We propose Outfox, a packet format based on layered encryption that is suitable for mixnets in which all paths have the same length and where all mix nodes are associated with a single layer. Outfox is a variant of the packet format Sphinx that removes unnecessary padding and optimizes the computation cost of packet processing by halving the number of public key operations performed by mix nodes. Outfox uses a KEM scheme as a building block and is quantum-safe when instantiated with a quantum-safe KEM scheme. To analyze the security of Outfox, we describe an ideal functionality for a layered replyable mixnet that requires reply-request indistinguishability, and a construction based on Outfox that realizes our ideal functionality.

翻译：本文提出Outfox，一种基于分层加密的包格式，适用于所有路径长度相同且所有混合节点均与单一层相关联的混合网络。Outfox是Sphinx包格式的变体，通过消除不必要的填充并将混合节点执行的公钥操作数量减半，优化了包处理的计算开销。Outfox使用KEM方案作为构建模块，当采用抗量子KEM方案实例化时具备抗量子安全性。为分析Outfox的安全性，我们描述了一种要求回复请求不可区分性的分层可回复混合网络理想功能，并提出基于Outfox实现该理想功能的构造方案。