Screenshot of Cryptocat 2.1.5
|Original author(s)||Nadim Kobeissi|
|Developer(s)||Cryptocat contributors |
|Initial release||19 May 2011|
|Stable release||2.2.2 / June 12, 2014|
|Available in||English, Arabic, Bulgarian, Burmese, Chinese, Danish, Dutch, Farsi, French, German, Greek, Hebrew, Hungarian, Italian, Japanese, Korean, Latvian, Norwegian, Polish, Portuguese, Romanian, Russian, Slovenian, Spanish, Swedish, Tibetan|
|License||Affero General Public License|
Cryptocat is an open source web and mobile application intended to allow secure, encrypted online chatting. Cryptocat uses end-to-end encryption and encrypts chats on the client side, only trusting the server with data that is already encrypted. Cryptocat is offered as an app for Mac OS X or as a browser extension for Google Chrome, Mozilla Firefox, Apple Safari, Opera and as a mobile app for iPhone.
Cryptocat's stated goal is to make encrypted communications more accessible to average users. The chat software aims to strike a balance between security and usability—offering more privacy than services such as Google Talk or Internet Relay Chat, while maintaining a higher level of accessibility than Pidgin. In June 2013, Cryptocat was used by journalist Glenn Greenwald while in Hong Kong to meet NSA whistleblower Edward Snowden for the first time, after other encryption software failed to work. In November 2013, Cryptocat was banned in Iran, shortly after the election of Iran's new president Hassan Rouhani who had promised more open Internet laws.
Cryptocat is developed by the Cryptocat team and is released under the GPLv3 license. In June 2014, Cryptocat was ranked first in a three-month study evaluating the security and usability of instant messaging encryption software, conducted by the German PSW Group.
Cryptocat allows any desktop with a modern web browser to quickly set up an end-to-end encrypted chat environment. The browser's accessibility is frequently touted by the project as the reason why it chose the platform. Cryptocat is currently compatible with Google Chrome, Mozilla Firefox, Apple Safari, Opera and also offers an application for iOS devices.
Cryptocat uses the Off-the-Record Messaging (OTR) protocol for encrypted private messaging, allowing two parties to chat in private. Cryptocat also uses its own group messaging protocol to allow for group instant messaging conversations. Since Cryptocat generates new key pairs for every chat, it implements a form of perfect forward secrecy. Cryptocat also offers encrypted file and photo sharing, allowing users to send documents and photos to each other using end-to-end encryption.
Cryptocat also may be used in conjunction with Tor in order to anonymize the client's network traffic. The project also plans to create an embedded version for use with Raspberry Pi devices for use by non-profits. As of July 2013, a Commotion-compatible version was in development.
Since 2013, Cryptocat has offered the ability to connect to Facebook Messenger to initiate encrypted chatting with other Cryptocat users. The feature was meant to help offer an alternative to the regular Cryptocat chat model which does not offer long-term contact lists:
Effectively, what Cryptocat is doing is benefitting from your Facebook Chat contact list as a readily available buddy list. As a compliment to Cryptocat’s ephemeral group chat feature, Encrypted Facebook Chat lets you view which of your friends are online and allows you to immediately set up encrypted chat with them. Users will still be able chat with non-Cryptocat users from within Cryptocat — although those conversations will not be encrypted.
— Cryptocat, Cryptocat, Now with Encrypted Facebook Chat, 
Cryptocat uses the Off-the-Record Messaging (OTR) protocol for encrypted private messaging, allowing two parties to chat in private. For group messaging, Cryptocat uses a group chat protocol deploying Curve25519, AES-256, and HMAC-SHA512, all industry standards for cryptography applications. All messages sent in Cryptocat, including group chat messages and file transfers, are end-to-end encrypted, which means that they can only be read by the intended recipients and not by the network during transit. Cryptocat provides cryptographic properties of confidentiality, integrity, authentication and forward secrecy for all conversations, and also provides deniability for file transfers and and private OTR chats.
In 2014, Cryptocat made improvements to user authentication, making it easier for users to authenticate and preventing MITM attacks. The improvements came after an audit by iSec Partners criticized the previous authentication model as insufficient.
Cryptocat also publishes its server configuration files and instructions for others to set up their own servers for the Cryptocat client to connect to.
Some versions of Cryptocat have been questioned for utilizing the browser to encrypt messages, which some researchers feel is less secure than the desktop environment. More recent versions have relied on browser-native random number generation which is considered more secure.[by whom?]
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 April 19, 2013. Private messages were not affected, and the bug had been resolved a month prior. After Thomas's research was released, Cryptocat issued a security advisory and requested that all users ensure that they had upgraded. Since 2011, a warning regarding the experimental nature of the project has been in place on the website's front page and within the software itself. The Cryptocat blog posted a warning, informing users that group conversations they had using the software in the past may have been compromised.
Cryptocat developer Nadim Kobeissi claims that he was detained and questioned at the U.S. border by the DHS in June 2012 about its censorship resistance. He tweeted about the incident afterwards, resulting in media coverage and a spike in the popularity of Cryptocat.
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