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RedPhone – Android Encrypted Voice Communication

RedPhone – Android Encrypted Voice Communication

ETP Update: Red Phone is now integrated in Whisper System’s “Signal” app which provides end to end encrypted text messaging and voice communication. Signal is available for iPhone and Android operating systems.

RedPhone by Open Whisper Systems, makes private communication simple. Free, world-wide, end-to-end encryption for your calls, securing your conversations so that nobody can listen in. RedPhone was originally developed by the well known security researcher Moxie Marlinspike, and was procured by Twitter when he joined the company in 2011. Redphone was briefly unavailable but has now returned as an independent open source project.

When first starting RedPhone, the app prompts you to register your phone number. This is so anyone with your phone number in their contact list will be able to know you have Redphone and are given the option to secure the call to you using Redphone. This only works if both parties have Redphone. Redphone acts as a dialer, resembling the phone dialer you use by default to make phone calls. When searching for a contact to call with Redphone only those who have installed Redphone or the Iphone version Signal, will show up in the contact list. RedPhone doesn’t ask for passwords, logins, or even for users to create an account. The app is designed with privacy in mind, so it requires as little from you as it can. Note that RedPhone uses an SMS message to confirm registration, so it might not work on a Wi-Fi only tablet.

  • RedPhone uses your normal phone number to make and receive calls, so you don’t need yet another identifier.
  • RedPhone calls are encrypted end-to-end, but function just like you’re used to.
  • Free and Open Source, enabling anyone to verify its security by auditing the code.
  • Uses wifi or data, not your plan’s voice minutes.
  • All RedPhone calls are free, including long distance and international.
  • Uses the ZRTP protocol created by PGP’s creator Phil Zimmermann.

When you and your Redphone recipient initiate a phone call both parties will exchange a one redphone-calltime encryption key. To verify you have successfully exchanged keys and there was no tampering or MITM attack against your session, you will both receive the same two random word ID. You both should repeat the words back to each other. The example given here is the words “swelter midsummer”. If the words on both ends match, your conversation is secure. If they are different, there is a problem and the call should be terminated.






If you receive a Redphone call, your Redphone app will take control of the call. Here is an example of an incoming call. You would just slide the phone icon to accept the call.








If you make a regular unsecured call to someone, and that person has Redphone or redphone-secure-call-optionSignal installed on their phone you will automatically get a prompt asking you if you would like to a secure call. This will happen even if the person is not in your contacts.







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