According to new legal docs ... Hart's former friend, Jonathan Jackson -- who's facing 2 felony counts for attempted extortion and extortion by threatening letter -- denies ever contacting Kevin about the sex tape or threatening him in any way.

Instead, Jackson claims he was contacted by a man who said he was a "Hollywood sex tape broker" and offered him $10k for the video. Jackson says he declined but began negotiation for a higher price ... but they never struck a deal.

According to the docs ... Jackson believes this sex tape broker was actually someone working on Hart's behalf to obtain the video and keep it under wraps. When the attempt failed, Jackson says Kevin "likely felt embarrassed and ashamed of his behavior" and came up with the extortion angle to make himself a victim.

Jackson claims the truth is there was never any extortion attempt or threat ... just a guy with a sex tape trying to "lawfully and legally engage in the sale of information to news outlets."

On that note ... Jackson also wants all of his electronic data obtained by a search warrant tossed from the criminal case. He claims law enforcement made up facts -- like saying he asked for $5 million from Hart -- to establish probable cause ... so the warrant was improperly authorized.