Smartphone apps often run with full privileges to access the network and sensitive local resources, making it difficult for remote systems to have any trust in the provenance of network connections they receive. Even within the phone, different apps with different privileges can communicate with one another, allowing one app to trick another into improperly exercising its privileges (a Confused Deputy attack). In QUIRE, we engineered two new security mechanisms into Android to address these issues. First, we track the call chain of IPCs, allowing an app the choice of operating with the diminished privileges of its callers or to act explicitly on its own behalf. Second, a lightweight signature scheme allows any app to create a signed statement that can be verified anywhere inside the phone. Both of these mechanisms are reflected in network RPCs, allowing remote systems visibility into the state of the phone when an RPC is made. We demonstrate the usefulness of QUIRE with two example applications. We built an advertising service, running distinctly from the app which wants to display ads, which can validate clicks passed to it from its host. We also built a payment service, allowing an app to issue a request which the payment service validates with the user. An app cannot not forge a payment request by directly connecting to the remote server, nor can the local payment service tamper with the request. 1

Abstract. Today’s smartphones and tablets offer compelling computing and storage capabilities enabling a variety of mobile applications with rich functionality. The integration of new interfaces, in particular near field communication (NFC) opens new opportunities for new applications and business models, as the most recent trend in industry for payment and ticketing shows. These applications require storing and processing security-critical data on smartphones, making them attractive targets for a variety of attacks. The state of the art to enhance platform security concerns outsourcing security-critical computations to hardware-isolated Trusted Execution Environments (TrEE). However, since these TrEEs are used by software running in commodity operating systems, malware could impersonate the software and use the TrEE in an unintended way. Further, existing NFC-based access control solutions for smartphones are either not public or based on strong assumptions that are hard to achieve in practice. We present the design and implementation of a generic access control system for NFC-enabled smartphones based on a multi-level security architecture for smartphones. Our solution allows users to delegate their access rights and addresses the bandwidth constraints of NFC. Our prototype captures electronic access to facilities, such as entrances and offices, and binds NFC operations to a software-isolated TrEE established on the widely used Android smartphone operating system. We provide a formal security analysis of our protocols and evaluated the performance of our solution. 1