  Wireless information and power transfer (WIPT) enables more sustainable and
resilient communications owing to the fact that it avoids frequent battery
charging and replacement. However, it also suffers from possible information
interception due to the open nature of wireless channels. Compared to
traditional secure communications, secrecy wireless information and power
transfer (SWIPT) carries several distinct characteristics. On one hand,
wireless power transfer may increase the vulnerability of eavesdropping, since
a power receiver, as a potential eavesdropper, usually has a shorter access
distance than an information receiver. On the other hand, wireless power
transfer can be exploited to enhance wireless security. This article reviews
the security issues in various SWIPT scenarios, with an emphasis on revealing
the corresponding challenges and opportunities for implementing SWIPT.
Furthermore, we provide a survey on a variety of physical layer security
techniques to improve secrecy performance. In particular, we propose to use
massive multiple-input multiple-output (MIMO) techniques to enhance power
transfer efficiency and secure information transmission simultaneously.
Finally, we discuss several potential research directions to further enhance
the security in SWIPT systems.
