buuctf base64

一眼base64换表
写脚本

from base64 import *
old ="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
new ="AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz0987654321/+"
enc="mTyqm7wjODkrNLcWl0eqO8K8gc1BPk1GNLgUpI"
a=""
for char in enc:
    idx=new.index(char)
    a+=old[idx]
a+="=="
print(b64decode(a))

flag{Special_Base64_By_Lich}
也可以手动在表后补一个等于，这样就不用在删除密文的=再后面补回来

from base64 import *
old ="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
new ="AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz0987654321/+="
enc="mTyqm7wjODkrNLcWl0eqO8K8gc1BPk1GNLgUpI=="
a=""
for char in enc:
    idx=new.index(char)
    a+=old[idx]
print(b64decode(a))