多媒體網路安全實驗室 Protecting the Privacy of Users in e-Commerce Environment Date： Reporter:Chien-Wen Huang Author: Chun-Hua Chen and Gwoboa Horng 出處: CCCT2004, Aug, 2004.

多媒體網路安全實驗室 Outline INTRODUCTION 1 BASIC DEFINITION OF OS-PIR AND OUR OS- PIR SCHEME 2 33 THEOREM AND PROOF 2 COMPARISONS TO OTHER PIR SCHEMES 4 CONCLUSIONS 5

多媒體網路安全實驗室 INTRODUCTION  Private Information Retrieval: PIR  A user to keep his preferences private from everybody including the server.  EX:Patent Databases 、 Pharmaceutical Databases. 1.The first research of PIR was done by Chor et al. in 1995.(communication complexity:O(n 1/k )) 2.To improve the complexity, Chor et al. introduced the notation of Computational PIR(CPIR) 3

多媒體網路安全實驗室 Private Information Retrieval EX: 使用者隨機選取 S = {5,15,47} ( 假定 n=10000, index i = 15, S ⊕ i = {5,47}) 4

多媒體網路安全實驗室  We propose a simple one-server PIR(OS-PIR) scheme to provide privacy protection for online users in e-commerce 1.The scheme is more practical than previous PIR schemes in e-commerce environment. 2.The scheme has theoretical security to user privacy. 5

多媒體網路安全實驗室 BASIC DEFINITION OF OS-PIR AND OUR OS-PIR SCHEME  1.The user produces a query: to database server. 2.The database server responds 3.The user reconstructs the desired bit x i.(by reconstruction function )  Correctness: For every,  Privacy: For every 6

多媒體網路安全實驗室 OS-PIR scheme(1) 1.The user randomly choose a small prime P 1 (e.g 19 or 101) and sends P 1 to the database server. In other words, =P 1. 2.The database server calculates and sends it back to the user. 1) 2) For k=2 to n do (a)Calculate the next bigger prime P k (b) (x k is the value of k bit of X) 3) 7

多媒體網路安全實驗室 OS-PIR scheme(2) 3)The user reconstructs the desired bit 1)Calculate the P i (the user knows P 1 already) 2)If mod P i =0 Then =1 Else =0 EX: The Database [0,1,0,0,1,0,0,1],and user choose randam prime P 1 =19 1. P 1 = =

多媒體網路安全實驗室 THEOREM AND PROOF  Our scheme proposed is OS-PIR,has information-theoretic security in the property of privacy. 1.Match the form of the OS-PIR scheme. 2.the user and the database server can calculate the value of Pi both. 3.Satisfy the property of privacy: Because the is P 1, a small prime randomly chosen by user. 9

多媒體網路安全實驗室 COMPARISONS TO OTHER PIR SCHEMES 10

多媒體網路安全實驗室 CONCLUSIONS  The OS-PIR scheme was proposed which has practical feasibility and it can be easily implemented.  It avoids the large management overheads of multi-servers and has theoretical security to users’ privacy. 11

多媒體網路安全實驗室