多階層分散時刻認証局の実装と実証実験

摘要

Digital time stamping based on digital signatures proved the existence of a digital data prior to a specific point in time and that the contents have not changed since that time. The centralized simple time-stamping authority has high administrative costs and lack of scalability of performance. Distributed time-stamping methods were proposed to solve the problems, but still have the problem to prepare many TSAs. We had shown that K = L + M among N for G-generation method is able to solve these existing problems. That method does the time-stamping to the mutuality by using many time-stamping units. In this report, we expanded our distributed time-stamping method. We append various attribute classes to the distributed time-stamping units, and introduced layered structure in the unit. We developed K = ∑_iL_i + ∑_j M_j among N for G-generation method. As that result, we are able to issue distributed time-stamps classified by each attribute of time-stamping unit. For example, it became possible that a distributed timestamps was built from the group of time stamps that it was issued from the time-stamping unit installed only in Japan. And also it improved the system tolerance for distributed denial of service attack more at former method for the multiple layer of time-stamping unit.%デジタルデータの存在，非改寵証明の有効な手段にデジタル署名による時刻認証法がある．従来の単独のデジタル署名による時刻認証局には運用コストや性能スケーラビリティの問題が存在し，その解決を試みた従来の分散時刻認証法には多数の時刻認証局をどうやって設置するかの問題が存在する．既存のこれらの問題を，我々は，多数の時刻認証ユニットを用いて相互に時刻認証を行うK＝L＋M among N for G-generation分散時刻認証法で解決出来ることを示して来た．今回、多数の時刻認証ユニットに様々な属性を付与して時刻認証ユニットに階層構造を導入して拡張し、K＝∑_iL_i＋∑_jM_j among N for G-generation分散時刻認証法とした。これにより時刻認証ユニットの属性毎に分散時刻認証が可能となり、例えば日本国内だけに設置されている時刻認証ユニットから発行されたタイムスタンプ群から分散時刻認証タイムスタンプを構築するということが可能になった．また多階層化により以前では信頼できる時刻認証ユニットが複数種類持てるようになり分散DoS攻撃耐性を向上させることが可能になった。