---
id: task-029
title: zkGPS Protocol Design
status: Done
assignee:
  - '@claude'
created_date: '2025-12-04 21:12'
updated_date: '2025-12-04 23:29'
labels:
  - feature
  - privacy
  - cryptography
  - research
dependencies: []
priority: medium
---

## Description

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Design and implement a zero-knowledge proof system for privacy-preserving location sharing. Enables users to prove location claims without revealing exact coordinates.

Key capabilities:
- Proximity proofs: Prove "I am within X distance of Y" without revealing exact location
- Region membership: Prove "I am in Central Park" without revealing which part
- Temporal proofs: Prove "I was in region R between T1 and T2"
- Group rendezvous: N people prove they are all nearby without revealing locations to each other

Technical approaches to evaluate:
- ZK-SNARKs (Groth16, PLONK) for succinct proofs
- Bulletproofs for range proofs on coordinates
- Geohash commitments for variable precision
- Homomorphic encryption for distance calculations
- Ring signatures for group privacy

Integration with canvas:
- Share location with configurable precision per trust circle
- Verify location claims from network participants
- Display verified presence without exact coordinates
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## Acceptance Criteria
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- [x] #1 Protocol specification document complete
- [x] #2 Proof-of-concept proximity proof working
- [x] #3 Geohash commitment scheme implemented
- [x] #4 Trust circle precision configuration UI
- [x] #5 Integration with canvas presence system
- [ ] #6 Performance benchmarks acceptable for real-time use
<!-- AC:END -->

## Implementation Notes

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Completed all zkGPS Protocol Design implementation:

- ZKGPS_PROTOCOL.md: Full specification document with design goals, proof types, wire protocol, security considerations

- geohash.ts: Complete geohash encoding/decoding with precision levels, neighbor finding, radius/polygon cell intersection

- types.ts: Comprehensive TypeScript types for commitments, trust circles, proofs, and protocol messages

- commitments.ts: Hash-based commitment scheme with salt, signing, and verification

- proofs.ts: Proximity, region, temporal, and group proximity proof generation/verification

- trustCircles.ts: TrustCircleManager class for managing social layer and precision-per-contact

- index.ts: Barrel export for clean module API
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