Cryptography and Lucas Sequence Discrete Logarithms

The concept of public key cryptography was first introduced by Diffie and Hellman in 1976 using discrete logarithm problem as base of difficulty. In 1985, T. ElGamal proposed public key cryptosystem scheme based on discrete logarithm problem. Elliptic curve cryptosystems were first proposed in 1985 independently by Neil Koblitz and Victor Miller. Elliptic curve cryptosystems are unique in using elliptic curve groups for arithmetic. This cryptosystem is based on discrete logarithm problem in the group of points of an elliptic curve defined over a finite field. The discrete logarithm problem in an elliptic curve group appears to be much harder than the discrete logarithm problem in other groups. Hence elliptic curves cryptosystem can match the security of other cryptosystems while using smaller key. In this paper we will discuss a VLSl implementation of elliptic curves cryptosystem for ElGamal encryption scheme.

A subexponential algorithm for discrete logarithms over hyperelliptic curves of large genus over GF( q)

In 1976 Diffie and Hellman [152] described the framework for public-key cryptography. It was not until 1978 that three designs for public-key cryptosystems were published. Rivest, Shamir, and Adleman [431] showed how the discrete logarithm and factorization problems could be used to construct a public-key cryptosystem. This is the well-known RSA cryptosystem. Merkle and Hellman [339] used the knapsack problem in their construction. McEliece [329] built a system based on error correcting codes. Later in 1985 ElGamal [163] designed a public-key cryptosystem using the discrete logarithm problem. Koblitz [283] and Miller [346] suggested the use of elliptic curves in the design of public-key cryptosystems. Nowadays, there are quite a few more suggestions as to how to design public-key cryptosystems, but none so popular as the RSA and ElGamal cryptosystems.

The new signature scheme presented by the authors in [13] is the first signature scheme based on the discrete logarithm problem that gives message recovery. The purpose of this paper is to show that the message recovery feature is independent of the choice of the signature equation and that all ElGamal-type schemes have variants giving message recovery. For each of the six basic ElGamal-type signature equations five variants are presented with different properties regarding message recovery, length of commitment and strong equivalence. Moreover, the six basic signature schemes have different properties regarding security and implementation. It turns out that the scheme proposed in [13] is the only inversionless scheme whereas the message recovery variant of the DSA requires computing of inverses in both generation and verification of signatures. In general, message recovery variants can be given for ElGamal-type signature schemes over any group with large cyclic subgroup as the multiplicative group of GF(2n) or elliptic curve over a finite field. The present paper also shows how to integrate the DLP-based message recovery schemes with secret session key establishment and ElGamal encryption. In particular, it is shown that with DLP-based schemes the same functionality as with RSA can be obtained. However, the schemes are not as elegant as RSA in the sense that the signature (verification) function cannot at the same time be used as the decipherment (encipherment) function.

Elliptic curves cryptography was introduced independently by Victor Miller (Miller, 1986) and Neal Koblitz (Koblitz, 1987(Koblitz, ) in 1985. .At that time elliptic curve cryptography was not actually seen as a promising cryptographic technique.As time progress and further research and intensive development done especially on the implementation side, elliptic curve cryptography is now being implemented widely.Elliptic curves cryptography offers smaller key size, bandwidth savings and faster in implementations when compared to the RSA (Rivest-Shamir-Adleman) cryptography which based its security on the integer factorization problem.The most interesting feature of the elliptic curves is the group structure of the points generated by the curves, where points on the elliptic curves form a group.The security of elliptic curves cryptography relies on the elliptic curves discrete logarithm problem.The elliptic curve discrete logarithm problem is analogous to the ordinary algebraic discrete logarithm problem, l = g x , where given the l and g, it is infeasible to compute the x.Elliptic curve discrete logarithm problem deals with solving for n the relation P = nG.Given the point P and the point G, then it is very hard to find the integer n.To implement the discrete logarithm problem in elliptic curve cryptography, the main task is to compute the order of group of the curves or in other words the number of points on the curve.Computation to find the number of points on a curve, has given rise to several point counting algorithms.The Schoof and the SEA (Schoof-Elkies-Atkin) point counting algorithms will be part of the discussion in this chapter.This chapter is organized as follows: Section 2, gives some preliminaries on elliptic curves, and in section 3, elliptic curve discrete logarithm problem is discussed.Some relevant issues on elliptic curve cryptography is discussed in section 4, in which the Diffie-Hellman key exchange scheme, ElGamal elliptic curve cryptosystem and elliptic curve digital signature scheme are discussed here accompanied with some examples.Section 5 discussed the two point counting algorithms, Schoof algorithm and the SEA (Schoof-Elkies-Atkin) algorithm.Following the discussion in section 5, section 6 summaries some similarities and the differences between these two algorithms.Section 7 gives some brief literature on these two point counting algorithms.Finally, section 8 is the concluding remarks for this chapter. Elliptic curvesElliptic curves obtained their name from their relation to elliptic integrals that arise from the computation of the arc length of ellipses (Lawrence & Wade, 2006).Elliptic curves are www.intechopen.com Cryptography and Security in Computing1 1 2 3 4 2 2 4 Fig. 1.1. 2(1 ) (1 ) yx x x   www.intechopen.com

The discrete logarithm problem (DLP) plays an important role in modern cryptography since it cannot be efficiently solved on a classical computer. Currently, the DLP based on the hyperelliptic curve of genus 2 (HCDLP) is widely used in industry and also a research field of hot interest. At the same time, quantum computing, a new paradigm for computing based on quantum mechanics, provides the ability to solve certain hard problems that cannot be efficiently solved on classical computers. In this paper, we consider the problem of solving the HCDLP in the paradigm of quantum computing. We propose a quantum algorithm for solving the HCDLP by applying the framework of quantum algorithm designed by Shor. The key of the algorithm is the realization of divisor addition. We solve the key problem and get analytical results for divisor addition by geometric meaning of the group addition. Therefore, the procedure can be efficiently realized on a quantum computer using the basic modular arithmetic operations. Finally, we conclude that the HCDLP defined over an n-bit prime field $$\mathbb {F}_{p}$$ can be computed on a quantum computer with at most $$13n+2\lfloor \log _{2}n\rfloor +10$$ qubits using $$2624n^{3} \log _{2}n-2209.2n^{3} + 1792n^{2} \log _{2}n-3012.8n^{2}$$ Toffoli gates. For current parameters at comparable classical security levels, there are fewer qubits and Toffoli gates to solve the HCDLP than the ones to solve the DLP based on elliptic curves.

There have been many digital signature schemes were developed based on the discrete logarithm problem on a finite field. In this study, we use the elliptic curve discrete logarithm problem to build new collective signature schemes. The cryptosystem on elliptic curve allows to generate digital signatures with the same level of security as other cryptosystems but with smaller keys. To extend practical applicability and enhance the security level of the group signature protocols, we propose two new types of collective digital signature schemes based on the discrete logarithm problem on the elliptic curve: i) the collective digital signature scheme shared by several signing groups and ii) the collective digital signature scheme shared by several signing groups and several individual signers. These two new types of collective signatures have combined the advantages of group digital signatures and collective digital signatures. These signatures have a fixed size and do not depend on the number of members participating in the creation of the final collective signature. One of the advantages of the proposed collective signature protocols is that they can be deployed on top of the available public key infrastructures.

The ElGamal cryptosystem was originally proposed by Taher ElGamal in 1985, in which its security level is based on the Discrete Logarithm Problem (DLP). ElGamal cryptosystem is relatively an expensive algorithm. For security guarantees, ElGamal cryptosystem requires modulo operation of large prime integer whose size range approximately from 1,024 to 4,096 bits. As a consequence of such requirement, the application of ElGamal cryptosystem is limited for securing only small messages such as secret keys. This paper aims to propose an efficient variant of ElGamal cryptosystem. The proposed scheme is designed based on quotient ring of polynomial, \( Z_{2} [x]/{ } \), where \( f\left( x \right) \) is an irreducible polynomial. The decryption algorithm was further optimized with the use of the multiplicative inverse of the generator g(x), which only generated once during the key generation algorithm, thus leading to a simpler and faster decryption process. The proposed scheme is as secure as the original ElGamal scheme, since both schemes are based on the DLP. The preliminary result shows that the proposed scheme minimizes complex arithmetic operations and achieves very practical performance compared to the classic ElGamal algorithm and its variants. The proposed \( F_{2}^{n} \) based ElGamal scheme outperforms the \( F_{p} \) based scheme by significantly reducing 69.74% of the numbers of required logic gates in the case study of VLSI implementation.

The discrete logarithm problem with auxiliary inputs (DLP-wAI) is a special discrete logarithm problem. Cheon first proposed a novel algorithm to solve the discrete logarithm problem with auxiliary inputs. Given a cyclic group $${\mathbb {G}}=\langle P\rangle $$G=?P? of order p and some elements $$P,\alpha P,\alpha ^2 P,\ldots , \alpha ^d P\in {\mathbb {G}}$$P,?P,?2P,?,?dP?G, an attacker can recover $$\alpha \in {\mathbb {Z}}_p^*$$??Zp? in the case of $$d|(p\pm 1)$$d|(p±1) with running time of $${\mathcal {O}}(\sqrt{(p\pm 1)/d}+d^i)$$O((p±1)/d+di) group operations by using $${\mathcal {O}}(\text {max}\{\sqrt{(p\pm 1)/d}, \sqrt{d}\})$$O(max{(p±1)/d,d}) storage ($$i=\frac{1}{2}$$i=12 or 1 for $$d|(p-1)$$d|(p-1) case or $$d|(p+1)$$d|(p+1) case, respectively). In this paper, we propose a new algorithm to solve another form of elliptic curve discrete logarithm problem with auxiliary inputs (ECDLP-wAI). We show that if some points $$P,\alpha P,\alpha ^k P,\alpha ^{k^2} P,\alpha ^{k^3} P,\ldots ,\alpha ^{k^{\varphi (d)-1}}P\in {\mathbb {G}}$$P,?P,?kP,?k2P,?k3P,?,?k?(d)-1P?G and multiplicative cyclic group $$K=\langle k \rangle $$K=?k? are given, where d is a prime, $$\varphi (d)$$?(d) is the order of K and $$\varphi $$? is the Euler totient function, the secret key $$\alpha \in {\mathbb {Z}}_p^*$$??Zp? can be solved in $${\mathcal {O}}(\sqrt{(p-1)/d}+d)$$O((p-1)/d+d) group operations by using $${\mathcal {O}}(\sqrt{(p-1)/d})$$O((p-1)/d) storage.

Identity-based signatures (IBS) can be verified using the signer identity information as the public key, and hence, there is no need for certificate management that proves the corresponding public key ownership. Unfortunately, none of the existing IBS schemes has security proven as tight as the discrete logarithm (DL) problem, the hardest problem in the cyclic group setting, under the standard EUF-CMA security model. Recently, the introduction of proving security in the algebraic group model (AGM), where the adversary’s computation is algebraic, enables some ordinary signature schemes to be proven tightly reducible under DL assumption and EUF-CMA. To date, however, it remains unknown whether IBS schemes can also be proven as secure as the DL problem in the AGM. Achieving tight security in IBS schemes under standard EUF-CMA is challenging, due to the need to take extra precautions against adaptive queries on user private keys by the adversary. In this work, we show, for the first time, an IBS scheme with tight security under DL assumption and EUF-CMA in the AGM. The scheme features a minimal signature size of two group elements, with a reduction loss factor of two.

We discuss analogs based on elliptic curves over finite fields of public key cryptosystems which use the multiplicative group of a finite field. These elliptic curve cryptosystems may be more secure, because the analog of the discrete logarithm problem on elliptic curves is likely to be harder than the classical discrete logarithm problem, especially over ${\text {GF}}({2^n})$. We discuss the question of primitive points on an elliptic curve modulo p, and give a theorem on nonsmoothness of the order of the cyclic subgroup generated by a global point.

This chapter presents another public-key cryptographic method used world-wide, the Diffie-Hellman key exchange. Section 8.5 introduced an efficient algorithm for finding \(h = g^{m}\) where g is an element of a finite group, for example when the group is the group of units modulo a prime p and m is a large exponent. The reverse problem, given g and h, find m, is called the discrete logarithm problem, and is a hard problem. The security of Diffie-Hellman key exchange and the closely related ElGamal cryptosystem is based on that fact. Needed for Diffie-Hellman are cyclic groups of large order. We find many such groups by proving the Primitive Root Theorem, which states that for every prime number p, the group of units of \(\mathbb {Z}_{p}\) is a cyclic group. The chapter concludes with two methods that can be more efficient than constructing log tables for solving the discrete logarithm problem; one method involves use of the Chinese Remainder Theorem.

Наведено порівняльний аналіз відомих протоколів узгодження таємного ключа через відкритий канал звʼязку. Запропоновано узагальнення відомого протоколу з використанням некомутативного множення матриць над простим скінченним полем на випадок довільного скінченного поля. A symmetric cryptosystem requires a secret key agreed by both parties. The Diffie-Hellman protocol was originally proposed for its exchange via an open communication channel. It is based on the computational complexity of the discrete logarithm problem in certain finite groups (the multiplicative group of a finite field, the group of points of an elliptic curve over a finite field). The availability of a powerful quantum computer will allow solving the discrete logarithm problem in these groups. Therefore, the issue of construction of secret key exchange protocols that will be resistant to attacks using a quantum computer has become urgent. The paper provides a comparative analysis of known protocols for a secret key exchange via an open communication channel. A generalization of the known protocol using non-commutative matrix multiplication over a prime finite field for the case of an arbitrary finite field is proposed. In this protocol, two high order elements from the general linear group over a finite field should be used, which satisfy an additional condition. It consists in the fact that each of the matrices cannot be reduced to a diagonal form by conjugation transformation. This condition follows from the considerations of avoiding an attack on the protocol. It is shown how to construct such elements. For the proposed generalization of the protocol, the sizes of public and private keys, secret key, the size of the finite field, which ensure the appropriate level of security, are calculated. The dimensions of matrices (elements of the general linear group) that we use are also given. The generalization of the protocol to the case of an arbitrary finite field increases the flexibility of choosing protocol parameters to ensure the desired level of security.

Research in the field of public key cryptography in general and digital signatures in particular is often considered and evaluated at two levels: The first level is considering the mathematical basis for constructing cryptographic and digital signature algorithms, especially these difficult problems: factorizing a large integer into prime factors, finding root problem, discrete logarithm problem, discrete logarithm problem on elliptic curve... The second level is constructing cryptographic and digital signatures algorithms on these hard problems including RSA, DSA, Schnorr, GOST R34.10-94. At the first level, research focuses mainly on improving algorithms for finding large primes, structures for strong primes and algorithms to attack these problems efficiently. At the second level, the research concentrates on improving the existing algorithms to enhance the safety or effective performance of the algorithm. In this article, the authors propose a solution to improve the security of digital signature schemes, implemented in both levels of digital signatures. At the first level, the authors propose a new hard problem - different from the hard problems used before and hasn’t been solved by anyone so far (except by "brute force attack" method). At the second level, the authors propose a method to construct new digital signature algorithms that can help create not only one but also a family of new digital signature algorithms with high security level for practical applications.

For a finite group G to be used in the MOR public key cryptosystem, it is necessary that the discrete logarithm problem(DLP) over the inner automorphism group Inn (G) of G must be computationally hard to solve. In this paper, under the assumption that the special conjugacy problem of G is easy, we show that the complexity of the MOR system over G is about log |G| times larger than that of DLP over G in a generic sense. We also introduce a group-theoretic method, called the group extension, to analyze the MOR cryptosystem. When G is considered as a group extension of H by a simple abelian group, we show that DLP over Inn (G) can be ‘reduced’ to DLP over Inn (H). On the other hand, we show that the reduction from DLP over Inn (G) to DLP over G is also possible for some groups. For example, when G is a nilpotent group, we obtain such a reduction by the central commutator attack.