Crypto-RSA-1

i春秋第二届春秋欢乐赛RSA256 WP
题目链接：RSA256

0x00 查看题目内容

下载文件并解压，发现压缩包里有三段密文以及一个公钥

0x01 使用openssl查看公钥

看到public.key以后用kali linux里的openssl查看
查看一下openssl 中rsa的相关命令

root@kali:~/Desktop# openssl rsa -help
Usage: rsa [options]
Valid options are:
-help              Display this summary
-inform format     Input format, one of DER NET PEM
-outform format    Output format, one of DER NET PEM PVK
-in val            Input file
-out outfile       Output file
-pubin             Expect a public key in input file
-pubout            Output a public key
-passout val       Output file pass phrase source
-passin val        Input file pass phrase source
-RSAPublicKey_in   Input is an RSAPublicKey
-RSAPublicKey_out  Output is an RSAPublicKey
-noout             Don't print key out
-text              Print the key in text
-modulus           Print the RSA key modulus
-check             Verify key consistency
-*                 Any supported cipher
-pvk-strong        Enable 'Strong' PVK encoding level (default)
-pvk-weak          Enable 'Weak' PVK encoding level
-pvk-none          Don't enforce PVK encoding
-engine val        Use engine, possibly a hardware device

0x02 把N转成十进制

因为N是十六进制数 所以得把N转换成十进制才能用在线分解网站将其分解

root@kali:~/Desktop# python
Python 2.7.15 (default, Jul 28 2018, 11:29:29)
[GCC 8.1.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> Modulus=0xD99E952296A6D960DFC2504ABA545B9442D60A7B9E930AFF451C78EC55D555EB
>>> Modulus
98432079271513130981267919056149161631892822707167177858831841699521774310891L

0x03因式分解

将n进行因式分解来得到我们的p和q (推荐使用http://factordb.com/)

0x04 生成私钥解密

import gmpy2
import rsa
p = 302825536744096741518546212761194311477
q = 325045504186436346209877301320131277983
n =9843207927151313098126791905614916163189282270716717785883184169952177431089
e = 65537
d = int(gmpy2.invert(e , (p-1) * (q-1)))
privatekey = rsa.PrivateKey(n , e , d , p , q)
with open("encrypted.message1" , "rb") as f:
print(rsa.decrypt(f.read(), privatekey).decode())
with open("encrypted.message2" , "rb") as f:
print(rsa.decrypt(f.read(), privatekey).decode())
with open("encrypted.message3" , "rb") as f:
print(rsa.decrypt(f.read(), privatekey).decode())