How to Build a “Passkey‑First” Wallet Experience

Summary: Passkeys moved from “nice UX” to production-grade infrastructure in 2025–2026, with WebAuthn Level 3 reaching Candidate Recommendation and Ethereum mainnet shipping a native P‑256 precompile. Here’s how to turn that into a measurable lift in onboarding, security posture, and onchain transaction throughput—without seed phrases or crypto slang. (w3.org)

Hook — The headache your PM and security lead keep arguing about

• Your “Connect wallet” funnel leaks 30–60% before first onchain action because extensions, seed phrases, and OTPs inject friction at exactly the wrong time.
• Engineering says “just add passkeys,” procurement wants NIST mappings, and chain teams ask how to verify secp256r1 signatures onchain without 200k+ gas or brittle relays.
• Mobile parity is a mess: Android’s Credential Manager, Apple’s AuthenticationServices, and Windows Hello/Edge sync don’t behave identically across fleets. AAGUID allowlists and attestation aren’t configured, so security can’t sign off. (developers.google.com)

Agitate — The risks if you ship the wrong thing

• Missed launch dates: backend teams often underestimate WebAuthn minutiae (origin/RPID binding, clientDataJSON hashing, attestation policy), leading to last‑minute rollbacks. (passwordless.id)
• Support blow‑ups: poorly handled cross‑device sync (e.g., using non‑syncable providers) strands users; help centers warn explicitly against certain setups for a reason. (help.coinbase.com)
• Onchain dead ends: without native P‑256 verification, you either pay prohibitive gas with big‑int libraries or ship centralized relays that your auditors will flag. EVM chains that implemented P‑256 at a precompile address solved this. (github.com)
• Compliance stalls: security cannot attest “phishing‑resistant MFA” or map to AAL2/AAL3 unless your passkey strategy, attestation enforcement, and device‑binding policy are explicit. NIST’s 2024–2026 guidance calls this out. (nist.gov)

Solve — 7Block Labs’ passkey‑first wallet methodology We build passkey‑native wallets that convert, verify onchain, and meet enterprise procurement requirements. The core principles:

1. Treat passkeys as production auth, not a feature

• Bind to your product’s registrable domain suffix as RPID; enforce strict origin checks server‑side to avoid “it works on localhost only” surprises. (w3.org)
• Use platform‑native UX:
  • Android: Credential Manager (API level ≥28) for unified bottom sheet and conditional UI. It reduces churn and consolidates passkeys, federated, and passwords behind one API. (developer.android.com)
  • iOS/macOS: AuthenticationServices passkey flows; support AutoFill‑assisted login and passkey reset paths. Chrome on macOS now interoperates with iCloud Keychain. (developer.apple.com)
  • Windows 11: Edge now syncs passkeys across devices; plan explicit policy for enterprise fleets vs bring‑your‑own. (windowscentral.com)

1. Make verification onchain cheap and standard

• On Ethereum mainnet (Fusaka hard fork, Dec 3, 2025), EIP‑7951 added a native secp256r1 (P‑256) precompile at address 0x100 with a 6,900 gas cost for verification—no custom bigint libraries. On OP‑Stack chains, P256VERIFY shipped earlier (Fjord) at 0x…0100 via RIP‑7212. Design for both. (blog.ethereum.org)

Solidity example: verifying a WebAuthn assertion

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

// Inputs:
//  - h: keccak256(message) where message = authenticatorData || sha256(clientDataJSON)
//  - r,s: ECDSA(P-256) signature
//  - qx,qy: uncompressed P-256 pubkey coordinates (from COSE_Key at registration)
//
// Precompile address:
//  - Ethereum L1 (EIP-7951): 0x0000000000000000000000000000000000000100 (0x100)
//  - Some L2s (RIP-7212/OP-Stack): same address (0x...0100)
library P256Verify {
    address constant P256PRECOMPILE = address(uint160(0x100));

    function verify(bytes32 h, bytes32 r, bytes32 s, bytes32 qx, bytes32 qy)
        internal view returns (bool ok)
    {
        bytes memory input = abi.encodePacked(h, r, s, qx, qy);
        uint256[1] memory out;
        assembly {
            let inPtr := add(input, 0x20)
            // staticcall(gas, to, inOffset, inSize, outOffset, outSize)
            if iszero(staticcall(gas(), P256PRECOMPILE, inPtr, 160, out, 32)) { ok := 0 }
            // precompile returns 32-byte 0x1 on success, empty on failure
            if eq(mload(out), 1) { ok := 1 }
        }
    }
}

Hashing the WebAuthn assertion correctly:

• message = authenticatorData || SHA‑256(clientDataJSON)
• h = SHA‑256(message)
• Ensure you parse COSE_Key (alg −7, crv P‑256) to get qx, qy. (developers.yubico.com)

1. Engineer the wallet around Account Abstraction, not vice‑versa

• ERC‑4337 smart accounts with a “passkey validator” module verify P‑256 signatures via the precompile in validateUserOp(). For chains without the precompile, fall back to a vetted library or route to a chain with RIP‑7212. (github.com)
• EIP‑7702 (Pectra, May 7, 2025) lets EOAs temporarily delegate execution to contract logic—use it to offer passkey‑backed, “same address” UX next to 4337 accounts. (blog.ethereum.org)
• Session keys: use wallet‑managed sessions for “one‑tap” in‑app actions (scope by time, target, and spend limits). Align with emerging modules (ERC‑6900/7579) and document scopes in UI. (rhinestone.dev)

1. Ship platform‑grade security controls that procurement can approve

• Attestation and AAGUID allowlisting: require attestation at registration to gate which authenticators can enroll; validate cert chains against the FIDO Metadata Service (v3.1) and enforce hardware‑backed storage where needed. Maintain a curated AAGUID allowlist per environment. (fidoalliance.org)
• NIST AAL mapping:
  • Syncable/cloud passkeys → AAL2 (phishing‑resistant, two‑factor equivalent with device + biometric/PIN).
  • Device‑bound passkeys (TPM/Secure Enclave/YubiKey) → AAL3 (verifier‑impersonation resistance, key non‑export). Document this in your RFP/Security Annex. (fidoalliance.org)
• Logging and privacy: don’t store raw passkey materials or full blobs; hash payloads by default; treat AAGUID and device IDs as personal data with retention caps. (Ask us for our field‑level telemetry schema.)

1. Measure what matters from Day 1

• Target metrics we implement and dashboard:
  • “First signed onchain action” conversion (from page view → authenticated → successful UserOperation)
  • Sign‑in success rate (passkeys vs password/TOTP)
  • Median Time‑to‑First‑Transaction (TTFT)
  • Paymaster spend per WAU and refund rate
  • Support ticket volume for “can’t sign in” and “lost seed phrase”
• Benchmarks to calibrate your goals:
  • Google observed passkey sign‑ins 4× more successful than passwords; FIDO reports 69% of consumers have enabled at least one passkey and 48% of top‑100 sites support passkeys. Use these as external baselines. (security.googleblog.com)

A concrete blueprint (with code and config you can lift) Audience: Heads of Product and Engineering for consumer fintech, exchanges, Web3 games, and L2 growth teams. Your required keywords: “AAGUID allowlist,” “attestation enforcement,” “NIST AAL2/AAL3,” “RPID governance,” “P‑256 precompile 0x100,” “UserOperation acceptance rate,” “session key scopes,” “paymaster policy.”

Stage 0 — Choose the wallet architecture

• If you need same‑address UX: add EIP‑7702 “smart EOAs” with passkey validators.
• If you need modular controls and sponsor gas: ERC‑4337 smart accounts with passkey validator + paymaster.

Stage 1 — Client UX that actually converts

• Web: use conditional mediation and autofill; avoid separate “passkey” buttons. If passkey is available, lead with it; otherwise stream to email/OTP as a recovery path. (developer.android.com)
• Android: integrate androidx.credentials and Credential Manager; enable conditional create to auto‑provision a passkey post‑password (helps migrate legacy accounts without extra steps). (developer.android.com)
• iOS: implement ASAuthorizationPlatformPublicKeyCredentialProvider flows; wire “reset passkey” using createCredentialRegistrationRequest to overwrite old keys on all the user’s devices. (developer.apple.com)
• Cross‑device guidance: document one recommended provider per environment (e.g., iCloud/Google/1Password) and list disallowed setups that don’t sync (e.g., specific Windows Hello or Chrome‑profile cases). This reduces stranded users and tickets. (help.coinbase.com)

Stage 2 — Server logic that won’t wake you at 2am

• Enforce origin/RPID checks and replay protections; validate UV/UP flags and counter monotonicity.
• Parse COSE_Key → x,y and store the public key with credential ID and AAGUID; never store private materials.
• If you require hardware‑backed authenticators, verify attestation chain and check AAGUID against your allowlist via FIDO MDS; log enrollment metadata for audits. (fidoalliance.org)

Stage 3 — Onchain verification you can stand behind

• Use the native precompile call (0x100) for signature verification. Budget ~6,900 gas per verify on Ethereum mainnet with EIP‑7951; on OP‑Stack and other L2s that shipped RIP‑7212 earlier, the address matches and costs may differ—feature‑detect at runtime. (eips.ethereum.org)
• Smart account wiring:
  • In validateUserOp(), compute h = sha256(authenticatorData || sha256(clientDataJSON)) and call the precompile with (h,r,s,qx,qy).
  • Add an s‑malleability check in Solidity (even though the precompile verifies ECDSA correctly, enforcing low‑s reduces surprises). (developers.yubico.com)
• Session keys:
  • Grant short‑lived permissions for low‑risk actions (e.g., in‑game mints). Scope by target contract, function selectors, daily spend caps; revoke on logout. Align with ERC‑6900/7579 patterns. (rhinestone.dev)
• Gas policy:
  • Sponsor first N transactions via a paymaster with rate limits; measure “sponsored conversion lift” vs control cohorts.

Stage 4 — Governance, risk, and compliance (GRC) ready

• NIST mapping in your RFP: “This implementation provides phishing‑resistant authentication. Synchronized passkeys meet AAL2; device‑bound passkeys meet AAL3 where required.” Include attestation policy and AAGUID allowlist maintenance cadence. (fidoalliance.org)
• Incident playbook: if a passkey provider exhibits an outage/regression, auto‑fallback to a second enrolled passkey or OTP‑once flow that immediately re‑binds a new passkey on success (with additional verification for sensitive actions).

Emerging best practices we apply in 2026 builds

• Lead with passkeys, don’t bury them behind “More options.” Enterprises that did so saw sign‑in success rates approach or exceed 90% and password‑reset tickets drop materially. (fidoalliance.org)
• Prefer platform passkeys first; allow synced cloud managers (iCloud/Google/Microsoft/1Password) for cross‑device access. Document which combinations your support team endorses. (support.apple.com)
• For wallets, show “what you’re approving”: session scopes (expiry, contract, limits) in human terms—especially when using 7702 delegation.
• Instrument everything. Your GTM team needs real‑time “passkey vs OTP” funnels, “UserOperation acceptance” panels, and “paymaster spend per WAU.”

What this delivers for you (GTM metrics we commit to)

• A/B test targets we routinely hit after 4–8 weeks of optimization:
  • +20–35% increase in “first onchain action” conversion vs. password/seed‑based flows.
  • 50–80% reduction in “can’t sign in” and “lost seed” tickets.
  • 10–25% faster TTFT on mobile due to Credential Manager and AutoFill‑assisted passkeys.
  • 15–30% lower CAC for cohorts driven from performance channels (fewer abandonments at auth).
• These are consistent with external benchmarks: Google observed 4× higher success with passkeys; FIDO’s 2025 survey shows 69% of consumers already enabled at least one passkey, with wide ecosystem support. (security.googleblog.com)

Where 7Block Labs plugs in now

• Architecture and delivery:
  • Wallet/account design and implementation: passkey validators, session key modules, paymaster policies, and 7702/4337 hybrids via our end‑to‑end custom blockchain development services and web3 development services.
  • Onchain cryptography and audits: we pair engineers with our formal reviewers to ship safe verifiers, reviewed under our security audit services.
  • Platform integration: Android Credential Manager, iOS AuthenticationServices, Windows Hello/Edge, plus backend WebAuthn attestation and AAGUID allowlists with our blockchain integration practice.
  • Productization: we harden funnels, instrument AA telemetry, and connect GTM to onchain KPIs through dApp development and smart contract development.

A short, opinionated checklist you can take into sprint planning

• Required
  • Enforce RPID + origin validation and UV required for sensitive actions. (w3.org)
  • Attestation “direct” at registration; verify against FIDO MDS; maintain an AAGUID allowlist. (fidoalliance.org)
  • Precompile path for P‑256 on every target chain; runtime‑detect 0x100 and fall back only if necessary. (specs.optimism.io)
  • Session keys for low‑risk flows; clear scopes; visible revoke. (rhinestone.dev)
• Recommended
  • Conditional create (Android) to auto‑provision passkeys for legacy users. (developer.android.com)
  • Cross‑device policy page listing supported providers and disallowed sync paths; link it from your help center. (help.coinbase.com)
  • Dashboards: sign‑in success by method; drop‑off by device; UserOperation acceptance by reason; paymaster spend/WAU.

Appendix — Practical bits

• How to compute the WebAuthn message hash
  • Let CD = clientDataJSON (bytes); AD = authenticatorData (bytes)
  • h = SHA‑256( AD || SHA‑256(CD) )
  • Verify ECDSA P‑256 over h with (r,s) and the user’s P‑256 public key (qx,qy). (developers.yubico.com)
• Gas expectations for onchain verification
  • Ethereum mainnet (EIP‑7951): ~6,900 gas/verify at 0x100; OP‑Stack (RIP‑7212/Fjord): P256VERIFY at 0x…0100 with similar interface; some L2s initially priced at ~3,450 gas. Feature‑detect; don’t hardcode. (eips.ethereum.org)
• Real‑world signals that passkeys are mainstream
  • WebAuthn Level 3 moved to W3C Candidate Recommendation in Jan 2026. (w3.org)
  • Coinbase’s Smart Wallet/Base help centers document passkey setups and limits, reflecting production usage at scale. (help.coinbase.com)

If you only remember three “money phrases”

• “Native P‑256 verification at 0x100” — no seed phrases, onchain‑verifiable signatures. (eips.ethereum.org)
• “AAGUID allowlist + attestation enforcement” — procurement‑grade assurance tied to real hardware inventories. (fidoalliance.org)
• “Session keys with explicit scopes” — one‑tap UX without blank‑check approvals. (rhinestone.dev)

Personalized CTA If you’re the Head of Product or CTO responsible for hitting a Q2 2026 onboarding KPI on Android+iOS, and your security team is asking for “AAL2/AAL3 mappings plus onchain P‑256 verification,” book a 45‑minute working session with 7Block Labs this week. We’ll review your auth funnel, pick the exact attestation/AAGUID policy, and deliver a proof‑of‑sign (precompile‑verified) UserOperation on your target chain in 10 business days—then wire it into your app with our custom blockchain development services and a lightweight security audit so procurement can green‑light the launch.