A CSR file is a Certificate Signing Request file that is used to request for SSL/TLS certificate. When you need to have your SSL/TLS certificate, you generate the CSR on the same server where it will finally be installed. This CSR file is shared with the Certificate Authority (CA) for creation of the certificate. It contains information such as common name, organization, country, and, more importantly, the public key that is integrated within your certificate file and is signed with the corresponding private key.
Applications that can open CSR files include OpenSSL and Microsoft IIS.
Certificate Signing Request File Format
A CSR file is created in a Base-64 PEM format that can be opened and viewed in a simple text editor such as Microsoft Notepad. It includes a header —–BEGIN NEW CERTIFICATE REQUEST—– at the start of the file and a footer —–END NEW CERTIFICATE REQUEST—– at the end of the file.