I have zero references, just that I've encountered that bit of "common knowledge" enough times among IR professors and military-connected people to take it as basically true. As any such hearsay/common-knowledge, it could be wrong. I've heard a lot of stuff like "headlines say French advisors arrived in Afghanistan, guess they needed some help with interrogations (ahem, torture)." I should have been more up-front about the quality of that statement (middling, I'd judge). The way those things are presented sometimes in e.g. Foreign Affairs sure seem to support that subtext. Strikes me as somewhat less "well it's denied officially, but nonetheless everyone knows..." than Israeli nuclear capabilities. Attempts to find any recent documentation of this are frustrated by modern search engines being terrible, and French torture in the Algerian conflict being so well-documented and infamous that results for that overwhelm everything else no matter how one tries to search past it (and Algeria would likely be mentioned in any long treatment of the topic, making it even harder to narrow in on more-recent examples). There's a definite sentiment of "the last Western government you want to come after you with black ops is France, because they'll be ripping out all your fingernails before they start asking questions, then they'll get really nasty"—sometimes stated almost exactly in those terms—that I've picked up, though. It's entirely possible this is a widespread but inaccurate notion, or even a deliberately-cultivated whisper campaign on France's part.