When building a website, running an e-commerce business, setting up a blog, or deploying a server, many beginners will encounter a term—SSL certificate. You may have heard that "SSL is a must," "browsers will warn of insecurity without SSL," and "HTTPS is more secure than HTTP," but when asked: What exactly is an SSL certificate? How does it work? Why does installing it make your website secure? Many people only have a superficial understanding.

　　Why do almost all websites now use SSL certificates?

　　In the early years, many websites used the HTTP protocol. Back then, browser address bars didn't display a padlock icon or a "not secure" warning, and people could still access websites normally.

　　However, with the development of the internet, problems gradually emerged: the HTTP protocol transmits data in "plaintext."

　　What does this mean? Simply put, the content users enter in their browsers, such as login usernames and passwords, phone numbers and email addresses in forms, and information submitted during payments, can be directly understood if intercepted by a third party during transmission.

　　Therefore, the role of SSL certificates emerges: to make data "incomprehensible" during transmission.

　　What exactly is an SSL certificate?

　　Essentially, an SSL certificate is a digital certificate with three core functions: encrypting data transmission, verifying website identity, and preventing data tampering.

　　When your website has an SSL certificate installed, the access method will change from http://example.com to https://example.com.

　　A small padlock will appear in the browser's address bar. This padlock is not decorative; it signifies that the current website is using SSL encrypted communication.

　　What core problem does an SSL certificate solve?

　　To truly understand the significance of SSL, let's imagine a scenario without SSL.

　　You enter your username and password in your browser, and the data is sent from your computer to a server. If there's an "eavesdropper," like someone listening to mail on the street, they can directly see what you sent.

　　SSL certificates solve these three problems: whether data can be eavesdropped on, whether the website being accessed is a "fake website," and whether data has been modified during transmission. SSL solves all three problems at once through encryption and verification mechanisms.

　　How do SSL certificates "prove a website's identity"?

　　Many beginners think SSL is just encryption, but it has another very important function: proving that the website you are visiting is genuine and not an imposter.

　　SSL certificates are not generated arbitrarily by the website itself; they are issued by a trusted Certificate Authority (CA).

　　The process is roughly as follows:

• The website applies for a certificate from a CA.
• The CA verifies the website's domain name or company information.
• After successful verification, the CA issues an SSL certificate.
• Browsers have a built-in "trust list" of these CAs.

　　When a user visits a website, the browser checks: Is the certificate issued by a trusted CA? Does the domain name match? Is the certificate expired or revoked? Only after successful verification will the browser display a padlock icon.

　　How SSL Certificates Work (Simplified Version)

　　Many people find the "working principle" complicated, but it can be understood with a relatable example.

　　You can think of SSL communication as a "three-step process."

　　Step 1: The server first presents its "identity card." When you visit an HTTPS website, the server first sends an SSL certificate to the browser, essentially telling you, "I am this website, this is my official proof."

　　The second step: The browser verifies the authenticity of the certificate. The browser checks if the certificate is trustworthy and matches the current domain. If there's a problem, it directly warns the user "Not secure."

　　The third step: Both parties negotiate an "encryption rule." After successful verification, the browser and server negotiate an encryption method known only to them. All subsequent data transmissions will be encrypted using this rule.

　　From this step onward, even if data is intercepted, it will just be a jumble of characters.

　　Why is HTTPS more secure than HTTP?

　　The biggest difference between HTTP and HTTPS lies in whether or not SSL encryption is used.

　　HTTP is characterized by: plaintext data transmission, inability to verify website identity, and vulnerability to eavesdropping and tampering.

　　HTTPS is characterized by: encrypted data transmission, verification of the website's true identity, and prevention of man-in-the-middle attacks.

　　Therefore, mainstream browsers now display "insecure" warnings for HTTP websites. This isn't the browsers "intentionally scaring" people; rather, HTTP is genuinely no longer suitable for the modern internet environment.

　　Are SSL certificates always paid?

　　This is one of the most frequently asked questions by beginners. The answer is: not necessarily.

　　Currently, SSL certificates can be broadly divided into two categories: free SSL certificates and paid SSL certificates.

　　Free certificates are suitable for personal blogs, small websites, and testing environments; paid certificates are typically used for corporate websites, e-commerce platforms, and financial websites.

　　There is no fundamental difference in "encryption strength" between the two; the main differences lie in the verification level, brand trust level, and after-sales and compensation mechanisms.

　　Frequently Asked Questions:

　　Q: Is a website absolutely secure once an SSL certificate is installed?

　　A: No. SSL only guarantees data transmission security; it does not prevent website program vulnerabilities, weak passwords, or server intrusion.

　　Q: Are SSL certificates bound to a domain name?

　　A: Yes. The certificate must match the corresponding domain name; otherwise, the browser will warn of a risk.

　　Frequency Questions: Q: What happens when a certificate expires?

　　A: After a certificate expires, the browser will directly display a "Not Secure" message, and many users will choose to close the website.

　　Q: Can an IP address use an SSL certificate?

　　A: Yes, but the use cases are limited. Most SSL certificates are still domain-based.

　　Q: Is HTTPS necessary for beginners building a website?

　　A: Yes. Whether it's a personal blog or a corporate website, HTTPS is already a basic configuration.