二、答题步骤

1.base64和异或

import string

from base64 import *

b=b64decode("aWdxNDs1NDFSOzFpa1I1MWliT08w")

data=list(b)


for k in range(0,200):

    key=""

    for i in range(len(data)):

        key+=chr(ord(data[i])^k)

    print (key)

igq4;541R;1ikR51ibOO0
hfp5:450S:0hjS40hcNN1
kes69763P93kiP73k`MM2
jdr78672Q82jhQ62jaLL3
mcu0?105V?5moV15mfKK4
lbt1>014W>4lnW04lgJJ5
oaw2=327T=7omT37odII6
n`v3<236U<6nlU26neHH7
aoy<3=<9Z39acZ=9ajGG8
`nx=2<=8[28`b[<8`kFF9
cm{>1?>;X1;caX?;chEE:
blz?0>?:Y0:b`Y>:biDD;
ek}8798=^7=eg^9=enCC<
dj|9689<_6<df_8<doBB=
gi:5;:?\5?ge\;?glAA>
fh~;4:;>]4>fd]:>fm@@?
ywa$+%$!B+!y{B%!yr__ 
xv`%*$% C* xzC$ xs^^!
{uc&)'&#@)#{y@'#{p]]"
ztb'(&'"A("zxA&"zq\\#
}se /! %F/%}F!%}v[[$
|rd!. !$G.$|~G $|wZZ%
qg"-#"'D-'}D#'tYY&
~pf#,"#&E,&~|E"&~uXX'
qi,#-,)J#)qsJ-)qzWW(
p~h-",-(K"(prK,(p{VV)
s}k.!/.+H!+sqH/+sxUU*
r|j/ ./*I *rpI.*ryTT+
u{m(')(-N'-uwN)-u~SS,
tzl)&(),O&,tvO(,tRR-
wyo*%+*/L%/wuL+/w|QQ.
vxn+$*+.M$.vtM*.v}PP/
IGQrIKrIBoo
HFPsHJsHCnn
KESpKIpK@mm
//等等

得到flag ：flag{jdr78672Q82jhQ62jaLL3}

总结

• 修改文件头
• crc32值爆破图像宽度