CONFidence CTF 2019 Count me in

source.py

import multiprocessing

from Crypto.Cipher import AES

from secret import key, flag

counter = 0

aes = AES.new(key, AES.MODE_ECB)

def chunk(input_data, size):

    return [input_data[i:i + size] for i in range(0, len(input_data), size)]

def xor(*t):

    from functools import reduce

    from operator import xor

    return [reduce(xor, x, 0) for x in zip(*t)]

def xor_string(t1, t2):

    t1 = map(ord, t1)

    t2 = map(ord, t2)

    return "".join(map(chr, xor(t1, t2)))

def pad(data):

    pad_byte = 16 - len(data) % 16

    return data + (chr(pad_byte) * pad_byte)

def worker_function(block):

    global counter

    key_stream = aes.encrypt(pad(str(counter)))

    result = xor_string(block, key_stream)

    counter += 1

    return result

def distribute_work(worker, data_list, processes=8):

    pool = multiprocessing.Pool(processes=processes)

    result = pool.map(worker, data_list)

    pool.close()

    return result

def encrypt_parallel(plaintext, workers_number):

    chunks = chunk(pad(plaintext), 16)

    results = distribute_work(worker_function, chunks, workers_number)

    return "".join(results)

def main():

    plaintext = """The Song of the Count

You know that I am called the Count

Because I really love to count

I could sit and count all day

Sometimes I get carried away

I count slowly, slowly, slowly getting faster

Once I've started counting it's really hard to stop

Faster, faster. It is so exciting!

I could count forever, count until I drop

1! 2! 3! 4!

1-2-3-4, 1-2-3-4,

1-2, i love couning whatever the ammount haha!

1-2-3-4, heyyayayay heyayayay that's the sound of the count

I count the spiders on the wall...

I count the cobwebs in the hall...

I count the candles on the shelf...

When I'm alone, I count myself!

I count slowly, slowly, slowly getting faster

Once I've started counting it's really hard to stop

Faster, faster. It is so exciting!

I could count forever, count until I drop

1! 2! 3! 4!

1-2-3-4, 1-2-3-4, 1,

2 I love counting whatever the

ammount! 1-2-3-4 heyayayay heayayay 1-2-3-4

That's the song of the Count!

""" + flag

    encrypted = encrypt_parallel(plaintext, 32)

    print(encrypted.encode("hex"))

if __name__ == '__main__':

    multiprocessing.freeze_support()

    main()

solve.py

from Crypto.Util.strxor import strxor

def pad(data):

    pad_byte = 16 - len(data) % 16

    return data + (chr(pad_byte) * pad_byte)

def unpad(data):

    last_char = data[-1]

    if ord(last_char) < 16:

        return data.rstrip(last_char)

    else:

        return data

def chunk(input_data, size):

    return [input_data[i:i + size] for i in range(0, len(input_data), size)]

def xor(*t):

    from functools import reduce

    from operator import xor

    return [reduce(xor, x, 0) for x in zip(*t)]

def xor_string(t1, t2):

    t1 = map(ord, t1)

    t2 = map(ord, t2)

    return "".join(map(chr, xor(t1, t2)))

def is_printable(data):

    for i in data:

        if ord(i)<32 or ord(i)>127:

            return False

    return True

plaintext = """The Song of the Count

You know that I am called the Count

Because I really love to count

I could sit and count all day

Sometimes I get carried away

I count slowly, slowly, slowly getting faster

Once I've started counting it's really hard to stop

Faster, faster. It is so exciting!

I could count forever, count until I drop

1! 2! 3! 4!

1-2-3-4, 1-2-3-4,

1-2, i love couning whatever the ammount haha!

1-2-3-4, heyyayayay heyayayay that's the sound of the count

I count the spiders on the wall...

I count the cobwebs in the hall...

I count the candles on the shelf...

When I'm alone, I count myself!

I count slowly, slowly, slowly getting faster

Once I've started counting it's really hard to stop

Faster, faster. It is so exciting!

I could count forever, count until I drop

1! 2! 3! 4!

1-2-3-4, 1-2-3-4, 1,

2 I love counting whatever the

ammount! 1-2-3-4 heyayayay heayayay 1-2-3-4

That's the song of the Count!

"""

output = "9d5c66e65fae92af9c8a55d9d3bf640e8a5b76a878cbf691d3901392c9b8760ebd5c62b22c88dca9d1c55098cbbb644ae9406ba32c8293bdd29139bbc2b4605bba51238f2cb399a9d0894ad9cbb8774be9406ce66fae89a6c8ef7ad9c4b87442ad1470af78e19da6d8c55096d2b9750ea8586fe668a085c2ef8a5e9cd3be6c4bba144ae66ba488e8df84418bceb2650ea84362bf0688dcabd3905d8d87a46d414626be04a58215b84263a620de3203fa4626be08e2940da35c61b82c98201ce15438cd67eb921cf77c28a969de321bf4433ea24ca59216a25b7bb662996106e11639e75ae09015bb4c2fb76d8c254fe15e6ab45cea817391547cab698c6d4ff35039b34df7df599e412fb67fde3200b55432a441f19817b01405962c9d2e1af9556aa447f09f0df75360ad6988241db91129a85deb8559a25b7bb660de084ff1cc3a0e8041bc71d71fb29883931d9d3e8f784ca743b065c91ea386909e1a9100925f4fa742b1718c1efec4d4d609df5bcb3b17e417bd268d5fe6ced4d65b9c40d6305eeb1df03e9050e68bcad241dd15b46453b85dae7cd112b2c3c7ca50dd4ddf2c1ff350f5349c5febcadbd2509c40d6340aad03bd258d5bb2d8cdc647d814d1335efe18f8718651e7c5d6b9609c57d12010fe50e939801ee1dbcbd74cce4739c1eeceba8ef87360b629ed82a6eb9d508ee381bb88e97363bf20a1cfe7a7e07cccf3cea788bd277fb265e9cde4a9b937808aa7ee85f22679a365f5c4ede5f478c0e482ab95bd3c79f731e9c9a8b6ff7cc2e6c0e0c897047fb22ba1e5afa8b778c2ef80abcabd1a37b42af4c2fce5fa60dde582a8c7971a37b42af4c2fce5e475c1f782b7cabd207bb832edd5a4e5e4130a976ad4a2fe86ac99c18491f9f6c86adae59cc4a9f33072f70ca6daede5e40b049272c8e6b980b798c69e9fb7f7891611c7758df0fc82b481d1ca9eb8e2cd5f118f26def6f693d2abc99982bce2855f038175d9e7ebcdf8a4dcca9faab0da1045857eceebed8ab68a89e0bff9f3c60a098426ceedec8daccdce8584bce6cc0d49c065c2f7f797f898c69e9fb5b0e05f019269dd88a8c2f8df89cac5f8b09d00ad16dc760ead7c3518baed47603c5b5251cc269cae93d1f8a4888699aff58942c8529f304af0362143f2bd1e37670d538753992129ff3c6c5befb21e7331590c950ac26917be39644dfba50b2b70117fcbccba57b209ae95721a1c9d36073d934b75014109102be14fb6a044a7cf9e468748976457f6342177f5a9042630622f97d2ba5a8c04a7890d4e5fcb445b7600d7c1be71b711b6b32b4444f078557ef82e4f0559225437b455aa9a0bbaff89c834531a45115125c933d6cd6cdca8f8".decode("hex")

chunks = chunk(pad(plaintext), 16)

keyStream_list = []

for i in range(0,len(chunks)-1):

    keyStream_list.append(strxor(chunks[i],output[i*16:(i*16)+16]).encode("hex"))

keyStream_list = list(set(keyStream_list))

for i in range(len(chunks)-1,len(output)/16):

    print "------------------------"

    for j in range(0,len(keyStream_list)):

        result = unpad(strxor(keyStream_list[j].decode("hex"), output[i * 16:(i * 16) + 16]))

        if is_printable(result):

            print result