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. This is a Free Culture License! You are free to use, distribute and modify it, including for commercial purposes, provided you acknowledge the source and share-alike.

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

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

LeD 2.0: Learning Dialogues Activity

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

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

Symmetric Cipher Model

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

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

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

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

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.

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

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

LbD 2.0: Learning by Doing Activity

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

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

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