Cryptography & Network Security

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.