Speaking on the Newstalk ZB Leader's Breakfast this morning, Mr Key was asked about claims Mr Greenwald would produce evidence of spying on China at the "Moment of Truth" event tonight.
Mr Key said he preferred to wait to see what Mr Greenwald delivered before commenting.
However, he did not believe did not believe it would relate to China. He would not rule out evidence of spying on other trading partners but said he would refuse to comment on anything like that because it related to foreign intelligence.
Mr Key also said he would be "highly surprised" if there was evidence the NSA had undertaken mass surveillance on New Zealanders. He said the US had different collection laws to New Zealand, but there was an informal agreement between the Five Eyes countries that they would not spy on each other.
Mr Key has promised to declassify documents proving the GCSB had not engaged in mass surveillance if that was what Mr Greenwald claimed. He suspected the event would be "a sound and light show."
"Dotcom is trying to save Dotcom's butt, and it is a relatively large one, so he's brought in three little butts to try and save his butt."
He also said the GCSB had not used mass surveillance information collected by the NSA. "We don't use our partners to circumvent the law."
Mr Key said he was confident with his previous statement that the first he had heard of Mr Dotcom was the day before the raid on his mansion - and had originally thought he was Korean because of his name.
The Solicitor-General had told him about the raid on a Kim Dotcom.
"I said 'is he Korean?' He said 'no, he's German." I said 'who's got a name like that?"
Mr Key also denied unequivocally that he was ever put under pressure over Mr Dotcom's residency by the US.
He said when the Warner Bros executives visited New Zealand it was not related to Mr Dotcom.
"It wasn't to encourage us to let Kim Dotcom into New Zealand, it was to get a better deal for the Hobbit."
Greenwald 'certain' GCSB contributes metadata to Five Eyes
Greenwald claims the NSA documents shows a 'phase one' of mass surveillance -- tapping into the cable which connects New Zealand to the internet -- was already completed. Phase two would represent "the sweeping up of large amounts of meta data indiscriminately".
Speaking on Radio New Zealand this morning, he said last year's controversial GCSB Bill represented Government spies "simply waiting for the new law that they knew they needed in order to be able to do the programme that they were in the process of implementing".
Greenwald conceded that it was "possible much later he [Mr Key] went and uprooted it all", but said "how can a Prime Minister say it's not in the public interest for the public to know their spy agency is planning on directing a system of mass surveillance on them?"
He was "certain" the GCSB contributes "large amounts of meta data about New Zealanders to the Five Eyes programme".
In documents to be published later today, Mr Snowden had written about how "he worked with and personally witnessed from the GCSB" which contributed to Five Eyes surveillance, he said.
"The documents themselves describe this programme and describe the progress being made, but the testimony of Edward Snowden first hand, about the material and the data he worked with, the amount of it that came from the GCSB, is extremely clear," Greenwald said.
Asked if he was drawing conclusions from partial information, he said: "I'm confident that I am, number one, accurately describing the documents that are in the NSA archives about this matter, which the public will be able to see for themselves and evaluate, and number two, my source Edward Snowden, who has never proven to be anything but entirely accurate whatever else you might think about him, is very definitive that large amounts of meta data have contributed to the Five Eyes programme about New Zealanders."
He also stressed that he had always intended to release this information prior to the election, and had received emails from New Zealanders over the last year asking him to do so.
"Being able to inform the citizenry in anticipation of an election, a really important election, I think is one of my duties as a journalist, and so I tried really hard to make sure the reporting was done prior to the election rather than after the election, when I think a lot of New Zealanders would have said, 'we wish you had told us this before we voted rather than after'."
Dotcom had simply offered him an opportunity to do so in a local setting at a "major event", he said.
He had been working on the New Zealand files for "many months", before the invite from Dotcom, he said.
His $25,000 appearance fee would be donated to a charity yet to be chosen.
- additional reporting Patrice Dougan, APNZ
