使用CPA4破解经典密码算法

下面是一段经过经典密码算法加密的密文（加密算法未知）：

yvvnerujjvnywhbdvkpchfgvjtzwqsuporqfzpoekkjgziicdwwkeejdsruef

 

whwseyejejhnaeepjbjwnuztavjswrthswlcdxqrnoclsodkrrfjtfhlfznbx

 

wyvdwdcwyzqlqrnevuiiienxzmwtdsyhgstwmvznrvhyihhcxjijhiojphvjw

 

srpejwnhrhirqbcdwnzqmwjpoibnbjdeshloewcfdhvzjgtdwsvntydyweyll

 

gjrrohfuyplppzrssvniejxhzjtrwyvvdecpttrieevhzlxsvunstovzwjfsa

 

svlsgzjcvwmseioidhsywsddisrjadhkcideivjzwwsfqjcwphvwtdtkatkjg

 

zjwfpjbjbofwgochaegfhmyodpjbkwtfukcixokkrseoaegbcdanjitckxaco

 

xvvdajdqgfxetrrskdewlwgketronoesoddshfxezqiitpeulshfdeiftiepr

 

pvkcfpbroqwechroqcwbadhfbuwlcwmokshzojkfnkzqlojhanbjfzjhvuxdr

 

neklrskdezqiswwtzjfpcamfufqvolrwjgkreewzfvesrvftzbauhasckpdhs

 

hzjskuzqkkrydawecjlvyqfjdlfysuwcfxwgvhajwbsvgbvwbsvjaegtqkkbv

 

ufhkdezufbzwnwrthswlcdhouamplshvdrrqyvvnejkjhiwiehiwiwnzdskfi

 

eershyatvfmbzyacdxdvytjrkqfwcylsunkmvqxtfktsdqzektaxxhwkokefz

 

cxukvustefzffzcuwfpjbjbofwgochwyrjjvnsrbxhywtkkjavjsxdrsrjdkk

 

jkfieevlodaaihyvvoadhmojylvdwzpjemhwkfnkvgnbrlrfijgjeoedqseri

 

irsavjtjkjhfhdwlkotkmrvritdajztavjswrthswlckfgxnonqtjvntyhqoj

 

pfvzistwdvvnhywsewgstkmvdsmdkrvvnazhaiwthyamvqxurienrrsewrvsm

 

mjecroqmuefwhwseptfpjbrjdkkjafnekkjkfieevlodadvyjzflskkjafnez

 

wngwqlcrkggaczinqzpivvyvrprvtzwiaaulktvneewfdgnorfmtikmrftotd

 

jlvyzzgejddwerocojmswlcrwprokvwgochtyhwsjjogrnbkenxutigenxlyo

 

chuegjfkdejdrstwtvjtfpphvrgjzkujsmmjecroiwwbeihsqvoaihtbcutyh

 

xhrntzqldfenkwmswkrdhwgknibhwocoogrnbkotfnjmkwcklhocziwijfvjc

 

vvfbuprrlswecmvwmcuotrnjomarpvnaghevafaghekkjdzcgplshyamzgizv

 

zrzoqgjdetrshzjuvgdclnedraskdakiwcdwmvqxhiwielsujasjltbrjdprz

 

fvhojwbvvnervlsearroqmjlernnbxbeddqsghaphwguknkwjbupotdwsrxol

 

wyvzokzqicwyodsjhzpimhssjoiedboiiugptfryeyrusjphrwismalfsrsep

 

ielywrpimhxzzgekkjkfieevkcfpbroqqfwcylsutkuivjwepeyufbnditkbo

 

jwtkhsrvzbpztavjoeodkzhlyhqdkknruwcnphvjfdsatnhjbkdefsucipuel

 

ywvoawitfuadkrrocaaegksdwlvftotdejrkqfqrjhdcldamhlfvwttrfqyas

 

kkfhljdvuxhrjdkkjkfieevlodalznjoepoeltqrxrzqnweetrodcilhzondg

 

abvulsikozqkfrjcvvfwuioidhssqtnkfhjprznjgdaijzmseoodhysrisfuh

 

zlxstktcjahvdiqfwcyhxbfpbrvjrfjaivzafneosjfzanthgikkncbgstwuj

 

hyvvuhrsuseposhrsewszvfwuxewrwskdexdrszodziksiankdsrkdakvhzvw

 

rkrjjvnyfqjplptyhtdgkrkxswkeejdktfndvgyctkatkjgjdoloibkxeulkt

 

vneewtdgkrkxswkeejitfrhlkkjufopvoyvrpmfufqvesgujotdiejnggwrkl

 

hicwrcbaocqasojwephvpnruhevdxhndeihqokalpztavjswrthswlckfgdwd

 

vgwodwtzfxhiedvvnfrjffujlripchkwvhdjztavjsedywfjacwjodofirroc

 

hcrwjufnivvxhrntzqlokqaegnhjjakltbrhlvdlivberwzfvotvdrgzjtyhk

 

wiotulawjeoedsrrjokkjfwevvlshyasvftbuzimlxwfjnfwycdankltbrpok

 

dqtlpsroysrisjswsrzatutgjboluiwwbeihshcaaxxjrzrijltbjwtwlwgkc

 

lrqhszpsvdxmwkrnhxhvnnjwthvjdkryvzjkkkfhkdijlxotkmgojhvhyulkt

 

vneewhicpuihgikdoehxhcuajdswkwlzdskywtjwwitgmvwmsdkskzjfvphvv

 

nazhailywvosrliafnathusfllvdwsnwrddsrrlpirfqywbchfbuphvujgekp

 

cdhsndeihyvrpijdxqcaaidxwebofwgochwydywjavzgjbkpodhnbkahidswj

 

wgzjfbkecgdxgzknwrwtfktsdqzrhemhqcwenkhwsjptydygknucbtikotrqi

 

wecsghhwwecroqmrioejyvvsodhshykuxknhjylvdwhywtkknggwsjltbtwri

 

ljgrlokhshzwlnknqyesfqqmekwshnbxqnkdudvzhfsjtlhlpwmwjyoluxszo

 

aelrdfntrqygkapkrboizskkngdwhuljafdadpfrbdaelfavibvuttkdezufb

 

zwnwdxkfieevhcdiikwjswqlcbfuiaejznhyphvitfdarzwfzpwnuffbrzatr

 

fqysodhsgwkokefzcdajiqclnijkjrzjrvfjbkueruxoeznfzfrruszwxhyam

 

fvydflucdwggkrkdrceciidswrjwfpjbjdejdnrzpsroxcfjefiyvvbamrzfz

 

pejstfkoffurijhidztavjbvffijatyhdoiaacotkvztfsqopshzojkvwrzql

 

oyaauvhoibmfkfadwdbkfbzwljrgsceemhxhywttrrpzjakltbfbdvyjzflmv

 

qyqfqrjhxoezeclystkmghywkeoevqwbanvaymvwrjintrqwfpjbjsoioiwef

 

oigfbkdewlwgksodhsgnkrcghigdecgnbkdedlircaervyoiatyhbopboizff

 

uboiwmsiagzrswkoaxujokkpgrwhljikbycrptidhhgqbclhcgenzrshfsodh

 

sgwkokefzcwnudqgfboiijarhedlircaervysijtvdrgkksyrbhyaiivyfvjg

 

Kkxoxwievywepeiqfhzknrotdgknvqygjdetrsqcqdvg

---

破解过程：

1.先确定是单表还是多表加密，通过统计字母频率

把密文复制到Ciphertext处，点击左侧Freq，就有统计字母频率的功能。

统计结果：

a  120  0.034

b   91  0.026

c  105  0.030

d  178  0.051

e  178  0.051

f  164  0.047

g   99  0.028

h  180  0.051

i  148  0.042

j  205  0.058

k  201  0.057

l  111  0.032

m   55  0.016

n  113  0.032

o  146  0.041

p   85  0.024

q   82  0.023

r  193  0.055

s  168  0.048

t  139  0.039

u   87  0.025

v  177  0.050

w  210  0.060

x   63  0.018

y   97  0.028

z  126  0.036

可以选择用图表的形式显示出来：

可以看到字母频率分布的较平均，没有某个字符概率很高或者概率很低，所以猜测这是一个多表加密的密文。（因为单表加密通常都会显示出语言的特征）

现在已经知道是多表加密了，那用的是哪种多表加密算法呢？

实际的办法就只能一个个尝试。

首先假设这是一个Vigenere密码算法加密的密文：

先要确定密钥的长度

用CAP的Kasiski，得知

String    Distance

yvv         273

yvv         707

yvv         868

yvv        1953

yvv        2765

yvv        3101

Yvv出现的距离：434 595 1680 2492 2828

最大公约数是7

猜测密钥的长度是7

再用CAP的Low Freq

输入密钥的长度7，给出的可能密钥是forward。

用CAP的Vigenere Cipher，输入keyword:forward，给出的原文是

there are very few people as entitledtoanalysethesimilaritiesanddif
ferencesbetweenmensandwomensfootballascarolinamoracefollowing
ayearplayingcareerduringwhichshebecamewidelyrecognisedasthegr
eatestitalianwomaninhistoryinshebeganacoachingcareerthatinclu
dedashortbutpioneeringstintatthehelmofamensclubseriecsviterbe
seinsincethenmoracehasmadeanameforherselfasoneofthetopcoaches
inwomensfootballandatvcommentatorforbothmensandwomensfootball
shehasalsobecomethefirstitalianwomantobeinductedintohercountr
ysfootballinghalloffameandallthatwhileworkingaslawyerinherspa
retimetheindefatigablemoraceslatestventureisasafifadevelopmen
tinstructorhavingjustconductedacourselastweekbetweenandoctobe
rattheiranianfootballacademyintehranthereshetrainediranianwom
enonthetechnicalaspectsofcoachingwomensfootballnotjustfootbal
lbutspecificallywomensfootballwhoeversaysthatthemensgameandth
ewomensgamearethesamehasclearlyneverworkedinaprofessionalenvi
ronmentshetoldfifacomasmuchaswomensfootballhasgrownoverthelas
tfewdecadesithasntbecomeanymoresimilartothemensgamewomenareph
ysicallydifferenttomenandthemorethewomensgamedevelopsthemorei
tisfullofspecificitiesthatrequireadifferentapproachfromacoach
justlikesayinvolleyballorbasketballtheresnopointingroupingita
llunderthesamecategorytheobviousphysicaldifferencesareonlythe
startingpointtheformerstrikeralsopointstokeytacticaldifferenc
esandtrainingmethodstakeaverysimpleexamplethepiggyinthemiddle
drillsshecontinuedyouremovethatfromamenstrainingsessionandyou
relostwhereasgenerallyspeakingfemaleplayersdonttendtocareabou
tthiskindofcompetitivenessinawarmupmoracehopesthatdevelopment
initiativeslikethewomensfootballcoachingcourseintehranwhichwa
sattendedbywomenonlywillhelptonarrowthegapbetweentheopportuni
tiesaffordedtomaleandfemalecoachesofcourseyouhavegreatcoaches
thatunderstandthewomensgamelikeantoniocabriniinitalyorphilipp
ebergerooinfrancesaidmoracebutwhatstrikesmeiswhensometeamsorc
lubschooseheadcoachesnotbasedonarsumorexperiencebutonlybecaus
etheyhappentobemenasisaidbeforethegameisdifferentandthatsclea
rtoeveryonebuttheopportunitiesaffordedtocoachesshouldntbediff
erentopportunitiesforallthegospelthatmoraceispreachingisparti
cularlyvaluableinthemiddleeastwherelatelywomensfootballhasmad
edramaticstridesiranforexamplefieldswomensnationalteamsfromal
lcategoriesstartingatuanditsnationalleaguefeaturesteamsinthef
irstdivisionandanotherfiveintheseconddivisionnottomentionatot
alfutsalteamsspreadacrossfourdifferentleaguedivisionsatfirstg
lanceitseasyforwesternstotendtothinkthatthisisacompletelydiff
erentculturebuthonestlyasanitalianwhatstruckmethemostwerethes
imilaritiessaidmoracepeoplearewarmandapproachableandtheresnop
lacewherethatisasclearasinfootballwhatisevidenttomeintehranis
agiganticpassionforfootballalevelofinterestthatstrulyoutstand
ingspecificallyamongthewomenthoughitsclearthatthispassioncarr
iesapotentialwhichisonlynowbeinguntappedhopefullythiscourseis
animportantsteptowardsthismahdiemohammadkhaniamemberoftheiran
ianfaswomenscommitteefullyagreeswiththeformeritalyandcanadaco
achwomensfootballhasflourishedinrecentyearsandnowadaysitsthem
ostpopularsportamongiranianwomenshesaiditsalsooneofthefavouri
tesportsformuslimwomenbecausetheyareallowedtoplaywhilewearing
aheadscarfmohammadkhanialsobelievesthatcombinationofdevelopme
ntcoursesandelitecompetitionslikenextyearsfifauwomensworldinj
ordanthefirstwomensworldcupheldinthemiddleeastarethewayforwar
dfortheregionitsagreatopportunitytoattractpublicopiniontowome
nsfootballandalsoforfemalemiddleeasternteamstoshowtheirstreng
thsagainstinternationalopponentssheconcluded

发现译文是有意义的，就把这个密文破解了。

如果发现译文是无意义的，就需要假设别的加密算法，根据假设的算法来使用相应的解密方法。