Lecture #2:Classical Cryptographic Techniques

Transposition or Permutation
ciphers hide the message contents by rearranging the order of the letters according to the following procedures

1. Message Reversal
This procedure requires that the plain text to be written backwards to produce a cipher text.

Plain text: MEET ME MONDAY MORNING
Cipher text: GININGROM YADNOM EM TEEM

This procedure is straightforward and easy to decipher a message ,simply reverse it

2. Geometric Patterns

The normal writing of a message follows a pattern from left to right, one line at a time . Message then form a geometrical pattern in the shape of a rectangular ,or any other geometrical pattern would disguise the message from a single horizontal line. It can be transposed into rectangular shapes of:
2.1. The Columns of Equal Length
This method base on dived the message to number of line have the columns of equal length (i.e., each line have number of letters change dynamic base on key)by writing the plaintext vertically:

Example: let , the plain text: THE SIMPLE STOPS SIBLE TANSPOSITIONS X X and Key : 4 1 5 3 2

T H E S I S T I E H
M P L E S E M S L P
T P O S S S T S O P
I B L E T E I T L B
R A N S P S R P N A
O S I T I T O I I S
O N S X X X O X S N

Cipher text: STIEH EMSLP STSOP EITLB SRPNA TOIIS