1、 1 Project Tourbillon Exploring privacy,security and scalability for CBDCs Final Report November 2023 Publication date:November 2023 Bank for International Settlements 2023.All rights reserved.Brief excerpts may be reproduced or translated provided the source is stated.ISBN 978-92-9259-711-5(online)

2、Project Tourbillon 2 Executive summary 3 Acronyms,abbreviations and definitions 5 1 Introduction 6 2 The prototypes 11 2.1 High level solution architecture 11 2.2 eCash 1.0(EC1)13 2.3 eCash 2.0(EC2)18 2.4 Implementation and testing setup 21 3 Results and considerations 22 3.1 Payer anonymity and oth

3、er policy objectives 23 3.2 Quantum-safe cryptography 23 3.3 Scalability 24 3.4 Privacy and security trade-offs 26 3.5 Implementation considerations 26 4 Conclusions and next steps 27 References 29 Annex A:Optimal denomination algorithm 32 Annex B:Sequence diagrams for rebalancing 34 Annex C:Threat

4、model and trust assumptions 36 Annex D:Quantum-safe blind signature scheme 40 Contributors 41 Project Tourbillon 3 Executive summary The use of cash is in decline worldwide as digital payments continue to grow.Over the past decade,the number of cashless payments has grown at an annual rate of 16%,wi

5、th more than one trillion transactions in CPMI countries alone.1 In this context,concerns about the potential erosion of privacy are being raised.2 Unsurprisingly,public consultations by central banks on retail central bank digital currencies(CBDCs)show that privacy is a fundamental user requirement

6、.3 Privacy is the right to keep personal information secret or known only to a trusted group of people.This implies that there are different levels of privacy.According to Bank of Canada et al(2021),payments can be(i)confidential,where only trusted parties see personal information(such as credit car