# Tagged Questions

Zero-knowledge proofs are an interactive method for one party to prove to another that a statement is true, without revealing anything other than the veracity of the statement.

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### Zero-knowledge proof for subset sum problem?

What is the currently most efficient (interactive) zero knowledge proof/argument for the subset sum problem? The most recent relevant paper I have found is Efficient Modular NIZK Arguments from Shift ...
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### Proof that a encrypted file has the same content as an (existing) original

Assume that Alice has a file F which she is going to send, in encrypted form, to Bob. Alice possesses F and the public encryption key K of Bob in form of an X509-certificate. She generates the file E ...
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### Verifying Without Knowing Key

Say user Bob sends an encrypted message to a server. People can download the message from this server and later get the key directly from Bob. Is it possible for the server to somehow verify that ...
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### Salary Negotiation Problem

Imagine Alice is applying for a new job. Alice has an idea of the minimum salary that she is willing to accept—let's call this value A. Bob, the hiring manager for ...
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### Zero-knowledge proof for the product of additive Paillier ciphers

Suppose that Alice received the cipher values: $E(x_1), E(x_2), ..., E(x_n)$ that are encrypted using Paillier cryptosystem by $n$ entities with Bob's public key. Alice computes $E(\sum x_i)$ from ...
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### How do they avoid Zero Knowledge Proofs in the paper Priced Oblivious Transfer: How to sell Digital Goods?

I don't understand a part of the paper Priced Oblivious Transfer - How to Sell Digital Goods. Particularly, the authors avoid using zero knowledge proofs and in section 3.3 they explain how they do ...
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### Why are zk-SNARKs possible, in layman's terms

zk-SNARK: Zero-Knowledge Succinct Non-interactive Argument of Knowledge From the Ethereum blog: One natural use case for the technology is in identity systems. For example, suppose that you want ...
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### The main differences between Sketch of Proof and Full proof

My question in general is: Question 1: What are the differences between sketch of proof and full proof? In simulation-based proof, in semi-honest model, we construct a view that is computationally ...
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### Simplified Fiat-Shamir example generates wrong output

I am trying to implement the Fiat-Shamir identification protocol, however the end results always fail to match. I am using algorithm's description from here. Preparation: Select 2 prime integers ...
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### What is the non-programmable random oracle model?

I would like to know the difference between the random oracle model and the non-programmable random oracle model. ​ What is the difference?
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### Zero-knowledge proof system which is not proof of knowledge?

I have learned that a zero-knowledge (ZK) proof system can be constructed by making use of the three-color problem. In this particular case, the proof system also happens to be proof of knowledge (POK)...
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### Zero knowledge-proof for discrete log that is not honest-verifier

Take a cyclic group of prime order. The Schnorr-protocol for proving knowledge of the discrete logarithm of some group element is honest-verifier zero-knowledge, meaning that if the verifier chooses ...
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### what is the difference between proofs and arguments of knowledge?

What is the difference between proofs and arguments of knowledge in the context of zero-knowledge? I have read this sentence in this ePrint: It is useful to distinguish between zero-knowledge ...
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### Two-party equality computation

Alice and Bob each secretly chooses an integer between 1 and 10, a and b. They want to know (with high probability) whether or ...
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### Why doesn't this operation reveal the voter's message?

I am working my way through this paper. I am trying to figure out the OR zero knowledge proof in figure 2. The prover is verifying that she has correctly voted, and that her input satisfies \log_gx=\...
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### Finding out the greater number under zero-knowledge conditions?

Is it possible to construct a zero knowledge proof that one encrypted number is larger (or not) than another encrypted number without releasing the values of either numbers?
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### Sigma-protocol for 3SAT problem

I have some questions from previous years exams, I hope you could help me with them. :) Let $g,h$ denote generators of a group $G$ of large prime order $n$ such that $\log_g h$ is unknown to anyone. ...
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### Zero Knowledge - Who is greater?

I just encountered the term "zero-knowledge" and wanted to know more about it. I understood that there is a zero knowledge protocol between two parties to determine whether $x$ is greater than, equal ...
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### Zero knowledge proof protocol example?

Alice is color blind. She never knows if her gloves are matched. Her brother Bob always teases her saying her gloves are mismatched and she should go change them. Alice wants to know if Bob ...
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### Homomorphism and Zero Knowledge in FIPS 140-2 compliant systems

I am analyzing a system that needs to be at least level 3 FIPS 140-2 compliant. The system may leverage from homomorphic and Zero Knowledge constructs, but, as far as I can see, the algorithms ...
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### Is there any zero-knowledge technique to verify proof of knowledge of shared secret key?

Generally, to verify knowledge/key generated between two interacting parties in an authentication protocol uses Hash, MAC, Digital Signatures or encryption (based on random challenge). But I would ...
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### Simulation based proofs: Simple examples

I am aware that,(in theory) in order to proof that a scheme is secure using simulation based proof we replace an adversary in real world with a simulator in ideal world. Then we try to show that their ...
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### Hamiltonian Path Zero Knowledge Proof using Commitments to a Series of Edges

Commonly, Zero Knowledge Proofs based on the Hamiltonian Path or Cycle problems are given as follows: The Prover has a graph $G$, for which he knows a Hamiltonian Path (or Cycle). $G$ is also known ...
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### In interactive proofs, do we assume that the prover can always solve the problem?

I'm having a difficult time understanding a concept from interactive proofs: A trivial interactive proof for the graph isomorphism problem is having the prover just send a permutation that shows an ...
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### What is an example of a secure sigma proof?

I want to implement Threshold Elgamal as described in section 6.3.1 and in the decryption phase each party must broadcast a sigma proof to show that it actually has a valid secret share of the secret ...
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### Hamiltonicity proof of knowledge

I'm learning the POK notion and definitions and as a self exercise I wante to prove the statement that the Hamiltonicity protocol is a POK system with knowledge error $1/2$. So the question will be ...
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### Proof that a hash matches an encrypted file

Assume that Alice has a file $F$ which she is going to send, in encrypted form to Bob. Alice possesses $F$ and an encryption key $K$. She sends to Bob the encryption of $F$ using $K$, $E(F,K)$ as ...
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### With ECDSA is there a way for the verifier to calculate any properties of $k$?

With ECDSA, given $(r,s)$ and $m$, is there a way for a verifier to calculate any (boolean) properties of $k$, without knowing $k$ or the private key $D_A$? (I understand that $k$ should be random, ...
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### How to prove knowledge of discrete logarithm in a product?

Definitions Suppose I have two large safe primes $p$ and $q$, and a composite number $N=pq$. I have $G$, a large cyclic subgroup of $\mathbb{Z}^{*}_{N}$; $g$ and $h$ are generators of $G$. I commit ...
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### How to prove that a commitment hides the decryption of an ElGamal ciphertext?

I've decided to remove a previous unanswered question of mine and break it down into smaller pieces so it's not such a loaded question. For this question I need to prove that I've committed to a ...
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### Is succinct verification of an arbitrary data transformation theoretically possible? Is it feasible? How?

Given input string S, and transformation (i.e. computer program) T, is it possible to provide a succinct proof that another binary string S' is identical to the output T(S)? By "succinct", I ...
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### Zero-Knowledge Proof of Subgraph Isomorphism

I'm trying to find a Zero-Knowledge proof of subgraph isomorphism in the following scenario: Alice and Bob both know about graphs G1 and ...
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### On the fly signatures and zero-knowledge

I am reading some articles which explain on the fly signatures (also called online/offine signatures). The principle is that a few operations do not depend of the message we want to sign, so these ...