Cryptology ePrint Archive: Report 2017/1046

Approximate Thumbnail Preserving Encryption

Byron Marohn and Charles V. Wright and Wu-chi Feng and Mike Rosulek and Rakesh B. Bobba

Abstract: Thumbnail preserving encryption (TPE) was suggested by Wright et al. as a way to balance privacy and usability for online image sharing. The idea is to encrypt a plaintext image into a ciphertext image that has roughly the same thumbnail as well as retaining the original image format. At the same time, TPE allows users to take advantage of much of the functionality of online photo management tools, while still providing some level of privacy against the service provider.

In this work we present three new approximate TPE encryption schemes. In our schemes, ciphertexts and plaintexts have perceptually similar, but not identical, thumbnails. Our constructions are the first TPE schemes designed to work well with JPEG compression. In addition, we show that they also have provable security guarantees that characterize precisely what information about the plaintext is leaked by the ciphertext image.

We empirically evaluate our schemes according to the similarity of plaintext and ciphertext thumbnails, increase in file size under JPEG compression, preservation of perceptual image hashes, among other aspects. We also show how approximate TPE can be an effective tool to thwart inference attacks by machine-learning image classifiers, which have shown to be effective against other image obfuscation techniques.

Category / Keywords: applications / format preserving encryption

Original Publication (with major differences): ACM CCS MPS 2017

Date: received 17 Oct 2017, last revised 31 Oct 2017

Contact author: cvwright at cs pdx edu

Available format(s): PDF | BibTeX Citation

Version: 20171031:144737 (All versions of this report)

Short URL: ia.cr/2017/1046

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