Foundations of Secure Storage for Encrypted Instant Messaging

在现代密码学中，构建和分析安全协议的黄金标准是首先定义一个安全模型，该模型以数学精确的方式指定协议的使用和攻击者的能力，然后通过简化定义良好的计算硬度假设(即。“可证明的安全性”方法)。在即时消息环境中安全存储消息和媒体的上下文中，尽管这个主题具有巨大的实际重要性，但我们仍然缺乏这种级别的安全性声明的清晰度和严谨性。先前对加密即时消息的绝大多数研究都集中在传输中的消息上，但现有的结果并没有提到存储在用户设备上的消息的隐私。本研究项目将通过提供第一个基本模型和可证明的安全结构来解决这一研究缺口，以便在即时消息传递环境中安全存储消息和媒体。我们将定义安全模型，以模块化的方式捕获所需的高级安全属性，例如前向安全性、后妥协安全性等。这将使我们能够正式地分析和理解现有协议的安全属性和限制，以便为即时消息空间中存在的各种用例开发有效且实用的替代解决方案。该建议的一个主要方面是构建和分析安全备份存储的可证明安全密钥派生方案，使用先进的密码技术进行遗忘计算。

The gold standard to construct and analyze security protocols in modern cryptology is to first define a security model that specifies the use of the protocol and the capabilities of an attacker in a mathematically-precise way, and then show the security of proposed protocols by reduction to well-defined computational hardness assumptions (aka. the "provable security" approach).In the context of secure storage of messages and media in instant messaging environments we are still lacking this level of clarity and rigor of security claims, despite the huge practical importance of this topic. The vast majority of prior research on encrypted instant messaging has focused on messages in transit, but existing results say nothing about the privacy of messages that are stored on a user's device(s). This research project will address this research gap by providing first foundational models and provably-secure constructions for secure storage of messages and media in instant messaging environments. We will define security models that capture desirable advanced security properties, such as forward security, post-compromise security, and more, in a modular fashion. This will enable us to formally analyze and understand the security properties and limitations of existing protocols, in order to develop efficient and practical alternative solutions for the wide variety of use cases that exist in the instant messaging space. A major aspect of the proposal is to construct and analyse provably-secure key derivation schemes for secure backup storage, using advanced cryptographic techniques for oblivious computation.