The Internet has plenty of images that are transformations (e.g., resize, blur) of confidential original images. Several scenarios (e.g., selling images over the Internet, fighting disinformation, detecting deep fakes) would highly benefit from systems allowing to verify that an image is the result of a transformation applied to a confidential authentic image. In this paper, we focus on systems for proving and verifying the correctness of transformations of authentic images guaranteeing: 1) confidentiality (i.e., the original image remains private), 2) efficient proof generation (i.e., the proof certifying the correctness of the transformation can be computed with a common laptop) even for high-resolution images, 3) authenticity (i.e., only the advertised transformations have been applied) and 4) fast detection of fraud proofs.. Our contribution consists of new definitions modelling confidentiality and adaptive adversaries, techniques to speed up the prover of a ZK-snark, an efficient construction relying on ad-hoc signatures and hashes, and a less efficient construction that works according to signatures and hashes included in the C2PA specifications. Experimental results confirm the viability of our approach, allowing to compute an authentic transformation of a high-resolution image on a common computer. Prior results instead either require expensive computing resources or provide unsatisfying confidentiality.

The Interested Party Information (IPI) system uniquely identifies the rights holders worldwide, making it possible to know for each subject and at any time which rights are protected, by whom and for which territories. Currently, this service is provided in a centralized way but in 2021, the Italian Society of Authors and Editors (SIAE) deployed a blockchain-based solution to completely decentralize this database to (a) provide greater guarantees to the rights holders as well as end users and (b) make a first tangible step in the path towards an all in-chain solution decentralizing a relevant component of the current architecture. This solution relied on early versions of Algorand smart contracts, delegating some off-chain verification to trusted third parties in many practical scenarios. Moreover, the Algorand technology has developed new tools, allowing us to design new techniques to reduce some of the trust assumptions of the original solution and enhance its efficiency at the same time. In this paper, we present the evolution of the solutions we designed to issue new on-chain non-conflicting rights representations, namely representations that are consistent with those already available on-chain. Our solution relies on smart contracts that have been implemented to run our experiments to prove (a) the feasibility of the proposed approach, (b) the scalability of the proposed solutions, and (c) the sustainability in terms of costs.