concealment writes "Butler said he had discovered that information stored within the bar codes of boarding passes is unencrypted, and so can be read in advance by technically minded travelers.
Simply by using a smartphone or similar device to check the bar code, travelers could determine whether they would pass through full security screening, or the expedited process." Link to Original Source
"The algorithm to do that is extremely nasty. You might want to mug
someone with it."
-- M. Devine, Computer Science 340