Interesting analysis: "Examining the Anomalies, Explaining the Value: Should the USA FREEDOM Act's Metadata Program be Extended?" by Susan Landau and Asaf Lubin.
> Abstract: The telephony metadata program which was authorized under Section 215 of the PATRIOT Act, remains one of the most controversial programs launched by the U.S. Intelligence Community (IC) in the wake of the 9/11 attacks. Under the program major U.S. carriers were ordered to provide NSA with daily Call Detail Records (CDRs) for all communications to, from, or within the United States. The Snowden disclosures and the public controversy that followed led Congress in 2015 to end bulk collection and amend the CDR authorities with the adoption of the USA FREEDOM Act (UFA). > > For a time, the new program seemed to be functioning well. Nonetheless, three issues emerged around the program. The first concern was over high numbers: in both 2016 and 2017, the Foreign Intelligence Surveillance Court issued 40 orders for collection, but the NSA collected hundreds of millions of CDRs, and the agency provided little clarification for the high numbers. The second emerged in June 2018 when the NSA announced the purging of three years' worth of CDR records for "technical irregularities." Finally, in March 2019 it was reported that the NSA had decided to completely abandon the program and not seek its renewal as it is due to sunset in late 2019. > > This paper sheds significant light on all three of these concerns. First, we carefully analyze the numbers, showing how forty orders might lead to the collection of several million CDRs, thus offering a model to assist in understanding Intelligence Community transparency reporting across its surveillance programs. Second, we show how the architecture of modern telephone communications might cause collection errors that fit the reported reasons for the 2018 purge. Finally, we show how changes in the terrorist threat environment as well as in the technology and communication methods they employ in particular the deployment of asynchronous encrypted IP-based communications has made the telephony metadata program far less beneficial over time. We further provide policy recommendations for Congress to increase effective intelligence oversight.