Security if God wills it

perdu Writeup (Nuit Du Hack 2018)

perdu was a 100-point forensics challenge at Nuit Du Hack 2018. I personally didn't beat it in time, mainly due to a lack of sleep, a high consumption of beer and the fact that socializing is much more amusing than flagging.

Although someone else from our team ended up flagging it, I decided to solve it after the event ended and write it up myself.

Challenge description

Because we can't access the platform anymore, this challenge shall remain without description for now. The description mentions data exfiltration, and we are provided with a file named perdu.pcap.


Opening the .pcap in wireshark, we can observe a lot of HTTP exchanges with

I spent a lot of time trying to figure out whether anything was hidden in the requests, but I came up with nothing.

After following several inconclusive leads, I noticed that all the TCP ports used in the communication were in the range [4000;4200].

Extracting data

Looking at the last 3 digits, it is natural to assume that the ports may be used to encode ASCII characters.

SIben and I came up with this cool oneliner to extract the data:

~$ tshark -r perdu.pcap -Y http.request -Tfields -e tcp.srcport | cut -c 2-4 | awk '{ printf("%c", $0); }'

It basically retrieves all the ports used in the HTTP requests, subtract 4000 to them and prints the result as an ASCII character.

The output is the following:

   ==Phrack Inc.==

                    Volume One, Issue 7, Phile 3 of 10

The following was written shortly after my arrest...

                       \/\The Conscience of a Hacker/\/


                               +++The Mentor+++

                          Written on January 8, 1986

        Another one got caught today, it's all over the papers.  "Teenager
Arrested in Computer Crime Scandal", "Hacker Arrested after Bank Tampering"...
        Damn kids.  They're all alike.

        But did you, in your three-piece psychology and 1950's technobrain,
ever take a look behind the eyes of the hacker?  Did you ever wonder what
made him tick, what forces shaped him, what may have molded him?
        I am a hacker, enter my world...
        Mine is a world that begins with school... I'm smarter than most of
the other kids, this crap they teach us bores me...
        Damn underachiever.  They're all alike.

        I'm in junior high or high school.  I've listened to teachers explain
for the fifteenth time how to reduce a fraction.  I understand it.  "No, Ms.
Smith, I didn't show my work.  I did it in my head..."
        Damn kid.  Probably copied it.  They're all alike.

        I made a discovery today.  I found a computer.  Wait a second, this is
cool.  It does what I want it to.  If it makes a mistake, it's because I
screwed it up.  Not because it doesn't like me...
                Or feels threatened by me...
                Or thinks I'm a smart ass...
                Or doesn't like teaching and shouldn't be here...
        Damn kid.  All he does is play games.  They're all alike.

        And then it happened... a door opened to a world... rushing through
the phone line like heroin through an addict's veins, an electronic pulse is
sent out, a refuge from the day-to-day incompetencies is sought... a board is
        "This is it... this is where I belong..."
        I know everyone here... even if I've never met them, never talked to
them, may never hear from them again... I know you all...
        Damn kid.  Tying up the phone line again.  They're all alike...

        You bet your ass we're all alike... we've been spoon-fed baby food at
school when we hungered for steak... the bits of meat that you did let slip
through were pre-chewed and tasteless.  We've been dominated by sadists, or
ignored by the apathetic.  The few that had something to teach found us will-
ing pupils, but those few are like drops of water in the desert.

        This is our world now... the world of the electron and the switch, the
beauty of the baud.  We make use of a service already existing without paying
for what could be dirt-cheap if it wasn't run by profiteering gluttons, and
you call us criminals.  We explore... and you call us criminals.  We seek
after knowledge... and you call us criminals.  We exist without skin color,
without nationality, without religious bias... and you call us criminals.
You build atomic bombs, you wage wars, you murder, cheat, and lie to us
and try to make us believe it's for our own good, yet we're the criminals.

        Yes, I am a criminal.  My crime is that of curiosity.  My crime is
that of judging people by what they say and think, not what they look like.
My crime is that of outsmarting you, something that you will never forgive me

        I am a hacker, and this is my manifesto.  You may stop this individual,
but you can't stop us all... after all, we're all alike.

                               +++The Mentor+++
Well done : ndh16_{e132697f156befd669df0726f06ab338f0a225da3267661cfa9bb720161b2af9}

Yay for the hacker manifesto, flagged!

Flag: ndh16_{e132697f156befd669df0726f06ab338f0a225da3267661cfa9bb720161b2af9}

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