**4. Summary**

Increasingly rich encryption principles have been exploited for halide perovskitebased security tags owning to their intriguing luminescent properties as response to a wide range of stimuli. Apart from the existing cases, the mechanochromism upon mechanical stress as well as the magnetochromism under altered magnetic field can be studied for perovskites with the aim of further enriching the diversity of authentication methods [102, 103]. Perovskite memristors as a new rising technology was also demonstrated to deliver switching electronic signals relative to the charged defects and halide motions inside the materials, providing an additional solution toward the design of PUF system [104]. All these unique optical and digital readout may overcome the limit of conventional clonable tags such as QR codes, watermarks, and raised print.

Future development of perovskite security tags is supposed to follow the taxonomy of predominant PUFs, including high encoding capacity, tunable security level, logically/physically reconfigurable functions, and switchable access between private and public. Based on the rational screening strategy of perovskite materials, micro- and nanoscale patterning techniques allow these functions to be multidimensionally integrated in a minimized tag, making security information more robust against third parties. Halide perovskites are bound to play a more important role in anti-counterfeiting arena and contribute to future smart flow of goods in a more fair and orderly global market.
