Reverse – Vault door 8

Vault door 8 - 450pt

Challenge

Apparently Dr. Evil's minions knew that our agency was making copies of their source code, because they intentionally sabotaged this source code in order to make it harder for our agents to analyze and crack into! The result is a quite mess, but I trust that my best special agent will find a way to solve it. The source code for this vault is here: VaultDoor8.java

Hints

Clean up the source code so that you can read it and understand what is going on.

Draw a diagram to illustrate which bits are being switched in the scramble() method, then figure out a sequence of bit switches to undo it. You should be able to reuse the switchBits() method as is.

Solution

You have a function that scrambles bits of every char of the string in input. You also have the output of this function when said string is the flag. Write the decode function, which is supposed to switch back the bits that the encoder had changed, bottom – top order. Apply this function to the encoded string of bytes in the source file and the flag will be restored.

picoCTF{s0m3_m0r3_b1t_sh1fTiNg_60bea5ea1}

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