Unbounded anonymous hierarchical IBE with continual-key-leakage tolerance

Modern cryptographic schemes are constructed under the fundamental assumption that secret keys are perfectly hidden from all possible attackers. In practice, however, keys and internal states may partially be leaked. Recently, cryptographic construction with key-leakage resilience has been a crucial research topic. In this work, we proposed an anonymous hierarchical identity-based encryption that can tolerate partial leakage of secret keys. Our results were as follows. First, we provided a tolerance for continual key leakage that can capture both memory leakage and continual leakage. We extended a dual-system encryption mechanism in orthogonal subgroups to achieve key-leakage resilience and implicitly employed an update algorithm to guard against continual leakage. Second, the delegation depth is unbounded, which means that no predetermined depth was imposed in the setup algorithm, thus making the scheme very flexible in practice. We employed a secret-sharing approach to split the master key into multiple shares in key components corresponding to the elements. Third, we analyzed and discussed the performance of allowable leakage-tolerance bounds and the leakage rate of the proposed scheme and gave an evaluation that attains about 40-70% leakage rate under the Advanced Encryption Standard 112 security level.