Privacy-Preserving Voting

Overview

Bitcoin Commons implements privacy-preserving voting through contribution-based voting and zap-to-vote mechanisms. The system uses quadratic voting (square root of contribution amount) to prevent vote buying while allowing contributors to express preferences.

Voting Mechanisms

Contribution-Based Voting

Contributors receive voting weight based on their contributions:

• Zaps: Lightning Network zap contributions (tracked for transparency, don’t affect governance)

Code: contributions.rs

Zap-to-Vote

Zaps to governance events are converted into votes:

• Proposal Zaps: Zaps to governance event IDs
• Vote Types: Support, Veto, Abstain
• Quadratic Weight: Vote weight = sqrt(zap_amount_btc)
• Message Parsing: Vote type extracted from zap message

Code: zap_voting.rs

Vote Weight Calculation

Quadratic Formula

Vote weight uses quadratic formula to prevent vote buying:

#![allow(unused)]
fn main() {
vote_weight = sqrt(zap_amount_btc)
}

Code: weight_calculator.rs

Participation Weight

Base participation weight from contributions:

• 90-Day Window: Contributions within 90 days
• Contribution Types: Zaps (tracked for transparency only)
• Cooling-Off Period: New contributions have reduced weight

Code: weight_calculator.rs

Combined Weight

Proposal vote weight uses higher of zap or participation:

#![allow(unused)]
fn main() {
base_weight = max(zap_weight, participation_weight * 0.1)
final_weight = apply_weight_cap(base_weight, total_system_weight)
}

Code: weight_calculator.rs

Vote Types

Support

Default vote type for proposal zaps:

• Default: If no message, vote is support
• Message Keywords: “support”, “yes”, “approve”
• Weight: Calculated from zap amount

Veto

Opposition vote:

• Message Keywords: “veto”, “oppose”, “against”
• Threshold: 40% of zap votes blocks proposal
• Independent: Zap veto independent of participation votes

Code: vote_aggregator.rs

Abstain

Neutral vote:

• Message Keywords: “abstain”, “neutral”
• Weight: Counted but doesn’t affect threshold
• Purpose: Express neutrality without blocking

Code: zap_voting.rs

Vote Processing

Zap Vote Processing

1. Receive Zap: Zap contribution received via Nostr
2. Check Proposal Zap: Verify zap is for governance event
3. Calculate Weight: Weight = sqrt(amount_btc)
4. Parse Vote Type: Extract from zap message
5. Check Duplicate: Prevent duplicate votes
6. Record Vote: Store in database

Code: zap_voting.rs

Vote Aggregation

Votes are aggregated for proposals:

1. Get Zap Votes: All zap votes for proposal
2. Get Participation Votes: Participation-based votes
3. Combine Totals: Sum support, veto, abstain weights
4. Check Threshold: Verify threshold met
5. Check Veto: Verify no veto blocking

Code: vote_aggregator.rs

Privacy Features

Pseudonymous Voting

Votes are linked to Nostr pubkeys, not real identities:

• Pubkey-Based: Votes tracked by sender pubkey
• No KYC: No identity verification required
• Privacy: Real identity not revealed

Quadratic Voting

Quadratic formula prevents vote buying:

• Square Root: Vote weight = sqrt(contribution)
• Diminishing Returns: Large contributions have proportionally less weight
• Fairness: Prevents wealthy contributors from dominating

Code: weight_calculator.rs

Cooling-Off Period

New contributions have reduced weight:

• Age Check: Contributions must be old enough
• Reduced Weight: New contributions use participation weight only
• Prevents Gaming: Prevents last-minute contribution manipulation

Code: weight_calculator.rs

Vote Aggregation

Vote Totals

#![allow(unused)]
fn main() {
pub struct VoteTotals {
    pub support_weight: f64,
    pub veto_weight: f64,
    pub abstain_weight: f64,
    pub total_weight: f64,
    pub support_count: u32,
    pub veto_count: u32,
    pub abstain_count: u32,
    pub total_count: u32,
}
}

Code: zap_voting.rs

Proposal Vote Result

#![allow(unused)]
fn main() {
pub struct ProposalVoteResult {
    pub pr_id: i32,
    pub tier: u8,
    pub threshold: u32,
    pub total_votes: f64,
    pub support_votes: f64,
    pub veto_votes: f64,
    pub abstain_votes: f64,
    pub zap_vote_count: u32,
    pub participation_vote_count: u32,
    pub threshold_met: bool,
    pub veto_blocks: bool,
}
}

Code: vote_aggregator.rs

Veto Mechanisms

Zap Veto

Zap votes can veto proposals:

• Threshold: 40% of zap votes must be veto
• Independent: Independent of participation votes
• Blocking: Veto blocks proposal approval

Code: vote_aggregator.rs

Database Schema

Proposal Zap Votes Table

CREATE TABLE proposal_zap_votes (
    id INTEGER PRIMARY KEY,
    pr_id INTEGER NOT NULL,
    governance_event_id TEXT NOT NULL,
    sender_pubkey TEXT NOT NULL,
    amount_msat INTEGER NOT NULL,
    amount_btc REAL NOT NULL,
    vote_weight REAL NOT NULL,  -- sqrt(amount_btc)
    vote_type TEXT NOT NULL,    -- 'support', 'veto', 'abstain'
    timestamp DATETIME NOT NULL,
    verified BOOLEAN DEFAULT FALSE
);

Code: 005_governance_contributions.sql

Integration with Nostr

Zap Tracking

Zaps are tracked via Nostr integration:

• Zap Tracker: Monitors Nostr zaps
• Event Filtering: Filters zaps to governance events
• Vote Conversion: Converts zaps to votes

Code: zap_tracker.rs

Governance Events

Governance events on Nostr:

• Event IDs: Unique identifiers for proposals
• Zap Targets: Zaps to event IDs become votes
• Real-Time: Votes processed in real-time

Benefits

1. Privacy: Pseudonymous voting via Nostr pubkeys
2. Fairness: Quadratic voting prevents vote buying
3. Accessibility: Anyone can vote via Lightning zaps
4. Transparency: All votes recorded on-chain/off-chain
5. Resilience: No single point of failure

Components

The privacy-preserving voting system includes:

• Zap-to-vote processor
• Vote weight calculator (quadratic formula)
• Vote aggregator
• Participation weight calculation
• Cooling-off period enforcement
• Zap tracking (for transparency, governance is maintainer-only multisig)

Location: blvm-commons/src/nostr/zap_voting.rs, blvm-commons/src/governance/weight_calculator.rs, blvm-commons/src/governance/vote_aggregator.rs