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HFIPay: Privacy-Preserving, Cross-Chain Cryptocurrency Payments to Human-Friendly Identifiers

Jian Sheng Wang

Abstract

Sending cryptocurrency to an email address or phone number should be as simple as a bank transfer, yet naive schemes that map identifiers directly to blockchain addresses expose the recipient's balances and transaction history to anyone who knows the identifier. HFIPay separates private routing, sender-side quote verification, and on-chain claim authorization. A relay resolves the human-friendly identifier off-chain and commits only a per-intent blinded binding rho_i plus the quoted payment tuple; the chain sees neither the identifier nor a reusable recipient tag. In a verified-quote deployment, the relay returns a sender-verifiable off-chain proof linking rho_i to an attested binding-key commitment, so the relay cannot substitute a different recipient before funding. To claim, the recipient proves in zero knowledge -- via ZK-ACE -- that the funded intent's blinded binding matches a handle derived from the same deterministic identity, authorizing release of the quoted asset and amount to a chosen destination. We formalize two privacy goals: enumeration resistance and pre-claim unlinkability, and distinguish a baseline deployment (relay trusted for binding correctness) from the verified-quote deployment (binding is sender-verifiable without a public registry). When composed with an NVM runtime, the same mechanism extends to cross-chain settlement. The result is a relay-assisted but non-custodial architecture: relays are privacy and availability dependencies, but cannot redirect funds.

HFIPay: Privacy-Preserving, Cross-Chain Cryptocurrency Payments to Human-Friendly Identifiers

Abstract

Sending cryptocurrency to an email address or phone number should be as simple as a bank transfer, yet naive schemes that map identifiers directly to blockchain addresses expose the recipient's balances and transaction history to anyone who knows the identifier. HFIPay separates private routing, sender-side quote verification, and on-chain claim authorization. A relay resolves the human-friendly identifier off-chain and commits only a per-intent blinded binding rho_i plus the quoted payment tuple; the chain sees neither the identifier nor a reusable recipient tag. In a verified-quote deployment, the relay returns a sender-verifiable off-chain proof linking rho_i to an attested binding-key commitment, so the relay cannot substitute a different recipient before funding. To claim, the recipient proves in zero knowledge -- via ZK-ACE -- that the funded intent's blinded binding matches a handle derived from the same deterministic identity, authorizing release of the quoted asset and amount to a chosen destination. We formalize two privacy goals: enumeration resistance and pre-claim unlinkability, and distinguish a baseline deployment (relay trusted for binding correctness) from the verified-quote deployment (binding is sender-verifiable without a public registry). When composed with an NVM runtime, the same mechanism extends to cross-chain settlement. The result is a relay-assisted but non-custodial architecture: relays are privacy and availability dependencies, but cannot redirect funds.

Paper Structure

This paper contains 48 sections, 5 theorems, 22 equations, 2 figures, 5 tables, 3 algorithms.

Table of Contents

  1. Introduction
  2. Motivation
  3. Privacy Challenge
  4. Our Approach
  5. Contributions
  6. System Model
  7. Participants
  8. Enrollment and Binding Modes
  9. Threat Model
  10. Design Goals
  11. Protocol
  12. Overview
  13. Recipient Setup and Binding
  14. Quote Generation and Intent Creation
  15. Funding
  16. ...and 33 more sections

Key Result

Lemma 3.1

In the verified-quote deployment, suppose a sender accepts a quote after verifying $(K_{B,e_i}, T_{\mathsf{bind},i}, \tau_B, \pi_i^{\mathsf{quote}})$ for fixed $(\texttt{intentId}_i, \rho_i)$, and later the chain accepts a claim proof $\pi_i$ for the same $(\texttt{intentId}_i, \rho_i, e_i)$. Under

Figures (2)

  • Figure 1: High-level protocol flow.
  • Figure 2: Cross-chain payment routing via n-Vm.

Theorems & Definitions (19)

  • Definition 1: Sender
  • Definition 2: Recipient
  • Definition 3: Relay Service
  • Definition 4: Binding Layer
  • Definition 5: Observer
  • Definition 6: EVM Address Derivation
  • Definition 7: Solana Address Derivation
  • Lemma 3.1: Quote-to-Claim Composition
  • proof : Proof sketch
  • Definition 8: Observer View
  • ...and 9 more