A CSR (Certificate Signing Request) file is a plain text file that contains information about the entity requesting a digital certificate from a certificate authority (CA). The file format for a CSR is specified in the X.509 standard and is based on the Privacy-Enhanced Mail (PEM) format.
A CSR file typically starts with a header line that identifies the file as a PEM-encoded file and includes the following information:
-----BEGIN CERTIFICATE REQUEST-----
The contents of the CSR follow this header and are encoded using Base64 encoding. The contents of the CSR include information about the entity and its public key. The file concludes with a footer line that indicates the end of the PEM-encoded file:
-----END CERTIFICATE REQUEST-----
A CSR file is typically generated using a key pair, which includes a private key and a public key. The private key is kept secret by the entity and is used to encrypt information. The public key is included in the CSR and is used by the certificate authority to issue the certificate.
It's important to keep the private key secure and to never share it with others. The private key is used to encrypt information and to sign transactions, and if it were to fall into the wrong hands, it could be used for malicious purposes.
The format of a CSR file is standardized and widely used, and CSR files can be generated using a variety of tools and programming languages. Once generated, a CSR file can be submitted to a certificate authority to request the issuance of a certificate.