The Implementation Of PKG And Security Analysis In The Identity-based Encryption System

Public Key Infrastructure (PKI), as a technology system in the information security field, provides the services of confidentiality, integrity, authentication and non-repudiation for the internet application. However, we have many complicated problems to resolve when using PKI. The public key and the public key owner are boundd by the digital certification in PKI system, and a serial of operations, such as certification register, management, storage, dispatch, revocation certification, and so on, should be done, at the same time, the certification library need to be run online.Identity-based Encryption (IBE) concept was introduced by Shamir. Several years later, a practical IBE scheme was designed by Dan Boneh and Matt Franklin in 2001 for solving PKI's problems. In this practical IBE scheme, any string about user's identity can be regarded as public key, for example, the user's telephone number, e-mail address or IP address, and the corresponding private key is generated safely by a trusted third party named as Private Key Generator (PKG). Compared IBE with PKI, IBE is advantageous in free certification management. In addition, key distribution and key revocation are not required. IBE is a flexible encryption and certification system for the character of the public key depending on its identity, and as a new secure scheme, it has become popular in the information secure field.The IBE system consists of two parts: PKG and user entities. PKG is the core of the IBE system, PKG is taking on the task of generating the master key, establishing system parameters, producing the user's private key, managing and distributing the user's private key. User entities are either the senders or the receivers of encrypted message, taking on the task of encryption and decryption.IBE scheme is based on the theory of the difficulty of the Bilinear Diffie-Hellmen, and can be implemented with the Weil pair. By the use of the Bilinear Map of Elliptic Curve, an algorithm is obtained, which can change a simple identity to a public key and private key pair. To understand the IBE scheme's theory is largely to master the concepts of Elliptic Curve, Bilinear Diffie-Hellmen, Bilinear Map and so on. It is need to study from its basic functions, main characters and implementing procedures.Identity-based encryption mechanism is composed of four algorithms, which are Setup, Extract, Encrypt and Decrypt. The input of Setup algorithm is a secure parameter and the output returns the system parameters and the master key. The system parameters are public, but the master key is private. The inputs of Extract algorithm are system parameters, master key and a unique identity and the output is a private key corresponding to the user's identity. The inputs of Encrypt algorithm are system parameters, identity and plain text and the output is cipher text. The inputs of Decryption algorithm are system parameters, cipher text and private key and the output is plain text.Based on the latest researching results of identity-based encryption system, and combined with Boenh-Franklin identity-based encryption scheme, a detailed design and implementation of PKG is given in this paper, which is a component of the IBE prototype. The security solutions are given, and then summed up a more comprehensive security rule during deploying a practical application by analyzing the internal and external security threats that the PKG is facing. To solve the key escrow issue, which is one of an internal threat, a new IBE scheme is put forward.In this paper, firstly, PKG is departed into four components, which including the master key generation, the establishment of system parameters, user's private key generation, and the user's private key and system parameters dispenser by analyzing the PKG's functions. After designing the whole flow and building the data structure, it shows the realization of PKG functions in software module level by decomposing the PKG operation flow. For master key and system parameters are all generated with random generator, big integer random generator is first designed and implemented with the Borrow Subtraction Algorithm. For user's private key is combined with master key and user's identity, a hash function of mapping user's identity to one point of Elliptic Curve is designed and then compute the point of private key with Add Subtraction Algorithm of multiples on Elliptic Curve. After the implementation of system parameters and user's private key, a multithread program is designed to dispense the system parameters and user's private key.Secondly, the security threats from internal and external that the PKG is facing are comprehensively analyzed, including the aspects of the master key management, key escrow, the Elliptic Curve Encryption system and the transmission procedure. The threat methods on Elliptic Curve are mainly analyzed in this paper, after that, several measures to the different threats are discussed. A more comprehensive security rule is summed up, which need to be obeyed during deploying a practical PKG application.In the last part of the paper, according to the analysis of the PKG security, key escrow is a problem that has not been well solved for a long time, so a new ID Alias-based Encryption scheme with a trusted third party is introduced in this paper based on the current researching results. A Trusted Authority (TA) is added to achieve trust transfer and the problem of key escrow is solved in this scheme. The user's private key is produced by the user and the PKG. It's convenient to update the private keys by importing the ID alias. The processes of ID alias registing, encryption and decryption are introduced comprehensively in the new schema. Then the potential threats in the new schema are analysed. The analysis shows the scheme is secure. Meanwhile the scheme solved the problem IBE faced during the stage of deployment and extended the application range of IBE system evidently.There are a few core algorithms about PKG in IBE system introduced in this paper, which are little appeared in current research results. There are some reference values to the research of the IBE system. In addition, the security rules which PKG has to obey during the stage of deployment summed up in this paper are important to improving the whole security of IBE system. What's more, in order to solving the key escrow issue, a new idea is shown in this paper, and it extended the thought about the forward IBE researching.