Buisson's lawyer, Gilles-William Goldnadel, said on Tuesday the recordings were authentic. He said his client had made them for historical research purposes and had not intended that they be made public.
Breach of privacy in France carries a penalty of up to one year in prison and 45,000 euros in fines.
In the published excerpts Sarkozy is heard discussing his electoral strategy and a 2011 cabinet reshuffle, while Bruni is recorded joking about how she had to put her modelling career on ice while she was France's first lady.
"I thought I was marrying a guy with a salary ... I had big contracts and now nothing," she is heard saying, adding that if Sarkozy went on to lose the election she at least could re-activate her career and start selling anti-wrinkle cream.
(Read more: Bruni-Sarkozy on the Bettencourt affair: The truth will comeout)
French media have said dozens of hours of further material could emerge from recordings that date back to 2011.
Goldnadel said the recordings, which Buisson made using a device in his pocket and later uploaded to his personal computer, had been stolen from Buisson and that he would file a complaint for theft against "persons unknown".
"There will be an investigation to determine exactly how these recordings were taken," Goldnadel told BFM TV. He added that his client thought he knew who had stolen them, but did not give names.
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