Week 2: Secrecy and Security Goals

Question 1

Define “plaintext”.

Answer 1

Message to be encrypted.

Question 2

Define “ciphertext”.

Answer 2

Encrypted message.

Question 3

Define “key”.

Answer 3

Secret used to transform plaintext to ciphertext.

Question 4

Define “keyspace”

Answer 4

The set of all possible keys.

Question 5

How does the One-time pad work?

Answer 5

• Pad that is exactly as long as message is chosen at random
• Message + Pad = Ciphertext
• Pad is never used again

Question 6

What are the issues with One-time pad?

Answer 6

• Generation, transportation and storage of pad requires too many resources.

Question 7

What defines Computational Secrecy?

Answer 7

• Short fixed length key

- Crackable given enough computer power

Question 8

What are the two types of adversaries?

Answer 8

Passive - observes ciphertext

Active - modifies ciphertext

Question 9

What does CIA stand for?

Answer 9

Confidentiality, Integrity, Availability

Question 10

Define “Confidentiality”.

Answer 10

keeping message secret

Question 11

Define “Integrity”.

Answer 11

keeping message from being undetectably modified

Question 12

Define “Availability”.

Answer 12

sending/receiving message is available to users

Question 13

Why is CIA useful?

Answer 13

Security model that helps think about different security components.

Question 14

Can one property of CIA be guaranteed without others?

Answer 14

No.