Prof Cannataci told the Parliamentary Joint Committee on Intelligence and Security on Tuesday evening that it was up in the air whether the legislation could achieve its aims and avoid introducing vulnerabilities in devices.
He spoke at length about what he described as weak oversight and accountability in the bill.
Tuesday marked the fourth day of hearings on the bill — officially known as the Telecommunications and other Legislation Amendment (Assistance and Access Bill) 2018 — and the PJCIS also heard from Margaret Stone, the inspector-general of intelligence and security, deputy Commonwealth ombudsman Jaala Hinchcliffe and Jake Blight, inspector-general of intelligence and security.
He said that the targets of the bill - seasoned organised criminals and terrorists - had the means to invest in their own algorithms and develop their own cryptography, defeating the point of the bill.
Also, he said, it was pertinent to note that the UK, which had a similar law, had not tried to get any big technology company to provide it with a means to access encrypted devices as the matter would result in prolonged litigation.
Asked by Senator Eric Abetz how he, as someone concerned with privacy, had made comments about the bill that extended to other realms. Prof Cannataci patiently explained how his field, privacy, was affected by various aspects of the bill.
In his submission to the committee, Prof Cannataci mentioned the fact that Australia had passed 70 counter-terrorism laws since the terrorist attacks on the world trade centre in New York on 11 September 2001.
"Concern has been expressed at the international level about trends in Australia's human rights performance," he pointed out. "This includes the UN Human Rights Committee who requested the Australian Government to reconsider the legality of its power in certain areas."
He said that the bill under consideration had been criticised as too broad and potentially undermining the privacy of Australians.
The PJCIS is due to hold another two days of hearings on 30 November and 4 December, before submitting its report to the government.