A former top U.S. surveillance official is heading north, to warn Canadians that they, too, could become susceptible to massive data-spying programs launched by their own government.

"Every democracy is going this way," William Binney, a former technical director of the U.S. National Security Agency, said ahead of a planned trip to a civil-liberties conference in Toronto on Friday.

"Unless democracies wake up and start saying 'We don't want our government to hold this data,' then they have a really good chance of losing their democracy."

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Speaking from his home near Fort Meade, Md., – in a phone interview that he said would certainly be transcribed by the U.S. authorities – the crypto-mathematician recalled how he spent decades working for the NSA before his relationship with U.S. security agencies soured.

During his career, he said, he had many opportunities to assess the capabilities of Canada's electronic-eavesdropping technicians. And "some of them are as good as anybody over here."

Yet, while Mr. Binney compliments the surveillance acumen of Communications Security Establishment Canada, he also urged the Canadian public to scrutinize CSEC – especially given its long-standing close ties to the NSA.

"They have integrated reps," he said, referring to how the agencies swap personnel. He pointed out that they also share technology, such as a very powerful, recently revealed Internet-surveillance tool, code-named "XKeyscore."

CSEC and NSA have been allies since forming as "foreign intelligence" agencies during the Cold War.

Lately, law enforcement agencies have been prevailing upon them to advance counterterrorism investigations, and bans against spying on citizens' telecommunications have become less ironclad.

CSEC circulated a rare statement last month reaffirming it does not eavesdrop inside Canada.

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"CSEC does not direct its activities at Canadians and is prohibited by law from doing so," its chief, John Forster, said in a rare public statement.

Yet, records recently obtained by The Globe show that CSEC has been developing its own secretive programs to "incidentally" monitor at least some Canadian telecommunications traffic.

Such programs are kept murky. This summer U.S. contractor Edward Snowden leaked a trove of documents showing how the NSA has been conducting dragnet surveillance on American telecommunications traffic, even as top officials publicly disavowed doing any domestic spying.

Some of Mr. Snowden's leaks speak to the NSA's close relationship with CSEC – suggesting, for example, that the two agencies teamed up to spy on foreign diplomats at a 2009 G20 meeting in London, and may have also been in cahoots to install a back door to spy on encrypted messages on the Internet in 2006.

Mr. Binney said Canadians should pay attention to the close partnership. He spent almost 37 years with the NSA, a career that culminated with the role of technical director of world analysis.

He helped develop a program known as "ThinThread," which he said could automatically isolate terrorist chatter from global telecommunications traffic – while refraining from dredging up privileged American conversations.

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He resigned seven weeks after the Sept. 11, 2001, attacks.

At the time, he said he was incensed to hear that NSA had started intercepting American-to-American telecommunications.

"They scrapped the Constitution, is what they did."

In 2007, armed federal agents raided Mr. Binney's house as part of an investigation concerning leaks about NSA programs.

He denies having leaked any secrets, and is now outspoken about what he considers the growing excesses of American surveillance.

Democracies such as Canada, he said, would be well advised to restrict what intelligence their government collects. Ultimately, he said, governments will never relinquish information once they get it.

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"You're giving people knowledge and power and it's human nature that they will use that," he said.