Research On Spatial Location Data Query For Blockchain Based Proof Of Location

With the rapid development of indoor and outdoor positioning technologies and wireless communication technologies,as well as the popularity of smart phones,tablet computers and other mobile devices,location based services have become an important part of people’s daily life.However,due to the existing positioning means are easy to be manipulated and the proliferation of virtual location software,location falsification has become a great security risk to obtain trusted location services,so proof of location arises at the historic moment.However,the traditional architecture for proof of location has security problems such as centralization and easy data tampering,and some blockchain based location proof solutions have bottlenecks such as insufficient support for spatial data processing,limited query methods provided,and low query efficiency,making it difficult to meet the query requirements of the blockchain based proof of location.Therefore,based on the spatial and spatio-temporal efficient query requirements of blockchain based proof of location,this paper takes ethereum as the blockchain research platform,and according to the characteristics of its smart contract programming language,introduces geohash spatial index and stcode spatiotemporal index,which are commonly used in the field of GIS,into the blockchain,explores and compares two kinds of query methods on and off the blockchain,so as to find out more suitable query method for the application of blockchain based proof of location.The main contributions of this paper are as follows:(1)This paper studies the structure of ethereum and location proof process.Based on this,geohash spatial index and stcode spatial-temporal index are introduced into ethereum smart contract.Combined with the characteristics of the smart contract programming language,the dynamic array and dictionary storage structures are adopted.At the same time,storing data in the original transfer transaction is selected as a comparison.To meet the query needs for blockchain based proof of location,this paper designs the corresponding spatial range query and spatio-temporal query methods according to the different storage ways.Finally,the spatial and spatio-temporal query experiments are carried out based on the geolife trajectory dataset to study the query efficiency of block traversal,dynamic array traversal in smart contract,and index query based on dictionary structure in smart contract.(2)Limited to the query performance of blockchain,the off-chain query method is designed as a comparison of on-chain.Firstly,according to the type of transaction in blockchain,this paper should study how to parse the data stored in transfer transaction and smart contract call transaction,and select which necessary fields to store in the database of postgresql under the blockchain.Then,according to the fields stored in the data table,this paper designs five query methods: no index,b-tree,gist,geohash and stcode,which for the geohash and stcode,puts forward a way of optimizing the query in order to reduce the number of geohash or stcode codes,and then uses the same experimental data and experimental conditions as the on-chain query.A two-stage offchain query strategy of off-chain query by database plus on-chain verification is designed to study and compare the query efficiency of on-chain and off-chain methods.(3)Based on the optimal query method and the location proof protocol,the research results are used to realize the prototype system.Firstly,the architecture and functional composition of the blockchain based proof of location system are analyzed,including the app for proof of location,dapp for the the blockchain and the certificate query system for proof of location.Then the prototype system for proof of location is implemented based on the optimal off-chain query method.