Software:Signal

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Short description: Privacy-focused encrypted messaging app
Signal
Logo of Signal (2020–present)
Developer(s)
  • Signal Technology Foundation,
  • Signal Messenger LLC and contributors
Initial release29 July 2014; 9 years ago (2014-07-29)[1][2]
Stable release(s) [±]
Operating system
TypeEncrypted voice calling, video calling and instant messaging
LicenseAGPL-3.0-only[5][6][7][8][lower-alpha 1][lower-alpha 2]

Signal is an encrypted messaging service for instant messaging, voice, and video calls.[9][10] The instant messaging function includes sending text, voice notes, images, videos, and other files.[11] Communication may be one-to-one between users or may involve group messaging.

The application uses a centralized computing architecture and is cross-platform software. It is developed by the non-profit Signal Foundation and its subsidiary Signal Messenger LLC. Signal's software is free and open-source. Its mobile clients, desktop client, and server are all published under the AGPL-3.0-only license.[6][5][7][8][lower-alpha 1][lower-alpha 2] The official Android app generally uses the proprietary Google Play Services, although it is designed to work without them. Signal is also distributed for iOS and desktop programs for Windows, macOS, and Linux. Registration for desktop use requires an iOS or Android device.[15][16]

Signal uses mobile telephone numbers as identifiers for users. It secures all communications with end-to-end encryption. The client software includes mechanisms by which users can independently verify the identity of their contacts and the integrity of the data channel.[17][18]

The non-profit Signal Foundation was launched in February 2018 with initial funding of $50 million from Brian Acton.[19] (As of January 2022), the platform had approximately 40 million monthly active users. (As of May 2021), it was downloaded more than 105 million times.[20][21]

Until the feature was removed in 2023, the Android version was also optionally capable of functioning as an SMS app.[17][22]

History

2010–2013: Origins

Signal is the successor of the RedPhone encrypted voice calling app and the TextSecure encrypted texting program. The beta versions of RedPhone and TextSecure were first launched in May 2010 by Whisper Systems,[23] a startup company co-founded by security researcher Moxie Marlinspike and roboticist Stuart Anderson.[24][25] Whisper Systems also produced a firewall and tools for encrypting other forms of data.[24][26] All of these were proprietary enterprise mobile security software and were only available for Android.

In November 2011, Whisper Systems announced that it had been acquired by Twitter. Neither company disclosed the financial terms of the deal.[27] The acquisition was done "primarily so that Mr. Marlinspike could help the then-startup improve its security".[28] Shortly after the acquisition, Whisper Systems' RedPhone service was made unavailable.[29] Some criticized the removal, arguing that the software was "specifically targeted [to help] people under repressive regimes" and that it left people like the Egyptians in "a dangerous position" during the events of the Egyptian revolution of 2011.[30]

Twitter released TextSecure as free and open-source software under the GPLv3 license in December 2011.[24][31][32][33] RedPhone was also released under the same license in July 2012.[34] Marlinspike later left Twitter and founded Open Whisper Systems as a collaborative Open Source project for the continued development of TextSecure and RedPhone.[1][35]

2013–2018: Open Whisper Systems

Open Whisper Systems' website was launched in January 2013.[35]

In February 2014, Open Whisper Systems introduced the second version of their TextSecure Protocol (now Signal Protocol), which added end-to-end encrypted group chat and instant messaging capabilities to TextSecure.[36] Toward the end of July 2014, they announced plans to merge the RedPhone and TextSecure applications as Signal.[37] This announcement coincided with the initial release of Signal as a RedPhone counterpart for iOS. The developers said that their next steps would be to provide TextSecure instant messaging capabilities for iOS, unify the RedPhone and TextSecure applications on Android, and launch a web client.[37] Signal was the first iOS app to enable end-to-end encrypted voice calls for free.[1][38] TextSecure compatibility was added to the iOS application in March 2015.[39][40]

Signal Android icon, 2015–2017
Signal icon, 2015–2020

From its launch in May 2010[23] until March 2015, the Android version of Signal (then called TextSecure) included support for encrypted SMS/MMS messaging.[41] From version 2.7.0 onward, the Android application only supported sending and receiving encrypted messages via the data channel.[42] Reasons for this included security flaws of SMS/MMS and problems with the key exchange.[42] Open Whisper Systems' abandonment of SMS/MMS encryption prompted some users to create a fork named Silence (initially called SMSSecure[43]) that is meant solely for the exchange of encrypted SMS and MMS messages.[44][45]

In November 2015, the TextSecure and RedPhone applications on Android were merged to become Signal for Android.[46] A month later, Open Whisper Systems announced Signal Desktop, a Chrome app that could link with a Signal mobile client.[47] At launch, the app could only be linked with the Android version of Signal.[48] On 26 September 2016, Open Whisper Systems announced that Signal Desktop could now be linked with the iOS version of Signal as well.[49] On 31 October 2017, Open Whisper Systems announced that the Chrome app was deprecated.[3] At the same time, they announced the release of a standalone desktop client (based on the Electron framework[7]) for Windows, macOS and certain Linux distributions.[3][50]

On 4 October 2016, the American Civil Liberties Union (ACLU) and Open Whisper Systems published a series of documents revealing that OWS had received a subpoena requiring them to provide information associated with two phone numbers for a federal grand jury investigation in the first half of 2016.[51][52][53] Only one of the two phone numbers was registered on Signal, and because of how the service is designed, OWS was only able to provide "the time the user's account had been created and the last time it had connected to the service".[52][51] Along with the subpoena, OWS received a gag order requiring OWS not to tell anyone about the subpoena for one year.[51] OWS approached the ACLU, and they were able to lift part of the gag order after challenging it in court.[51] OWS said it was the first time they had received a subpoena, and that they were committed to treat "any future requests the same way".[53]

In March 2017, Open Whisper Systems transitioned Signal's calling system from RedPhone to WebRTC, also adding the ability to make video calls with the mobile apps.[54][55][9]

Since 2018: Signal Technology Foundation

On 21 February 2018, Moxie Marlinspike and WhatsApp co-founder Brian Acton announced the formation of the Signal Technology Foundation, a 501(c)(3) nonprofit organization whose mission is "to support, accelerate, and broaden Signal's mission of making private communication accessible and ubiquitous".[56][19] Acton started the foundation with $50 million in funding and became the foundation's executive chairman after leaving WhatsApp's parent company Facebook in September 2017.[19] Marlinspike continued as Signal Messenger's first CEO.[56] (As of 2020), Signal ran entirely on donations, as a nonprofit.[57]

Between November 2019 and February 2020, Signal added iPad support, view-once images and videos, stickers, and reactions.[58] They also announced plans for a new group messaging system and an "experimental method for storing encrypted contacts in the cloud."[58]

Signal was reportedly popularized in the United States during the George Floyd protests. Heightened awareness of police monitoring led protesters to use the platform to communicate. Black Lives Matter organizers had used the platform "for several years".[59][57] During the first week of June, the encrypted messaging app was downloaded over five times more than it had been during the week prior to the murder of George Floyd.[59] In June 2020, Signal Foundation announced a new feature that enables users to blur faces in photos, in response to increased federal efforts to monitor protesters.[57][60]

On 7 January 2021, Signal saw a surge in new user registrations, which temporarily overwhelmed Signal's capacity to deliver account verification messages.[61] CNN and MacRumors linked the surge with a WhatsApp privacy policy change and a Signal endorsement by Elon Musk and Edward Snowden via Twitter.[61][62] The surge was also tied to the far-right attack on the United States Capitol.[63] International newspapers reported similar trends in the United Arab Emirates.[64] Reuters reported that more than 100,000 people had installed Signal between 7 and 8 January.[65]

Between 12 and 14 January 2021, the number of Signal installations listed on Google Play increased from over 10 million to over 50 million.[66][67][68][69] On 15 January 2021, due to the surge of new users, Signal was overwhelmed with the new traffic and was down for all users.[70][71] On the afternoon of 16 January, Signal announced via Twitter that service had been restored.[72]

On 10 January 2022, Moxie Marlinspike announced that he was stepping down from his role as CEO of Signal Messenger.[73] He continues to remain on the Signal Foundation's board of directors and Brian Acton has volunteered to serve as interim CEO during the search for a new CEO.[73]

In August 2022, Signal notified 1900 users that their data had been affected by the Twilio breach including user phone numbers and SMS verification codes.[74] At least one journalist had his account re-registered to a device he did not control as a result of the attack.[75]

In September 2022 Signal Messaging LLC announced that AI researcher and noted critic of big tech Meredith Whittaker would fill the newly created position of President.[76]

Usage

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Signal's userbase started in May 2010, when its predecessor TextSecure was launched by Whisper Systems.[23] According to App Annie, Signal had approximately 20 million monthly active users at the end of December 2020.[77] In January 2022, the BBC reported that Signal was used by over 40 million people.[78]

Developers and funding

Main page: Organization:Signal Foundation

The development of Signal and its predecessors at Open Whisper Systems was funded by a combination of consulting contracts, donations and grants.[79] The Freedom of the Press Foundation acted as Signal's fiscal sponsor.[56][80][81] Between 2013 and 2016, the project received grants from the Knight Foundation,[82] the Shuttleworth Foundation,[83] and almost $3 million from the US government–sponsored Open Technology Fund.[84] Signal is now developed by Signal Messenger LLC, a software company founded by Moxie Marlinspike and Brian Acton in 2018, which is wholly owned by a tax-exempt nonprofit corporation called the Signal Technology Foundation, also created by them in 2018. The Foundation was funded with an initial loan of $50 million from Acton, "to support, accelerate, and broaden Signal's mission of making private communication accessible and ubiquitous".[56][19][85] All of the organization's products are published as free and open-source software.

In November 2023, Meredith Whittaker revealed that she expected the annual cost of running Signal to reach $50 million in 2025, with the current cost estimated around $40 million.[86]

Features

Signal provides one-to-one and group[87] voice and video[9] calls with up to forty participants on iOS, Android, and desktop platforms.[88][89] The calls are carried via the devices' wired or wireless (carrier or WiFi) data connections.[38] The application can send text messages, documents files,[11] voice notes, pictures, GIFs,[90] and video messages. The platform also supports group messaging.

All communication sessions between Signal users are automatically end-to-end encrypted (the encryption keys are generated and stored on the devices, and not on servers).[91] To verify that a correspondent is really the person that they claim to be, Signal users can compare key fingerprints (or scan QR codes) out-of-band.[92] The platform employs a trust-on-first-use mechanism to notify the user if a correspondent's key changes.[92]

Until 2023, on Android users could opt into making Signal the default SMS/MMS application, allowing them to send and receive unencrypted SMS messages in addition to the standard end-to-end encrypted Signal messages.[36] Users could then use the same application to communicate with contacts who do not have Signal.[36] As of October 2022, this feature has been deprecated due to safety and security concerns, and was removed in 2023.[93][22]

TextSecure allowed the user to set a passphrase that encrypted the local message database and the user's encryption keys.[94] This did not encrypt the user's contact database or message timestamps.[94] The Signal applications on Android and iOS can be locked with the phone's pin, passphrase, or biometric authentication.[95] The user can define a "screen lock timeout" interval, providing an additional protection mechanism in case the phone is lost or stolen.[92][95]

Signal has a feature for scheduling messages.[96] In addition, timers may be attached to messages[97] to automatically delete the messages from both the sender's and the receivers' devices.[97] The time period for keeping the message may be between five seconds and one week,[97] and begins for each recipient once they have read their copy of the message.[98] The developers stressed that this is meant to be "a collaborative feature for conversations where all participants want to automate minimal data hygiene, not for situations where the recipient is an adversary".[97][98]

Signal's app icon may be changed from with a variety of colour themes for customization and the application name can also be customized.[99] Upcoming features includes hiding spoilers[100] as well adding other users via QR code.[101]

Signal excludes users' messages from non-encrypted cloud backups by default.[102]

Signal allows users to automatically blur faces of people in photos to protect identities.[103][104]

Signal includes a cryptocurrency wallet functionality for storing, sending and receiving in-app payments.[105] Apart from certain regions and countries,[105] the feature was enabled globally in November 2021.[106] (As of January 2022), the only supported payment method is MobileCoin.[105]

Limitations

Signal requires that the user provide a telephone number for verification,[107] eliminating the need for user names or passwords and facilitating contact discovery (see below).[108] The number does not have to be the same as on the device's SIM card; it can also be a VoIP number[107] or a landline as long as the user can receive the verification code and have a separate device to set up the software. A number can only be registered on one mobile device at a time.[109] Account registration requires an iOS or Android device.[15][16]

This mandatory connection to a telephone number (a feature Signal shares with WhatsApp, KakaoTalk, and others) has been criticized as a "major issue" for privacy-conscious users who are not comfortable with giving out their private number.[108] A workaround is to use a secondary phone number.[108] The ability to choose a public, changeable username instead of sharing one's phone number is a widely-requested feature.[108][110][111]

Using phone numbers as identifiers may also create security risks that arise from the possibility of an attacker taking over a phone number.[108] A similar vulnerability was used to attack at least one user in August 2022, though the attack was performed via the provider of Signal's SMS services, not any user's provider.[74] The threat of this attack can be mitigated by enabling Signal's Registration Lock feature, a form of two-factor authentication that requires the user to enter a PIN to register the phone number on a new device.[112]

When linking Signal Desktop to a mobile device, the conversations history will not be synced; only the new messages will be shown on Signal Desktop.[113]

Usability

In July 2016, the Internet Society published a user study that assessed the ability of Signal users to detect and deter man-in-the-middle attacks.[18] The study concluded that 21 out of 28 participants failed to correctly compare public key fingerprints in order to verify the identity of other Signal users, and that most of these users believed they had succeeded, while they had actually failed.[18] Four months later, Signal's user interface was updated to make verifying the identity of other Signal users simpler.[114]

In 2023, the French government is pushing for the adoption of a European encrypted messaging alternative to Signal and WhatsApp named Olvid as their secured platform for communications.[115]

Architecture

Encryption protocols

Main page: Signal Protocol

Signal messages are encrypted with the Signal Protocol (formerly known as the TextSecure Protocol). The protocol combines the Double Ratchet Algorithm, prekeys, and an Extended Triple Diffie–Hellman (X3DH) handshake.[116][117] It uses Curve25519, AES-256, and HMAC-SHA256 as primitives.[17] The protocol provides confidentiality, integrity, authentication, participant consistency, destination validation, forward secrecy, backward secrecy (a.k.a. future secrecy), causality preservation, message unlinkability, message repudiation, participation repudiation, and asynchronicity.[118] It does not provide anonymity preservation, and requires servers for the relaying of messages and storing of public key material.[118]

The Signal Protocol also supports end-to-end encrypted group chats. The group chat protocol is a combination of a pairwise double ratchet and multicast encryption.[118] In addition to the properties provided by the one-to-one protocol, the group chat protocol provides speaker consistency, out-of-order resilience, dropped message resilience, computational equality, trust equality, subgroup messaging, as well as contractible and expandable membership.[118]

In October 2014, researchers from Ruhr University Bochum published an analysis of the Signal Protocol.[17] Among other findings, they presented an unknown key-share attack on the protocol, but in general, they found that it was secure.[119] In October 2016, researchers from UK's University of Oxford, Queensland University of Technology in Australia, and Canada's McMaster University published a formal analysis of the protocol.[120][121] They concluded that the protocol was cryptographically sound.[120][121] In July 2017, researchers from Ruhr University Bochum found during another analysis of group messengers a purely theoretic attack against the group protocol of Signal: A user who knows the secret group ID of a group (due to having been a group member previously or stealing it from a member's device) can become a member of the group. Since the group ID cannot be guessed and such member changes are displayed to the remaining members, this attack is likely to be difficult to carry out without being detected.[122]

(As of August 2018), the Signal Protocol has been implemented into WhatsApp, Facebook Messenger, Skype,[123] and Google Allo,[124] making it possible for the conversations of "more than a billion people worldwide" to be end-to-end encrypted.[125] In Google Allo, Skype and Facebook Messenger, conversations are not encrypted with the Signal Protocol by default; they only offer end-to-end encryption in an optional mode.[102][126][123][127]

Up until March 2017, Signal's voice calls were encrypted with SRTP and the ZRTP key-agreement protocol, which was developed by Phil Zimmermann.[1][128] In March 2017, Signal transitioned to a new WebRTC-based calling system that introduced the ability to make video calls.[55] Signal's voice and video calling functionalities use the Signal Protocol channel for authentication instead of ZRTP.[129][54][9]

Authentication

To verify that a correspondent is really the person that they claim to be, Signal users can compare key fingerprints (or scan QR codes) out-of-band.[92] The platform employs a trust on first use mechanism in order to notify the user if a correspondent's key changes.[92]

Local storage

After receiving and decrypting messages, the application stored them locally on each device in a SQLite database that is encrypted with SQLCipher.[130] The cryptographic key for this database is also stored locally and can be accessed if the device is unlocked.[130][131] In December 2020, Cellebrite published a blog post announcing that one of their products could now access this key and use it to "decrypt the Signal app".[130][132] Technology reporters later published articles about how Cellebrite had claimed to have the ability to "break into the Signal app" and "crack Signal's encryption".[133][134] This latter interpretation was rejected by several experts,[135] as well as representatives from Signal, who said the original post by Cellebrite had been about accessing data on "an unlocked Android phone in their physical possession" and that they "could have just opened the app to look at the messages".[136][137] Similar extraction tools also exist for iOS devices and Signal Desktop.[138][139]

Servers

Signal relies on centralized servers that are maintained by Signal Messenger. In addition to routing Signal's messages, the servers also facilitate the discovery of contacts who are also registered Signal users and the automatic exchange of users' public keys. By default, Signal's voice and video calls are peer-to-peer.[9] If the caller is not in the receiver's address book, the call is routed through a server in order to hide the users' IP addresses.[9]

Contact discovery

The servers store registered users' phone numbers, public key material and push tokens which are necessary for setting up calls and transmitting messages.[140] In order to determine which contacts are also Signal users, cryptographic hashes of the user's contact numbers are periodically transmitted to the server.[141] The server then checks to see if those match any of the SHA256 hashes of registered users and tells the client if any matches are found.[141] The hashed numbers are thereafter discarded from the server.[140] In 2014, Moxie Marlinspike wrote that it is easy to calculate a map of all possible hash inputs to hash outputs and reverse the mapping because of the limited preimage space (the set of all possible hash inputs) of phone numbers, and that a "practical privacy preserving contact discovery remains an unsolved problem."[142][141] In September 2017, Signal's developers announced that they were working on a way for the Signal client applications to "efficiently and scalably determine whether the contacts in their address book are Signal users without revealing the contacts in their address book to the Signal service."[143][144]

Metadata

All client-server communications are protected by TLS.[128][145] Signal's developers have asserted that their servers do not keep logs about who called whom and when.[146] In June 2016, Marlinspike told The Intercept that "the closest piece of information to metadata that the Signal server stores is the last time each user connected to the server, and the precision of this information is reduced to the day, rather than the hour, minute, and second".[102]

The group messaging mechanism is designed so that the servers do not have access to the membership list, group title, or group icon.[42] Instead, the creation, updating, joining, and leaving of groups is done by the clients, which deliver pairwise messages to the participants in the same way that one-to-one messages are delivered.[147][148]

Federation

Signal's server architecture was federated between December 2013 and February 2016. In December 2013, it was announced that the messaging protocol Signal uses had successfully been integrated into the Android-based open-source operating system CyanogenMod.[149][150][151] Since CyanogenMod 11.0, the client logic was contained in a system app called WhisperPush. According to Signal's developers, the Cyanogen team ran their own Signal messaging server for WhisperPush clients, which federated with the main server, so that both clients could exchange messages with each other.[151] The WhisperPush source code was available under the GPLv3 license.[152] In February 2016, the CyanogenMod team discontinued WhisperPush and recommended that its users switch to Signal.[153] In May 2016, Moxie Marlinspike wrote that federation with the CyanogenMod servers had degraded the user experience and held back development, and that their servers will probably not federate with other servers again.[154]

In May 2016, Moxie Marlinspike requested that a third-party client called LibreSignal not use the Signal service or the Signal name.[154] As a result, on 24 May 2016 the LibreSignal project posted that the project was "abandoned".[155] The functionality provided by LibreSignal was subsequently incorporated into Signal by Marlinspike.[156]

Licensing

The complete source code of the Signal clients for Android, iOS and desktop is available on GitHub under a free software license.[6][5][7] This enables interested parties to examine the code and help the developers verify that everything is behaving as expected. It also allows advanced users to compile their own copies of the applications and compare them with the versions that are distributed by Signal Messenger. In March 2016, Moxie Marlinspike wrote that, apart from some shared libraries that are not compiled with the project build due to a lack of Gradle NDK support, Signal for Android is reproducible.[157] Signal's servers are partially open source, but the server software's anti-spam component is proprietary and closed source due to security concerns.[8][158]

Reception

Security

In October 2014, the Electronic Frontier Foundation (EFF) included Signal in their updated surveillance self-defense guide.[159] In November 2014, Signal received a perfect score on the EFF's secure messaging scorecard;[91] it received points for having communications encrypted in transit, having communications encrypted with keys the provider does not have access to (end-to-end encryption), making it possible for users to independently verify their correspondents' identities, having past communications secure if the keys are stolen (forward secrecy), having the code open to independent review (open source), having the security designs well-documented, and having a recent independent security audit.[91] At the time, "ChatSecure + Orbot", Pidgin (with OTR), Silent Phone, and Telegram's optional "secret chats" also received seven out of seven points on the scorecard.[91]

Former NSA contractor Edward Snowden has endorsed Signal on multiple occasions.[47] In his keynote speech at SXSW in March 2014, he praised Signal's predecessors (TextSecure and RedPhone) for their ease of use.[160][161] In December 2014, Der Spiegel leaked slides from an internal NSA presentation dating to June 2012 in which the NSA deemed Signal's encrypted voice calling component (RedPhone) on its own as a "major threat" to its mission of accessing users' private data, and when used in conjunction with other privacy tools such as Cspace, Tor, Tails, and TrueCrypt was ranked as "catastrophic" and led to a "near-total loss/lack of insight to target communications [and] presence".[162][163]

Following the 2016 Democratic National Committee email leak, it was reported by Vanity Fair that Marc Elias (the general counsel for Hillary Clinton's presidential campaign) had instructed DNC staffers to exclusively use Signal when saying anything negative about Republican presidential nominee Donald Trump.[164][165]

In March 2017, Signal was approved by the sergeant at arms of the U.S. Senate for use by senators and their staff.[166][167]

On 27 September 2019, Natalie Silvanovich, a security engineer working in Google's vulnerability research team at Project Zero, disclosed how a bug in the Android Signal client could let an attacker spy on a user without their knowledge.[168] The bug allowed an attacker to phone a target device, mute the call, and the call would complete - keeping the audio open but without the owner being aware of that (however they would still be aware of a ring and / or a vibration from the initial call).[169] The bug was fixed the same day that it was reported and patched in release 4.47.7 of the app for Android.[170]

In February 2020, the European Commission recommended that its staff use Signal.[171] Following the George Floyd protests, which began in May 2020, Signal was downloaded 121,000 times in the U.S. between 25 May and 4 June.[172] In July 2020, Signal became the most downloaded app in Hong Kong on both the Apple App Store and the Google Play Store after the passage of the Hong Kong national security law.[173]

(As of January 2021), Signal is a contact method for securely providing tips to major news outlets such as The Washington Post ,[174] The Guardian ,[175] The New York Times ,[176] and The Wall Street Journal .[177]

Candiru claims the ability to capture data from Signal Private Messenger with their spyware, at a fee of €500.000.[178]

On 9 August 2022, Ismail Sabri Yaakob, the Prime Minister of Malaysia, reported that his Signal account was "hacked" and infiltrated by a third party, sending out messages and impersonating the politician. No details were disclosed regarding the method used to gain access to the account.[179]

In-app payments

In April 2021, Signal announced the addition of a cryptocurrency wallet feature that would allow users to send and receive payments in MobileCoin.[180] This received criticism from security expert Bruce Schneier, who had previously praised the software. Schneier stated that this would bloat the client and attract unwanted attention from the authorities.[181] The wallet functionality was initially only available in certain countries, but was later enabled globally in November 2021.[106]

Blocking

  Countries where Signal's domain fronting is enabled by default
  Countries where Signal is blocked (March 2021)

In December 2016, Egypt blocked access to Signal.[182] In response, Signal's developers added domain fronting to their service.[183] This allows Signal users in a specific country to circumvent censorship by making it look like they are connecting to a different internet-based service.[183][184] (As of May 2022), Signal's domain fronting is enabled by default in Egypt, UAE, Oman, Qatar, Iran, Cuba, Uzbekistan and Ukraine .[185]

(As of January 2018), Signal was blocked in Iran.[186][187] Signal's domain fronting feature relies on the Google App Engine (GAE) service.[187][186] This does not work in Iran because Google has blocked Iranian access to GAE in order to comply with U.S. sanctions.[186][188]

In early 2018, Google App Engine made an internal change to stop domain fronting for all countries. Due to this issue, Signal made a public change to use Amazon CloudFront for domain fronting. However, AWS also announced that they would be making changes to their service to prevent domain fronting. As a result, Signal said that they would start investigating new methods/approaches.[189][190] Signal switched from AWS back to Google in April 2019.[191]

In January 2021, Iran removed the app from app stores,[192][193] and blocked Signal.[194] Signal was later blocked by China in March 2021.[195]

Audience

Use by activists

In 2020, the app was used for coordination and communication by protesters during the George Floyd protests as they relied on the app's end-to-end encryption to share information securely.[196]

In March 2021, the United Nations recommended Myanmar residents use Signal and Proton Mail to pass and preserve evidence of human rights violations committed during the 2021 coup.[197]

Controversial use

Signal's terms of service state that the product must not be used to violate the law.[198] According to a former employee, Signal's leadership at the time told him they would say something "if and when people start abusing Signal or doing things that we think are terrible".[198] In January 2021, the position of Signal's leadership was to take a "hands-off approach to moderation" as the company's employees are not able to read user messages and the Signal Foundation "don't want to be a media company".[198][199]

In 2016, authorities in India arrested members of a suspected ISIS-affiliated terrorist cell that communicated via Signal.[200]

Extremist right-wing militias and white nationalists use Signal for organizing their actions, including the Unite the Right II rally in 2018.[201][202][203][204]

The claim that Signal is used to fund terrorist or criminal activities is the justification for Turkey to criminalize the app for the general population, which Abdullah Bozkurt claims is a way the "government abuses its counterterrorism laws to punish critics, opponents and dissidents."[205][206]

See also

Notes

  1. ↑ 1.0 1.1 The iOS and Android clients were formerly published under the GPL-3.0-only license, and were updated to AGPL in 2022 and 2023 respectively.[12][13]
  2. ↑ 2.0 2.1 The source code for spam detection is not public.[14]

References

  1. ↑ 1.0 1.1 1.2 1.3 Greenberg, Andy (29 July 2014). "Your iPhone Can Finally Make Free, Encrypted Calls". Wired. https://www.wired.com/2014/07/free-encrypted-calling-finally-comes-to-the-iphone/. Retrieved 18 January 2015. 
  2. ↑ Marlinspike, Moxie (29 July 2014). "Free, Worldwide, Encrypted Phone Calls for iPhone". Open Whisper Systems. https://whispersystems.org/blog/signal/. 
  3. ↑ 3.0 3.1 3.2 3.3 Nonnenberg, Scott (31 October 2017). "Standalone Signal Desktop". Open Whisper Systems. https://signal.org/blog/standalone-signal-desktop/. 
  4. ↑ "Installing Signal - Signal Support". https://support.signal.org/hc/en-us/articles/360008216551#install_desktop. 
  5. ↑ 5.0 5.1 5.2 Signal. "Signal-Android". https://github.com/signalapp/Signal-Android. 
  6. ↑ 6.0 6.1 6.2 Signal. "Signal-iOS". https://github.com/signalapp/Signal-iOS. 
  7. ↑ 7.0 7.1 7.2 7.3 Signal. "Signal-Desktop". https://github.com/signalapp/Signal-Desktop. 
  8. ↑ 8.0 8.1 8.2 Signal. "Signal-Server". https://github.com/signalapp/Signal-Server. 
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 Mott, Nathaniel (14 March 2017). "Signal's Encrypted Video Calling For iOS, Android Leaves Beta". Purch Group, Inc.. http://www.tomshardware.com/news/signal-encrypted-video-calling-ios-android,33898.html. 
  10. ↑ Perez, Josh (2 September 2020). "Release v1.35.1". Signal. https://github.com/signalapp/Signal-Desktop/releases/tag/v1.35.1. 
  11. ↑ 11.0 11.1 Signal [@signalapp] (1 May 2017). "Today's Signal release for Android, iOS, and Desktop includes the ability to send arbitrary file types.". https://twitter.com/signalapp/status/859125874901135360. 
  12. ↑ "Update top-level LICENSE file to AGPL". Signal. 1 November 2022. https://github.com/signalapp/Signal-iOS/commit/9865d398f70aeb1888c1c537f29b043690a570b2. 
  13. ↑ "Update top-level LICENSE file to AGPL". Signal. 5 May 2023. https://github.com/signalapp/Signal-Android/commit/ace47c61b1aa4c32b8468343615e3e7288915dea. 
  14. ↑ O'Leary, Jim (1 November 2021). "Improving first impressions on Signal". https://signal.org/blog/keeping-spam-off-signal/. 
  15. ↑ 15.0 15.1 Ciobica, Vladimir (26 May 2021). "Signal Desktop". https://www.softpedia.com/get/Internet/Chat/Instant-Messaging/Signal-Desktop.shtml. 
  16. ↑ 16.0 16.1 Youngren, Jan (19 January 2021). "Signal messaging app review 2021". https://vpnpro.com/messaging-apps/signal-review/. 
  17. ↑ 17.0 17.1 17.2 17.3 Frosch et al. 2016
  18. ↑ 18.0 18.1 18.2 Schröder et al. 2016
  19. ↑ 19.0 19.1 19.2 19.3 Greenberg, Andy (21 February 2018). "WhatsApp Co-Founder Puts $50M Into Signal To Supercharge Encrypted Messaging". Wired. https://www.wired.com/story/signal-foundation-whatsapp-brian-acton/. Retrieved 21 February 2018. 
  20. ↑ Curry, David (11 January 2022). "Signal Revenue & Usage Statistics (2022)" (in en-US). Business of Apps. https://www.businessofapps.com/data/signal-statistics/. 
  21. ↑ "Signal Private Messenger - Apps on Google Play" (in en). Google. 28 January 2021. https://play.google.com/store/apps/details?id=org.thoughtcrime.securesms&hl=en_US&gl=US. 
  22. ↑ 22.0 22.1 "Removing SMS support from Signal Android (soon)". 12 October 2022. https://signal.org/blog/sms-removal-android/. 
  23. ↑ 23.0 23.1 23.2 "Announcing the public beta". Whisper Systems. 25 May 2010. http://www.whispersys.com/updates.html. 
  24. ↑ 24.0 24.1 24.2 Garling, Caleb (20 December 2011). "Twitter Open Sources Its Android Moxie | Wired Enterprise". Wired. https://www.wired.com/wiredenterprise/2011/12/twitter-open-sources-its-android-moxie/. Retrieved 21 December 2011. 
  25. ↑ "Company Overview of Whisper Systems Inc.". Bloomberg Businessweek. http://investing.businessweek.com/research/stocks/private/snapshot.asp?privcapId=141104009. Retrieved 4 March 2014. 
  26. ↑ Greenberg, Andy (25 May 2010). "Android App Aims to Allow Wiretap-Proof Cell Phone Calls". Forbes. https://www.forbes.com/sites/firewall/2010/05/25/android-app-aims-to-allow-wiretap-proof-cell-phone-calls/. 
  27. ↑ Cheredar, Tom (28 November 2011). "Twitter acquires Android security startup Whisper Systems". VentureBeat. https://venturebeat.com/2011/11/28/twitter-buys-whisper-systems/. 
  28. ↑ Yadron, Danny (9 July 2015). "Moxie Marlinspike: The Coder Who Encrypted Your Texts". The Wall Street Journal. https://www.wsj.com/articles/moxie-marlinspike-the-coder-who-encrypted-your-texts-1436486274. 
  29. ↑ Greenberg, Andy (28 November 2011). "Twitter Acquires Moxie Marlinspike's Encryption Startup Whisper Systems". Forbes. https://www.forbes.com/sites/andygreenberg/2011/11/28/twitter-acquires-moxie-marlinspikes-encryption-startup-whisper-systems/. 
  30. ↑ Garling, Caleb (28 November 2011). "Twitter Buys Some Middle East Moxie | Wired Enterprise". Wired. https://www.wired.com/wiredenterprise/2011/11/twitter-buys-moxie/. Retrieved 21 December 2011. 
  31. ↑ Aniszczyk, Chris (20 December 2011). "The Whispers Are True". https://blog.twitter.com/2011/whispers-are-true. 
  32. ↑ "TextSecure is now Open Source!". Whisper Systems. 20 December 2011. http://www.whispersys.com/updates.html. 
  33. ↑ Pachal, Pete (20 December 2011). "Twitter Takes TextSecure, Texting App for Dissidents, Open Source". Mashable. http://mashable.com/2011/12/20/textsecure-open-source/. 
  34. ↑ "RedPhone is now Open Source!". Whisper Systems. 18 July 2012. http://www.whispersys.com/updates.html. 
  35. ↑ 35.0 35.1 "A New Home". Open Whisper Systems. 21 January 2013. https://whispersystems.org/blog/welcome/. 
  36. ↑ 36.0 36.1 36.2 Donohue, Brian (24 February 2014). "TextSecure Sheds SMS in Latest Version". https://threatpost.com/textsecure-sheds-sms-in-latest-version/104456. 
  37. ↑ 37.0 37.1 Mimoso, Michael (29 July 2014). "New Signal App Brings Encrypted Calling to iPhone". Threatpost. http://threatpost.com/new-signal-app-brings-encrypted-calling-to-iphone/107491. 
  38. ↑ 38.0 38.1 Evans, Jon (29 July 2014). "Talk Private To Me: Free, Worldwide, Encrypted Voice Calls With Signal For iPhone". TechCrunch. AOL. https://techcrunch.com/2014/07/29/talk-private-to-me-free-worldwide-encrypted-voice-calls-with-signal/. 
  39. ↑ Lee, Micah (2 March 2015). "You Should Really Consider Installing Signal, an Encrypted Messaging App for iPhone". https://firstlook.org/theintercept/2015/03/02/signal-iphones-encrypted-messaging-app-now-supports-text/. 
  40. ↑ Geuss, Megan (3 March 2015). "Now you can easily send (free!) encrypted messages between Android, iOS". https://arstechnica.com/security/2015/03/now-you-can-easily-send-free-encrypted-messages-between-android-ios/. 
  41. ↑ Open Whisper Systems (6 March 2015). "Saying goodbye to encrypted SMS/MMS". https://whispersystems.org/blog/goodbye-encrypted-sms/. 
  42. ↑ 42.0 42.1 42.2 Rottermanner et al. 2015, p. 3
  43. ↑ BastienLQ (20 April 2016). "Change the name of SMSSecure". SilenceIM. https://github.com/SilenceIM/Silence/pull/383. 
  44. ↑ "TextSecure-Fork bringt SMS-Verschlüsselung zurück" (in de). 2 April 2015. http://www.heise.de/security/meldung/TextSecure-Fork-bringt-SMS-Verschluesselung-zurueck-2595471.html. 
  45. ↑ "SMSSecure: TextSecure-Abspaltung belebt SMS-Verschlüsselung wieder" (in de). 3 April 2015. http://derstandard.at/2000013841576/SMSSecure-TextSecure-Abspaltung-belebt-SMS-Verschluesselung-wieder. 
  46. ↑ Greenberg, Andy (2 November 2015). "Signal, the Snowden-Approved Crypto App, Comes to Android". Wired. https://www.wired.com/2015/11/signals-snowden-approved-phone-crypto-app-comes-to-android/. Retrieved 19 March 2016. 
  47. ↑ 47.0 47.1 Franceschi-Bicchierai, Lorenzo (2 December 2015). "Snowden's Favorite Chat App Is Coming to Your Computer". Vice Media LLC. http://motherboard.vice.com/read/signal-snowdens-favorite-chat-app-is-coming-to-your-computer. 
  48. ↑ Coldewey, Devin (7 April 2016). "Now's your chance to try Signal's desktop Chrome app". AOL Inc.. https://techcrunch.com/2016/04/07/nows-your-chance-to-try-signals-desktop-chrome-app/. 
  49. ↑ Marlinspike, Moxie (26 September 2016). "Desktop support comes to Signal for iPhone". Open Whisper Systems. https://whispersystems.org/blog/signal-desktop-ios/. 
  50. ↑ Coldewey, Devin (31 October 2017). "Signal escapes the confines of the browser with a standalone desktop app". Oath Tech Network. https://techcrunch.com/2017/10/31/signal-escapes-the-confines-of-the-browser-with-a-standalone-desktop-app/. 
  51. ↑ 51.0 51.1 51.2 51.3 Perlroth, Nicole; Benner, Katie (4 October 2016). "Subpoenas and Gag Orders Show Government Overreach, Tech Companies Argue". https://www.nytimes.com/2016/10/05/technology/subpoenas-and-gag-orders-show-government-overreach-tech-companies-argue.html. 
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  53. ↑ 53.0 53.1 "Grand jury subpoena for Signal user data, Eastern District of Virginia". Open Whisper Systems. 4 October 2016. https://whispersystems.org/bigbrother/eastern-virginia-grand-jury/. 
  54. ↑ 54.0 54.1 Marlinspike, Moxie (14 February 2017). "Video calls for Signal now in public beta". Open Whisper Systems. https://whispersystems.org/blog/signal-video-calls-beta/. 
  55. ↑ 55.0 55.1 Marlinspike, Moxie (13 March 2017). "Video calls for Signal out of beta". Open Whisper Systems. https://whispersystems.org/blog/signal-video-calls/. 
  56. ↑ 56.0 56.1 56.2 56.3 Marlinspike, Moxie; Acton, Brian (21 February 2018). "Signal Foundation". https://signal.org/blog/signal-foundation/. 
  57. ↑ 57.0 57.1 57.2 Wiener, Anna (19 October 2020). "Taking Back Our Privacy". The New Yorker. https://www.newyorker.com/magazine/2020/10/26/taking-back-our-privacy. Retrieved 27 October 2020. 
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  59. ↑ 59.0 59.1 Nierenberg, Amelia (12 June 2020). "Signal Downloads Are Way Up Since the Protests Began". The New York Times. https://www.nytimes.com/2020/06/11/style/signal-messaging-app-encryption-protests.html. 
  60. ↑ Lyngaas, Sean (4 June 2020). "Signal aims to boost protesters' phone security at George Floyd demonstrations with face-blurring tool" (in en). https://www.cyberscoop.com/george-floyd-protest-phone-security/. 
  61. ↑ 61.0 61.1 Hardwick, Tim (8 January 2021). "Encrypted Messaging App Signal Sees Surge in Popularity Following WhatsApp Privacy Policy Update" (in en). https://www.macrumors.com/2021/01/08/messaging-app-signal-sees-surge-signups/. 
  62. ↑ Duffy, Clare (12 January 2021). "Why messaging app Signal is surging in popularity right now". CNN. https://www.cnn.com/2021/01/12/tech/signal-growth-whatsapp-confusion/index.html. 
  63. ↑ Chau, David (20 January 2021). "Donald Trump supporters embrace Signal, Telegram and other 'free speech' apps". https://www.abc.net.au/news/2021-01-20/donald-trump-social-media-apps-free-speech-privacy/13071206. 
  64. ↑ Cabral, Alvin R.. "UAE WhatsApp users look for other messaging platforms over new terms" (in en). https://www.khaleejtimes.com/technology/uae-whatsapp-users-look-for-other-messaging-platforms-over-new-terms. 
  65. ↑ "Signal, Telegram see demand spike as new WhatsApp terms stir debate" (in en). Reuters. 8 January 2021. https://www.reuters.com/article/us-whatsapp-users-idUSKBN29D1TY. 
  66. ↑ Screenshot showing 40 million downloads between 12 and 14 January 2021.
  67. ↑ "Signal Private Messenger - Apps on Google Play". Google Play. 12 January 2021. https://play.google.com/store/apps/details?id=org.thoughtcrime.securesms. 
  68. ↑ "Signal Private Messenger - Apps on Google Play". 14 January 2021. https://play.google.com/store/apps/details?id=org.thoughtcrime.securesms. 
  69. ↑ "Signal hits 50 million installs on Play Store amid WhatsApp privacy concerns". Android Police. 14 January 2021. https://www.androidpolice.com/2021/01/14/signal-hits-50-million-installs-on-play-store-amid-whatsapp-privacy-concerns/. 
  70. ↑ "Signal Status". https://status.signal.org/. 
  71. ↑ "WhatsApp changes: Signal messaging platform stops working as downloads surge" (in en-GB). BBC News. 15 January 2021. https://www.bbc.com/news/technology-55684595. 
  72. ↑ @SignalApp (16 January 2021). "Signal is back!". https://twitter.com/SignalApp/status/1350595202872823809. 
  73. ↑ 73.0 73.1 Marlinspike, Moxie (10 January 2022). "New year, new CEO". Signal Messenger. https://signal.org/blog/new-year-new-ceo/. 
  74. ↑ 74.0 74.1 Page, Carly (15 August 2022). "Signal says 1,900 users' phone numbers exposed by Twilio breach". TechCrunch. https://techcrunch.com/2022/08/15/signal-phone-number-exposed-twilio/. 
  75. ↑ Franceschi-Bicchierai, Lorenzo (17 August 2022). "How a Third-Party SMS Service Was Used to Take Over Signal Accounts" (in en). VICE. https://www.vice.com/en/article/qjkvxv/how-a-third-party-sms-service-was-used-to-take-over-signal-accounts. 
  76. ↑ "Signal Has a New President and She Has a Plan" (in en). 6 September 2022. https://gizmodo.com/meredith-whittaker-new-president-of-signal-messaging-1849501653. 
  77. ↑ Singh, Manish (13 January 2021). "Signal's Brian Acton talks about exploding growth, monetization and WhatsApp data-sharing outrage". Yahoo. https://techcrunch.com/2021/01/12/signal-brian-acton-talks-about-exploding-growth-monetization-and-whatsapp-data-sharing-outrage/. 
  78. ↑ "Moxie Marlinspike leaves encrypted-messaging app Signal". BBC. 12 January 2022. https://www.bbc.com/news/technology-59937614. 
  79. ↑ O'Neill, Patrick (3 January 2017). "How Tor and Signal can maintain the fight for freedom in Trump's America". Scoop News Group. https://www.cyberscoop.com/tor-signal-funding-donald-trump-steve-bannon-encryption/. 
  80. ↑ Timm, Trevor (8 December 2016). "Freedom of the Press Foundation's new look, and our plans to protect press freedom for 2017". https://freedom.press/news/freedom-press-foundations-new-look-and-our-plans-protect-press-freedom-2017/. 
  81. ↑ "Signal". Freedom of the Press Foundation. https://freedom.press/crowdfunding/signal/. 
  82. ↑ "TextSecure". Knight Foundation. http://www.knightfoundation.org/grants/201499909/. 
  83. ↑ "Moxie Marlinspike". Shuttleworth Foundation. https://www.shuttleworthfoundation.org/alumni/moxie-marlinspike. 
  84. ↑ "Open Whisper Systems". Open Technology Fund. https://www.opentech.fund/results/supported-projects/open-whisper-systems/. 
  85. ↑ "Signal Technology Foundation". Pro Publica Inc.. 9 May 2013. https://projects.propublica.org/nonprofits/organizations/824506840. 
  86. ↑ Greenberg, Andy (16 November 2023). "Running Signal Will Soon Cost $50 Million a Year". https://www.wired.com/story/signal-operating-costs/. 
  87. ↑ Davenport, Corbin (14 December 2020). "Signal messaging now supports encrypted group video calls". https://www.androidpolice.com/2020/12/14/signal-messaging-now-supports-encrypted-group-video-calls/. 
  88. ↑ Vonau, Manuel (16 December 2021). "Signal significantly ups its video group call limit, surpassing WhatsApp". Android Police. https://www.androidpolice.com/signal-significantly-ups-its-video-group-call-limit-surpassing-whatsapp/. 
  89. ↑ Thatcher, Peter (15 December 2021). "How to build large-scale end-to-end encrypted group video calls". Signal Foundation. https://signal.org/blog/how-to-build-encrypted-group-calls/. 
  90. ↑ Lund, Joshua (1 November 2017). "Expanding Signal GIF search". Open Whisper Systems. https://signal.org/blog/signal-and-giphy-update/. 
  91. ↑ 91.0 91.1 91.2 91.3 "Secure Messaging Scorecard. Which apps and tools actually keep your messages safe?". Electronic Frontier Foundation. 4 November 2014. https://www.eff.org/node/82654. 
  92. ↑ 92.0 92.1 92.2 92.3 92.4 Rottermanner et al. 2015, p. 5
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  94. ↑ 94.0 94.1 Rottermanner et al. 2015, p. 9
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  96. ↑ "Schedule a Message on Signal Android – Signal Support". https://support.signal.org/hc/en-us/articles/5365881590682-Schedule-a-Message-on-Signal-Android. 
  97. ↑ 97.0 97.1 97.2 97.3 Greenberg, Andy (11 October 2016). "Signal, the Cypherpunk App of Choice, Adds Disappearing Messages". Wired. https://www.wired.com/2016/10/signal-cypherpunk-app-choice-adds-disappearing-messages/. Retrieved 11 October 2016. 
  98. ↑ 98.0 98.1 Marlinspike, Moxie (11 October 2016). "Disappearing messages for Signal". Open Whisper Systems. https://www.whispersystems.org/blog/disappearing-messages/. 
  99. ↑ "Introduce the ability to change the app icon. · signalapp/Signal-Android@c963e99". https://github.com/signalapp/Signal-Android/commit/c963e99dca76d8d334c7dfbf0d062305daebfaa2. 
  100. ↑ "Support for receiving formatted messages · signalapp/Signal-Desktop@d9d820e". https://github.com/signalapp/Signal-Desktop/commit/d9d820e72aeaf2175cee658e3325d58b63f17082. 
  101. ↑ "Add initial username link screen + QR code generation. · signalapp/Signal-Android@855e194". https://github.com/signalapp/Signal-Android/commit/855e194baaa50de00f90bd7cb7e3f4ac10b10b9c. 
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  103. ↑ O'Flaherty, Kate. "Signal Will Now Blur Protesters' Faces: Here's How It Works" (in en). https://www.forbes.com/sites/kateoflahertyuk/2020/06/04/secure-messaging-app-signal-launches-new-feature-to-protect-protestors-identities/. 
  104. ↑ Vincent, James (4 June 2020). "Signal announces new face-blurring tool for Android and iOS" (in en). https://www.theverge.com/2020/6/4/21280112/signal-face-blurring-tool-ios-android-update. 
  105. ↑ 105.0 105.1 105.2 "In-app Payments". Signal Messenger. https://support.signal.org/hc/en-us/articles/360057625692-In-app-Payments. 
  106. ↑ 106.0 106.1 Greenberg, Andy (6 January 2022). "Signal's Cryptocurrency Feature Has Gone Worldwide". Wired. https://www.wired.com/story/signal-mobilecoin-cryptocurrency-payments/. Retrieved 12 January 2022. 
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  108. ↑ 108.0 108.1 108.2 108.3 108.4 Lee, Micah (28 September 2017). "How to Use Signal Without Giving Out Your Phone Number" (in en-US). https://theintercept.com/2017/09/28/signal-tutorial-second-phone-number/. 
  109. ↑ "Troubleshooting multiple devices". Signal Messenger LLC. https://support.signal.org/hc/en-us/articles/360007320451-Troubleshooting-multiple-devices#desktop_multiple_device. 
  110. ↑ "Allow different kinds of identifiers for registration · Issue #1085 · signalapp/Signal-Android" (in en). https://github.com/signalapp/Signal-Android/issues/1085. 
  111. ↑ "Discussion: A proposal for alternative primary identifiers". 24 May 2018. https://community.signalusers.org/t/a-proposal-for-alternative-primary-identifiers/3023. 
  112. ↑ Lovejoy, Ben (21 May 2020). "Signal registration lock stops your account being hijacked on a new phone". https://9to5mac.com/2020/05/21/signal-registration-lock/. 
  113. ↑ Fedewa, Joe (27 January 2021). "How to Use Signal on Your Desktop Computer" (in en-US). https://www.howtogeek.com/710253/how-to-use-signal-on-desktop/. 
  114. ↑ Marlinspike, Moxie (17 November 2016). "Safety number updates". Open Whisper Systems. https://whispersystems.org/blog/safety-number-updates/. 
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  116. ↑ Unger et al. 2015, p. 241
  117. ↑ Marlinspike, Moxie; Perrin, Trevor. "The X3DH Key Agreement Protocol". https://signal.org/docs/specifications/x3dh/. 
  118. ↑ 118.0 118.1 118.2 118.3 Unger et al. 2015, p. 239
  119. ↑ Pauli, Darren. "Auditors find encrypted chat client TextSecure is secure". https://www.theregister.co.uk/2014/11/03/how_secure_is_textsecure_pretty_well_secure/. 
  120. ↑ 120.0 120.1 Brook, Chris (10 November 2016). "Signal Audit Reveals Protocol Cryptographically Sound". Kaspersky Lab. https://threatpost.com/signal-audit-reveals-protocol-cryptographically-sound/121892/. 
  121. ↑ 121.0 121.1 Cohn-Gordon et al. 2016
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  124. ↑ Marlinspike, Moxie (18 May 2016). "Open Whisper Systems partners with Google on end-to-end encryption for Allo". Open Whisper Systems. https://signal.org/blog/allo/. 
  125. ↑ "Moxie Marlinspike - 40 under 40". 2016. http://fortune.com/40-under-40/moxie-marlinspike-31/. 
  126. ↑ Marlinspike, Moxie (8 July 2016). "Facebook Messenger deploys Signal Protocol for end to end encryption". Open Whisper Systems. https://whispersystems.org/blog/facebook-messenger/. 
  127. ↑ Gebhart, Gennie (3 October 2016). "Google's Allo Sends The Wrong Message About Encryption". Electronic Frontier Foundation. https://www.eff.org/deeplinks/2016/09/googles-allo-sends-wrong-message-about-encryption. 
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  129. ↑ Greenberg, Andy (14 February 2017). "The Best Encrypted Chat App Now Does Video Calls Too". Wired. https://www.wired.com/2017/02/encryption-app-signal-enables-video-calls-new-privacy-tradeoff/. Retrieved 15 February 2017. 
  130. ↑ 130.0 130.1 130.2 Ganor, Alon (10 December 2020). "Cellebrite's New Solution for Decrypting the Signal App". Cellebrite. https://www.cellebrite.com/en/blog/cellebrites-new-solution-for-decrypting-the-signal-app/. 
  131. ↑ Matthew D. Green [@matthew_d_green] (10 December 2020). "Someone asked me what this Cellebrite post meant, and whether it's a big deal for Signal. From what I can see it just means Cellebrite can read your texts if they have your (unlocked) phone, which, duh.". https://twitter.com/matthew_d_green/status/1337106648016547843. 
  132. ↑ Edward Snowden [@Snowden] (15 December 2020). "No, Cellebrite cannot decrypt Signal communications. What they sell is a forensic device cops connect to insecure, unlockable phones to download a bunch of popular apps' data more easily than doing it manually. They just added Signal to that app list. That's it. There's no magic.". https://twitter.com/Snowden/status/1338859880384368641. 
  133. ↑ Benjakob, Omer (14 December 2020). "Israeli Phone-hacking Firm Claims It Can Now Break Into Encrypted Signal App". Haaretz. https://www.haaretz.com/israel-news/tech-news/.premium-israeli-spy-tech-firm-says-it-can-break-into-signal-app-previously-considered-safe-1.9368581. 
  134. ↑ Wakefield, Jane (22 December 2020). "Signal: Cellebrite claimed to have cracked chat app's encryption" (in en-GB). BBC News. https://www.bbc.com/news/technology-55412230. 
  135. ↑
  136. ↑ Marlinspike, Moxie (23 December 2020). "No, Cellebrite cannot 'break Signal encryption.'". Signal Messenger. https://signal.org/blog/cellebrite-and-clickbait/. 
  137. ↑ Signal [@signalapp] (17 December 2020). "No, Haaretz was duped. The original blog post was about accessing data on an unlocked Android phone in their physical possession. They could have just opened the app to look at the messages.". https://twitter.com/signalapp/status/1339362791153487874. 
  138. ↑ Betz, Bradford (9 February 2021). "Court documents show FBI may have tool to access private Signal messages on locked iPhones". FOXBusiness. https://www.foxbusiness.com/technology/fbi-tool-access-private-signal-messages-locked-iphones. 
  139. ↑ Abrams, Lawrence (23 October 2018). "Signal Desktop Leaves Message Decryption Key in Plain Sight" (in en-us). https://www.bleepingcomputer.com/news/security/signal-desktop-leaves-message-decryption-key-in-plain-sight/. 
  140. ↑ 140.0 140.1 "Privacy Policy". Signal Messenger LLC.. 25 May 2018. https://signal.org/legal/#privacy-policy. 
  141. ↑ 141.0 141.1 141.2 Moxie Marlinspike (3 January 2013). "The Difficulty Of Private Contact Discovery". Open Whisper Systems. https://whispersystems.org/blog/contact-discovery/. 
  142. ↑ Rottermanner et al. 2015, p. 4
  143. ↑ Marlinspike, Moxie (26 September 2017). "Technology preview: Private contact discovery for Signal". Open Whisper Systems. https://signal.org/blog/private-contact-discovery/. 
  144. ↑ Greenberg, Andy (26 September 2017). "Signal Has a Fix for Apps' Contact-Leaking Problem". Wired. https://www.wired.com/story/signal-contact-lists-private-secure-enclave. Retrieved 28 September 2017. 
  145. ↑ Frosch et al. 2016, p. 7
  146. ↑ Brandom, Russell (29 July 2014). "Signal brings painless encrypted calling to iOS". https://www.theverge.com/2014/7/29/5945547/signal-brings-painless-encrypted-calling-whisper-systems-moxie-marlinspike. 
  147. ↑ Moxie Marlinspike (5 May 2014). "Private Group Messaging". Open Whisper Systems. https://whispersystems.org/blog/private-groups/. 
  148. ↑ Moxie Marlinspike (24 February 2014). "The New TextSecure: Privacy Beyond SMS". Open Whisper Systems. https://whispersystems.org/blog/the-new-textsecure/. 
  149. ↑ Andy Greenberg (9 December 2013). "Ten Million More Android Users' Text Messages Will Soon Be Encrypted By Default". Forbes. https://www.forbes.com/sites/andygreenberg/2013/12/09/ten-million-more-android-users-text-messages-will-soon-be-encrypted-by-default/. 
  150. ↑ Seth Schoen (28 December 2013). "2013 in Review: Encrypting the Web Takes A Huge Leap Forward". Electronic Frontier Foundation. https://www.eff.org/deeplinks/2013/12/2013-review-encrypting-web-takes-huge-leap-forward. 
  151. ↑ 151.0 151.1 Moxie Marlinspike (9 December 2013). "TextSecure, Now With 10 Million More Users". Open Whisper Systems. https://whispersystems.org/blog/cyanogen-integration/. 
  152. ↑ CyanogenMod (7 January 2014). "android_external_whispersystems_WhisperPush". https://github.com/CyanogenMod/android_external_whispersystems_WhisperPush. 
  153. ↑ Sinha, Robin (20 January 2016). "CyanogenMod to Shutter WhisperPush Messaging Service on February 1". NDTV. http://gadgets.ndtv.com/mobiles/news/cyanogenmod-to-shutter-whisperpush-messaging-service-on-february-1-792064. 
  154. ↑ 154.0 154.1 Edge, Jake (18 May 2016). "The perils of federated protocols". https://lwn.net/Articles/687294/. 
  155. ↑ Le Bihan, Michel (24 May 2016). "README.md". LibreSignal. https://github.com/LibreSignal/LibreSignal/blob/master/README.md. 
  156. ↑ "Support for using Signal without Play Services · signalapp/Signal-Android@1669731" (in en). https://github.com/signalapp/Signal-Android/commit/1669731329bcc32c84e33035a67a2fc22444c24b. 
  157. ↑ Marlinspike, Moxie (31 March 2016). "Reproducible Signal builds for Android". Open Whisper Systems. https://whispersystems.org/blog/reproducible-android/. 
  158. ↑ "Improving first impressions on Signal" (in en). https://signal.org/blog/keeping-spam-off-signal/. 
  159. ↑ "Surveillance Self-Defense. Communicating with Others". Electronic Frontier Foundation. 23 October 2014. https://ssd.eff.org/en/module/communicating-others. 
  160. ↑ Eddy, Max (11 March 2014). "Snowden to SXSW: Here's How To Keep The NSA Out Of Your Stuff". PC Magazine: SecurityWatch. http://securitywatch.pcmag.com/security/321511-snowden-to-sxsw-here-s-how-to-keep-the-nsa-out-of-your-stuff. 
  161. ↑ "The Virtual Interview: Edward Snowden - The New Yorker Festival". The New Yorker. 11 October 2014. https://www.youtube.com/watch?v=fidq3jow8bc. 
  162. ↑ "Prying Eyes: Inside the NSA's War on Internet Security". Der Spiegel. 28 December 2014. http://www.spiegel.de/international/germany/inside-the-nsa-s-war-on-internet-security-a-1010361.html. 
  163. ↑ "Presentation from the SIGDEV Conference 2012 explaining which encryption protocols and techniques can be attacked and which not". Der Spiegel. 28 December 2014. http://www.spiegel.de/media/media-35535.pdf. Retrieved 23 January 2015. 
  164. ↑ Bilton, Nick (26 August 2016). "How the Clinton Campaign Is Foiling the Kremlin". Vanity Fair. http://www.vanityfair.com/news/2016/08/how-the-clinton-campaign-is-foiling-the-kremlin. Retrieved 1 September 2016. 
  165. ↑ Blake, Andrew (27 August 2016). "Democrats warned to use encryption weeks before email leaks". The Washington Times, LLC. http://www.washingtontimes.com/news/2016/aug/27/dems-urged-encrypt-their-communications-weeks-prio/. 
  166. ↑ Whittaker, Zack (16 May 2017). "In encryption push, Senate staff can now use Signal for secure messaging". ZDNet. http://www.zdnet.com/article/in-encryption-push-senate-approves-signal-for-encrypted-messaging/. 
  167. ↑ Wyden, Ron (9 May 2017). "Ron Wyden letter on Signal encrypted messaging". Zack Whittaker, ZDNet. https://www.documentcloud.org/documents/3723701-Ron-Wyden-letter-on-Signal-encrypted-messaging.html. 
  168. ↑ "Signal's Messenger Eavesdropping Exploit - SaltDNA CTO Shares His Views". https://saltdna.com/news/signal%27s-messenger-eavesdropping-exploit-saltdna-cto-shares-his-views. 
  169. ↑ "1943 - project-zero - Project Zero - Monorail". https://bugs.chromium.org/p/project-zero/issues/detail?id=1943. 
  170. ↑ "Signal Messenger Eavesdropping Exploit Confirmed—What You Need to Know". https://www.forbes.com/sites/daveywinder/2019/10/05/signal-messenger-eavesdropping-exploit-confirmedwhat-you-need-to-know. 
  171. ↑ "EU Commission to staff: Switch to Signal messaging app". 20 February 2020. https://www.politico.eu/article/eu-commission-to-staff-switch-to-signal-messaging-app/. 
  172. ↑ Molla, Rani (3 June 2020). "From Citizen to Signal, the most popular apps right now reflect America's protests" (in en). https://www.vox.com/recode/2020/6/3/21278558/protest-apps-signal-citizen-twitter-instagram-george-floyd. 
  173. ↑ Lee, Timothy B. (8 July 2020). "Hong Kong downloads of Signal surge as residents fear crackdown" (in en-us). https://arstechnica.com/tech-policy/2020/07/hong-kong-downloads-of-signal-surge-as-residents-fear-crackdown/. 
  174. ↑ "How to share documents and news tips with Washington Post journalists." (in en). The Washington Post. https://www.washingtonpost.com/anonymous-news-tips/. 
  175. ↑ Hoyland, Luke; Fenn, Chris. "Contact the Guardian securely" (in en). http://www.theguardian.com/help/ng-interactive/2017/mar/17/contact-the-guardian-securely. 
  176. ↑ "Tips" (in en-US). The New York Times. 14 December 2016. ISSN 0362-4331. https://www.nytimes.com/tips. 
  177. ↑ "WSJ.com Secure Drop". https://www.wsj.com/tips. 
  178. ↑ Marczak, Bill; Scott-Railton, John; Berdan, Kristin; Razzak, Bahr Abdul; Deibert, Ron (15 July 2021) (in en-US). Hooking Candiru: Another Mercenary Spyware Vendor Comes into Focus. https://citizenlab.ca/2021/07/hooking-candiru-another-mercenary-spyware-vendor-comes-into-focus/. Retrieved 20 July 2021. 
  179. ↑ "PM lodges report over hacked Telegram, Signal accounts". The Star. https://www.thestar.com.my/news/nation/2022/08/09/pm-lodges-report-over-hacked-telegram-signal-accounts. 
  180. ↑ Greenberg, Andy (6 April 2021). "Signal Adds a Payments Feature—With a Privacy-Focused Cryptocurrency". Wired. https://www.wired.com/story/signal-mobilecoin-payments-messaging-cryptocurrency/. Retrieved 12 January 2022. 
  181. ↑ "Signal Adds Cryptocurrency Support". 7 April 2021. https://www.schneier.com/blog/archives/2021/04/wtf-signal-adds-cryptocurrency-support.html. 
  182. ↑ Cox, Joseph (19 December 2016). "Signal Claims Egypt Is Blocking Access to Encrypted Messaging App". Vice Media LLC. https://motherboard.vice.com/en_us/article/nz755w/signal-claims-egypt-is-blocking-access-to-encrypted-messaging-app. 
  183. ↑ 183.0 183.1 Marlinspike, Moxie (21 December 2016). "Doodles, stickers, and censorship circumvention for Signal Android". Open Whisper Systems. https://whispersystems.org/blog/doodles-stickers-censorship/. 
  184. ↑ Greenberg, Andy (21 December 2016). "Encryption App 'Signal' Fights Censorship with a Clever Workaround". Wired. https://www.wired.com/2016/12/encryption-app-signal-fights-censorship-clever-workaround/. Retrieved 20 July 2017. 
  185. ↑ "SignalServiceNetworkAccess.kt". Signal Foundation. https://github.com/signalapp/Signal-Android/blob/main/app/src/main/java/org/thoughtcrime/securesms/push/SignalServiceNetworkAccess.kt. 
  186. ↑ 186.0 186.1 186.2 Frenkel, Sheera (2 January 2018). "Iranian Authorities Block Access to Social Media Tools". https://www.nytimes.com/2018/01/02/technology/iran-protests-social-media.html. 
  187. ↑ 187.0 187.1 "Domain Fronting for Iran #7311". 1 January 2018. https://github.com/WhisperSystems/Signal-Android/issues/7311. 
  188. ↑ Brandom, Russell (2 January 2018). "Iran blocks encrypted messaging apps amid nationwide protests". https://www.theverge.com/2018/1/2/16841292/iran-telegram-block-encryption-protest-google-signal. 
  189. ↑ Marlinspike, Moxie (1 May 2018). "A letter from Amazon". Open Whisper Systems. https://signal.org/blog/looking-back-on-the-front/. 
  190. ↑ Gallagher, Sean (2 May 2018). "Amazon blocks domain fronting, threatens to shut down Signal's account". https://arstechnica.com/information-technology/2018/05/amazon-blocks-domain-fronting-threatens-to-shut-down-signals-account/. 
  191. ↑ Parrelli, Greyson (4 April 2019). "Attempt to resolve connectivity problems for some users.". Signal Messenger LLC. https://github.com/signalapp/Signal-Android/commit/9aed2343c141b1b3809f7eaccce61c22e342fda7. 
  192. ↑ "حذف سیگنال از فروشگاه‌های نرم‌افزار آنلاین در ایران" (in fa). 15 January 2021. https://www.bbc.com/persian/iran-55679732. 
  193. ↑ "پیام‌رسان سیگنال به "دستور کمیته فیلترینگ" از فروشگاه‌های آنلاین در ایران حذف شد" (in fa). Radio Farda. https://www.radiofarda.com/a/signal-app-iran-government/31047041.html. 
  194. ↑ Jones, Rhett (27 January 2021). "Signal Blocked by Iran as Encrypted Messaging App's Popularity Explodes". https://gizmodo.com/signal-blocked-by-iran-as-encrypted-messaging-apps-popu-1846141987. 
  195. ↑ Rita, Liao (15 March 2021). "Rising encrypted app Signal is down in China". Verizon Media. https://techcrunch.com/2021/03/15/signal-is-down-in-china/. 
  196. ↑ Nierenberg, Amelia (11 June 2020). "Signal Downloads Are Way Up Since the Protests Began". https://www.nytimes.com/2020/06/11/style/signal-messaging-app-encryption-protests.html. 
  197. ↑ Nebehay, Stephanie (17 March 2021). "U.N. team seeks evidence linking Myanmar military leaders to crimes" (in en). Reuters. https://www.reuters.com/article/us-myanmar-politics-un-crimes-idUSKBN2B90XV. 
  198. ↑ 198.0 198.1 198.2 Newton, Casey (26 January 2021). "🚨 The battle inside Signal" (in en). https://www.platformer.news/p/-the-battle-inside-signal. 
  199. ↑ Cohn-Gordon et al. 2016
  200. ↑ Tripathi, Rahul (11 April 2016). "Dangerous Signal: This encrypted app is helping ISIS members in India to communicate". The Times of India. https://telecom.economictimes.indiatimes.com/news/dangerous-signal-this-encrypted-app-is-helping-isis-members-in-india-to-communicate/51774226. "A group of terrorist suspects in India said to be inspired by Islamic State wanted to emulate US whistleblower Edward Snowden and use encrypted communication tool Signal to stay in touch, it was revealed in interrogation by the National Investigation Agency (NIA)." 
  201. ↑ Frenkel, Sheera (11 January 2021). "Fringe Groups Splinter Online After Facebook and Twitter Bans". The New York Times. https://www.nytimes.com/2021/01/11/technology/fringe-groups-splinter-online-after-facebook-and-twitter-bans.html. "In the days since rioters stormed Capitol Hill, fringe groups like armed militias, QAnon conspiracy theorists and far-right supporters of President Trump have vowed to continue their fight in hundreds of conversations on a range of internet platforms. Some of the organizers have moved to encrypted messaging apps like Telegram and Signal, which cannot be as easily monitored as social media platforms." 
  202. ↑ Glaser, April (11 August 2018). "How White Supremacists Planned Their Rally in D.C.". Slate. https://slate.com/technology/2018/08/how-white-supremacists-planned-their-rally-in-d-c-and-what-it-tells-us-about-the-strength-of-their-movement.html. "This year, Kessler and his fellow white nationalist co-organizers switched much of their rally planning throughout the summer to private groups on Facebook Messenger and the encrypted texting app Signal..." 
  203. ↑ Daly, Kye (11 January 2021). "The online far right is moving underground". Axios. https://www.axios.com/the-online-far-right-is-moving-underground-e429d45d-1b30-46e0-82a3-6e240bf44fef.html. "Telegram and Signal are far more stable and secure and could prove more enduring homes and recruitment stations for far-right groups." 
  204. ↑ Glaser, April (9 October 2018). "White Supremacists Still Have a Safe Space Online". Slate. https://slate.com/technology/2018/10/discord-safe-space-white-supremacists.html. "A year later, in the runup to an ultimately barely attended sequel to Unite the Right in D.C., organizers appeared to stay off the platform, opting instead to discuss logistics over Facebook Messenger and the encrypted texting app Signal." 
  205. ↑ "Secure messaging app Signal has been effectively criminalized in Turkey - Nordic Monitor" (in en-US). 2021-07-08. https://nordicmonitor.com/2021/07/secure-messaging-app-signal-has-been-effectively-criminalised-in-turkey/. 
  206. ↑ "Turkey's new media law is bad news – but don't report it" (in en-US). https://www.brookings.edu/articles/turkeys-new-media-law-is-bad-news-but-dont-report-it/. 

Bibliography

External links




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