Lawful Intercept(ion) Primer Part 3 – How?

Welcome! Please comment and leave me a note telling me what you like and what you'd like to see more of. Sign up to my RSS Feed!
This entry is part of a wonderful series, Intercept»

In this final blog in the series, I will discuss the How of Lawful Intercept – how it is installed, how it is done, and what is involved in the process.


Firstly, let me clarify that, in the US, the capabilities described herein were mandatory since at least 2007.  In other words – your telecommunications provider MUST have them already in place.


In the beginning, Lawful Intercept, and yes, its unlawful cousin, were both called "wire tapping".  To wire tap you would need access, ideally physical access, to the telecommunication medium.  In other words, you would need to be able to tap into the

  • Phone (or computer) at either (or both) ends;
  • The wire connecting the end points; or
  • The telephony (or network) switch creating the connection.

It worked something like this:

Rotary Phone
Image by AZAdam via Flickr



Someone could have put a "bug" into a telephone set:




Or listen in on the wire (yep, really as simple as this):







Using a device such as a "buttset":









Or simply plug a listening, or a recording, device, into this, old style, telephony switch.





Today, however, things are more complicated.

When technologies such as Voice-over-IP () or cellular G3 and beyond are involved, there are at least two more challenges added to the mix.  These are encryption and path-sharing.

Under the term "encryption", with the rising sensitivity to privacy concerns, quiet a lot of conversations, be they voice or data, are now subject to mechanisms previously only used by governments.    One of the reasons for Lawful Intercept laws is the concern that terrorists or other malefactors will use such technologies to make sure that Law Enforcement will not be able to listen in.  There are mechanisms, such as the ones discussed below, that address this concern.

The term "path sharing" refers to the fact that today, especially under cellular connections, data and voice, and in many times, those data and voice "packets" from very many conversations at once, are sharing the path to the switch.  Imagine the difficulty picking up a single conversation from a commingling of 100,000!  This is clearly only the territory of computers today.

So how is it done?


Under the leadership of a European standards organization called ETSI, a standard for Lawful Interception emerged.  This standard, used virtually everywhere such interception is performed by Law Enforcement, is designed as follows:


ETSI's LI Model



Looking closely at the diagram, lets notice a few elements (from right to left):

  1. Firstly, the column marked "LEA" refers to the network, operated by Law Enforcement officials, and here it is the recipient of the intercepted information.
  2. The broken (or dashed) line marked "handover" is where interface is made between the telecommunications provider and Law Enforcement
  3. The three boxes in the "cloud" represent the "checks and balances" in the system.  In our case, they both serve to assure that no one point collects all information allowing some measure of privacy to the individuals intercepted. (the term CC above refers to the content of and the term IRI to intercept related information for the specific information of the call).

One note of caution.  As you can see from this system, it can support long-term listening.  It can also support automatic processing of data and, using computer technology it can support sorting through many, many calls at the same time, looking for such "keywords" as bomb or kill.

We should cherish living in a free society, where such measures are done by Judicial processes alone.   As we saw, in closed societies such as Iran, not only can the data collected be searched for trigger words such as Mousavi or demonstration but also used to pin point the source of the conversation, its destination, and serve as documentary evidence to prosecute, and indeed persecute, free expression.