SSL offload and acceleration

SSL certificates

An SSL certificate, which is an integral part of any SSL transaction, is a digital data form (X509) that identifies a company (domain) or an individual. The certificate has a public key component that is visible to any client that wants to initiate a secure transaction with the server. The corresponding private key, which resides securely on the Citrix ADC appliance, is used to complete asymmetric key (or public key) encryption and decryption.

You can obtain an SSL certificate and key in either of the following ways:

  • From an authorized certificate authority (CA), such as Verisign
  • By generating a new SSL certificate and key on the Citrix ADC appliance

Alternately, you can use an existing SSL certificate on the appliance.

Certificates are categorized into four types by the Citrix ADC appliance:

  • Server certificates: A server certificate authenticates the server’s identity to the client. On the front-end, the ADC appliance acts as a server. You bind a server certificate and a private key to an SSL virtual server on the ADC appliance.
  • Client certificates: A client certificate authenticates the client’s identity to the server. On the back-end, the ADC appliance acts as a client. You bind a client certificate and private key to the SSL service or service group on the ADC appliance.
  • CA certificates: CA certificates issue the end-user certificates (client and server certificates). A CA certificate can be a trusted root CA (self-signed by the certificate authority) or an intermediate CA (signed by a trusted root CA). Typically, CA certificates do not need private keys.
  • Unknown certificates: All other certificates fall in this category.

Important: Citrix recommends that you use certificates obtained from authorized CAs, such as Verisign, for all your SSL transactions. Use certificates generated on the Citrix ADC appliance for testing purposes only, not in any live deployment.

  • If while adding a certificate-key pair, you add a certificate file with the same name as an existing certificate file, the original certificate file is overwritten with no warning. This action might cause issues after the appliance is restarted because the original certificate file is no longer available in the /nsconfig/ssl directory.

  • Removing any certificate or key files in a cluster environment restricts further configuration on the ADC appliance. Add the files back at the same location to make any configuration changes.

Note: You can use the ADM SSL dashboard for ease of SSL certificate management and set notifications for certificates that are unused or soon to expire. For more information, see SSL certificate management.

SSL certificates