Something has confused me about boarding passes:

It seems that the Pre-Check checkmark on your boarding pass is what lets TSA officers know that you should be allowed to go in the Pre-Check lane.

Simple enough. Now, pretend you're a "bad guy".
Isn't it trivial for you to just print a fake boarding pass with the checkmark?

When you get your actual boarding pass, you can of course use it everywhere except at the security lane. For the security lane, you just use the fake one so they think you're Pre-Checked.

Do they even try to guard against this? If so, how? I haven't managed to figure it out.
If not... has it not occurred to them? Wouldn't this completely nullify any security benefit of Pre-Check?

(Note: while I realize that if they decide to check you anyway, then you'll be screwed, that's always a risk even if you really do have Pre-Check.)

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    Most TSA measures are to provide the impression of security, not to provide security. Most all of the rules are easily circumvented, and would be no more than a small nuisance to a dedicated terrorist. – Aganju Dec 13 '16 at 12:14
  • There is not much difference in security, pre-chek is more about convenience. About the only noteworthy security difference is that shoes don't go through the scanner. – user13044 Dec 13 '16 at 12:42
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    You Pre-Check status is encoded in the bar code which is scanned by the ID checker. There is/was a post somewhere out there that detailed the code and it's position. IIRC, the data itself is not encrypted but there's a hash value to detect tampering. – Johns-305 Dec 13 '16 at 15:41

Maybe it varies between airports, but where I have used PreCheck, it works as follows.

At the entrance to the security checkpoint, there is an agent who I'll call the "greeter". You show your boarding pass to the greeter, and if they see the check mark, they wave you into the PreCheck line.

But when you reach the front of the line, there's another agent at a podium with a barcode scanning terminal. You hand them your ID (driver's license, passport, etc) and scan the barcode on your boarding pass. I do not know for sure, but I would assume that the barcode encodes your name and PreCheck status, along with a cryptographic signature, or at least a link to a database with this information. This information is displayed to the agent on their terminal.

So if you were to take a non-PreCheck boarding pass and forge it by adding a check mark, you would get past the greeter, but all that would achieve is letting you stand in the wrong line. When you got to the ID check, the barcode would show that in fact you do not have PreCheck. Best case, you explain it away as some sort of mistake, and they send you back to the regular security line. Worst case, you get arrested.

Something similar would happen if you tried to take the boarding pass from an actual PreCheck passenger and change the name - they would see the name didn't match your ID.

The greeter is more for efficiency than security - they mostly just keep people from wasting their time by standing in the wrong line by mistake. They are more visible because you see them actually looking for the check mark on a boarding pass, but they are not really the functional part of the process.

  • The barcode does not encode pre-check status explicitly. It does include the information printed on the boarding pass. That being said, barcode data could be used to lookup precheck status in a database – gatorback Dec 13 '16 at 15:17
  • @gatorback: Interesting, where did you find that information? – Nate Eldredge Dec 13 '16 at 15:25
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    PreCheck status is encoded directly in the bar code. The readers are not online. 3L, again IIRC, means PreCheck. 3 beeps and LLL is displayed. – Johns-305 Dec 13 '16 at 16:56
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    @NateEldredge "Simplifying the Business Bar Coded Boarding Pass Implementation Guide" v 2009.. however, this article claims to the contrary puckinflight.wordpress.com/2012/10/19/… that pre-check status is encoded in the barcode – gatorback Dec 14 '16 at 4:12
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    @gatorback: TSA PreCheck began in 2011, so it isn't surprising that a document dated 2009 wouldn't describe it. – Nate Eldredge Dec 14 '16 at 4:19

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