[CryptoHack] General Challenge - XOR

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XOR Starter

 Given the string "label", XOR each character with the integer 13. Convert these integers back to a string and submit the flag as crypto{new_string}.

 The Python pwntools library has a convenient xor() function that can XOR together data of different types and lengths. But first, you may want to implement your own function to solve this.

 

"label" 이라는 문자열을 13이라는 정수형과 xor 연산을 하면 된다.

code = "label"

decode = []
for i in code :
  decode.append(ord(i) ^ 13)

for d in decode:
  print(chr(d))

crypto{aloha}

 

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XOR Properties

Let's try this out in action! Below is a series of outputs where three random keys have been XOR'd together and with the flag. Use the above properties to undo the encryption in the final line to obtain the flag.

KEY1 = a6c8b6733c9b22de7bc0253266a3867df55acde8635e19c73313
KEY2 ^ KEY1 = 37dcb292030faa90d07eec17e3b1c6d8daf94c35d4c9191a5e1e
KEY2 ^ KEY3 = c1545756687e7573db23aa1c3452a098b71a7fbf0fddddde5fc1
FLAG ^ KEY1 ^ KEY3 ^ KEY2 = 04ee9855208a2cd59091d04767ae47963170d1660df7f56f5faf

 Before you XOR these objects, be sure to decode from hex to bytes.

 

A^B 에서 A를 XOR 연산해주면 B 가 남는다는 사실을 이용하자.

(A^B) ^ A = B

 

from Crypto.Util.number import *

hint0 = "a6c8b6733c9b22de7bc0253266a3867df55acde8635e19c73313" # KEY1
hint1 = "37dcb292030faa90d07eec17e3b1c6d8daf94c35d4c9191a5e1e" # KEY1 ^ KEY2
hint2  = "c1545756687e7573db23aa1c3452a098b71a7fbf0fddddde5fc1" # KEY2 ^ KEY3
hint3 = "04ee9855208a2cd59091d04767ae47963170d1660df7f56f5faf" # KEY1 ^ KEY2 ^ KEY3 ^ FLAG

# KEY1 = hint0
KEY1 = bytes_to_long(bytes.fromhex(hint0))

# KEY2 = (KEY1 ^ KEY2) ^ KEY1
KEY2 = bytes_to_long(bytes.fromhex(hint1)) ^ KEY1

# KEY3 = (KEY2 ^ KEY3) ^ KEY2
KEY3 = bytes_to_long(bytes.fromhex(hint2)) ^ KEY2

# FLAG = (KEY1 ^ KEY2 ^ KEY3 ^ FLAG) ^ KEY1 ^ KEY2 ^ KEY3
FLAG = bytes_to_long(bytes.fromhex(hint3)) ^ KEY1 ^ KEY2 ^ KEY3

print(str(long_to_bytes(FLAG), "UTF-8"))

 

crypto{x0r_i5_ass0c1at1v3}

 

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Favourite Bite

For the next few challenges, you'll use what you've just learned to solve some more XOR puzzles.

I've hidden some data using XOR with a single byte, but that byte is a secret. Don't forget to decode from hex first.

73626960647f6b206821204f21254f7d694f7624662065622127234f726927756d