Chomper

Chomper is a lightweight emulation framework based on Unicorn. It is mainly used to emulate native programs on Android and iOS.

Features

• Basic emulation of ELF and Mach-O
• Support for a set of iOS system libraries (from iOS SDK 14.4.0)

Requirements

• Python 3.8+
• Unicorn 2.0.0+

Installation

$ pip install chomper

Usage

Emulate iOS executable files.

import uuid

from chomper import Chomper
from chomper.const import ARCH_ARM64, OS_IOS

# The system libraries will be automatically loaded from `rootfs_path` on iOS
emu = Chomper(
    arch=ARCH_ARM64,
    os_type=OS_IOS,
    rootfs_path="examples/ios/rootfs",
)

# Load main program
duapp = emu.load_module("examples/ios/apps/com.siwuai.duapp/DUApp")

s = "chomper"

# Construct arguments
a1 = emu.create_string("objc")
a2 = emu.create_string(s)
a3 = len(s)
a4 = emu.create_string(str(uuid.uuid4()))
a5 = emu.create_buffer(8)
a6 = emu.create_buffer(8)
a7 = emu.create_string("com.siwuai.duapp")

# Call function
emu.call_address(duapp.base + 0x109322118, a1, a2, a3, a4, a5, a6, a7)
result = emu.read_string(emu.read_pointer(a5))

Working with Objective-C.

from chomper import Chomper
from chomper.const import ARCH_ARM64, OS_IOS
from chomper.objc import ObjC

emu = Chomper(
    arch=ARCH_ARM64,
    os_type=OS_IOS,
    rootfs_path="examples/ios/rootfs",
)

objc = ObjC(emu)

emu.load_module("examples/ios/apps/cn.com.scal.sichuanair/zsch")

# Construct NSString object
a1 = objc.msg_send("NSString", "stringWithUTF8String:", "test")

# Call ObjC method
req_sign = objc.msg_send("ZSCHRSA", "getReqSign:", a1)

# Convert NSString object to C string
result_ptr = objc.msg_send(req_sign, "cStringUsingEncoding:", 4)
result = emu.read_string(result_ptr)

Emulate Android native libraries.

from chomper import Chomper
from chomper.const import ARCH_ARM64, OS_ANDROID

emu = Chomper(arch=ARCH_ARM64, os_type=OS_ANDROID)

# Load C standard and other libraries
emu.load_module("examples/android/rootfs/system/lib64/libc.so")
emu.load_module("examples/android/rootfs/system/lib64/libz.so")

libszstone = emu.load_module(
    "examples/apps/android/com.shizhuang.duapp/libszstone.so",
    exec_init_array=True,
)

s = "chomper"

a1 = emu.create_string(s)
a2 = len(s)
a3 = emu.create_buffer(1024)

result_size = emu.call_address(libszstone.base + 0x2F1C8, a1, a2, a3)
result = emu.read_bytes(a3, result_size)

Hook instructions.

def hook_code(uc, address, size, user_data):
    pass

symbol = emu.find_symbol("strlen")
emu.add_hook(symbol.address, hook_code)

Trace instructions.

# Trace all instructions
emu = Chomper(arch=ARCH_ARM64, os_type=OS_ANDROID, trace_instr=True)

# Trace instructions in this module
emu.load_module("examples/android/rootfs/system/lib64/libc.so", trace_inst=True)

Examples

Here are a fews examples of encryption emulations for security vendors.