In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption. There are variations of ciphers from classical simple cyphers (e.g., ceasar) to very complex modern cyphers (ie, Private Key, Public Key). In a CTF, individuals need to identify the cipher type then use tools and techniques to attempt to decode the messages.   This page will focus on simple ciphers. See the links below for Steganogrphy and Modern Ciphers.

Cipher Categories (High Level):

Substitution Ciphers:

Transposition Cipher

Modern Cryptography

Public / Private key: (see link)


Images and Audio: (see link)


  1. PicoCTF Learning Guide: Cryptography: How to Protect Your Data (17 pages)
  2. Va Cyber Range: Solving CTF Challenges: Cryptography (1:09:06)
  3. Va Cyber Range: Modern Cryptography (59:11)
  4. youtube: Asymmetric encryption – Simply explained (4:40)