CSR (Certificate Signing Request) is the message that’s sent to the CA in order to get a digital certificate created. A CSR is often generated on the same server on which the certificate is to be installed. Before creating a CSR, the applicant must first generate a public-private key pair. The public key is included in the CSR and is used by the CA to create the certificate while the private key (to be kept private again) is used to sign the information contained in the CSR.