CSR (Certificate Signing Request)

A Certificate Signing Request or CSR is a specially formatted encrypted message sent from a Secure Sockets Layer (SSL) digital certificate applicant to a certificate authority (CA). The CSR validates the information the CA requires to issue a certificate.

In a public key infrastructure (PKI) system, which enables secure data sharing among validated parties on the Internet, a CSR must be created before ordering and purchasing an SSL certificate. Applicants must first generate a key pair -- a private key which will be used to decrypt ciphertext and create digital signatures, and a public key to encrypt plaintext and verify digital certificates. Note that both the key pair and CSR must be created on the server on which the SSL certificate will be used; this is imperative to ensure the integrity of the key pair and PKI in general.

After the key pair is prepared, the CSR can be generated. Upon collecting all the necessary CSR data (see Table 1), the CA will use this data to build the certificate. How a CSR is generated depends on the webserver software used. Once the CSR is generated, it can be submitted to the CA. If the request is successfully validated, the CA will issue the SSL certificate.

Table 1

*When generating a CSR for a wildcard certificate, the common name should start with an * (e.g., *.mycompany.com)