Defining Security Flashcards
Explain the Security Game for Factor(-ization). What is public and what is not?
Private values p & q.
Public value N(=p*q).
Adv. wins when it can guess p’ and q’ such that their product is N witout p’ or q’ being N (or 1).
Explain the Security Game for RSA. What is public and what is not?
Private values p & q.
Public value N(=p*q).
Private value d
Public value e and y (cipher text).
Adv. wins when it can guess x (plain text) such that x^e = y mod N.
What is the equivelent problem for the RSA security game?
If you can succesfully factorize the value of N into p and q, then computing Euler’s totient number (Phi) is possible, which can compute d from e. Hence if N can be factorized, Adversaty will always win the RSA game.
Explain how adversary can win the game with PRF?
It can win the prf security game if it succesfully determines wether the result of the prf (y) was computed from x or randomly picked from the co-domain. This is essentially a yes-no question.
When the adversery has no advantage with the prf security game, what can we conclude.
Because an Advesary is not able to distinguish between a computed and a random value, we can asume that the (psuedo random) function is a “safe” random function.
If the Advesary has a non-negligable advantage, the prf is not safe.
Why does the oracle store responses in prf security game?
Asume b=0, thus the output was generated randomly. Asking the oracle to produce a result twice, would then result in two different responses. Where in the case of b=1, the result would be deterministic. Hence, one can quickly determine the value of b.
Thisis why responses are stored, to be consistent.
Explain what a one way function is
Easy to compute, but difficult to inverse operation.
f.i. discrete log problem
Explain what a trapdoor one way funcion is (compared to regular OW)
Inverting the operation can be made easy with additional information.
Is RSA OW? or even a Trapdoor OW? and why
Trapdoor OW, when factors p and q are known, it is trivial to find d (given e).
Is private key used for encryption or decryption (RSA)?
decryption, only the owner can decrypt
Is public key used for encryption or decryption?
encryption, everyone can encrypt a designated message.
Explain Security Game of OW-PASS
One Way Passive Attack:
Given the encryption scheme and the cipher text, the adversary tries to produce the orginal plain text.
Explain Security Game of OW-CPA
One Way Chosen Plaintext Attack:
Given the encryption scheme and the cipher text, the adversary tries to produce the orginal plain text. The adversary has access to the encryption oracle, that can compute the cipher text (using the correct key), given a plaintext.
Explain Security Game of OW-CCA
One Way Chosen Cipher Attack:
Given the encryption scheme and the cipher text, the adversary tries to produce the orginal plain text. The adversary has access to the encryption oracle, that can compute the cipher text, given a plaintext. The Adversary has access to the decryption oracle, that can decrypt a cipher text to its plaintext (again, using the correct key).
The catch is that the Adversary is not allowed to supply the decryption oracle with the original challenger’s ciphertext.
What property must an encryption scheme not have in order to pass OW-CPA.
It must not be possible to detect any patterns or structure in the cipher texts. When you are able to detect a structure based on the results of the encryption oracle, the system is not OW-CPA secure.
