What are SSL certificates for? A Complete Guide from Principles to Purchase and Installation

The core principle of an SSL certificate: The cornerstone of data security

An SSL certificate is not just a simple “file”; rather, it represents a comprehensive security protocol system based on the Public Key Infrastructure (PKI). Its primary value lies in establishing an encrypted and secure communication channel between the browser (the client) and the website server. This process is primarily accomplished through the “SSL/TLS handshake protocol.”

When a user visits a website that has an SSL certificate deployed (usually starting with “https://”), the browser sends a “handshake” request to the server. The server then sends its SSL certificate to the browser. This certificate contains crucial information: the domain name of the website, the digital signature of the certificate-issuing authority, the public key, and the validity period of the certificate, among other details.

After receiving the certificate, the browser performs a series of verifications: First, it checks whether the certificate was issued by a trusted certificate authority to ensure its authenticity. Second, it verifies that the domain name associated with the certificate matches the domain name of the website being visited. Finally, it confirms that the certificate is still within its valid period. Once all these verifications are passed, the browser uses the public key contained in the certificate to negotiate with the server and generate a temporary key (referred to as a session key) for the current session. All data transmitted between the browser and the server is then encrypted using this session key. As a result, even if the data is intercepted during transmission, attackers cannot decrypt it to obtain the plaintext information.

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Therefore, SSL certificates address two fundamental issues: First, they provide authentication, confirming that you are indeed the website you claim to be, preventing phishing sites from impersonating you; second, they encrypt data, ensuring that private information (such as passwords, credit card numbers, and chat content) is not intercepted or tampered with during transmission.

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The main types of SSL certificates and their applicable scenarios

Not all SSL certificates are the same; they are primarily classified into the following types based on the level of verification and the number of domains they protect, in order to meet the security requirements of different scenarios.

Domain Validation SSL Certificate

This is the type of certificate that offers the fastest issuance process and the lowest cost. The certificate issuing authority only verifies the applicant's ownership of the domain name (for example, by checking the WHOIS email associated with the domain name or by setting specific DNS resolution records). It primarily provides basic encryption capabilities for websites.

The DV certificate is very suitable for personal websites, blogs, testing environments, or internal tools that do not require a strong demonstration of a corporate identity to users. It is displayed in the browser address bar as a lock icon along with “https”.

Organizational Validation SSL Certificate

In addition to verifying the ownership of the domain name, the certificate issuing authority will also thoroughly examine the legitimacy of the applying company, such as checking the company’s business registration information and contact details (including phone numbers). The certificate will include the verified name of the company.

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OV certificates are suitable for commercial websites, corporate portals, government agencies, and other formal scenarios where user trust needs to be established. They not only encrypt data but also prove to users that the entity operating the website is a real, legitimate organization.

Extended Validation SSL Certificates (EV SSL)

This is the SSL certificate with the highest level of verification and the strictest requirements. Applicants must undergo the most comprehensive corporate identity verification process. Its most prominent feature is that, in certain browsers, the website address bar of a site with an EV SSL certificate will display the company’s name in green, in addition to the lock icon.

EV certificates are the preferred choice for industries with extremely high requirements for security and trust, such as finance, payments, and large e-commerce platforms. They can maximize the credibility of a website to users and effectively prevent phishing attacks.

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Multiple domain and wildcard certificates

All three of the above types can be extended based on their coverage scope. A multi-domain certificate allows a single certificate to protect multiple completely different domain names (for example…). example.com, example.net, shop.example.orgWildcard certificates can be used to protect a main domain name and all its subdomains at the same level with just one certificate. *.example.com It can protect blog.example.com, shop.example.com, pay.example.com This approach is highly flexible and efficient when managing corporate architectures with a large number of subdomains.

How to choose and purchase the right SSL certificate

When faced with the numerous SSL certificate providers in the market, making the right choice requires considering several key factors comprehensively.

The primary factor is to determine the required level of verification. If only basic encryption is needed, a DV (Domain Validation) certificate is sufficient; if you need to demonstrate the identity of your company, an OV (Organization Validation) certificate is essential; for critical financial transactions, the green address bar provided by an EV (Extended Validation) certificate serves as an important symbol of trust.

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Secondly, consider the need for domain name coverage. If there is only one main domain name, a single-domain certificate is the most cost-effective option. If you have multiple different main domain names, it is advisable to choose a multi-domain certificate to simplify management. If you have a structured subdomain system, a wildcard certificate offers the greatest advantages in terms of management convenience.

Thirdly, pay attention to the brand and compatibility of the certificate. It is crucial to choose a certificate issued by a globally trusted root certificate authority (CA), as this ensures that the certificate can be seamlessly recognized by almost all browsers, operating systems, and mobile devices. Well-known CA organizations typically have more stable root certificate implementations and wider market recognition.

Finally, compare the prices and services offered. The cost of certificates ranges from free DV certificates to expensive EV certificates, which can cost several thousand dollars. Paid certificates typically offer higher insurance amounts, more professional technical support, and more stringent audit requirements. For free certificates, it’s important to note that their validity periods are shorter (usually three months) and they require regular renewal; they generally do not include any commercial protection.

Best Practices for the Deployment, Installation, and Maintenance of SSL Certificates

After successfully purchasing a certificate, the correct deployment and ongoing maintenance are the final steps necessary to ensure the security benefits of the certificate are fully realized.

Certificate Issuance Application Process

After purchasing the certificate, you need to generate a “Certificate Signing Request” (CSR) file on your server. This file contains your public key as well as information about your website (such as the domain name and organizational details). Submit the CSR to the certificate authority (CA). Once the CA verifies the information, it will issue the official SSL certificate file, which typically includes the certificate itself, as well as any additional files required for setting up secure connections..crtOr.pemThe files, as well as any possible intermediate certificate chains, will be sent to you.

Server installation and configuration

The installation process varies depending on the type of server (such as Apache, Nginx, IIS, Tomcat), but the core steps are the same: you need to upload the obtained certificate file, private key file, and any intermediate certificate chain files to the designated location on the server, and then ensure that the server configuration files reference these file paths correctly. After the installation is complete, be sure to restart the server software to apply the new configuration changes.

Forced HTTPS redirection

After installing the certificate, it is necessary to apply it to all parts of the website.httpThe access results in a forced redirect to…httpsEnsure that users always access the website through an encrypted channel. This can typically be achieved by adding a rule file in the website’s root directory or by modifying the server configuration file.

Continuous monitoring and maintenance

SSL certificates have a clear expiration date (currently up to 13 months). It is essential to renew and re-install the certificate before it expires; otherwise, the website will display security warnings, preventing users from accessing it. It is recommended to set up calendar reminders or use certificate monitoring tools to automatically track the expiration date. Additionally, make sure that the server software is up to date to support the newer and more secure TLS protocols (such as TLS 1.2 or 1.3), and disable the outdated and insecure protocols (such as SSLv2, SSLv3, and TLS 1.0).

summarize

SSL certificates are essential for modern online security; they are by no means an optional feature. They establish a trustworthy connection between websites and users by using encryption and authentication mechanisms. Understanding how they work, selecting the appropriate type of SSL certificate based on the nature of the website, and following the correct deployment and maintenance procedures are fundamental responsibilities of every website operator. Deploying SSL certificates not only protects user data from man-in-the-middle attacks but also improves the website’s ranking in search engines and significantly enhances users’ confidence when accessing the site. Ultimately, this provides a solid foundation for the website’s professional image and business development.

FAQ Frequently Asked Questions

What are the differences in the display of DV, OV, and EV certificates in browsers?

DV certificates are displayed in the address bar with a lock icon and the word “Secure” (the exact wording may vary depending on the browser). OV and EV certificates also show a lock icon, but the verified organization name can be found in the certificate details. In addition, EV certificates used to display the company’s name in green directly in the address bar in some older browser versions. Although modern browsers have gradually adopted the lock icon as the standard display method, the highest level of authentication information is still provided in the certificate details.

What is the difference between a free SSL certificate and a paid one?

免费证书（如Let‘s Encrypt颁发的）通常是DV类型，提供了与付费DV证书相同的加密强度。主要区别在于：免费证书有效期短（90天），需要频繁续签，自动化部署是高效管理的必需；而付费证书提供更长的有效期、更灵活的域名覆盖选项（如通配符）、以及最重要的组织验证或扩展验证服务。此外，付费证书通常附带更高的责任保险金额和专业的技术支持服务。

Why does the website still display as insecure after the SSL certificate has been installed?

This could be caused by several reasons. The most common one is that the website page is loading non-HTTPS resources (such as images, JavaScript files, and CSS files) in combination with HTTPS content.http://(The protocol is introduced here.) Browsers will consider this as “mixed content” and warn that it is not secure. The solution is to ensure that all resource links on the web page use the correct protocol.https://Or a relative path.//Other possible reasons include the certificate not being installed correctly, an incomplete certificate chain, or incorrect server configuration that still allows (the certificate to be used).httpAccess, etc.

Can multiple-domain certificates and wildcard certificates be used together?

Certainly, some certificate authorities offer “multi-domain wildcard certificates.” These certificates allow you to add multiple primary domains, and each of these domains can use a wildcard format. For example, a single certificate can provide protection for multiple domains simultaneously.*.example.comand*.example.orgThis provides great flexibility for managing complex domain name structures, but such certificates are usually more expensive as well.

How to view the detailed information of a website’s SSL certificate?

In the browser, click on the lock icon on the left side of the address bar. From the pop-up menu, select an option such as “The connection is secure” or a similar one, and then click on “Certificate is valid”. In the certificate viewer window that appears, you can view detailed information about the certificate, including the entity to which it is issued, the validity period, the encryption algorithms used, and the entire certificate chain.