Comprehensive analysis of SSL certificates: types of differences, application process and installation and deployment guide

The core function and working principle of SSL certificates

In the digital age, the security of online communications is the cornerstone of trust. SSL certificates are a crucial technology designed precisely for this purpose, acting as the “digital passport” and “encrypted envelope” between websites and visitors. Their most obvious function is to display a secure lock icon in the browser’s address bar, indicating to users that the connection has been encrypted and verified. However, their significance extends far beyond that.

The core of an SSL certificate is the implementation of the HTTPS protocol, which is built upon the SSL/TLS protocol layer. Its working principle primarily involves two key processes: authentication and encrypted communication. When a user visits a website that has an SSL certificate deployed, the browser initiates a “handshake” process with the server. The server then sends its SSL certificate to the browser. The browser verifies whether the issuing authority of the certificate is trustworthy, whether the certificate is still valid, and whether the domain name in the certificate matches the website being accessed. This series of verifications ensures that the user is communicating with the actual, legitimate server, rather than a phishing website.

After the verification is successful, both parties will use the public-private key pair from the certificate to negotiate and generate a set of symmetric encryption keys for this session. All data transmitted between the browser and the server, including passwords, credit card numbers, and chat messages, will be encrypted and decrypted using this session key. Even if the data is intercepted during transmission, attackers will not be able to decipher its content, thus ensuring the confidentiality and integrity of the data.

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The main types of SSL certificates and their applicable scenarios

Not all websites require SSL certificates with the same level of security. Based on the level of verification and the scope of coverage, SSL certificates are mainly divided into three categories to meet the needs of different business scenarios.

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Domain Validation Certificate

Domain name validation certificates are the fastest-to-obtain and lowest-cost type of certificate. The certification authority only verifies the applicant’s ownership of the domain name, typically by sending a verification email to the email address registered for that domain name or by requiring the setting of specific DNS records. These certificates provide basic encryption capabilities and display a lock icon in the browser.

It is very suitable for personal blogs, small demonstration websites, or testing environments, where the primary requirement is to implement basic HTTPS encryption, without the need to display detailed organizational identity information. However, due to the lack of verification of the authenticity of the organizations using this service, it is not suitable for e-commerce, financial websites, or any other type of website that requires the clear display of the identity of the entity providing the service to users.

Organizational validation type certificate

Organizational validation certificates build upon DV (Domain Validation) certificates by adding a rigorous verification process to confirm the authenticity of the applicant’s organization. The Certificate Authority (CA) will check the organization’s business registration information and verify its actual existence, and may also contact the organization by phone to confirm these details. Once approved, the certificate will include the verified name of the enterprise.

When users click on the lock icon in the browser address bar, they can view the verified details of the company. This significantly enhances user trust. OV certificates are an ideal choice for businesses and government organizations, suitable for official websites, member login portals, internal systems, and online platforms that involve commercial transactions. They clearly communicate to users the legitimate entity behind the website.

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Extended Validation Certificate

Extended Validation (EV) certificates offer the highest level of verification and trust. In addition to completing all the review steps required for an OV certificate, the Certificate Authority (CA) conducts a more thorough background check on the applying organization to ensure its legal, operational, and physical authenticity. Websites that have obtained an EV certificate will have their address bar turn green in most major browsers, and the company’s name will be displayed directly next to the lock icon.

This prominent visual identifier provides visitors with the strongest sense of security. EV (Extended Validation) certificates are commonly used by large enterprises, financial institutions (such as banks and stock exchanges), well-known e-commerce platforms, and any websites that handle highly sensitive user information and transactions. It is the type of certificate that best demonstrates a brand’s credibility and commitment to security.

In addition, based on the number of domains they cover, SSL certificates can be classified into single-domain certificates, multi-domain certificates, and wildcard certificates. Wildcard certificates can protect a primary domain name and all its subdomains at the same level. *.example.comIt is very efficient when managing complex websites with a large number of subdomains.

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The process of applying for and verifying an SSL certificate

Obtaining an SSL certificate is not a complex technical task; rather, it involves a systematic process. The key to the process is to demonstrate to the certificate authority (CA) that you have control over the domain name in question, as well as the authenticity of your organization (for OV/EV certificates).

The first step is to generate a Certificate Signing Request (CSR). This is typically done on your server or through the hosting control panel. During the CSR generation process, a pair of keys is created: a private key and a public key. The private key must be stored securely on the server and must not be disclosed under any circumstances. The CSR file contains your public key, as well as the domain name for which you are applying for a certificate, your organization’s information (such as whether you are applying for an OV/EV certificate), and other relevant details. This CSR file serves as your “application” to the Certificate Authority (CA).

The second step is to select a CA (Certificate Authority) and submit your application. You need to choose one from the many trusted CAs, submit the CSR (Certificate Signing Request) file on their website following the instructions, and specify the type of certificate you require (DV, OV, or EV) as well as the validity period. You will also need to pay the corresponding fees.

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The third and most critical step is to complete the verification process. For DV (Domain Validation) certificates, the verification is usually automatic and quick; domain ownership is confirmed via email or DNS, and the certificate can be issued within a few minutes to a few hours. For OV (Organizational Validation) and EV (Extended Validation) certificates, a human review team from the CA (Certificate Authority) will get involved. They may contact your company’s registered phone number for verification and request scanned copies of legal documents such as your business license. The entire process may take 3 to 7 working days.

Finally, after the CA (Certificate Authority) approves the application and issues the certificate, you will receive a file containing the certificate chain. You need to configure this file together with the private key that was generated earlier on your web server (such as Nginx, Apache, or IIS) to complete the entire application process.

Mainstream Server SSL Certificate Installation and Deployment Guide

After successfully obtaining the certificate file, the final step in enabling HTTPS is to deploy it correctly on the server. The configuration process varies depending on the web server being used, but the basic principle remains the same: you need to associate the certificate file issued by the CA (Certificate Authority), any intermediate certificates, and your private key with the server’s configuration settings.

Nginx Server Deployment

For Nginx, deploying an SSL certificate mainly involves modifying the configuration file of the server block. You need to add the certificate file (which is usually in a specific format, such as PEM or DER) to the server block to enable SSL encryption..crtOr.pem(The end) and the private key file (usually named…).key(The end) Upload it to a secure directory on the server, for example. /etc/ssl/。

In the website’s Nginx configuration file, locate the server block that listens on port 80, and add a new server block to listen on port 443 (the default port for HTTPS). The key configuration instructions include: ssl_certificate(Refer to the path of your certificate file; if the CA provided a certificate bundle, you should include both the intermediate certificates and your primary certificate.) ssl_certificate_key(Points to the path of your private key file.) After the configuration is complete, use it. nginx -t Test the configuration syntax; once it is confirmed to be correct, proceed with the next step. systemctl reload nginx Reload the configuration to make the changes take effect.

Apache Server Deployment

On the Apache server, you need to ensure that… mod_ssl The module has been enabled. The certificate and private key files also need to be uploaded to the server. /etc/apache2/ssl/ Under the directory.

Edit the virtual host configuration file for your website. First, configure a virtual host that redirects HTTP (port 80) requests to HTTPS. Then, configure another virtual host that listens on port 443. In the configuration for this second virtual host, use… SSLCertificateFile The instruction specifies the path to your certificate file. Please use it accordingly. SSLCertificateKeyFile You need to specify the path to the private key file, and usually, you also need to use... SSLCertificateChainFile Specify the intermediate certificate file to ensure compatibility. After saving the configuration, use it. apachectl configtest Check the syntax, and then restart the Apache service.

Post-deployment checks and enforcement of HTTPS

Regardless of the server used, verification must be performed after the deployment is complete. Access https://您的域名Make sure that the browser displays the security lock icon and there are no security warnings. It is highly recommended to use online SSL testing tools (such as SSL Labs’ SSL Test) to conduct a thorough scan to verify whether the certificate is properly installed, whether the configuration is secure (for example, whether it supports outdated TLS 1.0/1.1), and whether best practices are being followed.

Finally, to ensure that all traffic is encrypted, it is necessary to set up a permanent 301 redirect from HTTP to HTTPS. This will prevent users from accessing the website via insecure HTTP connections and help search engines treat HTTPS pages as the standard version of the site, thereby avoiding duplicate content.

summarize

SSL certificates have evolved from an optional security enhancement to an essential infrastructure component for modern websites. They serve not only as encryption tools to protect the confidentiality of data transmission but also as “digital identities” that establish the credibility of a website. From basic domain name verification to rigorous organization-level validation, various types of certificates provide solutions that match the security needs and trust levels of individuals, businesses, and financial institutions. Understanding the application and validation processes, as well as knowing how to deploy them on mainstream servers, is a essential skill for every website manager, developer, and operations personnel. In the context of increasingly complex cybersecurity threats, correctly deploying and maintaining SSL certificates is the first step in building a secure and trustworthy online environment—and it is also key to gaining users’ long-term trust.

FAQ Frequently Asked Questions

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

DV certificates only display a lock icon and the word “Secure” in the browser address bar. When you click on the lock icon for an OV certificate, the verified organization name is displayed in the certificate details. EV certificates offer the most noticeable visual indication: in most browsers, the entire address bar turns green, and the company name is displayed statically next to the lock icon, directly within the address bar, without the need for the user to click to view it.

Do I definitely need to pay to apply for an SSL certificate?

不一定。存在许多受信任的证书颁发机构提供免费的DV证书，例如Let‘s Encrypt，其自动化流程非常适合个人网站和测试环境。然而，免费的DV证书通常有效期较短（如90天），需要定期续期，且不包含组织验证。对于需要展示企业身份（OV）或最高级别信任标识（EV）的商业网站，付费证书是必要的选择，它们提供更长的有效期、身份担保和保险赔付。

Can wildcard certificates protect all subdomains?

Wildcard certificates can protect all subdomains at a specific level, but they cannot provide protection across different levels of the domain hierarchy. For example, a wildcard certificate issued for… *.example.com The issued wildcard certificate can protect blog.example.com、shop.example.comBut it can't protect us dev.www.example.comThese are two levels of subdomains. If you need to protect multiple levels of subdomains or several completely different primary domains, you should consider using a multi-domain wildcard certificate or applying for a certificate for each domain individually.

What should I do if some resources on the website are loaded insecurely after the SSL certificate is deployed?

The “Mixed Content” warning appears because the web page is loaded via HTTPS, but some of its resources (such as images, JavaScript files, and CSS files) are still being loaded using the HTTP plain-text protocol. This undermines the overall security of the page. To resolve this issue, you need to carefully review the source code of the web page and modify all resource links (both absolute and relative paths) to use the HTTPS protocol. Alternatively, you can use protocol-relative URLs. // (The browser’s developer tools console typically lists unsafe resource links explicitly, making it the primary tool for troubleshooting this issue.)