In a function-hiding inner product functional encryption (FH-IPFE) scheme, both secret keys and ciphertexts are associated with vectors. Given a secret key for an $n$-dimensional vector $\mathit{x}$, and a ciphertext for an $n$-dimensional vector $\mathit{y}$, a decryptor learns the inner product value $⟨\mathit{x},\mathit{y}⟩$ and nothing else about both $\mathit{x}$ and $\mathit{y}$. FH-IPFE has been shown to be very useful in privacy-preserving computation. In this paper, we first propose a new (secret-key) FH-IPFE scheme and prove it the secure in the generic group model. Compared with the state-of-the-art scheme of Kim et al., the proposed scheme has comparable performance in decryption and reduces 1) the size of master key from $n^2$ to $3n-1$, 2) the setup complexity from $O\left(n^3\right)$ to $O\left(n\right)$, and 3) the encryption and key generation complexities from $O(n^2)$ to $O(n\log n)$. To the best of our knowledge, this is the most efficient construction based on pairings to date. Moreover, we apply our FH-IPFE scheme to build a fine-grained data sharing system, where data owners store their encrypted data on an untrusted server. Our design supports not only basic database operations but also statistical analyses on encrypted data. To achieve this goal, we also introduce a new security notion, partial-key exposure-resilient simulation-based security (PK-ER-SIM), for FH-IPFE, which enables lightweight clients to securely delegate heavy computations to a powerful server and may be independent of interest.

In the era of the Internet of Things, Bluetooth low energy (BLE/BTLE) plays an important role as a well-known wireless communication technology. While the security and privacy of BLE have been analyzed and fixed several times, the threat of side-channel attacks to BLE devices is still not well understood. In this work, we highlight a side-channel threat to the re-keying protocol of BLE. This protocol uses a fixed long term key for generating session keys, and the leakage of the long term key could render the encryption of all the following (and previous) connections useless. Our attack exploits the side-channel leakage of the re-keying protocol when it is implemented on embedded devices. In particular, we present successful correlation electromagnetic analysis and deep learning based profiled analysis that recover long term keys of BLE devices. We evaluate our attack on an ARM Cortex-M4 processor (Nordic Semiconductor nRF52840) running Nimble, a popular open-source BLE stack. Our results demonstrate that the long term key can be recovered within only a small amount of electromagnetic traces. Further, we summarize the features and limitations of our attack, and suggest a range of countermeasures to prevent it.

Side-channel attacks (SCAs) play an important role in the security evaluation of cryptographic devices. As a form of SCAs, profiled differential power analysis (DPA) is among the most powerful and efficient by taking advantage of a profiling phase that learns features from a controlled device. Linear regression (LR) based profiling, a special profiling method proposed by Schindler et al., could be extended to generic-emulating DPA (differential power analysis) by on-the-fly profiling. The formal extension was proposed by Whitnall et al. named SLR-based method. Later, to improve SLR-based method, Wang et al. introduced a method based on ridge regression. However, the constant format of L-2 penalty still limits the performance of profiling. In this paper, we generalize the ridge-based method and propose a new strategy of using variable regularization. We then analyze from a theoretical point of view why we should not use constant penalty format for all cases. Roughly speaking, our work reveals the underlying mechanism of how different formats affect the profiling process in the context of side channel. Therefore, by selecting a proper regularization, we could push the limits of LR-based profiling. Finally, we conduct simulation-based and practical experiments to confirm our analysis. Specifically, the results of our practical experiments show that the proper formats of regularization are different among real devices.

Time-division multiple access (TDMA) and code-division multiple access (CDMA) are two technologies used in digital cellular networks. The authentication protocols of TDMA networks have been proven to be vulnerable to side-channel analysis (SCA), giving rise to a series of powerful SCA-based attacks against unprotected subscriber identity module (SIM) cards. CDMA networks have two authentication protocols, cellular authentication and voice encryption (CAVE) based authentication protocol and authentication and key agreement (AKA) based authentication protocol, which are used in different phases of the networks. However, there has been no SCA attack for these two protocols so far. In this paper, in order to figure out if the authentication protocols of CDMA networks are sufficiently secure against SCA, we investigate the two existing protocols and their cryptographic algorithms. We find the side-channel weaknesses of the two protocols when they are implemented on embedded systems. Based on these weaknesses, we propose specific attack strategies to recover their authentication keys for the two protocols, respectively. We verify our strategies on an 8-bit microcontroller and a real-world SIM card, showing that the authentication keys can be fully recovered within a few minutes with a limited number of power measurements. The successful experiments demonstrate the correctness and the effectiveness of our proposed strategies and prove that the unprotected implementations of the authentication protocols of CDMA networks cannot resist SCA.