Cryptography is the practice of securing communication and information using techniques like encryption. There are two main types of cryptography - symmetric which uses the same key for encryption and decryption, and asymmetric which uses different public and private keys. The document discusses cryptography concepts like substitution and transposition ciphers, symmetric algorithms like DES and AES, and asymmetric uses like digital signatures. It provides examples and figures to illustrate cryptographic techniques and their applications for security and privacy in message transmission.

1. Lord Buddha Education Foundation
Name:Bijaya Khadka
Roll No:100115431
B.Sc IT(V),B
Cryptography

2. What is Cryptography?
Krypto =secret.
graphein =write.
Cryptography is also known as secret writing.

3. Process Involved in Cryptosystem
Plain
Text
DecryptionCipher TextEncryptionPlain
Text
Sending a
message
Sender Receiver
SECURITY or PRIVACY

4. Traditional Cryptography System
Cryptography
TranspositionSubstitution
Modern Cryptography System
Cryptography
AsymmetricSymmetric

5. Use the additive cipher with key = 15 to encrypt the message
“hello”.
Solution
We apply the encryption algorithm to the plaintext, character by
character:
The ciphertext is therefore “wtaad”.
Substitution Cipher

6. Transposition ciphers
Message: ENEMY ATTACKS TONIGHT
Cipher Text is :EAKI NTSG ETTH MAOT YCN
Figure: Transposition Cipher

7. Figure The general idea of symmetric-key cryptography
SYMMETRIC-KEY CRYPTOGRAPHY

8. DES
The Data Encryption Standard (DES) is a symmetric-key block cipher
published by the National Institute of Standards and Technology
(NIST) in 1977. DES has been the most widely used symmetric-key
block cipher since its publication .
Figure The general design of the DES encryption cipher
Example of Symmetric Key Cryptography

9. AES
The Advanced Encryption Standard (AES) is a symmetric-key block
cipher published by the US National Institute of Standards and
Technology (NIST) in 2001 in response to the shortcoming of DES,
Figure Encryption and decryption with AES
Example of Symmetric Key Cryptography

10. Figure The general idea behind asymmetric-key cryptography
ASYMMETRIC-KEY CRYPTOGRAPHY

11. Digital Signatures
 Made by encrypting a message digest with the sender’s
private key
 Receiver decrypts with the sender’s public key .
 DSS provides
o Sender authentication
o Verification of message integrity.

12. Final Words

13.  Your questions are welcome!