Abstract

We present and analyze User Discovery with Minimal information disclosure (UDM), a new protocol for user discovery in anonymous communication systems that minimizes the information disclosed to the system and users. UDM solves the following user-discovery problem. User Alice wishes to communicate with Bob over an anonymous communication system, such as cMix or Tor. Initially, each party knows each other’s public contact identifier (e.g., email address or phone number), but neither knows the other’s private platform identifier in the communication system. If both parties wish to communicate with each other, UDM enables them to establish a shared secret and learn each other’s private platform identifier. Unlike existing systems, including those based on private set intersection, UDM learns nothing about the social contacts of the users, is not vulnerable to off-line dictionary attacks that expose contact lists, does not reveal platform identifiers to users without the owner’s explicit permission, and enjoys low computation and communication complexity. Using the anonymous communication system, each pair of users who wish to communicate with each other uploads to the user-discovery system their private platform identifier, encrypted with a key derived from their shared secret. Indexing their request by a cryptographic tag derived from their shared secret, each user can then download each other’s encrypted private platform identifier. In doing so, UDM uses an untrusted user-discovery system, which processes and stores only public information or values encrypted with keys it does not know. Therefore, from the data values it processes, UDM cannot learn any information about the social contacts of its users.

摘要

我们以最少的信息披露 (UDM)呈现和分析用户发现，一种用于在匿名通信系统中发现用户的新协议，可最大限度地减少向系统和用户披露的信息。UDM 解决了以下用户发现问题。用户 Alice 希望通过匿名通信系统（例如 cMix 或 Tor）与 Bob 通信。最初，每一方都知道对方的公共联系人标识符（例如，电子邮件地址或电话号码），但都不知道对方在通信系统中的私有平台标识符。如果双方希望相互通信，UDM 使他们能够建立共享秘密并了解彼此的私有平台标识符。与现有系统（包括基于私有集合交集的系统）不同，UDM 对用户的社交联系人一无所知，不易受到暴露联系人列表的离线字典攻击，未经所有者明确许可，不会向用户透露平台标识符，具有较低的计算和通信复杂度。使用匿名通信系统，希望相互通信的每对用户将他们的私有平台标识符上传到用户发现系统，并使用从他们的共享秘密中派生的密钥进行加密。通过从他们的共享秘密派生的加密标签索引他们的请求，然后每个用户可以下载彼此的加密私有平台标识符。在此过程中，UDM 使用了一个不受信任的用户发现系统，该系统仅处理和存储公共信息或使用它不知道的密钥加密的值。因此，从它处理的数据值中，UDM 无法了解有关其用户社交联系的任何信息。