ctf

name	CTF•逆向工程
description	用于二进制、APK、WASM、固件、自定义虚拟机、字节码、游戏客户端、类恶意加载器以及反调试/反分析逻辑等逆向类 CTF 题;触发名:ctf-reverse
license	MIT
compatibility	Requires filesystem-based agent (Claude Code or similar) with bash, Python 3, and internet access for tool installation.
allowed-tools	Bash Read Write Edit Glob Grep Task WebFetch WebSearch
metadata	{"user-invocable":"false"}

CTF Reverse Engineering

Quick reference for RE challenges. For detailed techniques, see supporting files.

Prerequisites

Python packages (all platforms):

pip install frida-tools angr qiling uncompyle6 capstone lief z3-solver
# For Python 3.9+ bytecode: build pycdc from source
git clone https://github.com/zrax/pycdc && cd pycdc && cmake . && make

Linux (apt):

apt install gdb radare2 binutils strace ltrace apktool upx

macOS (Homebrew):

brew install gdb radare2 binutils apktool upx ghidra

radare2 plugins:

r2pm -ci r2ghidra   # Native Ghidra decompiler for radare2

Manual install:

• pwndbg — Linux: GitHub, macOS: brew install pwndbg/tap/pwndbg-gdb

Additional Resources

• tools.md - Static analysis tools (GDB, Ghidra, radare2, IDA, Binary Ninja, dogbolt.org, RISC-V with Capstone, Unicorn emulation, Python bytecode, WASM, Android APK, .NET, packed binaries)
• tools-dynamic.md - Dynamic analysis tools: Frida (hooking, anti-debug bypass, memory scanning, Android/iOS), angr symbolic execution (path exploration, constraints, CFG), lldb (macOS/LLVM debugger), x64dbg (Windows)
• tools-emulation.md - Emulation frameworks and side-channel tooling: Qiling (cross-platform OS-level emulation), Triton (DSE), Intel Pin instruction-counting + genetic algorithm side channel, opcode-only trace reconstruction, LD_PRELOAD time freeze and memcmp side-channel for byte-by-byte bruteforce
• tools-advanced.md - Advanced tools (Part 1): VMProtect/Themida analysis, binary diffing (BinDiff, Diaphora), deobfuscation frameworks (D-810, GOOMBA, Miasm), Qiling framework, Triton DSE, Manticore, Rizin/Cutter, RetDec, custom VM bytecode lifting to LLVM IR
• tools-advanced-2.md - Advanced tools (Part 2): advanced GDB (Python scripting, brute-force, conditional breakpoints, watchpoints, reverse debugging with rr, pwndbg/GEF), advanced Ghidra scripting, patching (Binary Ninja API, LIEF), GDB constraint extraction + ILP solver (BackdoorCTF 2017), GDB position-encoded input zero flag monitoring (EKOPARTY 2017), LD_PRELOAD execute-only binary dump (BackdoorCTF 2017), PEDA current_inst bit-by-bit flag scraper (CONFidence CTF 2019 Teaser)
• anti-analysis.md - Anti-analysis taxonomy: Linux anti-debug (ptrace, /proc, timing, signals, direct syscalls), Windows anti-debug (PEB, NtQueryInformationProcess, heap flags, TLS callbacks, HW/SW breakpoint detection, exception-based, thread hiding), anti-VM/sandbox (CPUID, MAC, timing, artifacts, resources), anti-DBI (Frida detection/bypass), code integrity/self-hashing, anti-disassembly (opaque predicates, junk bytes), MBA identification/simplification, comprehensive bypass strategies
• anti-analysis-ctf.md - CTF writeup techniques: SIGILL handler for execution mode switching (Hack.lu 2015), SIGFPE signal handler side-channel via strace counting (PlaidCTF 2017), instruction trace inversion with Keystone and Unicorn (MeePwn 2017), call-less function chaining via stack frame manipulation (THC 2018), parent-patched child binary dump via process_vm_writev (Google CTF Quals 2018)

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When to Pivot

• If you already understand the binary and now need heap, ROP, or kernel exploitation, switch to /ctf-pwn.
• If the challenge is really about recovering deleted files, PCAP data, or disk artifacts, switch to /ctf-forensics.
• If the target is a web app and you are only reversing a small client-side helper script, switch to /ctf-web.
• If the binary implements a machine learning model and the challenge is about model attacks or adversarial inputs, switch to /ctf-ai-ml.
• If the reversed binary's core logic is a cryptographic algorithm or math problem, switch to /ctf-crypto.
• If the binary is a real malware sample with C2, packing, or evasion behavior, switch to /ctf-malware.
• If the challenge is a toy VM, encoding puzzle, or pyjail rather than a real binary, switch to /ctf-misc.

Problem-Solving Workflow

1. Start with strings extraction - many easy challenges have plaintext flags
2. Try ltrace/strace - dynamic analysis often reveals flags without reversing
3. Try Frida hooking - hook strcmp/memcmp to capture expected values without reversing
4. Try angr - symbolic execution solves many flag-checkers automatically
5. Try Qiling - emulate foreign-arch binaries or bypass heavy anti-debug without artifacts
6. Map control flow before modifying execution
7. Automate manual processes via scripting (r2pipe, Frida, angr, Python)
8. Validate assumptions by comparing decompiler outputs (dogbolt.org for side-by-side)

Quick Wins (Try First!)

# Plaintext flag extraction
strings binary | grep -E "flag\{|CTF\{|pico"
strings binary | grep -iE "flag|secret|password"
rabin2 -z binary | grep -i "flag"

# Dynamic analysis - often captures flag directly
ltrace ./binary
strace -f -s 500 ./binary

# Hex dump search
xxd binary | grep -i flag

# Run with test inputs
./binary AAAA
echo "test" | ./binary

Initial Analysis

file binary           # Type, architecture
checksec --file=binary # Security features (for pwn)
chmod +x binary       # Make executable

Memory Dumping Strategy

Key insight: Let the program compute the answer, then dump it. Break at final comparison (b *main+OFFSET), enter any input of correct length, then x/s $rsi to dump computed flag.

Decoy Flag Detection

Pattern: Multiple fake targets before real check. Look for multiple comparison targets in sequence with different success messages. Set breakpoint at FINAL comparison, not earlier ones.

GDB PIE Debugging

PIE binaries randomize base address. Use relative breakpoints:

gdb ./binary
start                    # Forces PIE base resolution
b *main+0xca            # Relative to main
run

Comparison Direction (Critical!)

Two patterns: (1) transform(flag) == stored_target — reverse the transform. (2) transform(stored_target) == flag — flag IS the transformed data, just apply transform to stored target.

Common Encryption Patterns

• XOR with single byte - try all 256 values
• XOR with known plaintext (flag{, CTF{)
• RC4 with hardcoded key
• Custom permutation + XOR
• XOR with position index (^ i or ^ (i & 0xff)) layered with a repeating key

Quick Tool Reference

# Radare2
r2 -d ./binary     # Debug mode
aaa                # Analyze
afl                # List functions
pdf @ main         # Disassemble main

# Ghidra (headless)
analyzeHeadless project/ tmp -import binary -postScript script.py

# IDA
ida64 binary       # Open in IDA64

Deep-Dive Notes

Use field-notes.md after the first round of triage when you know what kind of target you have.

• Target formats: Python bytecode, WASM, Android, Flutter, .NET, UPX, Tauri
• Technique notes: anti-debug bypass, VM analysis, x86-64 gotchas, iterative solvers, Unicorn, timing side channels
• Platform notes: Godot, Roblox, macOS/iOS, embedded firmware, kernel drivers, game engines, Swift, Kotlin, Go, Rust, D
• Case notes: modern CTF-specific reversing patterns and older classic challenge patterns