- A5/0. No encryption at all.
- A5/1. "Stronger" encryption. This option is supposedly provided only on basestation equipment delivered in North America and Europe.
- A5/2. Weak encryption, exported to the rest of the world. The GSMA declared A5/2 obsolete in 2006 and mandated that it be phased out in networks and not supported in new handsets. I think.
- A5/3. True strong encryption, being phased in for UMTS systems and proposed as an upgrade for GSM systems.
My first question for anyone who happens to be reading this: What, specifically, was the GSMA's 2006 mandate regarding A5/2? Can anyone point me to an authoritative document?
My second question is more vexing. Let's assume for a minute that I really do have my facts right. Suppose you are using a post-2006 GSM phone somewhere outside of North America and Europe. The carrier's equipment isn't supposed to support A5/1. Your handset isn't supposed to support A5/2. A5/3 isn't available yet in non-UMTS networks. So what A5 variant are you using?