In this paper, we propose $\texttt{Tiramisu}$, as construction to build BB-SE NIZK arguments in the $\textit{updatable}$ CRS model. Similar to the $\texttt{COCO}$, $\texttt{Tiramisu}$ is suitable for modular use in larger cryptographic systems and allows building BB-SE NIZK arguments, but with $\textit{updatable}$ parameters. In the cost of one time CRS update, $\texttt{Tiramisu}$ gets arround the mentioned impossibility result by Bellare et al. Namely, by one time updating the CRS, all the parties eliminate the trust on a third-party and the protocol satisfies ZK and BB-SE in the $\textit{updatable}$ CRS model. Meanwhile, we define a variation of public-key cryptosystems with updatable keys, suitable for the updatable CRS model, and present an efficient construction based on the El-Gamal cryptosystem which can be of independent interest. We instantiate $\texttt{Tiramisu}$ and present efficient BB-SE zk-SNARKs with updatable parameters that can be used in protocols like Hawk, Gyges, Ouroboros Crypsinous while allowing the end-users to update the parameters and eliminate the needed trust.
Category / Keywords: cryptographic protocols / zk-SNARKs, Updatable CRS, Black-Box Simulation Extractability, COCO framework, UC-Security Date: received 22 Apr 2020, last revised 21 Oct 2020 Contact author: baghery karim at gmail com, ssedagha@esat kuleuven be Available format(s): PDF | BibTeX Citation Note: In Italian, Tiramisu literally means "pull me up, lift me up", or more literally "pull it up". Version: 20201021:122634 (All versions of this report) Short URL: ia.cr/2020/474