QCTF 2018线上赛 writeup

if (Oracle(C‘) == even):
    UB = (UB + LB)/2;
else:
    LB = (UB + LB)/2;

# coding=utf-8
# author:401219180
import binascii
import socket


def getevenOrodd(c):
    """nc连接获取even or odd"""
    adress = "47.96.239.28"
    port = 23333
    s = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
    s.connect((adress,int(port)))
    s.recv(1024)
    data = hex(c)[:-1] + "n"
    s.send(data)
    codeindex = s.recv(1024)
    s.shutdown(1)
    s.close()
    print codeindex
    return codeindex


def decrypt(n):
    LB = 0
    UB = n
    e = 65537
    c = int("0x4f377296a19b3a25078d614e1c92ff632d3e3ded772c4445b75e468a9405de05d15c77532964120ae11f8655b68a630607df0568a7439bc694486ae50b5c0c8507e5eecdea4654eeff3e75fb8396e505a36b0af40bd5011990663a7655b91c9e6ed2d770525e4698dec9455db17db38fa4b99b53438b9e09000187949327980ca903d0eef114afc42b771657ea5458a4cb399212e943d139b7ceb6d5721f546b75cd53d65e025f4df7eb8637152ecbb6725962c7f66b714556d754f41555c691a34a798515f1e2a69c129047cb29a9eef466c206a7f4dbc2cea1a46a39ad3349a7db56c1c997dc181b1afcb76fa1bbbf118a4ab5c515e274ab2250dba1872be0",16)
    while LB != UB:
        c1 = (pow(2,e,n) * c) % n
        if getevenOrodd(c1)[:-1] == "even":
            UB = (UB + LB) / 2
        else:
            LB = (UB + LB) / 2
        c = c1
    print LB

n=int("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",16)
decrypt(n)

LB = 560856645743734814774953158390773525781916094468093308691660509501812320
plaintext = binascii.unhexlify(hex(LB)[2:-1]) print(plaintext)

cpdic = {
    "a": "d","d": "e","g": "f","q": "r","h": "o","b": "m","u": "b","r": "a","t": "s","p": "i","k": "p","w": "t","z": "u","e": "n","x": "c","y": "l","l": "y","f": "w","m": "h","j": "g","i": "x","v": "k"
}

f1 = open("C:UsersfuzhiDesktopDownloadsencryption.encrypted","r") //本地文件
data1 = f1.read()
listdata1 = list(data1)
i = 0
for strindex in listdata1:
    if strindex in cpdic:
        listdata1[i] = cpdic[strindex]
    i += 1

s = "".join(listdata1)
print s

from gmpy2 import is_prime
from os import urandom
import base64

def bytes_to_num(b):
    return int(b.encode(‘hex‘),16)
    
def num_to_bytes(n):
    b = hex(n)[2:-1]
    b = ‘0‘ + b if len(b)%2 == 1 else b
    return b.decode(‘hex‘)

def get_a_prime(l):
    random_seed = urandom(l)

    num = bytes_to_num(random_seed)
    
    while True:
        if is_prime(num):
            break
        num+=1
    return num

def encrypt(s,n):
    p = bytes_to_num(s)
    p = pow(p,n)
    return num_to_bytes(p).encode(‘hex‘)    

def separate(n):
    p = n % 4
    t = (p*p) % 4
    return t == 1
    
f = open(‘flag.txt‘,‘r‘)
flag = f.read()
        
msg1 = ""
msg2 = ""
for i in range(len(flag)):
    if separate(i):
        msg2 += flag[i]
    else:
        msg1 += flag[i]

p1 = get_a_prime(128)
p2 = get_a_prime(128)
p3 = get_a_prime(128)
n1 = p1*p2
n2 = p1*p3
e = 0x1001
c1 = encrypt(msg1,n1)
c2 = encrypt(msg2,n2)
print(c1)
print(c2)

e1 = 0x1001
e2 = 0x101
p4 = get_a_prime(128)
p5 = get_a_prime(128)
n3 = p4*p5
c1 = num_to_bytes(pow(n1,e1,n3)).encode(‘hex‘)
c2 = num_to_bytes(pow(n1,e2,n3)).encode(‘hex‘)
print(c1)
print(c2)

print(base64.b64encode(num_to_bytes(n2)))
print(base64.b64encode(num_to_bytes(n3)))