Codes, Ciphers, Encryption and
• 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.
• A Caesar cipher is one of the simplest (and easiest cracked)
encryption methods. It is a Substitution Cipher that involves
replacing each letter of the secret message with a different
letter of the alphabet which is a fixed number of positions
further in the alphabet.
• Because each letter in the message has a direct translation
to another letter, frequency analysis can be used to decipher
the message. For example, the letter E is the most
commonly used letter in the English language. Thus, if the
most common letter in a secret message is K, it is likely that
K represents E. Additionally, common word endings such as
ING, LY, and ES also give clues.
• A brute-force approach of trying all 25 possible
combinations would also work to decipher the message.
In this example, each letter in the plaintext message has
been shifted 3 letters down in the alphabet.
• Plaintext: This is a secret message
Ciphertext: wklv lv d vhfuhw phvvdjh
PIGPEN / MASONIC CIPHER
The pigpen cipher (sometimes called the
masonic cipher or Freemason's cipher) is a
simple substitution cipher exchanging letters
for symbols based on a grid. The scheme was
developed and used by the Freemasons in the
early 1700s for record-keeping and
correspondence. The example key shows one
way the letters can be assigned to the grid
• To encipher, a table of alphabets can be used, termed a tabula recta, Vigenère square, or Vigenère
table. It consists of the alphabet written out 26 times in different rows, each alphabet shifted
cyclically to the left compared to the previous alphabet, corresponding to the 26 possible Caesar
ciphers. At different points in the encryption process, the cipher uses a different alphabet from one
of the rows. The alphabet used at each point depends on a repeating keyword.
• For example, suppose that the plaintext to be encrypted is:
• ATTACKATDAWNThe person sending the message chooses a keyword and repeats it until it matches
the length of the plaintext, for example, the keyword "LEMON":
• LEMONLEMONLEEach letter is encoded by finding the intersection in the grid between the plaintext
letter and keyword letter. For example, the first letter of the plaintext, A, is enciphered using the
alphabet in row L, which is the first letter of the key. This is done by looking at the letter in row L
and column A of the Vigenere square, namely L. Similarly, for the second letter of the plaintext, the
second letter of the key is used; the letter at row E and column T is X. The rest of the plaintext is
enciphered in a similar fashion:
• Plaintext: ATTACKATDAWN
• Key: LEMONLEMONLE
• Ciphertext: LXFOPVEFRNHR
• Decryption is performed by finding the position of the ciphertext letter in a row of the table, and
then taking the label of the column in which it appears as the plaintext. For example, in row L, the
ciphertext L appears in column A, which taken as the first plaintext letter. The second letter is
decrypted by looking up X in row E of the table; it appears in column T, which is taken as the
• The Playfair cipher encrypts pairs of letters (digraphs), instead of single letters. This is significantly
harder to break since the frequency analysis used for simple substitution ciphers is considerably
• Memorization of the keyword and 4 simple rules is all that is required to create the 5 by 5 table and
use the cipher.
• The Playfair cipher uses a 5 by 5 table containing a key word or phrase. To generate the table, one
would first fill in the spaces of the table with the letters of the keyword (dropping any duplicate
letters), then fill the remaining spaces with the rest of the letters of the alphabet in order (to
reduce the alphabet to fit you can either omit "Q" or replace "J" with "I"). In the example to the
right, the keyword is "keyword".
• To encrypt a message, one would break the message into groups of 2 letters. If there is a dangling
letter at the end, we add an X. We now take each group and find them out on the table. Noticing
the location of the two letters in the table, we apply the following rules, in order.
• If both letters are the same, add an X between them. Encrypt the new pair, re-pair the remining
letters and continue.
• If the letters appear on the same row of your table, replace them with the letters to their
immediate right respectively, wrapping around to the left side of the row if necessary.
• If the letters appear on the same column of your table, replace them with the letters immediately
below, wrapping around to the top if necessary..
• If the letters are on different rows and columns, replace them with the letters on the same row
respectively but at the other pair of corners of the rectangle defined by the original pair. The order
is important - the first letter of the pair should be replaced first..
• To decipher, ignore rule 1. In rules 2 and 3 shift up and left instead of down and right. Rule 4
remains the same. Once you are done, drop any extra Xs that don't make sense in the final message
and locate any missing Qs or any Is that should be Js.
•Encrypting the message "Hide the gold in the tree stump":
Message :HI DE TH EG OL DI NT HE TR EX ES TU MP
Encryption :BM OD ZB XD NA BE KU DM UI XM MO UV IF
Rail Fence Cipher
• In the rail fence cipher, the plaintext is written downwards on successive "rails" of
an imaginary fence, starting a new column when the bottom is reached. The
message is then read off in rows. For example, if we have 3 rails and a message of
"This is a secret message", you would write out:
• T S A C T S G
• H I S R M S E
• I S E E E A
• The last J is just a random letter to fill in the space. The secret message is then
condensed and regrouped.
• TSACT SGHIS RMSEI SEEEA
• To decipher a message you must know the number of rails that were used to
encipher it. You then break up the letters into equal groups for each rail. For
example, if you are using 3 rails, you would break the secret message into 3 equal
groups. Now you stack the groups on top of each other and read off the message
vertically. If you get gibberish, then there are probably some extra letters tacked
on the end of the message that are throwing off the grouping
OTHER TYPES OF CIPHERS
The numbers are now read off
horizontally and grouped into pairs.
41 14 14 31 44 12 13 53 25 42 53 31
The Polybius Square is used again to
convert the numbers back into letters
which gives us our