During the debate on the government's encryption laws that were passed with the help of the Labor party last week, Greens senator Jordon Steele-John went on the attack, targeting the Home Affairs secretary himself as the source of the legislation.

"This legislation is nothing more or less than the dark fantasy of a particular public servant – a man who has been working his way to the top of Australian government for decades, a man of a dangerous right-wing disposition who has successfully created a department in his image and who now stands on the cusp of achieving a lifelong goal of empowering the Australian government with the ability to keep the general populace, who he regards as nothing more or less than helpless sheep, safe and sound," Senator Steele-John said.

"I am talking, of course, of Michael Pezzullo, the head of the Department of Home Affairs, who has, for almost 10 years now, waited for a government stupid enough to pass this legislation and an opposition weak enough to let them do it."

The Greens' spokesman on digital rights and information technology said Mr Pezzullo had "no place in the Australian Public Service".

"He's a man of such dangerous ideas, of such a radical disposition, of such an absolute, ironclad belief in his own rightness, that he would force through legislation that he knows is flawed, that he knows places at risk the privacy of every Australian, that he knows will drive business out of this country and that he knows places us at risk of criminal activity, because he wants the power."

Senator Steele-John was forced to withdraw a comment where he described Mr Pezzullo as "nothing more or less than a snake that has waited in the grass for a helpless government".

In a letter to Senate President Scott Ryan, and also sent to Senator Steele-John, Home Affairs Minister Peter Dutton and Public Service Commissioner Peter Woolcott, Mr Pezzullo labelled the speech "sententious".

"How best to answer another's scorn," Mr Pezzullo opened.

"Answer according to the scorn, and one risks behaving like the other. Do not answer the scorn and one risks allowing the other to be wise in their own eyes," he wrote, describing his dilemma in how to react to the speech, which was made under parliamentary privilege.

Mr Pezzullo called the attack "unprovoked and vitriolic".

"These utterances were untroubled by facts or logic, lacked grace, and were devoid of basic courtesy. The speaker spoke of evils which have never happened, outside of some imaginary world," he said.

"The suggestion that through the 'sinister' and secret exercise by me of some hidden power that I possess, the government and opposition were somehow duped witlessly into supporting the bill in complete ignorance of its implications is preposterous, as is the insult that I am motivated by a dark vision of controlling the population."

The secretary said he didn't seek redress through the letter, but wanted to assure the Senate president and senators that he and the department could serve the government of the day.

The letter comes after a recent address where Mr Pezzullo described how public servants must ensure that governments always had their loyalty and could be assured they would always serve in the public interest as decided by the government of the day.