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This text explores the dynamics of encryption through the lens of Alice and Bob, who share a key to exchange secure messages, while Eve attempts to intercept them. It delves into various types of attacks, including eavesdropping and chosen plaintext/ciphertext scenarios. Despite the risks posed by potential attackers, the study emphasizes that robust algorithms like AES provide significant security, making them superior against various attack models. Additionally, it discusses the importance of confidentiality, integrity, and the need for layered defenses in encryption systems to combat vulnerabilities.
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Models - encryption • Alice and Bob have the same key k • Alice and Bob exchange encrypted messages • Eve wants to get the plaintext. What can she do? • What can Eve do? • The model we studied: eavesdropping, known plaintext, chosen plaintext/ciphertext • Bad news for the attacker • Any reasonable algorithm (e.g. AES) beats all of these • The best current (2012) attack on AES in the model breaks it in time 2126.2 and more than 280 chosen ciphertexts.
New security goals • We “know” how to do confidentiality, integrity and authentication. • Is anything else even needed • Hint: we need to work even with those we don’t completely trust • n-out-of n secret sharing • t-out-of n secret sharing
Administrative Details • Grade – 100% test • Office hours :Wednesday 13:00-14:00 • E-mail – niv.gilboa@gmail.com • Tel. 054-6501047 • Bibliography: • Security engineering / R. Anderson • Foundations of Cryptography, I and II/ O. Goldreich
Principles for the attacker • The model is a simplification • Complexity is your friend • Find the weakest link • Know the system • Model assumes that attacker has full knowledge. Real life is different. • Know the attacks
Know the system • An encryption system includes • Users • Physical environment • Plaintext storage & plaintext input • Encryption software / hardware • (Almost always) – a larger hardware / software system such as a computer • A key • A communication channel • Any of these elements can be vulnerable • The model considers just the communication link and input to the encryption algorithm
Know the Attacks • On users • Social attacks – bribe the user, threaten the user, swindle the user • Outside our scope • Physical environment • Input attacks: e.g. key loggers, a bug in the wall • Outside our scope
More attacks • Device hardware • Side channel attacks – e.g. timing • Fault attacks – e.g. glitch • Optical attacks • Chemical attacks • Question: so many options, why isn’t this part of the model? • Answer: they all require physical proximity and that is considered impossible
An economic approach • An attacker’s potential utility • Money, knowledge, ideology, vengeance • The risks • Cost of an attack • Probability of failure • Risk of getting caught • Example – table of attacks on encryption system
What about the defense? • A breach / exploit / attack has costs • Defense has its own costs • Problems • All attack avenues must be adequately blocked • Attacker’s model: plans, capabilities, utility are imperfectly known • Principles • Know the attacks and the defenses • Layered defense • Redundancy is good • But, remember the utility!
Shocking example Do you know what this is? Here’s a hint
