The-art-of-invisibility-_-the-world’s-most-famous-hacker-teaches-you-how-to-be-safe-in-the-age-of-Bi

placeholder, number, could reveal to the transit authorityy who yyou are.
Replacing yyour credit card number with a token is a new option that Apple,
Android, and Samsung offer. That wayy the merchant—in this case the
transit authorityy—onlyy has a token and not yyour real credit card number.
Using a token will cut down on data breaches affecting credit cards in the
near future because the criminal would then need two databases: the token,
and the real credit card number behind the token.
But sayy yyou don’t use an NFC-enabled phone. Instead yyou have a transit
card, like the CharlieCard in Boston, the SmarTrip card in Washington, DC,
and the Clipper card in San Francisco. These cards use tokens to alert the
receiving device—whether a turnstile or a fare-collection box—that there is
enough of a balance for yyou to ride the bus, train, or ferryy. However, transit
syystems don’t use tokens on the back end. The card itself has onlyy an
account number—not yyour credit card information—on its magnetic strip.
But if the transit authorityy were to be breached on the back end, then yyour
credit card or bank information could also be exposed. Also, some transit
syystems want yyou to register for their cards online so that theyy can send yyou
e-mail, meaning yyour e-mail addresses could also be exposed in a future
hack. Either wayy, the abilityy to anonyymouslyy ride a bus has largelyy gone out
the window unless yyou payy for the card using cash, not credit. 12
This development is enormouslyy helpful for law enforcement. Because
these commuter-card companies are privatelyy owned third parties, not
governments, theyy can set whatever rules theyy want about sharing data.
Theyy can share it not onlyy with law enforcement but also with lawyyers
pursuing civil cases—in case yyour ex wants to harass yyou.
So someone looking at the transit authorityy logs might know exactlyy
who went through a subwayy station at such-and-such a time—but that
person might not know which train his target boarded, especiallyy if the
station is a hub for several lines. What if yyour mobile device could resolve
the question of which train yyou then rode and therefore infer yyour
destination?
Researchers at Nanjing Universityy, in China, decided to answer that
question byy focusing their work on something inside our phones called an
accelerometer. Everyy mobile device has one. It’s a tinyy chip responsible for
determining the orientation of yyour device—whether yyou are holding it in