[FPGA Test CW340] OpenTitan simplified bitstream for SCA on AES

[parisaeliasi]

Description

Hello,

I’m trying to reproduce a simple AES test on the OpenTitan SoC, running on the CW340 FPGA board, with the goal of collecting power traces and evaluating the design against SCA.

In the OpenTitan repository, I found the file sw/device/sca/aes_serial.c, which I think is intended for use with the lowrisc/ot-sca project. This C file seems to be compiled into a binary and loaded onto a customized OpenTitan bitstream that is modified/simplified to enable SCA experiments. However:

• The lowrisc/ot-sca repo only contains bitstreams for CW310, not CW340.
  

• The bitstreams appear to be pre-built; there is no published source or script to regenerate them.
  

• There is no CW340-specific support in the ot-sca repo for building bitstreams or collecting traces.
  

On the other hand, in the cw340-luna-board repository, I found fpga/hdl/cw341_top.v, which may be related to a minimal AES or SCA setup, but I’m unsure how it is meant to be used.
I would appreciate any help with the following:

• Building a minimal OpenTitan bitstream for CW340 that includes AES and minimal peripherals for SCA.
  

• load a simple AES binary to it.
  

• Collecting power traces from CW340 for SCA.
  

Any guidance or working example would be greatly appreciated!

[nasahlpa]

Hi @parisaeliasi

Unfortunately there is currently no support for SCA measurements on CW340.

The necessary steps to get started on CW310 are the following:

• Build the SCA firmware that runs on OpenTitan from the OpenTitan master branch:
  ./bazelisk.sh build //sw/device/tests/penetrationtests/firmware:pen_test_sca_fpga_cw310_test_rom
• Build the FPGA bitstream from the ot-sca_cw310_aes branch:
  ./bazelisk.sh build //hw/bitstream/vivado:fpga_cw310_test_rom
• Place bitstream and the firmware into the objs/ directory of ot-sca.
• Adapt the AES capture config file to point to the new bitstream and firmware.
• Capture traces in ot-sca:
  ./capture_aes.py --capture_config configs/aes_sca_cw310.yaml --project aes_capture

For CW340, you need to adapt the steps above.

[parisaeliasi]

Hi @nasahlpa

Thanks a lot for your reply. Do you know if there are any plans to add support for CW340 in the near future?

In the meantime, I’d love to try adapting the CW310 setup. If possible, could you point me to any (general) steps or tips that might help?

[nasahlpa]

Hi @parisaeliasi

Unfortunately I think nobody is currently working on enabling CW340.

For the above steps:

• Check if you can build the binary with:
  ./bazelisk.sh build //sw/device/tests/penetrationtests/firmware:pen_test_sca_fpga_cw340_test_rom
  If this does not work, you need to modify the BAZEL build files accordingly.
• Check if the ot-sca_cw310_aes branch also has the changes for CW340. If yes, you can build the bitstream with:
  ./bazelisk.sh build //hw/bitstream/vivado:fpga_cw340_test_rom
  If not, you need to make also the changes for CW340.
• ot-sca does currently not support CW340. Although there is a draft PR available, it is quite outdated. So you would need to make the necessary changes to support this FPGA board.