There are all kinds of statements on radio,TV and written media about US SIGINT masking/unmasking procedures. Much of what is being said seems not to be justified in fact. So let’s look at what the procedures really are, and the overriding instruction.
US SIGINT operates under a series of “United States Signals Intelligence Directives” These documents are normally highly classified. BUT the Office of the Director of National intelligence” declassified the 2011 version of the main operable directive. This directive is USSID SP00218 (U) Legal Compliance and U.S. Persons Minimization Procedures” Issue date :25 January 2011 (See https://www.dni.gov/files/documents/1118/CLEANEDFinal%20USSID%20SP0018.pdf )
Why is this document cited above important, as Section 3 Policy states:
3.1 (U) The policy of the USSS is to TARGET or COLLECT only FOREIGN COMMUNICATIONS. THE USSS will not intentionally COLLECT communications to, from, or about U.S.PERSONS or persons or entities in the U.S. except as set forth in this USSID. If the USSS inadvertently COLLECTS such communications, it will process. Retain, or disseminate them only in accordance with this USSID.
This is the directive NSA, CIA and other foreign intelligence collectors operatives within.
I will not copy sections from the SP0018 (SEE https://www.dni.gov/files/documents/1118/CLEANEDFinal%20USSID%20SP0018.pdf
since they are very long. But the relevant sections are:
Section 4: COLLECTION
Section 7: DISSEMINATION
Now there will be disbelievers who will say ‘but do they have to really follow this procedure?’ The Office of the Director of National Intelligence (ODNI) performs semi-annual IG reviews of all intelligence activities. Minimization is one of the concerns. See the declassified 2015 review here (https://www.odni.gov/files/documents/FOIA/DF-2015-00062.pdf
I hope this clears up some misunderstanding. It’s somewhat involved to read SP0018, but that’s the document used. And its long to make sure U.S. persons’ rights are not abridged.