CD-R Acquisition Hashes Affected by Write Options

While conducting a validation study of proficiency test media we found that applying the same hash algorithm against a single CD using different applications resulted in different hashes. This was unexpected because the only plausible explanation of the different hashes would be if the CD media changed between hashing procedures. We formulated a series of experiments using several variables to determine the cause of the anomalous results. The results suggested that certain write options cause hash applications to report different hashes. We conclude with a discussion of possible consequences of these anomalies in a court of law, along with recommendations regarding best practices involving hashing procedures.