Poster: Towards a Digital Payment System for the Constrained Internet of Things Mikolai Gütschow TU Dresden mikolai.guetschow@tu-dresden.de Matthias Wählisch TU Dresden and Barkhausen Institut m.waehlisch@tu-dresden.de Abstract—In this poster, we start the discussion of the poten- tials and challenges of digital payment systems to advance digital services in the Internet of Things. We specifically focus on devices with constrained hardware resources. To enable multi-stakeholder machine-to-machine scenarios, we propose an e-cash approach that is privacy-friendly and al- lows for autonomous payment. We implement our approach using GNU Taler, a free-software e-cash implementation, and RIOT, a free and open-source operating system for the IoT. Our preliminary findings suggest that the deployment of e- cash systems is feasible in constrained IoT scenarios. They underscore the importance of concise, standard-compliant data encoding over computationally intensive compression techniques. 1. Introduction The Internet of Things (IoT) is projected to consist of 30 billion interconnected devices by 2030 [1]. Most of them will be constrained in terms of hardware resources to reduce manufacturing costs, enabling mass deployment of many different new applications. In principle, each of these IoT devices provides a service (e.g., sensing data, acting to external input), often in multi-stakeholder envi- ronments in which not all stakeholders necessarily collab- orate in a peer-to-peer manner. How to seamlessly offer advanced services in such networks is still an open topic. Providing an economic incentive could be one reason for cooperation. To enable, for example, data sharing between different stakeholders then requires autonomous machine-to-machine (M2M) payments such that the pay- ment is integrated with and running directly on the (con- strained) IoT devices, keeping the overhead of accounting and payment processing low. Additionally, such an IoT payment system must prioritize (meta-)data privacy pro- tection due to the sensitivity and scale of data involved. In this poster, we propose payments in the IoT based on blind signatures and a centralized architecture. Such a token-based approach allows for payer privacy and enables autonomous usage by design, thereby meeting two funda- mental requirements. Section 2 gives some examples of payment scenarios and typical constraints in the IoT, and shows that other approaches to digital payments do not fit the IoT use-case well. Section 3 discusses the required functionality to participate as a constrained device in such a system, elaborates on design choices for data transmis- sion formats, and briefly evaluates the proposed design using a proof-of-concept implementation of GNU Taler Internet Figure 1: A distributed IoT economy needs autonomous and privacy-respecting machine-to-machine payments. on RIOT. Section 4 concludes the poster by presenting challenges left for future work. 2. Background and Problem Statement This section discusses some common IoT scenarios depicted in Figure 1, how these scenarios benefit from IoT- integrated payments, and the requirements and challenges imposed by limited hardware resources. We also analyze currently available or proposed digital payment systems. IoT Scenarios. The vision of the Internet of Things (IoT) revolves around the seamless cooperation of intercon- nected devices, operating autonomously without direct human intervention. These devices exchange data or, more generally, services, often involving sensitive information regarding privacy. For instance, smart household appli- ances such as refrigerators can autonomously order sup- plies. Industry scenarios may involve the cooperation of many entities, for example, when goods are tracked from manufacturing to warehouse until hand-over to the end- customer, including automatic ordering of new supplies. Similarly, vehicles can autonomously handle payments for parking, tolls, and fuel, benefiting both auto