SSL Certificate (Secure Sockets Layer Certificate) is a digital certificate used to establish an encrypted connection on the Internet, which ensures the security and integrity of data when it is transmitted between the client and the server. Here are some key points of SSL Certificate:

1. Encrypted Communication:
2. SSL Certificate creates an encrypted channel between the client (such as browser) and the server through the SSL/TLS protocol, protecting the data from eavesdropping or tampering.
3. Authentication:
4. SSL Certificate verifies the identity of the server, ensuring that the user is connected to the server they intend to visit, not a fake website.
5. Certificate Authority (CA):
6. Certificate Authority is a trusted third party responsible for verifying the identity of the entity applying for the certificate and issuing SSL Certificate.
7. Certificate Type:
8. Domain Validation (DV): Only verifies the ownership of the domain name, with fast issuance and low price.
9. Organization Validation (OV): In addition to verifying the ownership of the domain name, it also verifies the legitimacy of the applicant entity.
10. Extended Validation (EV): Provides the highest level of validation, including detailed verification of the applicant entity, and the address bar displays green, increasing trust.
11. Multi-domain and Wildcard Certificates:
12. Multi-domain certificates allow multiple different domains to be protected under one certificate.
13. Wildcard certificates allow all subdomains under one main domain to be protected.
14. Certificate Chain:
15. SSL certificates usually contain a certificate chain, including server certificates, intermediate CA certificates, and root CA certificates. The browser verifies this chain to ensure the credibility of the certificate.
16. Certificate Revocation:
17. If a certificate is no longer valid or has been leaked, it can be revoked. Certificate Revocation List (CRL) and Online Certificate Status Protocol (OCSP) are two mechanisms for checking the status of a certificate.
18. SSL/TLS Protocol:
19. SSL certificates work with SSL/TLS protocols. TLS is an upgraded version of SSL. Currently, TLS 1.2 and TLS 1.3 are widely used.
20. Security and Performance:
21. Using strong cipher suites and algorithms can improve the security of SSL certificates, but may affect performance, especially on older devices.
22. Installation and Management:
23. Server administrators need to properly install and manage SSL certificates, including certificate application, installation, renewal, and revocation.

With the increase in network security threats, SSL certificates have become an important tool to protect the security of websites and user data. Most modern websites deploy SSL certificates to ensure the security of user data and the trust of the website.

SSL证书（Secure Sockets Layer Certificate）是一种用于在互联网上建立加密连接的数字证书，它确保了数据在客户端和服务器之间传输时的安全性和完整性。以下是SSL证书的一些关键点：

1. 加密通信：

   • SSL证书通过SSL/TLS协议在客户端（如浏览器）和服务器之间创建一个加密通道，保护数据不被窃听或篡改。

2. 身份验证：

   • SSL证书验证服务器的身份，确保用户连接到的是他们意图访问的服务器，而不是一个假冒的网站。

3. 证书颁发机构（CA）：

   • 证书颁发机构是受信任的第三方，负责验证申请证书的实体身份，并签发SSL证书。

4. 证书类型：

   • 域名验证（DV）：只验证域名所有权，颁发速度快，价格较低。
   • 组织验证（OV）：除了验证域名所有权外，还验证申请实体的合法性。
   • 扩展验证（EV）：提供最高级别的验证，包括对申请实体的详细验证，地址栏显示绿色，增加信任度。

5. 多域名和通配符证书：

   • 多域名证书允许在一个证书下保护多个不同的域名。
   • 通配符证书允许保护一个主域名下的所有子域名。

6. 证书链：

   • SSL证书通常包含一个证书链，包括服务器证书、中间CA证书和根CA证书，浏览器会验证这个链以确保证书的可信度。

7. 证书吊销：

   • 如果证书不再有效或被泄露，可以被吊销。证书吊销列表（CRL）和在线证书状态协议（OCSP）是检查证书状态的两种机制。

8. SSL/TLS协议：

   • SSL证书与SSL/TLS协议一起工作，TLS是SSL的升级版，目前广泛使用的是TLS 1.2和TLS 1.3。

9. 安全性和性能：

   • 使用强密码套件和算法可以提高SSL证书的安全性，但可能会影响性能，尤其是在旧设备上。

10. 安装和管理：

    • 服务器管理员需要正确安装和管理SSL证书，包括证书的申请、安装、续签和吊销。

随着网络安全威胁的增加，SSL证书已成为保护网站和用户数据安全的重要工具。大多数现代网站都部署了SSL证书，以确保用户数据的安全和网站的信任度。

SSL Labs Server Test is an online testing tool provided by Qualys. It comprehensively tests the certificate chain, security, performance, and protocol details of HTTPS websites, and gives a score, detailed test report, and improvement suggestions after the test is completed. Here are some key information about SSL Labs Server Test:

1. Test content:
2. SSL Labs Server Test analyzes the SSL/TLS configuration of the website, including supported protocol versions, cipher suites, certificate chains, key exchange algorithms, session resumption mechanisms, etc.
3. Rating criteria:
4. SSL Labs scores the security of the website based on the test results, and the scoring criteria will be updated as security practices evolve. For example, in the 2020 scoring criteria, TLS 1.0 and TLS 1.1 are considered insecure, so servers that support these protocols will receive lower scores.
5. Testing rules overview:
6. SSL Labs changed the algorithm in 2020, mainly modifying the scoring criteria for TLS 1.0 and TLS 1.1, because these older protocols use weak encryption algorithms and systems, such as SHA-1 and MD5, and have major security vulnerabilities.
7. Browser support:
8. Mainstream browsers such as Microsoft IE and Edge, Mozilla Firefox, Safari/Webkit, and Google Chrome are all planning to remove support for TLS 1.0 and TLS 1.1 in early 2020.
9. Secrets to get an A+ rating:
10. In order to get an A+ rating in the SSL Labs Server Test, the server configuration needs to support TLS 1.2 and TLS 1.3, enable HSTS (HTTP Strict Transport Security), do not display warnings, support TLS_FALLBACK_SCSV, and configure the appropriate cipher suite.
11. Testing Tools:
12. In addition to the online testing tools, SSL Labs also provides TestSSLServer, which is part of the SSL Labs Server Test that can be downloaded and run locally to test the SSL/TLS configuration of internal sites.
13. Best Practices:
14. SSL Labs recommends using a comprehensive SSL/TLS assessment tool to verify the configuration to ensure that the website is secure from the beginning, and to perform regular assessments to maintain security.

With SSL Labs Server Test, website administrators can understand the SSL/TLS configuration of the website and make adjustments based on the test results and recommendations to improve the security of the website.

国密SSL证书在等保（网络安全等级保护）和密评（商用密码应用安全性评估）中的应用主要体现在以下几个方面：

1. 助力等保合规建设：
   国密SSL证书遵循国密SSL协议，采用SM2/SM3国密算法，实现Web访问客户端到服务器端的HTTPS加密传输，并验证通信方的真实身份。这确保了通信网络数据传输的完整性和加密性，满足二级等保安全通信网络设计技术要求，助力二级等保合规建设。
2. 助力密评合规：
   根据《商用密码应用安全性评估管理办法》，网络与信息系统的运营者应当使用商用密码进行保护，并每年至少开展一次商用密码应用安全性评估。国密SSL证书满足密评的网络和通信安全相关密码应用技术要求，可助力过密评。
3. 落实等保2.0、关保安全通信设计要求：
   国密SSL证书通过SSL/TLS协议的加密认证机制，建立安全的网络连接并校验通信方的真实身份，实现网络传输的保密性、完整性，确保通信双方身份可信。这有助于等保二级及以上信息系统以及关键信息基础设施信息系统满足等保2.0安全通信设计要求。
4. 落实密码应用合规要求：
   国密SSL证书遵循国家标准技术规范并参考国际标准，支持SM2/SM3/SM4国产密码算法和国密安全协议。在密评中，通过使用国密SSL证书，可以确保系统采用的密码算法和技术符合国家标准和法规要求，满足商用密码应用的合规性要求。
5. 提升网络信息系统的安全性：
   国密SSL证书的应用不仅能够提升网络信息系统的安全性，同时满足我国网络安全和密码应用的各项法规要求。
6. 双证书部署全球信任：
   为解决国密算法在HTTPS加密应用中的兼容性问题，相关企业可以优选国密SM2/国际RSA双证书，既可满足国密合规要求，又可实现全球通用。

综上所述，国密SSL证书在等保、密评中的应用，对于确保网络通信安全、数据传输的保密性和完整性、以及满足国家法律法规要求方面发挥着重要作用。

Yes, you can purchase multi domain SSL certificates on 45SSL.com. According to search results, the multi domain SSL certificate provided by 45SSL.com can contain up to 300 domain names, including www and @ domains
This means that you can protect multiple websites or subdomains with one certificate, without the need to purchase separate certificates for each domain, saving costs and simplifying the management process.