Omniring: Scaling Up Private Payments Without Trusted Setup - Formal Foundations and Constructions of Ring Confidential Transactions with Log-size Proofs

Russell W.  F.  Lai; Viktoria Ronge; Tim Ruffing; Dominique Schröder; Sri Aravinda Krishnan Thyagarajan; Jiafan Wang

Paper 2019/580

Omniring: Scaling Up Private Payments Without Trusted Setup - Formal Foundations and Constructions of Ring Confidential Transactions with Log-size Proofs

Russell W. F. Lai, Viktoria Ronge, Tim Ruffing, Dominique Schröder, Sri Aravinda Krishnan Thyagarajan, and Jiafan Wang

Abstract

Monero is the largest cryptocurrency with built-in cryptographic privacy features. The transactions are authenticated using spend proofs, which provide a certain level of anonymity by hiding the source accounts from which the funds are sent among a set (known as a ring) of other accounts. Due to its similarities to ring signatures, this core cryptographic component is called Ring Confidential Transactions (RingCT). Because of its practical relevance, several works attempt to analyze the security of RingCT. However, due to the complexity of RingCT they are either informal, miss fundamental functionalities, or introduce undesirable trusted setup assumptions. Regarding efficiency, Monero currently deploys a scheme in which the size of the spend proof is linear in the ring size. This limits the ring size to only a few accounts, which in turn limits the acquired anonymity significantly and facilitates de-anonymization attacks. As a solution to these problems, we present the first complete rigorous formalization of RingCT as a cryptographic primitive. We then propose a generic construction of RingCT and prove it secure in our formal security model. By instantiating our generic construction with new efficient zero-knowledge proofs we obtain Omniring, a fully-fledged RingCT scheme in the discrete logarithm setting that provides the highest concrete and asymptotic efficiency as of today. Omniring is the first RingCT scheme which 1) does not require a trusted setup or pairing-friendly elliptic curves, 2) has a proof size logarithmic in the size of the ring, and 3) allows to share the same ring between all source accounts in a transaction, thereby enabling significantly improved privacy level without sacrificing performance. Our zero-knowledge proofs rely on novel enhancements to the Bulletproofs framework (S&P 2018), which we believe are of independent interest.

Metadata

Available format(s): PDF
Category: Cryptographic protocols
Publication info: Published elsewhere. Major revision. ACM CCS '19
DOI: 10.1145/3319535.3345655
Contact author(s): russell lai @ cs fau de
ronge @ cs fau de
crypto @ timruffing de
dominique schroeder @ fau de
sri aravinda thyagarajan @ fau de
wj016 @ ie cuhk edu hk
History: 2020-04-09: last of 2 revisions; 2019-05-30: received; See all versions
Short URL: https://ia.cr/2019/580
License: CC BY

BibTeX

@misc{cryptoeprint:2019/580,
      author = {Russell W.  F.  Lai and Viktoria Ronge and Tim Ruffing and Dominique Schröder and Sri Aravinda Krishnan Thyagarajan and Jiafan Wang},
      title = {Omniring: Scaling Up Private Payments Without Trusted Setup - Formal Foundations and Constructions of Ring Confidential Transactions with Log-size Proofs},
      howpublished = {Cryptology {ePrint} Archive, Paper 2019/580},
      year = {2019},
      doi = {10.1145/3319535.3345655},
      url = {https://eprint.iacr.org/2019/580}
}