1. Introduction Of System Security
Slide Prepared and Presented By:
Mr. Ankit S. Didwania
(RC-1093)
Open Education Resource (OER) by Ankit S. Didwania is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
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2. Learning Outcomes
Learner should be able to detect the process of Symmetric Cipher Model
Learner should be able to understand the basics of Cryptography and Cryptanalysis

3. Evaluation Strategy Sr. No. Question Type Mark 1
Multiple Choice Question (MCQ) 2
Brief Subjective 3
Detailed Subjective 5

4. LeD 2.0: Learning Dialogues Activity

5. Symmetric Encryption
Also referred as conventional / private-key / single-key encryption algorithm
In it, same key is shared by both the sender and receiver
Its classical algorithm, but still widely used
Modern algorithm uses public-key algorithm, invented in 1970’s

6. Some Basic Terminology
plaintext - original message
ciphertext - coded message
cipher - algorithm for transforming plaintext to ciphertext
key - info used in cipher known only to sender/receiver
encipher (encrypt) - converting plaintext to ciphertext
decipher (decrypt) - recovering ciphertext from plaintext
cryptography - study of encryption principles/methods
cryptanalysis (codebreaking) - study of principles/ methods of deciphering ciphertext without knowing key
cryptology - field of both cryptography and cryptanalysis

7. Symmetric Cipher Model

8. Cryptography characterize cryptographic system by:
type of encryption operations used
substitution / transposition / product
number of keys used
single-key or private / two-key or public
way in which plaintext is processed
block / stream

9. Cryptanalysis objective to recover key not just message
general approaches:
cryptanalytic attack
brute-force attack

10. Cryptanalytic Attacks
ciphertext only
only know algorithm & ciphertext, is statistical, know or can identify plaintext
known plaintext
know/suspect plaintext & ciphertext
chosen plaintext
select plaintext and obtain ciphertext
chosen ciphertext
select ciphertext and obtain plaintext
chosen text
select plaintext or ciphertext to en/decrypt

11. More Definitions unconditional security computational security
no matter how much computer power or time is available, the cipher cannot be broken since the ciphertext provides insufficient information to uniquely determine the corresponding plaintext
computational security
given limited computing resources (eg time needed for calculations is greater than age of universe), the cipher cannot be broken

12. Brute Force Search always possible to simply try every key
most basic attack, proportional to key size
assume either known / recognise plaintext
A brute-force attack involves trying every possible key until an intelligible translation of the ciphertext into plaintext is obtained. On average, half of all possible keys must be tried to achieve success.

13. Summary Learner should have understood the following:
working of Symmetric Cipher Model
the types of Cryptography
the basics of cryptanalysis

14. Acknowledgement
Book
“Cryptography and Network Security”, 4th edition, by William Stallings, Chapter 2 “Classical Encryption Techniques”

15. LbD 2.0: Learning by Doing Activity

16. Multiple Choice Questions (1 mark each)
1) Symmetic key cryptography is defined as _____ algorithm with _____ key is used for encryption and decryption.
same, same b) same, different
c) different,same d) different, different
2) Modern algorithm (invented in 1970’s) uses _____ key algorithm.
conventional b) public
c) single d) private

17. Subjective Questions Brief Subjective (3 marks each) :
1) What do you mean by brute-force attack?
2) What do you mean by cryptology?
Detailed Subjective (5 marks each) :
1) Give the requirement for secure use of conventional encryption
2) Which three dimension are used for characterizing cryptographic techniques

18. THANK YOU 