Recently, Liuet al. proposed an efficient privacy-preserving outsourced calculation framework with multiple keys. The building blocks of this framework are a modified homomorphic encryption scheme and a basic interactive protocol for computing the sum of two encrypted dates across two domains. We found that there is a mistake in the parameter setting of their modified homomorphic encryption scheme and a security leak in the basic interactive computation protocol. This security leak enables an adversary to compromise the privacy of users, which are claimed to be protected. By our analysis, we suggest that the proposed framework, without any modification, should be avoided for use in privacy-preserving outsourced computation, and a similar scheme should be carefully designed in the future.

Abstract Privacy‐preserving aggregation for smart grid communications, which precisely meets the requirement of periodically collecting users' electricity consumption while preserving privacy of each individual user, has been extensively studied in recent years. However, most of existing privacy‐preserving aggregation schemes are only focused on the summation aggregation. In this paper, based on the lattice cryptographic technique, we propose a novel privacy‐preserving dual‐functional aggregation scheme (PDA) for smart grid communications. With our proposed PDA scheme, each individual user just reports one data, then multiple statistic values, that is, mean and variance, of all users can be computed by the data & control center in the smart grid, while the privacy of each individual user can still be protected. Detailed security analyses demonstrate that our proposed PDA scheme is secure and robust. In addition, extensive performance evaluations also show that our proposed PDA scheme is efficient in terms of computational and communication overheads when the number of considered users is within an acceptable range. Copyright © 2015 John Wiley & Sons, Ltd.

Quite recently, Cheng and Jiang[1]designed an efficient homomorphic message authentication code (MAC) scheme for authentication in network coding, and claimed that the newly proposed scheme can achieve much higher security level with a formal security proof. However, in this comment, we will point out there exists a design flaw in their proposed scheme, leading to an inherent vulnerability, and also show an inaccuracy in their formal security proof. We hope that by identifying the design flaw, similar mistakes can be avoided in future design of homomorphic MAC authentication for network coding.