It was sparked by the firststory in a series of NZ Herald articles based on Snowden documents taken from the National Security Agency in the United States.
New Zealand's role in this is as a member of the Five Eyes spying club, along with Australia, Canada, the US and the UK. The GCSB's role includes surveillance targets across the Pacific, and fits with the Five Eyes imperative to cover the entire globe.
When Gwyn reports, there's a couple of things we need to get clear.
Dodgy maths?
First is what I believe to be the dodgy maths Dr Michael Cullen and Dame Patsy Reddy offered in
Former Deputy Prime Minister Michael Cullen who reviewed the spy agency laws with Dame Patsy Reddy. Photo / Christine Cornege
According to the review's report, the GCSB intercepts communications from a specific number of satellites. The GCSB has responsibility for about 120 satellites in fixed orbit above the Pacific - about a quarter of the world's total number of such satellites.
The review said about one billion communication events passed through those satellites each day.
There are 2.5 million litres in an Olympic-size pool and about 5 litres in a half-bucket. It works out at 0.0002 per cent. If the GCSB's assessment of one billion "communications events" on those satellites daily is accurate, it means it is only capable of intercepting 2000 of those.
That's an awfully big agency to exist to "intercept" just 2000 communication events a day. I don't believe it.
Mass surveillance?
The second thing to consider is that Gwyn's report will likely show we have moved beyond the question of whether all our communications are scooped up.
The Cullen/Reddy report stated: "The reality of modern communications is that it is often not possible to identify and copy a specific communication of interest in isolation. If a particular satellite might carry a relevant communication, the GCSB cannot search for that communication before interception occurs."
At the press conference presenting the report, Sir Michael was asked: "So it's more mass collection than mass surveillance?" He replied: "I think that's a fair term."
Cheryl Gwyn, the Inspector General of Security and Intelligence and Security. Photo / Mark Mitchell
The GCSB law says that the agency "must not ... do anything for the purpose of intercepting the private communications of a person who is a New Zealand citizen or a permanent resident of New Zealand".
I suspect the wiggle room is the title of that section of the GCSB Act: "Interceptions not to target New Zealand citizens or permanent residents for intelligence-gathering purposes."
"Target" is probably the escape clause - mass collection is untargeted but searching out communications is not.
It would be nice if somebody said it out loud.
Who's affected?
Gwyn's report will likely offer clarity on this because of the broad swathe of people who will be subject to mass collection.
How could the GCSB intercept communications from the Pacific without scooping up the information of New Zealanders?
We spend a lot of our time, collectively, in the Pacific. Many of us have family roots in island nations. Others will holiday there.
That's a key question considering the GCSB's area of responsiblity includes the Cook Islands, Niue and Tokelau, where people born there have default New Zealand citizenship.
Considering the nations that have automatic citizenship, it is likely fair to apply whatever Gwyn says about those countries to New Zealand itself.
It appears the GCSB scoops everything it can and that likely includes everything in New Zealand. And then, they sift through it for what they are allowed.
Edward Snowden's revelation the GCSB is spying on Pacific neighbours, as captured by NZ Herald cartoonist Rod Emmerson in 2015.
So what?
These things matter because Gwyn's reports are shedding greater light on the way our spy agencies operate. It's not all as palatable as the Cullen and Reddy review suggested, and that's important because the law changes mooted by the review are sugar-coated.
The amount of information Cullen is suggesting is captured by the GCSB is tiny. It does not seem credible the GCSB exists to "intercept" - not target - such a small amount.
If Cullen's math is wrong, then the difference between "collection" and "surveillance" might not be as clear in his mind as we would like it to be, especially given his recommendation to allow the GCSB to spy on us all.
And that's the important bit. It is said the law must allow the targeting of New Zealanders.
This is apparently to clear up legal confusion over whether the GCSB can assist domestic agencies, and when it can use its awesome technology to shine a spotlight on Kiwis.
Edward Snowden's revelation the GCSB is spying on Pacific neighbours, as drawn by NZ Herald cartoonist Rod Emmerson.
Given everything else - and Gwyn's Pacific report will help us understand this - it would appear to be less a change in the way the GCSB intercepts communications and more a move to deliberately focusing on New Zealanders and what we do.
That's why "full take" in the Pacific is on the GCSB task list - it covers a black spot. That's likely why the law change here is considered necessary.
That is typical Five Eyes behaviour. Having covered most of the globe, it has an unreasoning terror of the places it cannot see.
