Introduction

The specification is based on Preliminary Research on Private Routing (Mixnet) and some modifications on Loopix and Nym.

The purposes of this specification:

evaluating the privacy level of our Mixnet design
providing a blueprint for the Mixnet development

Goals

The goals of Mixnet are described in the Preliminary Research on Private Routing (Mixnet), but here we describe them more in details to explain the development specification clearly.

Glossary

$\{S \rightarrow R\}$: a communication from the sender $S$ to the receiver $R$.
$\{S \rightarrow \}$: a communication from the sender $S$ to any receiver.
$\{S \nrightarrow \}$: no communication from the sender $S$ to any receiver.
$\{ \rightarrow R\}$: a communication from any sender to the receiver $R$.
$\{ \nrightarrow R\}$: no communication from any sender to the receiver $R$.

Security Goals & Approaches

We introduce 4 security goals and approaches for each security goals. Most approaches have been adopted from Loopix with some modifications. The biggest difference is that all communications in the Ouroboros-Crypsinous-like consensus model are broadcasting: $\{S \rightarrow [R_n]\}$, as described in Ouroboros Crypsinous Messaging Model

Sender-receiver third-party unlinkability
- The inability of the adversary to distinguish whether $\{S_1 \rightarrow R_1, S_2 \rightarrow R_2\}$ or $\{S_1 \rightarrow R_2, S_2 \rightarrow R_1\}$ for any concurrently online honest sender $S_1$, $S_2$ and honest receiver $R_1$, $R_2$ of the adversary’s choice.
- Approach: Layered mix + Delay (+ Cover traffic)
  - It’s enough to mix packets only before starting broadcasting, then a global adversary cannot know who the message sender is.
Sender online unobservability
- The inability of an adversary to decide whether a specific sender $S$ is communicating with any receiver, $\{S \rightarrow \}$ or not $\{S \nrightarrow \}$ , for any concurrently online honest sender $S$ of the adversary’s choice.
- Approach: Cover traffic