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Coding Challenge for MI5

mi5.gov.uk

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Re: Coding Challenge for MI5

#23

Post by jamesbrownuhh »

OK, so, the obvious "congratulations" messages aside, what's really in that file?

Example: Take the PNG, convert it to another lossless format. Then convert that lossless format back to PNG.

Different file size, right? OK, the comment accounts for about 120 bytes.. but what about the rest? Why is it that much bigger?

"As I read, numbers I see. 'Twould be a great shame not to count this art among the great texts of our time" - count this art among the great texts... it's a one time pad, isn't it.

Re: Coding Challenge for MI5

#24

Post by teh_klev »

guessmyname wrote: post #13

1. Open PNG in text editor, see comment: As I read, numbers I see. 'Twould be a shame not to count this art among the great texts of our time 2. Threshold so some of the pixels are black and others are white. Save as ASCII PBM. 3. Strip the PBM header lines and remove newlines so that it's just 0's and 1's. 4. Now feed it through this program: #include main() { int c, l=0, n=1; while(EOF != (c=getchar())) { if(c == l…

You could have written this up in a Gist or PasteBin, provided a link and a spoiler message.

Re: Coding Challenge for MI5

#25

Post by slowrabbit »

Thought they'd make this challenge more challenging but I reckon anyone who does solve this is pretty smart and worth hiring for them. Remember its government so they aren't getting or even looking for the best of the best... they don't pay enough for the best.

Re: Coding Challenge for MI5

#26

Post by Retr0spectrum »

f_allwein wrote: post #17
guessmyname wrote: post #13

1. Open PNG in text editor, see comment: As I read, numbers I see. 'Twould be a shame not to count this art among the great texts of our time 2. Threshold so some of the pixels are black and others are white. Save as ASCII PBM. 3. Strip the PBM header lines and remove newlines so that it's just 0's and 1's. 4. Now feed it through this program: #include main() { int c, l=0, n=1; while(EOF != (c=getchar())) { if(c == l…

Huh. So who benefits from you posting the solution here?

It's not like its a particularly complex puzzle. If you don't want spoilers, don't read it.

Re: Coding Challenge for MI5

#27

Post by Retr0spectrum »

slowrabbit wrote: post #25

Thought they'd make this challenge more challenging but I reckon anyone who does solve this is pretty smart and worth hiring for them. Remember its government so they aren't getting or even looking for the best of the best... they don't pay enough for the best.

Yes. It would appear that their main criteria are actually mental stability and reliability.

Re: Coding Challenge for MI5

#28

Post by Retr0spectrum »

jamesbrownuhh wrote: post #23

OK, so, the obvious "congratulations" messages aside, what's really in that file? Example: Take the PNG, convert it to another lossless format. Then convert that lossless format back to PNG. Different file size, right? OK, the comment accounts for about 120 bytes.. but what about the rest? Why is it that much bigger? "As I read, numbers I see. 'Twould be a great shame not to count this art among the great texts of ou…

The alpha channel?

Edit: You're right though. Using imagemagick to clone it like so:

   convert puzzle.png puzzle2.png
results in an image that's at least 40% smaller. It might just be better compression, but there might be another layer of steganography going on.

Re: Coding Challenge for MI5

#29

Post by natch »

I have a coding challenge for them. Sadly, it's a really easy one that they missed on so far: Do a better-than-random shuffle so the did-you-know questions lower down on that page don't repeat so often.
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