Nearly all colour laser printers leave a pattern of tiny yellow dots all over the paper. These dots contain information about the printer and perhaps also about the time and date of the print, the IP of your computer and who knows what else. These codes are in there for at least a decade and the EFF has complained in vain. Reality Winner got cought with these dots – but perhaps they would have found out about her a bit later without them.
The EFF has a dorky video about that.
I have a laser printer in my office at school. What does it tell about me? I research that with help of GIMP 2.9 – which looks terrific and has a lot of nice new stuff on board.
And of course you get to see some of these new features.
The companion file contains the scan of the Ordnungsmaßnahmenverordung in different resolutions and the XCF file with the revealed code. The last paragraph on the page gives me the right to take away your phone and hand it back to your parents after a reasonable time – if it beeps again in my class. (A lot of kids would prefer the cane over this…. 😉 )
I forgot about the serial number of the printer – this will be updated soon.
00:00:50 Leaking from the NSA
00:01:35 Little yellow dots on laser print
00:03:00 Gimp 2.9 fired up
00:03:30 Search for the yellow dots
00:04:20 Colour Channels
00:06:00 Extract a colour component
00:06:40 Split view – new in filter dialogs
00:07:15 Searching for the pattern
00:07:55 New things in the layer dialog
00:08:30 Searching for the pattern
00:10:10 Crop tool
00:10:30 Measuring the pattern
00:11:35 Adding a precise grid
00:12:45 30 bytes of data in the yellow dots!
00:14:00 What’s not in the code?
00:15:00 Printing leaves traces
00:16:25 Blunder of “The Intercept”
00:17:00 Anonymising a scan with the threshold tool
00:18:30 The mono mixer for getting red back in
00:20:00 Return of the Minox for leakers?
00:21:00 We need a guide about OPSEC!
00:21:44 End of video