This lends further credence to the conclusion above: rather than doing targeted collection against specific individuals, NSA is collecting, or plans to collect, a broad class of data that is encrypted. For example, NSA might collect all PGP encrypted emails or all Tor traffic. In those cases, NSA could search Internet traffic for patterns associated with specific types of communications, rather than specific individuals’ communications. This would technically meet the definition of incidental collection because such activity would result in the collection of communications of U.S. persons who aren’t the actual targets of surveillance. Collection of all Tor traffic would entail a lot of this “incidental” collection because the communications of NSA targets would be mixed with the communications of a large number of non-target U.S. persons.
However, this “incidental” collection is inconsistent with how the term is typically used, which is to refer to over-collection resulting from targeted surveillance programs. If NSA were collecting all Tor traffic, that activity wouldn’t actually be targeted, and so any resulting over-collection wouldn’t actually be incidental. Moreover, greater use of encryption by the general public would result in an ever-growing amount of this type of incidental collection.