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https://github.com/pfalcon/scratchabit

Easily retargetable and hackable interactive disassembler with IDAPython-compatible plugin API
https://github.com/pfalcon/scratchabit

disassembler ida ida-plugin idapython reverse-engineering

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Easily retargetable and hackable interactive disassembler with IDAPython-compatible plugin API

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README 

        
ScratchABit

===========



ScratchABit is an interactive incremental disassembler with data/control

flow analysis capabilities. ScratchABit is dedicated to the efforts of

the OpenSource reverse engineering community (reverse engineering to

produce OpenSource drivers/firmware for hardware not properly supported

by vendors, for hardware and software interoperability, for security

research).



ScratchABit supports well-known in the community IDAPython API to write

disassembly/extension modules.



ScratchABit is a work in progress, features are added on as needed basis,

contributions are welcome.



ScratchABit is released under the terms of GNU General Public License v3

(GPLv3).



Requirements/manifesto

----------------------



1. Should not be written in an obfuscated language. These include languages

which are too low-level, which allow to access non-initialized variables,

which don't differentiate between variables and functions/procedures, which

start array indexes from arbitrary numbers, etc., etc. ScratchABit is

written in Python (modern version, Python3) for your pleasure and sanity.



2. User interface framework should allow user interaction of the needed

level, not add dependencies, bloat, issues, and incompatibilities between

framework's versions. ScratchABit currently uses simple full-screen text

user interface, using ANSI/VT100 terminal escape sequences (yes, even

curses library was deemed too bloat a dependency to force upon users).



3. Should leverage easy to use text formats to store "database", to

facilitate easy reuse and tool writing, and storage in version control

systems.



Installation

------------



To use ScratchABit, you need [Python3](https://www.python.org/) installed

(tested with Python 3.3 thru 3.7) and VT100 (minimum) or XTerm (recommended)

terminal or terminal emulator (any Unix system should be compliant, like

Linux/BSD/etc., see FAQ below for more).



Clone the code using:



    git clone --recursive https://github.com/pfalcon/ScratchABit



If you cloned code without `--recursive`, run `git submodule update --init`

in the ScratchABit directory.



ScratchABit now ships with [Capstone Engine](http://www.capstone-engine.org/)

based CPU plugin(s), which allow access to a number of CPU architectures.

To use it, recent Python bindings module for Capstone should be installed

(in the preference to packages shipped by OS distributions, which are often

outdated). The easiest way to install it is into the Python user packages

directory:



    pip3 install --no-cache-dir --user capstone



An alternative is to install it to a Python

[virtual environment](https://docs.python.org/3/library/venv.html) within

the ScratchABit directory:



    python3 -m venv .venv

    source .venv/bin/activate

    pip3 install --no-cache-dir capstone



Whenever you open a new terminal session to work with ScratchABit,

run `source .venv/bin/activate` command again to activate the virtual

environment.



If nothing of the above works, you can try to install the capstone

package system-wide (not recommended):



    sudo pip3 install --system capstone



Quick start

-----------



If you want to disassemble a file in self-describing executable format

(like ELF), just pass it as an argument to `ScratchABit.py`. The repository

includes a number of `example-*.elf` files for various architectures for

a quick start. For example, to try x86 32bit version:



    python3 ScratchABit.py example-x86_32.elf



Alternatively, if you want to disassemble a raw binary file, you need

to create a .def (definition) file, to specify what memory areas are

defined for the code, at which address to load binary file, etc. (Note:

a .def file may be useful for .elf and similar files too.) The repository

includes a simple x86_64 raw binary code, and the corresponding

[example-x86_64.def](example-x86_64.def) file (look inside for

description of available options):



    python3 ScratchABit.py example-x86_64.def



Press F9 to access menus (mouse works too in XTerm-compatible terminals).

Press F1 to get help about key bindings (most actions are also accessible

via menu). The workflow of ScratchABit is similar to other interactive

dissamblers (some previous experience or background reading may be helpful).



Using Plugins

-------------



IDAPython processor plugins can be loaded from anywhere on the Python

module path. Alternatively, you can symlink/copy the plugin `.py` file(s)

into the [`plugins/cpu/`](plugins/cpu/) subdirectory.



After the plugin is made available, create a new definition file based

on [`example-x86_64.def`](example-x86_64.def#L4) that sets the plugin module

name (without `.py` extenstion) in the `cpu xxx` line.



For a very simple example that uses an external plugin, see this

[esp8266.def file](https://gist.github.com/projectgus/f898d5798e3e44240796)

that works with the xtensa.py plugin from the

[ida-xtensa2 repository](https://github.com/pfalcon/ida-xtensa2).



TODO/Things to decide

---------------------



* ~~Currently uses multiple files for "database", each storing particular

  type of information. Switch to a single YAML file instead?~~

* ~~Add color (low priority, (unbloated!) patches welcome).~~

* ~~Few important UI commands to implement yet for comfortable work.~~ (

  All the most important commands should be there, other functionality is

  expected to be implemented using plugins).

* ~~Offer to save DB on quit if modified.~~

* Git integration for DB saving.

* ~~Improve robustness (add exception handler at the main loop level, don't

  abort the application, show to user/log and continue).~~

* Try to deal with code flow inconsistencies (e.g. within an instruction -

  low priority for intended usage) and data access inconsistencies (e.g.

  accessing individual bytes of previosly detected word - higher priority).

  (Improved in 1.4.)

* See how to support other types of IDAPython plugins besides just processor

  modules.

* Parse and use debugging information (e.g. DWARF) present in ELF (etc.)

  files.



FAQ

---



> Q: What processors/architectures are supported?



A: ScratchABit doesn't support any processor architectures on its own,

it is fully retargettable using IDAPython API plugins. Many plugins are

available, writing a new plugin is easy. To let users test-drive

ScratchABit, a simple x86 processor plugin is included in the

distribution, using [Pymsasid](https://github.com/pfalcon/pymsasid3)

disassembler under the hood.



From version 2.0, [Capstone](http://www.capstone-engine.org/) plugin

is also included, allowing access to a number of architectures,

including x86, ARM, MIPS, PowerPC, SPARC, etc. (architecture support

is enabled gradually based on user testing).



You can read about the plugins shipped together with ScratchABit in

the [README for `plugins/cpu/` dir](plugins/cpu/).



> Q: Debugger?



A: ScratchABit is dedicated to static analysis and easy support for

new CPU architectures (just code up an new CPU plugin in Python - you

can get initial results in few hours). Dynamic analysis wasn't conceived

to be a core feature and there're no immediate plans to implement it.

Patches are welcome though.



> Q: Decompiler?



A: There is a related project, called

[ScratchABlock](https://github.com/pfalcon/ScratchABlock) for deep

program analysis, transformation and decompilation. It's expected

that as ScratchABlock matures, some of its functionality will be

available within ScratchABit (perhaps via plugins).



> Q: I'm not on Linux, how can I run ScratchABit?



A: Install Linux in an emulator/VM on your system and rejoice.



> Q: Mandatory screenshot?



A: Sure:



![screenshot](https://raw.githubusercontent.com/pfalcon/ScratchABit/master/docs/scratchabit.png)