Cryptography is the science of protecting information through encoding, derived from Greek meanings of 'hidden' and 'writing'. It involves the processes of encryption and decryption, turning readable text into coded messages and back again, using various methods such as shift ciphers and modulo operations. The document provides examples and methods for encrypting and decrypting messages using these techniques.

1. CRYPTHOGRAPHY

2. CRYPTOGRAPHY
It is a science of protecting information
by encoding it into unreadable format.
Originated from two Greek words such
as “KRYPTO” which means hidden
and “GRAPHENE” which means
writing.
It is a method of making and
breaking of secret codes.

3. CRYPTOGRAPY is a science of encrypting and
decrypting written communication.
• ENCRYPTION
is the process of transforming plain text into
codes form using a certain algorithm.
• DECRYPTIO s the process of
returning/converting back the coded message
into plain text.

4. • PLAIN TEXT
• -refers to the original text
• CIPHER TEXT
• - refers to the coded text
• KEY
• - refers to the strings of
information that is used to reveal the
encryted message into readable form
CRYPTOGRAPHY

5. • SHIFT CIPHER (CEASAR CIPHER)
• -it is the simple type of
substitution cipher.
• - it uses shift in forming the key
of cryptography
SIMPLE METHODS

6. 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
shift cipher

7. • USING SHIFT 3 TO THE LEFT
shift cipher
A B C D E F G H I J K L M
D E F G H I J K L MN O P
N O P Q R S T U V WX Y Z
Q R S T U V WX Y Z A B C

8. • USING SHIFT 5 TO THE RIGHT
shift cipher
A B C D E F G H I J K L M
N O P Q R S T U V WX Y Z

9. • USING SHIFT 5 TO THE RIGHT
shift cipher
A B C D E F G H I J K L M
V WX Y Z A B C D E F G H
N O P Q R S T U V WX Y Z
I J K L M NO P Q R S T U

10. • USING SHIFT 3 TO THE LEFT,
• ENCRYPT THE WORD
“CRYPTOGRAPHY”
shift cipher
A B C D E F G H I J K L M
D E F G H I J K L M N O P
N O P Q R S T U V W X Y Z
Q R S T U V W X Y Z A B C

11. • USING SHIFT 5 TO THE RIGHT
• DECRYPT THE CIPHER TEXT
• “BJY DN BJJY”
shift cipher
A B C D E F G H I J K L M
V W X Y Z A B C D E F G H
N O P Q R S T U V W X Y Z
I J K L M N O P Q R S T U

12. • MODULO OPERATOR
• -the sender of the uses the key K
to encrypt and to decrypt the secret
message.
SIMPLE METHODS

13. modulo operator
• TO ENCRYPT:
1.express the letters of the
alphabet from 0-25
2. calculate Y=(C+K)mod 26
3. convert the number Y into a
letter following the order of the
letter of the alphabet

14. Modulo Operator
A B C D E F G H I J K L M
0 1 2 3 4 5 6 7 8 9 10 11 12
N O P Q R S T U V WX Y Z
13 14 15 16 17 18 19 20 21 22 23 24 25

15. modulo operator
A B C D E F G H I J K L M
0 1 2 3 4 5 6 7 8 9 10 11 12
N O P Q R S T U V W X Y Z
13 14 15 16 17 18 19 20 21 22 23 24 25
Encrypt the message
“MMW is fun to learn” let k = 5

16. Modulo operator
A B C D E F G H I J K L M
0 1 2 3 4 5 6 7 8 9 10 11 12
N O P Q R S T U V W X Y Z
13 14 15 16 17 18 19 20 21 22 23 24 25
M M W I S F U N T O L E A R N
12 12 22 8 18 5 20 13 19 14 11 4 0 17 13

17. modulo operator
M M W I S F U N T O L E A R N
12 12 22 8 18 5 20 13 19 14 11 4 0 17 13
+ 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5
17 17 27 13 23 10 25 18 24 19 16 9 5 22 18

18. modulo operator
Y = (17 17 27 13 23 10 25 18
24 19 16 9 5 22 18)mod26
Y = (17 17 1 13 23 10 25 18
24 19 16 9 5 22 18)

19. modulo operator
A B C D E F G H I J K L M
0 1 2 3 4 5 6 7 8 9 10 11 12
N O P Q R S T U V W X Y Z
13 14 15 16 17 18 19 20 21 22 23 24 25
17 17 1 13 23 10 25 18 24 19 16 9 5 22 18
R R B N X K Z S Y T Q J F W S

20. Modulo Operator
• TO DECRYPT:
• 1. express the letters of the
alphabet from 0-25
• 2. calculate C=(Y-K)mod 26
• 3. convert the number C into a
letter following the order of the
letter of the alphabet

21. modulo operator
A B C D E F G H I J K L M
0 1 2 3 4 5 6 7 8 9 10 11 12
N O P Q R S T U V W X Y Z
13 14 15 16 17 18 19 20 21 22 23 24 25
decrypt the cipher text
“RRBNXKZSYTQJFWS” let k = 5

22. modulo operator
A B C D E F G H I J K L M
0 1 2 3 4 5 6 7 8 9 10 11 12
N O P Q R S T U V W X Y Z
13 14 15 16 17 18 19 20 21 22 23 24 25
R R B N X K Z S Y T Q J F W S
17 17 1 13 23 10 25 18 24 19 16 9 5 22 18

23. modulo operator
M M W I S F U N T O L E A R N
17 17 1 13 23 10 25 18 24 19 16 9 5 22 18
- 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5
12 12 -4 8 18 5 20 13 19 14 11 4 0 17 13

24. modulo operator
Y = (12 12 -4 8 18 5 20
13 19 14 11 4 0 17
13)mod26
Y = (12 12 22 8 18 5 20
13 19 14 11 4 0 17 13)

25. Modulo Operator
A B C D E F G H I J K L M
0 1 2 3 4 5 6 7 8 9 10 11 12
N O P Q R S T U V W X Y Z
13 14 15 16 17 18 19 20 21 22 23 24 25
12 12 22 8 18 5 20 13 19 14 11 4 0 17 13
M M W I S F U N T O L E A R N

26. modulo operator
A B C D E F G H I J K L M
0 1 2 3 4 5 6 7 8 9 10 11 12
N O P Q R S T U V W X Y Z
13 14 15 16 17 18 19 20 21 22 23 24 25
ENCRYPT
“FATIMA” LET K=7