New answers tagged provable-security
0
This is part of how the notion of security is defined. In the definition, the adversary is an algorithm that produces a pair of messages, and then gets back (in return) a ciphertext. The adversary is then supposed to do something (predict whether the ciphertext is the encryption of the first message or the second message), but that's not relevant -- what ...
1
The adversary $\mathcal A$ is an entity (think of a computer program) designed to participate in the experiment $\operatorname{PrivK}^{\text{eav}}_{A,\Pi}$.
So the adversary produces two messages, then is given the encryption of one of them, and has to guess which one it was.
Of course, you can give the adversary other "ciphertexts" too, but this wouldn't ...
4
To prove that a scheme is not secure under such a definition you usually would propose an algorithm such that the experiment described in your question outputs $1$ with probability non-negligibly larger than $1/2$.
As this looks very much like a homework problem I will not give you a solution. However constructing the algorithm is actually very simple in ...
0
I assume that the paper you have read is the paper by Kobara and Imai in PKC 2001 (or its journal version), which proposed a padding scheme for the McEliece PKE scheme. In Lemma2, the authors showed CPA security of the padded scheme.
The first answer is NO. They are not.
Let $C(n,t) = \{z \mid z \in \{0,1\}^n, Hw(z) = t\}$, where $Hw(z)$ denotes $z$'s ...
5
Yes, your scheme is fine.
Nitpick: I think you mean that your goal is to generate a random number in the range $0\ldots n-1$ (not $0\ldots n$). Also, to avoid bias, you need to generate $m$ as a random number in the range $0 \ldots (\lfloor 2^{256}/n \rfloor \cdot n)-1$ (not $0\ldots \lfloor 2^{256}/n \rfloor \cdot n$).
This problem is known as secure ...
1
A standard approach in cryptography is to separate out the ideal specification (of what a scheme is supposed to achieve) from the particular instantiation (the implementation of the scheme).
To specify the security and functionality goals, sometimes cryptographers specify an "ideal functionality", which is an idealization of what we are hoping to achieve. ...
Top 50 recent answers are included
