2. TOPICS
Introduction to Cryptography, Cryptanalysis,
Cryptology
Substitution techniques
Transposition techniques
Symmetric and asymmetric cryptography
3. INTRODUCTION TO CRYPTOGRAPHY,
CRYPTANALYSIS, CRYPTOLOGY
Cryptography:- Cryptography is the art and science of achieving
security by encoding messages to make them non-readable.
Cryptanalysis:- Cryptanalysis is the technique of decoding cipher
text back to plaintext without knowing how they were initially
converted & key used.
Cryptology:- It is a combination of cryptography and Cryptanalysis.
Book Of
Security
Cryptography
R#5%^”;p0s89 -
$*-233409llgh
R#5%^”;p0s89 -
$*-233409llgh
Cryptanalysi
s
Book Of
Security
4. SUBSTITUTION TECHNIQUES
Caesar cipher:- The Caesar cipher involves replacing
each letter of the alphabet with the letter standing three
places further down the alphabet.
For example:-plain: meet me after the toga party cipher:
PHHW PH DIWHU WKH WRJD SDUWB
plain: a b c d e f g h i j k l m n o p q r s t u v w x y z
cipher: D E F G H I J K L M N O P Q R S T U V W X Y Z
A B C
5. MONO-ALPHABETIC CIPHER:- Here, Random
Substitution is used. In the plaintext message each A is
replaced with any alphabet i.e. B....Z.& each B replaced
with any alphabet A or C...Z.
POLYGRAM SUBSTITUTION CIPHER:- PolyGram
Substitution Cipher Technique replaces one block of plain
text with a block of cipher text. It does not work on a
Character-by-Character basis.
Example:
HELLO YUQQW
HELL TEUI
6. TRANSPOSITION TECHNIQUES
Rail Fence Cipher:- In the Rail Fence Cipher, the plain
text is written downwards on successive rails of an
imaginary fence then moving up when we get to the
bottom then message is then read off in rows.
Plaintext – Welcome Students
cipher text- WLOETDNSECMSUET
SIMPLE COLUMNAR TRANSPOSITION:- The message
is written in rows of fixed length and read out column by
column.
W L O E T D N S
E C M S U E T
7. Plain text message : come home tomorrow
Cipher text message : CMROERMTOEOWHMOO
• SIMPLE COLUMNAR TRANSPOSITION:- Plaintext-
attack postponed until two am Key: 4312567
Column Out 3 4 1 2 5 6 7
Plaintext:
Cipher text: TTNAAPTMTSUOAODWCOIXKNLYPETZ
c o m e h o
m e t o m o
r r o w
a t t a c k p
o s t p o n e
d u n t i l t
w o a m x y z
8. SYMMETRIC AND ASYMMETRIC
CRYPTOGRAPHY
Symmetric key cryptography: Involves the use of same key for
encryption and decryption.
Asymmetric key cryptography : Involves the use of one key for
encryption and another, different key for decryption.
