Preprint No. 95-1 A. Baraani-Dastjerdi, J. Pieprzyk, R. Safavi-Naini, and J.R. Getta ``A Cryptographic Mechanism for Object-Instance-based Authorization in Object-Oriented Database Systems'' ABSTRACT The paper suggests a mechanism for access control at the instance level of a class in object-oriented databases. The mechanism is based on the use of pseudorandom functions and sibling intractable functions. Each object instance is associated with access keys that ensure secure access to the object and all other related to it objects. The authorization system supports ownership and granting/revoking of access rights. ================================================================ Preprint No. 95-2 J. Pieprzyk and A. Goscinski ``Security Issues on the Internet'' ABSTRACT The paper presents an overview of security issues in the Internet. First security threats are discussed. Next some general issues of access control are considered with firewalls as a special case of the access control which allow to separate parts of the internet using packets screening techniques. Two solutions of firewals are shown, one based on so-called cryptographic tickets and the other based on a network security probe. Later a discussion on intrusion detection systems follows. The last part of the paper shows how to distribute cryptographic keys via insecure channels (Internet). ================================================================ ================================================================ Preprint No. 95-4 S. Bakhtiari, R. Safavi-Naini, J. Pieprzyk, ``Practical message authentication schemes'' ABSTRACT Use of encryption algorithms in message authentication is replaced by secure hash functions which are often faster than encryption algorithms. Tsudik has proposed three methods on message authentication which are only based on one-way hash functions and use some keys to make them secure. In this paper, we give a set of practical methods, each of which uses a fast collision free hash function (such as MD5) and provides secure message authentication. The idea of the proposed methods is almost similar to that of Tsudik's, but we are able to reduce the key length eight times compared to the Tsudik's constructions, while maintaining the same security. In our methods, the secret key is added using exclusive-or or assign operators (instead of concatenation) to make them faster. We also have proved that our methods belong to the Secure Keyed One-Way Hash Function (SKOWHF) group, if the underlying hash function is secure. ================================================================ Preprint No. 95-5 T. Hardjono ``Kuperee Simplified'' ABSTRACT In this current work we simplify the authentication protocol of Kuperee by removing all its features and presenting it in the minimum form required to achieve authentication in the Kerberos manner. This minimal form of Kuperee facilitates the further modification of the various parameters of Kuperee to achieve different effects, taking advantage of the fact that underlying Kuperee is a public-key cryptosystem which allows for various key compositions. Two approaches for authentication in Kuperee are discussed. The first relies on the sharing of a session secret-public key pair much in manner of the Needham-Schroeder protocol. The second approach is based on the use of a group-shared longer term public-key, which exploits the nature of the public key cryptosystem employed. ================================================================ Preprint No. 95-6 M. Esmaili, R. Safavi-Naini and J. Pieprzyk ``Computer Intrusion Detection: A Comparative Survey'' ABSTRACT Advances in computer and communication technologies have resulted in highly integrated distributed systems that allow users to access information and resources from all over the globe. By introducing many more possible attacking points, this interconnectivity adds new dimensions to the long standing problem of providing security in a computer system. Rapid increase in the number of reported intrusions, break-ins and computer thefts results in an ever-increasing need for applying effective computer security measures. The number of recently developed, or under development systems and tools that can be used for detection of abuse of computer systems is growing. In this report we present a comparative review of the state-of-the-art intrusion detection systems (IDS) and methods, underlining the strength and limitations of each. We also suggest directions for future development and research. ================================================================ Preprint No. 95-7 Ahmad Baraani-Dastjerdi, Josef Pieprzyk, Reihaneh Safavi-Naini, and Janusz R. Getta ``A Model of Content-based Authorization in Object-Oriented Databases based on Object Views'' ABSTRACT Several models of authorization have been proposed for object-oriented databases supporting different levels of granularity. However, these models do not support authorization based on database contents and context. A way of handling context and content-dependent authorization is by using views. In this paper, we present a model of authorization, based on a view model proposed by Bertino \cite{Bert92}, that supports content-based access control on instances of a class. ================================================================ Preprint No. 95-8 Hossein Ghodosi, Chris Charnes, Josef Pieprzyk, Rei Safavi-Naini `` Pseudorandom Sequences obtained from Expansions of Irrational Numbers'' ABSTRACT The main challenge in stream cipher design is to produce sequences that appear random. A number of keystream generators have been proposed and considered in the literature (several of those have been broken). The common characteristic of these keystream generators is that the obtained sequences are periodic. This paper proposes a novel method for the generation of pseudorandom sequences. The method is based on the expansion of irrational numbers. In contrast to previous methods, our method produces non-periodic sequences. It will be shown that binary sequences obtained from the expansions of irrational numbers behave randomly. In other words, the output sequences are indistinguishable from the truly random sequences. The advantages of our method, in contrast to the truly random generators (like tossing a coin), is that the sequences can be reproduced. The output of this pseudorandom generator is provably unpredictable provided the attacker does not know the secret seed. ================================================================ Preprint No. 95-9 S. Bakhtiari, R. Safavi-Naini, J. Pieprzyk, ``Cryptographic hash functions: a survey'' ABSTRACT This paper gives a survey on cryptographic hash functions. It gives an overview of all types of hash functions and reviews design principals and possible methods of attacks. It also focuses on keyed hash functions and provides the applications, requirements, and constructions of keyed hash functions. ================================================================ Preprint No. 95-12 H. Ghodosi, J. Pieprzyk, C. Charnes, R. Safavi-Naini, ``Cryptosystems for Hierarchical Groups'' ABSTRACT This paper addresses the problem of information protection in hierarchical groups. Higher level groups of participants can control the information flow (the decryption ability) to lower level groups. If a higher level group decides to allow a lower level group to read the message, it passes a go ahead ticket so the lower level group can decrypt the cryptogram and read the message. The formal model of top-down hierarchical cryptosystems is given. Two practical and efficient schemes are described. The first is based on the ElGamal system. The second applies the RSA system. In proposed schemes the dealer publishes a public key such that an individual can use it to send an encrypted message to the (hierarchical) group. Publication of both the group public key and the encryption method does not reveal the decision of the group. The lack of verifiability of retrieved messages in threshold ElGamal cryptosystems is also discussed. ================================================================ Preprint No. 95-13 H. Ghodosi, J. Pieprzyk, R. Safavi-Naini, `` Dynamic Threshold Cryptosystems'' ABSTRACT A new concept in group oriented cryptography -- {\it the dynamic threshold cryptosystem} -- is presented in the paper. The dynamic system has many advantages over the existing threshold cryptosystems. It is set up by the sender who can not only compose the group of recipients but select the threshold as well. Implementations of the dynamic system based on the ElGamal and the RSA public key cryptosystems are given and their properties are discussed. The proposed solutions are practical and non-interactive. There is no need for trusted dealers or tamper proof modules. The generalization of the concept for an arbitrary access structure concludes the paper. ================================================================ Preprint No. 95-14 C. Charnes, J. Pieprzyk, R. Safavi-Naini, ``Distributed Delegation Systems'' ABSTRACT In this paper we introduce unconditionally secure distributed delegation systems that allow groups of participants to collectively authorize a delegate to sign a message (construct an authentic message) on their behalf. We propose a model and investigate its properties when delegation is valid for one transmission. The model is extended to multiple delegation and constructions with more economical key exchange are proposed. ================================================================ Preprint No. 95-15 Marc Gysin and Jennifer Seberry, On the weighing matrices of order 4n and weight 4n - 2 and 2n - 1, Australas. J Combin., (to appear). ABSTRACT We give algorithms and constructions for mathematical and computer searches which allow us to establish the existence of W(4n, 4n-2) and W(4n,2n-1) for many orders 4n less than 4000. We compare these results with the orders for which W(4n,4n) and W(4n,2n) are known. We use new algorithms based on the theory of cyclotomy to obtain new T-matrices of order 43 and JM-matrices which yield W(4n,4n-2) for n = 5, 7, 9, 11, 13, 17, 19, 25, 31, 37, 41, 43, 61, 71, 73, 157. Key words and phrases: Weighing matrices, Hadamard matrices, conference matrices, cyclotomy. AMS Subject Classification: Primary 05B20. ================================================================ Preprint No. 95-16 C. Koukouvinos, M. Mitrouli and Jennifer Seberry, On the Smith normal form of D-optimal designs, J. Linear and Multilinear Algebra, (accepted). ABSTRACT The Smith normal forms (SNF) of D-optimal designs of size < 100 are determined by a computer search. A theorem is given for the Smith normal form of D-optimal designs of order 4t+2, when 4t+1 is square free and bounds for the minimum number of 2's which can appear in the SNF are derived. Key words and phrases: D-optimal designs, Smith normal form. AMS Subject Classification: Primary 62K05, 62K10, Secondary 15A21. ================================================================ Preprint No. 95-17 C. Koukouvinos, M. Mitrouli and Jennifer Seberry, On the Smith normal form of weighing matrices, Bulletin Inst. Comb. and Applic. (submitted) ABSTRACT The Smith normal forms (SNF) of weighing matrices are studied. We show that for all orders n \geq 49 the full~spectrum of Smith normal forms (SNF) exists for weighing matrices W(n,9) i.e. there exists a W(n,9) with SNF 1^(n-s/2) 3^s 9^n-s/2), for s in a set, which is described, of consecutive even or odd integers. Key words and phrases: Weighing matrices, Smith normal form. AMS Subject Classification: Primary 05B20, 62K05, Secondary 15A21. ================================================================ Preprint No. 95-18 C. Koukouvinos and Jennifer Seberry, New weighing matrices, Sankhya, Ser. A., (accepted subject to revision). ABSTRACT New weighing matrices and skew weighing matrices are given for many orders 4t \leq 100. These are constructed by finding new sequences with zero autocorrelation. These results enable us to determine for the first time that for 4t \leq 84 a W(4t, k) exists for all k = 1, ... , 4t-1 and also that there exists a skew-weighing matrix (also written as an OD(4t;1,k)) for 4t \leq 80, t odd, k = a^2 + b^2 + c^2, a, b, c integers except k = 4t-2 must be the sum of two squares. Key words and phrases: Autocorrelation, construction, associated polynomial,sequence. AMS Subject Classification: Primary 62K05, 62K10, Secondary 05B20 ================================================================ Preprint No. 95-19 Christos Koukouvinos and Jennifer Seberry, Weighing matrices and their applications, J. Statist. Planning Inf., (submitted). ABSTRACT Three major applications of weighing matrices are discussed. New weighing matrices and skew weighing matrices are given for many orders 4t \leq 100. We resolve the skew-weighing matrix conjecture in the affirmative for 4t \leq 88. AMS Subject Classification: Primary 62K05, 62K10, Secondary 05B20 ================================================================ Preprint No. 95-20 Christos Koukouvinos, Jennifer Seberry, A L Whiteman and Ming-yuan Xia, Optimal designs, supplementary difference sets and multipliers, J. Statist. Planning Inf., (submitted). ABSTRACT We investigate multipliers of 2-\{v;~q^2,~q^2; ~\lambda\} supplementary differences sets where cyclotomy has been used to construct D-optimal designs. Key words and phrases: Cyclotomy, multiplier, D-optimal designs, supplementary difference sets. AMS Subject Classification: Primary 62K05, 05B10, Secondary 11T22. ================================================================ Preprint No. 95-21 Cantian Lin and Jennifer Seberry, Regular symmetric equivalence of Hadamard matrices with constant diagonal, Australas. J. Combin., ================================================================ Preprint No. 95-22 Dinesh Sarvate and Jennifer Seberry, Group divisible designs, GBRDSDS and generalized weighing matrices, Utilitas Math., (submitted) ABSTRACT We give new constructions for regular group divisible designs, pairwise balanced designs, generalized Bhaskar Rao supplementary difference sets and generalized weighing matrices. In particular if p is a prime power and q divides p-1 we show the following exist: (i) GDD(2(p2+p+1), 2(p2+p+1), rp2, 2p2, l1=p2l, l2=(p2-p)r), m=p2+p+1, n=2), r=1,2 (ii) GDD(q(p+1), q(p+1), p(q-1), p(q-1), l1=(q-1)(q-2), l2=(p-1)(q-1)2/q, m=q, n=p+1), (iii) PBD(21,10;K), K= {3,6,7} and PBD(78,38;K), K= {6,9,45}, (iv) GW(vk,k2; EA(k)) whenever a (v,k,l)-difference set exists and k is a prime power, (v) PBIBD(vk2,vk2,k2,k2; l1 = 0,l2 = l, l3 = k) whenever a (v,k,l)-difference set exists and k is a prime power, (vi) We give a GW(21;9;Z3). ================================================================ Preprint No. 95-23 Ghulam Chaudhry and Jennifer Seberry, Critical sets in Room squares, Conference on Combinatorial Mathematics and Combinatorial Computing, Deakin, July, 1995. ABSTRACT In this paper we introduce critical sets in Room squares. We give the cardinality of the small s-critical sets ({\it ss-cs}) and large s-critical sets ({\it ls-cs}) for different classes of standardized Room squares of side $7$, $9$ and $11$. We also describe algorithms to compute {\it ss-cs} and {\it ls-cs} and conjecture l ower and upper bounds for {\it ss-cs} and {\it ls-cs}. We are modifying these to obtain proofs for the minimum and maximum size of {\it s-cs} and {\it l-cs}. ================================================================ Preprint No. 95-24 Marc Gysin and Jennifer Seberry, Multiplication of ternary complementary pairs, Conference on Combinatorial Mathematics and Combinatorial Computing, Deakin, Jul y, 1995. ABSTRACT We present a computer-search method for concatenating or "multiplying" binary or ternary complementary pairs. All multiplications by a particular number m are considered. The computer-search method is new and leads to a large set of new results. The results and equivalences are discussed and some applications and numerical consequences are shown. Keywords: Golay sequences, binary complementary pairs, ternary complementary pairs, autocorrelation function, Hadamard matrices, weighing matrices. ================================================================ Preprint No. 95-25 C. Koukouvinos, M. Mitrouli and Jennifer Seberry, On the Smith normal form of weighing matrices, CANT'95 - The Third Computational Algebra and Number Theory Conference, Macquarie University, April, 1995. ABSTRACT The Smith normal forms (SNF) of weighing matrices are studied. We show that for all orders n \geq 35 the full~spectrum of Smith normal forms (SNF) exists for weighing matrices W(n,9) ie there exists a W(n,9) with SNF 1^(n-s)/2 3^s 9^(n-s)/2, for s in a set, which is described, of consecutive integers. Key words and phrases: Weighing matrices, Smith normal form. AMS Subject Classification: Primary 05B20, 62K05, Secondary 15A21. ================================================================ Preprint No. 95-26 Jennifer Seberry, On Bose's method of mixed differences and Bhaskar Rao designs, presented at R. C. Bose Memorial Conference on Statistical Design and Related Combinatorics, Colorado Springs, 7-11 June, 1995. ABSTRACT In this paper we show that BIBD(v,b,r,k,\lambda), where v=pq or pq+1, when written in the notation of Bose's method of differences may often be used to find generalized Bhaskar Rao designs GBRD(p,b',r',k,\lambda;G) where G is a group of order q and vice versa. This gives many new GBRDs including a GBRD(9,5,5;Z_5) and a GBRD(13,7,7;Z_7). ================================================================ Preprint No. 95-27 Jennifer Seberry and Xian-Mo Zhang, ``Hadamard Matrices, Bent Functions and Cryptography'' ABSTRACT The recent incorporation of the HAVAL (Hashing Algorithm with Variable Lengths) into the Tripwire security package for SUN workstations and research for the latest LOKI family of algorithms, both of which use bent functions, have led many to ask us ``What are bent functions?''. This article is to help introduce bent functions to those who work in Combinatorial Theory. ================================================================