在多數且獨立的私密金鑰產生中心的環境下以身份為基礎的金鑰協議

Abstract

金鑰協議是用來讓兩個實體建構一把共用金鑰的協議，期間兩個實體都要對此協議給予一定的資訊。Diffie-Hellman金鑰協議是這個領域的基礎。近來，因為以身份為基礎的加密法掘起，以身份為基礎的金鑰協議也成為一個熱門的研究主題。以身份為基礎的金鑰協議乃是一個建立在以身份為基礎的環境下的一個金鑰協議。換句話說，在此環境下的金鑰協議，使用者的公開金鑰都是由使用者的身份衍生出來的。目前大多數的以身份為基礎的金鑰協議都是建立在同一個私密金鑰產生中心下面。然而，全世界只使用同一個私密金鑰產生中心是不實際也不合理的。此外，這樣的環境也沒有彈性。若系統參數的改變是必需的，因為每個實體都是在同一個私密金鑰產生中心之下，所有的實體都需要改變，所以想改變此參數幾手是不可能的。因此，我們會希望在每個不同的領域下，都會有一個不同的私密金鑰產生中心。我們更希望這些私密金鑰產生中心是完全獨立的，也就是說所有的私密金鑰產生中心都有它自己獨有的系統參數(例如：主要金鑰、群、成對函數)。此外，在完全獨立的私密金鑰產生中心的環境下，每個私密金鑰產生中心都可以任意選則自己的系統參數。

Key agreement is a process for two entities to agree on a shared secret key in a way that both entities contribute information to establish the shared key. Diffie-Hellman key agreement protocol is a seminal work in this problem area. Recently, because of the rising of identity-based cryptography, identity-based key agreement also becomes a hot research topic. An identity-based (ID-based) key agreement protocol is an key agreement protocol based on identity-based environments, that is, public keys are related to identities. However, most of existing ID-based key agreement protocols are based on single private key generator (PKG) environments. That is, only one entity is responsible to generate private keys for users. However, it is impractical that only one PKG exists in the whole world. The PKG becomes a single point of failure. Moreover, these environments are not scalable. If changing system parameters is required, it is infeasible to do so in single PKG environments. Because every entity in the world has to change its parameter accordingly. Therefore, it is natural that each administrative domain has its own PKG. A desirable feature of multiple PKG environments is to have multiple independent PKGs. That is, each PKG has its own unique system parameters, like a master key, groups, a pairing function, etc. Independent PKGs make each PKG has freedom to choose its own system parameters according to its need.