Tuesday, 2 April 2013

Decoding encryption on slashdot

For this years April Fools Day joke www.slashdot.org decided to 'encrypt' all posts.  Here is an example of the encrypted text:
Na nabalzbhf ernqre jevgrf"Nf Qryy'f (QRYY:ANFQND TF) obneq erivrjf guerr pbzcrgvat cebcbfnyf sbe gnxvat gur pbzcnal cevingr, vapyhqvat n $24.4 ovyyvba qrny yrq ol sbhaqre naq PRB Zvpunry Qryy naq Fvyire Ynxr Cnegaref, gur pbzcnal unf naabhaprq vg vf ragrevat gur 
I decided that as obviously this was a joke it wasn't going to be encrypted with anything difficult, thus if I couldn't crack it in my lunch hour then I should hang up my boots.

Finding a way in

The first step in solving any problem is to find something to latch onto.  For jigsaw problems this is often to find the corner or side pieces to build the frame.  For this puzzle I thought could I find an plaintext word that might have been used in the ciphertext.  'Most' slashdot posts start with:
beltsbear writes"Following a reasonable view of drug patents, the Indian courts have decided that making small changes to an existing 
 The interesting bit is that the story starts with writes.  If this is true of the encrypted version then it would mean that f('writes') = jevgrf  where f is the encryption algorithm

Pulling it apart

Both the words contain 6 characters.  I wondered if this was a simple encryption algorithm like a ceaser shift.  

ABCDEFGHIJKLMNOPQRSTUVWXYZ
                      |-----------------------| (13 CHARACTERS)
Each letter was simply shifted 13 spaces across.  This is known as a ROT(13) algorithm.  It requires no key.  Plenty of online tools exist to decode such text.  thus:

Na nabalzbhf ernqre jevgrf"Nf Qryy'f (QRYY:ANFQND TF) obneq erivrjf guerr pbzcrgvat cebcbfnyf sbe gnxvat gur pbzcnal cevingr, vapyhqvat n $24.4 ovyyvba qrny yrq ol sbhaqre naq PRB Zvpunry Qryy naq Fvyire Ynxr Cnegaref, gur pbzcnal unf naabhaprq vg vf ragrevat gur 
became
 An anonymous reader writes
"As Dell's (DELL:NASDAQ GS) board reviews three competing proposals for taking the company private, including a $24.4 billion deal led by founder and CEO Michael Dell and Silver Lake Partners, the company has announced it is entering the 

Going back to work

This wasn't difficult but I did enjoy pulling the puzzle apart and figuring it out.  At least I don't have to give up the day job
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