极客大挑战-三个也可以

三个也可以

密码学题目

题目给定文件如下：

# 解压后只有一个py文件
from Crypto.Util.number import getPrime,bytes_to_long
# from flag import FLAG

flag = bytes_to_long(flag)
p = getPrime(100)
q = getPrime(100)
r = getPrime(100)


n = p*q*r
e = 65537
c = pow(flag, e, n)     # flag**e %n == c

print(n)
print(c)

'''
798898099277934230940128318327632478801901355882614385038310680236381399664973004454688807
249128262668727227416761229197781088291962817031744463346178556057415901512114944554308575
'''

非常简单，写个python脚本直接算就可以了（思路来源于网上的师傅）

import gmpy2

p = 821285845529489288911031313917
q = 1005682191548299165290460437397
r = 967244547191154261539598250343
c = 249128262668727227416761229197781088291962817031744463346178556057415901512114944554308575
n = 798898099277934230940128318327632478801901355882614385038310680236381399664973004454688807

e=65537

phin = (p-1)*(q-1)*(r-1)


d=gmpy2.invert(e, phin)

print(d)

m = pow(c,d,n)

print(m)
print(hex(m))
print(bytes.fromhex(hex(m)[2:]))

解答结果如下所示：

40300244384284458664389035512497982223263215867565711201073618351763565714690247279940929
121814240979386959575434948378090701383537735070845
0x5359437b6e6f775f796f755f736f6c76655f69747d
b'SYC{now_you_solve_it}'

因此本题的flag为b'SYC{now_you_solve_it}'