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Suppose I want to print a human readable 10 digit serial using ordinary day today printer but the printer is communal printer and manned. My intention is for the person manning the printer to not read the code.

Initial inputs that i know is that printer is not a copier and person manning does not have a camera or smartphone to make a copy. There is no message interception between the printer and the computer printing it.

My method to print is in such a way that the paper is to be folded which will make creases on the paper if an attempt was made by human to read the code thereby letting the end user know that the code secret is known by another human or an attempt was made to read the code. However before I go about programming the print function, I was wondering if there are any techniques or methods that may be already out there.

Added bonus would be if the print is not copyable.

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  • Fill the page with several 10-digit serial numbers, and one with a slight different font that you can detect with closer examination, but someone manning the printer will not. – ThoriumBR Mar 17 at 10:53
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I've never heard of a cryptographic operator that works like this—you could certainly design a page that looks a certain way (e.g. has certain numbers on it) when folded up, but I've never heard of an automated way to do that.

In part, this is because you have one whopper of an XY problem here. First of all, I sincerely doubt your threat model is accurate—everyone and their aunt has a smartphone nowadays. Second of all, there are much more effective and less finicky ways to do what you'd like—for example:

  • Print thousands of codes on one page. Remember that the (n)th (9th, 73rd, 50th, whichever you choose at the time) one from the bottom is the real code. You need to use a different (n) each time, or you become vulnerable to known-plaintext, whenever someone figures out one of the real codes, notes where it is, and can steal the real codes from all the other pages.
  • Print thousands of codes on one page, prefixed by various letter combinations. Remember which letter combination you put before the real one. You need to use a different letter sequence each time, or you become vulnerable to known-plaintext, whenever someone figures out one of the real codes, notes what letter sequence it started with, and can steal the real codes from all the other pages.
  • Bypass the printer and write it down on a piece of paper with your own hand, it's just a 10-digit code...
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  • Try asking non tech people to write a 256 bit key. My higher ups wanted to store critical keys on a hard drive connected to internet for ease of access which I was against and as a compromise they now can print a digit code and I am to trust them to keep it safe without any blow back towards me. – Flood Gravemind Mar 17 at 17:06
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    Ahhh, so it needs to be safe storage as well...well, if your heart is set on a technique like this (instead of say, just putting it in a safe, or putting scratch coating like they use on lottery tickets), I'd go with the letter sequences one (there is a risk that the higher-up is an idiot and circles the right one instead of remembering the letters, but then there is a risk that the higher-up is an idiot and stores the foldy thing folded up; security is not foolproof when fools are trusted :P) – iridia Mar 17 at 18:17

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