nomos-specs/mixnet/mixnet.py

from __future__ import annotations

import random
from dataclasses import dataclass
from typing import List

from mixnet.fisheryates import FisherYates
from mixnet.node import MixNode


@dataclass
class Mixnet:
    mix_nodes: List[MixNode]

    # Build a new topology deterministically using an entropy.
    # The entropy is expected to be injected from outside.
    #
    # TODO: Implement constructing a new topology in advance to minimize the topology transition time.
    #       https://www.notion.so/Mixnet-Specification-807b624444a54a4b88afa1cc80e100c2?pvs=4#9a7f6089e210454bb11fe1c10fceff68
    def build_topology(
        self,
        entropy: bytes,
        n_layers: int,
        n_nodes_per_layer: int,
    ) -> MixnetTopology:
        num_nodes = n_nodes_per_layer * n_layers
        assert num_nodes < len(self.mix_nodes)

        shuffled = FisherYates.shuffle(self.mix_nodes, entropy)
        sampled = shuffled[:num_nodes]
        layers = []
        for l in range(n_layers):
            start = l * n_nodes_per_layer
            layer = sampled[start : start + n_nodes_per_layer]
            layers.append(layer)
        return MixnetTopology(layers)

    def choose_mixnode(self) -> MixNode:
        return random.choice(self.mix_nodes)


@dataclass
class MixnetTopology:
    layers: List[List[MixNode]]

    def generate_route(self) -> list[MixNode]:
        return [random.choice(layer) for layer in self.layers]