Rachel Noble, head of the Australian Cyber Security Centre (ACSC), said that she made the final decision to cancel their speeches because they "weren't consistent" with the conference, Senate estimates on Thursday revealed.
Ms Noble said as quoted by the Canberra Times: “The advice I made the decision on was a proposal for Dr Dreyfus and Mr Drake to [via video conference] have a panel with Edward Snowden. That was the first proposal. At that point my judgement was based on, I guess, the reputation of all of those speakers – that they are known public advocates for unauthorised disclosures or the leaking of classified information outside of legitimate or lawful whistleblowing schemes.
She added that the pair would "express views that are inconsistent with Australian government laws, and our processes and our values".
But Ms Dreyfus hit back on Twitter, stating that the talk was merely a thought bubble in the first stages of planning for the conference, stating that "the idea of Edward Snowden on a panel was floated in a phone call due to the newsworthiness of his new book being published".
She added that the ACSC did not reject the idea when it was raised, she said in a tweet thread.
"The idea didn’t go anywhere, as the ACSC well knows, since they saw the exact content of my talk abstract and Thomas Drake’s slides,” Ms Dreyfus said.
Ms Dreyfus also noted that the Australian government could not “build the country’s cybersecurity strength by shutting down experts" due to fears that speakers "might criticise laws or processes".
She added: "Australia has serious problems with its cybersecurity, as evidenced by a slew of high profile attacks. ACSC is tasked with addressing this. But sweeping debate under the carpet doesn’t fix those problems. The silencing of ideas and knowledge is not a recipe for success in solving our cybersecurity risks as a nation.
Mr Thomas Drake, a former US whistleblower for the NSA, and Suellete Dreyfus, a University of Melborne computer and information specialist, were disinvited from speaking at the high level CyberCon conference in October despite receiving invites to speak months prior to the event.
Mr Drake was to address surveillance and national security and Dr Dreyfus was to highlight using digital drop boxes to facilitate whistleblowing at the time. Mr Drake slammed the move as "hypocritical" at the time, stating that there was a "culture of fear about speaking up" in Australia.
Snowden, who leaked a trove of documents on the US National Security Agency's (NSA) spy programme in 2013, relocated to Russia to escape persecution from US authorities. Mr Snowden published his book, "Permanent Record" in September.