zero-knowledge-credentials

Client-side WebAuthn credential discovery for strict zero-knowledge apps. Deterministically derive a routing identifier and cryptographic root keys from a user-verifying authenticator, without accounts, identifiers, or server-side state.

Compatibility

• Runtimes: modern browsers with WebAuthn + PRF extension + user verification.
• Module format: ESM-only (no CJS build).
• Required globals / APIs: window, navigator.credentials, PublicKeyCredential, PRF extension, crypto.subtle, crypto.getRandomValues.
• TypeScript: bundled types.

Goals

• Enable strict local-first zero-knowledge for browsers.
• Deterministic, runtime-only derivation of an opaque ID and root keys.
• No storage, no networking, no server-side requirements.
• Explicit failure modes with stable error codes.

Installation

npm install @z-base/zero-knowledge-credentials
# or
pnpm add @z-base/zero-knowledge-credentials
# or
yarn add @z-base/zero-knowledge-credentials

Usage

These give a general idea and MUST NOT be interpreted as a full solution.

Register a credential

import {
  ZKCredentials,
  type ZKCredential,
  type ZKCredentialErrorCode,
} from '@z-base/zero-knowledge-credentials'

await ZKCredentials.registerCredential(
  'User display name',
  'platform' // or 'cross-platform'
)

Discover a credential

import { Bytes } from '@z-base/bytecodec'
import { Cryptosuite } from '@z-base/cryptosuite'
import { ZKCredentials } from '@z-base/zero-knowledge-credentials'

const root = await ZKCredentials.discoverCredential()

const id = root.id // routing identifier / OpaqueIdentifier
const hmacJwk = root.hmacJwk // HMAC root key / HMACJWK
const cipherJwk = root.cipherJwk // AES-GCM root key / CipherJWK

const cache = await caches.open('opaque-blobs')

let artifact = await cache.match(id) // {iv, ciphertext}

if (!artifact) {
  const challengeRaw = await fetch(`/api/v1/artifact/${id}/challenge`)
  const challengeText = await challengeRaw.text()
  const challengeBytes = Bytes.fromBase64UrlString(challengeText)
  const signature = await Cryptosuite.hmac.sign(hmacJwk, challengeBytes)
  const raw = await fetch(`/api/v1/artifact/${id}`, {
    headers: {
      Authorization: Bytes.toBase64UrlString(signature),
    },
  })
  artifact = await raw.json() // {iv, ciphertext}
}

const accountCredentials = await Cryptosuite.cipher.decrypt(cipherJwk, artifact)

// const {id, hmacJwk, cipherJwk} = accountCredentials
// repeat...
// const {profileCredentials, workspaceCredentials}  = resourceCredentials

Generate a credential

import { Bytes } from '@z-base/bytecodec'
import { Cryptosuite } from '@z-base/cryptosuite'
import { ZKCredentials } from '@z-base/zero-knowledge-credentials'

const profile = {
  name: 'Bob',
  preferences: {
    theme: 'dark',
  },
}

const credentials = await ZKCredentials.generateCredential()

const id = credentials.id // resource routing identifier / OpaqueIdentifier
const hmacJwk = credentials.hmacJwk // HMAC resource key / HMACJWK
const cipherJwk = credentials.cipherJwk // AES-GCM resource key / CipherJWK

const profileBytes = Bytes.fromJSON(profile)
const artifact = await Cryptosuite.cipher.encrypt(cipherJwk, profileBytes)
fetch(
  `/api/v1/artifact/${id}`,
  JSON.stringify({
    verifier: hmacJwk,
    state: {
      iv: Bytes.toBase64UrlString(artifact.iv),
      ciphertext: Bytes.toBase64UrlString(artifact.ciphertext),
    },
  }),
  {
    method: 'POST',
  }
)

Runtime behavior

Browsers

Uses WebAuthn PRF outputs to derive:

• id (SHA-256 -> base64url of rawId)
• cipherJwk (AES-GCM)
• hmacJwk (HMAC-SHA256)

Validation & errors

All failures are explicit and semantic. Errors are instances of ZKCredentialError with a stable code:

• unsupported
• aborted
• user-denied
• no-credential
• prf-unavailable
• key-derivation-failed

Tests

Suite: unit + integration (Node), E2E (Playwright) Matrix: Chromium / Firefox / WebKit + mobile emulation (Pixel 5, iPhone 12) Coverage: c8 — 100% statements/branches/functions/lines (dist via source maps)

Benchmarks

How it was run: npm run bench Environment: Node v22.14.0 (win32 x64) Results:

Benchmark	Result
fromPRF	5,224 ops/s (0.191 ms/op, 200 ops)
generateCredential	5,825 ops/s (0.172 ms/op, 50 ops)

Results vary by machine.

License

MIT