The Caesar Cipher is a very simple and common encryption method which does not appear often in full-fledged CTFs but forms part of the basis of cryptography. It simply shifts a string of letters a certain number of positions up or down the alphabet.
Let's say we want to encrypt the string
hello world to give to our friend whose favorite number is 3. We will shift our string left 3.
Taking the first letter
h in our string and going 3 places up the alphabet(as it is a left shift) gives us the letter
e. We then start our new, encrypted string with the letter.
Doing so for the whole original string creates a jumbled mess of incomprehensible letters to anyone but the reader with the proper decryption shift:
To let our friend read this, we would send him the final string with the instructions right 3, and either by hand, with a website, or with a script, he would be able to extract our message.
Caesar ciphers are usually presented in very low-point tasks, if at all, and can be easy to detect and check for. Strings containing incomprehensibly jumbled letters are possible Caesar ciphers and should be checked.
There are many approaches to cracking Caesar ciphers, but usually the best way to solve them is to write a script or run the string through a website which will print out all the possible shifts of a string. From those results the most comprehensible and logical solution can be chosen.