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When the Evidence is on the Cell Phone

At issue in two cell phone search cases before the Supreme Court: does technology exist to protect the evidence

3 min read
When the Evidence is on the Cell Phone
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On Tuesday, the United States Supreme Court heard arguments in two cases in which information found on cell phones, obtained by searching those phones without a warrant, led to convictions: United States v. Wurie and Riley v. California. At issue is whether the Fourth Amendment’s rules on unreasonable searches and seizures apply to cell phones.

Civil liberty groups and others argue that because phones can contain virtually every detail of a person’s life, including photos, videos, bank account information, and medical information, they are far different than the paper address books or notepads that previously might have been found on a suspect and legally searched without a warrant. Law enforcement agencies argue that if they don’t search the devices immediately, they could be wiped remotely.

Can they? Or can law enforcement officials prevent them from being wiped? This was a matter of debate during the Supreme Court arguments, with Deputy Solicitor General Michael Dreeben, representing the United States, listing a number of technical obstacles to delaying a search of a cell phone.

First on that list: Encryption, which Dreeben said, “kicks in automatically…and then…you need the password to open it….And law enforcement’s forensic labs aren’t going to be able to get around it except with extraordinary efforts and extraordinary time.”

In “my experience,” he said, “from the people that I had spoken with is that a lot of phones are arriving at the lab in a locked and encrypted state and it’s very tough to deal with that.”

I turned to Richard Mislan, a visiting assistant professor in the Rochester Institute of Technology’s computer security department, for his thoughts about just how real those technical obstacles, including encryption, are. Mislan wrote about the use of cell-phone based evidence in “Cellphone Crime Solvers,” published in the July 2010 issue of IEEE Spectrum.

Mislan agreed that more and more phones are password-protected these days, and new security tools like fingerprint access add a layer of difficulty. But he, says, “there are tools that are well known to the [law enforcement] community to deal with passwords.”

Dreeben also expressed concern over the fact that cell phones can be wiped remotely. “Even if an officer has a cell phone in his hand, he cannot guarantee, unless it's disconnected from the network or somehow protected from the network, that there won't be a remote wipe signal sent to the phone that will wipe its data,” Dreeben told the Court.

Indeed, Dreeben is correct that wiping a phone remotely isn’t hard—for example, Apple’s iOS devices include a simple tool, “Find My Iphone” and Android 2.2+ users can set up the “Device Policy” app to allow them to remotely erase all the data on their phones.

But law enforcement officials need to preserve the evidence on phones even when they are searched on the scene, not just later with a warrant, and tools exist to allow them to do so. The basic solution is a Faraday bag, a simple sleeve with a layer of conductive material, either a solid or a mesh, that prevents wireless signals from getting in or out. A sleeve is widely available and cheap, around $30. More sophisticated versions specifically designed to preserve evidence cost in the hundreds of dollars, hold multiple phones, and keep them charged while they are being transported.

The Justices quizzed Dreeben about the practicality of using such cases. Dreeben said, “If you throw a phone into a Faraday bag, which is supposedly going to be able to block network signals, when you open it up, it has to be similarly shielded or it will pick up a signal from a cell tower, and that will wipe the phone.” This, he pointed out, doesn’t always work:  “The F.B.I. tried to build a Faraday room in a building that they later discovered Verizon had put up a cell tower on it, and that cell tower put out a strong enough signal to go right through the Faraday room.”

Mislan indicated that most police departments understand the need to open phones in a protected enclosure and know where they can do so. They also know where the cell towers are.

Justice Sonia Sotomayor suggested that arresting officers simply put phones into airplane mode, preventing them from receiving calls or data. Dreeben’s counter-argument, essentially, was that phones are just too complicated. “It is not always possible to find airplane mode on all the 500, 600 models of phones that are out there,” he said. And, he said, consider that “The officer has a lot of things to do when he arrests suspects. Say he arrests five suspects in a car and they each have three cell phones. Trying to find and put each one of them into airplane mode and go the further step and...” (Sotomayor cut Dreeben off at this point.)

Five suspects might indeed have three cell phones each, in order to hide their identities when making certain calls. But, points out Mislan, these days, putting a phone into airplane mode is not rocket science. In recent years the wild world of phone operating systems has settled down to a dominant four—Apple iOs, Android, Windows Mobile, and Blackberry—and these are well understood. An arresting officer should have little trouble finding airplane mode.

The court is expected to issue its rulings on these cases in July.

Follow me on Twitter @TeklaPerry.

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Metamaterials Could Solve One of 6G’s Big Problems

There’s plenty of bandwidth available if we use reconfigurable intelligent surfaces

12 min read
An illustration depicting cellphone users at street level in a city, with wireless signals reaching them via reflecting surfaces.

Ground level in a typical urban canyon, shielded by tall buildings, will be inaccessible to some 6G frequencies. Deft placement of reconfigurable intelligent surfaces [yellow] will enable the signals to pervade these areas.

Chris Philpot

For all the tumultuous revolution in wireless technology over the past several decades, there have been a couple of constants. One is the overcrowding of radio bands, and the other is the move to escape that congestion by exploiting higher and higher frequencies. And today, as engineers roll out 5G and plan for 6G wireless, they find themselves at a crossroads: After years of designing superefficient transmitters and receivers, and of compensating for the signal losses at the end points of a radio channel, they’re beginning to realize that they are approaching the practical limits of transmitter and receiver efficiency. From now on, to get high performance as we go to higher frequencies, we will need to engineer the wireless channel itself. But how can we possibly engineer and control a wireless environment, which is determined by a host of factors, many of them random and therefore unpredictable?

Perhaps the most promising solution, right now, is to use reconfigurable intelligent surfaces. These are planar structures typically ranging in size from about 100 square centimeters to about 5 square meters or more, depending on the frequency and other factors. These surfaces use advanced substances called metamaterials to reflect and refract electromagnetic waves. Thin two-dimensional metamaterials, known as metasurfaces, can be designed to sense the local electromagnetic environment and tune the wave’s key properties, such as its amplitude, phase, and polarization, as the wave is reflected or refracted by the surface. So as the waves fall on such a surface, it can alter the incident waves’ direction so as to strengthen the channel. In fact, these metasurfaces can be programmed to make these changes dynamically, reconfiguring the signal in real time in response to changes in the wireless channel. Think of reconfigurable intelligent surfaces as the next evolution of the repeater concept.

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