Simon_96_64, ECB, key="SECCON{xxxx}", plain=0x6d564d37426e6e71, cipher=0xbb5d12ba422834b5
In the task we get the plaintext, ciphertext and the information what is the encryption. We also get the key with 4 missing characters. It seems like a good target to simply brute-force, because 4 bytes is not much.
We found the Simon algorithm at https://github.com/inmcm/Simon_Speck_Ciphers/blob/master/Python/simon.py and we prepared a simple brute-force script:
from crypto_commons.brute.brute import brute
from crypto_commons.generic import bytes_to_long
dataset = string.uppercase + string.lowercase + string.digits + string.punctuation + " "
def worker(a):
print(a)
for b in dataset:
for c in dataset:
for d in dataset:
# Simon_96_64, ECB, key = "SECCON{xxxx}", plain = 0x6d564d37426e6e71, cipher = 0xbb5d12ba422834b5
key = "SECCON{" + a + b + c + d + "}"
w = SimonCipher(bytes_to_long(key), key_size=96, block_size=64)
t = w.encrypt(0x6d564d37426e6e71)
if t == 0xbb5d12ba422834b5:
print(key)
sys.exit(0)
if __name__ == "__main__":
brute(worker, dataset, 7)Nothing special here, we simply try every 4 character combination as the key, until the ciphertext matches.
It was pretty slow so we used PyPy and multiprocessing to run in paralell on multiple cores.
After a while we got: SECCON{6Pz0}