BUUCTF-RSA

1. subject

Public key ：pub.key

-----BEGIN PUBLIC KEY-----
MDwwDQYJKoZIhvcNAQEBBQADKwAwKAIhAMAzLFxkrkcYL2wch21CM2kQVFpY9+7+
/AvKr1rzQczdAgMBAAE=
-----END PUBLIC KEY-----

Perform public key decomposition ：

Break down links ：RSA Public private key decomposition Exponent、Modulus,Rsa Public private key index 、 coefficient ( modulus ) decompose -- Error checking network  

obtain 10 Base number n=86934482296048119190666062003494800588905656017203025617216654058378322103517

decompose n:

 

import rsa
import gmpy2
e= 65537
n= 86934482296048119190666062003494800588905656017203025617216654058378322103517
p= 285960468890451637935629440372639283459
q= 304008741604601924494328155975272418463
phi=(p-1)*(q-1)
d= gmpy2.invert(e,phi)

key = rsa.PrivateKey(n,e,d,q,p)         # stay pkcs In the standard ,pkcs#1 Regulations , The private key contains (n,e,d,p,q)

with open("D:\\ctf\\flag\\flag.enc","rb") as f:  # In binary read mode , Read ciphertext 
    f = f.read()
    print(rsa.decrypt(f,key))           # f: Public key encryption results   key: Private key 
#b'flag{decrypt_256}\n'