Passkeys Explained - The Complete Guide to Passwordless Authentication 2024

DEFINITION

Passkeys are a passwordless authentication method based on FIDO2/WebAuthn standards. They use public-key cryptography and biometrics to provide phishing-resistant, frictionless login.

The House Key Analogy: Passwords are like a secret code that anyone who learns it can use. Passkeys are like a unique physical key—even if someone knows your house exists, they can’t get in without your specific key. And modern Passkeys are like a key that only works when YOU hold it (via biometric verification).

Why Passkeys Matter

Passkeys represent the biggest shift in authentication since passwords were invented:

The Password Problem	The Passkey Solution
Users reuse passwords across sites	Unique cryptographic key per site
Passwords can be phished	Cryptographically bound to domain
Passwords are stored on servers	Only public key stored, private never leaves device
Users forget passwords	Biometric unlock, nothing to remember
Password reset is expensive	No passwords to reset

Industry Adoption (2024):

✅ Google, Apple, Microsoft — full Passkey support
✅ GitHub, PayPal, eBay — consumer rollout
✅ 1Password, Dashlane, Bitwarden — Passkey management
✅ Okta, Auth0, Azure AD — enterprise integration

How Passkeys Work

The Cryptographic Foundation

Passkeys use asymmetric (public-key) cryptography:

Registration

Device generates a unique key pair. Private key stays on device (protected by biometrics). Public key is sent to the website.

Authentication

Website sends a random challenge. Device signs the challenge with the private key (after biometric verification). Website verifies signature with stored public key.

Verification

If signature is valid, the user is authenticated. No password transmitted. No shared secret on the server.

Why Passkeys Are Phishing-Resistant

The key insight: Passkeys are cryptographically bound to the website’s origin.

Example: You register a Passkey for bank.com

Legitimate site (bank.com):
→ Browser confirms origin is "bank.com"
→ Passkey for "bank.com" is used
→ Authentication succeeds ✅

Phishing site (bank-secure.com):
→ Browser confirms origin is "bank-secure.com"
→ No Passkey exists for this domain
→ Authentication fails ❌
→ Phishing attack blocked automatically

The browser enforces origin checking at the protocol level. Users can’t be tricked into using their Passkey on a fake site, even if it looks identical.

Types of Passkeys

Device-Bound Passkeys stay on one device and cannot be exported.

Examples:

Hardware security keys (YubiKey, Titan Key)
Some enterprise deployments

Pros:

✅ Highest security — key never leaves hardware
✅ Resistant to remote attacks
✅ Preferred for high-security use cases

Cons:

❌ Lost device = lost access (need backup)
❌ Can’t use the same Passkey on multiple devices
❌ Less convenient for consumers

Passkeys vs. Passwords + MFA

Aspect	Password + MFA	Passkey
Phishing resistance	❌ Codes can be phished in real-time	✅ Cryptographically impossible
User experience	😐 Type password, wait for code, enter code	😊 One touch (Face ID/fingerprint)
Password resets	❌ 30-40% of help desk calls	✅ None — nothing to forget
Credential stuffing	❌ Reused passwords are vulnerable	✅ Unique key per site
Server breach impact	❌ Hashed passwords can be cracked	✅ Public keys are useless to attackers
Account recovery	Via email (another password)	Via synced credential manager

Passkeys provide better security AND better UX. This is rare in security.

Implementing Passkeys

For Web Applications

The WebAuthn JavaScript API:

// REGISTRATION: Create a new Passkey
const credential = await navigator.credentials.create({
  publicKey: {
    challenge: new Uint8Array([/* server-generated challenge */]),
    rp: {
      name: "Example Corp",
      id: "example.com"
    },
    user: {
      id: new Uint8Array([/* unique user id */]),
      name: "jane@example.com",
      displayName: "Jane Doe"
    },
    pubKeyCredParams: [
      { alg: -7, type: "public-key" },   // ES256
      { alg: -257, type: "public-key" }  // RS256
    ],
    authenticatorSelection: {
      residentKey: "preferred",
      userVerification: "preferred"
    },
    timeout: 60000
  }
});

// Send credential.response to server for storage

// AUTHENTICATION: Use an existing Passkey
const assertion = await navigator.credentials.get({
  publicKey: {
    challenge: new Uint8Array([/* server-generated challenge */]),
    rpId: "example.com",
    userVerification: "preferred",
    timeout: 60000
  }
});

// Send assertion.response to server for verification

Libraries & SDKs

Don’t implement WebAuthn from scratch. Use these:

Language	Library
JavaScript	SimpleWebAuthn, @github/webauthn-json
Python	py_webauthn, fido2
Node.js	SimpleWebAuthn, fido2-lib
Go	go-webauthn/webauthn
Ruby	webauthn-ruby
Java	java-webauthn-server

Platform Integration

// Enable Passkeys in Auth0
// Dashboard → Authentication → Database → Password Policy
// Enable "Passkey" authentication

// Or via Management API:
const auth0 = new ManagementClient({...});
await auth0.connections.update(
  { id: connectionId },
  { options: { passkey: { enabled: true } } }
);

Auth0 Passkeys Documentation →

Admin Console → Security → Authenticators
→ Add Authenticator → FIDO2 (WebAuthn)

Configure:
- User verification: Preferred or Required
- Authenticator attachment: Platform, Cross-Platform, or Any
- Resident key: Required (for usernameless login)

Okta FIDO2 Documentation →

Entra Admin Center → Authentication methods
→ FIDO2 security key
→ Enable → Configure target users/groups

For Passkeys (Preview):
→ Enable "Passkeys (FIDO2)" under Authentication methods
→ Configure allowed AAGUID if restricting authenticators

Azure AD FIDO2 Documentation →

Migration Strategy: Passwords to Passkeys

Phase 1: Enable Passkeys (Parallel)

Current state: Password + MFA
↓
Add Passkey as optional login method
Users can register Passkeys while keeping password

Actions:

Enable Passkey authentication in your IdP/app
Encourage (don’t force) users to register Passkeys
Measure adoption rate

Phase 2: Prefer Passkeys

Login flow:
1. Check if user has registered Passkey
2. If yes → Offer Passkey login first
3. If no → Fall back to password
4. Prompt password users to register Passkey

Actions:

Make Passkey the prominent login option
Show password as secondary option
Implement “add Passkey” prompts post-login

Phase 3: Require Passkeys (High-Security)

For privileged users/sensitive apps:
├── Require Passkey registration
├── Disable password authentication
└── Hardware keys for admin access

Actions:

Require Passkey for admin accounts
Mandate for new employee onboarding
Maintain break-glass recovery process

Phase 4: Passwordless Organization

Target state:
├── All users authenticate with Passkeys
├── No passwords to phish, leak, or reset
├── Hardware keys for privileged access
└── Password only for legacy edge cases

Passkey User Experience

Registration Flow

User Initiates

”Add Passkey” button in security settings or post-login prompt.

Browser Prompt

System dialog appears asking to create a Passkey for this site.

Biometric Verification

Face ID, Touch ID, Windows Hello, or security key touch.

Confirmation

Passkey saved. User can now sign in without a password.

1. User navigates to login page
2. Clicks "Sign in with Passkey" (or autofill suggestion appears)
3. Biometric prompt (Face ID, Touch ID, etc.)
4. Authenticated! (< 3 seconds total)

No typing. No waiting for SMS. No copying codes.

Common Passkey Challenges

Challenge 1: Account Recovery

Problem: User loses all devices with synced Passkeys.

Solutions:

Approach	Implementation
Multiple devices	Encourage registering Passkeys on multiple devices
Backup codes	Provide one-time recovery codes at registration
Hardware key backup	Register a security key stored in safe location
Identity verification	Help desk with strong identity proofing

Challenge 2: Shared/Public Computers

Problem: Can’t use personal Passkey on shared computer.

Solutions:

Use security key (portable, works anywhere)
“Hybrid authentication” — scan QR with phone
Maintain password fallback for edge cases

Challenge 3: Cross-Platform Sync

Problem: Apple Passkeys don’t sync to Android, and vice versa.

Solutions:

Third-party password managers (1Password, Bitwarden) sync cross-platform
Register Passkeys on each platform
Use hardware security key as universal backup

Browser & Platform Support

Platform	Passkey Support
Chrome	✅ Full support (synced via Google account)
Safari	✅ Full support (synced via iCloud Keychain)
Edge	✅ Full support (synced via Microsoft account)
Firefox	✅ Support for hardware keys, synced Passkeys coming
iOS	✅ Full support (Safari, supported apps)
Android	✅ Full support (Chrome, supported apps)
Windows	✅ Windows Hello, hardware keys
macOS	✅ Touch ID, hardware keys

Security Considerations

What Passkeys Protect Against

Attack	Protection Level	How
Phishing	✅ Complete	Origin binding at protocol level
Credential stuffing	✅ Complete	Unique key per site
Server breach	✅ Complete	Only public keys stored
Keyloggers	✅ Complete	No typing involved
SIM swapping	✅ Complete	No phone numbers involved
MFA fatigue	✅ Complete	No push notifications

What Passkeys Don’t Protect Against

Attack	Notes
Device theft	Biometrics help, but device access is a risk
Malware on device	Advanced malware could intercept authentication
Cloud account compromise	Synced Passkeys only as secure as the sync account
Social engineering	Users could be tricked into actions post-authentication

Next Steps

WebAuthn Protocol

Deep dive into the WebAuthn specification and implementation details. WebAuthn Guide →

Passwordless Patterns

Explore passwordless authentication strategies beyond Passkeys. Passwordless Guide →

MFA Best Practices

Compare Passkeys with other MFA methods and plan your strategy. MFA Guide →

Zero Trust

Understand how Passkeys fit into a Zero Trust architecture. Zero Trust Guide →

Passkeys Explained - The Complete Guide to Passwordless Authentication 2024