Minimizing the Time of Spam Mail Detection by Relocating Filtering System to the Sender Mail Server

Unsolicited Bulk Emails (also known as Spam) are undesirable emails sent to massive number of users. Spam emails consume the network resources and cause lots of security uncertainties. As we studied, the location where the spam filter operates in is an important parameter to preserve network resources. Although there are many different methods to block spam emails, most of program developers only intend to block spam emails from being delivered to their clients. In this paper, we will introduce a new and efficient approach to prevent spam emails from being transferred. The result shows that if we focus on developing a filtering method for spams emails in the sender mail server rather than the receiver mail server, we can detect the spam emails in the shortest time consequently to avoid wasting network resources.Comment: 10 pages, 7 figure

An Efficient Group Key Management Using Code for Key Calculation for Simultaneous Join/Leave: CKCS

This paper presents an efficient group key management protocol, CKCS (Code for Key Calculation in Simultaneous join/leave) for simultaneous join/leave in secure multicast. This protocol is based on logical key hierarchy. In this protocol, when new members join the group simultaneously, server sends only the group key for those new members. Then, current members and new members calculate the necessary keys by node codes and one-way hash function. A node code is a random number which is assigned to each key to help users calculate the necessary keys. Again, at leave, the server just sends the new group key to remaining members. The results show that CKCS reduces computational and communication overhead, and also message size in simultaneous join/leave.Comment: 18 pages, 16 figures, 4 table

セキュアマルチキャスト通信におけるメンバ離脱時の鍵配送を効率化するグループ鍵管理に関する研究

IP multicast is an efficient way to transfer IP datagram from a source to multiplerecipients, which are the members of a multicast group. Recently, the rapid growth ofthe broadband internet has resulted in an increase in demand for using IP multicast asa means of group communication in applications such as real time video distribution.However, there are security issues that lead to vulnerability of IP multicast. One of thesolutions proposed for avoiding vulnerability is the group data encryption with groupkey.Because of security requirements, forward secrecy and backward secrecy, the groupkey should be changed on each membership change and redistributed securely to currentmembers. This process involves computational, communication and message sizeoverhead at leave.This dissertation proposes two protocols and associate algorithms for group key managementin secure multicast and shows the detailed design of the protocols and the resultsof their efficiency evaluations. Both protocols are based on hierarchy approachesin which the group is logically divided into subgroups.The first protocol is designed for real-time video distribution in large scale network.In this protocol, the group members are logically divided into subgroups and the group members are managed in logical hierarchy model. The keys are calculated by modularexponentiation function in multiplicative groups Zp and the security is based on thedifficulty of the discrete logarithm. In order to re-key efficiently at leave the modularmultiplicative inverse is introduced. The inverse values are the inverse of the correspondingmember secret assigned to each member. By using the inverse values at leave,the keys are calculated by the members rather than delivered by the key server. For thispurpose, each member node in subgroups stores the inverse value of the other membersin that subgroup with the exception of its own. By using inverse values at leavethe key update process is delegated to the member side. Managing the group in hierarchymodel and introducing inverse values increases the re-keying efficiency at leave.By these features, the first protocol is designed for real-time video distribution in largescale multicast groups.The second one is considered for video conference in small multicast groups. In thisprotocol, the subgroups are managed in logical hierarchy model where the height ofthe key tree is 1. The subgroup keys are generated by using modular exponentiationfunction in multiplicative groups Zp and the security is based on the difficulty of thediscrete logarithm. Based on this property, hint keys are introduced to update the keysat leave. A hint key for member i in a subgroup is generated by the secrets of theremaining members, the secret key of member i is not included, and the server secretassigned to that subgroup using modular exponentiation function. At leave, these hintkeys help the remaining members in the subgroups, where the leave event takes place,calculate the associate subgroup key by raising the hint key to the power of the membersecret modulo p. In this protocol, each member stores at most three keys, its membersecret, the corresponding subgroup key and the group key. Because of this property,this protocol would be adapted for small multicast groups where members cannot storemany keys in their systems because of memory limitation.電気通信大学200

暗号理論における数論とそのアルゴリズムの研究

Supervisor:石原　哉情報科学研究科修