| Cryptocat | |
|---|---|
 | |
 Cryptocat 3.1.24 running on Windows 10. | |
| Original author | Nadim Kobeissi |
| Developers | Nadim Kobeissi and contributors[1] |
| Initial release | 19 May 2011 (2011-05-19) |
| Final release | |
| Written in | JavaScript |
| Operating system | Cross-platform |
| Available in | 3 languages |
| Type | Secure communication |
| License | GNU General Public License |
| Website | crypto |
| Repository | |
Cryptocat is a discontinuedopen-sourcedesktop application intended to allow encryptedonline chatting available forWindows,OS X, andLinux.[3] It usesend-to-end encryption to secure all communications to other Cryptocat users. Users are given the option of independently verifying their buddies' device lists and are notified when a buddy's device list is modified and all updates are verified through the built-in update downloader.[4]
Cryptocat was created byNadim Kobeissi and further developed along with a community of open source contributors and is published under the terms of theGPLv3 license, although it has since been discontinued.
Cryptocat was first launched on 19 May 2011 as aweb application.
In June 2012, Kobeissi said he was detained at the U.S. border by theDHS and questioned about Cryptocat's censorship resistance. He tweeted about the incident afterwards, resulting in media coverage and a spike in the popularity of the software.[5]
In June 2013, security researcher Steve Thomas pointed out a security bug that could be used to decrypt any group chat message that had taken place using Cryptocat between September 2012 and 19 April 2013.[6][7] Private messages were not affected, and the bug had been resolved a month before. In response, Cryptocat issued a security advisory, requested that all users ensure that they had upgraded, and informed users that past group conversations may have been compromised.[7]
In February 2014, an audit by iSec Partners criticized Cryptocat's authentication model as insufficient.[8] In response, Cryptocat made improvements to user authentication, making it easier for users to authenticate and detectman-in-the-middle attacks.[9]
In February 2016, citing dissatisfaction with the project's current state after 19 months of non-maintenance, Kobeissi announced that he would be taking Cryptocat temporarily offline and discontinuing the development of its mobile application, pending a complete rewrite and relaunch of the software.[10] In March 2016 Kobeissi announced the re-release of Cryptocat, rewritten completely as desktop software instead of the original web application software, as a public beta and the resumption of the service.[11] The new desktop-centric approach allowed Cryptocat to benefit from stronger desktop integration, in a style similar toPidgin.
In February 2019, it was announced that Cryptocat would be discontinued.[12] As of December 2019, the cryptocat domain is for sale and links to the site for theWire messenger.[13]
Cryptocat allows its users to set upend-to-end encrypted chat conversations. Users can exchange one-to-one messages, encrypted files, photos as well as create and share audio/video recordings. All devices linked to Cryptocat accounts will receiveforward secure messages, even when offline.
All messages, files and audio/video recordings sent over Cryptocat are end-to-end encrypted. Cryptocat users link their devices to their Cryptocat account upon connection, and can identify each other's devices via the client's device manager in order to preventman-in-the-middle attacks. Cryptocat also employs aTrust on first use mechanism in order to help detect device identity key changes.
Cryptocat also includes a built-in auto-update mechanism that automatically performs a signature check on downloaded updates in order to verify authenticity, and employs TLScertificate pinning in order to prevent network impersonation attacks.
Originally in 2013, Cryptocat offered the ability to connect to Facebook Messenger to initiate encrypted chatting with other Cryptocat users.[14] According to the developers, the feature was meant to help offer an alternative to the regular Cryptocat chat model which did not offer long-term contact lists.[15] This feature was disconnected in November 2015.
In June 2013, Cryptocat was used by journalistGlenn Greenwald while inHong Kong to meetNSA whistleblowerEdward Snowden for the first time, after other encryption software failed to work.[16]
In November 2013, Cryptocat was banned inIran, shortly after the election of Iran's new presidentHassan Rouhani who had promised more open Internet laws.[17]
Cryptocat was listed on theElectronic Frontier Foundation's "Secure Messaging Scorecard" from 4 November 2014 until 13 March 2016. During that time, Cryptocat had a score of 7 out of 7 points on the scorecard. It had received points for having communications encrypted in transit, having communications encrypted with keys the provider did not have access to (end-to-end encryption), making it possible for users to independently verify their correspondent's identities, having past communications secure if the keys were stolen (forward secrecy), having its code open to independent review (open-source), having its security designs well-documented, and having completed an independent security audit.[18]
Cryptocat uses aDouble Ratchet Algorithm in order to obtainforward and future secrecy across messages, after a session is established using a four-wayElliptic-curve Diffie–Hellman handshake. The handshake mixes in long-term identity keys, an intermediate-term signed pre-key, and a one-time use pre-key.[19] The approach is similar to the encryption protocol adopted for encrypted messaging by theSignal mobile application. Cryptocat's goal is for its messages to obtain confidentiality, integrity, source authenticity, forward and future secrecy and indistinguishability even over a network controlled by an active attacker.[4] The forward secrecy features of the protocol that Cryptocat uses are similar to those first introduced byOff-the-Record Messaging.
Cryptocat uses theAdvanced Encryption Standard inGalois/Counter Mode for authenticated encryption,Curve25519 for Elliptic curve Diffie-Hellman shared secret agreement,HMAC-SHA256 for key derivation andEd25519 for signing.[20][21] In order to limit the effect of a long-term identity key compromise, long-term keys are used exclusively once for the initialAuthenticated Key Exchange, and once for signing a newly generated intermediate-term signed pre-key.
For the transport layer, Cryptocat adopts theOMEMO Multi-End Message and Object Encryption standard, which also gives Cryptocat multi-device support and allows for offline messaging.[4]
Cryptocat's network relies on aXMPP configuration served overWebSockets. According to the project's mission statement, Cryptocat's network only relays encrypted messages and does not store any data.[1] In addition to the Cryptocat client's end-to-end encryption protocol, client-server communication is protected byTLS.
From March 2011 until March 2016, Cryptocat was officially distributed through theGoogle Chrome Web Store, theApple App Store and other official channels controlled by targeted platforms. After Cryptocat's re-write into desktop software in March 2016, the software became distributed exclusively through Cryptocat's own servers, which also handle signed update delivery.[22]
