prog5

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prog5

Post by noname8135 on Sat Jun 14, 2014 8:55 am
([msg=81376]see prog5[/msg])

I found out about what's wrong with the file.
And after I did some experiments,
I made an assumption: there wasn't too many of "the pairs" before its broken,
(Am I even right?)
But the method is just not working(I use python to read file in binary mode and manipulate the content)

I do found something suspicious:
1. Why isn't the file contain '0x177245385090', which is a block delimiter?
I have read the source code of libbzip2 and that's how it tell from blocks to blocks.
2. There are two 0a(\n) in the very end of the file, it seems strange, since the end of a bz2 file shouldn't have that?

I've done so many research,
understand the file structure of bz2,
and read all related threads,
but none seems to help.
Would someone help pls~ I'm so stuck
If not the mission,
answer the two questions would be helpful, too.
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Re: prog5

Post by i404i on Fri Jun 27, 2014 11:27 pm
([msg=81828]see Re: prog5[/msg])

Well, Can someone tell me where should I start, what topics should I read up ?
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Re: prog5

Post by cyberdrain on Sat Jun 28, 2014 6:32 pm
([msg=81851]see Re: prog5[/msg])

I'd guess BZIP2 and PNG file structures and after that comparing the broken with a correct file (like stego), but I haven't done this one.
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Re: prog5

Post by alan on Sat Jul 26, 2014 6:20 am
([msg=82520]see Re: prog5[/msg])

Finally completed it... Did it with Python.

Here's some advice. Every nancy-roger pair, could be either nancy-roger or just nancy. But it's more likely to be just nancy.

The way I did it is I split the file into little pieces wherever I found nancy and roger. Like this

RANDOMDATA_MOREDATA_EVENMOREDATA_SOMEMOREDATA

Then I filled the missing spaces with nancys, and tried unpacking. If that failed, tried with one roger, then try roger with every nancy. If that fails, add another roger, try all combinations of two rogers with all nancys...

It's actually a pretty easy mission when I think of it.
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