The University of Babylon
Department of Software
LECTURE NOTES ON Classical Cryptographic
Techniques
By
Dr. Samaher Hussein Ali
College of Information Technology, University of Babylon, Iraq
Samaher@itnet.uobabylon.edu.iq
12 October 2014
Classical Cryptographic Techniques
have two basic components of classical ciphers : Substitution and Transposition
Classical Ciphers
Transposition
Substitution
Fig 1. Classical cipher Methods
In Transposition Ciphers the letters are arranged in a different order, such as the word message in the following:
Rotate text
EGASSEM
Rotate
every two
letters
EMSSGAE
MESSAGE
Rotate
every three
letters
SEMGASE
Rotate
every four
letters
SSEMEGA
In Substitution Ciphers letters are replaced by other letters , such as the word message in the following:
PHVVDJH
TLZZHNL
KEY=7
HZNNVBZ
KEY=21
KEY=3
MESSAGE
KEY=12
12 October 2014
YQEEMSQ
Dr. Samaher Hussein Ali
Notes of Lecture 2
Transposition Ciphers
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
THESI
MPLES
TPOSS
IBLET
RANSP
OSITI
ONSXX
STIEH
EMSLP
STSOP
EITLB
SRPNA
TOIIS
XOXSN
Cipher text: STIEH EMSLP STSOP EITLB SRPNA TOIIS
12 October 2014
Dr. Samaher Hussein Ali
Notes of Lecture 2
Transposition Ciphers
2.2. The Rows of Equal Length
This method base on dived the message to number of line have the rows of equal length (i.e., each line have number of
letters change dynamic base on key)by writing the plaintext horizontely:
Example: let , the plain text: THE SIMPLE STOPS SIBLE TANSPOSITIONS X X and Key : 4 7 1 6 2 3 5
T HE S I
IBLET
MP L E S
ONSXX
T P O S S
THESI
I B L E T
EOSITI
RA N S P
MPLES
OS I T I
TPOSS
ONS X X
RANSP
Cipher text: I B L E T O N S X X T H E S I E O S I T I M P L E S T P O S S R A N S P
This procedure produce a very limited degree of message security, however, geometrical patterns are useful an
intermediate step for another encryption procedure ,route transposition
3. Route transposition :
It is providing a way of further scrambling geometrically shaped message .
Example:
Let, the plain text: SEND HELP SOON
the cipher text:
SE
ND
HE
LP
SO
ON
The cipher text message is easily understood. The procedure provides very little security. We can increase the
scrambling if we make use of the rectangle (2*6)as intermediate step. Then the cipher text become:
the cipher text: SNHLSO
EDEPON
12 October 2014
Dr. Samaher Hussein Ali
Notes of Lecture 2
Transposition Ciphers
4. Zig Zag Transposition
In this method, The plaintext divided into fixed lengths. one length contains every even positioned letter of the
message. The transposing process follow this type of pattern(zig zag)
Example:
Let, the plain text: SEND HELP SOON, and depth=2 find cipher text:
the cipher text: SNHLSO
EDEPON
* Reversed Zig Zag Transposition
The enciphering starts with the last letter of the plain text and continues back to the beginning of the message first the
odd positioned letters are taken and then even positioned “ ones
Example:
Let, the plain text:
the cipher text:
SEND HELP SOON
NOPEDEOSLHNS
5. Route variations
Route transpositions can go in many different directions:
 Horizontal
 Vertical
 Diagonal
 Clockwise
 Counter clockwise
If we use the message in (3*4) geometric shapes, several of these route transpositions can be illustrated:
12 October 2014
Dr. Samaher Hussein Ali
Notes of Lecture 2
Transposition Ciphers
5.1. Horizontal Route
SEND
NOOS
HELP
PLEH
SOON
DNES
5.2. Vertical Routes
SDLO
NSEN
EHPO
OPHE
NESN
OLDS
5.3. Digonal Routes
S E DL
NOSE
N HPO
OPHN
E SON
L D ES
5.4. Clockwise
SEND
OONH
SPLE
1
S
E
N
D
O
O
N
H
S
P
L
E
L
E
2
3
5.5. Counter Clockwise
SPLE
OONH
SEND
S
P
O
O
N
H
S
E
N
D
2
1
12 October 2014
Dr. Samaher Hussein Ali
Notes of Lecture 2
Classical Cryptographic Techniques
As a result classical ciphers : substitution and transposition
Classical
Cipher
Methods
Message
Reversal
Horizontal
Transposition
Substitution
Methods
Methods
Geometric
Patterns
Route
variations
Vertical
Diagonal
Zig Zag
Transposition
Clockwise
Route
transposition
Next
Lecture
Counter
Clockwise
Fig 2. Expending of Classical cipher Methods
12 October 2014
Dr. Samaher Hussein Ali
Notes of Lecture 2