As data storage and processing increasingly shift to the cloud, the risk of data breaches also rises. One way to address this is using Homomorphic Encryption (HE), which allows for data processing while the data remains encrypted, unlike traditional methods. However, current HE libraries support only addition and multiplication, requiring users to implement other mathematical functions themselves. To this end, we developed and analyzed basic mathematical functions in a previous work. Since polynomial approximations are more common in HE, this paper expands on that by examining and comparing polynomial approximations of these functions with the previously implemented methods. Our findings indicate that while polynomial approximations offer the benefit of low multiplication depth, the previously implemented methods generally outperform them in most scenarios despite their higher computational cost.

In recent years, digital services have experienced significant growth, exemplified by platforms like Netflix achieving unprecedented revenue levels. Some of these services employ subscription models, with certain content requiring additional payments or offering third-party products. To ensure the widespread availability of diverse digital services anytime and anywhere, providers must have control over content accessibility. To address the multifaceted challenges in this domain, one promising solution is the adoption of attribute-based encryption (ABE). Over the years, various approaches have been proposed in the literature, offering a wide range of features. In a prior study [18], we assessed the security of one of these proposed approaches and identified one that did not meet its promised security standards. In this research we focuses on conducting a security analysis for another ABE scheme to pinpoint its shortcomings and emphasize the critical importance of evaluating the safety and effectiveness of newly proposed schemes. Specifically, we uncover an attack vector within this ABE scheme, which enables malicious users to decrypt content without the required permissions or attributes. Furthermore, we propose a solution to rectify this identified vulnerability.

The critical component in any IoT application is the communication between devices. This must not only function smoothly, but also be secured. An important step in securing IoT communication is its encryption. However, in order for IoT devices to encrypt their communication with each other, they must first agree on appropriate cryptographic keys. In practice, the generation and distribution of such keys is usually managed by a central authority. However, this centralized approach has the disadvantages that (i) a central authority must be trusted, (ii) the central authority represents a single point of failure, and (iii) the central authority may be far away and thus communication with it takes a long time. To overcome these drawbacks, distributed group key agreement approaches have also been proposed. Since these distributed approaches were not originally developed for IoT devices, their performance on such devices is unknown. Therefore, in this work, we investigate the performance of a distributed group encryption scheme on IoT devices. To this end, we have built a measurement environment for distributed group encryption schemes and compare centralized and distributed group encryption schemes for IoT. Our measurements show that under perfect network conditions, the distributed approach performs worse than the centralized approaches in terms of time and memory requirements. However, our measurements also show that the distributed approach allows a group of 5 members to agree on a key in less than a minute. Thus, the distributed method can be used for small IoT groups if agreeing on a key is not time-sensitive.

The interconnectivity of devices on the Internet of Things (IoT) provides many new and smart applications. However, the integration of many devices - especially by inexperienced users - might introduce several security threats. Further, several often used communication protocols in the IoT domain are not out-of-the-boxsecured. On the other hand, security inherently introduces overhead, resulting in a decrease in performance. The Message QueuingTelemetry Transport (MQTT) protocol is a popular communication protocol for IoT applications - for example, in Industry 4.0, railways, automotive, or smart homes. This paper analyzes the influence on performance when using MQTT with TLS in terms of throughput, connection build-up times, and energy efficiency using a reproducible testbed based on a standard off-the-shelf microcontroller. The results indicate that the impact of TLS on performance across all QoS levels depends on (i) the network situation and (ii) the connection reestablishment frequency. Thus, a negative influence of TLS on the performance is noticeable only in deteriorated networksituations or at a high connection reestablishment frequency.