Cryptography

Cryptography is the study of techniques to allow secure communication and data storage in presence of attackers. The features that it aims to provide are: Confidentiality: data can be accessed only…

A modern practical assumption is to build ciphers such that a successful attack is carried only if a computational hard problem is solved. Examples of such hard computational problems are: Solve a…

Our attacker knows a set of plaintexts which can be encrypted and he wants to understand which one is being encrypted. Ideal attacker: cannot tell which plaintext was encrypted out of two he chose…

Confidentiality does not means integrity. Changes in the ciphertext are undetected. Message Authentication Codes (MAC) consists of adding a small piece of information (tag) allowing us to test for…

We would like to have the following features: Agreeing on a short secret over a public channel Confidentially sending a message over a public authenticated channel without sharing a secret with the…

We’d like to be able to verify the authenticity of a piece of data without a pre-shared secret. Using asymmetric encryption we can build digital signatures, which: Provide strong evidence that data…

Both in asymmetric encryption and digital signatures, the public key must be bound to the correct user identity. If public keys are not authentic: A MITM attack is possible on asymmetric encryption…

Shannon’s information theory is a way to quantify information and to mathematically frame communication. A communication takes place between two endpoints: sender: made of an information source and…

More exercises aviable at overthewire.org . 2021-2022 DEMO Exam exercise 2 (5 points) You have intercepted two ciphertexts: c1 = 1111100101111001110011000001011110000110 c2 =…