Crypto Reading Group -Roy Stracovsky

In this talk, I will present joint work with Joseph Jaeger which enhances the security and functionality of anamorphic cryptography. We first enhance the security of anamorphic signatures by proposing two parallel notions of unforgeability (against the aforementioned dictator or instead a recipient) which close gaps in existing definitions termed robustness (Banfi, Gegier, Hirt, Maurer, and Rito, Eurocrypt 2024) and private anamorphism (Kutylowski, Persiano, Phan, Yung, and Zawada, Crypto 2023). Previously proposed anamorphic schemes do not necessarily achieve our new definitions but can sometimes be made to do so by modifying the scheme or by leveraging stronger assumptions on the underlying building blocks.

For our second enhancement, we introduce techniques to stealthily exchange keys via anamorphic cryptosystems, allowing covert communication between users that do not a priori share a double key. We propose and analyze multiple protocols in a four-quadrant security model capturing passive versus active adversaries who may or may not perform key compromise.