比較器ネットワークを用いた安全なマルチパーティプロトコル

We consider statistical analysis with preserving the privacy of respondents. Wepropose a secure multiparty protocol using comparator networks for variouscomputations in statistical analysis. The comparator networks sort or searchtheir input values to obtain the maximum, minimum, median, quartiles, andso on. In the protocol, both the input values of a comparator network andthe intermediate outputs are kept secret, assuming the presence of an honestmajority. The proposed protocol employs secure circuit evaluations which canbe applied to compute a comparator network safely. The secure circuit evaluationis one of the cryptographic protocols that enables arbitrary operationson encrypted data without decryption. To anonymize the input values of theprotocol, we use the MIX-net, which is a cryptographic anonymous channel.The input values are shuffled by the MIX-net before applying a comparatornetwork. We discuss the effectiveness of the protocol for computing severalstatistics through a comparator network. We also introduce an application ofthe protocol to a secure (m+1)-st price auction, in which the highest m bidderswin and pay a uniform price determined by the (m + 1)-st price.We give another result of studies in merging networks. A merging networkis a comparator network that merges two sorted sequences. Let M(m, n) be theminimum number of comparators that construct an (m, n)-merging network,i.e., an optimal (m, n)-merging network consists of M(m, n) comparators. Weshow that Batcher’s (6, 8k+7)-, (9, 16k+9)-, (7, 8)-merging networks are optimalfor all k 0. Under an assumption of the existence of several comparatorsin an optimal merging network, we show that M(n, n) = M(n － 1, n) + 1 =M(n － 2, n) + 3.電気通信大学200

Privacy enhanced active RFID tag

In the coming future ubiquitous society, Radio Frequency Identification (RFID) tags will be affixed to every product and person. This technology is anticipated to be a key technology that will be utilized by various ubiquitous services where these tags will be used to identify things and people and will automatically take advantage of contextual information such as location. On the other hand, a problem is arising where the excellent tracking ability of RFID is abused and personal privacy is being violated. This paper clarifies the active tag privacy problem and proposes a method for protecting personal privacy regarding the active RFID tags. In the proposed method, reencryption technologies are used to make the tag ID variable. Since variable IDs generated from one ID are cannot be linked to one another by third parties, RFID privacy problems based on a fixed ID can be abated. Furthermore, we introduce an active tag prototype that implements the proposed method and evaluated its effectiveness