openwifi/doc/app_notes/csi_fuzzer.md

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Author: Xianjun jiao
SPDX-FileCopyrightText: 2021 UGent
SPDX-License-Identifier: AGPL-3.0-or-later
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[ACM WiSec 2021. Openwifi CSI fuzzer for authorized sensing and covert channels](https://dl.acm.org/doi/pdf/10.1145/3448300.3468255)

CSI (Channel State Information) of WiFi systems is available in some WiFi chips and can be used for sensing the environment (keystrokes, people, object) passively and secretly.

## Concept

How could a CSI fuzzer stop unauthorized sensing?

![](./csi-fuzzer-system-before-vs-now.png)

CSI fuzzer implementation principle.

![](./csi-fuzzer-principle.png)

## Demo instructions

Thanks to the full-duplex capability and CSI extraction feature of openwifi, you can monitor the artificial channel response via [side channel](./csi.md) by Tx-Rx over the air coupling without affecting the normal operation/traffic of openwifi. Before the self-monitoring, the auto-mute during Tx needs to be disabled.

The full demo steps are:

```
ssh root@192.168.10.122
(password: openwifi)

cd openwifi

./fosdem-11ag.sh
(setup openwifi AP)

./sdrctl dev sdr0 set reg xpu 1 1
(Disable auto-muting to listen self-TX)

insmod side_ch.ko num_eq_init=0

./side_ch_ctl wh1h2001
./side_ch_ctl wh6hffffffff
(Let's only monitor self-beacon-TX CSI over-the-air loopback)

./side_ch_ctl g1
```
Go to openwifi/user_space/side_ch_ctl_src, and run `python3 side_info_display.py 0`. You should see the over-the-air loopback CSI when CSI fuzzer is not enabled. Then stop the python3 side_info_display.py script to ease the next step.

Start another ssh session to the openwifi board:
```
ssh root@192.168.10.122
(password: openwifi)

cd openwifi

./csi_fuzzer_scan.sh 1
(CSI fuzzer applies possible artificial CSI by scanning all values)
(csi_fuzzer.sh is called. Please read both scripts to understand these commands)
```

Go to openwifi/user_space/side_ch_ctl_src, and run `python3 side_info_display.py 0`. Now you should see that CSI keeps changing like in this [video](https://youtu.be/aOPYwT77Qdw).

# Further explanation on parameters

CSI fuzzer in openwifi system architecture and related commands.

![](./csi-fuzzer-implementation.png)

# Example fuzzed CSI

CSI self-monitoring before fuzzing.

![](./csi-fuzzer-beacon-ant-back-0.jpg)

CSI self-monitoring after  fuzzing command: `csi_fuzzer.sh 1 45 0 13`

![](./csi-fuzzer-beacon-ant-back-1-45-0-13.jpg)

`csi_fuzzer_scan.sh` can scan the c1 and c2 in different styles/modes by calling `csi_fuzzer.sh`.