攻防世界-密码学-babyrsa

文章目录

1. 题目信息
2. 分析
3. 解题

题目信息

点击获取在线场景来得到在线场景。

分析

就是一个最常规的RSA Oracle，在CTF Wiki中RSA部分有介绍。

解题

交互解题的Python脚本如下：

from pwn import pwnlib
from pwnlib.tubes.remote import remote
from time import sleep
from Crypto.Util.number import *

e=0x10001
n=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
c=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

def check(guess,err):
    for m in range(guess-err,guess+err):
        if pow(m,e,n)==c:
            return m
    return

def solve():
    low,high=0,n
    cnt=0
    while high-low>4:
        cnt+=1
        tt=(pow(2,cnt*e,n)*c)%n
        r=remote('111.200.241.244',44451)
        re=r.recv()
        r.sendline(hex(tt)[2:])
        re=r.recv().strip('\n')
        r.close()
        if re=='odd':
            low=(low+high)//2
        else:
            high=(low+high)//2
        print len(bin(high-low))-2
        sleep(0.5)
    m=check(low,150)
    if not m:
        print 'try again!'
        return
    return long_to_bytes(m)

if __name__=='__main__':
    print(solve())