Metadata related to lawful interception has been in the news a bit lately. You may have seen last week the Australian Federal Police (AFP) called for more access to electronic metadata as a Senate committee evaluates Australian mass surveillance laws.
Probably most people understand that lawful interception (wiretapping or phonetapping) has moved beyond connecting alligator clips to a phone line, but “metadata” might be a bit of a mystery.
If you have ever wondered why you need to provide identifying information such as a driver’s licence when you purchase a new phone, “metadata” is a big part of the answer.
So what is metadata?
Metadata is information about communication, rather than the content of the communication itself.
We are all familiar with metadata. It consists of such things as telephone numbers, email addresses, webpage addresses and the like. It is what we see when we look at our telephone bill.
The reason it is in the news now is that modern telecommunications has caused an explosion in new forms of metadata.
When telecommunications mainly consisted of voice and perhaps short message service (SMS) the actual content of the communications was rarely collected. Capturing, recording, storing and listening to voice conversations was expensive and, at least during the early stages of an investigation, probably of limited value.
What was useful though was information about the call – information as to who was talking to whom and how often, enabled investigators to construct a model of the relationships between those of interest.
Maybe at a later stage conversations would be recorded, but usually intercepts requested by the authorities delivered information about the call, rather than the call itself – in other words, the “metadata."
Even before smartphones and the internet, metadata from the mobile phone system was surprisingly rich. Metadata could provide information as to whether the call was forwarded and where it was forwarded to, whether or not it was answered, and so on.
Such information is invaluable in building up a model of relationships. But not only did the phone network provide information about the participants to a call, it could also provide approximate information about where the call was made.
Since mobile phones are connected to the network via nearby base stations usually located only a few kilometres away, metadata reporting which basestation the handset is attached to gives location information accurate to a few kilometres.
Also, since the phone is connected to a basestation whenever it is switched on, the phone can provide continuous location information regardless as to whether or not calls are made.