Cryptography 2

Question	Answer
What is the importance of models and definitions?	Models and definitions aid understanding of the task to be achieved
What do threat models and security definitions enable?	Evaluation and comparison of schemes
What does a "clear" threat model and security definition allow?	Understanding of the security guarantees provided by the scheme
A clear threat model and security definition enables...	schemes to be used as components of a larger system (scheme modularity)
Cryptography currently requires 4 computational assumptions, one of which is... (1)	1. Allowing researchers to validate the assumption
Cryptography currently requires 4 computational assumptions, which are... (2)	2. Allowing meaningful comparison between schemes based on different assumptions
Cryptography currently requires 4 computational assumptions, which are... (3)	3. Practical implications in case assumptions are wrong
Cryptography currently requires 4 computational assumptions, which are... (4)	Enabling proofs for security
Skytale is an example of a...	transposition cipher
In a transposition cipher, what is kept the same and what is changed?	Letters are not changed, but letter order IS changed
The Caesar cipher is an example of a...	substitution cipher
In a substitution cipher, what is kept the same and what is changed?	Letters are changed but their order remains the same
When using modular arithmetic what are we looking for?	The number that occurs as a remainder when one number is divided by another
8 mod 3 = ?	2
means... Image: Image (binary/octet-stream)	the elements from {0...N-1}
(CAN...) Image: Image (binary/octet-stream)	Can be used to identify the alphabet in which A=0 ... Z=25
The caesar cipher has a shift amount of...	3
25 = 35 mod 10 why is this correct?	(25-35) = 10 which can be cleanly divided by 10
25 != (35 mod 10) why is this correct?	(35 mod 10) = 5 which is not equal to 25
5 = (35 mod 10) why is this correct?	(35 mod 10) = 5 which is equal to 5
Ring of Congruence Example [3] + [4] = [7] = [2] {... -8, -3, 2, 7 ... } What is the significance of Z5? Image: Image (binary/octet-stream)	ZN is the N that we use to divide... in this case 5
ROT13 is an X that has a key of Y	shift cipher that has a key of 13
The Vigenere cipher is...	polyalphabetic
The Vigenere cipher applies...	several substitution ciphers with different keys to different text positions

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