What is RSA key used for?
RSA key is required for securing transmission of data through sites that have SSL certificates installed.
The encryption of data by SSL certificates is based on using two keys – public and private. Public key (its bits are embedded into CSR code) is used to encrypt data prior to sending it to server on which the certificate has been installed. It is sent to every internet user that submits information at site secured by the certificate. Private key (RSA key that is always generated along with the CSR) is necessary to decrypt data that has been encrypted using public key. Neither NameCheap nor Certification Authorities have access to your private key. It is generated locally on your server and is never transmitted to us. The integrity of your SSL certificate depends on your private key being controlled exclusively by you. This is intended to make data transmission via SSL secure and safe. Private key should not be revealed to any third-parties for them not to compromise your certificate.