What is an SSL certificate?
When you visit a website, have you ever noticed the “little lock” icon on the left side of the browser’s address bar? This icon indicates that the connection between you and the server is secure and encrypted. The key to all of this is the SSL certificate. An SSL (Secure Sockets Layer) certificate – which is now more accurately referred to as a TLS (Transport Layer Security) certificate – is a digital certificate used to verify the identity of a website and establish an encrypted connection during internet communications.
Its working principle is based on asymmetric encryption technology. After an SSL certificate is installed on the server, it provides the “public key” to any client (such as a browser) that attempts to establish a connection. This public key is used to encrypt the information sent by the client, and this information can only be decrypted by the “private key” held by the server, which is paired with the public key. This process ensures that sensitive data, such as login credentials, credit card information, and private messages, cannot be stolen or tampered with by third parties during transmission, thereby safeguarding the confidentiality and integrity of the data.
A valid SSL certificate typically contains the following key information: the domain name of the certificate holder, the name of the certificate issuing authority, the serial number and expiration date of the certificate, the public key of the certificate holder, and the digital signature of the public key by the issuing authority. This signature is the cornerstone of trust; it is signed by a trusted third party, the certificate issuing authority (CA), to prove to users that the identity of the website has been verified.
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Common Types of SSL Certificates and How to Choose One
Understanding the different types of SSL certificates is the first step in making the right choice. Based on the level of verification and the scope of coverage, SSL certificates are mainly divided into three categories.
Domain Name Validation Certificate
Domain name validation certificates are also known as DV SSL (Domain Validation Secure Sockets Layer) certificates. This is the type of certificate with the lowest level of validation and the fastest issuance process (usually within a few minutes). The certificate authority only verifies the applicant’s control over the specific domain name (for example, by sending a validation email to the email address registered for that domain name or by setting specific DNS records). It does not verify any information about the organization. As such, DV SSL certificates are suitable for personal websites, blogs, or internal testing environments, and are primarily used to provide basic HTTPS encryption.
Organization validation certificate
Organizational Validation (OV) SSL certificates not only verify the ownership of a domain name but also involve a manual review by the certificate authority to confirm the authenticity and legitimacy of the applying company or organization. This review includes checking the company’s registration information, contact details (such as phone numbers), etc. The verification process typically takes 1–3 working days. OV certificates display the verified information about the organization in their details, which enhances trust for users. They are suitable for commercial websites, corporate official websites, and any online platforms that require a high level of credibility.
Extended Validation Certificates
Extended Validation (EV) SSL certificates represent the highest level of verification and trust. In addition to meeting all the requirements of the OV (Organizational Validation) level, the certification authority (CA) conducts a more thorough and standardized review of the enterprise’s identity. The most distinctive feature of EV SSL certificates is that when users access a website with an EV SSL certificate using a mainstream browser, the address bar not only displays a security lock but also the verified, green name of the enterprise. This provides users with a significant sense of confidence and makes EV SSL the preferred choice for industries such as finance and e-commerce that handle highly sensitive transactions.
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.
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Detailed Explanation of the SSL Certificate Application Process
Applying for an SSL certificate is a standardized process. Following these key steps will ensure a smooth application.
第一步是选择合适的证书类型和证书颁发机构。你需要根据网站的性质、预算和对信任度的要求，从上一节介绍的DV、OV、EV类型中进行选择。同时，你需要选择一家受信任的CA或通过其授权的经销商购买。流行的CA包括DigiCert、Sectigo、Let‘s Encrypt（提供免费DV证书）等。
The second step is to generate a Certificate Signing Request (CSR). This is a crucial part of the application process. You need to create a CSR file on the server where you will install the certificate. This can usually be done through server management tools (such as the SSL/TLS manager in cPanel) or via the command line (using OpenSSL). When generating the CSR, you must enter your domain name information accurately and create a key pair (a public key and a private key). The CSR file contains your public key and identity information, while the server will securely store the private key; it must not be disclosed under any circumstances.
The third step is to submit the application for review and verification. You need to submit the generated CSR (Certificate Signing Request) file to the certificate authority (CA) of your choice. For DV (Domain Validation) certificates, the verification process is usually automated and is completed via email or DNS records. For OV (Organizational Validation) and EV (Extended Validation) certificates, the CA’s review team will contact you to assess the corporate documents you have provided (such as a business license) according to their strict criteria. Once the verification is successful, the CA will issue the SSL certificate file (usually in the .crt or .pem format) and send it to you via email.
Installation and Configuration of SSL Certificates
After obtaining the SSL certificate file, the next step is to install it on your server. The installation process varies depending on the type of server you are using.
Apache Server Installation
For Apache servers, you need to upload the certificate file (.crt or.pem) and the key file to a specified directory on the server. This directory is usually…/etc/ssl/Or use a custom path. Next, you need to edit the website’s virtual host configuration file to ensure that it contains instructions pointing to the correct paths for the certificate file and private key file, and to enable the SSL engine. Finally, restart the Apache service to apply the changes.
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Nginx Server Installation
On the Nginx server, the installation process is similar. Upload the certificate file and the private key file to the server, for example:/etc/nginx/ssl/Inside the directory, edit the website’s Nginx configuration file. In the corresponding server block, locate the port that is being listened on, and add the paths for the SSL certificate and private key. After completing the configuration, you will also need to restart the Nginx service.
Post-installation checks and enforcement of HTTPS
After the installation is complete, verification is necessary. You can visit your website using a browser to check whether a security lock icon is displayed in the address bar. A more professional approach is to use online SSL testing tools, which will thoroughly examine the integrity of the certificate chain, the supported protocols, and the strength of the encryption suite, and provide ratings and recommendations.
A crucial subsequent step is to configure the 301 redirect from HTTP to HTTPS. This ensures that even if users access the website using the old HTTP links, they will be automatically and permanently redirected to the secure HTTPS version. This not only guarantees that all traffic is encrypted and protected, but it also benefits search engine optimization (SEO).
summarize
SSL certificates have evolved from an optional security enhancement to an essential infrastructure component for modern websites. They are not only a critical technology for protecting user data and preventing man-in-the-middle attacks but also play a vital role in establishing a website’s credibility and improving its search engine rankings. Every step in the process—from understanding the principles of encryption, to selecting the right type of certificate (DV, OV, or EV) based on specific needs, to completing the application, verification, installation, and configuration—is crucial. Regular maintenance, including timely renewal before the certificate expires, is necessary to ensure the continuous security of your website. Embrace HTTPS to create a safer online environment for your website and its users.
FAQ Frequently Asked Questions
What is the difference between a free SSL certificate and a paid one?
免费SSL证书（如Let‘s Encrypt颁发的）通常是域名验证类型，仅提供基础的加密功能，签发和续期自动化程度高。
Paid SSL certificates offer a wider range of options, including OV (Organized Validation) and EV (Extended Validation) types, which provide a higher level of authentication and trust indication (such as the company name being displayed in the address bar). They usually come with a higher warranty amount and professional technical support, making them more suitable for commercial and e-commerce websites.
What should I do if the website still displays as insecure after the SSL certificate has been installed?
This issue is usually caused by several common reasons: First, the website page may contain resources that use the HTTP protocol, such as images, scripts, or style sheet links. You need to change the URL of all these resources to start with “HTTPS”. Second, it could be that the certificate chain is incomplete, preventing the browser from verifying the certificate issuer. You need to install the intermediate certificate files on the server along with the domain name certificate correctly. Finally, please check whether the HTTPS listening configuration is set up correctly, and ensure that no firewalls or CDN settings are blocking port 443.
Can an SSL certificate be used on multiple domain names?
Conventional single-domain SSL certificates can only protect one fully qualified domain name. However, you can purchase multi-domain certificates to protect multiple distinct domain names, or you can buy wildcard certificates to protect a main domain name and all its subdomains at the same level.
What are the consequences of not renewing an expired SSL certificate?
After a certificate expires, the browser will display a prominent “unsafe” warning to the user when accessing the website, and in some cases, it may even prevent the user from continuing to access the site. This can significantly affect the user experience and the website’s reputation.
At the same time, search engines will lower the rankings of unsafe websites, and all data transmitted after the certificate expires will no longer be encrypted, posing a risk of theft. Therefore, it is very important to set up reminders or enable the automatic renewal feature with the certificate authority.
What's next, what's next?
Extended reading and practical knowledge
The following are related to the topic of this article and are suitable for further in-depth reading. Prioritize starting with the article that is closest to your current problem, and gradually expanding to surrounding topics usually works better.
- What is an SSL certificate? A comprehensive explanation from its principles to the process of applying for and using it.
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