CTF TOPIC · 9 FLAGS · 18 MIN

Encodings and bytes

Base64, base32, hex, binary, decimal, octal, URL encoding and layered encodings.

Encodings change how data is written without hiding it: anyone can reverse them, no key required. Learn to recognise each one by its alphabet. Hex uses 0-9 and a-f; base64 uses letters, digits, + and / with = padding; base32 uses A-Z and 2-7; binary is 0s and 1s in groups of eight; decimal and octal are numbers per byte. Many challenges stack several layers, so decode one at a time and look again.

A first example

base64('flag') = ZmxhZw== ; hex('fl') = 66 6c ; binary('f') = 01100110.

First moves

1. Search for flag{ in case it is already plain
2. Identify the alphabet using the signal table
3. Decode one layer and look again
4. Count layers in your notes so you never lose your place

The challenges

• A different alphabet · Easy · 20 XP
• Two digits at a time · Easy · 20 XP
• Peel the layers · Medium · 30 XP
• Ones and zeros · Easy · 20 XP
• Numbers that spell · Easy · 20 XP
• Percent signs · Easy · 20 XP
• Shouting alphabet · Medium · 30 XP
• Base eight · Medium · 30 XP
• Onion of encodings · Medium · 30 XP