The European Central Bank is preparing for the potential issuance of a central bank digital currency (CBDC), called the digital euro. A recent regulatory proposal by the European Commission defines several requirements for the digital euro, such as support for both online and offline payments. Offline payments are expected to enable cash-like privacy, local payment settlement, and the enforcement of holding limits. While other central banks have expressed similar desired functionality, achieving such offline payments poses a novel technical challenge. We observe that none of the existing research solutions, including offline E-cash schemes, are fully compliant. Proposed solutions based on secure elements offer no guarantees in case of compromise and can therefore lead to significant payment fraud. The main contribution of this paper is PayOff, a novel CBDC design motivated by the digital euro regulation, which focuses on offline payments. We analyze the security implications of local payment settlement and identify new security objectives. PayOff protects user privacy, supports complex regulations such as holding limits, and implements safeguards to increase robustness against secure element failure. Our analysis shows that PayOff provides strong privacy and identifies residual leakages that may arise in real-world deployments. Our evaluation shows that offline payments can be fast and that the central bank can handle high payment loads with moderate computing resources. However, the main limitation of PayOff is that offline payment messages and storage requirements grow in the number of payments that the sender makes or receives without going online in between.

To mitigate interrupt-based stepping attacks (notably using SGX-Step), Intel introduced AEX-Notify, an ISA extension to Intel SGX that aims to prevent deterministic single-stepping. In this work, we introduce AEX-NStep, the first interrupt counting attack on AEX Notify-enabled Enclaves. We show that deterministic single-stepping is not required for interrupt counting attacks to be practical and that, therefore, AEX-Notify does not entirely prevent such attacks. We specifically show that one of AEX-Notify's security guarantees, obfuscated forward progress, does not hold, and we introduce two new probabilistic interrupt counting attacks. We use these attacks to construct a practical ECDSA key leakage attack on an AEX-Notiy-enabled SGX enclave. Our results extend the original security analysis of AEX-Notify and inform the design of future mitigations.

A common form of phishing training in organizations is the use of simulated phishing emails to test employees' susceptibility to phishing attacks, and the immediate delivery of training material to those who fail the test. This widespread practice is dubbed embedded training; however, its effectiveness in decreasing the likelihood of employees falling for phishing again in the future is questioned by the contradictory findings of several recent field studies.

Due to the popularity of blockchain-based cryptocurrencies, the increasing digitalization of payments, and the constantly reducing role of cash in society, central banks have shown an increased interest in deploying central bank digital currencies (CBDCs) that could serve as a digital cash-equivalent. While most recent research on CBDCs focuses on blockchain technology, it is not clear that this choice of technology provides the optimal solution. In particular, the centralized trust model of a CBDC offers opportunities for different designs. In this paper, we depart from blockchain designs and instead build on ideas from traditional e-cash schemes. We propose a new style of building digital currencies that combines the transaction processing model of e-cash with an account-based fund management model. We argue that such a style of building digital currencies is especially well-suited to CBDCs. We also design the first such digital currency system, called Platypus, that provides strong privacy, high scalability, and expressive but simple regulation, which are all critical features for a CBDC. Platypus achieves these properties by adapting techniques similar to those used in anonymous blockchain cryptocurrencies like Zcash to fit our account model and applying them to the e-cash context.

In this paper, we present findings from a largescale and long-term phishing experiment that we conducted in collaboration with a partner company. Our experiment ran for 15 months during which time more than 14,000 study participants (employees of the company) received different simulated phishing emails in their normal working context. We also deployed a reporting button to the company’s email client which allowed the participants to report suspicious emails they received. We measured click rates for phishing emails, dangerous actions such as submitting credentials, and reported suspicious emails. The results of our experiment provide three types of contributions. First, some of our findings support previous literature with improved ecological validity. One example of such results is good effectiveness of warnings on emails. Second, some of our results contradict prior literature and common industry practices. Surprisingly, we find that embedded training during simulated phishing exercises, as commonly deployed in the industry today, does not make employees more resilient to phishing, but instead it can have unexpected side effects that can make employees even more susceptible to phishing. And third, we report new findings. In particular, we are the first to demonstrate that using the employees as a collective phishing detection mechanism is practical in large organizations. Our results show that such crowd-sourcing allows fast detection of new phishing campaigns, the operational load for the organization is acceptable, and the employees remain active over long periods of time.

Smart contracts are programmable, decentralized and transparent financial applications. Because smart contract platforms typically support Turing-complete programming languages, such systems are often said to enable arbitrary applications. However, the current permissionless smart contract systems impose heavy restrictions on the types of computations that can be implemented. For example, the globally-replicated and sequential execution model of Ethereum requires low gas limits that make many computations infeasible.

Intel SGX enables protected enclaves on untrusted computing platforms. An important part of SGX is its remote attestation mechanism that allows a remote verifier to check that the expected enclave was correctly initialized before provisioning secrets to it. However, SGX attestation is vulnerable to relay attacks where the attacker, using malicious software on the target platform, redirects the attestation and therefore the provisioning of confidential data to a platform that he physically controls. Although relay attacks have been known for a long time, their consequences have not been carefully examined. In this paper, we analyze relay attacks and show that redirection increases the adversary's abilities to compromise the enclave in several ways, enabling for instance physical and digital side-channel attacks that would not be otherwise possible.

Recent research has demonstrated that Intel's SGX is vulnerable to software-based side-channel attacks. In a common attack, the adversary monitors CPU caches to infer secret-dependent data accesses patterns. Known defenses have major limitations, as they require either error-prone developer assistance, incur extremely high runtime overhead, or prevent only specific attacks.

Mobile application spoofing is an attack where a malicious mobile app mimics the visual appearance of another one. A common example of mobile application spoofing is a phishing attack where the adversary tricks the user into revealing her password to a malicious app that resembles the legitimate one. In this paper, we propose a novel spoofing detection approach, tailored to the protection of mobile app login screens, using screenshot extraction and visual similarity comparison. We use deception rate as a novel similarity metric for measuring how likely the user is to consider a potential spoofing app as one of the protected applications. We conducted a large-scale online study where participants evaluated spoofing samples of popular mobile app login screens, and used the study results to implement a detection system that accurately estimates deception rate. We show that efficient detection is possible with low overhead.

Mobile application phishing happens when a malicious mobile application masquerades as a legitimate one to steal user credentials. Personalized security indicators may help users to detect phishing attacks, but rely on the user's alertness. Previous studies in the context of website phishing have shown that users tend to ignore personalized security indicators and fall victim to attacks despite their deployment. Consequently, the research community has deemed personalized security indicators an ineffective phishing detection mechanism. We revisit the question of personalized security indicator effectiveness and evaluate them in the previously unexplored and increasingly important context of mobile applications. We conducted a user study with 221 participants and found that the deployment of personalized security indicators decreased the phishing attack success rate to 50%. Personalized security indicators can, therefore, help phishing detection in mobile applications and their reputation as an anti-phishing mechanism in the mobile context should be reconsidered.

Cloud platforms that use logical partitions to allocate dedicated resources to VMs can benefit from small and therefore secure hypervisors. Many-core platforms, with their abundant resources, are an attractive basis to create and deploy logical partitions on a large scale. However, many-core platforms are designed for efficient cross-core data sharing rather than isolation, which is a key requirement for logical partitions. Typically, logical partitions leverage hardware virtualization extensions that require complex CPU core enhancements. These extensions are not optimal for many-core platforms, where it is preferable to keep the cores as simple as possible.

Trusted computing technologies for mobile devices have been researched, developed, and deployed over the past decade. Although their use has been limited so far, ongoing standardization may change this by opening up these technologies for easy access by developers and users. In this survey, we describe the current state of trusted computing solutions for mobile devices from research, standardization, and deployment perspectives.

A trusted execution environment (TEE) is a secure processing environment that is isolated from the normal processing environment where the device operating system and applications run. The first mobile phones with hardware-based TEEs appeared almost a decade ago, and today almost every smartphone and tablet contains a TEE like ARM TrustZone. Despite such a large-scale deployment, the use of TEE functionality has been limited for developers. With emerging standardization this situation is about to change. In this tutorial, we explain the security features provided by mobile TEEs and describe On-board Credentials (ObC) system that enables third-party TEE development. We discuss ongoing TEE standardization activities, including the recent Global Platform standards and the Trusted Platform Module (TPM) 2.0 specification, and identify open problems for the near future of mobile hardware security.

The recent dramatic increase in the popularity of "smartphones" has led to increased interest in smartphone security research. From the perspective of a security researcher the noteworthy attributes of a modern smartphone are the ability to install new applications, possibility to access Internet and presence of private or sensitive information such as messages or location. These attributes are also present in a large class of more traditional "feature phones." Mobile platform security architectures in these types of devices have seen a much larger scale of deployment compared to platform security architectures designed for PC platforms. In this paper we start by describing the business, regulatory and end-user requirements which paved the way for this widespread deployment of mobile platform security architectures. We briefly describe typical hardware-based security mechanism that provide the foundation for mobile platform security. We then describe and compare the currently most prominent open mobile platform security architectures and conclude that many features introduced recently are borrowed, or adapted with a twist, from older platform security architectures. Finally, we identify a number of open problems in designing effective mobile platform security.

“Pairing” is the establishment of authenticated key agreement between two devices over a wireless channel. Such devices are ad hoc in nature as they lack any common preshared secrets or trusted authority. Fortunately, these devices can be connected via auxiliary physical (audio, visual, tactile) channels which can be authenticated by human users. They can, therefore, be used to form the basis of a pairing operation. Recently proposed pairing protocols and methods are based upon bidirectional physical channels. However, various pairing scenarios are asymmetric in nature, i.e., only a unidirectional physical channel exists between two devices (such as between a cell phone and an access point). In this paper, we show how strong mutual authentication can be achieved even with a unidirectional visual channel, where prior methods could provide only a weaker property termed as presence. This could help reduce the execution time and improve usability of prior pairing methods. In addition, by adopting recently proposed improved pairing protocols, we propose how visual channel authentication can be used even on devices that have very limited displaying capabilities, all the way down to a device whose display consists of a cheap single light-source, such as a light-emitting diode. We present the results of a preliminary usability study evaluating our proposed method.

Securely storing and using credentials is critical for ensuring the security of many modern distributed applications. Existing approaches to address this problem fall short. User memorizable passwords are flexible and cheap, but they suffer from bad usability and low security. On the other hand, dedicated hardware tokens provide high levels of security, but the logistics of manufacturing and provisioning such tokens are expensive, which makes them unattractive for most service providers. A new approach to address the problem has become possible due to the fact that several types of general-purpose secure hardware, like TPM and M-shield, are becoming widely deployed. These platforms enable, to different degrees, a strongly isolated secure environment. In this paper, we describe how we use general-purpose secure hardware to develop an architecture for credentials which we call On-board Credentials (ObCs). ObCs combine the flexibility of virtual credentials with the higher levels of protection due to the use of secure hardware. A distinguishing feature of the ObC architecture is that it is open: it allows anyone to design and deploy new credential algorithms to ObC-capable devices without approval from the device manufacturer or any other third party. The primary contribution of this paper is showing and solving the technical challenges in achieving openness while avoiding additional costs (by making use of already deployed secure hardware) and without compromising security (e.g., ensuring strong isolation). Our proposed architecture is designed with the constraints of existing secure hardware in mind and has been prototyped on several different platforms including mobile devices based on M-Shield secure hardware.

WLAN link layer security has been well studied but very little work exists in the area of intuitive access control inside home networks. In this paper we propose an approach that allows fine-grained access control without overburdening users with difficult questions or complicated configuration tasks. The proposed concept originated from a user needs study and user trials, and it builds on the existing WiFi Protected Setup standard.

Recently several researchers and practitioners have begun to address the problem of how to set up secure communication between two devices without the assistance of a trusted third party. McCune et al., (2005) proposed that one device displays the hash of its public key in the form of a barcode, and the other device reads it using a camera. Mutual authentication requires switching the roles of the devices and repeating the above process in the reverse direction. In this paper, we show how strong mutual authentication can be achieved even with a unidirectional visual channel, without having to switch device roles. By adopting recently proposed improved pairing protocols, we propose how visual channel authentication can be used even on devices that have very limited displaying capabilities

The increasing popularity and variety of consumer multimedia devices is driving the need for networked homes. Yet setting up a secure wireless network is a daunting task for most ordinary users. Recently, there have been several proposals for easing this process. However, none of the proposals consider the problem of how to make it easy to manage visitor access. In this paper, we motivate the requirements for visitor management, show the shortcomings of the current easy setup proposals in this regard, and propose a new setup procedure that makes it easy to manage visitor access to wireless networks. Our contributions are twofold: first we present an approach to assigning categories to client devices at admission time so that selective revocation of clients based on those categories becomes possible. Then we present the idea of admission tickets, a flexible and secure way to delegate conditional access rights. We report the results and experience of prototyping of the proposed procedure using the HostAP framework.