Questions tagged [universal-composability]

The framework of universal composability (UC) is a general-purpose model for the analysis of cryptographic protocols.

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How to write proofs for universal composable security?

Recently, I learn Ran Canetti's famous paper, "Universally Composable Security: A New Paradigm for Cryptographic Protocols". But I find it very difficult to grasp. When I read the paper that ...
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Security proof regarding a zero-knowledge counterexample that is secure in the stand-alone model but insecure in the UC model

Background The following zero-knowledge (ZK) counterexample is described in Canetti's work [Security and Composition of Cryptographic Protocols: A Tutorial, page 26] to show that there exists some ...
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Failure of parallel composition

Is there a simple example of a cryptographic protocol that is secure when used on its own (with only one instance active at a time) but becomes insecure in a concurrent setting, i.e., a failure of ...
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Can ideal functionalities share variables

I am trying to define an ideal world for a protocol that requires two functionalities to interact with each other. Lets call them $\mathcal{F}_1$ and $\mathcal{F}_2$. Now $\mathcal{F}_1$ maintains a ...
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Are zkSTARKs simulation sound extractable in the random oracle model?

I've recently become interested in simulation sound extractable zero-knowledge proofs for use in UC-secure protocols. I've also become interested in the recent instantiation of PCIPs called zkSTARKs. ...
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Detail about reactive simulatability framework

I'm trying to understand the framework of reactive simulatability using *"PfWa2_00AsyncModel"* from this publication which is a tech report behind the paper A model for Asynchronous Reactive Systems ...
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Formal Verification for Multiparty Computation and Homomorphic Encryption?

I've recently found some work on the use of Formal Verification Software, like ProVerif for enclaves. I wonder is if its feasible to have something similar for MPC and Homomorphic Encryption and ...
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Session IDs in (simple) universal composability

In the simple UC framework paper, there is a brief discussion on session identifiers (sids) on page 13. It states The main protocol is given a session identifier sid but it is not entirely clear to ...
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Universal composability: Can an ideal functionality call other ideal functionalities?

I'm new to universal composability. I'm trying to define a protocol, $\pi$, in UC. The protocol involves 3 parties: A, B, and a smart contract $C$. Parties A and B interact with each other and with $C$...
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37 views

Abstract Cryptography: why local simulators?

In the paper that introduced Abstract Crypto [MauRen11], the Theorem 2 page 15 states that, basically, if there exists some local simulators that can be pluged on a resource $S$ such that this new ...
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147 views

Why is this functionality chosen for UC-NIZK?

A correct proof (a proof which is indistinguishable from previously sent proof) can be tagged as wrong by the ideal functionality here if the adversary sends no witness. And, let's say P is a party ...
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Efficient universally composable protocols for aggregate statistics

Let's say we have multiple parties $P_1, \dots P_n$ that gather personal data, and a party $C$ that is interested in aggregate statistics on these data, i.e. the average value. An ideal functionality ...
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Proofs of security for anonymity in a multi-party setting

I'm looking for material that proves the anonymity of parties in a non-interactive setting. I would like to know if there are simulation based proofs (UC) and property based proofs (game based) for ...
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Are theorems 2 and 3 in the Town Crier paper (Zhang et al, 2016) proven using the UC framework?

I am reading the paper ‘Town Crier: An Authenticated Data Feed for Smart Contracts’ by Zhang et al (2016), but there is something I just cannot wrap my head around. In Section 7 and Appendix C, it ...
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Why a simulator can obtain a corrupted party's input to some subrountine ideal functionality $F$ "for free" in $F$-hybrid model?

In "How To Simulate It" (page 45, line 10), Lindell noted that, in the $f_{\textsf{zk}}$-hybrid model (where $f_{\textsf{zk}}$ denotes the ideal zero-knowledge functionality) in the stand-...
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UC-secure commitment in the ROM

Looking at the question Is this a UC-secure commitment scheme in the ROM?, I was wondering, is the commitment scheme proposed in the answer (which uses $H(M||r)$ as commit) secure in the UC-model, ...