[CISCN 2021华南]guess lingfeng的WriteUp

Oracle Attack

from Crypto.Util.number import *
from pwn import *

def proof_of_work():
    rev = r.recvuntil(b"sha256(XXXX+")
    suffix = r.recv(16).decode()
    rev = r.recvuntil(b" == ")
    tar = r.recv(64).decode()

    def f(x):
        hashresult = hashlib.sha256(x.encode() + suffix.encode()).hexdigest()
        return hashresult == tar

    prefix = util.iters.mbruteforce(f, string.digits + string.ascii_letters, 4, 'upto')
    r.recvuntil(b'Give me XXXX:')
    r.sendline(prefix.encode())



while True:
    r = remote('node4.anna.nssctf.cn', 28101)
    proof_of_work()
    r.recvuntil(b'Welcome to the guess system!')
    r.recvuntil(b'N = ')
    n = int(r.recvline().decode().strip())
    e = 65537
    r.recvuntil(b'Your enc flag:')
    c = int(r.recvline().decode().strip())
    flag=''
    cipher=c
    e1=pow(2,e,n)
    from tqdm import tqdm
    for i in tqdm(range(500)):
        cipher= c*pow(2,i*e,n)%n
        cx=hex(cipher)[2:]
        r.sendlineafter(b'Your guess:','0')
        r.sendlineafter(b'Your cipher (hex):',cx)
        a=r.recvline().decode()
        if 'Lost' in a:
            flag+='1'
        elif 'Win' in a:
            flag+='0'
    print(flag)
    r.close()
a=''
for j in range(8):
    m=[]
    for i in range(j,len(a),8):
        m.append(int(a[i:i+8],2))
    print(bytes(m))
from pwn import *
import  hashlib
#-892f-7d399e38dccd
#9a3-892f-7d399e38dccd}
#c-ba17-49a3-892f-7d39

s1='flag{'
suffix='c-ba17-49a3-892f-7d399e38dccd}'
tar=b'036b0c98ee6b1bdcaa86d36586ffdd660504f536db04fe0631f68f1bea2eec7a'
import hashlib
import itertools
import hmac
from tqdm import tqdm
key = '036b0c98ee6b1bdcaa86d36586ffdd660504f536db04fe0631f68f1bea2eec7a'
dir = '1234567890abcdef'
dir_list = itertools.product(dir, repeat=7)
for j in tqdm(dir_list):
    m=s1+''.join(j) + suffix
    hash = hashlib.sha256()
    hash.update(bytes(m, encoding='utf-8'))
    res = hash.hexdigest()
    if res[0:32] == key[0:32]:
        print(j)
        print(res)
        exit(0)