稜鏡計畫自2007年開始實施，此計畫允許美國政府透過合作對象如谷歌、蘋果、Facebook與微軟的協助，即時監控美國以外的使用者，或是與國 外人士通信的美國公民。監控人物層級高至國家如屆時德國總理梅克爾與巴西總統羅賽夫。此計畫於2013年由愛德華·史諾登揭露，當時的史諾登只是美國國安局外包商的員工竟能獲得高機密文件，讓美國政府當時的處境更加難堪。
iOS 載點:
https://itunes.apple.com/us/app/signal-private-messenger/id874139669
Android 載點:
https://play.google.com/store/apps/details?id=org.thoughtcrime.securesms&hl=zh_TW
Signal 桌面版:
Signal Desktop Chrome Web Store
Open Whisper Systems團隊有鑑於此，為了防範政府部門侵犯個人隱私，開發《Signal》加密通訊軟體，此App於2015年5月在iOS上推出，Android版本也在11月2日推出。
此軟體提供SMS訊息的收發、影片和語音通話，所有訊息都經過加密處理，加密後的隱私性符合電子前線基金會(Electronic Frontier Foundation)的7項安全標準，其中包含訊息是否加密與軟體開發者是否能閱讀訊息...等檢測。Open Whisper Systems甚至開放《Signal》的程式原始碼，除了供大眾檢驗並無置入後門軟體知外，也讓使用者能進一步研發更多的應用方式。
Android版本的《Signal》，則整合了原本用於加密通話的《RedPhone》，與傳遞加密訊息的《TextSecure》，如今Android用戶可以用更簡單的方式保護個人隱私。
最佳代言人史諾登也在推特上與大家分享了版本的整合消息，且表示他每天都在使用《Signal》，還順便標記了FBI，顯然對於此軟體的加密方式非常有信心。
Android版本甫上架不到兩天，Signal下載次數已破一百萬，或許史諾登的「登」高一呼有加成效果，但如此驚人的下載數量仍說明了，大多數人對於網路通訊的隱私性並不信任。
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Privacy is possible, Signal makes it easy.
Using Signal, you can communicate instantly while avoiding SMS fees, create groups so that you can chat in real time with all your friends at once, and share media or attachments all with complete privacy. The server never has access to any of your communication and never stores any of your data.
★ Say Anything. Signal uses an advanced end to end encryption protocol that provides privacy for every message every time.
★ Open Source. Signal is Free and Open Source, enabling anyone to verify its security by auditing the code. Signal is the only private messenger that uses open source peer-reviewed cryptographic protocols to keep your messages safe.
★ Be Yourself - Signal uses your existing phone number and address book. There are no separate logins, usernames, passwords, or PINs to manage or lose.
★ Group Chat. Signal allows you to create encrypted groups so you can have private conversations with all your friends at once. Not only are the messages encrypted, but the Signal server never has access to any group metadata such as the membership list, group title, or group icon.
★ Fast. The Signal protocol is designed to operate in the most constrained environment possible. Using Signal, messages are instantly delivered to friends.
★ Speak Freely - Make crystal-clear phone calls to people who live across town, or across the ocean, with no long-distance charges.
Signal is not currently compatible with tablets, but support for larger screens is on our roadmap and will be included in a future release!
For support, questions, or more information, please visit:
http://support.whispersystems.org
Source code:
https://github.com/WhisperSystems/Signal-Android
參考資料:
官方網站 - Open Whisper Systems
Signal Desktop
How to: Use Signal on iOS
How to: Use Signal on Android
