In this work we construct an alternative Unauthenticated Model, intended to build a theoretic security framework to cover communications protocols whose characteristics may not always concur with the specifics of already existing models for authenticated exchanges. This model is constructed from the notion of commitment schemes, employing ephemeral information, therefore avoiding the exchange of long-term cryptographic material. From this model, we propose a number of Commitment-based protocols to establish a shared secret between two parties, and study their resistance over unauthenticated channels. This means analyzing the security of the protocol itself, and its robustness against Man-in-the-Middle attacks, by formalizing their security under this model. The key-exchange protocols are constructed from KEX and KEM primitives, to show that this model can be applied to both established and new paradigms. We highlight the differences that arise naturally, due to the nature of KEM constructions, in terms of the protocol itself and the types of attacks that they are subject to. We provide practical go-to protocols instances to migrate to, both for KEM-based and KEX-based cryptographic primitives.

翻译：本文构建了一种替代性的未认证模型，旨在建立一个理论安全框架，以涵盖那些特性可能不完全符合现有认证交换模型具体要求的通信协议。该模型基于承诺方案的概念构建，采用临时性信息，从而避免了长期密码材料的交换。基于此模型，我们提出了若干基于承诺的协议以实现双方共享密钥的建立，并研究其在未认证信道下的抗攻击能力。这意味着需要通过在该模型下形式化协议的安全性，分析协议自身的安全性及其对中间人攻击的鲁棒性。密钥交换协议基于KEX和KEM原语构建，以证明该模型可同时适用于既有范式与新兴范式。我们重点阐述了因KEM构造特性而自然产生的差异，包括协议本身及其所面临攻击类型的差异。针对基于KEM和基于KEX的密码原语，我们提供了可直接迁移使用的实用协议实例。