In this work, we present homomorphic encryption-based vaults (Haults), a permissioned privacy-preserving smart wallet protocol for VM-enabled blockchains that keeps users' balances confidential, as well as the amounts transacted to other parties. To comply with regulations, we include optional compliance features that allow specific entities (the auditors) to retrieve transaction amounts or execute force transfers when necessary. Our solution uses ElGamal over elliptic curves to encrypt balances, combined with zero-knowledge proofs to verify the correctness of transaction amounts and the integrity of the sender's updated balance, among other security checks. We provide a detailed explanation of the protocol, including a security discussion and benchmarks from our proof-of-concept implementation, which yield great results. Beyond in-contract issued tokens, we also provide a thorough explanation on how our solution can be compatible with external ones (e.g., Ether or any ERC20).

翻译：本研究提出了一种基于同态加密的保险库协议（Haults），这是一种面向虚拟机区块链的许可式隐私保护智能钱包协议，能够确保用户余额及交易金额的机密性。为满足监管要求，我们引入了可选的合规功能，允许特定实体（审计方）在必要时获取交易金额或执行强制转账。该方案采用椭圆曲线上的ElGamal加密算法对余额进行加密，并结合零知识证明来验证交易金额的正确性、发送方更新后余额的完整性及其他安全检查。我们提供了协议的详细说明，包括安全性讨论及概念验证实现的性能基准测试，结果表现优异。除合约内发行的代币外，我们还深入阐述了本方案如何与外部代币系统（如以太币或任何ERC20标准代币）保持兼容性。