0

I'm reading about image steganography at the moment. I got a test file to experiment with. I noticed a strange code block at the end of the PNG file when I opened it with vim:

xref
0 14
0000000000 65535 f
0000007361 00000 n
0000000019 00000 n
0000000209 00000 n
0000007504 00000 n
0000000229 00000 n
0000006570 00000 n
0000006591 00000 n
0000006783 00000 n
0000007097 00000 n
0000007274 00000 n
0000007306 00000 n
0000007603 00000 n
0000007700 00000 n
trailer
<</Size 14/Root 12 0 R
/Info 13 0 R
/ID [ <9AED3720B5C23ED368E99654D498CF4A>
<9AED3720B5C23ED368E99654D498CF4A> ]
/DocChecksum /B1C5AEC599F1457AC4BB4C058905BFD9
>>
startxref
7875
%%EOF

Is this a usual ending for PNG files or did I discover hidden (but not understandable) information?

closed as off-topic by kasperd, Xander, Rory Alsop Mar 3 '17 at 7:48

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about Information security within the scope defined in the help center." – kasperd, Xander, Rory Alsop
If this question can be reworded to fit the rules in the help center, please edit the question.

  • 1
    That is not a PNG file. – kasperd Mar 2 '17 at 22:47
  • These are the last lines from the file I obtained when I open it in vim. And the file is displayable and shows a logo. So it is somehow valid PNG. – drsm0 Mar 2 '17 at 22:58
5

That block seems to contain PDF syntax.

Here you can find information about the PDF format. The page provides this sample file where you might recognize the syntax for the cross-reference table (xref) and the trailer section:

%PDF-1.7
1 0 obj
  << /Type /Catalog
     /Pages 2 0 R
  >>
endobj

2 0 obj
  << /Type /Pages
     /Kids [3 0 R]
     /Count 1
  >>
endobj

3 0 obj
  << /Type /Page
     /Parent 2 0 R
     /MediaBox [0 0 600 400]
     /Resources << >>
  >>
endobj

xref
0 4
00000000000 65535 f
00000000010 00000 n
00000000069 00000 n
00000000141 00000 n
trailer
  << /Root 1 0 R
     /Size 4
  >>
startxref
249
%%EOF

Not the answer you're looking for? Browse other questions tagged or ask your own question.