Congressional Oversight Committee Wants Warrants to Rein in Police Abuse of Cell-Site Simulators

  • A bipartisan Congressional committee’s recent report showcases troubling details about police abuse of cell-site simulators, and calls on Congress to pass laws ensuring that this powerful technology is only deployed with a court-issued probable cause warrant.

    Cell-site simulators, often called IMSI catchers or Stingrays, masquerade as cell phone towers and trick our phones into connecting to them so police can track down suspect targets, but their use also collects the data and location of innocent bystanders and extracts unnecessary sensitive data in the process.

    EFF has long opposed law enforcement’s use of cell-site simulators as incompatible with the protections of the Fourth Amendment because they indiscriminately gather information on countless innocent people who have the misfortune of being in the vicinity of a suspect target. They also disproportionately burden minority communities. Unless and until cellular technology evolves beyond the vulnerability that makes cell-site simulators possible, we’re advocating for strong regulation, transparency, and public oversight of the use of such technology by law enforcement.

    Accordingly, EFF applauds Rep. Jason Chaffetz (R-Utah), chairman of the U.S. House Committee on Oversight and Government Reform, along with U.S. Rep. Elijah Cummings (D-Maryland), the ranking member of that Committee, for their recent report on cell-site simulators. The bipartisan committee called on Congress to enact a law requiring a warrant based on probable cause prior to using cell-site simulators in domestic investigations. The report provides new information to the public about these shadowy tools, and recommends important privacy safeguards.

    The Many Problems with Cell-Site Simulators

    Cell-site simulators “trick” our phones into connecting to them as they would to a cell phone tower in order to log our IMSI numbers (a number which uniquely identifies you on the cellular network), location, and potentially capture the content of our communications. Police most often use cell-site simulators to locate wanted persons. They do so by gathering the IMSI numbers of all phones in the vicinity, until the cell-site simulator finds the IMSI the police are looking for. Then the cell-site simulator targets that IMSI to help police triangulate its location.

    Police can also use cell-site simulators for many other purposes. For example, police have used them to identify the IMSI numbers at protests, and thus track the people at the protests who brought their phones. And some cell-site simulators may be configured to capture the content and metadata of our phone calls and text messages. This includes the audio of a cell phone call, the text message sent and received, email message content, and much more.

    Cell-site simulators exploit the fact that cellular phones have no way to check whether the cell tower they are connecting to is a “real” cell tower being operated by the phone company. This means that cellular phones can easily be tricked into connecting to a cell site simulator without any indication to the owner. Unfortunately, if police can use fake cell towers to force our phones to leak our private information, there is nothing to stop criminals and foreign nations from learning to do the same (in fact a cell-site simulator can be built right now for about $1,500).

    Cell-site simulators are dangerous tools. They may disrupt phone service, including 911 calls, and, because strong evidence shows cell-site simulators are used most frequently in communities of color, this disruption would disproportionately impact those communities.

    Cell-site simulators are a form of dragnet surveillance that indiscriminately seize information from everyone in the area, innocent and target alike. They may even locate people inside highly protected places like their homes.

    EFF has long raised concerns about cell-site simulators. We do so, for example, before courts and the Federal Communications Commission. Last fall, we deployed technologists and lawyers to the Standing Rock Sioux Reservation in North Dakota to investigate possible cell-site simulator surveillance of the Water Protectors.

    The House Oversight Committee’s Findings

    On December 16, 2016, the House Oversight Committee released its Report on Law Enforcement Use of Cell-Site Simulation Technologies. It calls for Congress to pass legislation that creates a clear, national framework to ensure that cell site simulators do not infringe on citizens’ constitutional rights. But first, it made many important and troubling findings.

    The Oversight Report found no uniform standard for the use of cell-site simulators by law enforcement. Also, when the committee first began its investigation in April 2015, “federal law enforcement entities could obtain a court’s authorization to use cell-site simulators by meeting a standard lower than probable cause.” Indeed, a DOJ guidance bulletin, promulgated in 1997 and followed through 2015, took the position that there were no constitutional or statutory limits on police use of cell-site simulators without a warrant—a position with which EFF vehemently disagrees.

    Moreover, the Oversight Committee found that state and local agencies frequently sign non-disclosure agreements with cell-site simulator manufacturers and the FBI. These NDAs prohibit the public from learning about cell-site simulator use in domestic investigations and condition possession and use on an agreement to “dismiss a criminal case at the FBI’s request rather than produce information that could compromise the devices.” This means that the government would rather tank its own investigation than reveal the extent of its intrusion into citizens’ privacy for fear of igniting public outcry.

    In a criminal prosecution in Wisconsin, EFF helped expose the government’s use of a cell-site simulator—a fact police had kept hidden from the accused and from multiple judges.

    The Oversight Report also found that nine federal agencies, mostly within the U.S. Departments of Justice and Homeland Security, spent nearly $100 million between 2010 and 2014 to acquire more than 400 cell-site simulators. Specifically:

    The Oversight Report’s other notable findings include:

    1. DHS allows state and local law enforcement to buy cell-site simulators using more than $1.8 million in federal grants, some of which were administered through FEMA.
    2. The majority of states have failed to pass laws requiring law
      enforcement to obtain a warrant based on probable cause before using
      cell-site simulators.
    3. Many state and local law enforcement agencies get court approval to use
      cell-site simulators based on the far less protective “relevance”
      standard designed for pen register/trap and trace technology to seize
      telephone metadata from service providers.
    4. Cell-site simulators range in cost from $41,500 to $500,000 per unit.

    Cell-Site Simulator Policy Changed Only After Public Inquiry

    In response to Congressional investigation and just prior to formal Congressional hearings on the issue, DOJ & DHS significantly changed their discretionary internal policies to require a probable cause search warrant before using cell-site simulators – a major about-face from the policy in use since 1997. The new policies also direct that warrant applications explicitly inform courts that police intend to use a cell-site simulator in the search. These are critical limits.

    However, one provision of the new guidelines raises concerns. Warrant applications must affirm that law enforcement won’t use data collected on people who aren’t the targets of the investigation “absent further order of the court.” This implies that law enforcement will make investigative use of non-target data if they can get permission from a court to do so. In other words, when agents get a warrant to use a cell-site simulator against a suspect target, and in doing so inevitably capture private phone information from countless innocent bystanders, the new policy still lets agents use that incidentally captured information against those bystanders if they get court permission.

    This is tantamount to a general warrant for digital data prohibited by the Fourth Amendment. Such non-target information should actively be separated and purged from storage prior to examination by law enforcement in order to safeguard the constitutional rights of innocent individuals. Law enforcement cannot be permitted to expand its initial search into a dragnet fishing expedition.

    The DOJ should strengthen its policy and delete any non-target data retrieved by a cell-site simulator as soon as the target is located without reviewing the non-target data acquired.

    While the new voluntary policies of DOJ and DHS are a step in the right direction, they are no substitute for a law passed by Congress. Unlike a federal statute, members of the public cannot enforce them, and the new administration can change them—or get rid of them completely—on a whim.

    The Oversight Committee’s Recommendations

    After making these findings, and after examining the new DOJ and DHS policies, the Oversight Committee made several helpful recommendations. These include:

    1. DOJ and DHS should not fund or approve cell-site simulator use by state and local law enforcement absent a probable cause warrant requirement.
    2. Non-disclosure agreements with cell-site simulator manufacturers, like the Harris Corporation which makes Stingrays, must be set aside and replaced with agreements that require clarity, transparency, and candor to the court and public.
    3. State and local law enforcement agencies should adopt cell-site simulator policies that are at least as protective as the DHS and DOJ policies.
    4. Federal and state lawmakers should pass legislation that requires probable cause warrants before law enforcement may deploy a cell-site simulator.

    Need for Federal Legislation Limiting Cell-Site Simulator Use by Law Enforcement

    EFF joins the House Oversight Committee’s recommendation to Congress to pass federal legislation requiring all law enforcement agencies (local, state, and federal) to obtain a warrant based upon probable cause prior to use of CSSs. In addition, EFF encourages Congress to set forth clear guidelines for any exceptions to the warrant requirement so as to make sure that the exceptions of “exigent circumstances,” “the need to protect human life or avert serious injury”, and “hot pursuit of a fleeing felon,” do not swallow the rule requiring warrants.

    Of particular concern is law enforcement’s potential use of cell-site simulators against peaceful civil protestors under the guise of such exceptions. Congress should ban the use of cell-site simulators against people who are exercising their First Amendment rights.

    Finally, in the interest of maintaining public oversight of law enforcement’s use of such surveillance technology, EFF recommends that Congress enact a transparency policy that requires law enforcement agencies to produce annual reports on the number of times an agency uses cell-site simulators, as well as against whom, when, where, and how.

    Long term, we hope that cell service providers will fix their protocols to ensure that cell-site simulators can’t vacuum up data on cell phone usage. But Congress can’t wait until that day to safeguard our privacy.

    In a time when civil protest and disobedience is ever increasing, it is critical that our democracy protect the privacy and civil liberties of its citizens against government overreach as technology advances. Please call on Congress to pass a warrant requirement for cell-site simulator use and other intrusive surveillance technologies by emailing your member of Congress today.

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Tmux Commands

screen and tmux

A comparison of the features (or more-so just a table of notes for accessing some of those features) for GNU screen and BSD-licensed tmux.

The formatting here is simple enough to understand (I would hope). ^ means ctrl+, so ^x is ctrl+x. M- means meta (generally left-alt or escape)+, so M-x is left-alt+x

It should be noted that this is no where near a full feature-set of either group. This - being a cheat-sheet - is just to point out the most very basic features to get you on the road.

Trust the developers and manpage writers more than me. This document is originally from 2009 when tmux was still new - since then both of these programs have had many updates and features added (not all of which have been dutifully noted here).

Action tmux screen
start a new session tmux OR
tmux new OR
tmux new-session
re-attach a detached session tmux attach OR
tmux attach-session
re-attach an attached session (detaching it from elsewhere) tmux attach -d OR
tmux attach-session -d
screen -dr
re-attach an attached session (keeping it attached elsewhere) tmux attach OR
tmux attach-session
screen -x
detach from currently attached session ^b d OR
^b :detach
^a ^d OR
^a :detach
rename-window to newname ^b , <newname> OR
^b :rename-window <newn>
^a A <newname>
list windows ^b w ^a w
list windows in chooseable menu ^a "
go to window # ^b # ^a #
go to last-active window ^b l ^a ^a
go to next window ^b n ^a n
go to previous window ^b p ^a p
see keybindings ^b ? ^a ?
list sessions ^b s OR
tmux ls OR
tmux list-sessions
screen -ls
toggle visual bell ^a ^g
create another window ^b c ^a c
exit current shell/window ^d ^d
split window/pane horizontally ^b " ^a S
split window/pane vertically ^b % ^a |
switch to other pane ^b o ^a <tab>
kill the current pane ^b x OR (logout/^D)
collapse the current pane/split (but leave processes running) ^a X
cycle location of panes ^b ^o
swap current pane with previous ^b {
swap current pane with next ^b }
show time ^b t
show numeric values of panes ^b q
toggle zoom-state of current pane (maximize/return current pane) ^b z
break the current pane out of its window (to form new window) ^b !
re-arrange current panels within same window (different layouts) ^b [space]
Kill the current window (and all panes within) ^b killw [target-window]
  • Criteo is an ad company. You may not have heard of them, but they do retargeting, the type of ads that pursue users across the web, beseeching them to purchase a product they once viewed or have already bought. To identify users across websites, Criteo relies on cross-site tracking using cookies and other methods to follow users as they browse. This has led them to try and circumvent the privacy features in Apple’s Safari browser which protects its users from such tracking. Despite this apparently antagonistic attitude towards user privacy, Criteo has also been whitelisted by the Acceptable Ads initiative. This means that their ads are unblocked by popular adblockers such as Adblock and Adblock Plus. Criteo pays Eyeo, the operator of Acceptable Ads, for this whitelisting and must comply with their format requirements. But this also means they can track any user of these adblockers who has not disabled Acceptable Ads, even if they have installed privacy tools such as EasyPrivacy with the intention of protecting themselves. EFF is concerned about Criteo’s continued anti-privacy actions and their continued inclusion in Acceptable Ads.

    Safari Shuts out Third Party Cookies…

    All popular browsers give users control over who gets to set cookies, but Safari is the only one that blocks third-party cookies (those set by a domain other than the site you are visiting) by default. (Safari’s choice is important because only 5-10% of users ever change default settings in software.) Criteo relies on third-party cookies. Since users have little reason to visit Criteo’s own website, the company gets its cookies onto users’ machines through its integration on many online retail websites. Safari’s cookie blocking is a major problem for Criteo, especially given the large and lucrative nature of iPhone’s user base. Rather than accept this, Criteo has repeatedly implemented ways to defeat Safari’s privacy protections.

    One workaround researchers detected Criteo using was to redirect users from sites where their service was present to their own. For example, if you visited and clicked on a product category, you would be first diverted to and then redirected to Although imperceptible to the user, this detour was enough to persuade the browser that is a site you chose to visit, and therefore a first party entitled to set a cookie rather than a third party. Criteo applied for a patent on this method in August 2013.

    …And Closes the Backdoor

    Last summer, however, Apple unveiled a new version of Safari with more sophisticated cookie handling—called Intelligent Tracking Prevention (ITP)—which killed off the redirect technique as a means to circumvent the cookie controls. The browser now analyzes if the user has engaged with a website in a meaningful way before allowing it to set a cookie. The announcement triggered panic among advertising companies, whose trade association, the Interactive Advertising Bureau, denounced the feature and rushed out technical recommendations to work around it. Obviously the level of user “interaction” with Criteo during the redirect described above fails ITP’s test, which meant Criteo was locked out again.

    It appears that Criteo’s response was to abandon cookies for Safari users and to generate a persistent identifier by piggybacking on a key user safety technology called HSTS. When a browser connects to a site via HTTPS (i.e. a site that supports encryption), the site can respond with an HTTP Strict Transport Security policy (HSTS), instructing the browser to only contact it using HTTPS. Without a HSTS policy, your browser might try to connect to the site over regular old unencrypted HTTP in the future—and thus be vulnerable to a downgrade attack. Criteo used HSTS to sneak data into the browser cache to produce an identifier it could use to recognize the individual’s browser and profile them. This approach relied on the fact that it is difficult to clear HSTS data in Safari, requiring the user to purge the cache entirely to delete the identifier. For EFF, it is especially worrisome that Criteo used a technique that pits privacy protection against user security interests by targeting HSTS. Use of this mechanism was documented by Gotham City Research, an investment firm who have bet against Criteo’s stock.

    In early December, Apple released an update to iOS and Safari which disabled Criteo’s ability to exploit HSTS. This led to Criteo revising down their revenue forecasts and a sharp fall in their share price.

    How is Criteo Acceptable Advertising”****?

    "… w__e sort of seek the consent of users, just like we had done before_."__1_ - Erich Eichmann, CEO Criteo

    _"Only users who don’t already have a Criteo identifier will see the header or footer, and it is displayed only once per device. Thanks to [the?] Criteo advertisers network, most of your users would have already accepted our services on the website of another of our partner. On average, only 5% of your users will see the headers or footers, and for those who do, the typical opt-out rate is less than .2%._" - Criteo Support Center

    Criteo styles itself as a leader in privacy practices, yet they have dedicated significant engineering resources to circumventing privacy tools. They claim to have obtained user consent to tracking based on a minimal warning delivered in what we believe to be a highly confusing context. When a user first visits a site containing Criteo’s script, they received a small notice stating, _"_Click any link to use Criteo’s cross-site tracking technology." If the user continues to use the site, they are deemed to have consented. Little wonder that Criteo can boast of a low opt-out rate to their clients.

    Due to their observed behaviour prior to the ITP episode, Criteo’s incorporation into the Acceptable Ads in December 2015 aroused criticism among users of ad blockers. We have written elsewhere about how Acceptable Ads creates a clash of interests between adblocking companies and their users, especially those concerned with their privacy. But Criteo’s participation in Acceptable Ads brings into focus the substantive problem with the program itself. The criteria for Acceptable Ads are concerned chiefly with format and aesthetic aspects (e.g. How big is the ad? How visually intrusive? Does it blink?) and excludes privacy concerns. Retargeting is unpopular and mocked by users, in part because it wears its creepy tracking practices on its sleeve. Our view is that Criteo’s bad behavior should exclude its products from being deemed “acceptable” in any way.

    The fact that the Acceptable Ads Initiative has approved Criteo’s user-tracking-by-misusing-security-features ads is indicative of the privacy problems we believe to be at the heart of the Acceptable Ads program. In March this year, Eyeo announced an Acceptable Ads Committee that will control the criteria for Acceptable Ads in the future. The Committee should start by instituting a rule which excludes companies that circumvent explicit privacy tools or exploit user security technologies for the purpose of tracking.


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  • Have you ever sent a motivational text to a friend? If you have, perhaps you tailored your message to an activity or location by saying “Good luck in the race!” or “Have fun in New York!” Now, imagine doing this automatically with a compuuuter. What a great invention. Actually, no. That’s not a good invention, it’s our latest Stupid Patent of the Month.

    U.S. Patent No. 9,069,648 is titled “Systems and methods for delivering activity based suggestive (ABS) messages.” The patent describes sending “motivational messages,” based “on the current or anticipated activity of the user,” to a “personal electronic device.” The patent provides examples such as sending the message “don’t give up” when the user is running up a hill. The examples aren’t limited to health or exercise. For example, the patent suggests sending messages like “do not fear” and “God is with you” when a “user enters a dangerous neighborhood.”

    The patent’s description of its invention is filled with silly, non-standard acronyms like ABS for “activity based suggestive” messages or EBIF for “electronic based intelligence function.” These silly acronyms create an illusion of complexity where plain, descriptive language would reveal the mundane nature of the supposed invention. For example, what the patent grandly calls EBIF appears to be nothing more than standard computer processing.

    The ’648 patent is owned by Motivational Health Messaging LLC. While this may be a new company, at least one of the people behind it has been involved in massive patent trolling campaigns before. And the two named inventors have both been inventors on patents that trolls have asserted hundreds of times. One is also an inventor listed on patents asserted by infamous patent troll Shipping and Transit LLC. The other named inventor is the inventor on the patents asserted by Electronic Communication Technologies LLC. Those two entities (with their predecessors) brought over 700 lawsuits, many against very small businesses. In other words, the ’648 patent has been issued to Troll Co. at 1 Troll Street, Troll Town, Trollida USA.

    We believe that the claims of the ’648 patent are clearly invalid under the Supreme Court’s decision in Alice v. CLS Bank, which held abstract ideas do not become eligible for a patent merely because they are implemented in conventional computer technology. Indeed, the patent repeatedly emphasizes that the claimed methods are not tied to any particular hardware or software. For example, it states:

    The software and software logic described in this document … which comprises an ordered listing of executable instructions for implementing logical functions, can be embodied in any non-transitory computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions.

    The ’648 patent issued on June 30, 2015, a full year after the Supreme Court’s Alice ruling. Despite this, the patent examiner never even discussed the decision. If Alice is to mean anything at all, it has to be applied to an application like this one.

    In our view, if Motivational Health Messaging asserts its patent in court, any defendant that fought back should prevail under Alice. Indeed, we would hope that the court would strongly consider awarding attorney’s fees to the defendant in such a case. Shipping & Transit has now had two fee awards made against it for asserting patents that are clearly invalid under Alice. And the Federal Circuit recently held that fee awards can be appropriate when patent owners make objectively unreasonable argument concerning Alice.

    In addition to the problems under Alice, we believe the claims of the ’648 patent should have been rejected as obvious. When the application was filed in 2012, there was nothing new about sending motivational messages or automatically tailoring messages to things like location. In one proposed embodiment, the patent suggests that a “user walking to a hole may be delivered ABS messages, including reminders or instructions on how to play a particular hole.” But golf apps were already doing this. The Patent Office didn’t consider any real-world mobile phone applications when reviewing the application.

    If you want to look for prior art yourself, Unified Patents is running a crowdsourcing contest to find the best prior art to invalidate the ’648 patent. Aside from the warm feelings that come from fighting patent trolls, there is a $2000 prize pool.

    Despite the weakness of its patent, Motivational Health Messaging LLC might still send out demand letters. If you receive such a letter, you can contact EFF and we can help you find counsel.

    We have long complained that the Patent Office promotes patent trolling by granting obvious and/or abstract software patents. The history of the ’648 patent shows how the Patent Office’s failure to properly review applications leads to bad patents falling into the hands of trolls.

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