I am planning to organize a sort of treasure hunt and I would like to know some easy ways to encrypt a message. I'd say something in between Ceasar's Cipher -shift each letter of a word of a fixed position- and Vigenere's Cipher, which I suppose is too difficult for an average person who has no knowledge of Cryptography. Can you suggest me some easy ways (easy for a person who has no specific knowledge) to encrypt sentences or words? I need two different methods as long as I have three riddles to be solved and for one of them I'll use Ceasar's. Any help will be appreciated! Thank you very much!
Here are some examples of simple ciphers you could use:
- Base64 - a very common encoding (i.e Y2lwaGVy => cipher)
- Caesar Cipher, or, you can specifically use ROT13
- Morse Code (i.e .... . .-.. .-.. --- => Hello)
- Hexadecimal (i.e 8 5 12 12 15 => Hello)
- Braille (⠉⠊⠏⠓⠑⠗ => cipher)
- A1Z26 - each letter is represented by its order number
- Atbash cipher - where a=z, b=y etc.
- xor with a keyword (iczbox ^ a => cipher)
- Binary code (i.e 01100011 01101001 01110000 01101000 01100101 01110010 => cipher)
- Use the periodic table to encode a message (i.e 6 53 15 1 68 => CIPHER)
- Ascii numbers (i.e 072 101 108 108 111 => Hello)
- Vigenere Cipher with a keyword
To add to pirate's answer -
A mirror cipher may be simple enough - you know, where the ciphered text would read:
:daer dluow txet derehpic eht erehw ,wonk uoy - hguone elpmis eb yam rehpic rorrim A
Or perhaps an ascii cipher, where you spell out words with letters... of course, you run the risk of someone misreading what you write, but that's up to you to make sure your message is clear.
Per Caesar ciphers, I always thought it might be a clever clue to give the name of a Caesar alongside the encrypted text - so that the nth number to shift in the cipher would be given by the nth Caesar.
You could also use a substitution, so that every letter gets replaced by another letter but not all with the same distance (like Caesar’s rotation).
It works like this: you choose a key (word or sentence), remove all duplicate letters and add the letters of the alphabet that weren’t used. Then put the regular alphabet above it. Every letter of your message then gets replaced by the letter of the alphabet you just constructed.
Key: some nice little message
Message: you found it
abcdefghijklmnopqrstuvwxyz |||||||||||||||||||||||||| vvvvvvvvvvvvvvvvvvvvvvvvvv somenicltagbdfhjkpqruvwxyz
Encrypted message: yhu ihufe tr
These are all really great suggestions. My personal favourite hand cipher is the Playfair cipher. It's part of a larger group of ciphers known as "polygrams". Essentially how they work is by encoding a set of letters at a time in a specific fashion (usually involcing making something called a polybius square which is a 5 x 5 textbox containing the alphabet).
There's really good directions here that'll better visualize it for you because I suck at explaining things.
One thing to note in decoding Playfair ciphers is that you're most likely want to give the key to solving it.
Yes, it is possible to solve it without a key in a method called cribbing, but that's kind of tedious and takes a lot of time if you're new at it.
There's some other variations of Playfair ciphers, my other favourite being the foursquare variant.
Playfair ciphers are more challenging in general than the mono/poly-alphabetic cipher, since they don't follow traditional frequent letter analysis techniques.
Polyalphabetic ciphers are nice alternative as well, since it's possible to break without a key but takes less time than polygram ciphers.
Monoalphabetic is only used for encoding really simple texts, and in Puzzling SE, rot13 is commonly used when you don't want to spoil something in the comments. However, I would advise against using a Caeser cipher, since those can be broken really quickly, especially because of the software.
If you want, you can try using a plain old keyword substitution cipher, except not reveal the cipher, so people actually have to solve it by hand.
Hope this helped!
After checking the other answers, looks like pigpen wasn't mentioned yet, it's quite popular on this site at least.