![]() ![]() In response to questions from Ars about the Brown case, the company would only issue its standard statement: “Child exploitation is a horrific crime. The company possesses the crypto keys.ĭropbox won't confirm or deny that it uses PhotoDNA. ![]() After all, Dropbox encrypts user data, bragging on its website about how "we store your file data using 256-bit AES encryption and use an SSL/TLS secure tunnel to transfer files between you and us." But this only makes content sent to Dropbox secure from outsiders-not from Dropbox itself. It also doesn't work on encrypted files, which might seem to rule out its use by services like Dropbox. ![]() PhotoDNA is free to use-and companies like Facebook, Twitter, and Kik all do-but it has one significant limitation: it does not currently work on videos. In July 2015, though, Microsoft moved PhotoDNA into its Azure cloud and offered qualified Internet companies access to the tool via a REST application programming interface. But the requirement for local installations meant hardware and IT know-how, preventing PhotoDNA from being more widely used, especially by smaller companies. PhotoDNA has become the standard solution for automated processing of imagery at Internet scale. ![]() (In 2009, the head of NCMEC said that his group was currently reviewing 250,000 suspect child sex abuse images each week.) To find a match, Internet companies can host a local instance of PhotoDNA on their own servers, which scans user-uploaded photos, generates a signature for each, and then compares them against the NCMEC database. Microsoft donated PhotoDNA to the National Center for Missing and Exploited Children (NCMEC), which maintains a massive database of PhotoDNA signatures for child pornography images. Microsoft claims that its multi-hashing system is powerful enough to detect illegal images even after basic tweaks such as re-cropping or watermarking. Taken together, these hashes make up the "PhotoDNA signature" of an image any future picture that generates the same signature is almost certain to be a copy of the original image. Each piece of image data then passes through a one-way hashing function which generates a unique number based on the square's shading pattern. In 2009, Microsoft built a tool called PhotoDNA that automates the scanning and matching process, converting incoming images to grayscale and chopping them up into tiny squares. This is not particularly difficult to do. According to a prosecutor's affidavit seen by Ars Technica, Dropbox discovered the videos in December 2014.ĭropbox won't discuss the specific techniques it uses to identify child pornography, though the company has for some time been the target of speculation that it proactively scans user uploads against a database of known illegal imagery. His associated e-mail address contained the date of his birthday, while his Dropbox username was "Dustin Brown." At some point, Brown began to acquire videos of both pubescent and pre-pubescent girls engaged in sex acts, and he uploaded them from IP addresses in the village of Morton, in the nearby town of Pekin, and in Chicago. Brown had been using Dropbox to store files but had made no serious effort to hide his identity. ![]()
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