Polybius

##ctf.show

#BJDCTF2020Polybius

题目

密文：ouauuuoooeeaaiaeauieuooeeiea
hint：VGhlIGxlbmd0aCBvZiB0aGlzIHBsYWludGV4dDogMTQ=

1、hint中存在大小写字母、0、=判断其为Base64

 

 解得密文长度为14

2、题目很明显的提示是Polybius，所以上脚本

import itertools
s="aeoiu"
ciper="ouauuuoooeeaaiaeauieuooeeiea"
sumresult=[]
numsumresult=[]
for i in itertools.permutations(s,5):#找出所有全排列
    sumresult.append("".join(i))
for i in sumresult:
    temp=""
    for j in ciper:
        temp+=str(i.index(j)+1)
    numsumresult.append(temp)
for i in numsumresult:
    flag=""
    for j in range(0, len(i),2):
        xx=(int(i[j])-1)*5+int(i[j+1])+96
        if xx>ord('i'):
            xx+=1
        flag+=chr(xx)
    print(flag)

3、运行得到

peznmfdberxmif
odtnmfebdwsmkf
ueztrfcbemyrhf
ydtzwfcbdmuwhf
scntrfebcworkf
xcnzwfdbcrpwif
kezghldceswhol
idtghlecdxrhpl
kezgiqcdeowisq
idtgkvcedprkxv
hcngiqedcymiuq
hcngkvdecumkyv
ueztslbcehysml
ydtzxlbcdhuxml
peznoqbdeixorq
odtnpvbedkspwv
xcnzyqbdcipyrq
scntuvbeckouwv
rbgtslecbxispl
wbgzxldcbskxol
mbgnoqedbyhouq
mbgnpvdebuhpyv
wbgzyqcdbokysq
rbgtuvcebpiuxv
pkznlbifkqxldb
oitnlbkfivsleb
ukztqbhfklyqcb
yitzvbhfiluvcb
shntqbkfhvoqeb
xhnzvbifhqpvdb
kpzgfcolpqwfdc
iotgfcplovrfec
kuzgfdsqulwfcd
iytgfexvylrfce
hsngfduqsvmfed
hxngfeyvxqmfde
upztqcmlpfyqbc
yotzvcmlofuvbc
puznldrqufxlbd
oytnlewvyfslbe
xsnzvdrqsfpvbd
sxntqewvxfoqbe
rmgtqcplmviqec
wmgzvcolmqkvdc
mrgnlduqrvhled
mwgnleyvwqhlde
wrgzvdsqrlkvcd
rwgtqexvwliqce
ekzacmihksvcom
ditacmkhixqcpm
ekzadrhikovdsr
ditaewhkipqexw
chnadrkihyldur
chnaewikhuleyw
epzabhomprvbih
dotabhpmowqbkh
euzabisrumvbhi
dytabkxwymqbhk
csnabiurswlbki
cxnabkywxrlbik
epzadsmopivdrs
dotaexmpokqewx
euzacorsuhvcmo
dytacpwxyhqcmp
csnaeyrusklewy
cxnaduwyxildru
bmgadspomyfdus
bmgaexopmufeyx
brgacousrxfcpo
bwgacpyxwsfcop
brgaeysurpfexy
bwgaduxywofdsu
ukztsmfhkcyslm
yitzxmfhicuxlm
pkznorfikdxoqr
oitnpwfkiespvw
xhnzyrfihdpyqr
shntuwfkheouvw
upztrhlmpbyrfh
yotzwhlmobuwfh
puznmiqrubxmfi
oytnmkvwybsmfk
xsnzwiqrsbpwfi
sxntrkvwxborfk
kpzgislopdwiqs
iotgkxlpoerkvx
kuzghoqsucwhlo
iytghpvxycrhlp
hsngkyqusemkvy
hxngiuvyxdmiqu
wmgzyslomdkyqs
rmgtuxlpmeiuvx
wrgzxoqsrckxlo
rwgtspvxwcislp
mrgnpyqurehpvy
mwgnouvywdhoqu
qfatsmkhfxdspm
vfazxmihfsexom
lfanorkifycour
lfanpwikfucpyw
vfazyrhifoeysr
qfatuwhkfpduxw
qlatrhpmlwdrkh
vlazwhomlrewih
lqanmiurqwcmki
lvanmkywvrcmik
vqazwisrqmewhi
qvatrkxwvmdrhk
flagispolybius
flagkxoplubkyx
fqaghousqxbhpo
fvaghpyxvsbhop
fqagkysuqpbkxy
fvagiuxyvobisu
vlazysmolieyrs
qlatuxmplkduwx
vqazxorsqhexmo
qvatspwxvhdsmp
lqanpyruqkcpwy
lvanouwyvicoru

4、从中找出具有一定实意的字符串

5、解得：BJD{flagispolybius}