“科来杯”第九届山东省大学生网络安全技能大赛决赛部分wp

 

1.损坏的流量包

wireshark打不开，丢进winhex里，找关键字flag

哎，没找到。

那就仔细看看，在最后发现一串类似base64的密文

base64解密

得到flag

2.签到题

一个游戏，

查看源码，发现有一个提示

10课星星获得flag，玩十关再查看源码得到flag

听说可以改代码，但我太菜了，我是打到第十关得到的flag，后期会尽量学会然后更新的！

3.ctf的起源

base64隐写，之前前面有详细总结过，这里就不多说了

脚本跑出flag

import base64
b64chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
with open('flag.txt', 'rb') as f:
    bin_str = ''
    for line in f.readlines():
        stegb64 = str(line, "utf-8").strip("\n")
        rowb64 =  str(base64.b64encode(base64.b64decode(stegb64)), "utf-8").strip("\n")
        offset = abs(b64chars.index(stegb64.replace('=','')[-1])-b64chars.index(rowb64.replace('=','')[-1]))
        equalnum = stegb64.count('=') #no equalnum no offset
        if equalnum:
            bin_str += bin(offset)[2:].zfill(equalnum * 2)
        print (''.join([chr(int(bin_str[i:i + 8], 2)) for i in range(0, len(bin_str), 8)])) 
#flag{944776b2c95a350bb27d7038d42b273a}

4.简单的rsa

rsa共模攻击

直接上脚本

# -*- coding: utf-8 -*-
"""
Created on Tue Nov  3 20:11:03 2020

@author: zhao
"""

import libnum
from gmpy2 import invert
# 欧几里得算法
def egcd(a, b):
  if a == 0:
    return (b, 0, 1)
  else:
    g, y, x = egcd(b % a, a)
    return (g, x - (b // a) * y, y)

def main():
  n = 20429315528655111523073560675648813309162375303954090348572329091957960032412518712093691044501240262294304779722690063594446637140928522882936561204180425968593685714138402078212148627806816974924904301217144262198933589412344408694401386330925556100970326676200349102533012051159456051076045413561059070291766268594455676378031127514060030926838750670330939410961355756909171469945402924037610757364146531235448523106870829710488056210511070536574177473906753241807683881800419949735443822439277498329376433536971257102334607742626401589209417830185425783917209141580607207923687068496513264733739213966151881471319
  c1 = 12051796366524088489284445109295502686341498426965277230069915294159131976231473789977279364263965099422235647723775278060569378071469131866368399394772898224166518089593340803913798327451963589996734323497943301819051718709807518655868569656941242449109980876397661605271517459716669684900920279597477446629607627693769738733623143693170696779851882404994923673483971528314806130892416509854017091137325195201225617407959645788145876202882024723106204183257094755002924708009138560347432552090905489132135154932987521239299578509008290614398700799670928805692609756924823628055245227290288940649158862576448537833423
  c2 = 16648382384980770705624348910895797622774711113202207693584907182552301186239613809347201161450012615995859738410661452438496756353485538305614949211776668793864984429696790944750894691957799234264508530084026894611228513698963347402329109838109621609770406925700520983387811451074838470370044678634099202003480925903267508744006195455234025325060817223813858985074720872124168142943926467694676717713503559007112874381750005406371400109962943508349497151148446064846096531445037416174913915923050332242843403926133165817310272633884358263778516770288515592959832151762499526363131801945163501999337808208074381212795
  e1 = 4106294671
  e2 = 4103337937
  s = egcd(e1, e2)
  s1 = s[1]
  s2 = s[2]
  # 求模反元素
  if s1<0:
    s1 = - s1
    c1 = invert(c1, n)
  elif s2<0:
    s2 = - s2
    c2 = invert(c2, n)

  m = pow(c1,s1,n)*pow(c2,s2,n) % n
  m=int(m)
  print (libnum.n2s(m))

if __name__ == '__main__':
  main()

得到flag

第一次参加这种比赛，见识了大佬们的风采，老萌新瑟瑟发抖，努力不做老萌新！