、bl.24No.3
M盯 2007
JOURNALOFELECTRONICS(CHINA)
THE Z一ERROR LINEAR COMPLEXITY OFZ雌一PERIODIC BINARY
SEQUENCESWITHLINEARCOMPLExITYZn一1’
Zhu Fengxlang QIW七nfeng
(DCpartmentofA即八edMdthe二at葱cs,Zhe。夕名入。。Zh扣。at落nEn娜neeri啊 流该。e。葱t,,Zhe。夕zhoo4j次刃2,Ch毖。a)
Abstract Linear comPlexityand裕errorlinear com Ple对tyofthestream ciPheraretwo imPortant
standardstoscalethe randomicityofkeystream s.FortheZ”一periodicperiodicbinarysequencewith
linearcomplexityZ介一landk=2,3,thenulnberofsequenceswithgiven裕errorlinearcomplexityand
theexpected裕errorlinearcomplexityareprovided.Moreove r,theproportionofthese明enceswhose
k-errorlinearcomp1exityisbiggerthan theexpectedvalueisanalyzed·
Keywords Linear complexity;系errorlinear comple对ty;Periodicbinarysequences;Chan一Galnes
algorithm
CLC
DOI
TN918.1
10.10()7/511767一006一0005一9
1.Introduction
The linear comPlexityofabinaryN--Periodic
sequences=(50,51,…,斯一1)co,denotedbyLC(5),15
definedastheleng’thoftheshOrtestlinearfeedback
shift registerthat generatess.Thelinear com-
Plexityofthezerosequenceisdefinedtobe0.The
concePtoflinear comPlexityisveryusefulinthe
studyofthe securityofstream ciPhersincryPtoL
ogy.Periodicse职encesthat aresuitableaskey
stream sshouldPossessalargelinearcomPlexityto
thwartanattackbytheBerlekamp一Mass盯 algo-
rithm.Forthesimilar reason,keystream sshould
havethewopertythatalteringafewtermsshould
notcauseasignificantdecreaseofthe linear com-
plexity.Accordingtothisre卿irement,ameasure
ofthecomPlexityofPeriodicsequenceswas Pro-
posedbystampandMartinll]basedonanearlier
measurebyDing,XiaoandshanIZ].
Definitfon1Let3=(5。,51,…,5二_1)cobean N--pe-
riodic binary sequence.For an integer o兰
k三N,the裕errorlinear complexityLC*(5)isthe
smallestlinearcomP1ex1tythatcanbeobtainedby
altering无orfewerofthe 气,0三艺三N一1.
InthiscorresPondence,we willfocusonthe
importantcaseofbinarysequenceswith(notnec-
essarilytheshortest)periodN=2“.Somerelated
concePtsarelistedas follow s.
TheHam mingweightofan N-Periodicsequence
sisdefinedas thenumberofnonzerobitsinPer
period ofs,denoted 饰 W(5).Similaxly,the
HammingweightofavectorsNisdefinedasthe
nu汕erofnonzerobits,denotedbyw(sN).0卜
viously,foranN--Periodicsequenceswithperiod
sN,W(5)=w(sN).
Thegeneratingfunctionofan infinitebinary
sequences=(5。,51,气,…)isdenoted饰 5(x)=50+
slx+凡x,+·…Similarly,thegeneratingfunction
ofavectorsN=【505,…5二_1」〔衅 isdenoted勿
、万(劝二50+slx+szx,+.二+知_1尹一‘.Thenfor an
N-periodicbinaxysequenceswithperiodsNwe
have
5(x)=sN(x)(1+xN+x,N+…)=sN(x)/(1+xN)
Itiswellknownthatthelinear comPlexityof
these明encesis[刘
LC(5)=N一心9(gcd(xN+1,sN(x))) (1)
FOrconvenience,we makenodifferent between
IManuscriptreceiveddate:Janu娜 4,2006;reviseddate:
June 19,2006.
SupPortedbytheNationalNaturalScienceFoundationof
China(No·60373092).
Commu nicationauthor:ZhuFengxlang,bornin1977,
female,Ph.D.docent.DePartmentofAPPliedMathe-
matics,ZhengzhouInformationEngineeringUniversity,P·
0.Box1O01一745,Zhengzhou450O02,China.
Email:fengweizhu_2002@163.com.
the
sN
se明ence£=(50,51,…,5二_,)coandthevector
a d -
f o r
I n
了
一[5051…断一小thenLC(5)一LC(5(”)).
dition,whenN=2”,we 由notes(”)==
simplicit犷
11.Pre劝tninaries
InRef.【3〕,Kurosawa,etal·
that the
mininlum value
comPlexityofa
kznin forwhichthe裕error
Zn一Periodicbinaryseqllen‘
linear
王 8 15