Zero-Knowledge Proofs

Alice: "I work at TechCorp"
Bob: "Prove it - show me your employee ID"
Alice: *shows ID with name, photo, employee number*

Alice: "I work at TechCorp"
Bob: "Prove it"
Alice: *generates cryptographic proof*
Bob: *verifies proof* "Confirmed: You work at TechCorp"

import Semaphore
 
let identity = try Identity.generateRandom()
// identity.privateKey - NEVER share
// identity.commitment - Public identifier

struct Group {
    let id: UUID
    let name: String
    var members: Set<String> // Identity commitments
    let depth: Int = 20       // Merkle tree depth
}

let proof = try semaphore.generateProof(
    identity: identity,
    groupId: groupId,
    signal: "I'm a verified member",
    externalNullifier: "unique-context-id"
)

┌─────────────────────────────────────┐
│         Swift App Layer             │
│  (BusinessCard, P2P, Storage)       │
└──────────────┬──────────────────────┘
               │
┌──────────────▼──────────────────────┐
│      Mopro Swift Bindings           │
│   (Swift wrapper for Rust libs)     │
└──────────────┬──────────────────────┘
               │
┌──────────────▼──────────────────────┐
│       Mopro Rust Core               │
│  (ZK circuits, Semaphore logic)     │
└──────────────┬──────────────────────┘
               │
┌──────────────▼──────────────────────┐
│      Platform (iOS/ARM64)           │
│  (Hardware-accelerated crypto)      │
└─────────────────────────────────────┘

import Mopro
 
class ZKProofService {
    private let mopro: MoproCircom
 
    init() {
        // Initialize with Semaphore circuit
        self.mopro = try! MoproCircom()
        try! mopro.initialize(
            zkeyPath: Bundle.main.path(forResource: "semaphore", ofType: "zkey")!,
            wasmPath: Bundle.main.path(forResource: "semaphore", ofType: "wasm")!
        )
    }
}

extension ZKProofService {
    func generateProof(
        identity: Identity,
        groupId: UUID,
        signal: String
    ) throws -> SemaphoreProof {
        // Prepare circuit inputs
        let inputs = [
            "identitySecret": identity.privateKey,
            "identityPathElements": groupMerkleTree.pathElements,
            "identityPathIndices": groupMerkleTree.pathIndices,
            "signal": signal,
            "externalNullifier": groupId.uuidString
        ]
 
        // Generate proof (takes 1-3 seconds on device)
        let proof = try mopro.generateProof(inputs: inputs)
 
        return SemaphoreProof(
            proof: proof.proof,
            publicSignals: proof.publicSignals,
            nullifier: calculateNullifier(identity, groupId)
        )
    }
}

extension ZKProofService {
    func verifyProof(
        _ proof: SemaphoreProof,
        groupId: UUID,
        expectedSignal: String
    ) throws -> Bool {
        // Verify cryptographic proof
        let isValid = try mopro.verifyProof(
            proof: proof.proof,
            publicSignals: proof.publicSignals
        )
 
        guard isValid else { return false }
 
        // Verify signal matches
        guard proof.signal == expectedSignal else { return false }
 
        // Verify nullifier hasn't been used before
        guard !isNullifierUsed(proof.nullifier, in: groupId) else {
            throw ZKError.nullifierAlreadyUsed
        }
 
        return true
    }
}

// Alice joins TechCorp group
let techCorpGroup = try Group.create(name: "TechCorp Employees")
try techCorpGroup.addMember(commitment: alice.commitment)
 
// Alice proves employment to Bob
let proof = try alice.generateProof(
    groupId: techCorpGroup.id,
    signal: "I work at TechCorp"
)
 
// Bob verifies (learns nothing about Alice's identity)
let isEmployee = try verifyProof(proof, groupId: techCorpGroup.id)
// Result: true ✓

// Event organizer creates group
let conferenceGroup = try Group.create(name: "Tech Conference 2024")
 
// Add attendees (only commitments, not identities)
for attendee in attendees {
    try conferenceGroup.addMember(commitment: attendee.commitment)
}
 
// Attendee proves participation
let proof = try attendee.generateProof(
    groupId: conferenceGroup.id,
    signal: "I attended Tech Conference 2024"
)

let certifiedGroup = try Group.create(name: "AWS Certified Developers")
 
// Professional generates proof
let proof = try professional.generateProof(
    groupId: certifiedGroup.id,
    signal: "I am AWS certified"
)
 
// Potential employer verifies
let isCertified = try verifyProof(proof, groupId: certifiedGroup.id)

let alumniGroup = try Group.create(name: "Stanford Alumni")
 
let proof = try graduate.generateProof(
    groupId: alumniGroup.id,
    signal: "I'm a Stanford graduate"
)

class GroupService {
    func createGroup(name: String, description: String) throws -> Group {
        let group = Group(
            id: UUID(),
            name: name,
            description: description,
            members: []
        )
 
        // Store group locally
        try storage.save(group)
 
        return group
    }
 
    func addMember(commitment: String, to group: Group) throws {
        var updatedGroup = group
        updatedGroup.members.insert(commitment)
 
        // Rebuild Merkle tree with new member
        updatedGroup.merkleTree = buildMerkleTree(from: updatedGroup.members)
 
        try storage.save(updatedGroup)
    }
}

class MembershipService {
    func requestMembership(
        identity: Identity,
        groupId: UUID
    ) throws -> MembershipRequest {
        return MembershipRequest(
            groupId: groupId,
            commitment: identity.commitment, // Share only commitment
            timestamp: Date()
        )
    }
}

class ProofCache {
    private var cache: [String: SemaphoreProof] = [:]
 
    func getCachedProof(
        identity: Identity,
        groupId: UUID,
        signal: String
    ) -> SemaphoreProof? {
        let key = "\(identity.commitment)-\(groupId)-\(signal)"
        return cache[key]
    }
 
    func cacheProof(
        _ proof: SemaphoreProof,
        identity: Identity,
        groupId: UUID,
        signal: String
    ) {
        let key = "\(identity.commitment)-\(groupId)-\(signal)"
        cache[key] = proof
    }
}

class IdentityStorage {
    func saveIdentity(_ identity: Identity) throws {
        let data = try JSONEncoder().encode(identity.privateKey)
 
        let query: [String: Any] = [
            kSecClass as String: kSecClassGenericPassword,
            kSecAttrAccount as String: "zk-identity",
            kSecValueData as String: data,
            kSecAttrAccessible as String: kSecAttrAccessibleWhenUnlockedThisDeviceOnly
        ]
 
        let status = SecItemAdd(query as CFDictionary, nil)
        guard status == errSecSuccess else {
            throw IdentityError.storageFailed
        }
    }
}

struct NullifierStore {
    private var usedNullifiers: Set<String> = []
 
    mutating func markAsUsed(_ nullifier: String) {
        usedNullifiers.insert(nullifier)
    }
 
    func isUsed(_ nullifier: String) -> Bool {
        return usedNullifiers.contains(nullifier)
    }
}