From HTB Hardware Challenge MP => https://www.virustotal.com/gui/file/6fa8aaf50d4bb5faa97b7e60cf8cc3b01f094dbd6e4b8adfeea0667a06d6578c/detection

i2c_lcd_decoder.py

import pandas as pd

################
# Useful docs on how I2C driver communicates with LCD
# https://datasheet4u.com/datasheet-parts/LCD-1602A-datasheet.php?id=519148
# https://www.nxp.com/docs/en/data-sheet/PCF8574_PCF8574A.pdf
# https://controllerstech.com/i2c-lcd-in-stm32/
###
# CSV file was created from using program called Logic which reads data from a Logic Analyzer
# I exported the file after using the I2C decoder for the SDA & SCL pins on logicdata file provided
################


# Every 18 bits is an i2c packet as seen here https://www.picotech.com/images/uploads/library/topics/_med/i2c-packet-format.jpg
# The last 8 bits minus the ACK packet are the data bits
def append_i2c_packets(data, clock):
    bit_counter = ''		# store the 1's and 0's in here
    bin_array = []
    n = 1
    for _ in range(len(data)-n):
	# only after clock is LOW then HIGH, is data bit considered active
        if clock[n] == 1 and clock[n-1] == 0:
            if len(bit_counter) == 18:
                val = int(bit_counter[9:-1], 2)
                bin_array.append(val)
                bit_counter = ''
            else:
                bit_counter += str(data[n])
        n += 1
    return bin_array


# we now place them in 4 byte chunks since the middle two writes (numbers) are the 
# RS and EN pins, and they aren't set; 
# So the actual writes we want are the first and last byte of the 4 byte chunk.
def seperate_into_4byte_chunks(bin_array):
    chunk_array = []
    n = 0
    for _ in range(int(len(bin_array) / 4)):
        chunk_array.append(bin_array[n:n+4])
        n += 4
    return chunk_array


# Taking only the four data pins, that gives us two nibbles of data. 
# The first byte gets shifted left four bits and then the second byte gets added to it. 
# ((X >> 4) << 4) | (Y >> 4) = Z.
def decode_chunks(chunk_array):
    n = 0
    for arr in chunk_array:
        for _ in range(len(arr)):
            decoded_byte = ((arr[n] >> 4) << 4) | (arr[n+3] >> 4)
        if(decoded_byte < 127):
            print(chr(decoded_byte), end='')
            # password gets printed after every '*' character

						
def main():
    df = pd.read_csv("i2c_data_bin.csv")
    print(df.columns)

    data = df[' Channel 0']
    clock = df[' Channel 1']

    packets = append_i2c_packets(data, clock)
    chunk_array = seperate_into_4byte_chunks(packets)
    decode_chunks(chunk_array)


if __name__ == '__main__':
    main()