====== Bitstream Encryption ======
Several ZTEX FPGA Boards support Bitstream encryption, e.g. [[http://www.ztex.de/usb-fpga-2|USB-FPGA Modules 2.16, 2.13, 2.14 and 2.18]].

The key which is used to decrypt the bitstream is stored in special low power memory of the FPGA which is powered by a battery. This battery is an option and not installed by default.

Using encrypted bitstreams is quite simple:

  - Generate an encrypted bitstream either (**ISE**) using the ''bitgen'' option ''-g Encypt:Yes'' and ''-g KeyFile:<.nky file>'' or (**Vivado**) using the constraints <code tcl>set_property BITSTREAM.ENCRYPTION.ENCRYPT Yes [current_design]
set_property BITSTREAM.ENCRYPTION.ENCRYPTKEYSELECT bbram [current_design]
set_property BITSTREAM.ENCRYPTION.KEYFILE <.nky file> [current_design]</code> If no key file (.nky file) is given a new one with random key is created. 
  - Upload the key (.nky file) to the FPGA through JTAG using Xilinx tools
  - FPGA now accepts the encrypted bitstream (no special load technique is required but some options like bitstream compression may not work)