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ABIDecoder,
ABIEncoder,
Bytes,
Checksum256,
KeyType,
PublicKey,
Signature,
} from '@wharfkit/antelope'
import {decode as cborDecode, decodeFirst} from 'cborg'
import elliptic from 'elliptic'
import {Decoder} from './decoder'
const {ec} = elliptic
export function createPublic(
attestationResponse: {
attestationObject: ArrayBuffer
clientDataJSON: ArrayBuffer
},
logging = false
) {
const clientData = decodeBinaryJson(attestationResponse.clientDataJSON)
const origin = clientData.origin
Iif (typeof origin !== 'string') {
throw new Error('Missing origin in client data')
}
const originUrl = new URL(origin)
Iif (originUrl.protocol !== 'https:') {
throw new Error('WebAuthn keys require https')
}
const attestationObject = cborDecode(new Uint8Array(attestationResponse.attestationObject))
Iif (!(attestationObject.authData instanceof Uint8Array)) {
throw new Error('Missing auth data')
}
const authData = decodeAuthData(attestationObject.authData)
const ecPoint = getECPoint(authData.credentialPublicKey)
const compressed = new Uint8Array(33)
compressed[0] = ecPoint.y[31] & 0x01 ? 0x03 : 0x02
compressed.set(ecPoint.x, 1)
const abiEncoder = new ABIEncoder()
abiEncoder.writeArray(compressed)
abiEncoder.writeByte(getUserDataFlag(authData.flags, logging))
abiEncoder.writeString(originUrl.hostname)
return new PublicKey(KeyType.WA, abiEncoder.getBytes())
}
export function createSignature(
publicKey: PublicKey,
assertionResponse: {
signature: ArrayBuffer
authenticatorData: ArrayBuffer
clientDataJSON: ArrayBuffer
}
) {
const decoder = new Decoder(assertionResponse.signature).derDecoder(0x30)
const r = fixPoint(decoder.readDer(0x02))
const s = fixPoint(decoder.readDer(0x02))
const authenticatorData = Bytes.from(assertionResponse.authenticatorData)
const clientDataJSON = Bytes.from(assertionResponse.clientDataJSON)
const message = new Bytes()
message.append(authenticatorData)
message.append(Checksum256.hash(clientDataJSON))
const curve = new ec('p256')
const pk = curve.keyFromPublic(publicKey.data.array.slice(0, 33)).getPublic()
const m = Checksum256.hash(message).array
const recid = (curve.getKeyRecoveryParam as any)(m, {r, s}, pk)
const encoder = new ABIEncoder()
encoder.writeByte(recid + 31)
encoder.writeArray(r)
encoder.writeArray(s)
authenticatorData.toABI(encoder)
clientDataJSON.toABI(encoder)
return new Signature(KeyType.WA, encoder.getBytes())
}
export function recoverPublic(signature: Signature, message: Bytes, logging = false): PublicKey {
const signatureData = signature.data.array
const messageDigest = Checksum256.hash(message).array
const recid = signatureData[0] - 31
const r = signatureData.subarray(1, 33)
const s = signatureData.subarray(33, 33 + 32)
const curve = new ec('p256')
const point = curve.recoverPubKey(messageDigest, {r, s}, recid)
const compressedKeyPoint = new Uint8Array(point.encodeCompressed())
const extraDataView = signatureData.subarray(65)
const extraDataDecoder = new ABIDecoder(extraDataView)
const authenticatorDataBytes = Bytes.fromABI(extraDataDecoder)
const clientDataJSONBytes = Bytes.fromABI(extraDataDecoder)
const clientData = decodeBinaryJson(clientDataJSONBytes.array.slice().buffer)
const origin = clientData.origin
Iif (typeof origin !== 'string') {
throw new Error('Missing origin in client data during recovery')
}
const originUrl = new URL(origin)
Iif (originUrl.protocol !== 'https:') {
throw new Error('WebAuthn keys require https')
}
const authDataForFlagsDecoder = new Decoder(authenticatorDataBytes.array)
Iif (!authDataForFlagsDecoder.canRead(32 + 1)) {
throw new Error('Authenticator data is too short to read flags.')
}
authDataForFlagsDecoder.readArray(32)
const abiEncoder = new ABIEncoder()
abiEncoder.writeArray(compressedKeyPoint)
const flags = authDataForFlagsDecoder.readByte()
abiEncoder.writeByte(getUserDataFlag(flags, logging))
abiEncoder.writeString(originUrl.hostname)
return new PublicKey(KeyType.WA, abiEncoder.getBytes())
}
export function getUserDataFlag(flags: number, logging = false): number {
let byte = 0x00
if (flags & 0x01 /* user present */) {
Iif (logging) {
// eslint-disable-next-line no-console
console.info('present flag', flags)
}
byte = 0x01
}
if (flags & 0x04 /* user verified */) {
Iif (logging) {
// eslint-disable-next-line no-console
console.info('verified flag', flags)
}
byte = 0x02
}
Iif (logging) {
// eslint-disable-next-line no-console
console.info('final user data flag:', byte)
}
return byte
}
export function verifyPublic(signature: Signature, message: Bytes, publicKey: PublicKey) {
const signatureData = signature.data.array
const messageDigest = Checksum256.hash(message).array
const publicKeyData = publicKey.getCompressedKeyBytes()
const curve = new ec('p256')
const r = signatureData.subarray(1, 33)
const s = signatureData.subarray(33, 33 + 32)
return curve.verify(messageDigest, {r, s}, publicKeyData as any)
}
export function recoverPotentialPublicKeysFromAssertion(
assertionResponse: AuthenticatorAssertionResponse,
logging = false
): PublicKey[] {
const authenticatorData = Bytes.from(assertionResponse.authenticatorData)
const clientDataJSON = Bytes.from(assertionResponse.clientDataJSON)
const message = new Bytes()
message.append(authenticatorData)
message.append(Checksum256.hash(clientDataJSON))
const decoder = new Decoder(assertionResponse.signature).derDecoder(0x30)
const r = fixPoint(decoder.readDer(0x02))
const s = fixPoint(decoder.readDer(0x02))
const keys: PublicKey[] = []
for (let recid = 0; recid < 4; recid++) {
try {
const encoder = new ABIEncoder()
encoder.writeByte(recid + 31)
encoder.writeArray(r)
encoder.writeArray(s)
authenticatorData.toABI(encoder)
clientDataJSON.toABI(encoder)
const signature = new Signature(KeyType.WA, encoder.getBytes())
const key = recoverPublic(signature, message, logging)
keys.push(key)
} catch {
// Ignore errors, try next recid
}
}
Iif (!keys.length) {
throw new Error('Unable to recover any potential public keys from signature')
}
return keys
}
function decodeAuthData(authData: Uint8Array) {
const decoder = new Decoder(authData)
const rpIdHash = decoder.readArray(32)
const flags = decoder.readByte()
const counter = decoder.readNum(4)
const aaguid = decoder.readArray(16)
const credentialId = decoder.readArray(decoder.readNum(2))
const [credentialPublicKey] = decodeFirst(decoder.remainder(), {useMaps: true}) as [
Map<number, any>,
Uint8Array,
]
return {
rpIdHash,
flags,
counter,
aaguid,
credentialId,
credentialPublicKey,
}
}
function getECPoint(credentialPublicKey: Map<number, any>) {
const kty = credentialPublicKey.get(1)
Iif (kty !== 2 /* EC */) {
throw new Error(`Unsupported key type: ${kty}`)
}
const alg = credentialPublicKey.get(3)
Iif (alg !== -7 /* EC2 */) {
throw new Error(`Unsupported key algorithm: ${alg}`)
}
const crv = credentialPublicKey.get(-1)
Iif (crv !== 1 /*P-256*/) {
throw new Error(`Unsupported ec key curve: ${crv}`)
}
const x = credentialPublicKey.get(-2)
const y = credentialPublicKey.get(-3)
Iif (!(x instanceof Uint8Array) || !(y instanceof Uint8Array)) {
throw new Error('Invalid public key data')
}
return {x, y}
}
function decodeBinaryJson(data: ArrayBuffer) {
const decoder = new TextDecoder()
return JSON.parse(decoder.decode(data))
}
// chrome sometimes returns curve points that are not 32 bytes, so we need to make sure they are
function fixPoint(x: Uint8Array) {
if (x.length === 32) {
return x
}
const rv = new Uint8Array(32)
rv.fill(0)
let si = 0
while (x[si] === 0 && si < x.length - 1) {
si++
}
rv.set(x.slice(si), 32 - x.length + si)
return rv
}
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