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Flashcards

Cryptography III

Alex Neves Computer Science Bachelors Degree Inglês 23 flashcards

Flashcards do conjunto (23)

  1. 1What is integer factorisation?Expressing an integer as the multiplication of a list of primes
  2. 2Why is it useful?Hard/Slow to compute for large values
  3. 3What is a semi-prime?A number which is the product of two primes (n = pq)
  4. 4What is Euler's Totient?The number of values between 1-(n-1) which are relatively prime with n
  5. 5What does relatively prime mean?A number is relatively prime with another if their GCD is 1
  6. 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)
  7. 7What is RSA?Asymmetric encryption algorithm used for encryption and authentication.
  8. 8What mathematical principle does it rely one?Integer factorisation
  9. 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
  10. 10How can we encrypt / decrypt with RSA?E: M^e mod n = C
    D: C^d mod n = M
  11. 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
  12. 12What is a hash function?Take any length message and produce a fixed-length hash
  13. 13What is it used for?- Message authentication
    - Message integrity
    - Passwords
  14. 14How are they constructed?From any block cipher in CBC mode
  15. 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)
  16. 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.
  17. 17What is a MAC?Message Authentication Code
  18. 18What is it used for?Authentication and integrity of messages
  19. 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
  20. 20What is a digital signature?Verifies sender identity
  21. 21What are the 3 common digital signature algorithms?1. DSA (Digital Signing Algorithm) based off DH
    2. RSA Signing based off RSA
    3. ECDSA
  22. 22What is a digital certificate?A certificate signed by a Certificate Authority (CA) to very the identity of a sender
  23. 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
    Continue communications

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Bachelors Degree Computer Science (Computer Security) FlashCards sobre Cryptography III, criado por Alex Neves em 22-05-2016.
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Alex Neves
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