10 Simple Ciphers You Should Know

Throughout history, ciphers have been used to hide a secret from prying eyes. It has been a game between code makers and code breakers. Today I will be highlighting simple encryption algorithms and history’s most famous codes.

Most of these simple ciphers were invented long before the first computers. They are based on substitution and transposition of single plaintext characters.

These simple ciphers or classical ciphers have been used in the past world wars by armies to secure their top-level communications.

However, these algorithms are not secure enough for protecting information by today’s standards but there is no harm knowing how to encode and decode simple messages among your friends.

For sensitive information, I would recommend using proven modern algorithms that offer better security when sharing sensitive information.

Simple Ciphers

Sharing simple encrypted messages between your friends is easier than you think. Try out these simple ciphers which can be replicated with just paper and pencil:

  • Caesar cipher. This is a simple substitution cipher where each letter of the plaintext is replaced with another letter that has been either shifted up or down the alphabet.
  • ROT13. This is a monoalphabetic substitution cipher where the letters of the alphabet are shifted by 13 spaces to encrypt simple messages.
  • Book cipher. This is a homophonic substitution cipher that uses letters of subsequent words in a given text or book as a key to encrypt messages.
  • Playfair cipher. It’s a polygraphic substitution cipher that encrypts pairs of letters commonly called digraphs, unlike other simple substitution ciphers like Caesar cipher that encrypts with a single letter.
  • Two square cipher. It’s a polygraphic substitution cipher which encrypts by replacing pairs of plaintext letters with another two letters based on two keyword tables.
  • Four square cipher. It’s also a polygraphic cipher which encrypts by replacing each pair of plaintext letters with another two letters, based on the four 5 by 5 encryption tables.
  • Running key cipher. It’s a polyalphabetic substitution cipher where each letter of the plaintext is shifted along some number of alphabet positions in one specific direction.
  • Nihilist cipher. It’s a polyalphabetic cipher that creates a Polybius square for a given key, and then an additional key to creating the ciphertext.
  • Rail fence cipher. It’s a transposition cipher that encrypts by writing a text in zig-zag and then read from left to right.
  • Route cipher. It’s also a transposition cipher that encrypts the plaintext letters based on the shape of an imaginary path drawn on a grid.

Now I want to hear from you.

What is your best method of encrypting simple messages?

Or maybe I missed your favorite cipher.

Either way, let me know by leaving a comment below.

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