密码学--＞buuctf49~60

最新推荐文章于 2025-03-24 08:53:48 发布

crypto_lee

最新推荐文章于 2025-03-24 08:53:48 发布

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分类专栏： crypto 文章标签：密码学

本文链接：https://blog.youkuaiyun.com/qq2489021103/article/details/116176126

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本文详细介绍了buUCTF比赛中的多个密码学挑战，包括rsa的爆破、古典密码解密、RSA的共模攻击等，涉及多种加密解密方法和技巧，如猪圈密码、圣堂武士密码、栅栏密码、凯撒密码、维吉尼亚加密等，并提供了部分解密工具和思路。

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密码学–>buuctf49~60

49.bbbbbbrsa

from base64 import b64encode as b32encode
from gmpy2 import invert,gcd,iroot
from Crypto.Util.number import *
from binascii import a2b_hex,b2a_hex
import random

flag = "******************************"

nbit = 128

p = getPrime(nbit)
q = getPrime(nbit)
n = p*q

print p
print n

phi = (p-1)*(q-1)

e = random.randint(50000,70000)

while True:
	if gcd(e,phi) == 1:
		break;
	else:
		e -= 1;

c = pow(int(b2a_hex(flag),16),e,n)

print b32encode(str(c))[::-1]

# 2373740699529364991763589324200093466206785561836101840381622237225512234632

题目先给了p和n,d但是e是50000到70000之间随机的一个数字，爆破e就行了

from gmpy2 import *
from Crypto.Util.number import *
import base64
p = 177077389675257695042507998165006460849
n = 37421829509887796274897162249367329400988647145613325367337968063341372726061
c = '==gMzYDNzIjMxUTNyIzNzIjMyYTM4MDM0gTMwEjNzgTM2UTN4cjNwIjN2QzM5ADMwIDNyMTO4UzM2cTM5kDN2MTOyUTO5YDM0czM3MjM'
c = int(base64.b64decode(c[::-1]))
q = n //p
phi = (p-1)*(q-1)
for i in range(50000,70001):
    if gcd(i,phi) == 1:
        d = invert(i, phi)
        m = long_to_bytes(pow(c,d,n))
        if b"{" in m and b"}" in m:
            print(m)

注意要先把c逆转再base64解码。题目中也给了c的10进制值。。。。
flag{rs4_1s_s1mpl3!#}
50.古典密码知多少
在这里插入图片描述
先猪圈密码，圣堂武士密码，标准银河字母解码得到：
FGCPFLIRTUASYON
再栅栏解密得到flag
猪圈密码及其变种：

圣堂武士密码：

标准银河字母：

在这里插入图片描述

flag{CRYPTOFUN}
51.RSA

from Crypto.Util.number import getPrime,bytes_to_long

flag=open("flag","rb").read()

p=getPrime(1024)
q=getPrime(1024)
assert(e<100000)
n=p*q
m=bytes_to_long(flag)
c=pow(m,e,n)
print c,n
print pow(294,e,n)

p=getPrime(1024)
n=p*q
m=bytes_to_long("BJD"*32)
c=pow(m,e,n)
print c,n

'''
output:
12641635617803746150332232646354596292707861480200207537199141183624438303757120570096741248020236666965755798009656547738616399025300123043766255518596149348930444599820675230046423373053051631932557230849083426859490183732303751744004874183062594856870318614289991675980063548316499486908923209627563871554875612702079100567018698992935818206109087568166097392314105717555482926141030505639571708876213167112187962584484065321545727594135175369233925922507794999607323536976824183162923385005669930403448853465141405846835919842908469787547341752365471892495204307644586161393228776042015534147913888338316244169120  13508774104460209743306714034546704137247627344981133461801953479736017021401725818808462898375994767375627749494839671944543822403059978073813122441407612530658168942987820256786583006947001711749230193542370570950705530167921702835627122401475251039000775017381633900222474727396823708695063136246115652622259769634591309421761269548260984426148824641285010730983215377509255011298737827621611158032976420011662547854515610597955628898073569684158225678333474543920326532893446849808112837476684390030976472053905069855522297850688026960701186543428139843783907624317274796926248829543413464754127208843070331063037
381631268825806469518166370387352035475775677163615730759454343913563615970881967332407709901235637718936184198930226303

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