End to End Authentication of Caller ID in Heterogeneous Telephony Systems

来电显示欺骗是一个全球性的电信行业未解决的问题。这个问题已经影响了全球数十亿的电话用户，成为广泛的欺诈和社会工程攻击的推动者。它还严重扰乱了需要对呼叫者进行可靠认证的公共服务（例如，警察或医疗紧急呼叫）。根据Ofcom的数据，英国消费者每年在英国所有网络中接到50亿个骚扰电话。来电显示欺骗是欺诈者和骗子用来隐藏身份和避免追踪的常用技术。互联网工程任务组（IETF）已经成立了一个特别工作组来解决这个问题，并提出了一个名为STIR/SHAKEN的解决方案。STIR/SHAKEN提案的灵感来自HTTPS网络通信，并试图将同样的方法从网络浏览器应用到电话上。然而，这个建议有两个主要缺点。首先，它需要一个公共密钥基础设施（PKI），而PKI的设置和维护成本很高。除了与PKI相关的成本和操作问题外，还不清楚谁应该充当全球受信任的证书颁发机构（ca）。其次，STIR/SHAKEN被设计为只适用于SIP系统（VoIP），离开SS7系统（固定电话和移动电话）的范围。这极大地限制了所建议的解决方案的有效性。我们建议研究在不需要任何PKI的情况下，为SIP和SS7系统实现端到端呼叫者id身份验证的替代方法。我们的主要思想是利用回调会话中的DTMF信令作为可信通道，向声称的调用方发送短代码，并结合密码身份验证密钥交换（PAKE）协议在数据通道上执行密钥交换，以建立共享的高熵会话密钥，然后使用该密钥对调用方ID进行端到端的身份验证。我们的工业合作伙伴对提出的解决方案进行了积极评价。然而，该提案的可行性仍需要通过研究、原型设计以及在现实世界的电信环境中对性能、安全性和可用性进行全面评估来进一步证实，这将与我们的工业合作伙伴密切合作。我们把这项工作分为三个主要阶段。第一阶段（第1-18个月）将侧重于设计一个没有PKI的调用者ID身份验证框架。这包括基于无pki密钥交换协议的架构设计（工作包1），可以以最小的通信延迟适应拟议框架的一轮PAKE (WP 2)，以及可以有效地将呼叫者ID身份验证状态传达给最终用户的用户界面（WP 3）。第二阶段（19-36月）将侧重于构建原型，涵盖SIP （WP 4.1）和SS7 （WP 4.2）系统。最后阶段（第37-48个月）将侧重于从安全性、性能和可用性方面对开发的原型进行评估。

Caller ID spoofing is a global unsolved problem in the telecommunication industry. This problem has affected billions of telephone users worldwide as an enabler for widespread fraud and social engineering attacks. It has also seriously disrupted public services that require reliable authentication of the caller (e.g., police or medical emergency calls). According to Ofcom, UK consumers receive 5 billion nuisance calls per annum across all networks in the UK. Caller ID spoofing is a common technique used by fraudsters and scammers to hide the identity and to avoid tracing. The Internet Engineering Task Force (IETF) has formed a special working group to tackle this problem with a proposed solution called STIR/SHAKEN. The STIR/SHAKEN proposal is inspired by the HTTPS web communication and attempts to apply the same approach from web browsers to telephones. However, this proposal has two major drawbacks. First of all, it requires a Public Key infrastructure (PKI), which is expensive to set up and to maintain. Besides the cost and operational issues associated with a PKI, it remains unclear who should act as globally trusted certificate authorities (CAs). Second, STIR/SHAKEN is designed to only work with the SIP system (VoIP), leaving SS7 systems (landline and mobile phones) out of scope. This significantly limits the effectiveness of the proposed solution. We propose to investigate alternative ways to achieve end-to-end authentication of caller IDs for both SIP and SS7 systems without requiring any PKI. Our main idea is to leverage the DTMF signalling in a call-back session as a trusted channel to send a short code to the purported caller, in conjunction with a password authenticated key exchange (PAKE) protocol to perform key exchange over a data channel to establish a shared high-entropy session key which is then used to authenticate the caller ID end-to-end. This proposed solution has been positively reviewed by our industrial partners. However, the feasibility of this proposal still needs to be further confirmed through research, prototyping, and a comprehensive evaluation of performance, security and usability in real-world telecommunication settings, which will be done in close collaboration with our industrial partners.We divide the work into three main stages. The first stage (month 1-18) will focus on designing a caller ID authentication framework without a PKI. This includes the architectural designs (Work Package 1) based on PKI-free key exchange protocols, a one-round PAKE (WP 2) which can fit in the proposed framework with the minimised communication latency, and a user interface (WP 3) which can effectively communicate the caller ID authentication status to the end user. The second stage (month 19-36) will focus on building prototypes, which will cover both the SIP (WP 4.1) and SS7 (WP 4.2) systems. The final stage (months 37-48) will focus on the evaluation of the developed prototypes in terms of security, performance and usability.