No. 20-2570 ___________________________

United States of America

lllllllllllllllllllllPlaintiff - Appellee

v.

Christopher Allen Shipton

lllllllllllllllllllllDefendant - Appellant ____________

Appeal from United States District Court for the District of Minnesota ____________

Submitted: June 16, 2021 Filed: July 23, 2021 ____________ Before GRUENDER, ARNOLD, and STRAS, Circuit Judges. ____________ ARNOLD, Circuit Judge.

After a police officer downloaded part of a computer file containing child pornography on a peer-to-peer network from an IP address connected to Christopher Shipton, investigators searched his home and digital devices and uncovered additional illicit files, and so the government charged him with two counts of possessing child pornography. See 18 U.S.C. § 2252(a)(4)(B), (b)(2). Shipton moved to suppress the evidence gathered during the search on the ground that the officer who downloaded the file had conducted a warrantless search in violation of the Fourth Amendment. He also requested that the software the officer used to facilitate the sharing be tested to ensure it was reliable and that it did not gain access to private areas of Shipton's computer. The district court1 denied Shipton's motion and request, and he appeals. We affirm.

As many of our cases on the subject have shown, peer-to-peer networks provide common forums for those who trade child pornography on the internet. Users may connect to a peer-to-peer network and share files on their computer with others. Law enforcement agencies have developed programs that mimic ordinary users of peer-to-peer networks that are designed to help identify child-pornography purveyors. Like ordinary participants in the network, officers can search for and obtain child pornography from other users. But they can also compare a retrieved file's "hash value," which is essentially a particular file's digital signature, with the hash values of files known to contain child pornography. When the values match, investigators can pretty much be assured that the file at issue contains child pornography.

In this case, a Minneapolis police officer used a program called RoundUp eMule to search for users on a peer-to-peer network who were sharing child pornography. The officer downloaded part of a file—a video that played for twenty to thirty seconds—from an IP address in or around St. Paul, Minnesota. Using the file's hash value, the officer was able to obtain the complete file and determined that it contained child pornography. After subpoenaing the relevant internet service provider, the officer learned that Shipton was the person associated with the IP address. According to the search warrant application, investigators also learned that

1 The Honorable Patrick J. Schiltz, United States District Judge for the District of Minnesota, adopting the report and recommendation of the Honorable Katherine Menendez, United States Magistrate Judge for the District of Minnesota.

-2- Shipton was a registered sex offender who was convicted in June 2015 of possessing child pornography. Further, a search of the Child Protection System database, which, the magistrate judge explained, "compiles hash values of previously identified child pornography and documents hits that have occurred for certain IP addresses," revealed that Shipton had advertised 92 known or suspected child pornography files near the time the officer here was investigating Shipton. These 92 files were uncovered by programs simi