Why no DSP for LML?

[GMPX]

As most people in the Diesel tuning industry know, EFILive offers on the fly switchable tuning for many different ECM types from 2001 to current models, but the one we get asked a lot about is the E86A and E86B LML ECM, so I've decided to make this a sticky thread so anyone can find the truth behind it and why we can't offer DSP5 for these ECM's.

For any switchable tuning to work EFILive needs to modify the original Operating code of the ECM to perform the switching functionality, on the E86A & E86B (aka Bosch EDC17) the operating system code is protected with a Digital Signature. The correct digital signature for the OS data can only be generated by Bosch as they hold the private keys.

Although the OS data in the ECM is not encrypted (yet) the contents are signed to produce a unique 'digest' that is validated when the ECM is flashed via the OBD-II port.
Like the image below shows, the 'Input' is some text, the 'Hash function' alters the text to create a unique 'Digest'.

Picture from : https://en.wikipedia.org/wiki/Public-key_cryptography


When flashing the ECM after the OS section(s) have completed the ECM will verify the data written generates the correct Digest that Bosch would have created for that section of code. And that right there is where we hit a wall, we cannot generate the correct numbers so the ECM will accept the modified data as valid, instead it knows the data is modified and will not complete the flash process.
If you look at the image above you can see that it is impossible to take the data in the pink boxes and generate the text in Blue when we have no idea how Bosch created the Hash function (I believe they use a 1024 bit Key), but that is what we would need to be able to do for the ECM to accept any modifications to the OS code.

Sadly there is no way to switch off this security check using any tricks via the OBD-II port, but this is the only reason we've never pursued DSP5 for the LML engine. Sometimes you just can't beat technology and for what it is worth there is no way to brute force figure the digests out either.

Cheers,
Ross