A judge was heading the investigation and provided the legal go-ahead for the actions. The legal justification is twofold: evidence of organized crime uncovered in a preliminary investigation and (!) lack of declaration of cryptographic solution deployment , which is apparently a thing [0] when it’a not used for authentication or data integrity control!

I’m extremely surprised by the latter, it seems that one has to declare any operational use of cryptography when it’s not for those two uses.

[0] https://www.ssi.gouv.fr/uploads/2015/03/ANNEXE-I.pdf