NiKrause · NiKrause · Feb 24, 2026 · Feb 24, 2026
diff --git a/packages/iso-webauthn-varsig/package.json b/packages/iso-webauthn-varsig/package.json
@@ -1,7 +1,7 @@
 {
   "name": "@le-space/iso-webauthn-varsig",
   "type": "module",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "description": "WebAuthn varsig encoding/decoding helpers.",
   "author": "Nico Krause <post@nicokrause.com> (nicokrause.com)",
   "license": "MIT",

diff --git a/packages/iso-webauthn-varsig/readme.md b/packages/iso-webauthn-varsig/readme.md
@@ -2,6 +2,36 @@
 
 WebAuthn varsig encoding/decoding helpers for Ed25519 and P-256.
 
+Implements the **non-recursive** WebAuthn varsig layout per [Gozala's suggestion](https://github.com/ChainAgnostic/varsig/pull/11#discussion_r2766471176) on the ChainAgnostic varsig spec.
+
+## Wire Format
+
+All multi-byte integers are unsigned varint-encoded.
+
+```abnf
+webauthn-varsig = webauthn-varsig-header
+                 client-data-length client-data-json
+                 authenticator-data-length authenticator-data
+                 signature-hash-algorithm encoding-info signature-bytes
+
+webauthn-varsig-header = varsig-prefix varsig-version inner-algorithm curve webauthn-marker
+varsig-prefix = %x34
+varsig-version = %x01
+inner-algorithm = %xED / %xEC       ; EdDSA / ECDSA
+curve = %xED01 / %x1200             ; Ed25519 / P-256 (multicodec)
+webauthn-marker = %x300001           ; private-use multicodec
+
+client-data-length = 1*unsigned-varint
+client-data-json = *OCTET
+authenticator-data-length = 1*unsigned-varint
+authenticator-data = *OCTET
+signature-hash-algorithm = 1*unsigned-varint  ; multihash code (default 0x12 = SHA-256)
+encoding-info = 1*unsigned-varint             ; payload encoding (default 0x5f = raw)
+signature-bytes = *OCTET                      ; raw WebAuthn signature
+```
+
+This layout avoids recursion (no nested varsig-body) and aligns with the [dialog-db](https://github.com/dialog-db/dialog-db) Go/Rust reference implementation.
+
 ## Usage
 
 ```js
@@ -18,10 +48,21 @@ const assertion = {
   signature: new Uint8Array([/* ... */]),
 }
 
+// Encode with defaults (SHA-256 hash, raw encoding)
 const varsig = encodeWebAuthnVarsigV1(assertion, 'Ed25519')
+
+// Or with explicit signature metadata
+const varsig2 = encodeWebAuthnVarsigV1(assertion, 'P-256', {
+  signatureHashAlgorithm: 0x12, // SHA-256
+  encodingInfo: 0x5f,           // raw
+})
+
 const decoded = decodeWebAuthnVarsigV1(varsig)
 const clientData = parseClientDataJSON(decoded.clientDataJSON)
 
+console.log(decoded.signatureHashAlgorithm) // 0x12
+console.log(decoded.encodingInfo)           // 0x5f
+
 const result = await verifyWebAuthnAssertion(decoded, {
   expectedOrigin: clientData.origin,
   expectedRpId: new URL(clientData.origin).hostname,
@@ -34,3 +75,4 @@ console.log(result.valid)
 ## Notes
 
 - Ed25519 WebAuthn credentials are not supported on all platforms. If your authenticator does not return an Ed25519 key, you must fall back to P-256.
+- **Breaking change in v0.2.0**: The wire format changed from v0.1.0. Encoded bytes from the old format are not compatible with this version. See [issue #1](https://github.com/NiKrause/iso-repo/issues/1) for details.
diff --git a/packages/iso-webauthn-varsig/src/decoder.js b/packages/iso-webauthn-varsig/src/decoder.js
@@ -1,16 +1,13 @@
-import { varintDecode } from './utils.js'
 import {
-  VARSIG_PREFIX,
-  VARSIG_VERSION,
-  INNER_EDDSA,
-  INNER_ECDSA,
   CURVE_ED25519,
   CURVE_P256,
-  MULTIHASH_SHA256,
-  MULTIHASH_SHA256_LEN,
+  INNER_ECDSA,
+  INNER_EDDSA,
+  VARSIG_PREFIX,
+  VARSIG_VERSION,
   WEBAUTHN_WRAPPER,
-  PAYLOAD_ENCODING_RAW,
 } from './multicodec.js'
+import { varintDecode } from './utils.js'
 
 /**
  * @typedef {import('./types').DecodedVarsigV1} DecodedVarsigV1
@@ -19,14 +16,12 @@ import {
  */
 
 /**
- * Decode a WebAuthn varsig v1 into its components.
+ * Decode a WebAuthn varsig v1 (non-recursive layout) into its components.
  *
- * Format:
- * - prefix (0x34)
- * - version (0x01)
- * - signature-algorithm metadata (varints)
- * - payload-encoding metadata (varint)
- * - assertion serialization
+ * Wire format:
+ *   header: prefix version innerAlgorithm curve webauthnMarker
+ *   body:   clientDataLen clientDataJSON authDataLen authenticatorData
+ *           signatureHashAlgorithm encodingInfo signatureBytes
  *
  * @param {Uint8Array} varsig
  * @returns {DecodedVarsigV1}
@@ -40,19 +35,14 @@ export function decodeWebAuthnVarsigV1(varsig) {
     throw new Error('Unsupported varsig header')
   }
 
+  // --- header: 3 varints ---
   let offset = 2
   const [innerAlgorithm, innerAlgorithmLen] = varintDecode(varsig, offset)
   offset += innerAlgorithmLen
   const [curve, curveLen] = varintDecode(varsig, offset)
   offset += curveLen
-  const [multihashCode, multihashCodeLen] = varintDecode(varsig, offset)
-  offset += multihashCodeLen
-  const [multihashLength, multihashLengthLen] = varintDecode(varsig, offset)
-  offset += multihashLengthLen
   const [webauthnMarker, markerLen] = varintDecode(varsig, offset)
   offset += markerLen
-  const [payloadEncoding, payloadEncodingLen] = varintDecode(varsig, offset)
-  offset += payloadEncodingLen
 
   /** @type {SignatureAlgorithm | null} */
   const algorithm =
@@ -76,22 +66,21 @@ export function decodeWebAuthnVarsigV1(varsig) {
     throw new Error(`Unexpected P-256 curve code: 0x${curve.toString(16)}`)
   }
 
-  if (multihashCode !== MULTIHASH_SHA256) {
-    throw new Error('Unsupported multihash header')
-  }
-
-  if (multihashLength !== MULTIHASH_SHA256_LEN) {
-    throw new Error('Unsupported multihash header length')
-  }
-
   if (webauthnMarker !== WEBAUTHN_WRAPPER) {
     throw new Error('Missing WebAuthn extension marker')
   }
 
-  if (payloadEncoding !== PAYLOAD_ENCODING_RAW) {
-    throw new Error('Unsupported payload encoding')
+  // --- body: clientData, authData, signature metadata, signature ---
+  const [clientDataLen, clientDataLenLen] = varintDecode(varsig, offset)
+  offset += clientDataLenLen
+
+  if (offset + clientDataLen > varsig.length) {
+    throw new Error('Invalid clientDataJSON length')
   }
 
+  const clientDataJSON = varsig.slice(offset, offset + clientDataLen)
+  offset += clientDataLen
+
   const [authDataLen, authDataLenLen] = varintDecode(varsig, offset)
   offset += authDataLenLen
 
@@ -102,15 +91,10 @@ export function decodeWebAuthnVarsigV1(varsig) {
   const authenticatorData = varsig.slice(offset, offset + authDataLen)
   offset += authDataLen
 
-  const [clientDataLen, clientDataLenLen] = varintDecode(varsig, offset)
-  offset += clientDataLenLen
-
-  if (offset + clientDataLen > varsig.length) {
-    throw new Error('Invalid clientDataJSON length')
-  }
-
-  const clientDataJSON = varsig.slice(offset, offset + clientDataLen)
-  offset += clientDataLen
+  const [signatureHashAlgorithm, sigHashLen] = varintDecode(varsig, offset)
+  offset += sigHashLen
+  const [encodingInfo, encInfoLen] = varintDecode(varsig, offset)
+  offset += encInfoLen
 
   const signature = varsig.slice(offset)
   if (signature.length === 0) {
@@ -121,12 +105,11 @@ export function decodeWebAuthnVarsigV1(varsig) {
     algorithm,
     innerAlgorithm,
     curve,
-    multihashCode,
-    multihashLength,
     webauthnMarker,
-    payloadEncoding,
     authenticatorData,
     clientDataJSON,
+    signatureHashAlgorithm,
+    encodingInfo,
     signature,
   }
 }

diff --git a/packages/iso-webauthn-varsig/src/encoder.js b/packages/iso-webauthn-varsig/src/encoder.js
@@ -1,59 +1,63 @@
 import {
-  VARSIG_PREFIX,
-  VARSIG_VERSION,
-  INNER_EDDSA,
-  INNER_ECDSA,
   CURVE_ED25519,
   CURVE_P256,
+  INNER_ECDSA,
+  INNER_EDDSA,
   MULTIHASH_SHA256,
-  MULTIHASH_SHA256_LEN,
   PAYLOAD_ENCODING_RAW,
+  VARSIG_PREFIX,
+  VARSIG_VERSION,
   WEBAUTHN_WRAPPER,
 } from './multicodec.js'
 import { concat, varintEncode } from './utils.js'
 
 /**
  * @typedef {import('./types').WebAuthnAssertion} WebAuthnAssertion
  * @typedef {import('./types').SignatureAlgorithm} SignatureAlgorithm
+ * @typedef {import('./types').EncodeOptions} EncodeOptions
  */
 
 /**
- * Encode a WebAuthn assertion as varsig v1.
+ * Encode a WebAuthn assertion as varsig v1 (non-recursive layout).
  *
- * Format:
- * - varsig prefix (0x34)
- * - varsig version (0x01)
- * - signature algorithm metadata (varints)
- * - payload encoding metadata (varint)
- * - assertion serialization
+ * Wire format:
+ *   header: prefix version innerAlgorithm curve webauthnMarker
+ *   body:   clientDataLen clientDataJSON authDataLen authenticatorData
+ *           signatureHashAlgorithm encodingInfo signatureBytes
  *
  * @param {WebAuthnAssertion} assertion
  * @param {SignatureAlgorithm} [algorithm]
+ * @param {EncodeOptions} [options]
  */
-export function encodeWebAuthnVarsigV1(assertion, algorithm = 'Ed25519') {
+export function encodeWebAuthnVarsigV1(
+  assertion,
+  algorithm = 'Ed25519',
+  options = {}
+) {
   const { authenticatorData, clientDataJSON, signature } = assertion
 
   validateWebAuthnAssertion(assertion)
 
   const innerAlgorithm = algorithm === 'Ed25519' ? INNER_EDDSA : INNER_ECDSA
   const curve = algorithm === 'Ed25519' ? CURVE_ED25519 : CURVE_P256
+  const sigHashAlg = options.signatureHashAlgorithm ?? MULTIHASH_SHA256
+  const encInfo = options.encodingInfo ?? PAYLOAD_ENCODING_RAW
 
   const header = new Uint8Array([VARSIG_PREFIX, VARSIG_VERSION])
-  const authDataLenBytes = varintEncode(authenticatorData.length)
   const clientDataLenBytes = varintEncode(clientDataJSON.length)
+  const authDataLenBytes = varintEncode(authenticatorData.length)
 
   return concat([
     header,
     varintEncode(innerAlgorithm),
     varintEncode(curve),
-    varintEncode(MULTIHASH_SHA256),
-    varintEncode(MULTIHASH_SHA256_LEN),
     varintEncode(WEBAUTHN_WRAPPER),
-    varintEncode(PAYLOAD_ENCODING_RAW),
-    authDataLenBytes,
-    authenticatorData,
     clientDataLenBytes,
     clientDataJSON,
+    authDataLenBytes,
+    authenticatorData,
+    varintEncode(sigHashAlg),
+    varintEncode(encInfo),
     signature,
   ])
 }
@@ -64,7 +68,10 @@ export function encodeWebAuthnVarsigV1(assertion, algorithm = 'Ed25519') {
  * @param {WebAuthnAssertion} assertion
  */
 export function validateWebAuthnAssertion(assertion) {
-  if (!assertion.authenticatorData || assertion.authenticatorData.length === 0) {
+  if (
+    !assertion.authenticatorData ||
+    assertion.authenticatorData.length === 0
+  ) {
     throw new Error('authenticatorData is required and cannot be empty')
   }
 

diff --git a/packages/iso-webauthn-varsig/src/index.js b/packages/iso-webauthn-varsig/src/index.js
@@ -2,43 +2,40 @@
  * WebAuthn Varsig - Public API.
  */
 
+export { decodeWebAuthnVarsigV1, parseClientDataJSON } from './decoder.js'
+
+export { encodeWebAuthnVarsigV1, validateWebAuthnAssertion } from './encoder.js'
 export {
-  WEBAUTHN_ED25519,
-  WEBAUTHN_P256,
-  ED25519_PUB,
-  P256_PUB,
-  VARSIG_PREFIX,
-  VARSIG_VERSION,
-  INNER_EDDSA,
-  INNER_ECDSA,
+  ALGORITHM_TO_MULTICODEC,
   CURVE_ED25519,
   CURVE_P256,
+  ED25519_PUB,
+  getAlgorithm,
+  INNER_ECDSA,
+  INNER_EDDSA,
+  isWebAuthnMulticodec,
+  MULTICODEC_TO_ALGORITHM,
   MULTIHASH_SHA256,
   MULTIHASH_SHA256_LEN,
+  P256_PUB,
   PAYLOAD_ENCODING_RAW,
+  VARSIG_PREFIX,
+  VARSIG_VERSION,
+  WEBAUTHN_ED25519,
+  WEBAUTHN_P256,
   WEBAUTHN_WRAPPER,
-  ALGORITHM_TO_MULTICODEC,
-  MULTICODEC_TO_ALGORITHM,
-  isWebAuthnMulticodec,
-  getAlgorithm,
 } from './multicodec.js'
-
-export { encodeWebAuthnVarsigV1, validateWebAuthnAssertion } from './encoder.js'
-
-export { decodeWebAuthnVarsigV1, parseClientDataJSON } from './decoder.js'
-
 export {
-  verifyWebAuthnAssertion,
+  base64urlToBytes,
+  bytesEqual,
+  bytesToBase64url,
+  concat,
+  varintDecode,
+  varintEncode,
+} from './utils.js'
+export {
   reconstructSignedData,
   verifyEd25519Signature,
   verifyP256Signature,
+  verifyWebAuthnAssertion,
 } from './verifier.js'
-
-export {
-  varintEncode,
-  varintDecode,
-  concat,
-  base64urlToBytes,
-  bytesToBase64url,
-  bytesEqual,
-} from './utils.js'
diff --git a/packages/iso-webauthn-varsig/src/test-utils.js b/packages/iso-webauthn-varsig/src/test-utils.js
@@ -11,11 +11,7 @@
  * @param {{ userPresent?: boolean, userVerified?: boolean, signCount?: number }} [options]
  */
 export function createMockAuthenticatorData(options = {}) {
-  const {
-    userPresent = true,
-    userVerified = true,
-    signCount = 1,
-  } = options
+  const { userPresent = true, userVerified = true, signCount = 1 } = options
 
   const rpIdHash = new Uint8Array(32)
   for (let i = 0; i < 32; i++) {