Flashcards
Cryptography III
Cards in this deck (23)
- 1What is integer factorisation?Expressing an integer as the multiplication of a list of primes
- 2Why is it useful?Hard/Slow to compute for large values
- 3What is a semi-prime?A number which is the product of two primes (n = pq)
- 4What is Euler's Totient?The number of values between 1-(n-1) which are relatively prime with n
- 5What does relatively prime mean?A number is relatively prime with another if their GCD is 1
- 6How can we calculate Euler's Totient for prime numbers?For any prime, ET = P-1.
For 2 primes multiplied together,
ET = (P-1)(Q-1) - 7What is RSA?Asymmetric encryption algorithm used for encryption and authentication.
- 8What mathematical principle does it rely one?Integer factorisation
- 9Describe the 3 steps of generating a public/private key pair using RSA1. Calculate N=PQ for 2 large primes
2. Select a value E that is relatively prime with the totient of N
3. Calculate the multiplicative inverse D such that (e * d) mod ET(N) = 1 - 10How can we encrypt / decrypt with RSA?E: M^e mod n = C
D: C^d mod n = M - 11Why is RSA secure?We can only calculate d by knowing the totient of n, which requires solving the prime factors of n, p and q
- 12What is a hash function?Take any length message and produce a fixed-length hash
- 13What is it used for?- Message authentication
- Message integrity
- Passwords - 14How are they constructed?From any block cipher in CBC mode
- 15What are the 3 properties of a strong hash function?1. Avalanche effect (Small input changes cause large output changes)
2. One-way (Cannot calculate M from H(M)) 3. Collision Resistance (Cannot find two different messages which produce the same hash) - 16Discuss hash functions and output lengthGiven a hash of N output bits, the birthday paradox means a collision can be found after 2^n/2 attempts.
A large N is needed to avoid collisions. - 17What is a MAC?Message Authentication Code
- 18What is it used for?Authentication and integrity of messages
- 19Explain HMACCombines a hash function with MAC. Produces a hash of the message combined with a shared key.
Appends HMAC to the message.
Guarantees message hasn't changed and is from the expected sender - 20What is a digital signature?Verifies sender identity
- 21What are the 3 common digital signature algorithms?1. DSA (Digital Signing Algorithm) based off DH
2. RSA Signing based off RSA
3. ECDSA - 22What is a digital certificate?A certificate signed by a Certificate Authority (CA) to very the identity of a sender
- 23What's the sender verification process when connecting to a server?Receive their certificate
Verify genuinity of the sender using the associated CA's public key
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- Bachelors Degree Computer Science (Computer Security) Flashcards on Cryptography III, created by Alex Neves on 22/05/2016.
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- Alex Neves
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