setec@astronomy:~$ file mysterious_binary
mysterious_binary: ELF 64-bit LSB executable, stripped
setec@astronomy:~$ strings mysterious_binary | head -5
UPX!
$Info: This file is packed with the UPX executable packer $

When faced with a black box—whether it’s a binary, an API, or a complex system—most people see an impenetrable wall. A reverse engineer sees a puzzle begging to be solved.

The Three Pillars of Reverse Engineering

1. Systematic Observation

Before touching anything, watch. Systems tell you their secrets if you know how to listen.

# What's it doing?
strace -e trace=network ./mysterious_binary

# Who's it talking to?
netstat -tupln | grep LISTEN

# What files is it touching?
lsof -p $(pgrep mysterious_binary)

Every system call, every network connection, every file access is a breadcrumb leading back to understanding.

2. Methodical Experimentation

Once you understand the baseline behavior, start poking:

def probe_api_endpoint(base_url, endpoint):
    """Systematic API exploration"""
    for method in ['GET', 'POST', 'PUT', 'DELETE', 'PATCH', 'HEAD', 'OPTIONS']:
        response = requests.request(method, f"{base_url}{endpoint}")
        print(f"{method} {endpoint}: {response.status_code}")

        if response.status_code == 405:
            continue  # Method not allowed
        if response.headers.get('content-type', '').startswith('application/json'):
            print(f"  Response: {response.json()}")

Small inputs, controlled changes, documented results. Build your understanding iteratively.

3. Pattern Recognition

The more systems you reverse, the more patterns emerge. Authentication schemes, encoding methods, protocol structures—they all follow predictable patterns.

A Real Example: Cracking a “Secure” API

I recently encountered an API that claimed to use “military-grade encryption.” Red flag #1: marketing speak in technical docs.

Initial Reconnaissance

setec@astronomy:~$ curl -v https://api.example.com/secure-data
< HTTP/1.1 401 Unauthorized
< WWW-Authenticate: Custom realm="secure-api"
< X-Encryption-Method: AES-256-CUSTOM

Interesting. Custom authentication and a custom encryption method. Let’s dig deeper.

Traffic Analysis

# Capture traffic during a "secure" login
tcpdump -i any -w login_capture.pcap host api.example.com

# Analyze the captured packets
tshark -r login_capture.pcap -Y "http" -V

What we found:

  • Authentication token passed in plain text header
  • “Encrypted” payload was just Base64-encoded JSON
  • The “custom AES” was actually just XOR with a static key

The Revelation

import base64

def decrypt_custom(encrypted_data):
    """Their 'military-grade' encryption"""
    decoded = base64.b64decode(encrypted_data)
    key = b"SUPER_SECRET_KEY_123"  # Found in JS bundle

    result = bytearray()
    for i, byte in enumerate(decoded):
        result.append(byte ^ key[i % len(key)])

    return result.decode('utf-8')

# Test it
encrypted = "SGVsbG8gV29ybGQh"  # From API response
print(decrypt_custom(encrypted))
# Output: {"user_data": "confidential_info"}

The “secure” API was using XOR with a hardcoded key found in their client-side JavaScript. This is why we don’t trust marketing claims about security.

Tools of the Trade

Static Analysis

# Binary analysis
objdump -d binary_file
readelf -a binary_file
xxd binary_file | less

# Web application
curl -s https://site.com | grep -o 'src="[^"]*\.js"' | wget -i -
grep -r "api" downloaded_js_files/

Dynamic Analysis

# System-level monitoring
strace -f -e trace=all program
ltrace program
tcpdump -A -i any port 80 or port 443

# Application-level
gdb program
python -m pdb script.py

Specialized Tools

# Web security
burpsuite
owasp-zap

# Binary analysis
ghidra
radare2
ida-free

# Network analysis
wireshark
nmap

The Ethics of Curiosity

Reverse engineering walks a fine line. The same techniques used to understand and improve systems can be used maliciously. Some guidelines:

  1. Respect boundaries: Don’t access systems you don’t own or have permission to test
  2. Responsible disclosure: If you find vulnerabilities, report them properly
  3. Educational intent: Focus on learning and improving security, not exploitation
  4. Document everything: Your research should be reproducible and beneficial to others

Building the Mindset

The best reverse engineers aren’t necessarily the most technical—they’re the most curious. They question assumptions, probe boundaries, and refuse to accept “because it works” as an answer.

Exercise: Daily Practice

Pick one system you interact with daily and spend 15 minutes trying to understand it better:

# Your shell
echo $SHELL
man bash | head -50

# Your network
ip route show
dig +trace google.com

# Your browser
about:config  # (Firefox)
chrome://settings/  # (Chrome)

Every day, choose something different. Over time, you’ll build an intuitive understanding of how systems connect and interact.

The Bigger Picture

In Sneakers, the protagonists discover that controlling information means controlling power. In our field, understanding systems means understanding their limitations, their security boundaries, and their potential for improvement.

Every closed system is an opportunity to learn. Every “secure” black box is a challenge to understand and verify.

setec@astronomy:~$ echo "Trust, but verify"
Trust, but verify
setec@astronomy:~$ echo "Question everything"
Question everything
setec@astronomy:~$ echo "No more secrets"
No more secrets

The next time you encounter a system that seems mysterious or impenetrable, remember: someone built it, which means someone can understand it. That someone might as well be you.

Tools and techniques mentioned in this post are for educational and security research purposes. Always ensure you have proper authorization before testing systems you don’t own.