www.archives .gov/declassification/iscap/redaction-codes.html
According to that, We have
>1.4 (b) Foreign government information
>1.4 (d) Foreign relations or foreign activities of the United States, including confidential sources
I'm guessing the B1 is
>3.3 (b) (1) Reveal the identity of a confidential human source, a human intelligence source, a relationship with an intelligence or security service of a foreign government or international organization, or a nonhuman intelligence source; or impair the effectiveness of an intelligence method currently in use, available for use, or under development