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IoT Reversing Field Manual Cheat Sheet by

Quick notes/intro for router debugging and rooting. Including tools, terms, and tactics.

Serial Protocols

UART

Deta­ils
UART is a serial protocol used for intere­cting with the system. May return a shell, and or access to the filesy­stem. Seperate from JTAG.

Enum­erate Pinout [Multi­met­er]
TX - Voltage fluctuates at boot1 from 0 to 3.3/5.5v
RX - Constant low value below VCC and above GND
GND - Voltage is constant 0, has 4 traces in a crosss shape2
VCC - Normally not used to if device already powered, should not fluctaute
1 Fluctu­ation is caused from the debug messages being sent.
2 Testing continuity of GND to other pins, shows other pins that may be grounded

Square outlined pin, normally is "pin 1"

JTAG

Deta­ils
Used for on-chi­p-d­ebu­gging, generally allows for access to a GNU Debugger (GDB) for the JTAG host. Pinout for hidden console may be found with JTAGen­um/­JTA­Gul­ator. Then access GDB with a Bus Pirate or Shikra USB-to­-Serial devices and debug applic­ations using OpenOCD software.

Accessing Serial Consoles

BASH
sudo dmesg | grep -iC 5 usb
sudo screen -L /dev/t­tyUSB0 115200

Alter­nat­ively, use the Arduino IDE serial console. Useful when input is off with the screen utility
In the screen command, 115200 is the baud rate of the serial commun­ica­tions

The baud rate can be determined using -
https­://­git­hub.co­m/d­evt­tys­0/b­aud­rat­e.git
 

Hardware Physical Tools

JTAGulator
Identifies JTAG & UART pinouts.
JTAGen­um1
Identifies JTAG pinouts
Bus Pirate2
FT232RL - USB to Serial, Use SOIC8 Clip to dump firmwarez
Shikra3
FT232H(Q) - USB to Serial
RS-232 Generic Adapter4
USB to Serial
1 JTAGenum Setup Tutorial:
https­://­p16.pr­aet­ori­an.c­om­/bl­og/­jta­gul­ato­r-v­s-j­tag­enu­m-t­ool­s-f­or-­ide­nti­fyi­ng-­jta­g-p­ins­-in­-io­t-d­evices
2 Bus Pirate Pinout Inform­ation
http:­//d­ang­ero­usp­rot­oty­pes.co­m/d­ocs­/Co­mmo­n_B­us_­Pir­ate­_ca­ble­_pi­nouts
3 Shikra Pinout [UART] D0 - TX, D1 - RX
See also, Adafruit FT232H Breakout -
https­://­cdn­-le­arn.ad­afr­uit.co­m/d­own­loa­ds/­pdf­/ad­afr­uit­-ft­232­h-b­rea­kou­t.pdf
4 Male DB9: GND - Pin 5, TX - Pin 3, RX - Pin 2

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