Design of a Threshold-based Authentication System Which Provides Attributes Using Secret Sharing

Abstract

In identity federation, each service provider verifies the identity of a user based on authentication performed by an authentication server called an Identity Provider (IdP). When the IdP suffer troubles like an unauthorized person has cracked into the IdP or the IdP is unreachable due to a network problem, all services in the federation are affected by them. Simple replication of servers for the IdP causes privacy concern because raw attribute values of users must be copied to many servers, including some servers that may not be fully trusted. In order to maintain the function as an IdP even under such troubles, we propose a system in which servers of the IdP are distributed and cooperate using threshold-based authentication and secret sharing. In this paper, we design the system from the viewpoint of management of attribute values so that an administrator of the IdP can update the values anytime while keeping consistency of attribute values among the servers in the IdP.

ID連携は，単一の認証サービスの結果を連携しているサービスが利用するため, 認証サービスへの不正アクセスや, ネットワークの障害が起こると, 連携している全てのサービスの利用に影響が出る. これを防ぐために複数の認証サービスを利用すると, ユーザの属性情報を分散させなければならず, プライバシー保護上の課題がある. 著者らは, 閾値型認証と秘密分散を用いて上記の問題点を解決するシステムを提案している. 本稿では, 分散時でも管理者が能動的に属性情報を管理でき, 属性情報更新時も整合性が維持できるように提案手法の詳細な設計を行う.