Cryptography is the discipline of using codes and ciphers to encrypt a message and make it unreadable unless the recipient knows the secret to decrypt it. Encryption has been used for many thousands of years. The following codes and ciphers can be learned and used to encrypt and decrypt messages by hand.
Monoalphabetic Ciphers
A monoalphabetic cipher is a substitution cipher that uses the same substitution across the entire message. For example, if you know that the letter A is enciphered as the letter K, this will hold true for the entire message. These types of messages can be cracked by using frequency analysis, educated guesses or trial and error.
Caesar Cipher
Atbash Cipher
Keyword Cipher
Pigpen / Masonic Cipher
Polybius Square
Polyalphabetic Ciphers
In a polyalphabetic cipher, the substitution of one letter for another may change throughout the message. For example, the letter A may be encoded as the letter K for part of the message, but later on it might be encoded as the letter W.
Vigenère Cipher
Beaufort Cipher
Autokey Cipher
Running Key Cipher
Polygraphic Ciphers
Instead of substituting one letter for another letter, a polygraphic cipher performs substitutions with two or more groups of letters. This has the advantage of masking the frequency distribution of letters, which makes frequency analysis attacks much more difficult.
Playfair Cipher
Bifid Cipher
Trifid Cipher
Four-square cipher
Transposition Ciphers
Unlike substitution ciphers that replace letters with other letters, a transposition cipher keeps the letters the same, but rearranges their order according to a specific algorithm.
Rail Fence
Route Cipher
Columnar Transposition
Other Ciphers and Codes
There are lots of other interesting codes and ciphers that have been used throughout history.
Book Cipher
Beale Cipher
Morse Code
Tap Code
One-time Pad
Scytale
Semaphore
ASCII
Steganography
Techniques and Resources
There are many different techniques that you can use to crack an encryption.
