Security policy settings
The Security section includes the policy setting for configuring session encryption and encryption of logon data.
SecureICA minimum encryption level
This setting specifies the minimum level at which to encrypt session data sent between the server and a user device.
Important: For the Virtual Delivery Agent 7.x, this policy setting can be used only to enable the encryption of the logon data with RC5 128-bit encryption. Other settings are provided only for backwards compatibility with legacy versions of Citrix Virtual Apps and Desktops.
For the VDA 7.x, encryption of session data is set using the basic settings of the VDA’s Delivery Group. If Enable Secure ICA is selected for the Delivery Group, session data is encrypted using RC5 (128 bit) encryption. If Enable Secure ICA is not selected for the Delivery Group, session data is encrypted with Basic encryption.
When adding this setting to a policy, select an option:
- Basic encrypts the client connection using a non-RC5 algorithm. It protects the data stream from being read directly, but it can be decrypted. By default, the server uses Basic encryption for client-server traffic.
- RC5 (128 bit) logon only encrypts the logon data using RC5 128-bit encryption and the client connection using Basic encryption.
- RC5 (40 bit) encrypts the client connection using RC5 40-bit encryption.
- RC5 (56 bit) encrypts the client connection using RC5 56-bit encryption.
- RC5 (128 bit) encrypts the client connection using RC5 128-bit encryption.
The settings you specify for client-server encryption can interact with any other encryption settings in your environment and your Windows operating system. Consider a higher priority encryption level is set on either a server or user device. In this case, the settings you specify for published resources can be overridden.
You can raise encryption levels to further secure communications and message integrity for certain users. If a policy requires a higher encryption level, Citrix Receivers using a lower encryption level are denied connection.
SecureICA does not perform authentication or check data integrity. To provide end-to-end encryption for your site, use SecureICA with TLS encryption.
SecureICA does not use FIPS-compliant algorithms. If this setting is an issue, configure the server and Citrix Receivers to avoid using SecureICA.
SecureICA uses the RC5 block cipher as described in RFC 2040 for confidentiality. The block size is 64 bits (a multiple of 32-bit word units). The key length is 128 bits. The number of rounds is 12.
Keys for the RC5 block cipher are negotiated when a session is created. Negotiation is performed using the Diffie-Hellman algorithm. This negotiation uses Diffie-Hellman public parameters. These parameters are stored in the Windows registry when the Virtual Delivery Agent is installed. Public parameters are not secret. The result of the Diffie-Hellman negotiation is a secret key, from which the session keys for the RC5 block cipher are derived. Separate session keys are used for user logon, and for data transfer. Also, separate session keys are used for traffic to and from the Virtual Delivery Agent. Therefore there are four session keys for each session. The secret keys and session keys are not stored. Initialization vectors for the RC5 block cipher are also derived from the secret key.