Historically there are lots of passive attackers (and we don't know or think about them because they're passive), while a lot of them have been reluctant to bec

Historically there are lots of passive attackers (and we don't know or think about them because they're passive), while a lot of them have been reluctant to become active attackers (because we might notice them!). E.g. you could try to randomly record both ends of a TCP connection and then compare them out-of-band to see if someone in between tampered with the contents. (Although my late former colleague was working on a tool to do that and it turns out that there's a lot of noise and complexity to contend with in trying to make it practical, e.g. because of packet loss, retransmission, fragmentation, and changes like NAT by middleboxes that consider themselves benign.) Random example of a passive communications interception attacker: https://en.wikipedia.org/wiki/RAF_Menwith_Hill#/media/File:Menwith_Hill_radomes_x_26.jpg https://en.wikipedia.org/wiki/RAF_Menwith_Hill#/media/File:M... Another example: https://en.wikipedia.org/wiki/Orion_(satellite)#/media/File:Orion_MENTOR4_(USA-202).jpg https://en.wikipedia.org/wiki/Orion_(satellite)#/media/File:... There are lots more where those came from!