Monitoring nuclear weapons stockpiles with radio waves
In this con­tain­er, the researchers test­ed how robust and how repro­ducible the radio fin­ger­print is. The tech­nol­o­gy detects move­ments of the blue bar­rel. Cred­it: RUB, Mar­quard

An inter­na­tion­al research team has pro­posed a new method for mon­i­tor­ing nuclear dis­ar­ma­ment treaties. The IT secu­ri­ty experts devel­oped a mech­a­nism that uses radio waves to remote­ly mon­i­tor whether any changes are being made in a spe­cif­ic room.

The researchers describe how robust and secure the approach is in the jour­nal Nature Com­mu­ni­ca­tions, pub­lished online. Teams from the Max Planck Insti­tute for Secu­ri­ty and Pri­va­cy (MPI-SP) in Bochum, Ruhr Uni­ver­si­ty Bochum, the School of Pub­lic and Inter­na­tion­al Affairs at Prince­ton Uni­ver­si­ty, the Uni­ver­si­ty of Con­necti­cut, Har­vard Uni­ver­si­ty, PHYSEC GmbH, and Tech­nis­che Uni­ver­sität Berlin col­lab­o­rat­ed on the devel­op­ment.

The researchers approached their project from a sce­nario in which State A wants to ensure that there are no changes in State B’s nuclear weapons stockpile—and to do so with­out per­ma­nent on-site mon­i­tor­ing. Specif­i­cal­ly, a major threat is indi­cat­ed by the removal of stored nuclear war­heads to pre­pare them for deploy­ment.

“Our sys­tem uses two anten­nas to record a radio fin­ger­print of the room,” explains Dr. Johannes Tobisch, who earned his Ph.D. on this research field in the CASA Clus­ter of Excel­lence at Ruhr Uni­ver­si­ty Bochum and MPI-SP and has since moved on to work in indus­try. One of the anten­nas emits a radio sig­nal that is reflect­ed off the walls and objects in the room.

The oth­er anten­na records the sig­nal. The record­ed sig­nal is char­ac­ter­is­tic: if the objects were moved only min­i­mal­ly, this would notice­ably change the radio fin­ger­print. Major changes, such as the removal of a stored nuclear war­head, can thus be reli­ably detect­ed.

Monitoring nuclear weapons stockpiles with radio waves
These adjustable mir­rors are at the heart of the radio wave tech­nol­o­gy. Cred­it: RUB, Mar­quard

Mir­rors to guar­an­tee secu­ri­ty

How­ev­er, this method can only work if state B mea­sures the radio fin­ger­print at pre­cise­ly the time when state A requests it. It’s there­fore nec­es­sary to pre­vent State B from record­ing the radio fin­ger­print and send­ing the record­ing instead of a just-mea­sured sig­nal. “That would be like some­one stick­ing a pho­to in front of a sur­veil­lance cam­era,” says Tobisch.

For this rea­son, a set­up with 20 rotat­ing mir­rors is ini­tial­ly installed in the room that is to be mon­i­tored. If the posi­tion of the mir­rors changes, the radio fin­ger­print also changes. State A would record the radio fin­ger­prints for dif­fer­ent mir­ror posi­tions dur­ing a one-time on-site vis­it and store them in a secret data­base.

Peri­od­i­cal­ly, State A could remote­ly request State B to send the radio fin­ger­print for a par­tic­u­lar mir­ror position—and com­pare the mea­sured data with the record in their secret data­base. If the data don’t match, there must have been a change in the room.

“Sev­en­ty per­cent of the world nuclear weapons are kept in stor­age for mil­i­tary reserve or await­ing dis­man­tle­ment,” says Dr. Sebastien Philippe from Prince­ton Uni­ver­si­ty.

“The pres­ence and num­ber of such weapons at any giv­en site can­not be ver­i­fied eas­i­ly via satel­lite imagery or oth­er means that are unable to see into the stor­age vaults. Because of the dif­fi­cul­ties to mon­i­tor them, these 9,000 nuclear weapons are not account­ed for under exist­ing nuclear arms con­trol agree­ments. This new ver­i­fi­ca­tion tech­nol­o­gy address­es this long-stand­ing chal­lenge and con­tributes to future diplo­mat­ic efforts that would seek to lim­it all nuclear weapon types.”

Monitoring nuclear weapons stockpiles with radio waves
To ensure suf­fi­cient safe­ty, sev­er­al mir­rors are need­ed. The researchers used 20 of them for their exper­i­ments. Cred­it: RUB, Mar­quard

Set­up in a field test

To test the idea, the researchers set up a con­tain­er with mov­able bar­rels on the cam­pus of Ruhr Uni­ver­si­ty Bochum, Ger­many, which they mon­i­tored using radio wave tech­nol­o­gy. Using this set­up, they showed that radio fin­ger­prints could be reli­ably repro­duced for indi­vid­ual mir­ror set­tings. Dif­fer­ent mir­ror set­tings also pro­duced a vari­ety of eas­i­ly dis­tin­guish­able radio fin­ger­prints. If the researchers moved one of the bar­rels in the con­tain­er, a few mil­lime­ters of dis­place­ment were enough to show up in the radio fin­ger­print.

The team also ana­lyzed whether it’s pos­si­ble to deci­pher how mir­ror posi­tions and radio fin­ger­prints cor­re­spond to each oth­er using machine learn­ing. Algo­rithms can indeed pre­dict radio fin­ger­prints if they rec­og­nize a num­ber of mir­ror posi­tions and the cor­re­spond­ing radio sig­nals. Find­ing the con­nec­tion, how­ev­er, takes longer the more mir­rors there are in the set­up.

“With 20 mir­rors, it would take eight weeks for an attack­er to decode the under­ly­ing math­e­mat­i­cal func­tion,” points out Tobisch. “Because of the scal­a­bil­i­ty of the sys­tem, it’s pos­si­ble to increase the secu­ri­ty fac­tor even more.”

“The tech­nol­o­gy com­bines cyber-phys­i­cal secu­ri­ty assess­ments, pre­vi­ous­ly only pos­si­ble on data and secu­ri­ty chips, with cross-sys­tem physics in a com­plete­ly new way. This enables new lev­els of trust, espe­cial­ly for the Inter­net of Things,” says Pro­fes­sor Chris­t­ian Zenger, head of the Secure Mobile Com­mu­ni­ca­tion research group at Ruhr Uni­ver­si­ty Bochum and CEO of PHYSEC GmbH.

“This research project is an excel­lent exam­ple of how nov­el tech­nolo­gies at the inter­face between secu­ri­ty engi­neer­ing and radio tech­nolo­gies can be used to solve prob­lems that are of great impor­tance to soci­ety,” says Pro­fes­sor Christof Paar of the Max Planck Insti­tute in Bochum.

“At a time of height­ened geopo­lit­i­cal ten­sions and with a new nuclear arms race brew­ing, this work is par­tic­u­lar­ly time­ly and rel­e­vant,” con­cludes Sébastien Philippe.