What is an SSL certificate? A complete guide from application to installation

In today's internet environment, website security is the cornerstone of user trust. When you see a green lock icon in the browser address bar, or when a website address starts with “https”, it means that the website is using an SSL certificate to encrypt and protect the transmission of your data. SSL certificates not only protect user privacy but also play a crucial role in search engine rankings and compliance requirements.

This article will provide an in-depth analysis of SSL certificates and offer a comprehensive guide from understanding the basic concepts to the actual deployment of SSL certificates.

What is an SSL certificate?

An SSL certificate, whose full name is Secure Sockets Layer Certificate, is now commonly carried by its successor, the TLS protocol. However, people still refer to it as an SSL certificate. It is a type of digital certificate used to establish an encrypted connection between a server (a website) and a client (a browser), ensuring that all data transmitted remains private and secure.

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The core working principle of SSL certificates

The working principle of an SSL certificate is based on asymmetric encryption technology. When a user visits a website that uses HTTPS, the server presents its SSL certificate to the browser. The browser then verifies the validity and authenticity of the certificate. Once the verification is successful, both parties negotiate and generate a temporary, unique “session key” that will be used for symmetric encryption in subsequent communications. This process is known as the “SSL/TLS handshake.”

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This mechanism ensures that even if the data is intercepted during transmission, attackers cannot decrypt its contents, thereby protecting sensitive information such as login credentials, credit card details, and personal data.

The key information contained in an SSL certificate includes:

A standard SSL certificate contains the following important information:
* 域名： 证书颁发给哪个域名。
* 证书持有者： 拥有该域名的组织或个人。
* 颁发机构： 签发证书的证书颁发机构。
* 有效期： 证书的生效日期和到期日期。
* 公钥： 用于加密信息的密钥部分。

Why do websites need SSL certificates?

Deploying SSL certificates is no longer the exclusive domain of large e-commerce or financial websites; it has become a standard requirement for all websites. The main reasons for this are as follows:

Ensure data security and user privacy

This is the most fundamental purpose of an SSL certificate. It encrypts all communications between the user’s browser and the website server, preventing man-in-the-middle attacks, eavesdropping, and data tampering. For websites that involve logging in, making payments, or collecting personal information, this is a legal and ethical requirement.

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Improve Search Engine Ranking

Major search engines (such as Google and Baidu) have recognized HTTPS as a positive indicator for search rankings. Websites with an SSL certificate generally receive higher rankings in search results compared to HTTP websites under the same conditions, which is crucial for website traffic and visibility.

Establish user trust and brand reputation

Browsers clearly indicate whether a website is secure or not. For websites that have a valid SSL certificate installed, a lock icon and the word “Secure” are displayed in the address bar. On the other hand, for HTTP websites or HTTPS websites with certificate issues, the browser displays a “Not Secure” warning, which can significantly affect users’ trust in the website and may lead to a loss of users.

Meet compliance requirements.

Many industry standards and legal regulations, such as the data security standards for the payment card industry and the European Union's General Data Protection Regulation (GDPR), explicitly require the encryption of sensitive data during transmission. The use of SSL certificates is a crucial step in fulfilling these requirements.

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The main types of SSL certificates

Based on the level of validation and the number of domain names covered, SSL certificates are mainly classified into the following categories:

Domain Validation Certificate

This is the type of certificate with the fastest issuance speed and the lowest cost. The Certificate Authority (CA) only verifies the applicant’s control over the domain name (usually through email or DNS records). It is suitable for personal websites, blogs, or testing environments, and only provides basic encryption capabilities. The browser will display a lock icon to indicate the presence of a secure connection.

Organizational validation type certificate

In addition to DV (Domain Validation) checks, CAs (Certification Authorities) also verify the actual existence of the applying organization (such as company name, address, phone number, etc.). The certificate information includes the verified organization name, which helps to demonstrate the entity behind the website and enhances user trust. This is suitable for corporate websites and general commercial websites.

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Extended Validation Certificate

This is the type of certificate with the strictest verification process and the highest level of security. The Certificate Authority (CA) conducts a comprehensive background check on the applying organization. Websites that have installed EV certificates will display the company’s name in green in the address bar of most browsers, which is the highest indication of trust. These certificates are typically used by banks, financial institutions, and large e-commerce platforms.

Classified by the number of domain names

• Single-domain name certificate: Protects a fully qualified domain name.
• Multi-domain certificate: One certificate can protect multiple different domain names.
• Wildcard Certificate: Protects a primary domain name and all its subdomains at the same level, for example… *.example.com It can protect blog.example.com、shop.example.com It’s very convenient to manage.

How to apply for and install an SSL certificate?

The following is the standard process for applying for and installing an SSL certificate.

Step 1: Generate a certificate signing request

First of all, you need to generate a CSR (Certificate Signing Request) file on your website server. This process will create a pair of keys: a private key and a public key. The private key must be kept absolutely confidential and stored on the server, while the CSR file contains your public key as well as the information you are requesting the certificate for (such as the domain name and your organization). You can generate the CSR through the server control panel or using command-line tools.

Step 2: Submit the application to the CA and complete the verification

Select a trusted Certificate Authority (CA) and purchase the required type of SSL certificate from their official website. During the application process, paste the content of the CSR (Certificate Signing Request) file into the designated field. Then, follow the CA’s instructions to verify the domain name ownership or organizational information, depending on the type of certificate you have chosen.

Step 3: Download and install the certificate.

After the verification is successful, the CA will issue the certificate file (usually in a digital format)..crtOr.pemYou need to upload the certificate file, along with any required intermediate certificate chain files, to your website server. The installation process varies depending on the server software you are using.

Step 4: Configure the server and enforce the use of HTTPS

After installing the certificate, you need to specify the paths for the certificate and private key in the server configuration, and enable the SSL/TLS module. Finally, and most importantly, you should configure the website to redirect all HTTP requests to HTTPS, ensuring that users always access the site via a secure connection.

Step 5: Testing and Verification

After the installation is complete, visit your website using a browser and check whether a lock icon appears in the address bar. You can also use various online SSL verification tools to thoroughly check whether the certificate has been installed correctly and whether the configuration is secure.

summarize

SSL certificates are the cornerstone of building a secure and trustworthy internet. They protect data using encryption techniques, establish trust through authentication processes, and directly impact a website’s performance in search engines as well as the user experience. There are various types of SSL certificates, ranging from cost-effective DV (Domain Validation) certificates to highly secure EV (Extended Validation) certificates, each designed to meet the needs of different scenarios. Although the application and installation processes involve technical details, most website owners can successfully deploy SSL certificates by following clear instructions or by using tools provided by hosting service providers.

Understanding and implementing SSL certificates is not only a technical task, but also a demonstration of responsibility towards website visitors. It is the first step towards the success of any online business.

FAQ Frequently Asked Questions

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

免费证书通常指Let‘s Encrypt等机构颁发的DV证书，其提供的加密强度与付费DV证书相同。主要区别在于：免费证书有效期较短，需要频繁续期；一般没有技术支持服务；不提供组织验证或扩展验证。付费证书则提供更长的有效期、专业的技术支持、更高的保险赔付额度以及OV/EV等更高级别的验证。

Will installing an SSL certificate affect the speed of the website?

Enabling HTTPS encryption does indeed introduce additional computational overhead, primarily during the TLS handshake phase when a connection is established. However, with the improved performance of modern server hardware and the optimization of the TLS protocol, this impact has become negligible. On the contrary, since HTTP/2 typically requires use of HTTPS, features such as multiplexing provided by HTTPS can significantly enhance page loading speeds. Overall, the benefits outweigh the drawbacks.

What will happen if the SSL certificate expires?

Once a certificate expires, the browser will display a clear “unsafe” warning to the user, indicating that the connection is not secure and may prevent the user from accessing the website. This can lead to a loss of user trust and a significant decrease in website traffic. Therefore, it is essential to renew and re-install the certificate before it expires. It is recommended to set up reminders or use certificate services that support automatic renewal.

Can an SSL certificate be used on multiple servers?

This depends on the authorization and permissions granted by the certificate. Typically, a single certificate can be installed on multiple servers as long as those servers serve the same domain name. For example, multiple web servers set up for load balancing or backup purposes can share the same certificate. However, it is important to ensure that the private key of the certificate is securely distributed and managed across all the servers. Multi-domain certificates or wildcard certificates can be deployed on different servers within the range of domain names they cover.