5504836
Description
Flashcards by Alex Neves, updated more than 1 year ago
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Created by Alex Neves
almost 8 years ago
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| Question | Answer |
| Briefly describe Public-key Encryption | Two keys, one public one private. Infeasible to calculate private key from a public key. Security achieved through intractable mathematical problems. |
| What is Public-key Encryption used for? | Symmetric key exchange and sender verification |
| 5 differences between symmetric and asymmetric encryption | 1 vs 2 key. Small vs large key size. Fast vs slow. Long term comms vs key exchange / verification. SP Networks vs Mathematical problems |
| State the 3 mathematical principles used in asymmetric cryptology | - Large (typically prime) numbers - Modular arithmetic - Integer factorisation |
| What is the congruence relation? | a === b (mod n) => a (mod n) = b (mod n) |
| Give the eqivalences of modular arithmetic | ((a mod n) + (b mod n)) mod n = (a + b) mod n |
| What is a discrete logarithm? Draw the expression | Combining logs with modular arithmetic. Hard to compute and requires brute force. |
| What is a primitive root? | A generator for a prime P which, when raised to an exponent and modular P, produces all values between 0 and P-1 |
| What is DHKEX? | Diffie-Hellman Key Exchange. Exchanges symmetric keys in private using discrete logarithms. |
| Describe the 5 steps of DHKEX | <See notes> |
| Why is DHKEX secure? Draw equation to be solved | Symmetric key g^ab can only be solved by knowing either private exponents, a or b. |
| What is DHKEX vulnerable to? | Man-in-the-middle attacks. Intercept initial comms and create two separate key exchanges between A and B. |
| Describe the Logjam attack. | 512-bit DH attack. Number field sieve to precompute 3/4 stages of DH for a given prime. Final stage computed at attack time. Works since same primes are often used (Oakley Group 2) |
| What is PFS? | Perfect forward secrecy. Establish a new symmetric key each session. Known as Ephemeral Mode in practice. |
| What is Elliptic Curve? | An alternative to modular arithmetic and discrete logs. Uses a curve to decide key in the form of y^2 = x^3 + ax + b. Stronger than other methods for the same key size |
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