Abstract:Chandran, et al. introduce the direction of position based cryptography at CRYPTO 2009. In position based cryptography, the position of a party is used to be its unique "credential" in order to realize the cryptographic tasks, such as position based encryption, position based signature, position based key exchange and so on. Position based key exchange, as a basic primitive in position based cryptography, can be used to establish a shared key based on the position of the participant. 7R EHJLQ ZLWK WKLV SDSHU SUHVHQWV WKH QRWLRQV RI WKH SURYHUWRYHUL¿HU PRGH DQG WKH SURYHUWRSURYHU PRGH IRU SRVLWLRQ EDVHG NH\ H[FKDQJH ,Q WKH SURYHUWRYHUL¿HU PRGH D VHFUHW NH\ FDQ EH VKDUHG EHWZHHQ D SURYHU DQG WKH YHUL¿HUV DFFRUGLQJ WR WKHposition of the prover. While in the prover-to-prover mode, two provers located at the valid positions can negotiate a shared NH\ ZLWK WKH KHOS RI WKH YHUL¿HUV DQG DQ\ RWKHU SDUW\ ZKRVH SRVLWLRQ LV LOOHJDO FDQQRW REWDLQ WKH VKDUHG NH\ $W WKH VDPH WLPH WKLV SDSHU IRUPDOL]HV WZR VHFXULW\ GH¿QLWLRQV DJDLQVW FROOXGLQJ DGYHUVDULHV SRVLWLRQ EDVHG SURYHUWRYHUL¿HU NH\ H[FKDQJH DQGposition based prover-to-prover key exchange. Then, this paper introduces the bounded retrieval model and the implementations of position based key exchange in two modes based on the bounded retrieval model. Finally, this paper discusses the position based key exchange protocols in two modes from both security and performance perspectives.