ctf-writeup/2023/SpringForwardCTF 2023/A new hope

A new hope

So we found this on a thumbdrive. I know, I know, don't load random USBs, but look... Things are weird right now and I figured it might be something.

All it has is this half of a program and a weird mashing of letters and numbers.

Maybe it's nothing, but it might be something. Think you can check?

About the Challenge

We were given 2 files encrypt.py and log.txt. Here is the content of the encrypt.py file

def encrypt(message, key):
    encrypted = ""
    for i in range(len(message)):
        encrypted += chr(ord(message[i]) ^ ord(key[i % len(key)]))
    return encrypted.encode("utf-8").hex()

message = #//////ERROR ERROR ERROR
key = #/////// ERROR OERROR ERROR ERROR
encrypted = encrypt(message,key)

The script just encrypt the xoring the message using the key. And here is the content of the log.txt file

SWYgeW91J3JlIHJlYWRpbmcgdGhpcywgeW91IGJldHRlciBiZSBtZS4KTW9zdCBsaWtlbHkgeW91IGZvcmdvdCwgdGhhdCB0aW1lIGlzIHRoZSBrZXkuCg==
mpq_wxkdim_qe_WTNQ
tvp euaapnbqpr vafhlk abtx ogwi aaif qr xxeg qe


072923373661312c3f2d66273661276537203f652429232b73352f283661312c3f2d6627362f22653124202a2124663c3c346a65322f22652a2e3365302028653b242a357334352d363366313b2835653a2f68653d28252628297529231e2b760c7124740c36062b2e6f661c3c3466282632326520282b353f3866233c2d2a2a2461322d36613624272966233c3366203d2d2f223b35232b3e2428317d616b1711

There is some encoded msg that encoded in different way and then there is an encrypted message

How to Solve?

Decode the message first to know what is the key. Use Base64 Decoder and Vigenere Cipher, here is the decoded message

If you're reading this, you better be me.
Most likely you forgot, that time is the key.
the_secret_is_SAFE
and absolutely nobody will know what my plan is

We know the key is SAFE and we need to XOR the encrypted message with the key

nicc{h3lp_m3_0b1_w@n}