Extensive research has been done on the security of symmetric encryption algorithms in the black-box attack contexts, where the execution platforms are supposed to be secure. Recent studies intend to secure encryption algorithms in a more challenging but widely adopted scenario, the white-attack context (WBAC), where the adversaries have full visibility of the implementations of cryptosystems and full control over execution platforms. Various of approaches for protecting symmetric encryption algorithms in the WBAC have been proposed. Unfortunately, most existing approaches have been broken. This paper proposes a novel approach for securing symmetric encryption algorithms based on substitution-permutation network (SPN). Our key idea is to incorporate additional secret components into lookup tables to expand and dramatically change the inner states of encryption. Unlike existing approaches, these components do not need to be annihilated in adjacent rounds, and the ciphertext remains essentially unchanged. To recover the plaintext, only simple operations and the standard decryption algorithm are required. Our approach can be applied to protect SPN-based symmetric encryption algorithms such as AES. Security analysis indicates that the approach is expected to be resistant to both existing and unknown attacks. Furthermore, experimental evaluation shows that our approach performs well on various platforms.

The threshold digital signature technique is important for decentralized finance (DeFi) applications such as asset custody and cross-chain interoperations. The Edwards-curve digital signature algorithm (EdDSA) is widely used in blockchains, e.g., Libra/Diem; however, no suitable threshold solution exists. Therefore, to bridge this gap, we propose a threshold EdDSA that allows n parties to generate keys in a decentralized and distributed manner. Any t + 1-of-n parties can generate standard EdDSA signatures. This scheme supports an arbitrary threshold (t, n) and has been proven to be secure against at most t malicious adversaries. The theoretical analysis (computation complexity and communication footprints) and experimental results demonstrate that the proposed scheme performs efficiently on cloud servers and embedded devices. Furthermore, the proposed scheme is integrated with Tendermint, a blockchain framework that uses EdDSA, to generate keys and sign transactions in a decentralized manner, which indicates that this scheme is compatible with blockchains for supporting DeFi applications.

In cloud computing, since virtual machines (VMs) running on the same physical server share CPU caches, adversaries can exploit CPU's vulnerabilities to launch shared cache attacks (e.g., Spectre vulnerability) for illegally accessing sensitive data (e.g., key of symmetric encryption) on other VMs. Since it is difficult to fix such vulnerabilities, in this paper, we propose a novel solution that leverages two salient features of white-box encryption to protect data against such attacks: white-box encryption turns the keys and code into unintelligible programs; it is provably secure even if part of its critical data is accessed by adversaries. Although there are many white-box schemes, they cannot be used in our solution due to their limitations. Therefore, we propose a new white-box encryption scheme with highly efficient instances. These instances are parameterized, and can be configured according to the tradeoff between security margin and storage cost. Moreover, our scheme is provably secure in the space-hardness model. The evaluation shows that our solution works well in public clouds and outperforms other methods.