Outsourcing encrypted data to cloud servers that has become a prevalent trend among Internet users to date. There is a long list of advantages on data outsourcing, such as the reduction cost of local data management. How to securely operate encrypted data (remotely), however, is the top-rank concern over data owner. Liang et al. proposed a novel encrypted cloud-based data share and search system without loss of privacy. The system allows users to flexibly search and share encrypted data as well as updating keyword field. However, the search complexity of the system is of extreme inefficiency, O(n d)O(nd), where dd is the total number of system files and nn is the size of query formula. This article, for the first time, leverages the 'oblivious cross search' technology in public key searchable encryption context to reduce the search complexity to only O(nf(w))O(nf(w)), where f(w)f(w) is the number of files embedded with the 'least frequent keyword' ww. The new scheme maintains efficient encrypted data share and keyword field update as well. This article further revisits the security models for payload security, keyword privacy and search token privacy (i.e., search pattern privacy) and meanwhile, presents security and efficiency analysis for the new scheme.

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This paper introduces the results of several different security analysis of two new block ciphers: Raindrop and FBC, which are the two candidates of block cipher designs submitted to the Chinese Cryptographic Algorithms Design Competition in 2019. Raindrop applies two-branch Feistel structure, while FBC block cipher is based on the four-way dual Feistel structure design. We give detailed security evaluation on Raindrop and FBC, using differential, linear, impossible difference and boomerang cryptanalysis approaches. For Raindrop, we achieved the results as follows: differential attack on 12-round Raindrop based on the 11-round distinguisher with the computational complexity of 2^62.41; linear attack on 13-round Raindrop based on 12-round distinguisher with the computational complexity of 2^106.3; impossible differential attack on 18-round Raindrop based on 12-round distinguisher with the computational complexity of 2^102.83; and boomerang attack on 15-round Raindrop based on 14-round distinguisher with the computational complexity of 2^224.6. For FBC, results are as follows: differential attack on 12-round FBC based on 11-round distinguisher with the computational complexity of 2^93.41; linear attack on 11-round FBC based on 10-round distinguisher with the computational complexity of 2^112.54; impossible differential attack on 11-round FBC based on 7-round distinguisher with the computational complexity of 2^94-54; and boomerang attack on 13-round FBC based on 12-round distinguisher with the computational complexity of 2^247.67. At present, the best records achieved are 18-round impossible differential attack for Raindrop-128-128 and 13-round boomerang attack for FBC128-256. The statistical distinguishers we built are similar to the proposals but we provide the concrete key recovery attacks in this study.

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Outsourcing a huge amount of local data to remote cloud servers that has been become a significant trend for industries. Leveraging the considerable cloud storage space, industries can also put forward the outsourced data to cloud computing. How to collect the data for computing without loss of privacy and confidentiality is one of the crucial security problems. Searchable encryption technique has been proposed to protect the confidentiality of the outsourced data and the privacy of the corresponding data query. This technique, however, only supporting search functionality, may not be fully applicable to real-world cloud computing scenario whereby secure data search, share as well as computation are needed. This work presents a novel encrypted cloud-based data share and search system without loss of user privacy and data confidentiality. The new system enables users to make conjunctive keyword query over encrypted data, but also allows encrypted data to be efficiently and multiply shared among different users without the need of the "download-decrypt-then-encrypt" mode. As of independent interest, our system provides secure keyword update, so that users can freely and securely update data's keyword field. It is worth mentioning that all the above functionalities do not incur any expansion of ciphertext size, namely, the size of ciphertext remains constant during being searched, shared and keyword-updated. The system is proven secure and meanwhile, the efficiency analysis shows its great potential in being used in large-scale database.@en