What is an SSL certificate? How to apply for and install it to enable HTTPS encryption on a website?

Understand the core concepts of SSL certificates

An SSL certificate, also known as a Secure Sockets Layer certificate, has now evolved into its successor, the TLS protocol, but the industry still commonly refers to it as an SSL certificate. It is a type of digital certificate that establishes an encrypted connection between the client (such as a browser) and the server (such as a website), ensuring the confidentiality and integrity of all transmitted data. Its core functions are identity authentication and data encryption.

You can think of it as the digital passport of a website. When a user visits an HTTPS-enabled website, the SSL certificate verifies the authenticity of the website to the browser and negotiates with the browser to establish a secure encrypted tunnel. This tunnel protects all data transmitted during the process, including login credentials, credit card information, and personal privacy, preventing them from being subject to man-in-the-middle attacks, data eavesdropping, and tampering.

Recommended Reading The Ultimate Guide to SSL Certificates: Types, Options, Installation and Deployment。

After deploying an SSL certificate, the website address will change from “HTTP” to “HTTPS”, and a lock icon will appear in the browser address bar, which directly conveys the trust signal of “this connection is secure” to users. For any modern website involving user data interaction, an SSL certificate has become a necessity rather than an optional feature.

The main types of SSL certificates and how to choose them

According to the different verification levels and security requirements, SSL certificates are mainly divided into the following three categories. Understanding the differences between them is the first step towards making the right choice.

Domain Validation Certificate
A DV certificate is the type with the lowest acquisition cost and the fastest issuance speed. The certificate authority only verifies the applicant's ownership of the domain name (for example, through email verification or DNS resolution record verification). It provides basic encryption functionality and is suitable for personal websites, blogs, or test environments, but it only verifies the domain name and does not display the company name.

Recommended Reading What is SSL Certificate? Principle, type and installation configuration full analysis。

Organizational validation type certificate
The OV certificate, based on the DV certificate, adds a rigorous review of the applicant's organizational authenticity. The CA will verify the enterprise's business license, phone number, and other physical information. After issuance, the certificate details will include the verified company name. This significantly enhances the credibility of the website and is suitable for corporate websites, financial institutions, and e-commerce platforms, making it the mainstream choice for commercial websites.

Extended Validation Certificate
An EV certificate is the most rigorously verified and highest-security level certificate. Applicants must pass the most stringent organizational identity verification. Its most notable feature is that, in some browsers, the address bar of websites enabled with EV certificates will directly display the green corporate name. This provides the most intuitive security indicator for high-value transactions, banks, large e-commerce platforms, and other websites with extremely high trust requirements.

In addition, based on the number of domains covered, they can be divided into single-domain certificates, multi-domain certificates, and wildcard certificates. Wildcard certificates can protect a main domain and all its sub-domains at the same level, which is very convenient to manage.

Recommended Reading SSL certificates in detail: from the type of choice to the Nginx server installation and configuration of the whole guide。

Detailed steps: Applying for and obtaining an SSL certificate

The process of applying for an SSL certificate has become increasingly standardized. The following are the common core steps involved.

First step: Generate a certificate signing request. This is the key starting point of the application process. You need to generate a pair of asymmetric keys (private key and public key) on your server and create a CSR file based on this. The CSR contains your public key, the domain name to be bound, organizational information, etc. Please be sure to generate and properly store the private key in a secure environment, and it must never be leaked.

The second step: Submit the application and verify it. Submit the generated CSR to the certificate authority or its distributor of your choice. Depending on the type of certificate you purchased, proceed to the corresponding verification process. For DV certificates, you may only need to click on the link in the email or set the specified DNS records. For OV and EV certificates, the CA's verification team will verify the corporate information you submitted through methods such as phone calls and third-party databases, a process that may take several working days.

The third step: verification and certificate issuance. Once the CA completes all verification steps and confirms that your identity and that of your organization are legitimate and valid, it will issue an SSL certificate. The certificate is typically provided in the form of an encrypted text, which contains your domain name, public key, issuing CA information, and a digital signature.

Recommended Reading What is an SSL Certificate? A complete guide from principle to purchase and installation。

Guidelines for installing mainstream server environments

After obtaining the certificate file, you need to deploy it to your website server. Below are the installation steps for several mainstream servers.

Install the Apache server
Apache typically requires three files: your domain name certificate, the CA intermediate certificate, and the private key file. You need to edit Apache's virtual host configuration file, locate the configuration block for the corresponding site, and ensure that the `SSLCertificateFile` directive points to your certificate file, the `SSLCertificateKeyFile` directive points to the private key file, and the `SSLCertificateChainFile` directive points to the intermediate certificate file. After making the changes, restart the Apache service to enable the configuration to take effect.

Install the Nginx server
The configuration of Nginx is more concise. In the server configuration block of the website, use the `ssl_certificate` directive to specify the path to the certificate file (usually, you need to merge your domain certificate and intermediate certificate into one file), and use the `ssl_certificate_key` directive to specify the path to the private key file. After saving the configuration file, you can apply the new SSL settings by executing the reload command.

\nCloud platform and virtual host
If you are using cloud service providers such as Alibaba Cloud and Tencent Cloud, or virtual hosting management panels like cPanel/Plesk, the process will be more graphical. You can usually find the “Upload Certificate” or “One-Click Deployment” options on the SSL certificate management page of the cloud server or in the “Security” module of the host. All you need to do is paste the certificate content and the private key content into the corresponding text boxes according to the interface prompts, and the system will automatically complete the deployment.

Regardless of the method used, after installation, make sure to access your HTTPS website using a browser to verify that the lock icon is displayed normally, and that clicking on the lock icon shows the correct certificate information without any security warnings.

The necessary checks and optimizations after installation

The successful installation of the certificate is not the end. To ensure the best security and performance, subsequent steps are also necessary.

First, implement the redirection. To prevent users from accessing the site via the old HTTP protocol and to unify the SEO weight, all HTTP accesses must be forcibly redirected to HTTPS. This can be achieved by adding a 301 redirection rule in the server configuration.

Secondly, conduct a security scan and rating. Visit a professional SSL server testing website and enter your domain name for a comprehensive check. These tools will evaluate whether the encryption suite configuration of your server is secure, whether it supports vulnerable old protocols, whether the certificate chain is complete, etc., and provide a rating and improvement suggestions. According to the suggestions, disable insecure protocols.

Furthermore, set up a certificate renewal reminder. SSL certificates have an expiration date, usually one year. If the certificate expires, the website will become inaccessible and serious security warnings will appear. It is essential to complete the renewal and redeployment before the certificate expires. It is recommended to set up a calendar reminder or use a certificate service that supports automatic renewal.

Finally, consider implementing HTTP/2. Modern browsers only enable the HTTP/2 protocol for HTTPS websites, which can significantly improve page loading speed. Check and enable the HTTP/2 support of the server to further enhance the performance of the website.

summarize

An SSL certificate is the cornerstone for implementing HTTPS encryption on websites, ensuring the security of data transmission, and building user trust. To deploy an SSL certificate, first understand its working principle, select an appropriate certificate level based on the type of website, and then follow the standard process of generating a CSR, passing verification, and obtaining and installing the certificate. After installation, mandatory redirection, security configuration optimization, and certificate lifecycle management are essential to ensuring long-term stable and secure operation. In today's internet environment, deploying an SSL certificate for a website has become a fundamental and critical security practice.

FAQ Frequently Asked Questions

Q: What's the difference between free SSL certificates and paid ones? How reliable are they?
Free certificates typically refer to DV certificates issued by organizations such as Let's Encrypt. They are no different from paid DV certificates in terms of encryption strength. The main differences are: free certificates have a shorter validity period and require more frequent automatic renewal; they usually do not provide technical support; and they do not offer commercial insurance compensation guarantees. For individuals or small projects, free certificates are an excellent choice. Paid certificates, on the other hand, offer greater value in terms of OV/EV verification, technical support, insurance protection, and the option to purchase longer validity periods (such as two years).

Q: After installing an SSL certificate, what should I do if some resources on the website (such as images and JavaScript) fail to load securely?
This problem is called “mixed content”. The reason is that the main part of the webpage is loaded via HTTPS, but some of the resources it references (such as images, CSS, and JavaScript files) still use the HTTP protocol. This will cause the browser to display a “not secure” warning. The solution is to check the webpage source code and change all the reference links to HTTPS (including absolute and relative paths), or use protocol-relative URLs.

Q: Can an SSL certificate be used for multiple domains or subdomains?
Yes, but you need to select the corresponding certificate type. A single-domain certificate only protects one complete domain name. A multi-domain certificate allows you to add multiple different domain names to the same certificate. A wildcard certificate can protect a main domain and all its subdomains at the same level, for example, `*.example.com` can protect `blog.example.com` and `shop.example.com`, but it cannot protect `a.b.example.com`. Please choose according to your actual domain structure.

Q: If the certificate is about to expire or has already expired, how should it be handled?
If the certificate is about to expire, you should contact your certificate provider to renew and reissue it before it expires. The process is similar to applying for a new certificate, which requires generating a new CSR and completing the verification. After obtaining the new certificate, replace the old certificate file on the server and restart the service. If the certificate has already expired, website access will be interrupted and a warning will appear. At this time, you should immediately complete the renewal, issuance, and deployment process. It is recommended to set a renewal reminder at least one month in advance.