Secure mobile calls and text messages
TextSecure and RedPhone are Android-only apps that encrypt text messages and voice calls between phones running the same applications. They have been developed by Whisper Systems, a company headed by renowned security researcher Moxie Marlinspike. Both applications are free and open source, and have been designed to be exceptionally easy to set up and use without worrying about obtaining and storing public keys.
RedPhone runs over Wi-Fi or data connection rather than the mobile phone network, while TextSecure runs over standard SMS channels.
Calls, texts, email and videoconferencing
Silent Circle is for iOS and Android. The company is led by Phil Zimmermann, the creator of the PGP encryption program, and offers four apps for secure email, text messaging, voice calls (with up to six people) and video conferencing with other Silent Circle users.
The apps themselves are free to download, but to use them requires a subscription (currently $120 - £80 - for 12 months.)
For an extra $288 (£193) per year you can also make use of the company's Out-Circle Access service, which allows you to use the apps to communicate with anyone - not just other Silent Circle users.
Your communications are secure from your phone to Silent Circle's servers, after which they are sent on to their destination unsecured. This can be useful if you are abroad and suspect that the local communications infrastructure may not be secure, but need to contact someone who is not an existing Silent Circle user.
Threema is a secure mobile messaging application that lets you send encrypted text messages, photos and video clips. It can find other Threema users from your contacts automatically and collect their public keys, or you can add them manually.
When Threema finds a contact automatically it gives them an orange verification level. This lets you know that you have not collected their public key in person, so it may not be genuine.
As an alternative, the application can generate a scannable QR code containing key information which you can scan directly from a contact's phone into yours. Contacts added like this are given a more secure green verification level to let you know that you have personally verified their source.
Threema costs £1.37 for Android and £1.49 for iOS.
Quick online text encryption
Infoencrypt is a free, simple web-based service that allows you to type in a message and choose a password for its encryption. You can then copy and paste the encrypted text into any email program and send it.
The recipient receives the encrypted text along with Infoencrypt's web address, and decrypts it by copying and pasting it onto the web page, typing in the password and clicking decrypt.
The obvious problem is how the recipient knows the password. It clearly can't be included in the email, so to use Infoencrypt you either need to have arranged a password beforehand, or to send it by a different method such as text message or phone call.
It's also important to bear in mind that the site provides no information about the encryption algorithm it uses, so there is no way to verify it's real level of security.