Overview of the Crypto Kit updates in Citrix Workspace 1904

Applicable Products

Citrix Workspace App 1904 for Windows and later.

Objective

This feature is an important change to the secure communication protocol. Cipher suites with the prefix TLS_RSA_ do not offer forward secrecy and are considered weak. These cipher suites were deprecated in Citrix Receiver version 13.10 with an option for backward compatibility.

In this release, the TLS_RSA_ cipher suites have been removed entirely. Instead, this release supports the advanced TLS_ECDHE_RSA_ cipher suites. If your environment is not configured with the TLS_ECDHE_RSA_ cipher suites, client launches are not supported due to weak ciphers.

This document aims to detail the changes to the cipher suites.

What’s New?

The following advanced cipher suites are supported:

  • TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (0xc030)

  • TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384 (0xc028)
  • TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA (0xc013)

In earlier releases, the GPO configuration that was available under the below Computer Configuration node which allowed to enable the deprecated cipher suites has been removed now.

Administrative Template > Citrix Component > Citrix Workspace > Network Routing > Deprecated Cipher Suites


The following cipher matrix provides the ciphers supported by the latest SSL SDK:

Expected failure scenarios and edge cases

  • TCP

    • OPEN mode: Session launch is not supported when the client is configured for GOV and the VDA for COM. This happens because a common cipher suite is absent.

    • FIPS/NIST(SP800-52) compliance mode: Session launch is not supported when the VDA is configured for COM the client for COM, GOV, or ANY, or the other way around. This happens because a common cipher suite is absent.
  • DTLS v1.0 supports the following cipher suites:
  • TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
  • TLS_EMPTY_RENEGOTIATION_INFO_SCSV
  • DTLS v1.2 supports the following cipher suites:
    • TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
    • TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384
    • TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
    • TLS_EMPTY_RENEGOTIATION_INFO_SCSV
  • Therefore, session launch is not supported from a client configured for GOV to a VDA configured for COM. Also, fallback to TCP is not supported. When you use DTLS v1.0, session launch is not supported for clients configured for GOV because a common cipher suite is absent.

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The following matrices provide details of internal and external network connections:

  • Matrix for internal network connections (Citrix Gateway scenario)

  • Matrix for external network connections (Citrix Gateway scenario)

Note: When NetScaler Gateway is used

  1. For the EDT to work, NetScaler Gateway must be of version 12.1 or higher since the older versions doesn’t support ECDHE cipher suites in DTLS mode.

  2. NetScaler Gateway doesn’t support DTLS 1.2 so TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 and TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384 are not supported and NetScaler Gateway must be configured to use TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA for it to work in DTLS 1.0

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