6674 IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 59, NO. 10, OCTOBER 2013 A Family of Five-Weight Cyclic Codes and Their Weight Enumerators Zhengchun Zhou, Cunsheng Ding, Senior Member, IEEE, Jinquan Luo, Member, IEEE, and Aixian Zhang Abstract—Cyclic codes are a subclass of linear codes and have applications in consumer electronics, data storage systems, and communication systems as they have efficient encoding and decoding algorithms. In this paper, a family of -ary cyclic codes whose duals have three pairwise nonconjugate zeros is proposed. The weight distribution of this family of cyclic codes is determined. It turns out that the proposed cyclic codes have five nonzero weights. algorithms (see [12] for details). Thus, the study of the weight distribution of a linear code is important in both theory and applications. An linear code over is called cyclic if implies . By identifying any vector with Index Terms—Cyclic codes, exponential sum, quadratic form, weight distribution, weight enumerator. any code I. INTRODUCTION A N linear code over the finite field is an -dimensional subspace of with minimum (Hamming) distance , where is a prime. Let denote the number of codewords with Hamming weight in a code of length . The weight enumerator of is defined by The sequence is called the weight distribution of the code. Clearly, the weight distribution gives the minimum distance of the code and, thus, the error correcting capability. In addition, the weight distribution of a code allows the computation of the error probability of error detection and correction with respect to some error detection and error correction Manuscript received February 05, 2013; revised May 28, 2013; accepted May 31, 2013. Date of publication June 11, 2013; date of current version September 11, 2013. Z. Zhou was supported in part by the Natural Science Foundation of China under Grant 61201243, in part by the Hong Kong Research Grants Council under Grant 600812, in part by the application fundamental research plan project of Sichuan Province, and in part by the Fundamental Research Funds for the Central Universities under Grants SWJTU12CX053, SWJTU12ZT15, and SWJTU12ZT14. C. Ding was supported by The Hong Kong Research Grants Council, Project No. 600812. J. Luo was supported in part by the Norwegian Research Council under Grant 191104/V30, in part by the National Science Foundation (NSF) of China under Grant 60903036, in part by the NSF of Jiangsu Province under Grant 2009182, and in part by the Open Research Fund of the National Mobile Communications Research Laboratory, Southeast University (No. 2010D12). Z. Zhou is with the School of Mathematics, Southwest Jiaotong University, Chengdu 610031, China, and also with the State Key Laboratory of Integrated Services Networks, Xidian University, Xi’an 710071, China (e-mail: zzc@home.swjtu.edu.cn). C. Ding is with the Department of Computer Science and Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong (e-mail: cding@ust.hk). J. Luo is with the Department of Informatics, University of Bergen, N-5020 Bergen, Norway (e-mail: jinquan.luo@ii.uib.no). A. Zhang is with the Department of Mathematical, Xi’an University of Technology, Xi’an 710048, China (e-mail: zhangaixian1008@126.com). Communicated by I. F. Blake, Associate Editor for Complexity and Cryptography. Digital Object Identifier 10.1109/TIT.2013.2267722 of length over corresponds to a subset of . The linear code is cyclic if and only if the corresponding subset in is an ideal. It is well known that every ideal of is principal. Let , where is monic and has the least degree. Then, is called the generator polynomial and is referred to as the parity-check polynomial of . A cyclic code is called irreducible if its parity-check polynomial is irreducible over . Otherwise, it is called reducible. A cyclic code over is said to have zeros if all the zeros of the generator polynomial of the code form conjugate classes, or equivalently, the generator polynomial has irreducible factors over . The weight distributions of both irreducible and reducible cyclic codes have been interesting subjects of study for many years. The determination of weight distributions is a hard problem in general. For information on the weight distribution of irreducible cyclic codes, the reader is referred to the recent survey [4]. Information on the weight distribution of reducible cyclic codes could be found in [5], [9], [15]–[17], [21], [23], and [25]. For the duals of the known cyclic codes whose weight distributions were established, most of them have at most two zeros (see [4], [5], [9], [10], [15]–[17], and [21]–[23]), only a few of them have three or more zeros (see [9], [13], [15], and [25]). The objective of this paper is to settle the weight distribution of a family of five-weight cyclic codes whose duals have three zeros. This paper is organized as follows. Section II defines the family of cyclic codes. Section III presents results on quadratic forms which will be needed in subsequent sections. Section IV solves the weight distribution problem for the family of cyclic codes. Section V concludes this paper and makes some comments. II. FAMILY OF CYCLIC CODES In this section, we introduce the family of cyclic codes to be studied in the sequel. Before doing this, we first give some notations which will be fixed throughout the paper unless otherwise stated. 0018-9448 © 2013 IEEE ZHOU et al.: FAMILY OF FIVE-WEIGHT CYCLIC CODES AND THEIR WEIGHT ENUMERATORS Let be an odd prime and , where is odd and . Let and , where is any positive integer with . The conclusions in the following lemma will be used in the sequel and their proofs can be found in [18] and [20]. Lemma 2.1: With the notations above, we have 1) ; 2) ; 3) ; and 4) for . Let be a generator of the finite field , and let denote the minimal polynomial of over for any integer . Note that by Lemma 2.1. Thus, , and are irreducible polynomials over of degree . Since there does not exist any positive integer such that to is called a quadratic form over sented as 6675 if it can be repre- where . That is, is a homogeneous polynomial of degree 2 in the ring . The rank of the quadratic form is defined as the codimension of the -vector space That is, , where is the rank of . In order to determine the weight distribution of the aforementioned code , we need to deal with the exponential sum of the following form: (3) for any such that , and there does not exist any positive integer the elements , , and are not the conjugate of each other and have distinct minimal polynomials over . So the polynomials , and are distinct. Define where is a complex primitive th root of unity, and function from to satisfying 1) for all ; and 2) is a quadratic form over . Note that any nonsquare in is also a nonsquare in is odd. It is easy to verify that (1) has degree and is a factor of . Then, Let be the cyclic code with parity-check polynomial . Then, has length and dimension . Using the well-known Delsarte’s Theorem [2], one can prove that (2) where the codeword and denotes the absolute trace from to . Let and be the cyclic code . Then, is a subwith parity-check polynomial code of with dimension . Trachtenberg [20] proved that has three nonzero weights and determined its weight distribution. The objectives of this paper are to show that has five nonzero weights and settle the weight distribution of this class of cyclic codes. III. MATHEMATICAL FOUNDATIONS In this section, we give a brief introduction to quadratic forms over finite fields which will be useful in the sequel. Quadratic forms have been well studied (see the monograph [14] and the references therein) and have applications in sequence design (see [11], [19], and [20]), and coding theory (see [9], [15], [16], and [25]). Definition 3.1: Let , where and is a basis for over . A function from is a since (4) where is a fixed nonsquare in . The following result can be traced back to Trachtenberg [20] whose proof is based on (4) and the classification of quadratic forms over finite fields in odd characteristic. For more details, we refer the reader to [20, pp. 30–36] and [19, Lemma 4]. Lemma 3.2: Let be defined by (3) and be the rank of the quadratic form . Then, if is odd, and otherwise. IV. WEIGHT DISTRIBUTION OF THE FAMILY OF CYCLIC CODES In this section, we shall establish the weight distribution of the code of (2) defined in Section II. To this end, we need a series of lemmas. Before introducing them, for any , we define (5) and (6) be defined by (5). Then, Lemma 4.1: Let for any . And for any , the quadratic form has rank for some . Proof: Recall that , and for . Thus, and for any . This together with the linear properties of the 6676 trace function means that Note that where , over . Thus, calculate the rank of IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 59, NO. 10, OCTOBER 2013 for any . and is a basis of is a quadratic form over . We now . Note that TABLE I VALUE DISTRIBUTION OF Case B, when : In this case, for each equation system (9) has the same number of solutions as , the where which has the same number of solutions as We need to calculate the number of roots of the linearized polynomial . Let . Then (10) Squaring both sides of each equation in (10), we have (7) . Clearly, has the same number of roots in as Fix an algebraic closure of ; then, all roots of form a vector space over of dimension at most 4 since its degree is at most for any . Note that , it is straightforward (see [20, Lemma 4]) to verify that elements in that are linearly independent over are also linearly independent over . Therefore, the roots of in form a vector space over of dimension at most 4. Thus, the rank of is at least for any . This completes the proof. Lemma 4.2: Let denote the number of solutions of the following system of equations: which implies that since . Conversely, for any , it is clear that is a solution to (10) since and for each . Thus, (10) has exactly solutions. Summarizing the results of the two cases above, we have that . This completes the proof. The following lemma is the key to establishing the weight distribution of the proposed code . Its proof is lengthy and is presented in the Appendix. Lemma 4.4: Let denote the number of solutions of the following system of equations: (8) (11) Then, Proof: The conclusion follows directly from the observation that is a solution of (8) if and only if . Lemma 4.3: Let denote the number of solutions of the following system of equations: (9) Then, Proof: We distinguish between the following two cases to calculate the number of solutions of (9). Case A, when : In this case, by Lemma 4.2, the number of solutions of (9) is equal to . Then, Proof: See the Appendix. Theorem 4.5: Let be defined by (6). Then, as runs through , the value distribution of is given by Table I. Proof: It is clear that if . Otherwise, by Lemmas 4.1 and 3.2, we have To determine the distribution of these values, we define ZHOU et al.: FAMILY OF FIVE-WEIGHT CYCLIC CODES AND THEIR WEIGHT ENUMERATORS where . Then, the value distribution of is as follows TABLE II WEIGHT DISTRIBUTION OF THE CODE 6677 IN THEOREM 4.6 (12) where immediately have and . By (12), we Combining (13) and (14) gives (13) On the other hand, we have The value distribution of depicted in Table I then follows from the values of , and , and the analysis above. The following is the main result of this paper. Theorem 4.6: Let be the code in (2). Then, is a cyclic code over with parameters and where and is the number of solutions of (8). Similarly, we have Furthermore, the weight distribution of is given by Table II. Proof: The length and dimension of the code follow directly from the definition of . We only need to determine its minimal weight and weight distribution. In terms of exponential sums, the weight of the codeword in is given by and where and are the number of solutions of (9) and (11), respectively. Applying Lemmas 4.2, 4.3, and 4.4, we have (14) (15) 6678 IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 59, NO. 10, OCTOBER 2013 TABLE III WEIGHT DISTRIBUTION OF THE CODE IN THEOREM 5.1 where is given by (6), and in the fifth identity, we used the fact that for any and . The minimal weight and weight distribution of then follow from (15) and the value distribution of the exponential sum depicted in Table I. Example 4.7: Let , , and . Then, the code is a code over with the weight enumerator which agrees with the weight distribution in Table II. Example 4.8: Let , and . Then, the code is a code over with the weight enumerator Finally, we would mention some applications of the codes with five weights considered in this paper. Cyclic codes with a few weights are of special interest in authentication codes as certain parameters of the authentication codes constructed from these cyclic codes could be easily computed [7], and in secret sharing schemes as the access structures of the secret sharing schemes derived from such cyclic code can be easily determined [1], [6], [24]. Cyclic codes with a few weights are also of special interest in designing frequency hopping sequences [3], [8]. APPENDIX A PROOF OF LEMMA 4.4 (16) It is then obvious that For any lutions which agrees with the weight distribution in Table II. Example 4.9: Let , , and . Then, the code is a code over with the weight enumerator , let denote the number of soof the following system of equations: For any lutions , let denote the number of soof the following system of equations: (17) Since and are odd, , we have (18) which agrees with the weight distribution in Table II. V. SUMMARY AND CONCLUDING REMARKS In this paper, we studied a family of five-weight cyclic codes. The duals of the cyclic codes have three zeros. The weight distribution of this family of cyclic codes is completely determined. We mention that the weight distribution of can also be settled in a more general case where is odd. In what follows we only report the conclusion. The proof is similar to that of Theorem 4.6. Theorem 5.1: Let , be odd, and . Let be the code in (2). Then, is a cyclic code over with parameters Furthermore, the weight distribution of Table III. is given by We distinguish among the following three cases to calculate . Case A, : In this case, since is a solution of (17) if and only if . Thus, . Case B, , and ( or ): In this case, without loss of generality, we suppose that . By Lemma 2.1, , and thus, is odd . It then follows from the second equation in (17) that . This leads to which means that the first equation in (17) cannot hold since . Therefore, in this case. Case C, , and . In this case, for any given , equation system (17) has the same number of solutions as (19) ZHOU et al.: FAMILY OF FIVE-WEIGHT CYCLIC CODES AND THEIR WEIGHT ENUMERATORS where as and . Clearly, does. By Lemma 5.2, we have 6679 Thus is uniquely determined by . Substituting (22) into the second equation of (21), we obtain runs over (23) Let . Then, (23) is equivalent to (24) is not a square in , then If (24) has no solution, i.e., . Otherwise, suppose that and are two solutions of (24). We then have Summarizing all the cases above, we have This completes the proof. Lemma 5.2: Let denote the number of solutions of (19), where . Then, we have the following conclusions. B1 . B2 When runs over , for cases for cases in the remaining cases. The proof of Lemma 5.2 is lengthy and technical. We first prove some auxiliary results. APPENDIX B AUXILIARY RESULTS FOR PROVING LEMMA 5.2 (25) or (26) Clearly, (25) and (26) have the same number of solutions . Note that . Thus, both (25) and (26) have no solution or exactly solutions. If , then and . However is not a square, thus, and . In this case, (25) and (26) become the same equation and have solutions. If , then (25) and (26) have distinct solutions. Based on the above analysis, we conclude Define . We prove Lemma 5.2 only for the case that The proof for the case is similar and omitted. Hence, we assume that from now on. A) Case 1: In (19), we substitute with and obtain the following system of equations: Note that the first equation in (21) has solutions in thanks to [14, Lemma 6.24]. When runs through all these solutions, the second equation in (21) will give a -to-1 correspondence (20) . Our task is to compute the number of where solutions of (20). To this end, we first compute the number of solutions of the following system of equations: if . Therefore which leads to (21) where . Lemma 5.3: Let symbols and notations be the same as before. As for (21), we have if for elements for the remaining Proof: Let (21). It is clear that that and This completes the proof. Lemma 5.4: Let symbols and notations be the same as before. As for equation system (20), we have if for pairs for the remaining . be a solution of the first equation in . Let . It then follows (22) . be any solution of (20). Let Proof: Let . It then follows from the first equation in (21) that (27) 6680 IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 59, NO. 10, OCTOBER 2013 It then follows from Lemma 5.4 that Using the second and third equations in (20), we obtain and Let and for pairs for the remaining (28) Then, . The proof is then completed. B) Case 2: Lemma 5.6: Let denote the number of solutions of (19) such that is a square and is a nonsquare or . Then and It follows from the first equation in (28) that if for pairs for the remaining (29) Combining the first equation in (28) and (29), we obtain . This case is symmetric to Case 1. Hence, the proof of this lemma is similar to that of Lemma 5.5 and is omitted. with and C) Case 3: In (19), we substitute obtain the following system of equations: Hence, (30) (31) Note that . Our task is to compute the number of where solutions of (31). To this end, we first compute the number of solutions of the following system of equations: if and only if (32) By (30), is uniquely determined by . Therefore, is uniquely determined by . In addition, it is easily seen that if and only if . Hence the number of solutions of (20) is the same as that of (21). The desired conclusions then follow from Lemma 5.3. Lemma 5.5: Let denote the number of solutions of (19) such that is a square and is a nonquare or . Then if for pairs for the remaining . where Lemma 5.7: Let symbols and notations be the same as before. As for (32), we have if for elements for the remaining Proof: Choose such that . . From (33) we can assume (34) . is a Proof: Consider now the solutions of (20). If solution of (20), so are , and . If , there are indeed four different solutions of (20), but they give only one solution of (19). Since is a quadratic nonresidue in , . However, it is possible that . If , then . In this case, we have two special solutions of (20). They give only one solution of (19). with . It is easy to see that all the solutions of (33) can be expressed as in (34) with a unique Substituting (34) into . (35) we obtain (36) ZHOU et al.: FAMILY OF FIVE-WEIGHT CYCLIC CODES AND THEIR WEIGHT ENUMERATORS Denote by if . Then, (36) is equivalent to 6681 . Therefore (37) Let and have . From (34) and be the two solutions of (37). Then, we , we have The proof is now finished. Lemma 5.8: Let symbols and notations be the same as before. As for equation system (31), we have which implies • If , then . Since is odd, . It follows that . This implies that . For a fixed , recall that and are the two solutions of (37). Then, we have (38) or (39) If which implies are the two solutions of (38), then which is equivalent to , since due to Lemma 2.1. As a consequence, if (38) has solutions, then it has exactly solutions. If , then (39) and (38) have the same solutions. In this case and . But can be excluded since, otherwise, , then which contradicts to . The remaining case is which corresponds to . In this case, we have solutions of which gives exactly the same number of solutions of (32). If , then (39) has the same number of solutions as (38) and moreover, their solutions are distinct. Therefore, (38) and (39) both have solutions or no solutions in . • If and , then . Note that , if for pairs for the remaining pairs . Proof: The proof of this lemma is similar to that of Lemma 5.4 and is derived from Lemma 5.7. The details of the proof are omitted here. Lemma 5.9: Let denote the number of solutions of (19) such that both and are squares. Then if for pairs for the remaining . and is not in except for the exception case will not occur since Summarizing up, we conclude . But . Define Note that (33) has solutions in thanks to in [14, Lemma 6.24]. When runs through all these solutions, (35) will give a -to-1 correspondence Proof: Consider now the solutions of (31). If is a solution of (31), so are , , and . If , there are indeed four different solutions of (31), but they give only one solution of (19). However, it is possible that . If , (31) has four special solutions and . They give only two solutions of (19). It then follows from Lemma 5.8 that If , then the four distinct solutions give only one solution of (19). In this case, it then follows from Lemma 5.8 that for pairs for the remaining . The proof is then completed. D) Case 4: Lemma 5.10: Let denote the number of solutions of (19) such that both and are either nonsquares or zero. Then if for pairs for the remaining . Proof: The proof of this lemma is similar to that of Lemma 5.9 and is omitted here. 6682 IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 59, NO. 10, OCTOBER 2013 APPENDIX C PROOF OF LEMMA 5.2 and of (19) are counted Note that the solutions more than once in Cases 1–4. By analyzing the proofs of Lemmas 5.5, 5.6, 5.9, and 5.10, we have When , is the sum of the solutions given in Lemmas 5.5, 5.6, 5.9, and 5.10. This completes the proof. ACKNOWLEDGMENT The authors are very grateful to the reviewers and the Associate Editor, Prof. Ian F. Blake, for their comments and suggestions that improved the presentation and quality of this paper. Z. Zhou would like to thank Prof. X. Tang for his encouragement. REFERENCES [1] C. Carlet, C. Ding, and J. Yuan, “Linear codes from perfect nonlinear mappings and their secret sharing schemes,” IEEE Trans. Inf. Theory, vol. 51, no. 6, pp. 2089–2102, Jun. 2005. [2] P. Delsarte, “On subfield subcodes of modified Reed-Solomon codes,” IEEE Trans. Inf. Theory, vol. IT-21, no. 5, pp. 575–576, Sep. 1975. [3] C. Ding, R. Fuji-Hara, Y. Fujiwara, M. Jimbo, and M. Mishima, “Sets of frequency hopping sequences: Bounds and optimal constructions,” IEEE Trans. Inf. Theory, vol. 55, no. 7, pp. 3297–3304, Jul. 2009. [4] C. Ding and J. Yang, “Hamming weights in irreducible cyclic codes,” Discrete Math., vol. 313, no. 4, pp. 434–446, Feb. 2013. [5] C. Ding, Y. Liu, C. Ma, and L. Zeng, “The weight distributions of the duals of cyclic codes with two zeros,” IEEE Trans. Inf. Theory, vol. 57, no. 12, pp. 8000–8006, Dec. 2011. [6] C. Ding and A. Salomaa, “Secret sharing schemes with nice access structures,” Fundamenta Informaticae, vol. 71, no. 1–2, pp. 65–79, 2006. [7] C. Ding and X. Wang, “A coding theory construction of new systematic authentication codes,” Theoretical Comput. Sci., vol. 330, no. 1, pp. 81–99, 2005. [8] C. Ding, Y. Yang, and X. Tang, “Optimal sets of frequency hopping sequences from linear cyclic codes,” IEEE Trans. Inf. 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Xu, “The weight distributions of cyclic codes and elliptic curves,” IEEE Trans. Inf. Theory, vol. 58, no. 12, pp. 7253–7259, Dec. 2012. [22] M. Xiong, “The weight distributions of a class of cyclic codes,” Finite Fields Appl., vol. 18, no. 5, pp. 933–945, Sep. 2012. [23] J. Yuan, C. Carlet, and C. Ding, “The weight distribution of a class of linear codes from perfect nonlinear functions,” IEEE Trans. Inf. Theory, vol. 52, no. 2, pp. 712–717, Feb. 2006. [24] J. Yuan and C. Ding, “Secret sharing schemes from three classes of linear codes,” IEEE Trans. Inf. Theory, vol. 52, no. 1, pp. 206–212, Jan. 2006. [25] X. Zeng, L. Hu, W. Jiang, Q. Yue, and X. Cao, “Weight distribution of a -ary cyclic code,” Finite Fields Appl., vol. 16, no. 1, pp. 56–73, Jan. 2010. Zhengchun Zhou received the B.S. and M.S. degrees in mathematics and the Ph.D. degree in information security from Southwest Jiaotong University, Chengdu, China, in 2001, 2004, and 2010, respectively. From 2012 to 2013, he was a postdoctoral member in the Department of Computer Science and Engineering, the Hong Kong University of Science and Technology. He is currently an associate professor with the School of Mathematics, Southwest Jiaotong University. His research interests include sequence design and coding theory. Cunsheng Ding (M’98–SM’05) was born in 1962 in Shaanxi, China. He received the M.Sc. degree in 1988 from the Northwestern Telecommunications Engineering Institute, Xian, China; and the Ph.D. in 1997 from the University of Turku, Turku, Finland. From 1988 to 1992 he was a Lecturer of Mathematics at Xidian University, China. Before joining the Hong Kong University of Science and Technology in 2000, where he is currently Professor of Computer Science and Engineering, he was Assistant Professor of Computer Science at the National University of Singapore. His research fields are cryptography and coding theory. He has coauthored four research monographs, and served as a guest editor or editor for ten journals. Dr. Ding co-received the State Natural Science Award of China in 1989. Jinquan Luo (M’09) was born in February 1980, Anhui, China. He received the B.S. degree from Zhejiang University, Hangzhou, China, in July 2001 and the Ph.D. degree from Tsinghua University, Beijing, China, in January 2007, both in mathematics. He joined Yangzhou University, China, in 2007 and later become a Research Fellow at Nanyang Technological University, Singapore from 2009. Currently, he servers as postdoctor at the Department of Informatics, University of Bergen, Norway. His major research interests are coding theory, cryptology, and number theory. Aixian Zhang received the M.S degree and the Ph.D degree in mathematics from the Capital Normal University, Beijing, China, in 2010 and 2013, respectively. She is currently a Lecturer of Xi’an University of Technology. Her current research interests are coding theory and algebraic number theory.