encoding-toolkit

What this skill does

Automatically detects the encoding format of an input string and performs encode/decode conversions across Base64, URL encoding, Hex, HTML entities, ROT13, and JWT formats. Uses only standard tools: base64, python3, and xxd.

When to use

• Analyzing encoded strings found in web requests or responses
• Stripping multiple encoding layers in CTF challenges
• Inspecting JWT token headers and payloads
• Converting payloads into various formats for WAF bypass testing

Prerequisites

• python3 (uses standard library, no extra installation needed)
• base64 command (built into Linux/macOS)
• xxd command (built into Linux/macOS)

Inputs

Variable	Description	Example
INPUT	Input string to convert	SGVsbG8gV29ybGQ=
MODE	Operation to perform (see list below)	base64-decode

Workflow

Step 1: Auto-detect encoding

INPUT="SGVsbG8gV29ybGQ="

echo "=== Auto-detect encoding ==="
python3 - <<PYEOF
import re, base64, urllib.parse, sys

data = """${INPUT}"""

results = []

# Base64 detection
if re.fullmatch(r'[A-Za-z0-9+/]*={0,2}', data) and len(data) % 4 == 0 and len(data) > 0:
    try:
        decoded = base64.b64decode(data).decode('utf-8', errors='replace')
        results.append(f"[Base64 possible] decoded: {decoded[:80]}")
    except Exception:
        pass

# URL encoding detection
if '%' in data:
    try:
        decoded = urllib.parse.unquote(data)
        results.append(f"[URL encoding possible] decoded: {decoded[:80]}")
    except Exception:
        pass

# Hex detection
if re.fullmatch(r'[0-9a-fA-F]+', data) and len(data) % 2 == 0:
    try:
        decoded = bytes.fromhex(data).decode('utf-8', errors='replace')
        results.append(f"[Hex possible] decoded: {decoded[:80]}")
    except Exception:
        pass

# HTML entity detection
if '&' in data and ';' in data:
    import html
    decoded = html.unescape(data)
    results.append(f"[HTML entity possible] decoded: {decoded[:80]}")

# JWT detection
if data.count('.') == 2 and re.match(r'^[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+$', data):
    results.append("[JWT possible] 3-part dot structure detected -> use Step 4 JWT decode")

if results:
    for r in results:
        print(r)
else:
    print("Auto-detection failed -> specify MODE manually for conversion")
PYEOF