Wide Web, its design itself has some significant security issues, mainly because it is a Plain Text Transmission Protocol. This means that all data transmitted between the client and the server, including passwords, personally identifiable information, sensitive business data, etc., is unencrypted and can be easily intercepted and read by any third party (attacker) capable of monitoring network traffic.

Key security issues include:

1. Data Leakage and Eavesdropping:

   • Since the transmitted content is in plaintext, any attacker who has mastered network sniffing techniques (such as using tools like Wireshark) or who is listening between the user and the server, or the server and the proxy, can capture detailed information about HTTP requests and responses.
   • This can lead to the disclosure of sensitive information (such as usernames, passwords, credit card numbers, personal information, etc.), causing serious privacy breaches and identity theft risks.

2. Man-in-the-Middle Attacks:

   • An attacker can insert themselves into the communication path between the client and the server, acting as a “man-in-the-middle.” They can intercept, tamper with, read, or replay HTTP requests and responses.
   • For example, an attacker can intercept login credentials submitted by the user and then send them to the real server, while keeping a copy for themselves, thereby stealing the user’s account.
   • Because HTTP does not have a built-in verification mechanism to confirm the identity of the communicating parties, this type of attack is relatively easy to implement.

3. Cross-Site Scripting Attacks:

   • Although XSS itself is a vulnerability at the website application level, it usually retrieves data from the server (such as dynamically generated content, requests for data from third-party services, etc.) through HTTP GET or POST requests, and then embeds this data into the web page without sufficient filtering.
   • If the data returned by the server contains malicious scripts injected by the attacker, these scripts will be executed in the user’s browser when other users visit the web page, thereby stealing user data, session cookies, or performing other malicious operations.

4. Denial of Service Attacks:

   • An attacker can send a large number of invalid or malicious HTTP requests to the server, consuming the server’s resources (such as bandwidth, CPU, memory), making it unable to respond to legitimate user requests, resulting in service disruption.

5. Session Hijacking:

   • The HTTP protocol itself does not provide mechanisms to guarantee the confidentiality and integrity of the session. If the user uses a session in an HTTP application that does not use HTTPS, it is easier for an attacker to intercept the Cookie containing the Session ID, thereby taking over the user’s session and impersonating the user.

The Relationship Between HTTPS and HTTP? Why is HTTPS Needed?

Due to the inherent security issues described above, HTTP has gradually been replaced or used in conjunction with HTTPS (HTTP Secure). HTTPS adds an SSL/TLS protocol layer on top of HTTP, providing the following security mechanisms:

• Encryption: Encrypts data using keys, ensuring that data is protected even when transmitted over public networks, preventing eavesdropping.
• Authentication: Verifies the identity of the server through digital certificates, preventing man-in-the-middle attacks, and letting users know they are communicating with the real server.
• Data Integrity: Ensures that the data transmitted is not tampered with during transmission.

It is precisely because of these security features that HTTPS has become the standard for modern Web applications to protect user data, maintain privacy, and build user trust. It is essential to enforce the use of HTTPS for websites that handle sensitive information (such as e-commerce, online banking, social media, login pages, etc.), and websites that need to comply with data protection regulations (such as GDPR).