CNS Lab 01 - Breaking PRNGs for Fun and Profit Part 1/2

First laboratory for the Computer Network Security (CNS) course at Tor Vergata during scholar year 2022-2023. In the laboratory we introduced the idea behind Pseudo-Random-Number-Generators (PRNGs) and we have analyzed two specific types of PRNGs, the "The Middle Square Method" and the "Linear Congruential Generator", abbreviated as LCG. We have defined the main equations defining an LCG, and we have seen how to discover all the parameters of a given LCG starting from a sequence of outputs. In terms of practical application, we have seen that the C standard library implements various types of PRNGs, and among these (at least up until glibc version 2.36) we also find a version of LCG with specific fixed parameters. ------------------------------------------------------ LECTURE MATERIAL: - https://teaching.leonardotamiano.xyz/cns/labs/lab_01/ - https://teaching.leonardotamiano.xyz/class-material/cns/prngs_01/slides/prngs_01_slides.html - https://teaching.leonardotamiano.xyz/class-material/cns/prngs_01/code.zip ------------------------------------------------------ TIMESTAMPS: 00:00:00 Introduction 00:04:30 What is randomness? 00:13:38 What is Pseudo-Randomness? 00:25:38 A First PRNG: Middle Square method 00:31:55 A Second PRNG: Linear Congruential Generator 00:38:19 LCG in rand() libc 00:42:05 How to break LCG 01:05:30 Why the attack fails sometimes 01:09:00 Towards Next Lecture 01:11:46 Extra: Debugging rand()