The trifid cipher is a classical cipher ; combines the techniques of fractionation and transposition to achieve a certain amount of confusion and diffusion: each letter of the ciphertext depends on three letters of the plaintext and up to three letters of the key.
The trifid cipher uses a table to fractionate each plaintext letter into a trigram, mixes the constituents of the trigrams, and then applies the table in reverse to turn these mixed trigrams into ciphertext letters. Delastelle notes that the most practical system uses three symbols for the trigrams:
The cipher requires a 27-letter mixed alphabet, so plus ( + ) sign will be included.
A traditional method for constructing a mixed alphabet from a key word or phrase is to write out the unique letters of the key in order, followed by the remaining letters of the alphabet in the usual order.
Example :
Key : FELIX MARIE DELASTELLE ( Note! You could always change the key )
It would result to : FELIXMARDSTBCGHJKNOPQUVWYZ+.
To each letter in the mixed alphabet we assign one of the 27 trigrams (111, 112, ..., 333) by populating a 3 × 3 × 3 cube with the letters of the mixed alphabet, and using the Cartesian coordinates of each letter as the corresponding trigram.
Layer 1 Layer 2 Layer 3
1 2 3 1 2 3 1 2 3
1 F E L 1 S T B 1 O P Q
2 I X M 2 C G H 2 U V W
3 A R D 3 J K N 3 Y Z +
From this cube we build tables for enciphering letters as trigrams and deciphering trigrams as letters:
Enciphering alphabet Deciphering alphabet
A = 131 J = 231 S = 211 111 = F 211 = S 311 = O
B = 213 K = 232 T = 212 112 = E 212 = T 312 = P
C = 221 L = 113 U = 321 113 = L 213 = B 313 = Q
D = 133 M = 123 V = 322 121 = I 221 = C 321 = U
E = 112 N = 233 W = 323 122 = X 222 = G 322 = V
F = 111 O = 311 X = 122 123 = M 223 = H 323 = W
G = 222 P = 312 Y = 331 131 = A 231 = J 331 = Y
H = 223 Q = 313 Z = 332 132 = R 232 = K 332 = Z
I = 121 R = 132 + = 333 133 = D 233 = N 333 = +
The encryption protocol divides the plaintext into groups of fixed size (plus possibly one short group at the end): this confines encoding errors to the group in which they occur, [6] an important consideration for ciphers that must be implemented by hand. The group size should be coprime to 3 to get the maximum amount of diffusion within each group: Delastelle gives examples with groups of 5 and 7 letters. He describes the encryption step as follows: [7]
For example, if the message is aide-toi, le ciel t'aidera, and the group size is 5, then encryption proceeds as follows:
a i d e - t o i l e c i e l t ' a i d e r a
1 1 1 . 1 2 3 1 1 . 1 2 1 1 1 . 2 1 1 1 1 . 1 1
3 . 2 3 1 . 1 1 . 2 1 1 . 2 2 . 1 1 1 . 3 2 . 3 1 3 . 3
1 1 . 3 2 2 1 1 . 3 2 1 1 2 . 3 2 1 1 3 . 2 2 1
F M J F V O I S S U F T F P U F E Q Q C
In this table the periods delimit the trigrams as they are read horizontally in each group, thus in the first group we have 111 = F, 123 = M, 231 = J, and so on.
Trifid cipher
In order to split letters into three parts, it is necessary to represent them by a group of three signs or numbers. Knowing that n objects, combined in trigrams in all possible ways, give n × n × n = n 3 , we recognize that three is the only value for n; two would only give 2 3 = 8 trigrams, while four would give 4 3 = 64, but three give 3 3 = 27.
We start by writing vertically under each letter, the numerical trigram that corresponds to it in the enciphering alphabet: then proceeding horizontally as if the numbers were written on a single line, we take groups of three numbers, look them up in the deciphering alphabet, and write the result under each column.
Credits to Wikipedia.
YOU ARE READING
CODES & CIPHERS
Non-FictionCompilation of codes, ciphers & some abbreviations to shorten the message before encrypting them. Learn the easiest way to remember Morse Code too.
