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Protected Password 4
Posted: Thu Jan 23, 2014 7:13 pm
by trofi
I've hand-edited .class a bit to remove "strange" jsr/pop pair to nop/nop
and ran a soot disassembler on it (soot didn't know jsr).
Some manual bit shifting cleaning and original algorithm is clear:
Code: Select all
[ 'a' + i + 2 * j
| i <- [0 ..2]
, j <- [0..2]
]
Posted: Mon May 12, 2014 10:07 am
by Hippo
I have studied the bytecode and tried several decompilers.
The main problem was ishl where I tested on longs how it behaves ... the modulus of shiftamount ...
and on ints it uses another modulus.
Yes, the 0x200041 and so looked strange, but I were not sure the byte codes generated were ok ...
Posted: Fri May 19, 2017 2:42 pm
by adark
I used the FernFlower decompiler and it worked perfectly fine - everything else I tried choked, though.
De-obfuscated the various `stop` and `run` calls, but it turns out the actual math didn't need any de-obfuscation at all: the first loop creates the correct sequence in a 3x3 grid and the second must just run a comparison.
Lots of unnecessary loops and try/catch blocks in the original code, this challenge would have been a lot more difficult if FernFlower didn't exist.
