Content Privacy and Access Control on Image-Sharing Platforms

Kun He 1, 2
2 CIDRE - Confidentialité, Intégrité, Disponibilité et Répartition
CentraleSupélec, Inria Rennes – Bretagne Atlantique , IRISA_D1 - SYSTÈMES LARGE ÉCHELLE
Abstract : In recent years, with the rapid development of image-sharing platforms, more and more users prefer to share their photos through these platforms than using e-mail or personal webpages, which makes image-sharing become easier. Most of the platforms allow the users to specify who can access to the images, it may result a feeling of safety and privacy. However, once users upload their images, privacy is not guaranteed, since at least the provider of the image-sharing platform can clearly know the contents of any published images. Therefore, uploading an unreadable image is a good solution to protect user’s privacy. According to some existing researches, encrypting images before publishing them should be a top priority. In this way, only the authorised users who can decrypt the encrypted image can access to the contents of the published images. By studying the existing methods, we found that there are three challenges when proposing an encryption algorithm for the images published on image-sharing platforms. Firstly the encrypted result has to be viewed as a correct image format (often a JPEG image) by the image-sharing platforms. Therefore, an encryption algorithm which preserves image format after encryption is required. Secondly, the algorithm should be secure, i.e. the adversary cannot get any information of plaintext image from the encrypted image. We aim to provide IND-CPA property for the encryption algorithm. Thirdly, the algorithm has to be compatible with basic processing of the digital data in each image-sharing platforms, that means the decryption algorithm can recover the plaintext image with a high quality even the encrypted image is processed by the platforms. In this thesis, our main goal is to propose an encryption algorithm to protect JPEG image privacy on different image-sharing platforms and overcome the three challenges (image format preserving, security guarantee, processing compatibility). We first propose an encryption algorithm which can meet the requirements of the first two points. We then implement this algorithm on several widely used image-sharing platforms (Facebook, Flickr, Pinterest, Google+, Twitter, Instagram, Weibo, Wechat). However, the results show that it cannot recover the plaintext image with a high quality after downloading the image from some of the image-sharing platforms we tested (Facebook, Instagram, Weibo and Wechat). This encryption algorithm can be only used to protect the privacy on the other four platforms. Therefore, we improve this algorithm to add the correcting mechanism, in order to reduce the losses of image information during uploading the encrypted image on each platforms and reconstruct the downloaded images with a high quality.
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Kun He. Content Privacy and Access Control on Image-Sharing Platforms. Cryptography and Security [cs.CR]. CentraleSupélec, 2017. English. ⟨tel-01636207⟩

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