xctf攻防世界 CRYPTO高手进阶区 cr3-what-is-this-encryption

1. 进入环境

题目给出了一长串字符，我们将其提出来，发现是p，q，e，c，因此猜测可能是RSA相关的解密问题。
查一查RSA的具体操作流程：

2. 代码解题

参考网上的wp，先安装两个包：

pip install libnum
pip install pycryptodome

接着上代码：

import libnum
from Crypto.Util.number import long_to_bytes

p = int(
    "0xa6055ec186de51800ddd6fcbf0192384ff42d707a55f57af4fcfb0d1dc7bd97055e8275cd4b78ec63c5d592f567c66393a061324aa2e6a8d8fc2a910cbee1ed9",
    16)
q = int(
    "0xfa0f9463ea0a93b929c099320d31c277e0b0dbc65b189ed76124f5a1218f5d91fd0102a4c8de11f28be5e4d0ae91ab319f4537e97ed74bc663e972a4a9119307",
    16)
e = int(
    "0x6d1fdab4ce3217b3fc32c9ed480a31d067fd57d93a9ab52b472dc393ab7852fbcb11abbebfd6aaae8032db1316dc22d3f7c3d631e24df13ef23d3b381a1c3e04abcc745d402ee3a031ac2718fae63b240837b4f657f29ca4702da9af22a3a019d68904a969ddb01bcf941df70af042f4fae5cbeb9c2151b324f387e525094c41",
    16)

c = 0x7fe1a4f743675d1987d25d38111fae0f78bbea6852cba5beda47db76d119a3efe24cb04b9449f53becd43b0b46e269826a983f832abb53b7a7e24a43ad15378344ed5c20f51e268186d24c76050c1e73647523bd5f91d9b6ad3e86bbf9126588b1dee21e6997372e36c3e74284734748891829665086e0dc523ed23c386bb520

n = p * q

# invmod就是求mod的逆，invmod(a, n)则返回 1 / a (mod n).
d = libnum.invmod(e, (p - 1) * (q - 1))

m = pow(c, d, n)
string = long_to_bytes(m)
print(string.decode())

得到最终答案为：ALEXCTF{RS4_I5_E55ENT1AL_T0_D0_BY_H4ND}

标签：what,invmod,16,int,encryption,RSA,libnum,pip,进阶
来源： https://blog.csdn.net/l8947943/article/details/122874075