Siemens EEPROM Decoder

This is a tool used to encrypt and decrypt EEPROM dumps from early 90's Siemens ECUs. Tested and developed on SIMK41/43 but certainly applies to a lot more ECUs from that era. If you test it out on a ECU different than SIMK41/43 - let me know, I'll update the readme.

Usage

Decryption:

python3 decrypt.py d <filename>

Output will be saved to _decrypted.bin

Encryption:

python3 decrypt.py e <filename>

Output will be saved to _encrypted.SIE

How does it work?

In SIMK41/43's case, EEPROM data lines are crossed. Due to this, in every pair of bytes, bits are switched as so:

0  -  3
1  -  11
2  -  2
3  -  10
4  -  1
5  -  9
6  -  0
7  -  8
8  -  12
9  -  4
10  -  13
11  -  5
12  -  14
13  -  6
14  -  15
15  -  7

In hardware variant 5WY19, there's a NXP 74HCT574D chip on the PCB responsible for unscrambling the data.

For more information about SIMK41/SIMK43 ECUs, visit https://opengk.org