Adaptor Signatures and Applications
Sri AravindaKrishnan Thyagarajan
Video
Abstract:
Adaptor signatures extend the functionality of regular signatures through the computation of \emph{pre-signatures} on messages for statements of NP relations. Pre-signatures are publicly verifiable; they simultaneously hide and commit to a signature of an underlying signature scheme on that message. Anybody possessing a corresponding witness for the statement can adapt the pre-signature to obtain the ``regular'' signature. Adaptor signatures have numerous applications for conditional payments in blockchain systems, like payment channels~(CCS'20, CCS'21), private coin mixing (CCS'22), and oracle-based payments (NDSS'23). Despite their popularity, \emph{all} known constructions are (1) derived from identification schemes via the Fiat-Shamir transform in the random oracle model or (2) require modifications to the underlying signature verification algorithm, thus making the construction useless in the setting of cryptocurrencies.
In this talk, we will see how to construct the first adaptor signature schemes for Camenisch-Lysyanskaya (CL), Boneh-Boyen-Shacham (BBS+), and Waters signatures. Our constructions rely on a new abstraction of digital signatures, called \emph{dichotomic signatures}, which covers the essential properties we need to build adaptor signatures. We will also briefly review the latest security model for adaptor signatures. Finally, to prove its security, we will look at a novel non-black-box proof technique called transparent reductions, that might be of independent interest.
Bio:
Sri AravindaKrishnan Thyagarajan, or Aravind in short, is an honorary lecturer who will start his position as a lecturer at The University of Sydney’s School of Computer Science this July. His research focuses on applied cryptography and decentralized systems like Blockchains. He aims at developing provably secure cryptographic tools in combination with game-theoretic techniques to address privacy, scalability, and efficiency issues in decentralized applications. Previously, he was a postdoc at NTT Research and Carnegie Mellon University supervised by Elaine Shi. He finished his Ph.D. at the University of Erlangen Nuremberg, Germany with Dominique Schröder as his advisor in 2021.