Staying connected while on the go is a balancing act. On the one hand, connecting means sharing. If we don’t share our e-mail address, phone number, and maybe location, most of the apps we love just won’t work. We need website passwords and credit card numbers with us at all times, but we sure do not want to share them. Even if we lose our phone. That’s where Mobile Cipher comes in.

Mobile Cipher from Bulgaria-based Leon Anavi allows you to protect any text using a secret key you select. The resulting code is also a string of text, so you can store or transmit it however you like, including via SMS.

Mobile Cipher is a a free app, and it is compatible with Symbian OS – S60 3.1, 3.2, and 5.0 devices (a complete list is available on the developer’s website). I tested it on my Nokia N97.

Enter any text you want to protect.

Mobile Cipher opens with a screen into which you enter the text you want to protect. You can either type the text directly or paste text that you copied from another app.

Choose encode ...

... and enter your secret key.

Mobile Cipher encrypts your text using a secret key that you choose. Note the app sets the text input block to accept only digits. I asked the developer about this restriction, and he told me it is for usability reasons. His encryption algorithm could easily accept secret keys that consist of strings of any Unicode characters, including for example Cyrillic characters. However, he wanted the app to be compatible with SMS transmission, including the ability to send your secret key via SMS. Forcing the secret key to use only digits insures this compatibility.

The resulting secret code is still characters, compatible with SMS and other text-only processes.

Once you have the encrypted text string, you can do with it anything you can do with any other text string. Mobile Cipher includes a menu option for you to send the text as an SMS.   You can also paste the text into a notes field in your contacts list, providing for example safe girlfriend notes. I have a ToDo note that holds website passwords and is easily accessible from the home screen of my Nokia N97.

If you text the code to a friend, the friend will need your secret key. They can then decode your message either with Mobile Cipher installed on their Nokia, or they can use a service on the Mobile Cipher website.

Paste any encrypted text into the app ...

... and decode it using the same secret key you used to encode the message.

Note the your secret key is applied PER MESSAGE. This means you can encode text you want to share with friends using one key (that you share with them) while encoding other messages with a secret key you never share. This has two ramifications:

• The app does not store your key anywhere. This is secure, but if you forget your key you are out of luck. The app can’t recover what it didn’t store. You would not want it to be able to divulge a key to someone hacking your device anyway.
• If you make a mistake when entering the encryption key, you’re also out of luck. Watch the screen as you type in the key — you will see each character for a moment before the screen obscures it.

The back story on Mobile Cipher is interesting, too. The app was developed by Leon Anavi in his spare time for entry in the Nokia Call4Mobile Applications contest in Bulgaria. Leon received help from Nokia Bulgaria to register to Ovi as an individual, to sign Mobile Cipher through public beta of Nokia Signing Symbian apps for free (now no longer in beta) and to promote it to Ovi Store. If you check out his site, you’ll see the sort of reach individuals can get with a good idea, some creative coding, and Ovi Store. Mobile Cipher has been downloaded from 127 counties, with approximately 30% of all downloads coming from India. Approximately 70% of the devices using the app are Nokia touch-enabled (Symbian OS, S60 5.0) devices.

While you’re on his site, check out his web implementation of the mobile cipher algorithm. If you send a friend an encrypted message, he or she can decode it from the web even if that individual doesn’t have Mobile Cipher installed on his/her Nokia.

If you store secrets on your mobile device (and we’re guessing you might …) check out Mobile Cipher. It’s free, it’s easy to use, and it avoids a lot of panic if you momentarily lose your mobile and wonder who might be looking through it.