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Electronic medical data have significant advantages over paper-based patient records when it comes to storage and retrieval. However, most existing medical data sharing schemes have security risks, such as being prone to data tampering and forgery, and do not support the ability to verify the authenticity of the data source. To solve these problems, we propose a medical data sharing scheme based on attribute cryptosystem and blockchain technology in this paper. First, the encrypted medical data are stored in the cloud, and the storage address and medical-related information are written into the blockchain, which can ensure efficient storage and eliminate the possibility of irreversible modification of the data. Second, the proposed scheme combines attribute-based encryption (ABE) and attribute-based signature (ABS), which achieves the sharing of medical data in many-to-many communications. The ABE achieves data privacy and fine-grained access control, and the ABS verifies the authenticity of the source of the medical data while protecting the signer's identity. Moreover, the data user outsources most of the operations of medical data ciphertext decryption to the cloud service provider (CSP), which can greatly reduce the computational burden. Finally, results of the analysis show that our scheme satisfies the requirements for confidentiality and unforgeability in the random oracle model, and that the proposed scheme offers higher computational performance than other similar schemes. INDEX TERMS Attribute-based cryptosystem, blockchain, confidentiality, electronic medical data, unforgeability.

Abstract-Millimetre-Wave frequencies are a front runner contender for the next generation body-centric wireless communications. In this paper, design of a very low profile antenna is presented for body-centric applications operating in the millimetre-wave frequency band centred at 60 GHz. The antenna has an overall size of 14×10.5×1.15 mm 3 and is printed on a flexible printed circuit board. The performance of the antenna is evaluated in off-body, on-body and body-to-body communication scenarios using a realistic numerical phantom and verified through measurements. The antenna has a bandwidth of 9.8 GHz and offers a gain of 10.6 dBi in off-body (free space) configuration while 12.1 dBi in on-body configuration. It also acheives an efficiency of 74% in off-body and 63% in on-body scenario. The small and flexible structure of the antenna along with excellent impedance matching, broad bandwidth, high gain and good efficiency makes it a suitable candidate to attain simultaneous data transmission/reception at millimetre-wave frequencies for the 5G body-centric applications.

A CPW‐fed wide slot ultrawideband antenna with notch band characteristic is presented numerically and experimentally. The radiation patch is implemented using Cantor set fractal technology. By setting two symmetrical triangular tapered corners at the bottom of the wide slot, the impedance bandwidth of the proposed antenna can be enhanced. In addition, a T‐shaped tuning stub suspends at the top of the wide slot to achieve the notch band characteristic. Experimental and numerical results show that the proposed antenna, with compact size of 26 × 21 mm2, has an impedance bandwidth range from 2.8 to 11 GHz for voltage standing‐wave ratio less than 2, except the rejected band 5–6.3 GHz. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1227–1230, 2012

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