CS642 Midterm 1 PDF

What is security? Terms: Adversary - any entity trying to circumvent the security infrastructure, ranging in goals and sophistication Risk - at-risk valued resources that can be misused ○ Ex: data, time, confidence, trust, reputation...

What is security? Terms: Adversary - any entity trying to circumvent the security infrastructure, ranging in goals and sophistication Risk - at-risk valued resources that can be misused ○ Ex: data, time, confidence, trust, reputation Threats - a specific means by which an attacker can put a system at risk ○ Ex: an ability/goal of an attacker ○ Threat Model - a collection of threats that are deemed important for a particular environment Vulnerability - a systematic artifact that exposes the user, data, or system to a threat ( a weakness in a system) ○ Sources of vulnerability? → bad software/hardware, bad design, bad policy/configuration, system misuse, unintended purpose or environment ○ Ex: buffer-overflow, WEP key leakage Attack - when someone attempts to exploit a vulnerability ○ Compromise - occurs when an attack is successful Trust - the degree to which an entity is expected to behave ○ Trust model - describes, for a particular environment, who is trusted to do what? CIA model ○ Confidentiality Info becomes known only to authorized people ○ Integrity Info stored in a system is correct (not modified) ○ Availability Info, or service, is available when needed Information Security goals Prevent misuse, but don’t stop good things from happening Strategies to deal with attacks ○ Prevention Prevent an attack (ex: firewalls) ○ Detection Detect an ongoing attack; alert (ex: intrusion detection) ○ Recovery Recover from an attack (ex: backup) CIA model —--------- What can cryptography do/not do? What is a caesar cipher (ROTX)? What is a substitution cipher? - Why are they breakable? What is a polyalphabetic cipher (Vigenere)? What is shared key cryptography? What is the unbreakable cipher? What are Kerckhoffs’ principles Explain DES (Data Encryption Standard) Is a block cipher (fixed sized input) 8-byte input and an 8-byte key (56-bits+8 parity bits) Explain AES (Advanced Encryption Standard) Replacement for DES/accepted symmetric key cipher ○ Variable key lengths ○ Small code and memory footprint What are block ciphers and stream ciphers? Block → input is fixed blocks of some length Stream → stream of input (bitwise encryption) What are the two principles of cipher design? Confusion - make the relationship between the input and the output asa complex (non-linear) as possible ○ Mainly accomplished by substitution (Ex: s-box) Diffusion - Spread the influence of each input bit across many output bits ○ Mainly accomplished by permutation (Ex: Fiestal structure What are birthday attacks? A name used to refer to a class of brute-force attacks What are one way and collision resistant hashing algorithms? One way - (computationally) hard to invert h() ○ You cannot go backward Collision resistant - hard to find two data x1 and x2 such that h(x1) == h(x2) ○ Cannot find two items that hash to the same value - How do hashes work as authenticators? What are the rules/principles of crypto use? Terms: Cryptography - the art/science of developing and using cryptosystems Cryptosystem - method of disguising (encrypting) plaintext messages so that only select parties can decipher (decrypt) the ciphertext Cryptanalysis - the art/science of breaking cryptosystems Cryptology - the combined study of cryptography and cryptanalysis Encryption Algorithm - Algorithm used to make content unreadable by all but the intended users ○ E(plaintext, key) = ciphertext ○ D(ciphertext, key) = plaintext Algorithm → public | Key → private (principle of open design) Unconditional or probabilistic security - cryptosystem offers provable guarantees, irrespective of computational abilities of an attacker Conditional or computational security - cryptosystem is secure assuming a computationally bounded adversary, or under certain hardness assumptions Ciphertext-only attack - adversary only has the ciphertext available and wants to determine the plaintext encrypted Known-plaintext attack - adversary learns one or more pairs of ciphertext/plaintext encrypted under the same key, tries to determine plaintext based on a different ciphertext Chosen-plaintext attack - adversary can obtain the encryption of any plaintext, tries to determine the plaintext for a different ciphertext Chosen-ciphertext attack - adversary can obtain a plaintext of any ciphertext except the one the adversary wants to decrypt Hash chain MAC (Message Authentication Control) - used in protocols to authenticate content, authenticates integrity for data d ○ Flaw: block hash algorithms means new content can be added HMAC - MAC that is collision resistant and attacker cannot computer proper digest without knowing k ○ HMAC(K, d) = H(K + H(K + d)) Hash algorithm - the compression of data into a hash value —-------------- What is encryption using a private key? What are digital signatures? Models physical signatures in digital world ○ Association between private key and document Asserts that document is authentic and non-reputable Secret vs. public key crypto? Secret key cryptography - Symmetric keys, where A single key (k) is used for E and D ○ D(E(p, k), k) = p Public key cryptography - Each key pair consists of a public and private component ○ K+ (public key), k - (private key) ○ D(E(p, k+), k-) = p ○ D(E(p, k-), k+) = p Terms: Diffie-Hellman Protocol ○ For two participants p 1 and p 2 ○ Setup: Pick a prime number p and a primitive root* of p g (