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119 Harv. L. Rev. F. 38 (2005-2006)
Fourth Amendment Search and the Power of the Hash

handle is hein.journals/forharoc119 and id is 45 raw text is: FOURTH AMENDMENT SEARCH AND THE POWER OF THE HASH Richard P. Salgado* Replying to Orin S. Kerr, Searches and Seizures in a Digital World, ing HARV. L. REV. 53I (2005). I. THE POWER OF HASHING Hashing is a powerful and pervasive technique used in nearly every examination of seized digital media. The concept behind hash- ing is quite elegant: take a large amount of data, such as a file or all the bits on a hard drive, and use a complex mathematical algorithm to generate a relatively compact numerical identifier (the hash value) unique to that data. Examiners use hash values throughout the foren- sics process, from acquiring the data, through analysis, and even into legal proceedings. Hash algorithms are used to confirm that when a copy of data is made, the original is unaltered and the copy is identi- cal, bit-for-bit. That is, hashing is employed to confirm that data analysis does not alter the evidence itself. Examiners also use hash values to weed out files that are of no interest in the investigation, such as operating system files, and to identify files of particular interest. It is clear that hashing has become an important fixture in forensic examinations. What is not clear is whether the use of hashing impli- cates the Fourth Amendment, and if so, how. Is there a search when an examiner simply calculates the hash value of a hard drive in the data duplication process? Is there any Fourth Amendment moment if an examiner uses hashing to identify files on the media that are of in- terest but that are not within the scope of the search warrant or au- thority? What if those files constitute digital contraband? Does hash- based examination for child pornography fall outside the Fourth Amendment, allowing investigators throughout the country to look for child pornography on any seized electronic storage device, regardless of the nature of the investigation, without a warrant? This Reply examines those questions within the framework of Pro- fessor Kerr's exposure theory of search. I conclude that when used as part of the imaging process, hashing reveals no meaningful hints as * Lecturer in Law, Stanford Law School; Certified Instructor, SANS Institute; Member, Board of Directors, Honeynet Project; Senior Legal Director, Yahoo!, Inc. (The statements ex- pressed herein should not be taken as a position or endorsement of Yahoo!, Inc. or its subsidiaries and may not reflect the opinion of their affiliates, joint ventures, or partners). Thanks to Kyle French for his thoughtful insights. 38

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