I was recently thinking about SMS encryption (you know, the short messages sent from your cell phone). Or MMS encryption for that matter. Are there any Free Software solutions to implement such a thing, based on well-known crypto primitives and proven implementations thereof?
From a quick glance I could not find anything usable, only lots of commercial, closed-source "solutions" which cost money and are basically crap.
I was thinking about hacking together a small Java application (so that most modern phones can run it) which basically asks for a password and pipes your text through AES before sending the SMS. On the receiver's side, you enter the same password and get to see the plaintext. That's pretty much it.
If you want something more elaborate you can use public-key crypto (basically embed GnuPG or similar into the application), but the above should be fine for most uses.
Anyways, I do not want to start implementing something like this if there are other, more mature projects out there which do the same...
Why you'd want to do this (other than simple paranoia, or the fact that governments and other institutions are spying on everyone these days, whether they're allowed to or not)? Well, one good reason for SMS encryption is when you're using some kind of SMS gateways, e.g. a website which gives you 2-3 free SMS per month if you sign up with them and give them tons of personal data. That alone is crappy enough, but you don't want their admins to be able to read and store all your SMSes in addition (which consist of simple plain-text, transmitted though HTTP in this case!). Neither should any local or remote scriptkiddy who knows how to use a sniffer be able to read your private SMSes.
Solution: Write the text in your favorite text editor, pipe it through aespipe (for example), cut'n'paste the result in the web form of the SMS service. The receiver does everthing backwards and you're done.