Anonymity Study Based On Identity Encryption Scheme

With the wide popularity of information technology, computer networks and e-commerce, people’s life and social development have greatly benefited from it. Meanwhile the popularity also brings a lot of serious information security risks. As the cornerstone and the core of information security, cryptography can effectively solve the security communication problem and protect users’privacy. It plays an important role in information security. Most public key encryption systems equip a public key infrastructure to distribute public keys and the infrastructure can authenticate user’s public key certificate, identify a user using the certificate, and guarantees the integrity of public keys. In such a system, the generation, distribution, management, cancellation and maintenance of certificate will take a lot of time and resources.Shamir first proposed the idea of identity-based encryption which uses the users’ identity as a public key. The private key can be generated by a trusted third party. Compared with traditional public key encryption systems, the identity-based encryption system depends no longer on a public key infrastructure to generate certificates. It greatly decreases the computational complexity of the encryption system. At present, identity-based encryption system has become a hot topic in public key cryptography research.A realistic problem of identity-based encryption system is that:when a sender uses the receiver’s identity information as a public key to encrypt a message, receiver’s identity information may be obtained easily by adversary. As a result, the identity information of the receiver will be leaked easily. To protect the privacy of receivers, it is necessary to research anonymous IBE scheme. This dissertation mainly studies anonymous IBE schemes, and the main works are as followings:1. This paper first introduces the development process and research background of IBE. Then intensively studies the anonymity of IBE schemes, and analyzes the anonymity of some typical IBE schemes.2. Extends the Groups in Waters IBE Scheme to bilinear groups with composite orders, and constructs an anonymous identity based encryption scheme based on the bilinear groups. Since the new IBE scheme slightly improves Waters IBE scheme and only adds the anonymity to it, it has no obvious advantages on the efficiency and security.3. It is an open problem proposed by Gentry how to construct an anonymous identity-based encryption scheme based on a weaker computational complexity assumption. In this paper, we propose a new anonymous IBE scheme which is based on the DBDH assumption. This scheme is secure against adaptive chosen plaintext attack. We analyze the anonymity of the scheme and prove that it is correct and secure. Our scheme is superior in the recipient anonymity and is without using pairing computations in the encryption. Compared to Gentry’s scheme, ours is based on a more common difficulty assumption and makes up the vacancy of anonymous IBE scheme under DBDH difficulty assumption.4. Further research is done based on previous scheme. In this paper, we, based on a weaker computational complexity assumption, propose a publicly verifiable anonymous IBE scheme being secure against adaptive chosen ciphertext attack. The security of this scheme can be tightly reduced to solving the decisional bilinear Diffie-Hellman problem (DBDH). Our scheme does not need pairing computation at encryption phase, is publicly verifiable at decryption phase, and makes a recipient anonymous. Compared with Gentry’s scheme, ours achieves stronger security based on a weaker computational complexity assumption, and improves the encryption efficiency. Therefore, it can be better used in practical applications.