Post-Quantum ID-based Ring Signatures from Symmetric-key Primitives

Ring signatures and ID-based cryptography are considered promising in terms of application. A ring signature authenticates messages while the author of the message remains anonymous. ID-based cryptographic primitives suppress the need for certificates in public key infrastructures (PKI). In this work, we propose a generic construction for post-quantum ID-based ring signatures (IDRS) based on symmetric-key primitives from which we derive the first two constructions of IDRS. The first construction named PicRS utilizes the Picnic digital signature to ensure its security while the second construction XRS is motivated by the stateful digital signature XMSS instead of Picnic, allowing a signature size reduction. Both constructions have a competitive signature size when compared with state-of-the-art lattice-based IDRS. XRS can achieve a competitive signature size of 889KB for a ring of 4096 users while the fully stateless PicRS achieves a signature size of 1.900MB for a ring of 4096 users. In contrast, the shortest lattice-based IDRS achieves a signature size of 335MB for the same ring size

A Survey on Exotic Signatures for Post-Quantum Blockchain: Challenges & Research Directions

Blockchain technology provides efficient and secure solutions to various online activities by utilizing a wide range of cryptographic tools. In this paper, we survey the existing literature on post-quantum secure digital signatures that possess exotic advanced features and which are crucial cryptographic tools used in the blockchain ecosystem for (i) account management, (ii) consensus efficiency, (iii) empowering scriptless blockchain, and (iv) privacy. The exotic signatures that we particularly focus on in this work are the following: multi-/aggregate, threshold, adaptor, blind and ring signatures. Herein the term exotic refers to signatures with properties which are not just beyond the norm for signatures e.g. unforgeability, but also imbue new forms of functionalities. Our treatment of such exotic signatures includes discussions on existing challenges and future research directions in the post-quantum space. We hope that this article will help to foster further research to make post-quantum cryptography more accessible so that blockchain systems can be made ready in advance of the approaching quantum threats