A Multiparty Commutative Hashing Protocol based on the Discrete Logarithm Problem

Abstract

Let $\mathcal{X}$ and $\mathcal{Y}$ be two sets and suppose that a set of participants $P=\{P_1,P_2,\dots,P_n\}$ would like to calculate the keyed hash value of some message $m\in\mathcal{X}$ known to a single participant in $P$ called the data owner. Also, suppose that each participant $P_i$ knows a secret value $x_i\in\mathcal{X}$. In this paper, we will propose a protocol that enables the participants in this setup to calculate the value $y=H(m,x_1,x_2,\dots ,x_n)$ of a hash function $H:\mathcal{X}^{n+1}\rightarrow\mathcal{Y}$ such that the function $H$ is a one-way function, participants in $P\backslash\{P_i\}$ cannot obtain $x_i$, participants other than the data owner cannot obtain $m$, and the hash value $y=H(m,x_1,x_2,\dots ,x_n)$ remains the same regardless the order of the secret $x_i$ values.