Permissive action links for individual bullets

I read with interest about US Patent application 20060117632, which proposes to apply the notion of cryptographic accessory control to individual bullets in firearms. Only after an authentication protocol has convinced the tiny microprocessor in a cartridge that it is OK to potentially kill someone, it will close a transistor switch that normally blocks the electrical ignition mechanism.

It does not seem to me technically infeasible, or even cost prohibitive, to apply security mechanisms comparable to those we have come to expect to be used in weapons of mass destruction also to smaller weapon systems that were designed to kill only a few people at a time.

(The idea could be extended. If we add a chip to each cartridge, we might as well place it into the bullet itself. The bullet processor could then store in its NVRAM an audit log of the certification chain that ultimately authorized the firing of this bullet. With the right packaging, NVRAM chips can be made extremely tough and withstand hundreds of km/sĀ² acceleration, much more than the conditions a normal bullet faces when penetrating a body. Having a log file in each bullet that identifies who is responsible for firing it could make the forensic investigation of shootings and war crimes so much easier.)

About Markus Kuhn

I'm a Senior Lecturer at the Department of Computer Science and Technology, working on hardware and signal-processing aspects of computer security.

12 thoughts on “Permissive action links for individual bullets

  1. it’s not technically infeasable, but there are huge reliability concerns to be worked out.

    guns already have problems with misfires, adding hardware + code to the triggering mechanism is not likely to improve reliability, even if the shot is authorized.

    not to mention that there are the same concerns as with the application of DRM to content, at least under the U.S. philosophy towards firearms.. if you wouldn’t trust Sony with control of your computer, why would you trust the government with control of your firearm (with reference to civilians)?

    these have been the primary concerns with integral biometric locks applied to guns, and schemes to prevent police firearms from firing for anyone but police – despite the fact that officers (unlike civilians, since they generally carry openly) are regularly killed with their own weapons, most officers I have heard on the matter have negative opinions about such devices…

    having a code-induced misfire when you do need to shoot can be just as lethal as someone getting a handle on your gun.

    IIRC, many of the computers once used in early fly-by-wire systems in airplanes were originally mechanical or analog in nature, largely because code was not considered reliaible enough.

  2. Some interesting stuff here. I think we should keep auditability separate from authorisation.


    I was reading a trashy novel the other day that described a “Tazer” gun discharging, and apparently when the electrodes fire (i think the mechanism is explosive), the catridge containing them scatters myriads of tiny ID discs around. This should allow discharge to be identified, though time stamping is not so easy. The electronic solution Markus describes could add timestamps to bullets which would be nice. But you could do this in other ways maybe, for instance by having time-dependent moving lumps in the barrel which create striations in the bullets as they are fired. Or in the casings for that matter.

    I think what is really noteworthy is that if the auditability can be inextricably linked to the bullet, the potential for tracking the path of that bullet from factory-to-flesh is much enlivened. Howver I’m not sure that arms dealers want that level of accountability for the later consequences of re-selling, and I’m not sure soldiers want that level of fine grain scrutiny of their actions.

    One possible benefical use of this technology for western military however would be to disprove information warfare by the enemy claiming that their air strikes/raids caused large numbers of civilian casualties. That is of course assuming that the true casualties are low, rather than it being a military cover up.

    Here’s a crazy idea, can we design cryptographically authenticated shrapnel? If a falling bomb can write to millions of Nvram chips on the surface just before it explodes, and embed these in the surrounding people, then this proves they are bona fide casualties, and could provide date and location stamp. Practical issues with the technology here I know, but let’s just do the thought experiment…

    If the bomb does turn out to miss, and the military in question then “revokes” a particuar bomb, then shrapnel cryptographically traceable to it can be traded in at the hospital for a prosthetic arm/leg paid for by a military compensation fund.

    Sorry the above is a little sick. Such is the nature of warfare.


    The same guys who are worried about their live weapon being stolen and used to shoot them are also worried about their weapon being ready to use when they need it, and being reliable. The bigger difficulty in my mind is not the reliability of the authorisation mechanism, but the time and complexity of authorisation, as this conflicts between “readyness to use” and “theft protection”.

    Clearly anyone who is worried their enemy will abuse the permission system to disable their weapon can just use a good old-fashioned weapon. There will be plenty of traditional guns around… they can always go for a crossbow if necessary.

  3. The one and only solution to controlling firearms is to make people understand we cannot just go around killing each other, even in cases of burglary.

    Instead of spending half a dusin billion dollar on patching firearms it will be alot cheaper to send a few hundred famous people around which the younger people actually trust, and let them tell them that killing people is like pissing in their own pants in the long term.

    Roy Andre

  4. I have to agree with Robert, and to some degree Roy, here. Adding another layer of complication to firearms isn’t the answer. Education is the key. Well, education and the freedom to bear arms. Without either we are sitting ducks.

  5. As a patent goes, it’s doomed in the UK and other places, prior art that a lot of people will have seen is “Judge Dredd” the movie where DNA of the officer and other information are encoded onto the chip in the bullet.

    As a further idea back in the early 1990’s I was on a course at Kingston University where a bod from ITN was looking for solutions to a problem they where going to see. Basically they where going to switch their News Gathering repository from edited archive storage to large arrays of Hard Drives holding raw footage. The idea was to only edit what was needed in a JIT type fashion, however the problem was how do you identify what is important in such a large amount of storage.

    THe solution I propsed was to put a GPRS receiver digital inclinomiter and compass onto each and every cammera thus all the footage would be automatically spatially aware of where it was taken and at what time. Therefor whenever a story came in it’s location would be known and a search for related footage would be relativly trivial (than by other methods).

    You could apply the same method to the gun so that when it is fired the location of the gun the direction and inclination it was pointing in would be recorded in the bullet. So even if the bullet is moved at a later stage the original location of the crime can be located.

  6. “Judge Dredd” isn’t prior art. At least, I don’t think it would be. While it did put forth the idea, it never had a working model, just a bunch of props and Hollywood movie magic.

  7. I take it the proposed smart bullets are fired by specially designed new guns which accept ony the smart bullets? If not, hand loading conventional bullets is not exactly rocket science.

    In any case, anyone choosing to circumvent the scheme will simply use one of the hundreds of millions of conventional guns currently available. Even if these were not available, an improvised single shot shotgun can easily made be made from plumbing supplies. It works much like the bang sticks divers sometimes carry as defense against sharks.

    I predict the proposed scheme will not be accepted, and would not work if it were.

  8. @pwyll

    From my reading the control mechanisum is not in the gun, but actually in the round of amunition. In which case making your own gun or using one currently in existance will not enable you to fire it.

    If say the NY Police Dept decided that all their officers guns where to work this way, then it certainly would reduce the number of Officer down cases where they have been shot by their own guns.

    Likewise if the UK Government decided to make had guns available again then they could insist on this method (with the added proviso that approved targets where the only thing that could be fired at). However the published figures that showed the number of “non-domestic” shootings with privatley owned hand guns (prior to the ban) was extreamly small.

    In the UK the majority of the guns that find their way onto the street where not obtained illegaly or through a theft. The majority have been purchased quite legitamatly second hand in countries with lax gun controles and imported into the UK. Or they are converted replicas or disabled guns that have been re-enabled.

    IF you examin the makings of a gun in a home workshop (see history of the SMG/Sten/Plumbers delight and the Ingram) about the only thing you cannot easily make are,

    1, Rifeling in the barrel (not realy required for a hand gun)
    2, Casing for the round of amunition.

    And most importantly

    3, The percusion cap used in the case of the round

    The first can be fairly easily got around by buying an Air Rifle or some such and cutting the barell down.

    Manufacture of the round of amunitions case in small caliber auto load wepons is not a simple task, in large calliber such as a manual load shot gun this is considerably easier (and reasonably possible for home workshop)

    It’s the manufacture of the percusion cap that presents the most dificult problem (for a home workshop) which is why most self loaders buy them in.

    There are essentially two issues with manufacture one, the forming of the percussion cap case, the second and perhaps the more difficult, is the making of the fulminate or chlorate initiator and reliably filling the case. You could very easily take your fingers off just by handeling the less stable initiator compounds.

    However there is a (fairly simple) way around this, go into a toy shop that sells Cap Guns and buy the caps, then all you need to do is make a round casing that easily accomidates the toy gun cap (oh you would need to lift the paper wadding out with a pin first šŸ˜‰

    So although the patent is fairly well though out in which area to make secure your basic point about going in a different direction (such as Home Build) is quite valid.

    However I sugest that as long as other Countries have lax gun laws then apart from the problem of an Police Officer shot with their own wepon and Domestic accident / crime the patent is not actually worth a great deal.

  9. A society with a strict right to bear arms would certainly not be one I would want to live in. Just consider: about 20% of all humans experience some serious psychiatric problem at least once during their lifetime. I really do not want them to have easy access to tools of destruction. People kill already enough other people on the road with cars; why would you want to add to the problem by further distributing consumer products optimized to be lethal in the hands of any troubled individual? If we really need guns at all, I prefer the strictest controls to be applied to them to ensure that their use is based on a broad consensus of society, and is not entirely in the hand of any single individual.

    Note that even the often misquoted Second Amendment of the U.S. Constitution grants citizens a right to bear arms only in the context of “well regulated militia”! I am happy to argue that the spirit of the Second Amendment ā€“ interpreted in today’s health-and-safety concious societies ā€“ means that “well regulated militia” ought to think today seriously about permissive action links for any commercially available amunition.

  10. From the Emerson Law School:

    Amendment II.

    A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.

    It is easy to misquote it, and it is singularly just as easy to say it is misquoted and used out of context. The Second Amendment allows for a well regulated militia and provides for the citizenry to be armed. The reasoning behind this is summed up in this pithy little quote:

    Fear the government that fears your gun.

    And for good reason. A well armed citizenry is the only obstacle for an out of control government seeking to make itself all-powerful within its borders, and outside of its borders as well. Look at current tyrannical governments such as North Korea and China. Look at past ones such as Rome, and feudal Japan. It was the restriction upon weapons that gave rise in feudal Japan to the ninja clans. The restriction of weapons has only empowered criminals througout history, whether those criminals are individuals maiming and murdering and stealing or governments maiming and murdering and stealing.

    As for your statistic, Samuel Clemens had something to say about them.

    There are three types of lies. Lies, damn lies and statistics.

    20% of humans out of an estimated 6 billion, is about 120 million people worldwide. If you’re afraid of such a minority perpatrating crimes undetected, you are very paranoid. Statistics are especially meaningless outside of context and doubly misleading.

  11. Whilst in many ways I see the sense in this, a firearm is but one means of killing someone, and in my opinion, a very easy way in which to do so, given the lesser restrictions on proximity, compared to, say, a knife. Equally, I believe that one could more easily pull a trigger than plunge a knife into someone, with the necessary force required and greater probability of physical resistance.

    Joseph: 20% is 1 in 5. If you have 20% of 5 billion (five thousand million) you have 1 billion. 20% of 6 billion is therefore 1.2 billion (one thousand two hundred million), not 120 million. I believe this is only marginally more than the entire population of China. Perhaps you might wish to reconsider?

    Society’s greatest weapon is its voice. Apathy is therefore a greater threat than a lack of weapons. Too often we stand by and do nothing, whilst those who lead us, especially in America, commit morally detestable acts. The US Bill of Rights, Article 8, states that “cruel and unusual punishments” will not be inflicted upon its citizens, yet America has consistently inflicted such punishments on others as of late.

    Social conditions lead to inaction. Possessing a gun will not help me state an intellectually convincing reason for why an argument should be rejected; but it might win me the fight. That doesn’t mean that I was right, but it does mean that I am left.

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