Accountable Authority Identity-based Encryption Scheme In Standard Model

In traditional public key cryptography system, a public key for user’s identity is usuallyto be bound by public key certificate which is issued by the certificate authority center.However, authentication and storage of certificates sharply increase the computation andstorage overhead. At the same time, it makes the certificate management complicated andincreases system burden. Identity-based cryptography system can solve above problems. Inthis system, the public key can be identity information of the user, while the private key isgenerated by the trusted central authority--the private key generator. It does not need to savethe user’s public key certificate directory and simplify the management process and reducesystem load.Identity-based cryptography system solves the problems in traditional public keycryptography, but there are still many problems, such as identity information extraction,authentication, private key distribution and key escrow problems.The thesis will focus on a study on the ciphersystem and provable safety of accountableauthority identity-based encryption scheme in the standard model about the key escrowproblems in identity-based cryptography system, It specifically contains:(1) Due to anonymity and key escrow problem in the IBE scheme, a accountableauthority and anonymous identity-based encryption scheme based on the idea of reducingtrust in the PKG and anonymity in a group of composite order is proposed, which is securewithout random oracles. The analysis shows that the proposed scheme is able to meet theproperties of anonymity and reducing trust in the PKG under the decisional bilinearDiffie-Hellman assumption and discrete logarithm assumption. The scheme can not onlyprotect the privacy of the receivers, but also solve the problem of key escrow. It has strongpractical value.(2) Towards the weakness of reducing trust in the PKG of identity-based encryptionscheme security in the white box model or weak black box model, a fuzzy and black-boxaccountable authority identity-based encryption scheme based on the idea of fuzzyidentity-based encryption scheme and black box model is proposed, which is secure in the standard model. Security analysis shows that the proposed scheme satisfies the properties ofIND-ID-CPA under the decisional bilinear Diffie-Hellman assumption. The scheme can alsoeffectively track the dishonest private key generations and users to avoid cheating behaviour.