HW4 Q1

HW4 Q1

student (guest) 19 Dec 2017 18:10

1. In subsection (a) : "Any scheme that is CPA-secure is also KPA-secure (in either the secret-key or public-key setting)". Just to make sure, does the part in parentheses mean that the proof should satisfy both settings or could be setting-specific ?

2. I understand that the definition given for the Known plaintext setting is completely not adaptive, as it should. Still, the adversary chooses the messages. How could it be considered to be a Known Plaintext ?

Re: HW4 Q1

nbitansky 19 Dec 2017 20:20

1. The proof is oblivious of whether it's the secret-key setting or the public-key setting.
2. You're asking for justification for the name, right? I think the answer would be "history". The sort of attacks that were originally considered (say in WWII) were weaker —- the attacker didn't really get to choose the messages, but could sometimes predict some of them. Today, the two definitions KPA vs CPA indeed focus on the adaptivity aspect.