Summary: Security And Cryptography

Read the summary and the most important questions on Security and cryptography

• Lecture 4

  This is a preview. There are 3 more flashcards available for chapter 21/09/2016
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• What happens in the initial round of the AES algorithm?

  : Left matrix is text, middle matrix is key.

• Give the definitions of divisor, prime, GCD and co-prime

  Co-prime = relative prime.

• On what problem is the Al Gamal algorithm based? Give the 3 steps of the algorithm:

  Based on the discrete log problem. Steps are equal to RSA!

• Lecture 6

  This is a preview. There are 3 more flashcards available for chapter 28/09/2016
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• What is the maximum period for a feedback shift register with m registers?

  2^{m}-1

• It is shown that LFSR is not safe when 2m bits plain/ciphertext, what are possible solutions?

  1. Use multiplexer to combine multiple LFSR.
  2. Use non-linear FSR

• Lecture 7

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• What hash function is currently the standard? What family is it from? Name some other hashing functions from this family.

  SHA-3

• Lecture 8

  This is a preview. There are 7 more flashcards available for chapter 05/10/2016
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• What are the two purposes of digital signatures?

  1. Message integrity: message is not altered during transmission
  2. Source authentication: the source of the message is verified

• Lecture 10

  This is a preview. There are 7 more flashcards available for chapter 12/10/2016
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• Show an example of DES-MAC and explain the benefit compared with using a simple hash function:

  : Benefit is that for a simple hash function an attacker can easily replace the hash string for his modified message, and pretend as if that is the 'original hash string'. DES-MAC relies on a key that only Alice and Bob know. This key is used to calculate the MAC.

• Show how a symmetric algorithm is used in CFB mode.

  : Only interesting if you want blocks smaller than 64 bits.

• Show how a symmetric algorithm is used in CTR mode.

  You can now decrypt in an arbitrary sequence: