basilfx / lpc_checksum

Python script to calculate LPC firmware checksums.

lpc_checksum

Python script to calculate LPC firmware checksums, based on the C version by Roel Verdult. It can be used as a standalone application, or as a Python module that integrates directly in a build environment (e.g. SCons). It does not need to be compiled.

Requirements

The only requirement is Python 3.9 or newer.

Installation

This module can be installed from Pypi via pip install lpc_checksum.

Alternatively, you can install the latest version by cloning this repository and run python setup.py install.

Usage

There are two ways of using lpc_checksum.

Standalone

When installed via Pip or from source, the command lpc_checksum should be available on your PATH. By default, it assumes the input file is a binary file.

lpc_checksum <firmware.bin|hex> [--format=bin] [--read-only]

Program exits with a non-zero error code when it failed.

As a module

import lpc_checksum

checksum = lpc_checksum.checksum(input_file, [read_only=True])

On error, an exception will be raised.

Tests

To run the tests, please clone this repository and run poetry run pytest.

Contributing

See the CONTRIBUTING.md file.

License

See the LICENSE.md file (MIT license).

lpc_checksum's Issues

Can't run lpc_checksum

sudo pip install lpc_checksum
lpc_checksum mybinary.bin
-> Error: ord() expected string of length 1, but int found

Running on Python 3.7

Tool computes incorrect checksum on internal 32-bit overflow

In your script you attempt to do a 32-bit unsigned add in python.

lpc_checksum/lpc_checksum.py

Line 88 in 14ff53e

result = (result + value) % 0xFFFFFFFF

However, when an overflow occurrs, meaning the result is larger than 32 bits, the upper bits are discarded by the CPU and only the lower 32 bits are retained. Thus it's wrong to do modulo, there should be an AND. For reference, see https://stackoverflow.com/a/210747/5296568

Example: The original program and your script compute different values for this firmware.bin.

gcc -o lpcrc lpcrc.c && lpcrc.exe firmware.bin && python lpcrc.py firmware.bin
-- lpcrc.exe --
succesfully updated crc to: 02b6aa66
-- lpcrc.py --
Firmware path: firmware.bin
Wrote checksum 0x2b6aa63 into binary.

When patching it with the python script, openocd complains

** Programming Started **
Warn : Verification will fail since checksum in image (0x02b6aa63) to be written to flash is different from calculated vector checksum (0x02b6aa66).
Warn : To remove this warning modify build tools on developer PC to inject correct LPC vector checksum.
** Programming Finished **
** Verify Started **
Error: checksum mismatch - attempting binary compare
embedded:startup.tcl:449: Error: ** Verify Failed **

The script returns the same checksum as the C program after applying the patch above for & instead of %.