CodeGate2010 pre-qual for digital forensics

#1 - 300 point

Suspects exchange the secret key through their own file.
Find the key!

#2 – 600 point

An incident occurred, assumed that a guy committed suicide.
How can you assume that? Find the clue!

#3 – 600 point

Find the key!

http://ctf.codegate.org/thisiswhereiuploadmyfiles/CC2A8B4FA2E1FA6BD7FE9B8EFC86BCB7
Substitute for those who are not in Korea : http://www.mediafire.com/?wyhexdmzzdm

#4 – 1000 point

This data has been acquired from the  suspect's disk.
Find the hidden key!

Consequently, our challenges have any mistakes. we desire to solve from digital forensic points of view. 
Solutions will go public early next week. Have fun!!
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You find solutions to following site :
http://www.box.net/shared/4ep3jtncoi