The Improvement And Realization Of ElGamal Digital Signature Algorithm

The information security has become more and more crucial with the development of computer and network technologies. The digital signature is one of key techniques in information security, especially in the authentication, data integrity, and non-repudiation. It has been widely used in military, communication, e-commerce and e-government, etc., and will become more and more popular after the e-signature law is put in practice.Public–key cryptosystem is one of the research hotspots in current cryptograph. Since one of keys can be open, public-key cryptosystem has basic use for data encryption, besides for digital signature and identity recognition, and it is very fit for secret-key negotiation anti distributing in the internet. There are many public-key Cryptographic systems, such as RSA, ElGamal, elliptical-curve public-key cryptosystem, Rabin public-key cryptosystem and knapsack public-key cryptosystem since 1976 when Diffie and Hellman brought forward the conception of public-key cryptosystem. It is believed that the RSA cryptosystem based on factorization problem and the ElGamal cryptosystem based on unite discrete logarithm problem are the most practical and prospecting. But, how to select appropriate parameters and hove to establish secure instances rapidly has become more and more important with computers running faster and current cryptograph analysis technology developing rapidly. Digital signature is a main application of public-key cryptosystem. Now, the most popular digital signature systems are RSA, ElGamal and its transmutation, such as Schnorr and DSA. Though we can avoid some attacks by hash function, but if the system parameters are not appropriate, there always exists threats to security. So it is necessary to research selecting in designing application instances.One of two most important signature scheme was given by T.ElGamal in 1985, whose security is based on the difficulty of computing discrete logarithm over finite fields. Digital signature schemes with message recovery have obvious advantages: smaller bandwidth for signature scheme of small message, generation of short certificate, direct use in the scheme.ElGamal algorithm is the discrete logarithm problem of security. Generalized ElGamal signature program directed at the former ElGamal signature scheme to be improved increase the number of hidden parameters than the original ElGamal algorithm has stronger security. This paper presents a generalized ElGamal-based programs to improve signatures from the group signature scheme, with generalized ElGamal signature program of the same security. And broaden the scope of its application to the user group's signature. Signed group-oriented groups cryptography issue of a branch, in 1991 by Chaum and Van Heyst made. Make ElGamal type digital signature and certification programs in areas such as e-commerce system can be more widely applied.ElGamal and its transmutations are researched deeply in this paper. Firstly, various attack methods to ElGamal are analyzed and studied. Based on the studies, three kinds of attack methods are summarized. Wholly attack, by which signer's keys are ciphered out; arbitrary attack, by which valid signature are forged for arbitrary messages; by constructing special parameter, some valid signature are forged for special messages. Secondly, fundamentals and methods for selecting parameters are summed up in establishing instances of ElGamal signature system, according to the various attack methods to ElGamal. Thirdly, a new digital signature system is put forward. By adding a random number, making the link of the private-key and two random numbers more closely than it in the ElGamal digital signature scheme, makes it difficult to attack random numbers. Even if successful attack,was also difficult to attack the private-key by the random number.