A Certificate Signing Request (CSR) file is a core document in SSL/TLS certificate applications. Essentially, it's an encrypted data file containing public key information and the certificate applicant's information. CSR files are typically stored in PEM format or Base64 encoded text for easy transmission between different platforms and Certificate Authorities (CAs). The file records crucial certificate information, including the applicant's organization name, city, province, country code, domain name, and email address, as well as the public key used to generate the certificate. It's important to note that the CSR file does not contain the private key; this key is generated independently and stored on the server during CSR generation to ensure security.

　　The primary function of the CSR file is to submit the certificate application to the CA. The SSL/TLS certificate issuance process involves public-key cryptography, where the server needs to generate a key pair: a private key and a public key. The private key is stored on the server and must never be disclosed, while the public key must be submitted to the CA so that, after verifying the applicant's identity, the CA can bind the public key with the relevant certificate information to generate the official SSL/TLS certificate. The Certificate Submission Request (CSR) file is the carrier of this submission process. It encapsulates the public key and applicant information into a structured file, ensuring information integrity and secure transmission. Through the CSR file, the Certificate Authority (CA) can verify domain ownership, organization identity, and the applicant's legitimacy, ultimately issuing a formal certificate that enables HTTPS encrypted access to the website.

　　Furthermore, the CSR file helps ensure the security and controllability of the certificate generation process. Because the CSR file contains only the public key and not the private key, even if intercepted by a third party during transmission, it cannot be decrypted or misused, thus preventing the leakage of sensitive information. The CSR file also contains digital signature information, generated by the applicant's private key, used to prove that the CSR file was indeed created by the private key holder, preventing tampering and forgery. When applying for a certificate, the CA uses this signature for verification, ensuring the legitimacy and integrity of the public key, thereby establishing a chain of trust. This mechanism not only protects the applicant but also ensures the secure operation of the certificate system.

　　The CSR file generation process is relatively fixed, typically generated by server administrators or developers executing commands on the server. Taking OpenSSL as an example, the typical steps for generating a CSR file include first generating a private key file, then generating the CSR file based on the private key, and inputting information such as the domain name, organization name, city, and country code during the generation process. After generation, the administrator submits the CSR file to the Certificate Authority (CA), which verifies the applicant's identity and returns a signed certificate file. It is important to note that the CSR file must correspond to the private key; otherwise, the issued certificate cannot be used properly on the server. Simultaneously, the private key must be properly safeguarded, as any leakage will compromise certificate security and could even lead to man-in-the-middle attacks.

　　CSR files have various use cases in practice. The most common scenario is applying for SSL/TLS certificates for websites to achieve HTTPS encrypted access. Certificates obtained through CSR files can be deployed on web servers, providing a secure encrypted channel for user browsers and ensuring the confidentiality and integrity of data during transmission. Furthermore, CSR files can also be used to apply for code signing certificates, email encryption certificates, etc. These scenarios also rely on submitting public key information through the CSR file, which is then verified and issued by the CA to ensure secure communication and trusted identity. CSR files are a fundamental component of modern internet security systems, serving as a crucial bridge for encrypted communication and identity authentication.

　　Several key points must be considered when using CSR files. First, the information entered when generating the CSR file must be accurate. For example, the domain name must match the type of certificate being applied for, and the organization information must be consistent with the company's registration information; otherwise, the CA may refuse to issue the certificate or the certificate may fail browser trust verification. Second, the private key must be consistent with the CSR file. Any attempt to replace the public key or use a different private key will result in certificate installation failure. Third, for security, the private key should be properly stored. It is recommended to store it encrypted and restrict access to prevent malicious acquisition. Finally, after generating the CSR file, it can be used to apply for the same public key certificate from multiple CAs, but each time a certificate is applied for, it is still necessary to ensure that the private key is not leaked to maintain certificate security.

　　The existence of CSR files not only improves the security of certificate applications but also optimizes the certificate management process. Through the standardized CSR file format, enterprises can flexibly deploy certificates across multiple servers without transferring private keys between different systems, thereby reducing operational risks. CSR files can also be used in conjunction with automated certificate management tools to enable batch certificate applications, automatic renewals, and centralized management, improving operational efficiency. For large enterprises or companies providing SaaS services, this standardization and controllability are crucial, helping to maintain the overall information security system and avoid configuration errors or security vulnerabilities caused by manual operations.