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Reverse Engineering with Frida

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Ben Campbell edited this page Mar 20, 2024 · 1 revision

This is for historical info; it is no longer necessary unless you're trying to make sense of the phone application or XML code.

Finding the PSK and IV (no longer necessary)

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You will need to set the dishwasher to "Local network only" in the setup application so that your phone will connect directly to it, rather than going through the cloud services.

You'll also need a rooted Android phone running frida-server and the find-psk.frida script. This will hook the callback from the OpenSSL library hcp::client_psk_callback that is called when OpenSSL has made a connection and now needs to establish the PSK.

frida --no-pause -f com.bshg.homeconnect.android.release -U -l find-psk.frida

It should start the Home Connect application and eventually print a message like:

psk callback hint 'HCCOM_Local_App'
psk 32 0x6ee63fb2f0
           0  1  2  3  4  5  6  7  8  9  A  B  C  D  E  F  0123456789ABCDEF
00000000  0e c8 1f d8 c6 49 fa d8 bc e7 fd 34 33 54 13 d4  .....I.....43T..
00000010  73 f9 2e 01 fc d8 26 80 49 89 4c 19 d7 2e cd cb  s.....&.I.L.....

Which gives you the 32-byte PSK value to copy into the hcpy program.

SSL logging

The Frida script will also dump all of the SSL traffic so that you can see different endpoints and things. Not much is documented yet.

Note that the TX from the phone on the websocket is "masked" with an repeating 4-byte XOR that is sent in the first part of each messages. The script could be augmented to decode those as well. The replies from the device are not masked so they can be read in the clear.

Retrieving home appliance configuration

frida-trace -o initHomeAppliance.log -f "com.bshg.homeconnect.android.release" -U -j '*!initHomeAppliance''

PSK can also be found in the last section of the config as base64url encoded.

echo 'Dsgf2MZJ-ti85_00M1QT1HP5LgH82CaASYlMGdcuzcs"' | tr '_\-"' '/+=' | base64 -d | xxd -g1

The IV is also there for devices that use it. This needs better documentation.

TODO: document the other frida scripts that do sendmsg() and Encrypt() / Decrypt() tracing

hcpy

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The hcpy tool can contact your device, and if the PSK is correct, it will register for notification of events.

RX: {'sID': 2354590730, 'msgID': 3734589701, 'resource': '/ei/initialValues', 'version': 2, 'action': 'POST', 'data': [{'edMsgID': 3182729968}]}
TX: {"sID":2354590730,"msgID":3734589701,"resource":"/ei/initialValues","version":2,"action":"RESPONSE","data":[{"deviceType":"Application","deviceName":"py-hca","deviceID":"1234"}]}
TX: {"sID":2354590730,"msgID":3182729968,"resource":"/ci/services","version":1,"action":"GET"}
TX: {"sID":2354590730,"msgID":3182729969,"resource":"/iz/info","version":1,"action":"GET"}
TX: {"sID":2354590730,"msgID":3182729970,"resource":"/ei/deviceReady","version":2,"action":"NOTIFY"}
RX: {'sID': 2354590730, 'msgID': 3182729968, 'resource': '/ci/services', 'version': 1, 'action': 'RESPONSE', 'data': [{'service': 'ci', 'version': 3}, {'service': 'ei', 'version': 2}, {'service': 'iz', 'version': 1}, {'service': 'ni', 'version': 1}, {'service': 'ro', 'version': 1}]}
RX: {'sID': 2354590730, 'msgID': 3182729969, 'resource': '/iz/info', 'version': 1, 'action': 'RESPONSE', 'data': [{'deviceID': '....', 'eNumber': 'SX65EX56CN/11', 'brand': 'SIEMENS', 'vib': 'SX65EX56CN', 'mac': '....', 'haVersion': '1.4', 'swVersion': '3.2.10.20200911163726', 'hwVersion': '2.0.0.2', 'deviceType': 'Dishwasher', 'deviceInfo': '', 'customerIndex': '11', 'serialNumber': '....', 'fdString': '0201', 'shipSki': '....'}]}

Feature UID mapping

There are other things that can be hooked in the application to get the mappings of the uid to actual menu settings and XML files of the configuration parameters.

In the xml/ directory are some of the device descriptions and feature maps that the app downloads from the Home Connect servers. Note that the XML has unadorned hex, while the websocket messages are in decimal.

For instance, when the dishwasher door is closed and then re-opened, it sends the messages for 'uid':512, which is 0x020F hex:

RX: {... 'data': [{'uid': 527, 'value': 1}]}
RX: {... 'data': [{'uid': 527, 'value': 0}]}

In the xml/dishwasher-description.xml there is a statusList that says uid 0x020f is a readonly value that uses enum 0x0201:

    <status access="read" available="true" enumerationType="0201" refCID="03" refDID="80" uid="020F"/>

In the xml/dishwasher-featuremap.xml there is a mapping of feature reference UIDs to names:

    <feature refUID="020F">BSH.Common.Status.DoorState</feature>

as well as mappings of enum ids to enum names and values:

    <enumDescription enumKey="BSH.Common.EnumType.DoorState" refENID="0201">
      <enumMember refValue="0">Open</enumMember>
      <enumMember refValue="1">Closed</enumMember>
    </enumDescription>
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