This is a small, unfinished idea I had, but I'd be interested in hearing any feedback anybody here might have to offer. Normally we talk about cryptography to secure communications, but this is an idea rather about verifying the authenticity of media.

[Quick backround: OpenWatch is a global citizen media network using mobile phones as the basis for a free worldwide press. We care very much about the authenticity of citizen media, and have designed some systems which attempt to improve the verifiability of citizen media.]

The problem is that sometimes media artifacts are presented as a record of a current event, when in fact they from different events. An example of this was when images of a marathon race in Istanbul were presented as images of the recent Occupy Gezi protests.

Now, imagine the globe divided into a grid coordinate system, say 100,000 units (or perhaps 2³², if IP rather than physical address is to be used). Based on their physical location, reporters can contact a server and are assigned a key with which to sign or encrypt their media to. This then ties a media object to a physical space. This can be further improved to include both time and space by dividing a space-day into a number of units, suppose 1440, such that different keys would be handed out at different times of the day, thus further tying a document to a moment in time as well.

Does anybody know if any systems like this have ever been discussed or designed in the past? I suppose this is somewhat similar to the RSA-keyfob system, although this allows for anonymous access without pre-arrangement as well.

R