Present ZKP Proof

Journey 3: Present Proof to Verifier

Present passport-derived zero-knowledge proofs (age ≥ 18, humanhood) to verifiers. Supports two paths:

Path 1 — App-to-App: verifier has Solidarity → scan QR, verify locally, < 1s, no network
Path 2 — Web Verifier: verifier has no app → scan QR → opens self-hosted webpage, browser-side WASM verification

Parallel Timeline

Prover Side

Entry Point A: Self-initiated (Me Tab)

Me Tab → tap [Present →] on a proof → Face ID → [PR-1b]

Entry Point B: Passive (scan Verifier’s QR)

Share Tab → [📷 Scan] → scan openid4vp:// QR → [SC-2] Router → [PR-1]

[PR-1] Proof Request Review (triggered from Verifier QR)


┌─────────────────────────────────┐
│  Bar ABC requests confirmation: │
│                                 │
│  ✅ You are 18+                  │
│                                 │
│  Not shared:                    │
│  ✕ Name                         │
│  ✕ Date of birth                │
│  ✕ Passport number              │
│                                 │
│  Source: Passport · 🟢 Gov-level │
│                                 │
│  [Decline]  [Present with Face ID]│
└─────────────────────────────────┘

Technology: parse OID4VP presentation_definition, search local credential store for matching VCs.

[PR-1b] Self-Initiated QR Display


┌──────────────────────────────────────────┐
│                                          │
│  🟢 Age ≥ 18                             │
│                                          │
│       ┌──────────────────────┐           │
│       │                      │           │
│       │    [Smart QR Code]   │           │
│       │                      │           │
│       └──────────────────────┘           │
│                                          │
│  Not revealed: name, DOB, passport no.   │
│                                          │
│  ⏱ [Circular progress] 45s remaining    │
│                                          │
│  [Close]                                 │
└──────────────────────────────────────────┘

Countdown expires → auto re-sign and refresh QR + toast “QR Code refreshed”

Smart QR design (one QR, two paths, zero decision):


QR content = https://verify.solidarity.app/p/{proof_id}#{signed_vp_token}

Verifier situation	Behavior
Has Solidarity App	App intercepts as Universal Link, extracts VP token from fragment → local verify
No App (default camera)	Opens browser, extracts proof from URL fragment → WASM verify

Privacy: proof is in the URL fragment (#), server never sees it. Prover doesn’t need to know if verifier has the app.

Code:

solidarity/Views/ScanViews/ProofPresentationFlowSheet.swift
solidarity/Services/Identity/OID4VPPresentationService.swift

[PR-2] Proof Signing & Submission


Generating and submitting proof... (1-3s)

Technology:

Face ID unlocks Keychain
Use pairwise DID key for this verifier’s domain (creates new per-RP key pair if needed)
Sign vp_token with pairwise DID key (ECDSA P-256)
Submit to verifier via OID4VP redirect_uri

[PR-3] Proof Presented ✅


[Green checkmark animation]
Proof submitted ✅
The verifier can confirm you're 18+,
but sees none of your other information.

Auto-closes after 3 seconds.

Verifier Side (In-App)

[VF-1] Verification Success ✅


┌──────────────────────────────────────────┐
│                                          │
│       [Green shield ✅ zoom-in]          │
│                                          │
│       This person is an adult            │
│       Age ≥ 18                           │
│                                          │
│  ── Verification Details ──────────      │
│  Source: Passport · 🟢 ZKP Verified      │
│  Signed: 2025-03-15 14:30               │
│  ⚠️ This proof doesn't include name      │
│                                          │
│  [Done]                                  │
└──────────────────────────────────────────┘

Plain-language headline (not just technical fields):

Proof Type	Headline
`age_over_18`	This person is an adult (Age ≥ 18)
`is_human`	This person is a real human (Passport verified)
`verified_contact_count`	This person has N face-to-face verified contacts

Verification speed: < 1s — skip loading screen, animate directly to result.

[VF-1c] Verification Failed ❌


┌──────────────────────────────────────────┐
│   [Red shield ❌ + Haptic .error]        │
│                                          │
│   Verification Failed                    │
│                                          │
│   IF expired / replay attack:            │
│     "Expired. Ask them to present again" │
│                                          │
│   IF other (invalid sig / bad format):  │
│     "This proof cannot be verified"      │
│                                          │
│   [Scan Again]    [Close]                │
└──────────────────────────────────────────┘

Technical verification (in-app):

Parse VP token (compact JWT)
Verify ZK proof (mopro verifier)
Check nonce + expiry (replay prevention)
Extract public signals

Code:

solidarity/Services/Identity/ProofVerifierService.swift
solidarity/Services/Identity/ProofVerifierService+VPToken.swift

Verifier Side (Web — No App)

[VF-W] Web Verifier

Triggered: default camera scans Smart QR → opens verify.solidarity.app in browser


┌──────────────────────────────────────────┐
│  [Solidarity Logo]                       │
│                                          │
│       ✅ This person is an adult         │
│       Age ≥ 18                           │
│                                          │
│  Source: Passport · 🟢 ZKP Verified      │
│                                          │
│  This proof doesn't include name or      │
│  any other personal information.         │
│  ─────────────────────                   │
│  What is a zero-knowledge proof?         │
│  The person used their passport to       │
│  generate a mathematical proof that      │
│  they're 18+, revealing nothing else.   │
│  ─────────────────────                   │
│  [Download Solidarity App]               │
└──────────────────────────────────────────┘

Technology:

Self-hosted static web + WASM ZK verifier (snarkjs or mopro-wasm)
Proof is in URL fragment → server never sees it (server-side privacy)
Verification logic runs in browser
iOS App Clip: Universal Link can trigger App Clip for native experience

VP Token Structure (OID4VP)


{
  "iss": "did:key:z6Mk...",
  "iat": 1710000000,
  "exp": 1710000045,
  "nonce": "verifier-provided-nonce",
  "aud": "https://bar-abc.example.com",
  "vp": {
    "@context": ["https://www.w3.org/2018/credentials/v1"],
    "type": ["VerifiablePresentation"],
    "holder": "did:key:z6Mk...",
    "verifiableCredential": [
      "eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCJ9..."
    ]
  }
}

A single VP can carry multiple VC JWTs.

Code: solidarity/Services/Identity/OID4VPPresentationService.swift (wrapCredentialsAsVP)