BUUCTF - re [SUCTF2019]SignIn
定位到关键函数
题目是Signin,有三段字符,特别注意65537,RSA中经常看到。程序调用了 __gmpz_init_set_str 函数,通过搜索得知这是一个 GNU 高精度算法库,官方文档地址:https://gmplib.org/manual/
经过分析:
c=ad939ff59f6e70bcbfad406f2494993757eee98b91bc244184a377520d06fc35
n=103461035900816914121390101299049044413950405173712170434161686539878160984549
e=65537
分解n,得到
p=366669102002966856876605669837014229419
q=282164587459512124844245113950593348271
然后RSA解密
import gmpy2
import binascii
p = 282164587459512124844245113950593348271
q = 366669102002966856876605669837014229419
c = 0xad939ff59f6e70bcbfad406f2494993757eee98b91bc244184a377520d06fc35
n = 103461035900816914121390101299049044413950405173712170434161686539878160984549
e = 65537
phi_n = (p - 1) * (q - 1)
d = gmpy2.invert(gmpy2.mpz(e), phi_n)
flag = gmpy2.powmod(c, d, n)
print(binascii.unhexlify(hex(flag)[2:]))
#b'suctf{Pwn_@_hundred_years}'