Questions tagged [hardness-assumptions]
Mathematical problems that are thought to be difficult to solve for all cases in polynomial time
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What does the "static" assumption mean?
We can prove the security of a cryptographic scheme in standard model and non-standard model.
Standard models like using some computational assumptions, on the other hand, non-standard models like ...
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Special indistinguishability problem
I need some help for the following simple game:
An adversary is given a multiplicative group $\mathbb{G}$ and the 4-tuple $(g_1, g_2, g_3, g_1^a \cdot g_2^b \cdot g_3^c)$ where $g_1$, $g_2$ and $g_3$ ...
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(type-3) Variant of the decisional Diffie-Hellman
At a high level, the Uber assumption states that it is not possible to compute (distinguish) linearly independent elements. In the decisional version, the problem is restricted to $G_T$, but it is ...
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Average- and worst-case complexity
The terms "average-case", "worst-case" hardness are quite confusing.
What do they mean when they say certain problems (like lattices)
have an average-case to worst-case ...
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Given two unrelated generators $G_1$ and $G_2$, and a third with $H = G_1 + G_2$. Is it hard to compute $xG_1$ from $xH$?
Given some group in which both discrete logarithms and the computational Diffie-Hellman problem are hard. Furthermore, two random, unrelated group generators $G_1, G_2$, and a third generator defined ...
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What's wrong with this simple reduction of discrete logarithms to the Diffie-Hellman problem?
This recent paper shows that discrete logarithms are solvable if you have an oracle for the Diffie–Hellman problem. However, to me, it seems there is a much simpler reduction and I wonder where I am ...
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Is the composite order matrix-DDH secure?
I recently read a paper that proposed a matrix-DDH which is a matrix variant of DDH assumption. The brief definition is follows:
Let $G$ be a group of prime order $q$.
Then, the matrix-DDH says that ...
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Variant of Decisional Diffie Hellman
Given a cryptographic prime $p$ and a generator $g$ of $\mathbb{F}_p$, the Decisional Diffie Hellman problem asks us to distinguish
$(g^a, g^b, g^{ab})$ from $(g^a, g^b, g^z)$ for random $a, b, z$. ...
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Hardness of a modified version of NTRU
Let the modified NTRU be $h=f/g$ such that $f$ is not necessarily a short polynomial, is the NTRU problem still hard in this case?
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A random access machine with lots of random data on its tape is a stronger assumption than the existence of OWFs
Suppose we have a random access machine with $(n+1)2^n$ random bits on its tape. This assumption is weaker than assuming the existence of a random oracle, but using this assumption we can construct a ...
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Two LWE samples with the same secret
I am considering the following problem related to Learning with Errors. Recall that the LWE assumption is that no adversary can distinguish $(A,As+e)$ from $(A,u)$ with non-negligible advantage, where ...
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When does the need of random data become an assumption?
Suppose an encrypion scheme uses a random string to encrypt and decrypt, which is publicly available, such as an IV or nonce. In all the cases I am aware of, the existence of say an IV is not "...
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Proving stategies for computational properties
As far as I understand, a property is computational if it holds in a computationally-bounded context, so for ANY computationally-bounded involved entity (even if an unbounded one could discover the ...
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Models and assumptions in the post quantum world
I'm currently trying to get an overview of post-quantum cryptography. Now I'm struggling with correlations and adjustments of the PQ-world and the Modern-world of cryptography.
My Questions:
Can you ...
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What kind of assumptions usually go into the design of block ciphers?
What are some standard assumptions made in showing the security of a block cipher?
For example, is it commonly assumed that $P\not=NP$? To this end, are there any block ciphers whose security does ...
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Why is the discrete logarithm problem hard?
Why is the discrete logarithm problem assumed to be hard?
Someone else asked the same question but the answers only explain that exponentiation is in $O(\log(n))$ while the fastest known algorithms to ...
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Breaking CDH also breaks DHI
I am trying to show that by breaking the Computational Diffie-Hellmann (CDH) assumption one also breaks the Diffie-Hellmann inverse assumption. Unfortunately, I am a bit stuck and do not know where to ...
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Definition of Multilin DDH
I am on the abbreviation mutlin. DDH, which probably stands for mutliniear Decision Diffie Hellmann. I am currently looking for a definition for this term, but unfortunately cannot find a source. Can ...
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Definition of the strong Diffie Hellman problem
I am looking for the definition of the strong Diffie Hellmann problem. However, I can only find definitions for the $\ell$ or $q$-strong Diffie Hellmann.
Is it possible that the strong Diffie Hellman ...
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LWE with the matrix A repeated
Consider the following version of Learning With Errors.
You are either given $(A, As_1 + e_1, As_2 + e_2, \ldots, As_k + e_k)$ or $(A, u_1, u_2, \ldots, u_k)$, where
$A$ is an $m \times n$ matrix ...
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Can Shor's algorithm factor over finite fields/rings/groups?
Shor's algorithm can (efficiently) solve equations of the form:
$$n = pq$$
and
$$n = x^{2} + y^{2}$$
This question is simple: Can Shor's algorithm solve these equations in polynomial time when they ...
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Can Shor's algorithm factor over the gaussian integers?
This is related to this question about solving the following expression:
$$x^{2} + y^{2}$$
This can be factored over the gaussian integers as
$$(x + iy)(x - iy)$$
If one could factor a sum of two ...
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Why RLWE is lighter than LWE and why we can pick $a_i$ as a permutation of $a_1$ in RLWE but not LWE?
In LWE, we have
$$<a_1,s> + e + \mu_1\in \mathbb{Z}_q$$
for a secret key $s\in \{0,1\}^n$ and $a_1\in \mathbb{Z}_q^n$
This is an encryption of a number $\mu_1$. If we want to encrypt $n$ ...
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What does hard instance mean in cryptography?
I'm learning cryptography recently. I read that for game-based formal security analysis, it is important to embed the hard instance during reduction. Does "hard instance" mean hard-to-solve ...
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The existence of OWFs vs $\mathbf{EXP} \neq \mathbf{BPP}$
In CRYPTO 2021, Liu and Pass published a paper with title "On the Possibility of Basing Cryptography on $\mathbf{EXP} \neq \mathbf{BPP}$.
One of the main results of this work can be interpreted ...
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LWE and extended trapdoor claw free functions
Let $q \geq 2$ be a prime integer. Consider two functions, given by:
$$f(b, x) = Ax + b \cdot u + e~~~(\text{mod}~q),$$
$$g(b, x) = Ax + b \cdot (As + e') + e~~~(\text{mod}~q),$$
where we have:
\begin{...
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Hardness of a variant of the CDH problem
Given $g$, a generator of a multiplicative group (over some finite field or elliptic curve), and the group elements $\left( g^x, g^a, g^b, g^c, g^{x(a+b)}, g^{x(b+c)} \right)$, is possible to ...
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Which of the following is considered cryptographically hard/easy?
Which of the following are easy, if any? Which are hard? and why.
Case 1) Given $x^3 \bmod N$, where $N$ is a composite number and we don't know any of the factors of $N$, find $x$.
Case 2) Given $x^...
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What are security reductions of symmetric-key algorithms?
I was reading Wikipedia page of post-quantum cryptography. It says that it is desirable for cryptographic algorithms to be reducible to some particular mathematical problem, that is intractability of ...
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Solve DLOG using a probabilistic algorithm for DLOG lsb
Following the question Can I know from a Bitcoin public key if the private key is odd or even?
The answer there gives a simple algorithm for solving the Discrete Logarithm Problem when given an oracle ...
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Would being able of factoring integers efficiently have some consequences over Elliptic Curve Cryptography?
Let's assume you can factor integers in a very efficient manner. Would that endanger the security of e.g. elliptic curve cryptography, or is there no link between the two ? You can often read that ...
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DDH to DLIN reduction
I read multiple times that it should be feasible to show a reductions from Decisional Diffie Hellmann. Could you give examples?
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Developments in ABE using Pairings
What are the recent developments in Attribute-Based Encryption (ABE) using Pairings assumptions?
Is pairings the most viable assumption while designing ABE. What other assumptions are used for ABE ...
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Strong Diffie Hellman in bilinear groups
The $n$-strong Diffie Hellman assumption state that given the subset $\{g, g^s,\cdots,g^{s^n}\} \subseteq \mathbb{G}$ in a cyclic group $\mathbb{G}$ of prime order $p$, a PPT algorithm cannot output $...
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Does breaking CDH also break DLP? [duplicate]
Does breaking the computational Diffie-Hellman problem in a group also always break discrete logarithms in that group?
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The security of DDH with multiple instances?
Let $G$ be a finite group of prime order $p$, and $g$ a generator of $G$.
The standard DDH is hard to distinguish two distributions
$$
\{ (g, g^a, g^b, g^{ab}) : a, b \leftarrow \mathbb{Z}_p\} \text{ ...
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Decisional Diffie-Hellman Assumption over Group of Quadratic Residue
Consider the Decision Diffie-Hellman (DDH) over $QR_n$ (the quadratic residue group over $n=pq$ where $p$ and $q$ are safe primes).According to Boneh's paper, DDH should be hard over $QR_n$ (https://...
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Linking Decisional Diffie-Hellman, Discrete Logarithm, and Knowledge of Exponent Assumptions
I'm curious about the relation between the Discrete Logarithm and Decisional Diffie-Hellman. Is it safe to have an assumption like the following to link the two?
Given uniformly and independently ...
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Small modulus to noise ration in LWE implies better security
I don't quite understand why a smaller quotient between modulus $q$ and the noise's standard deviation implies better security against known attacks.
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Group of quadratic residue over Blum integer
Let $x$ be a random element from $QR_n$, the quadratic residue group over Blum integer n (where $n=p*q$ and $p$ and $q$ are safe primes), and $g$ a generator of $QR_n$. Are the following ...
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Is there any relation between Decisional Composite Residuosity Assumption and Square roots in elliptic curve groups assumption?
We have DCRA and ECSQRT assumptions.
ECSQRT: Square roots in elliptic curve groups over Z/nZ
Definition: Let E(Z/nZ) be the elliptic curve group over Z/nZ. Given a point Q ∈ E(Z/nZ). Compute all ...
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Gap between DLog and CDH
Is there any concrete group in which one CDH is exponentially easier (even it's still hard) than DLog.
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Choosing rings for PLWE
In [ELOS15], the authors give an attack on RLWE, and claim that "the hardness of Ring-LWE is...
dependent on special properties of the number field" chosen; whereas, responding to prior ...
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Hard instances of matrix factorization
Are there any hard problems related to matrix factorization?
Suppose $E$ is hermitian with public eigenvectors such that $U^T\Lambda U = E$ with $U$ public but $E,\Lambda$ secret. Given $X$ secret, we ...
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Hard Problems in Pairings
I want to know whether the following problem is considered as a hard problem in complexity theory or not?
Given $g,g^a,g^b \in G_1$ (for unknown $a,b\in \mathbb{Z}_p^{\ast}$), compute $e(g,g)^{ab^2}\...
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Is this an instance of a Diffie-Hellman problem?
Let $\mathbb{G}$ be a cyclic group of order $p$ with generator $g$, and let $m\in\mathbb{G}$.
Problem: Given $c=m.g^{k.a}$ and $v=g^a$, where $k,a \in \mathbb{Z}^*_p$, output $k$.
Is this an instance ...
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Is this asymmetric (public key) cryptosystem based on a 16x16 s-table safe and useful?
May be this is absolutely off-topic, but here is. The cryptosystem description follows. Any hints of what to do with it, or flaws found are welcomed.
This description is here as well.
We will use a ...
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Weak Decisional Diffie-Hellman Problem
Is this problem still hard?
Given $$(g,g^a,g^b,c)$$ decide if $c=a\cdot b$?
If there is an adversary that solves the standard Decisional Diffie-Hellman Problem then it can solve my new problem. But I ...
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Is this problem with anti-circulant matrices hard?
If there is an obvious way to solve this problem, please give it a chance before downvoting, I beg you. Also, some insight into the resultant asymmetric cryptosystem will be welcomed (described in the ...
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what is the probability for an adversary to find the new key after adding new entropy in a group where computational diffie hellman is hard?
Let's say I have an Elliptic curve group $E(\mathbb{F}_q)$ with base Point $G$ and large prime order $n$. Computational Diffie-Hellman is assumed to be hard in that group.
$H: \{0,1\}^*\rightarrow \{...
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