message

465 points

Maybe this message is from aliens.

https://static2017.teamrois.cn/misc_745cfbae1f7e94f0a49e9f81a69d72e4/msg_bc5c27abe80477b13ec5ba03dcaf7cf0.zip

We are given the following text file (originally - a single long line, split into several lines for clarity):

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7fffffffffffffffffffffffffffffffbffff0e10419dff07fdc3ffdaeab
6deffdbfff6ffed7f7aef3febfffb7ff1bfbc675931e33c79fadfdebbae7
aeddedb7dafef7dc37df7ef6dbed777beedbedb77b6de24718f260e0e718
79fffffffffffffffffffffffffffffffffffffffffff07f87fc7f9fffff
fffdbfbbfdbfeffffffffebfdffdfff7ffffff871c33e6fe7bffffffd5ae
feed62dcffffffeadf9fb8bb0efffffff56df5db6dbf7ffffffaa0c21e19
e3bffffe07ffffffffff9fffffffffffffffffffffffffffffffffffffff

Converting it to a binary file and doing a file and binwalk on it brings no useful results. However it does look like it has some repeating patterns in it. Let’s convert it into a binary string representation with the following script:

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print bin(int(open("msg.txt","r").read(),16))[2:].replace("0",".").replace("1","#")

The script generates series of .’s and #’s. Let’s copy the output into Notepad++, reduce the font to a minimum (press Ctrl+- repeatedly), and resize the window continuously to see if we can spot something.

The following pattern is revealed:

The flag is RCTF{ArEciBo_mEsSaGe}.