Questions tagged [multiparty-computation]
Multi-party computation (MPC) allows a set of parties, each with a private input, to securely and jointly perform any computation over their inputs.
0
votes
1answer
31 views
Oblivious transfer with trusted third party Trent
I am trying to solve this exercise.
Assume an oblivious transfer protocol that uses a trusted third party Trent.
Alice's messages $M_0$ and $M_1$ are binary values of length $k$. Bob's message ...
0
votes
0answers
44 views
MPC using homomorphic encryption
Is there a way to implement secure square root protocol between two parties (using homomorphic encryption)?
I couldn't find existing solutions in literature.
My desired protocol is as follows:
...
2
votes
2answers
60 views
Algorithm for binary less than in MPC
Given binary shares $[a_{l-1}]_p,...,[a_0]_p, [b_{l-1}]_p,...,[b_0]_p$ such that $a = \sum_{i=0}^{l-1} a_i2^i,b = \sum_{i=0}^{l-1} b_i2^i $
for $a,b \in Z_p$, how to compute $a \overset{?}{\lt} b$ in ...
1
vote
1answer
92 views
Interactive Homomorphic Encryption
Let's say that I have a plain computational process that consists of several divisions and I do not want to do it with non-interactive homomorphic encryption.
I would like to ask how can I call this ...
2
votes
1answer
45 views
Blind Computation
Let's say that there are two parties. Party $A$ has ciphertexts $c_1, c_2$ encrypting data $m_1,m_2$ respectively. $A$ does not know the secret key to decrypt $c_1, c_2$. Party $B$ has the secret key.
...
6
votes
1answer
73 views
Algorithm for computing modular inverse in MPC
Is there any known algorithm for calculating $a^{-1} \pmod{q}$, where $ q < p$ and $F_{p}$ is the prime field of the MPC, in a linear secret sharing scheme ?
I have tried using the standard ...
6
votes
0answers
59 views
Distributed generation of random integers with prescribed sum
While reading this document I came across the following problem. Assume you have $n$ clients. The clients need to generate random integers in $\mathbb{Z}_p$, say $T_i$ for $i \in \{1, \ldots, n\}$, ...
0
votes
2answers
66 views
Difference between Zero Knowledge Proofs and Multi Party Computation
I am struggling with understanding the difference between the two. From what I am putting together, they have different adversarial models, MPC adds the condition of collusion between parties i.e. ...
0
votes
1answer
44 views
What (Where) is the formal definition of Multiparty Computation? [closed]
I'm just curious where we can see a (original) formal definition of MPC.
What (Where) is the formal definition of MPC?
We have a bunch of tools to build a MPC protocol.
Is oblivious transfer (or OT-...
4
votes
1answer
55 views
Under what conditions is broadcast possible? (Cryptographically, and in the model of Maurer 2006)
In this paper, Ueli Maurer uses a very cool model to generalize a number of results about broadcast, secret sharing and secure multiparty computation. Rather than talking about an adversary being ...
0
votes
0answers
44 views
How to ensure a trusted computing of a function in untrusted Cloud server?
Could you please let me know the latest practical techniques and cryptographic schemes that allow hiding function execution in an untrusted Cloud?
1
vote
2answers
64 views
Multi-secret sharing (Packed secret sharing) - Some questions
In the publication - "Communication complexity of secure computation", I have encountered a small problem - on page 5 of the literature under the heading "Theorem 1" they have described a $(c,d; k,n)$ ...
1
vote
1answer
66 views
Is the simulation-based proof difficult and needed? [closed]
What is the role for simulation-based proof under the semi-honest model without considering malicious adversaries?
I agree with that a view of a some party is important to prove that a protocol is ...
0
votes
1answer
50 views
MPC on boolean circuits
I am reading about Yao's and GMW protocols and was wondering if there is any perfectly secure MPC protocol in the semi-honest setting, where the underlying circuit is a Boolean circuit (eg. n=3 and t=...
2
votes
1answer
46 views
Commitment in two party protocols
I have been reading Fast Secure Two-Party ECDSA Signing by Lindell, and I see that in key generating and signing (pages 9-10, especially visible from Figure 1), only the first party performs a ...
3
votes
1answer
78 views
Testing whether a secret value is zero without security bits (in SPDZ)
To test whether a secret value $[x]$ is zero, where $x \in [0,2^{k−1}]$, SPDZ uses the a based on the method of Catrina and de Hoogh [1].
This method requires to working on a field with modulus $p>...
0
votes
0answers
33 views
Using SPDZ over smaller field
While trying to implement SPDZ of a function (using the fresco framework[1]),
it enforce me to work on a larger field than the one that I need.
This occur because I'm trying to use functions such as "...
0
votes
2answers
107 views
How to compute secure sum using secure multparty computation?
Suppose there are three voters $P$, $Q$ and $R$, and each will vote only on one candidate out of $X$, $Y$ or $Z$, with a 6 bit vote vector corresponding to $X
$, $Y$ and $Z$ respectively (with 2 bits ...
0
votes
0answers
26 views
Adding new participants to a multiparty signature scheme
I'm looking for a signature scheme that allows a group of N parties, without the help of a trusted dealer, to:
Jointly create a group public key $P$
Produce a valid signatures for an arbitrary ...
7
votes
3answers
132 views
How to determine the layers of a circuit?
In many cryptographic applications like Multiparty Computation (MPC) or Fully Homomorphic Encryption (FHE), you consider a function $f$ described by a circuit over some algebraic structure, typically ...
1
vote
1answer
39 views
In Multi-party communication, how can I find that one encrypted value is negative or not?
I'm using Pailier Cryptosystem as an additive homomorphic system in my scenario. I have two parties: Alice and Bob.
Alice has one pair of (SK, Pk) keys. She encryptes one value using her public key ...
2
votes
1answer
66 views
computing INV in boolean circuit for MPC
Is it feasible to generate an efficient MPC function that compute $a^{-1}$ for $a \in \mathbb{F_q}$, with Boolean circuit?
The naive way seems impossible since the depth of the computation might ...
2
votes
1answer
45 views
What is shared-input for Multi Party Computation?
I heard shared input.
For example, original values $x,y \in M$ are divided into pairs of shares $(x_1,x_2)$ and $(y_1, y_2)$ such that $x_1 + x_2 = x \text{ and } y_1 + y_2 = y$.
Each share is ...
1
vote
0answers
69 views
Multi-Party Offline Key Exchange Using Public and Private Keys
I hope the title already explains the problem I have in mind; but let me lay out some more details.
Given public-private key pairs $P_A, P_B, P_C, ... P_Z$, (first $3$ of which are owned by our usual ...
1
vote
0answers
27 views
complete functionality for fair multiparty computation
I found a statement in a paper "We reduce the fairness problem in MPC to the problem of fair decryption. Fair decryption was shown to be a complete functionality for fair MPC (shown by Dov Gordon in ...
1
vote
1answer
68 views
Check if $a<b$ in a trustless scenario
Let's say Alice has access only to a value $a$ and Bob has access to both $a$ and $b$. I need ...
1
vote
0answers
31 views
Threshold Bitcoin signature scheme
Any advice would be appreciated:
It seems to me that using an uncomplicated combination of a shamir scheme and schnorr it's fairly trivial to have a threshold signature scheme.
I think it's also ...
3
votes
2answers
158 views
How to use Homomorphic encryption for secure computing Arctan() function?
In the multi-party communication(MPC), if partyA has the coordinate(x1 y1) and partyB has the coordiante(x2,y2), how two parties can securely compute Arctan((y1-y2)/(x1-x2)) without revealing their ...
4
votes
2answers
122 views
Atomic multi-party commitments
Alice and Bob publicly choose the messages $M_A$ and $M_B$ and independently sign them (Alice privately signs $M_A$, Bob signs $M_B$).
Now Alice and Bob are looking for a protocol that allows them to:...
3
votes
3answers
71 views
communication efficient private lookup
I have a scenario where a client has a private set and the server has a large public set, we would like an estimate of the intersection size or more specifically the percent of the private set covered ...
1
vote
1answer
152 views
AES encryption using MPC SPDZ protocol
I'm reading the article about SPDZ protocol for secure multiparty computation (and also improvements for offline phase like MASCOT).
However I'm thinking about practical application of SPDZ for AES ...
3
votes
1answer
106 views
Can we convert a pseudorandom function (PRF) to an Oblivious PRF (OPRF) through an Oblivious Transfer (OT) protocol?
I'm a software engineer, so I generally think in building blocks. And I'm not so familiar with the Math notation in Crytography, so I'll stick with function calls and function blueprints (which I ...
2
votes
1answer
84 views
How can Alice enable Bob to look-up values in a private map
I think this problem is similar to private set intersection, yet distinct in a way where:
Alice has an extensive Mapping of say id to name
id1 -> John Doe
id2 -> Jane Doe
id3 -> Edgar ...
4
votes
1answer
96 views
Secure Computation: Reactive Functionalities in the Hybrid Model for Standalone Security
A common approach to make (secure computation) protocol descriptions and proofs simpler is to describe them in a hybrid model, where the protocol in the real world has access to some auxiliary ideal ...
2
votes
2answers
82 views
Multiparty secret generation protocol
The goal is to create a secret S on a trusted server by having users A, B and C each send a private seed to the server, in such a way that any 2 of them can later recover S by resubmitting their ...
1
vote
1answer
50 views
Difference in the Powers of Simulator and Environment in Universal Composability
I know that in UC model, environment controls the real world adversaries but there is still a simulator wrapped around these real-world adversaries in the ideal world (which we sometimes collectively ...
5
votes
1answer
132 views
Extractability for Simulator in Malicious Model
It is sometimes required while proving the security of a protocol in the malicious setting that the simulator is able to extract the witness set of the adversary, who tends to be the prover of ...
0
votes
1answer
32 views
Private set supporting adding elements and proving elements exist
Is it possible to construct such a set that parties can
Add elements to the set without revealing the elements or knowing the elements presently in the set.
Proving to other parties that a certain ...
0
votes
1answer
58 views
Enforcing Randomness in Malicious Setting
I was going through some lecture notes where it said that if we have a 2-party protocol that requires both the parties to generate random integers during the course of protocol, then if we migrate the ...
0
votes
0answers
31 views
Anti-collusion cryptography/schemes for multi party authentication
Due to the fact that 95+%, if I remember correctly, of security breaches are done by insiders (due to malicious intent or incompetence), I made a (experimental) server that uses Shamir Secret Sharing ...
6
votes
1answer
135 views
In coin flipping protocols, why aborting is allowed, and why the non-aborting party flips a coin at the end?
To convey how an adversary can bias the coin, most often a simple commitment-based two party coin-tossing protocol is given, as in [1]:
Alice sends Bob the commitment $c = commit(x)$
Bob sends Alice ...
0
votes
0answers
25 views
How to assert that n distinct users have generate an aggregate signature?
If We have n users, each one generate message m1 and signs it to generate (σ1).
then by using aggregate signature scheme, we get the aggregate signature of all messages m from n users.
Is there a ...
2
votes
1answer
96 views
About DDH over cyclic group Z*p^2
To construct a secure multiparty computation function, we need to use the cyclic group G = Z*p^2 with p is a large prime. However, we are uncertain that DDH holds over this group.
Can you show that ...
2
votes
0answers
55 views
Necessity of Randomness when Privately Computing a Sum
I want to show that no 1-private deterministic protocol exists for calculating a sum of $n \geq 3$ parties (within the realms of Perfect rather than Computational Security). I'm having trouble showing ...
1
vote
0answers
77 views
Optimized Random-OT Security in Standard Model
I was going through the paper - " Efficient Oblivious Transfer and
Extensions for Faster Secure Computation" by Asharov et al. where the authors propose an optimized OT protocol along with a Random-OT ...
2
votes
0answers
21 views
Computationally secure ORAMs with O(lg n)-bit words: shouldn't they fail with $n^{-O(1)}$ probability?
Virtually all "hierarchical" Oblivious RAMs use "cryptographically secure" hash functions to determine the position of an item at a given level; and implicitly assume (as can be evinced from the cost ...
5
votes
1answer
89 views
Can Secure Multi-party Computation be used to reconstruct secret shares?
When using Shamir's Secret Sharing is it possible to use Secure Multi-Party Computation to reconstruct the original secret without revealing one's secret share?
When searching I have found results ...
3
votes
1answer
43 views
Is it possible to carry out multiplication of BGW protocol without communication?
I read the following famous two papers related to multiparty computation and I have a question like title.
[AL17] Gilad Asharov, and Yehuda Lindell. "A full proof of the BGW
protocol for perfectly ...
1
vote
0answers
25 views
Secure multiparty computation connectivity bound
I read some papers which studied the relation between the fault tolerance in secure multiparty computation and the connectivity of the underlying communication graph. Here I consider information-...
0
votes
0answers
56 views
How to perform homomorphic multiplication using Shamirs secret sharing
Shamir's secret sharing (SSS) support additive homomorphism. The problem with it while dealing with multiplication is it will increase the polynomial degree and as a result number of shares required ...
