In Vivado 2016.3 and later versions, Xilinx has added the ability to encrypt HDL source files with IEEE 1735 v2 encryption.
How do I enable IEEE-1735 Version 2 encryption in Vivado?
The IEEE-1735 v2 encryption feature requires a license which can be requested by emailing email@example.com.
Note: Encryption license features are tied to specific Vivado versions. When requesting a license, include the exact version of Vivado (for example, 2016.3, 2016.4) for which a license is required.