- In classical cryptography, Trifid Cipher is a cipher invented around 1901 by Felix Delastelle, which extends the concept of the Bifid cipher to a third dimension, allowing each symbol to be fractionated into 3 elements instead of two.
- While the Bifid uses the Polybius square to turn each symbol into coordinates on a 5 × 5 (or 6 × 6) square, the trifid turns them into coordinates on a 3 × 3 × 3 cube. As with the bifid, this is then combined with transposition to achieve diffusion. However a higher degree of diffusion is achieved because each output symbol depends on 3 input symbols instead of two. Thus the Trifid was the first practical trigraphic substitution.
[ENCRYPTION]
First, a mixed alphabet cubic analogue of the Polybius square is drawn up.
Layer I:
1 2 3
1 F J O
2 R X C
3 Y B S
Layer II:
1 2 3
1 V Z L
2 G D P
3 M W T
Layer III:
1 2 3
1 E U Q
2 N H A
3 . K I
or
F111 C 132 W 223 U 321
R 112 S 133 L 231 H 322
Y 113 V 211 P 232 K 323
J 121 G 212 T 233 Q 331
X 122 M 213 E 311 A 332
B 123 Z 221 N 312 I 333
O 131 D 222 . 313
Let us try to encrypt PANDORA. If letter P is found in layer two, column three and row two, letter P will turn into 232. The same process repeats to the remaining letters of the message. Now, we have 232 332 312 222 131 112 332. Rewrite the series of numbers vertically under the secret message.
P A N D O R A
2 3 3 2 1 1 3
3 3 1 2 3 1 3
2 2 2 2 1 2 2
We then regroup the numbers into three horizontally and we now have 233 211 333 123 132 222 122. Then we change it into letters using the three layers.
233 211 333 123 132 222 122 will now become TVIBCDX. Our encrypted message is TVIBCDX.
[DECRYPTION]
To decrypt a message encrypted in trifid cipher, you must find the three numbers (Layer x Column x Row) of the letters of the encrypted message. You then rewrite the numbers horizontally based on the number of letters of the encrypted message, then regroup them vertically and you will search for the letter it stands for using the layers.
Solution:
TVIBCDX
= 233 211 333 123 132 222 122
= P A N D O R A
2 3 3 2 1 1 3
3 3 1 2 3 1 3
2 2 2 2 1 2 2
= 232 332 312 222 131 112 332
= PANDORA
