凯撒密码

顺序的代替表

class Caesar:
    def __init__(self, offset=3):
        l = list("abcdefghijklmnopqrstuvwxyz")
        u = list("ABCDEFGHIJKLMNOPQRSTUVWXYZ")
        a = list('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')
        offset %= 26
        b = l[offset:]+l[:offset] + u[offset:]+u[:offset]
        self.emap = dict(zip(a, b))
        self.dmap = dict(zip(b, a))
    def encode(self, text):
        tmp = [ (x in self.emap and self.emap[x] or x) for x in text]
        return ''.join(tmp)
    def decode(self, text):
        tmp = [ (x in self.dmap and self.dmap[x] or x) for x in text]
        return ''.join(tmp)

sr1 = "VprPGS{jnvg_bar_cyhf_1_vf_3?}"
ca8 = Caesar(8)
ca5 = Caesar(5)
sr1 = ca8.decode(sr1)
sr1 = ca5.decode(sr1)
print(sr1)

IceCTF{wait_one_plus_1_is_3?}