New TSA rules

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Here is the newly released list of prohibited and allowed items, which takes effect Thursday.


  • Ammunition
  • Baseball bats
  • Boxcutters
  • Cattle prods
  • Firearms
  • Golf clubs
  • Hammers
  • Ice axe/picks
  • Knives, excluding round-bladed, butter and plastic
  • Lighters
  • Meat cleavers
  • Pellet or BB guns
  • Pool cues
  • Razors
  • Scissors, metal with pointed tips and blades longer than four inches
  • Ski poles
  • Spray paint


  • Cigar cutters
  • Corkscrews
  • Cuticle cutters
  • Eyelash curlers
  • Knitting and crochet needles
  • Nail clippers or files
  • Disposable razors
  • Scissors, with a cutting edge of less than four inches
  • Tweezers
  • Tools, seven inches long or less, including screwdrivers, wrenches and pliers
  • Walking canes

The first thing you learn about designing security systems is to ask what your threat model is. So, what threat model does this correspond to? Because superficially it doesn't make that much sense. As far as I can tell, knitting needles1 are at least as dangerous as ice picks and much more dangerous than cigarette lighters (yes, yes, I know about Richard Reid, but it's not like it's really that hard to build a cigarette lighter that will get through a metal detector if you're really trying, and of course magnesium ribbon burns hot and can be easily lit with matches). Similarly, a slock is more dangerous than a ski pole, pool cue, a can of spray paint, or even a boxcutter.

The answer, it seems to me, is that these are the items that appear dangerous and that it's not too inconvenient to take away from people (which, I assume is why spray paint but not, say, spray deodorant, and pool cues and not canes, even though a cane probably makes a better weapon). But that's not what you do if you're trying to actually have security. It's what you do if you want to appear to be trying to have security (what Schneier calls security theatre).

So, every so often the TSA publishes these revisions to the allowed and prohibited lists and everyone complains about how stupid they are, but they never really explains the reasoning behind any particular list. 4 years after September 11, I think it's about time we had a serious conversation about it, because I'm getting pretty tired of taking my shoes off.

1 Ordinary knitting needles are generally not that strong, but it would be easy to manufacture a stainless or titanium needle that was plenty strong, useful as a weapon, and indistinguishable from an ordinary knitting needle. Anyone with access to a lathe would find this a trivial job.


I think knitting needles, or any other stabbing weapon, are red herrings. Try controlling a crowd while trying to remove the knitting needle from the chest of the first person that you stabbed. Not so easy. Now a slashing weapon -- that'll get you some crowd control. Might not kill many people, but they might stop rushing you if you slice up their arms and faces enough.

A reasonable threat model, but that takes ice picks off the list, right?

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