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Identity-based cryptography is a type of public-key cryptography in which a publicly known string representing an individual or organization is used as a public key. The public string could include an email address, domain name, or a physical IP address. The first implementation of identity-based signatures and an email-address based public-key infrastructure (PKI) was developed by Adi Shamir in 1984,〔Adi Shamir, (Identity-Based Cryptosystems and Signature Schemes ). ''Advances in Cryptology: Proceedings of CRYPTO 84, Lecture Notes in Computer Science'', 7:47--53, 1984〕 which allowed users to verify digital signatures using only public information such as the user's identifier. Under Shamir's scheme, a trusted third party would deliver the private key to the user after verification of the user's identity, with verification essentially the same as that required for issuing a certificate in a typical PKI. Shamir similarly proposed identity-based encryption, which appeared particularly attractive since there was no need to acquire an identity's public key prior to encryption. However, he was unable to come up with a concrete solution, and identity-based encryption remained an open problem for many years. The first practical implementations were finally devised by Sakai in 2000,〔 〕 and Boneh and Franklin in 2001.〔 〕 These solutions were based on bilinear pairings. Also in 2001, a solution was developed independently by Clifford Cocks.〔 〕 ==Usage== Identity-based systems allow any party to generate a public key from a known identity value such as an ASCII string. A trusted third party, called the private key generator (PKG), generates the corresponding private keys. To operate, the PKG first publishes a master public key, and retains the corresponding master private key (referred to as ''master key''). Given the master public key, any party can compute a public key corresponding to the identity ''ID'' by combining the master public key with the identity value. To obtain a corresponding private key, the party authorized to use the identity ''ID'' contacts the PKG, which uses the master private key to generate the private key for identity ''ID''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「ID-based cryptography」の詳細全文を読む スポンサード リンク
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