The Minister responsible for the Government Communications Security Bureau (GCSB) said the reasons why a Chinese tech company won't be involved in the rollout of 5G technology here are classified.
The GCSB has turned down Spark's proposed use of Huawei equipment in its new network because it would raise significant national security risks.
Andrew Little said he was briefed on the decision on Monday but cannot divulge what the risks might be.
"Spark notified the GCSB two or three months ago, GCSB has carried out an assessment on the technology that Spark proposes to introduce and has assessed that technology as posing a national security risk. That assessment was notified to Spark today."
"Spark have indicated they will have a close look at the reasons for GCSB's assessment then if Spark wishes to continue with their proposal they then have the option of working with the GCSB on looking at mitigation of [those risks]."
Mr Little said the 5G technology was more sophisticated than older network technology and was not currently in use in New Zealand.
"The principal difference between 5G technology and the conventional 4G and 3G technology is that the conventional technology has an infrastructure core and then peripheral technology such as cellphone towers and the like and they can, in effect, be kept separate but you cannot do that with 5G technology."
"Every component of 5G technology, every component of the network is integrated and therefore access to one component can lead to access to the entire network."
He said the GCSB investigation into the network was standard practice.
"What happens under the relevant legislation is that if a telco wants to introduce new technology to their network then they have to notify the GCSB. The GCSB then does an assessment of that technology to see whether or not it poses a threat to national security.
He said the GCSB decision was not a complete deal-breaker for Spark's rollout of 5G.
"Spark has said they are committed to rolling out 5G by the end of 2020, there's no reason why they can't stick to that timetable. They have known that they'd have to go through this process... it's underway and there's still work to do."
Meanwhile 2degrees is seeking clarification from the GCSB about the use of Huawei's radio network equipment.
The company said it had seen Spark's statement and was concered about the decision, which would limit options.
It said it was important for the industry to have multiple vendors to choose from in order to maintain price competitiveness.
2degrees corporate affairs head Matthew Bolland said it would be a real disappointment for competition if Huawei could not be used in the roll out of the 5G network, which 2degrees was committed to building.
Last week technology journalist Bill Bennett told Nine to Noon the proposed 5G network is much broader that the earlier versions.
"There are few phones - in fact I don't think there's any at the moment on sale in New Zealand - which are actually 5G ready," he says.
"It's not such a big deal because 5G isn't about mobile phones ... it's more about a wireless communications infrastructure."
He said with 5G the mobile internet speeds will be faster - but at a certain point that doesn't make a difference.
"Mobile phone speeds are not actually noticeably slow, you only need a couple of megabits per second to download high quality, high definition video … having it run 10 times as fast, 20 times as fast isn't that big of a deal to a phone user."
He said the real advantage 5G would bring is something called network slicing.
"It means that a company like Spark can divide up its 5G network and sell off private bits of it to other organisations. So, for example, you could have a private network on the 5G network for, say a freight company.
"Its trucks can talk to base and talk to each other and so on - and will never meet congestion because they've got spectrum set aside for their use."
He says that ability is particularly essential for something like autonomous vehicles.
"They're not that autonomous, they have to report back," he said.
"You don't want a car that's travelling at 100km/h to have to compete with people chatting to each other on Facebook to get some spectrum to get it to turn its brakes on in a hurry."