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@hellman
Created May 3, 2020 20:53
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De1CTF 2020 - Mini Pure Plus
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#!/usr/bin/env python3
# coding=utf-8
import os,random,sys,string
import binascii
from pyfinite import ffield
from FLAG import flag
import sympy
import numpy as np
from Crypto.Util.number import long_to_bytes
ROUND = 16
F = ffield.FField(24)
flag = ''.join(['%02x' % b for b in flag.encode(encoding="utf-8")])
def pad(plain):
pad_length = (6 - len(plain) % 6 ) % 6
return plain + chr(pad_length) * pad_length
def genkeys():
keys=[]
for _ in range(ROUND):
key = os.urandom(3)
key_int = int(binascii.hexlify(key),16)
keys.append(key_int)
return keys
def Mul(q1,q2):
return F.Multiply(q1,q2)
def fbox(x):
return Mul(Mul(x,x),x)
def enc_block(plain,keys):
l = int(binascii.hexlify(plain[:3]),16)
r = int(binascii.hexlify(plain[3:]),16)
for i in range(ROUND):
l , r = r , l ^ fbox(keys[i] ^ r)
l , r = r , l
result = (hex((l << 24) + r)[2:]).rjust(12,'0')
return result
def encrypt(plain, keys):
p = ''
for i in range(0,len(plain),2):
p += chr(int(plain[i:i+2],16))
plain = pad(p).encode(encoding='utf-8')
cipher = ''
for i in range(0,len(plain),6):
cipher += enc_block(plain[i:i+6],keys)
return cipher
keys = genkeys()
with open('pt.txt','r') as ptfile:
with open('ct.txt','w') as ctfile:
while True:
pt = ptfile.readline().rstrip('\n')
if pt == '':
break
ct = encrypt(pt,keys)
ctfile.write(ct + '\n')
p = sympy.nextprime(2**24)
arr = np.random.randint(0,p,(ROUND,ROUND-2),dtype='int64')
keys = np.array(keys)
res = np.mod(np.dot(keys,arr),p)
with open('data.txt','w') as f:
f.write('Array: ' + str(arr) + '\n')
f.write('Result: ' + str(res) + '\n')
with open('flag.txt','w') as f:
ct = encrypt(flag,keys)
f.write(ct)
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