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challenge_14.py
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challenge_14.py
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#! /usr/bin/python3
import os, binascii, random, sys, base64, string
from Crypto.Cipher import AES
# from random import randrange
randomKey = os.urandom(16)
obj = AES.new(randomKey,AES.MODE_ECB)
def encrypt(stringToEncypt, key):
a = bytes(a ^ b for (a, b) in zip(stringToEncypt, key))
return a
def aesCBC_encrypt(plaintextBytes, iv):
print("cbc")
blocks = len(plaintextBytes)//16
ciphertext = bytes()
for i in range(blocks):
temp = plaintextBytes[i*16:(i+1)*16]
xorResult = encrypt(temp,iv)
cipher = obj.encrypt(xorResult)
ciphertext += cipher
iv = cipher
return ciphertext
def aesCBC_decrypt(ciphertext, iv):
blocks = len(ciphertext)//16
plaintext = bytes()
for i in range(blocks):
temp = ciphertext[i*16:(i+1)*16]
# print(type(temp))
xor = obj.decrypt(temp)
plaintext += encrypt(xor, iv)
iv = temp
return plaintext
def aesECB_encrypt(ciphertext, iv):
# print("ecb")
# obj = AES.new(key, AES.MODE_ECB)
return obj.encrypt(ciphertext)
# print(plaintext)
def aesECB_decrypt(ciphertext, iv):
# obj = AES.new(key, AES.MODE_ECB)
return obj.decrypt(ciphertext)
# print(plaintext)
def pkcs7(plaintext, blocksize):
padding = blocksize - len(plaintext) % blocksize
pad = chr(padding)
# print(bytes(''.join((plaintext, pad*padding)),'utf-8'))
return ''.join((plaintext, pad*padding))
def randomEncrypt(randomString):
randomString = str(randomString)
iv = os.urandom(16)
randomString = pkcs7(randomString, 16)
randomString = bytes(randomString, 'utf-8')
x = random.randint(2,2)
ciphertext = aesCBC_encrypt(randomString,iv) if x==1 else aesECB_encrypt(randomString,iv)
return ciphertext
def detectECB(ciphertext):
blocksNum = len(ciphertext)//16
blocks = []
for i in range(blocksNum):
blocks.append(ciphertext[i*16:(i+1)*16])
blocks = list(dict.fromkeys(blocks))
if(len(blocks) != blocksNum):
print("ECB DETECTED")
return True
return False
def find_block_size():
current_ctxt = None
for i in range(2, 20):
previous_ctxt = current_ctxt or aesECB_encrypt(pkcs7("A"*1,16),21)
current_ctxt = aesECB_encrypt(pkcs7("A"*i,16),12)
if previous_ctxt[:16] == current_ctxt[:16]:
# print("length::::" + str(i-1))
return i-1
def detectPrexifLength(prefix,target):
for i in range(32,49):
inp = i*'A'
# print(inp)
cipher = aesECB_encrypt(pkcs7(prefix + inp + target,16),None)
if(detectECB(cipher)):
print("i = " + str(i - 32))
# print(len(prefix))
return (i - 32)
# print(randomKey)
# randomString = os.urandom(16)
# input = sys.argv[1]
# print(os.urandom(4))
letters = string.ascii_lowercase
randomS = ( ''.join(random.choice(letters) for i in range(random.randint(0,33))) )
decoded = base64.b64decode("Um9sbGluJyBpbiBteSA1LjAKV2l0aCBteSByYWctdG9wIGRvd24gc28gbXkgaGFpciBjYW4gYmxvdwpUaGUgZ2lybGllcyBvbiBzdGFuZGJ5IHdhdmluZyBqdXN0IHRvIHNheSBoaQpEaWQgeW91IHN0b3A/IE5vLCBJIGp1c3QgZHJvdmUgYnkK")
print("length = " + str(len(randomS)))
# random prefix
input = detectPrexifLength(randomS,decoded.decode())*'A' + "AAAAAAAAAAAAAAAA"
print(input)
# inputLen = len(sys.argv[1])
randomString = bytes(input, 'utf-8')
find_block_size()
# print(obj.block_size)
randomString += decoded
randomString = bytes(randomS, "utf-8") + randomString
print(randomString)
print(input)
decoded = decoded.decode('utf-8')
# print(randomString)
# cipher = randomEncrypt(randomString)
# print(cipher[:16])
# print(cipher[16:32])
cipher = aesECB_encrypt(pkcs7(input,16),None)
# print(cipher[:16])
# print(cipher[16:32])
# ascii = list(range(ord('a'), ord('z') + 1)) +list(range(ord('A'), ord('Z') + 1)) +[ord(' ')]
paddings = ""
for blocksize in range(16):
paddings += str(blocksize)
allChars = string.ascii_letters + string.digits + string.punctuation + string.whitespace + string.printable + string.hexdigits + string.whitespace
# allChars = [chr(i) for i in range(127)]
foundChars = ""
for j in range(len(pkcs7(randomString.decode(),16))//16):
for i in range(16):
dict = {}
trancatedInput = input[i:len(input) - 1]
# print("trancatedInput: " + trancatedInput)
cipher = aesECB_encrypt(pkcs7(randomS +trancatedInput + decoded,16), None)
ccc = (pkcs7(randomS + trancatedInput+decoded,16)[(j*16):(j*16 +16)])
# print("--------")
# print(ccc)
# print(bytes(ccc[len(ccc)-1],'utf-8'))
# for ch in ccc:
# print(ch in allChars)
for c in allChars:
# print(c)
fullCandidate = (trancatedInput + foundChars + c)
candidate = fullCandidate[-16:]
print("fullCandidate: " + fullCandidate + " candidate :" + candidate + " length: " + str(len(candidate)) + "foundchars: " + foundChars + "\n")
candidate = candidate[len(candidate) - 16: len(candidate)]
# print(candidate)
try:
dict[aesECB_encrypt(candidate, None)] = candidate
except:
print(detectPrexifLength(randomS,decoded))
# print(dict)
# print(dict[cipher[:16]][15])
# if(len(dict[cipher[(j*16):(j*16 +16)]]) == 16):
try:
key = cipher[(j*16):(j*16 +16)]
foundChars += dict[key][15]
except:
continue
# print()
# print(i,j)
print("found text: " + foundChars)