Biblio

In this paper, we consider a wireless federated learning (FL) system concerning differential privacy (DP) guarantee, where multiple edge devices collaboratively train a shared model under the coordination of a central base station (BS) through over-the-air computation (AirComp). However, due to the heterogeneity of wireless links, it is difficult to achieve the optimal trade-off between model privacy and accuracy during the FL model aggregation. To address this issue, we propose to utilize the reconfigurable intelligent surface (RIS) technology to mitigate the communication bottleneck in FL by reconfiguring the wireless propagation environment. Specifically, we aim to minimize the model optimality gap while strictly meeting the DP and transmit power constraints. This is achieved by jointly optimizing the device transmit power, artificial noise, and phase shifts at RIS, followed by developing a two-step alternating minimization framework. Simulation results will demonstrate that the proposed RIS-assisted FL model achieves a better trade-off between accuracy and privacy than the benchmarks.

Nowadays, image captchas are being widely used across the Internet to defend against abusive programs. However, the ever-advancing capabilities of computer vision techniques are gradually diminishing the security of image captchas; yet, little is known thus far about the vulnerability of image captchas deployed in real-world settings. In this paper, we conduct the first systematic study on the security of image captchas in the wild. We classify the currently popular image captchas into three categories: selection-, slide- and click-based captchas. We propose three effective and generic attacks, each against one of these categories. We evaluate our attacks against 10 real-world popular image captchas, including those from tencent.com, google.com, and 12306.cn. Furthermore, we compare our attacks with 9 online image recognition services and human labors from 8 underground captcha-solving services. Our studies show that: (1) all of those popular image captchas are vulnerable to our attacks; (2) our attacks significantly outperform the state-of-the-arts in almost all the scenarios; and (3) our attacks achieve effectiveness comparable to human labors but with much higher efficiency. Based on our evaluation, we identify the design flaws of those popular schemes, the best practices, and the design principles towards more secure captchas.

De-anonymizing the authors of anonymous code (i.e., code stylometry) entails significant privacy and security implications. Most existing code stylometry methods solely rely on static (e.g., lexical, layout, and syntactic) features extracted from source code, while neglecting its key difference from regular text – it is executable! In this paper, we present Sundae, a novel code de-anonymization framework that integrates both static and dynamic stylometry analysis. Compared with the existing solutions, Sundae departs in significant ways: (i) it requires much less number of static, hand-crafted features; (ii) it requires much less labeled data for training; and (iii) it can be readily extended to new programmers once their stylometry information becomes available Through extensive evaluation on benchmark datasets, we demonstrate that Sundae delivers strong empirical performance. For example, under the setting of 229 programmers and 9 problems, it outperforms the state-of-art method by a margin of 45.65% on Python code de-anonymization. The empirical results highlight the integration of static and dynamic analysis as a promising direction for code stylometry research.