In today’s internet world, website security is the cornerstone of building user trust. When you see the small lock icon in the browser address bar or when a website’s URL starts with “https,” it means that the website is using an SSL certificate. This is not just a symbol of security; it also provides a strong guarantee for the privacy of users’ data. The core function of an SSL certificate is to establish an encrypted channel, ensuring that all information transmitted between the user’s device and the website server—whether it’s login credentials, credit card numbers, or private messages—cannot be intercepted or tampered with by third parties, thus creating a secure communication environment.
The working principle of SSL certificates
The core objective of the SSL/TLS protocol is to enable secure communication. Its working principle incorporates three key technologies: asymmetric encryption, symmetric encryption, and digital certificate verification, which together ensure the confidentiality, integrity, and authenticity of data during transmission.
Recommended Reading The Ultimate Guide to SSL Certificates: Types, Options, Installation and Deployment。
Asymmetric encryption and key exchange
The initiation of the handshake process relies on asymmetric encryption algorithms, such as RSA or ECDSA. The server possesses a key pair consisting of a public key and a private key. At the beginning of the handshake, the server sends its SSL certificate, which contains its public key, to the client (browser). The client then uses this public key to encrypt a randomly generated “pre-master key” and sends it back to the server. Only the server, which possesses the corresponding private key, can decrypt this information, thereby enabling both parties to obtain the same “pre-master key.” The essence of this process is to securely exchange a shared secret that will be used for subsequent communications.
Symmetric encryption ensures transmission efficiency.
Once both parties have securely exchanged the “pre-master key,” they use a specific algorithm (such as one based on the pre-master key and random numbers exchanged during the handshake process) to derive the same “session key.” All subsequent data transmissions at the application layer will be encrypted and decrypted using a symmetric encryption algorithm (such as AES) and this session key. Symmetric encryption is fast in terms of encryption and decryption, which significantly improves the efficiency of data transmission, making it suitable for real-time encryption of large amounts of data.
Certificate verification ensures that the identity is credible.
Throughout the entire handshake process, authentication is crucial for preventing man-in-the-middle attacks. After receiving the server’s certificate, the client (browser) does not trust it unconditionally. Instead, it performs a series of rigorous verification steps:
1. Check the validity period of the certificate to ensure it is still within the valid range.
2. Verify the digital signature of the certificate. The certificate is issued by a trusted certificate authority (CA). The client uses the root certificate’s public key, which is built into the browser or operating system, to verify the validity of the server certificate’s signature. This establishes a chain of trust, ensuring that the certificate was indeed issued by a credible CA.
3. Check whether the “Common Name” or “Alternative Name for Users” field in the certificate matches exactly with the domain name of the website you are accessing.
The connection will only be established if all verifications are passed, and the security lock in the address bar will then appear.
Recommended Reading SSL Certificate Explained: From principle to deployment, comprehensive protection of website security。
The main types of ## SSL certificates are:
Based on the level of security verification and the number of domains they cover, SSL certificates are mainly divided into the following types to meet the needs of different scenarios.
Domain Validation Certificate
A DV (Domain Validation) certificate is the fastest and most cost-effective way to obtain a certificate. The Certificate Authority (CA) only verifies the applicant’s control over the domain name, typically by sending a verification email to the email address registered with the domain or by adding a specific TXT record to the domain’s DNS records. Since the organization’s identity is not verified, DV certificates only provide basic encryption and are suitable for personal websites, blogs, or internal testing environments.
Organizational validation type certificate
An OV certificate builds upon the foundation of a DV certificate by adding additional rigorous checks on the authenticity and legitimacy of the applying organization (such as a company or government agency). The Certificate Authority (CA) verifies the company’s business registration information, phone numbers, and other relevant details. Once the verification is successful, the certificate details will include the name of the organization. This provides a higher level of trust compared to a DV certificate, making it suitable for websites that need to demonstrate their credibility, such as corporate websites or e-commerce platforms.
Recommended Reading What is SSL Certificate? Principle, type and installation configuration full analysis。
Extended Validation Certificate
EV certificates represent the highest level of verification and the greatest level of trust. In addition to completing all the organizational verification requirements required for OV certificates, the CA (Certificate Authority) also conducts additional, in-depth manual reviews to ensure that the entity applying for the certificate actually exists both legally and physically. Browsers display the company name in green in the address bar for websites that have EV SSL certificates; this is a sign of the highest level of security and credibility. EV certificates are commonly used by financial institutions and large e-commerce platforms.
Multiple domain and wildcard certificates
In addition to verifying the level of security, certificates can also be classified based on the number of domains they cover. Multi-domain certificates allow for the protection of multiple completely different domains using a single certificate. Wildcard certificates, on the other hand, can protect a primary domain and all its subdomains at the same level; for example, `*.example.com` can protect `www.example.com`, `mail.example.com`, `shop.example.com`, and so on, providing a flexible and cost-effective solution for organizations with multiple subdomains.
How to Choose and Purchase an SSL Certificate for ##
When faced with the wide range of SSL certificate products available on the market, making a wise choice requires considering various factors such as the nature of the website, business requirements, and budget.
First, determine the verification level based on the type of website. For personal blogs or non-commercial websites, a DV (Domain Validation) certificate is sufficient. For small and medium-sized business (SMB) websites that handle user logins or display the company’s image, an OV (Organization Validation) certificate is a more appropriate choice, as it allows the company’s information to be displayed in the certificate details. For websites involving online transactions or financial services, it is highly recommended to use an EV (Extended Validation) certificate to gain users’ confidence with the highest level of trust indication.
Recommended Reading SSL certificates: from principle to deployment, comprehensive protection of website data transmission security。
Secondly, assess the domain name coverage requirements. If there is only one primary domain name, a single-domain certificate will suffice. If there is one primary domain name along with multiple fixed secondary domains (such as websites for different brands), a multi-domain certificate is more convenient for management. If you have one primary domain name and a large number of dynamic subdomains, a wildcard certificate offers the best cost-effectiveness and flexibility.
When selecting a certificate authority (CA), it is advisable to prefer globally recognized or domestically well-known CAs such as DigiCert, Sectigo, GlobalSign, or domestic providers like CFCA and XinAn Century. The root certificates of these CAs are widely pre-installed in various browsers and operating systems, ensuring better compatibility. It is also important to compare factors such as price, after-sales service, and compensation guarantees (in the event of security incidents caused by certificate issues) before making a decision.
## SSL Certificate Installation and Deployment Process
After successfully obtaining the certificate file, it needs to be correctly deployed on the website server. The main steps include generating a key pair, submitting a certificate request, installing the certificate, and enforcing HTTPS redirection.
Generate a private key and a certificate request.
First, generate a strongly encrypted private key file on the server using the appropriate tool. Next, use this private key to create a Certificate Signing Request (CSR) file. The CSR file contains information about your organization as well as the domain name that will be issued a certificate for. This file serves as the basis for submitting the request to the Certificate Authority (CA) for review and issuance.
Submit the CSR (Certificate Signing Request) for CA (Certificate Authority) verification.
Submit the content of the generated CSR (Certificate Signing Request) file to the CA (Certificate Authority) you purchased. Depending on the type of certificate you selected, the CA will initiate the corresponding verification process. For DV (Domain Validation) certificates, you only need to complete the verification of domain name control; for OV (Organizational Validation) or EV (Extended Validation) certificates, you will need to provide organizational certification documents for manual review as required by the CA.
Install the certificate on the server.
Once the CA review is approved, you will receive the issued certificate files. These typically include a main certificate file and one or more intermediate CA certificates. Depending on the type of your server, you need to upload the certificate files, the private key file, and the intermediate chain of certificates to the designated directories on the server, and correctly specify the paths to these files in the server configuration files. The configuration process varies for different server software.
Configuring HTTP to HTTPS redirection
After the certificate is installed, to ensure that all traffic is transmitted over a secure connection and to improve SEO rankings, it is necessary to forcibly redirect all HTTP requests to HTTPS. This is typically achieved by adding redirection rules in the web server configuration.
Finally, be sure to use an online SSL testing tool to conduct a comprehensive check on the configured HTTPS website. This will ensure that the certificate chain is complete, the protocol version is secure, the cipher suite is properly configured, and there are no known security vulnerabilities.
## Summary
SSL certificates have evolved from an optional security enhancement to an essential infrastructure component for modern websites. By utilizing encryption and authentication, they protect the privacy and integrity of data transmitted over the internet. They are crucial for building user trust, enhancing a brand’s professional image, and meeting compliance requirements. Understanding the underlying principles of encryption, selecting the right type of certificate based on specific needs, and properly installing and configuring it are all essential steps in mastering the complete knowledge of SSL certificates. Embracing HTTPS is not only about adopting security measures but also about embracing a more trustworthy future for the internet.
FAQ Frequently Asked Questions
Are SSL certificates and TLS certificates the same thing?
Yes, what we commonly refer to as an “SSL certificate” today mostly refers to certificates based on the newer and more secure TLS protocol. Since SSL is the predecessor of TLS and its name is more well-known, the industry has traditionally continued to use the term “SSL certificate” to refer to these security certificates that are used to enable HTTPS.
What is the difference between free SSL certificates and paid certificates?
免费证书通常指Let‘s Encrypt等机构颁发的DV证书，其提供了与付费DV证书相同的基础加密功能。主要区别在于：免费证书有效期短，需要频繁续期；缺乏商业保险赔付；在技术支持和服务上较为有限。付费的OV/EV证书则提供组织身份验证、更长的有效期、专业的技术支持和高额的保障赔付。
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 process used to establish the connection. However, with the improved hardware performance of modern servers and the optimization of the TLS protocol, this impact has become negligible. On the contrary, enabling HTTPS allows the use of modern networking protocols such as HTTP/2, which can significantly speed up page loading times. The performance benefits gained from using HTTP/2 typically far outweigh the minor additional costs associated with encryption.
Can an SSL certificate be used on multiple servers?
Yes, but there are certain conditions and technical requirements. You can deploy the same certificate and private key on multiple servers, as long as these servers are providing services for the domain name protected by that certificate. This is commonly used in load balancing clusters or primary/secondary server setups. It’s important to note that the private key must be kept secure; any leakage of the private key can compromise the security of all servers that use that certificate.
What could be the reasons for a browser to display a “connection is not secure” warning?
This indicates that there is an issue with the HTTPS connection to the website. Common causes include: the certificate has expired; the issuing authority of the certificate is not trusted by the browser; the domain name on the certificate does not match the domain name of the website being visited; the website page is loading unsafe resources using the HTTP protocol; or there are security vulnerabilities in the server’s SSL/TLS configuration. It is necessary to investigate the issue based on the specific error message displayed by the browser.
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.
- What is an SSL certificate? A comprehensive guide to understanding the principles, types, and installation procedures of digital certificates.
- In-depth Analysis of SSL Certificates: From Beginner to Expert – Comprehensive Protection for Website Security
- What is an SSL certificate and how does it work
- Comprehensive Guide to SSL Certificates: From Principles and Types to Practical Details on Deployment and Management
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