IN THE UNITED STATES COURT OF APPEALS FOR THE FIFTH CIRCUIT United States Court of Appeals Fifth Circuit

No. 17-41116 FILED August 17, 2018 Lyle W. Cayce UNITED STATES OF AMERICA, Clerk

Plaintiff - Appellee v. HENRY FRANKLIN REDDICK,

Defendant - Appellant

Appeal from the United States District Court for the Southern District of Texas

Before KING, SOUTHWICK, and HO, Circuit Judges. JAMES C. HO, Circuit Judge: Private businesses and police investigators rely regularly on “hash values” to fight the online distribution of child pornography. Hash values are short, distinctive identifiers that enable computer users to quickly compare the contents of one file to another. They allow investigators to identify suspect material from enormous masses of online data, through the use of specialized software programs—and to do so rapidly and automatically, without the need for human searchers. Hash values have thus become a powerful tool for combating the online distribution of unlawful aberrant content. The question in this appeal is whether and when the use of hash values by law enforcement is consistent with Case: 17-41116 Document: 00514605839 Page: 2 Date Filed: 08/17/2018

No. 17-41116 the Fourth Amendment. For the Fourth Amendment concerns not efficiency, but the liberty of the people “to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures.” There is no precedent in our circuit concerning the validity of these investigative tools under the Fourth Amendment, and to our knowledge no other circuit has confronted the precise question before us. This case therefore presents an opportunity to apply established Fourth Amendment principles in this new context. One touchstone of our Fourth Amendment jurisprudence is that the Constitution secures the right of the people against unreasonable searches and seizures conducted by the government—not searches and seizures conducted by private parties. Under the private search doctrine, the Fourth Amendment is not implicated where the government does not conduct the search itself, but only receives and utilizes information uncovered by a search conducted by a private party. The private search doctrine decides this case. A private company determined that the hash values of files uploaded by Mr. Reddick corresponded to the hash values of known child pornography images. The company then passed this information on to law enforcement. This qualifies as a “private search” for Fourth Amendment purposes. And the government’s subsequent law enforcement actions in reviewing the images did not effect an intrusion on Mr. Reddick’s privacy that he did not already experience as a result of the private search. Accordingly, we affirm the judgment of the district court. I. In technical terms, a hash value is “an algorithmic calculation that yields an alphanumeric value for a file.” United States v. Stevenson, 727 F.3d 826, 828 (8th Cir. 2013). More simply, a hash value is a string of characters obtained by processing the contents of a given computer file and assigning a sequence of numbers and letters that correspond to the file’s contents. In the 2 Case: 17-41116 Document: 00514605839 Page: 3 Date Filed: 08/17/2018

No. 17-41