The StingRay is an IMSI-catcher (International Mobile Subscriber Identity), a controversial cellular phone surveillance device, manufactured by the Harris Corporation. Initially developed for the military and intelligence community, the StingRay and similar Harris devices are in widespread use by local and state law enforcement agencies across the United States and possibly covertly in the United Kingdom. Stingray has also become a generic name to describe these kinds of devices.
The StingRay is an IMSI-catcher with both passive (digital analyzer) and active (cell site simulator) capabilities. When operating in active mode, the device mimics a wireless carrier cell tower in order to force all nearby mobile phones and other cellular data devices to connect to it.
The StingRay family of devices can be mounted in vehicles, on airplanes, helicopters and unmanned aerial vehicles. Hand-carried versions are referred to under the trade name KingFish.
Active mode operations
- Extracting stored data such as International Mobile Subscriber Identity (“IMSI”) numbers and Electronic Serial Number (“ESN”),
- Writing cellular protocol metadata to internal storage
- Forcing an increase in signal transmission power,
- Forcing an abundance of radio signals to be transmitted
- Interception of communications content
- Tracking and locating the cellular device user,
- Conducting a denial of service attack
- Encryption key extraction.
Passive mode operations
- conducting base station surveys, which is the process of using over-the-air signals to identify legitimate cell sites and precisely map their coverage areas
- radio jamming for either general denial of service purposes or to aid in active mode protocol rollback attacks
Active (cell site simulator) capabilities
In active mode, the StingRay will force each compatible cellular device in a given area to disconnect from its service provider cell site (i.e., operated by Verizon, AT&T, etc.) and establish a new connection with the StingRay. In most cases, this is accomplished by having the StingRay broadcast a pilot signal that is either stronger than, or made to appear stronger than, the pilot signals being broadcast by legitimate cell sites operating in the area. A common function of all cellular communications protocols is to have the cellular device connect to the cell site offering the strongest signal. StingRays exploit this function as a means to force temporary connections with cellular devices within a limited area.
Extracting data from internal storage
During the process of forcing connections from all compatible cellular devices in a given area, the StingRay operator needs to determine which device is a desired surveillance target. This is accomplished by downloading the IMSI, ESN, or other identifying data from each of the devices connected to the StingRay. In this context, the IMSI or equivalent identifier is not obtained from the cellular service provider or from any other third-party. The StingRay downloads this data directly from the device using radio waves.
In some cases, the IMSI or equivalent identifier of a target device is known to the StingRay operator beforehand. When this is the case, the operator will download the IMSI or equivalent identifier from each device as it connects to the StingRay. When the downloaded IMSI matches the known IMSI of the desired target, the dragnet will end and the operator will proceed to conduct specific surveillance operations on just the target device.
In other cases, the IMSI or equivalent identifier of a target is not known to the StingRay operator and the goal of the surveillance operation is to identify one or more cellular devices being used in a known area. For example, if visual surveillance is being conducted on a group of protestors, a StingRay can be used to download the IMSI or equivalent identifier from each phone within the protest area. After identifying the phones, locating and tracking operations can be conducted, and service providers can be forced to turn over account information identifying the phone users.
Forcing an increase in signal transmission power
Cellular telephones are radio transmitters and receivers much like a walkie-talkie. However, the cell phone only communicates with a “repeater” inside a nearby cell tower installation. At that installation, the devices take in all cell calls in its geographic area and repeat them out to other cell installations which repeat the signals onward to their destination telephone (either by radio or land-line wires). Radio is used also to transmit a caller’s voice/data back to the receiver’s cell telephone. The two-way duplex phone conversation then exists via these interconnections.
To make all that work correctly, the system allows automatic increases and decreases in transmitter power (for the individual cell phone and for the tower repeater, too) so that only the minimum transmit power is used to complete and hold the call active, “on,” and allows the users to hear and be heard continuously during the conversation. The goal is to hold the call active but use the least amount of transmit power, mainly to conserve batteries and be efficient. The tower system will sense when a cell phone is not coming in clearly, and will order the cell phone to boost transmit power. The user has no control over this boosting; it may occur for a split second or for the whole conversation. If the user is in a remote location, the power boost may be continuous. In addition to carrying voice or data, the cell phone also transmits data about itself automatically, and that is boosted or not as the system detects need.
Coding of all transmissions allows two nearby cell user users no cross talk or interference between the two (this coding is not encryption, which is another, different coding). The boosting of power, however, is limited by the design of the devices to a maximum setting. The standard systems are not “high power” and thus can be overpowered by clandestine systems using much more boosted power that can then take over a user’s cell phone. If overpowered that way, a cell phone will not indicate the change due to the clandestine radio being programmed to hide itself from normal detection. The ordinary user can not know if their cell phone is captured via overpower boosts or not. (There are other ways of clandestine capture that need not overpower, too.)
Just as a person shouting drowns out someone whispering, the boost in RF watts of power into the cell telephone system can overtake and control that system—in total or only a few, or even only one, conversation. This strategy only requires more RF watts of power, and thus it is more simple than other types of clandestine controls. Power boosting equipment can be installed anywhere there can be an antenna, including in a vehicle, perhaps even in a vehicle on the move. Once a clandestine boosted system takes control, any manipulation is possible from simple recording of the voice or data to total blocking of all cell phones in the geographic area.
Tracking and locating
A StingRay can be used to identify and track a phone or other compatible cellular data device even while the device is not engaged in a call or accessing data services.
Denial of service
The FBI has claimed that when used to identify, locate, or track a cellular device, the StingRay does not collect communications content or forward it to the service provider. Instead, the device causes a disruption in service. Under this scenario, any attempt by the cellular device user to place a call or access data services will fail while the StingRay is conducting its surveillance.
Interception of communications content
By way of software upgrades, the StingRay and similar Harris products can be used to intercept GSM communications content transmitted over-the-air between a target cellular device and a legitimate service provider cell site. The StingRay does this by way of the following man-in-the-middle attack: (1) simulate a cell site and force a connection from the target device, (2) download the target device’s IMSI and other identifying information, (3) conduct “GSM Active Key Extraction” to obtain the target device’s stored encryption key, (4) use the downloaded identifying information to simulate the target device over-the-air, (5) while simulating the target device, establish a connection with a legitimate cell site authorized to provide service to the target device, (6) use the encryption key to authenticate the StingRay to the service provider as being the target device, and (7) forward signals between the target device and the legitimate cell site while decrypting and recording communications content.
The “GSM Active Key Extraction” performed by the StingRay in step three merits additional explanation. A GSM phone encrypts all communications content using an encryption key stored on its SIM card with a copy stored at the service provider. While simulating the target device during the above explained man-in-the-middle attack, the service provider cell site will ask the StingRay (which it believes to be the target device) to initiate encryption using the key stored on the target device. Therefore, the StingRay needs a method to obtain the target device’s stored encryption key else the man-in-the-middle attack will fail.
GSM primarily encrypts communications content using the A5/1 call encryption cypher. In 2008 it was reported that a GSM phone’s encryption key can be obtained using $1,000 worth of computer hardware and 30 minutes of cryptanalysis performed on signals encrypted using A5/1. However, GSM also supports an export weakened variant of A5/1 called A5/2. This weaker encryption cypher can be cracked in real-time. While A5/1 and A5/2 use different cypher strengths, they each utilize the same underlying encryption key stored on the SIM card. Therefore, the StingRay performs “GSM Active Key Extraction” during step three of the man-in-the-middle attack as follows: (1) instruct target device to use the weaker A5/2 encryption cypher, (2) collect A5/2 encrypted signals from target device, and (3) perform cryptanalysis of the A5/2 signals to quickly recover the underlying stored encryption key. Once the encryption key is obtained, the StingRay uses it to comply with the encryption request made to it by the service provider during the man-in-the-middle attack.
In passive mode, the StingRay operates either as a digital analyzer, which receives and analyzes signals being transmitted by cellular devices and/or wireless carrier cell sites, or as a radio jamming device, which transmits signals that block communications between cellular devices and wireless carrier cell sites. By “passive mode,” it is meant that the StingRay does not mimic a wireless carrier cell site or communicate directly with cellular devices.
Base station (cell site) surveys
A StingRay and a test phone can be used to conduct base station surveys, which is the process of collecting information on cell sites, including identification numbers, signal strength, and signal coverage areas. When conducting base station surveys, the StingRay mimics a cell phone while passively collecting signals being transmitted by cell sites in the area of the StingRay.
Base station survey data can be used to further narrow the past locations of a cellular device if used in conjunction with historical cell site location information (“HCSLI”) obtained from a wireless carrier. HCSLI includes a list of all cell sites and sectors accessed by a cellular device, and the date and time each access was made. Law enforcement will often obtain HCSLI from wireless carriers in order to determine where a particular cell phone was located in the past. Once this information is obtained, law enforcement will use a map of cell site locations to determine the past geographical locations of the cellular device.
However, the signal coverage area of a given cell site may change according to the time of day, weather, and physical obstructions in relation to where a cellular device attempts to access service. The maps of cell site coverage areas used by law enforcement may also lack precision as a general matter. For these reasons, it is beneficial to use a StingRay and a test phone to map out the precise coverage areas of all cell sites appearing in the HCSLI records. This is typically done at the same time of day and under the same weather conditions that were in effect when the HCSLI was logged. Using a StingRay to conduct base station surveys in this manner allows for mapping out cell site coverage areas that more accurately match the coverage areas that were in effect when the cellular device was used.
Usage by law enforcement
In the United States
The use of the devices has been frequently funded by grants from the Department of Homeland Security. The Los Angeles Police Department used a Department of Homeland Security grant in 2006 to buy a stingray for “regional terrorism investigations”. However, according to the Electronic Frontier Foundation, the “LAPD has been using it for just about any investigation imaginable.”
In addition to federal law enforcement, military and intelligence agencies, StingRays have in recent years been purchased by local and state law enforcement agencies. According to the American Civil Liberties Union, 42 law enforcement agencies in 17 states own StingRay technology. In November 2014, Slate reported that at least 46 state and local police departments, from Sunrise, Florida, to Hennepin County, Minnesota, use cell-site simulators, with a price-tag of US$16,000 to more thanUS$125,000 for each unit. In 2015, it was reported that the Baltimore Police Department‘s frequency in using the device was “inexplicably high”. In some states, the devices are made available to local police departments by state surveillance units. The federal government funds most of the purchases with anti-terror grants.
In 2006, Harris employees directly conducted wireless surveillance using StingRay units on behalf the Palm Bay Police Department — where Harris has a campus — in response to a bomb threat against a middle school. The search was conducted without a warrant or Judicial oversight.
Outside the United States
Privacy International and The Sunday Times reported on the usage of Stingrays and IMSI catchers in Ireland, against the Irish Garda Síochána Ombudsman Commission (GSOC), which is an oversight agency of the Irish police force Garda Síochána.
On June 10, 2015 the BBC reported on an investigation by Sky News about possible false mobile phone towers being used by the London Metropolitan Police. Commissioner Bernard Hogan-Howe refused comment.
The increasing use of the devices has largely been kept secret from the court system and the public. In 2014, police in Florida revealed they had used such devices at least 200 additional times since 2010 without disclosing it to the courts or obtaining a warrant. The American Civil Liberties Union has filed multiple requests for the public records of Florida law enforcement agencies about their use of the cell phone tracking devices.
Local law enforcement and the federal government have resisted judicial requests for information about the use of stingrays, refusing to turn over information or heavily censoring it. In June 2014, the American Civil Liberties Union published information from court regarding the extensive use of these devices by local Florida police. After this publication, United States Marshals Service then seized the local police’s surveillance records in a bid to keep them from coming out in court.
In some cases, police have refused to disclose information to the courts citing non-disclosure agreements signed with Harris Corporation. The FBI defended these agreements, saying that information about the technology could allow adversaries to circumvent it. The ACLU has said “potentially unconstitutional government surveillance on this scale should not remain hidden from the public just because a private corporation desires secrecy. And it certainly should not be concealed from judges.”
In 2015 Santa Clara County pulled-out of contract negotiations with Harris for StingRay units, citing onerous restrictions imposed by Harris on what could be released under public records requests as the reason for exiting negotiations.