ThresholdandMulti-signatureSchemesfromLinearHashFunctions
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发布时间: 2025-08-31 01:39:25 阅读量: 4 订阅数: 14 AIGC 

# Threshold and Multi-signature Schemes from Linear Hash Functions
## 1. Introduction
Linear hash functions offer a new perspective for constructing threshold and multi - signature schemes. We first define a function $\Phi(x) := x + u(B)z^{\ast}$, where $z^{\ast} \in D$ and $u(B) \in S^q$ are defined by the following claim.
### 1.1 Claim 2
There exists $z^{\ast} \in D$ such that $F(z^{\ast}) = 0$ and for any matrix $A \in S^{\ell\times q}$ where $0 < \ell < q$, there exists a vector $u(A) \in S^q$ and $i \in [q]$ such that $Au(A) = 0 \land \exists i \in [q] : u(A)_i z^{\ast} \neq 0$.
**Proof**: Since $F$ is not a monomorphism from $D$ to $R$, there exists a non - zero element $z^{\ast} \in D$ such that $F(z^{\ast}) = 0$. As $S$ is a field and $A$ has rank at most $\ell < q$, there exists a non - zero vector $u(A) \in S^q$ such that $Au(A) = 0$. Also, since $u(A)$ is non - zero, there exists $i \in [q]$ such that $u(A)_i \neq 0$, and since $S$ is a field and $z^{\ast} \neq 0$, we have $u(A)_i z^{\ast} \neq 0$.
### 1.2 Analysis of $\Phi$
- **Execution identity**: For simplicity, let $u = u(B)$. The executions of $A$ given $(par, x)$ and $(par, \Phi(x))$ are identical. Since $F(\Phi(x)) = F(x)+u\cdot F(z^{\ast}) = F(x)$, the challenges output by $Chal$ are the same. For the $j$ - th query to $PI$, if the prior views of $A$ are identical, $A$ makes the same query. Also, $A$ receives the same value from $PI$ in both executions. By induction, the views of $A$ are identical, so $\Phi(x) \in W_A$ and $\Phi$ is a map from $W_A$ to $W_A$.
- **Winning condition**: It is clear that $x \in W_B \vee \Phi(x) \in W_B$. Since the executions of $A$ given $x$ and $\Phi(x)$ are identical, and there exists $i \in [q]$ such that $u_iz^{\ast} \neq 0$, either $y_i \neq x_i$ or $y_i \neq x_i + u_i\cdot z^{\ast}$, meaning $WIN_B$ occurs either in the execution given $x$ or $\Phi(x)$.
- **Bijection proof**: Since the domain and range of $\Phi$ are $W_A$ (a finite set), it suffices to show $\Phi$ is an injection. For any $x_1,x_2 \in W_A$ such that $\Phi(x_1)=\Phi(x_2)$, the executions of $A$ given $x_1$ and $x_2$ are identical, so the query matrix $B$ is the same. Then $\Phi(x_1)=x_1 + uz^{\ast}$ and $\Phi(x_2)=x_2 + uz^{\ast}$, which implies $x_1 = x_2$. So $\Phi$ is an injection.
## 2. Schemes Based on Linear Hash Functions
A cyclic group $G$ of prime size $p$ with generator $g$ can be related to a linear hash function described by $(S, D, R, F)$. Here, $R$ corresponds to the group $G$, the pre - image under $F$ corresponds to the discrete logarithm to base $g$, and $S$ corresponds to the field of scalar $\mathbb{Z}_p$. The $AOMPR$ game is analogous to the $AOMDL$ game, suggesting a way to transform $AOMDL$ - secure schemes into $AOMPR$ - secure schemes based on linear hash functions.
### 2.1 Multi - signatures
#### 2.1.1 MuSig2 Overview
MuSig2 is a two - round multi - signature scheme with key aggregation, and the first signing round is message - independent.
#### 2.1.2 Syntax
A two - round multi - signature scheme with key aggregation is a tuple of algorithms $MS=(Setup, KeyGen, KeyAgg, PreSign, PreAgg, Sign, SignAgg, Ver)$:
| Algorithm | Function |
| --- | --- |
| $Setup(1^{\kappa})$ | Returns a system parameter $par$ |
| $KeyGen()$ | Returns a pair of secret and public keys $(sk, pk)$ |
| $KeyAgg(L)$ | Takes a multiset of public keys $L$ (size at most $2^{\kappa}$) and returns an aggregate public key $apk$ |
| $PreSign()$ | Each signer runs this to get $(pp, st)$ |
| $PreAgg(\{pp_1,\cdots,pp_n\})$ | Aggregator runs this to get $app$ |
| $Sign(st, app, sk, pk, m, L)$ | Signer runs this to get $out$ |
| $SignAgg(\{out_1,\cdots,out_n\})$ | Aggregator runs this to get the signature $\sigma$ |
| $Ver(apk, m, \sigma)$ | Verifies if $\sigma$ is valid for $apk$ and $m$ |
The signing protocol for $n$ signers to sign a message $m$ is as follows:
```mermaid
graph LR
classDef startend fill:#F5EBFF,stroke:#BE8FED,stroke - width:2px
classDef process fill:#E5F6FF,stroke:#73A6FF,stroke - width:2px
A([Start]):::startend --> B(Each signer: <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> 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