With the rapid advancement of cloud computing and the exponential growth of data, the demand for secure data querying and sharing has become increasingly prominent. Identity-Based Encryption with Keyword Search (IBEKS) and Hierarchical IBEKS (HIBEKS) address the issue of secure data querying, as it enables resource-constrained clients to effectively search for encrypted data stored in the cloud. However, existing HIBEKS schemes lack flexible data-query mechanisms among users in the same level, are highly vulnerable to attacks launched by quantum computers and Keyword Guessing Attacks (KGA), and lead to relatively high end-to-end latency. To meet more complex and diverse application requirements and address these vulnerabilities, we introduce a novel primitive called Hierarchical Identity-Based Puncturable Encryption with Keyword Search (HIBPEKS). The decryption keys held by higher-level users are capable of generating decryption keys for lower-level users, thereby enhancing the ability to perform multi-level encrypted data queries within the user group. In addition, to control the query of encrypted data, higher-level users can use specific tags to puncture decryption keys (for lower-level users), so that lower-level users will no longer be able to query the parts of the data associated with the punctured tags. Technically, we have improved the previous lattice-based IBEKS schemes and implemented an efficient and flexible data query mechanism in a hierarchical setting by exploiting Puncturable Encryption (PE) techniques. Moreover, we formalize the security model of HIBPEKS and prove its security within the framework of the random oracle model. Finally, we experimentally evaluate HIBPEKS and show that HIBPEKS is computationally efficient and practical.

Mobile agents are useful in collaborative business systems due to their mobility and autonomy, which can roam over the Internet to purchase goods and services on behalf of their owners. However, given attacks from a malicious host, it is a challenge to securely sign a contract on behalf of the owner (the original signer). In this paper, we propose an intrusion-resilient undetachable digital signature (IR-UDS) approach to mitigate the security risk of signing key leakage on the signer's host, base device, and potentially malicious remote hosts, as well as the risk of misusing the signing algorithm on remote hosts. An attacker will be unable to forge the past and future signatures as long as the base device is secure, even if the current signing key of the original signer has been gained. When the base device is compromised, although the future signatures could be forged, all past signatures remain secure. Furthermore, the encrypted signing function has been combined with the original signer's requirement to prevent the misuse of signing algorithm and the exposure of original signing key on malicious hosts. Security analysis has indicated that our scheme can defeat a variety of attacks, and experimental evaluations have demonstrated the good performance of the scheme.