October 6, 2022

Archives for 2019

Every move you make, I’ll be watching you: Privacy implications of the Apple U1 chip and ultra-wideband

By Colleen Josephson and Yan Shvartzshnaider

The concerning trend of tracking of user’s location through their mobile phones has very serious privacy implications. For many of us, phones have become an integral part of our daily routine. We don’t leave our homes without and take them everywhere we go. It has become alarmingly easy for services and apps to collect our location and send them to third-parties while the user is unaware. Location tracking generally works poorly indoors. Tracking services can infer your general location up to a building using current technologies like GPS, WiFi, cellular triangulation. However, your movements inside can’t be precisely tracked. This level of obfuscation is about to disappear as a new radio technology called ultra-wideband communications (UWB) becomes mainstream.

In its recent iPhone launch, Apple introduced the U1 ultra-wideband chip in the iPhone 11. Ultra-wideband communications use channels that have a bandwidth of 500Mhz or more, with transmissions at a low power. In this blog post, we would like to give a brief introduction into the technology behind the chip, how it operates and discuss some of its promises as well as implications for our day-to-day activities.

Figure 1: UWB consumes a wide bandwidth, at 500+Mhz. In comparison, a broadband WiFi channel is 20Mhz.

Why would users want ultra-wideband? On the iPhone 11 Pro product page, Apple says, “The new Apple‑designed U1 chip uses Ultra Wideband technology for spatial awareness — allowing iPhone 11 Pro to understand its precise location relative to other nearby U1‑equipped Apple devices. It’s like adding another sense to iPhone, and it’s going to lead to amazing new capabilities”. For now, the features available to the U1 chip are restricted to “[pointing] your iPhone toward someone else’s, and AirDrop will prioritize that device so you can share files faster”. 

However, as the number of devices equipped with a UWB chip grows, it will enable a broad spectrum of applications. UWB is not a new technology, but we are seeing a renewed interest due to vastly improved operational distance. Over the years, researchers have developed a variety of UWB applications such as estimating room occupancy, landslide detection, and human body position/motion tracking. Perhaps the leading use case for UWB technology has been precise indoor localization, with accuracies between 10-0.5cm. Indoor localization  is the process of finding the coordinates of a target (i.e. a phone) relative to one or more fixed-point anchors that also contain UWB radios. The relative coordinates are then mapped to a reference (e.g. blueprints) to provide an absolute location. High-accuracy localization is especially useful in contexts where traditional GPS is not accurate enough, or cannot reach. A number of other technologies have been explored for indoor localization, such as WiFi and Bluetooth, but the accuracy of these techniques is on the order of meters1, not centimeters.

The key to enabling centimeter-level localization is the wide bandwidth of UWB. Transmissions that occupy a broad bandwidth are short in duration and known as pulses or impulses. These short duration impulses allow accurate measurement of time of flight (ToF): the time it takes for a signal to propagate from point A to point B. Radio frequency (RF) waves travelling through air have a velocity that is very close to the speed of light. This means that if we can accurately measure time of flight, then we know the distance between A and B.  Similar to how bats use echolocation to sense their environment, UWB pulses can be used to sense distances between two transmitters. The shorter the duration of the impulse, the more precise the distance measurement will be. There are a few different ways to use this information for localization/positioning, but the most common for navigation is time difference of arrival. This system relies on having three or more anchors that are also equipped with UWB chips. The anchors have synchronized clocks. To calculate the position of the phone, the anchors forward their ToF measurements to a central service that knows the absolute location of the anchors (e.g. mapped onto blueprints) and calculates where the phone is located relative to the anchors. 

Figure 2: Time Difference of Arrival (TDoA) UWB localization system 

For now indoor localization is not common, since most buildings do not have an UWB anchor infrastructure. However, in October 2019 it was announced that Cisco is teaming up with Czech company Sewio to integrate UWB chips in wireless access points. This is a major step towards enabling ubiquitous indoor localization, as it will make it much more likely that any building with WiFi can also support indoor localization. The new Cisco access points will support IEEE 802.15.4z, an ultra-wideband communications standard that was designed by the UWB Alliance, an organization that receives input from members like Apple, Decawave, Samsung and Huawei. Apple’s U1 chip adheres to the same standard, so the U1 and the Cisco access points will be able to communicate. If an Apple U1 chip responds to ranging exchanges initiated by the Cisco access points, then it is a simple matter of the owner of the network running a location calculation service to obtain the Apple U1 chip’s position. 

What makes the current generation of UWB chips stand out is that for the first time they will be deployed in mobile phones, which for a lot of people is an inseparable part of their daily routine. While it is promoted by Apple as just another sensor to “Share. Find. Play. More precisely than ever,“ this technology has the power to disrupt existing societal norms. Suddenly businesses will be able to track an individual’s location within their stores down to the centimeter, which gives them the power to track which products you look at in real-time. Similar to the debated facial recognition technology, UWB localization offers a new capability to capture and ultimately profile identities of a user. Essentially, the new chip is a marketer’s dream in a box. Shops already track your purchases, leading to cases like the infamous 2012 case where Target unintentionally divulged a teen’s pregnancy to her father. When a store has UWB-enabled access points, it will be easy to monitor a phone’s location indoors and track what you considered purchasing in addition to what you actually purchase. Even without UWB, Cisco already has a feature that lets stores track your presence via phone WiFi, “to engage users and optimize marketing strategies”. 

This WiFi tracking is possible even if your device is not associated with the network, because devices with the WiFi chip enabled periodically send out probe packets to discover which networks are available. A similar technique could be used with UWB to enable even more precise tracking throughout the store. This means that your location information could be used even if location permissions are closely monitored for apps on the phone. The Cisco/Sewio announcement off the bat mentions a “location-based marketing in retail” as a potential use case. In a mall-wide network setup, the routers could retain information that will enable inferring your movements in other stores as well.  Essentially, offering a physical world analogy to web tracking. Companies like Five Tier, JCDecaux and other use existing location tracking technologies to display ads to the users in the vicinity on nearby screens, even billboards. Current WiFi-based phone tracking lets retailers monitor which store you are in, but with UWB, companies will be able to monitor which products you are looking at. This information could be used to push targeted ads that could follow you both physically and online. Imagine going to browse for jewelry, and then seeing billboards for diamonds follow you as you drive home, and have that continue on your web browser and smart TV once you get home. 

Historically companies have opted to chase the marketing dream instead of respecting users’ privacy. Companies like Google and Facebook argue that they provide users with adequate privacy controls, but privacy researchers disagree. Furthermore, privacy choices are often eroded either by bugs or misleading requests. One recent incident report by Brian Kreb, details how Apple continues to collect location information, despite location-based system services being disabled. According to Brian, Apple’s response stated, “this behavior is tied to the inclusion of a new short-range technology that lets iPhone 11 users share files locally with other nearby phones that support this feature, and that a future version of its mobile operating system will allow users to disable it”.  And even if location services are reduced or disabled, some apps constantly try to get users to turn these services back on. As Figure 3 shows, some messages are deceptive, causing users to believe that the app won’t work without re-enabling high-accuracy (WiFi-assisted) location. And even if the apps using location data are trustworthy, choosing to leave high precision location services enabled can still allow stores with UWB infrastructure to closely track you without your explicit consent by using one-way ranging with probe packets2 (see in Application of IEEE Std 802.15.4).

Figure 3: Some mobile phone apps repeatedly encourage users to turn on location permissions that are not actually necessary.

UWB technology could disrupt our preconceived privacy expectations about how our location data is shared and used. In a recent empirical study Martin, Kirsten E., and Helen Nissenbaum show that “that tracking an individual’s place – home, work, shopping – is seen to violate privacy expectations, even without directly collecting GPS data, that is, standard markers representing location in technical systems.”  

It can also offer potential benefits to the consumer. For example, we can envision an UWB localization service that helps you find a specific store inside a large mall, navigate underground tunnel systems such as those featured in the cities of Montreal and Seoul, or helps you navigate to the precise location of where an item is located in a store. Nevertheless, given the current state of privacy policies, confusing controls, and with the current privacy regulations being poorly equipped to address the potential violation of users’ privacy expectations in public places, without proper oversight, there is a significant risk in these types of technologies being misused for nefarious purposes such tracking and surveillance. As these technologies become pervasive, it becomes vital to fully consider the implications of these techniques on our way of life, specifically the effect they have on the established societal norms and expectations.

In this blog post we outlined what UWB is and how it can be used to track location with unprecedented accuracy. While accurate location tracking could be useful, users often find that their data is used in unexpected ways that requires close reading of dense legal agreements. This flow of information is legal, but still violates users’ privacy expectations. These expectations are even more deeply violated when a phone’s location can be tracked despite carefully selected privacy settings on the device. Although this level of ubiquitous centimeter-level tracking is not yet a reality, the pieces are rapidly falling in place. Now is the time to act, before the norms of privacy erode further. Regulators, businesses and end-users need to work together to design a system that can benefit both businesses and customers without unexpected consequences for the customers. 

We would like to thank Helen Nissenbaum for providing feedback on the early drafts.


1. Research projects in wifi localization have achieved accuracies of 10-30cm, but commercially available localization solutions are accurate within meters.
2. Recall that probe packets are sent out periodically to let your device sense which networks you can join. All a retailer needs to do to track your location is collect the timestamps that your device’s probes arrive at their anchors. Some users may erroneously believe that encryption protects them from this kind of tracking, but only packet payloads (not headers) are encrypted. Sequence numbers and source IDs are contained in the UWB standard packet headers.

2020 Workshop on Technology and Consumer Protection

Christo Wilson and I are pleased to announce that the Workshop on Technology and Consumer Protection (ConPro ’20) is returning for a fourth year, co-located with the IEEE Symposium on Security and Privacy in May 2020.

As in past years, ConPro seeks a diverse range of technical research with implications for consumer protection. Past talks have covered dating fraud, ad targeting, mobile app data practices, privacy policy readability, algorithmic fairness, social media phishing, unwanted calls, cryptocurrency security, and much more.

Unlike past years, ConPro 2020 will accept talk proposals for early stage research ideas in addition to short papers. Do you have a new project or idea that you’d like to refine? Are you curious about which project directions could yield the greatest impact? Pitch a talk for ConPro, and get feedback and suggestions from its diverse, engaged audience.

Each year of ConPro, I’ve been heartened by the enthusiasm towards research that can help improve consumer welfare. If this is important to you too, we hope you’ll submit a paper or talk proposal. We’re always excited to expand our community! The submission deadline is January 23, 2020.

CITP Call for Visitors 2020-21

The Center for Information Technology Policy is an interdisciplinary research center at Princeton University that sits at the crossroads of engineering, the social sciences, law, and policy.

CITP seeks applicants for various visiting positions each year. Visitors are expected to live in or near Princeton and to be in residence at CITP on a daily basis. They will conduct research and participate actively in CITP’s programs.

For all visitors, we are happy to hear from anyone working at the intersection of digital technology and public life, including experts in computer science, sociology, economics, law, political science, public policy, information studies, communication, and other related disciplines.

We have a particular interest this year in candidates working on issues related to Artificial Intelligence (AI), Blockchain and Cryptocurrencies.

There are three job postings for CITP visitors: 1) Microsoft Visiting Researcher Scholar/Visiting Professor of Information Technology Policy, 2) Visiting IT Policy Fellow, and 3) Postdoctoral Research Associate or more senior IT policy researcher. For more information about these positions and to apply, please see our hiring page.

For full consideration, all applications should be received by December 31, 2019.

Enhancing the Security of Data Breach Notifications and Settlement Notices

[This post was jointly written by Ryan Amos, Mihir Kshirsagar, Ed Felten, and Arvind Narayanan.]

We couldn’t help noticing that the recent Yahoo and Equifax data breach settlement notifications look a lot like phishing emails. The notifications make it hard for users to distinguish real settlement notifications from scams. For example, they direct users to URLs on unfamiliar domains that are not clearly owned by the company that was breached nor any other trusted entity. Practices like this lower the bar for scammers to create fake phishing emails, potentially victimizing users twice. To illustrate the severity of this problem, Equifax mixed up domain names and posted a link to a phishing website to their Twitter account. Our discussion paper presents two recommendations to stakeholders to address this issue.

First, we recommend creating a centralized database of settlements and breaches, with an authoritative URL for each one, so that users have a way to verify the notices distributed. Such a database has precedent in the Consumer Product Safety Commission (CPSC) consumer recall list. When users receive notice of a data breach, this database would serve as a reliable authority to verify the information included in the notice. A centralized database has additional value outside the data breach context as courts and government agencies increasingly turn to electronic notices to inform the public, and scammers (predictably) respond by creating false notices.

Second, we recommend that no settlement or breach notice include a URL to a new domain. Instead, such notices should include a URL to a page on a trusted, recognizable domain, such as a government-run domain or the breached party’s domain. That page, in turn, can redirect users to a dedicated domain for breach information, if desired. This helps users avoid phishing by allowing them to safely ignore links to unrecognized domains. After the settlement period is over, any redirections should be automatically removed to avoid abandoned domains from being reused by scammers.

Content Moderation for End-to-End Encrypted Messaging

Thursday evening, the Attorney General, the Acting Homeland Security Secretary, and top law enforcement officials from the U.K. and Australia sent an open letter to Mark Zuckerberg. The letter emphasizes the scourge of child abuse content online, and the officials call on Facebook to press pause on end-to-end encryption for its messaging platforms.

The letter arrived the same week as a widely shared New York Times article, describing how reports of child abuse content are multiplying. The article provides a heartbreaking account of how the National Center for Missing and Exploited Children (NCMEC) and law enforcement agencies are overburdened and under-resourced in addressing horrible crimes against children.

Much of the public discussion about content moderation and end-to-end encryption over the past week has appeared to reflect two common technical assumptions:

  1. Content moderation is fundamentally incompatible with end-to-end encrypted messaging.
  2. Enabling content moderation for end-to-end encrypted messaging fundamentally poses the same challenges as enabling law enforcement access to message content.

In a new discussion paper, I provide a technical clarification for each of these points.

  1. Forms of content moderation may be compatible with end-to-end encrypted messaging, without compromising important security principles or undermining policy values.
  2. Enabling content moderation for end-to-end encrypted messaging is a different problem from enabling law enforcement access to message content. The problems involve different technical properties, different spaces of possible designs, and different information security and public policy implications.

I aim to demonstrate these clarifications by formalizing specific content moderation properties for end-to-end encrypted messaging, then offering at least one possible protocol design for each property.

  • User Reporting: If a user receives a message that he or she believes contains harmful content, can the user report that message to the service provider?
  • Known Content Detection: Can the service provider automatically detect when a user shares content that has previously been labeled as harmful?
  • Classifier-based Content Detection: Can the service provider detect when a user shares new content that has not been previously identified as harmful, but that an automated classifier predicts may be harmful?
  • Content Tracing: If the service provider identifies a message that contains harmful content, and the message has been forwarded by a sequence of users, can the service provider trace which users forwarded the message?
  • Popular Content Collection: Can the service provider curate a set of content that has been shared by a large number of users, without knowing which users shared the content?

The discussion paper is inherently preliminary and an agenda for further interdisciplinary research (including my own). I am not yet prepared to normatively advocate for or against the protocol designs that I describe. I am not claiming that these concepts provide sufficient content moderation capabilities, the same content moderation capabilities as current systems, or sufficient robustness against evasion. I am also not claiming that these designs adequately address information security risks or public policy values, such as free speech, international human rights, or economic competitiveness.

I do not know if there is a viable path forward for content moderation and end-to-end encrypted messaging that will be acceptable to technology platforms, law enforcement, NCMEC, civil society groups, information security experts, and other stakeholders. I do have confidence that, if such a path exists, we will only find it through open research and dialogue.