This document provides an overview of cryptography. It discusses security threats and goals, then defines cryptography as using mathematics to encrypt and decrypt data. It describes basic terms like plaintext, encryption, ciphertext, and decryption. The document outlines symmetric and asymmetric key cryptography, and examples of techniques like transposition ciphers, substitution ciphers, stream ciphers, and block ciphers. It concludes that cryptography should be used to implement network security and prevent data leakage through encryption and decryption techniques.

1. Submitted by- ASMITA PAL
0201CS141017
Submitted to- Asst. Prof. Deepti Tamrakar
Dept. of Computer Science & Engg.

2. Overview
Security
Security Threats
Security Goals
What is Cryptography
Basic Terms
Encryption & Decryption
Transmission Techniques
Categories of Cryptography
Comparison
Conclusion

4. Security Threats

5. Security Goals

6. What is Cryptography?
• Cryptography is the science of using
mathematics to encrypt and decrypt data.
• Cryptography enables you to store
sensitive information or transmit it across
insecure networks so that it cannot be
read by anyone except the intended
recipient.

7. Basic Terms
• Plaintext: Data that can be read and understood
without any special measures.
• Encryption: The method of disguising plaintext in
such a way as to hide its substance is called
encryption.
• Cipher text: Encrypting plaintext results in
unreadable gibberish called cipher text.
• Decryption: The process of reverting cipher text to
its original plaintext is called decryption.
• Key: some secret piece of information that
customizes how the cipher text is.

8. Basic Terms cont.
• Cryptanalysis: The art of breaking ciphers,
i.e. retrieving the plaintext without knowing
the proper key.
• Cryptographers: People who do
cryptography.
• Cryptanalysts: Practitioners of cryptanalysis.
• Cryptology: The branch of mathematics that
studies the mathematical foundations of
cryptographic methods.

9. Encryption & Decryption

10. Why Use Cryptography?
• For “secret writing”
• To establish a shared secret when
other people (eavesdroppers) are
listening.
• TYPES
Mainly classified into two types:
1. Symmetric key cryptography
2. 2. Asymmetric key cryptography

11. Transmission Techniques

12. Categories of Cryptography

13. Symmetric Key Cryptography

14. Transposition Cipher
• In classical cryptography, a transposition
cipher changes one character from the
plaintext to another i.e. the order of the
characters is changed.

15. Substitution Cipher
• Substitution cipher is a method of
encryption by which units of plaintext are
substituted with cipher text according to a
regular system.

16. Stream Cipher
• A Stream Cipher is a symmetric or secret key encryption
algorithm that encrypts a single bit at a time. With a
Stream Cipher, the same plaintext bit or byte will encrypt
to a different bit or byte every time it is encrypted.
• e.g. : Plain text: Pay 100
Binary of plain text: 010111101
(hypothetical)
Key: 100101011 --
---
Perform XOR
____________________
Cipher text 110010110 ----
-

17. Block Cipher
• Block cipher technique involves encryption of
one block of text at a time. Decryption also takes
one block of encrypted text at a time. Length of
the block is usually 64 or 128 bits.
• e.g. : Plain text: four and five
Four and five
Key Key Key
wvfa ast wvfa ---
cipher text

18. Asymmetric Key Cryptography
Public key cryptography is an asymmetric scheme that uses a Pair of
keys for encryption: a Public key, which encrypts
data, and a corresponding Private key (secret key) for decryption.

19. Keys Used In
Cryptography

20. Conclusion
• Cryptography, being an art of encrypting and
decrypting confidential information and private
messages, should be implemented in the network
security to prevent any leakage and threat.
• It can be done by using any of these techniques
discussed above for fortifying the personal data
transmission as well as for secure transaction.
• By using of encryption & decryption techniques a fair
unit of Confidentiality, Authentication, Integrity, Access
control and Availability of data is maintained.