To get the basic idea of AGSES, imagine the following situation:
There are two people (person A and person B), geographically separated from each other. Each of them has a key able to unlock a box which cannot be opened by anybody else. Person A thinks up a code (e.g. N8ZG95), writes it on a piece of paper, puts it into the box and locks the box with their key. The box is forwarded to person B (no matter by which means). Person B opens the box with his key and reads the code – as a consequence, person A and person B know the code . If person B now calls person A and tells them the code (N8ZG95), person A knows for sure that the person on the other end of the line definitely is person B. It is utterly insignificant whether the call has been encrypted or not in order for person A to clearly identify his/her conversational partner as person B.