2 Oct 2011 adulau   » (Journeyer)

2011-10-02 Try and Vet Tshirt Crypto Challenge Hack.lu2011 The Solution

Try and Vet T-Shirt Cryptographic Contest at Hack.lu 2011

The Challenge

What Did You Get During Hack.lu 2011?

From the hack.lu website, you got a text message including a message stream. During the conference, you got a t-shirt.

The horrible "Beer Scrunchie" subverted the hack.lu 2011 conference to hide some cryptographic materials. He especially abused the t-shirt for hack.lu 2011 to transmit under cover activities. We still don't know at which extend "Beer Scrunchie" abused the t-shirt. Everything is possible just like those trojan t-shirts discovered...
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Solution

The message on the website gave already some clues especially that:

If you decode the message encoded in Base64, you'll see that the stream of data in binary is starting in the following way : "Salted__…." That's the behaviour of the OpenSSL? salted encryption scheme prefixing with "Salted__" to announce that the first 8 bytes of the encrypted stream are reserved for the salt. This gives the indication that the message has been probably encrypted with an OpenSSL? tool or library. If you look carefully look at the encryption schemes available in OpenSSL?:

aes-128-cbc    aes-128-ecb    aes-192-cbc    aes-192-ecb    aes-256-cbc    
aes-256-ecb    base64         bf             bf-cbc         bf-cfb         
bf-ecb         bf-ofb         cast           cast-cbc       cast5-cbc      
cast5-cfb      cast5-ecb      cast5-ofb      des            des-cbc        
des-cfb        des-ecb        des-ede        des-ede-cbc    des-ede-cfb    
des-ede-ofb    des-ede3       des-ede3-cbc   des-ede3-cfb   des-ede3-ofb   
des-ofb        des3           desx           rc2            rc2-40-cbc     
rc2-64-cbc     rc2-cbc        rc2-cfb        rc2-ecb        rc2-ofb        
rc4            rc4-40 

There are not so many algorithms written by Bruce Schneier in a default OpenSSL? except Blowfish (bf-*). Usually cryptographer recommends to use the "default" mode and in this case, bf is Blowfish in CBC mode. So this is highly probable…

Where Is The Key?

As you didn't use the t-shirt until now, there is a good guess that the key is hidden somewhere. If you look carefully at the text in the back of the hack.lu 2011 t-shirt, you'll see many typographic errors. The interesting part is to compare the typographic errors from the original text as published by Phrack. Please note the typo in the URL (even if the URL works, doesn't mean that's the correct one ;-).

The original text from Phrack (original.txt)

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 for. 
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 Conscience of a Hacker, The Mentor, January 8, 1986, 
http://www.phrack.org/issues.html?issue=7&id=3#article 

The text from the hack.lu 2011 t-shirt (modified.txt)

This is our world now... the world of the electron and the swich, the beauty of the baud,
We make use of a service already exeisting without paying for what could be dirt-cheep if it
was'nt run by profofiteering gluttons, and you call us cricriminal. We explore... and you call
us criminals. We seek after knowledge... and you call us criminals. We exist without skin
colo, without nationlity, without rrligious bias... and you call us crimnals. 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 judginfg people by what thy say and think,
not what they look like. my crime is that of outmarting you, something that you will
never forgive me for.
I am a hacker, and this is my manifasto.
you may stop this individul, but you can't stop us all... after all, we're all alike.


The Conscience of a Hacker, The Mentor, January 8, 1986, 
http://www.phrack.org/issues.html?issue=7$id=3#article 

So you can build a key from the differences but how? That's the most difficult part (as there are many different way to do it). As there is no natural way to generate a key, I decided to go for a long key that can be read easily from the original text. To build back the key from original to modified you can use word diff and use your favorite GNU tools for word diff. We just discarded the punctuation and we didn't care about the case sensitivity.

wdiff -i -3 original.txt modified.txt | egrep -o "(\[-(.*)-\])" | sed -e "s/-//g" | sed -e "s/\[//g" | sed -e "s/\]//" | sed -e "s/\.$//g" | sed -e "s/,//g" 
| sed ':a;N;$!ba;s/\n//g'

The key to decrypt the message generated from the above wdiff is the following:

switchbaudexistingdirtcheapwasn'tprofiteeringcriminalscolornationalityreligiouscriminalsjudgingtheyoutsmartingmanifestoindividualhttp://www.phrack.org/issues.html?issue=7&id=3#article

and to decrypt the message, you'll need to use OpenSSL? in the following way used the guessed parameters:

openssl enc -d -a -bf -in encrypted.txt -out decrypted.txt 

and the original decrypted message is:

I'm Beer Scrunchie and I'm the author or co-author of various block ciphers, pseudo-random number generators and stream ciphers.

In 2012, there will be two major events: the proclamation of a winner for the NIST hash function competition and probably the hack.lu 2012 infosec conference
.

I hope that my Skein hash function will be the winner.

If you are reading this text and be the first to submit to tvtc@hack.lu, you just won a hack.lu ticket for next year. If I'm winning the NIST competition wit
h my hashing function,
you'll get a second free ticket...

Bruce

I got one correct answer 5 days after the conference showing that the difficulty to get back the key was bound to the uncertainty of the key generation. Next year, it's possible that we make a multi-stage t-shirt challenge for hack.lu 2012… from something more easy to something very difficult.

Tags: crypto infosec ctf conference hacklu

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