In this work, we present the first leakage-resilient identity-based encryption (LR-IBE) scheme that features (almost) tight security under the multi-challenge setting, in which the adversary could receive multiple challenging ciphertexts from multiple users. Meanwhile, our construction enjoys security against chosen-ciphertext attack (CCA) under the Matrix Decisional Diffie-Hellman (MDDH) assumption. Apart from admitting the continual leakage of secret key, we provide strong security via additionally allowing the continual leakage of the master secret key.

In this work, we develop a hash proof system with auxiliary inputs (HPSAI), whose performance is as efficient as the underlying hash proof system (HPS). Moreover, we show that our HPSAI is a practical tool for the creation of leakage-resilient public key encryption (LR-PKE). In particular, we obtain a CCA-secure LR-PKE scheme that is able to leak most of the secret key information-theoretically with any hard-to-invert leakage function. Furthermore, our construction enjoys pairing-free and constant ciphertext size.

The US Standard (EC)DSA is currently almost the most popular digital signature scheme. Chinese and Russian governments also proposed their counterparts: SM2 and GOST R 34.10 (GOST). Nowadays, there are already many industrial applications supporting SM2 and GOST digital signatures. Unfortunately, the existing analyses for SM2 and GOST are rather limited when compared to ECDSA. This paper focuses on the security of SM2 and GOST from the viewpoints of RKA security (related-key attack) and sKRKA security (strong known related key attack). RKA captures the real attacks of tampering and fault injection in hardware-stored secret keys. sKRKA, a recently proposed security model modified from RKA, captures the real attacks in the BIP-32 HD wallet and the stealth address used in Monero. It was proved that ECDSA is insecure in the RKA model (ICISC 2015) and but secure in the sKRKA model (NSS 2019). In this work, we proved that GOST is insecure in both RKA and skRKA models, but SM2 is secure in both RKA and sKRKA models. This result well differentiates the security of ECDSA, SM2 and GOST, and demonstrates that Chinese SM2 is capable to construct secure cryptocurrency systems using BIP-32 HD wallet or stealth address, as secure as ECDSA, but outperforms ECDSA in resisting tampering or fault injection attacks.

Summary With the dramatic growth of smart phones and social network services, location‐based service has become increasingly popular in our daily life, which also brings great privacy leakage about user's location information. Thus, privacy‐preserving location sharing is still a significant problem. In this paper, two models of our scheme are verifiable, supporting location query on homomorphic encrypted ciphertext with searching index and trapdoor. The characteristics of our scheme are that it (1) allows users to share their current location without leaking any location information to the untrusted server; (2) protects users from the cheating of untrusted server's malicious behavior by verifying query result; (3) supports a novel personalized query according to users' classifications of social network friends; (4) the user does not have to be online to make permissions for accessing his shared location, and (5) model 2 does not rely on any trusted third party server to perform any computation. The security analysis shows that it ensures secure location sharing in social scenarios.