Biblio

Thumbnail preserving encryption (TPE) was suggested by Wright et al. [Information Hiding & Multimedia Security Workshop 2015] 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 two 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 & 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.

We present simple, practical, and powerful new techniques for garbled circuits. These techniques result in significant concrete and asymptotic improvements over the state of the art, for several natural kinds of computations. For arithmetic circuits over the integers, our construction results in garbled circuits with free addition, weighted threshold gates with cost independent of fan-in, and exponentiation by a fixed exponent with cost independent of the exponent. For boolean circuits, our construction gives an exponential improvement over the state of the art for threshold gates (including AND/OR gates) of high fan-in. Our construction can be efficiently instantiated with practical symmetric-key primitives (e.g., AES), and is proven secure under similar assumptions to that of the Free-XOR garbling scheme (Kolesnikov & Schneider, ICALP 2008). We give an extensive comparison between our scheme and state-of-the-art garbling schemes applied to boolean circuits.