import base64 a = "s1XWgtaLvfyEeYUi42Mo36NR9DKrVjbTpPuwHc5lA8dC0OSxzknm7qGJBIZFQh+/" a = [i for i in a] b = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/" b = [i for i in b] # SlashRootCTF{7h1s_i5_n0t_a_b3t4_tE5t_k3y} c = "3akPbN6noa6GDNzheoO4ratIDRftbLsheWO4ratIDRfv3W7keWsF3akPbN6n4R2CiogzUq109RccVH2cDw7qUq109RccVHIPrN3hoa6x" d = list(map(lambda x: a.index(x), c)) e = ''.join(list(map(lambda x: b[x], d))) f = base64.b64decode(e) print(f)