Questions tagged [hard-core-predicate]
A hard-core predicate of a one-way function $f$ is a predicate b (i.e., a function whose output is a single bit) which is easy to compute (as a function of x) but is hard to compute given $f(x)$.
21 questions
0
votes
0
answers
51
views
Hard-Сore Functions and Hard-to-Approximate Functions
Definition of a hard-core:
Let $h: \{0, 1\}^* \rightarrow \{0, 1\}^*$ be a poly-time-computable function s.t. $|h(x)| = |h(y)| (\forall |x| = |y|)$ and let $l(n) := |h(1^n)|$
$h$ is a hard-core of a ...
- 1
1
vote
1
answer
120
views
Prove that there is no universal Hard-Core Predicates
A polynomial-time-computable predicate $b:\{0,1\}^* \to \{0,1\}$ is called a universal hard-core predicate if for every one-way function $f$, the predicate $b$ is a hard-core of $f$.
I need to prove ...
- 33
0
votes
0
answers
44
views
One way function bulit by singular matrices
Our one-way function $F:\mathbb{F}_q^{n\times n}\times \mathbb{F}_q^{n\times n}\to\mathbb{F}_q^{n\times n}$ differs from traditional OWFs, which focus on being hard to invert. Instead, ours aims to be ...
- 456
0
votes
0
answers
49
views
One-way function constructed by multivariable polynomials
Although the conjecture regarding the existence of one-way functions remained open, there are numerous NP-based methods for constructing diverse one-way functions, including DL, lattice, and subset ...
- 456
2
votes
1
answer
148
views
Goldreich Levin Theorem
I am running into the Goldreich Levin Theorem.
According to what I know a predicate $h: \{ 0,1 \}^* \to \{ 0,1 \} $ is a hardcore predicate for a function $f: \{ 0,1 \}^* \to \{ 0,1 \}^* $ if:
$h$ is ...
- 123
1
vote
1
answer
133
views
Question on Simulation based security proof for Oblivious Transfer (OT) against semi-honest adversaries
I'm currently reading this How To Simulate It – A Tutorial on the Simulation Proof Technique.
On p. 10, there is a proof using simulation for 1/2-OT, against semi-honest adversaries. Briefly, the ...
- 992
1
vote
1
answer
628
views
Suppose there exists a one-way function, show that there exists a one-way function with none of its input bit is a hardcore bit
I just learnt the definition of hardcore bit, and I have no intuition about this. I want to know what are the possible approaches to this problem.
- 31
0
votes
0
answers
50
views
PRGs from OW functions
Given a OW function $f:\{0,1\}^n\to\{0,1\}^n$ with hardcore predicate $h(x)$, you can build a PRG $G$ by setting $$G(s):=f(s)\Vert h(s), \quad s\leftarrow\{0,1\}^n.$$
The expansion condition for $G$ ...
0
votes
0
answers
193
views
XOR of all bits of $f(x)$ a hard-core bit
Why consider a random $r$ in building a hardcore predicate in Goldreich Levin theorem? Why not consider just the XOR of all bits of the input?
- 261
3
votes
1
answer
187
views
Understanding Lindell's proof of (semi-honest) oblivous transfer
In Lindell's tutorial "How to simulate it" [2016/046], section 4.3, he gives a semi-honest protocol for oblivious transfer, based on enhanced trapdoor permutations and a corresponding hard-...
- 461
3
votes
1
answer
271
views
Hard-core bits from RSA assumption
I am trying to understand better the hard-core bit property from the RSA assumption. The paper by Håstad and Nåslund shows that every single bit is hard-core. By the result itself, two or more bits ...
- 295
0
votes
0
answers
322
views
How to prove that a predicate is not hard-core?
How can I prove that given a predicate $hc$ and a one-way function $f$ that $hc$ is not hard-core?
I was thinking about something like that:
i define $f(x) = (g(x), hc(x))$ that is one-way but $hc$ ...
- 63
3
votes
0
answers
170
views
Does weak hardcore bit(s) implies strong hardcore bit(s)?
It is well known that weak OWF implies strong OWF
by concatenating several evaluations of weak OWF (see e.g. here),
where weak OWF is defined as
$ \exists $ poly $Q$, $\forall$ PPT $\mathcal A$ such ...
- 31
1
vote
1
answer
236
views
A modification of the Blum-Micali construction
Consider the following modification of the Blum-Micalli construction (denoted by BM):
$G_l(x) = f^l(x) || BM^l(x)$
I am asked the following questions about it:
Show it is a PRG of fixed stretch ...
- 1,243
3
votes
1
answer
501
views
Why can't we construct a PRG from a one-way function and hc, but only one-way permutation
From Katz & Lindell's book, theorem 7.19:
Let f be a one way permutation with hard-core predicate hc.
Then the algorithm $G(s)=f(s)||hc(s)$ is a PRG with expansion factor $\ell(n)=n+1$.
But what ...
- 31
0
votes
1
answer
1k
views
Katz/Lindell Problem 7.6
Let $f$ be a length-preserving one-way function, and let $\text{hc}$ be a hard-core predicate of $f$. Define $G$ as $G(x)=f(x)\|\text{hc}(x)$. Is $G$ necessarily a pseudorandom generator?
The answer ...
- 468
1
vote
0
answers
85
views
Lsb as hard core predicate in a sign-hash scheme
Given a random oracle and a deterministic signature scheme.
Is the following $hc(x)$ an hardcore predicate of $H(SIG_k(x))$ ?
$$hc(x)=lsb(H(SIG_k(x)))$$
How would I get to think about this? I saw a ...
- 793
1
vote
0
answers
456
views
Generic hardcore predicate for one way functions
I'm going over hardcore predicates now and trying to understand the concept.
Some lecture slides I've seen online imply that there cannot be a generic hardcore predicate for all one way functions ...
- 225
0
votes
1
answer
261
views
What Does This Symbol Mean? (Hardcore Predicates for One-Way Functions)
I am studying Pseudorandom Number Generators and when reading the discussion on One-Way Functions and Hardcore Predicates, I came upon this equation.
$$b(x,r)=\displaystyle \bigoplus_jx_jr_j$$
I ...
- 33
0
votes
0
answers
455
views
what is the difference between one way function and hard core predicate?
Does anyone know what the difference between a one way function is and a hard core predicate? Are they related to each other or different?
- 1
4
votes
1
answer
827
views
Hard-core predicates: should the adversary be given $1^n$?
In most (all?) classical sources such as the book of Goldreich (2001), hard-core predicated are defined thus:
A polynomial-time computable predicate $b : \{0,1\}^* \to \{0,1\}$ is a hard-core of a ...
- 8,202