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Add PRF extension support

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This commit is contained in:
mimi89999
2026-02-16 11:41:29 +01:00
parent c2d1837024
commit da56420912
5 changed files with 238 additions and 13 deletions
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app/src/main/java/pl/lebihan/authnkey/CTAP.kt
+14 -5
View File
@@ -24,7 +24,8 @@ data class AuthenticatorData(
val rpIdHash: ByteArray,
val flags: Int,
val signCount: Long,
val attestedCredentialData: AttestedCredentialData?
val attestedCredentialData: AttestedCredentialData?,
val extensions: CborMap?
) {
val userPresent: Boolean
get() = (flags and CTAP.AUTH_DATA_FLAG_UP) != 0
@@ -51,6 +52,7 @@ data class AuthenticatorData(
var offset = 37
val hasAt = (flags and CTAP.AUTH_DATA_FLAG_AT) != 0
val hasEd = (flags and CTAP.AUTH_DATA_FLAG_ED) != 0
val attestedCredentialData = if (hasAt) {
if (data.size < offset + 18) return null
@@ -66,14 +68,21 @@ data class AuthenticatorData(
val credentialId = data.sliceArray(offset until offset + credIdLen)
offset += credIdLen
val credentialPublicKey = CborDecoder.decode(
data.sliceArray(offset until data.size)
) as? Map<*, *> ?: return null
val remaining = data.sliceArray(offset until data.size)
val credentialPublicKey = CborDecoder.decode(remaining) as? Map<*, *> ?: return null
// Advance offset past the COSE key
val consumed = CborDecoder.measureFirstValue(remaining)
offset += consumed
AttestedCredentialData(aaguid, credentialId, credentialPublicKey)
} else null
return AuthenticatorData(rpIdHash, flags, signCount, attestedCredentialData)
val extensions = if (hasEd && offset < data.size) {
val remaining = data.sliceArray(offset until data.size)
CborMap.decode(remaining)
} else null
return AuthenticatorData(rpIdHash, flags, signCount, attestedCredentialData, extensions)
}
}
}
app/src/main/java/pl/lebihan/authnkey/Cbor.kt
+9
View File
@@ -158,6 +158,15 @@ class CborDecoder private constructor(private val data: ByteArray) {
companion object {
fun decode(data: ByteArray): Any? = CborDecoder(data).readValue()
/**
* Measure how many bytes the first CBOR value in the data occupies.
*/
fun measureFirstValue(data: ByteArray): Int {
val decoder = CborDecoder(data)
decoder.readValue()
return decoder.pos
}
}
private fun readValue(): Any? {
app/src/main/java/pl/lebihan/authnkey/CredentialProviderActivity.kt
+135 -8
View File
@@ -813,6 +813,20 @@ class CredentialProviderActivity : AppCompatActivity() {
authSelection?.optString("residentKey", "preferred")
)
// Parse extensions
val extensions = requestJson.optJSONObject("extensions")
val credPropsRequested = extensions?.optBoolean("credProps", false) ?: false
val prfRequested = extensions?.has("prf") == true
// Check if authenticator supports hmac-secret (CTAP2 backing for PRF)
val authenticatorSupportsHmacSecret = deviceInfo?.extensions?.contains("hmac-secret") == true
// Build CTAP extensions map
val ctapExtensions = mutableMapOf<String, Any>()
if (prfRequested && authenticatorSupportsHmacSecret) {
ctapExtensions["hmac-secret"] = true
}
// Build clientDataJSON with proper origin
val origin = computeOrigin()
val clientData = providedClientDataHash.let { hash ->
@@ -847,6 +861,7 @@ class CredentialProviderActivity : AppCompatActivity() {
excludeList = if (excludeList.isNotEmpty()) excludeList else null,
requireResidentKey = residentKey.requiresResidentKey(),
requireUserVerification = false, // UV is provided by pinUvAuthParam
extensions = if (ctapExtensions.isNotEmpty()) ctapExtensions else null,
pinUvAuthParam = pinUvAuthParam,
pinUvAuthProtocol = if (pinProtocol != null) 1 else null
)
@@ -876,15 +891,19 @@ class CredentialProviderActivity : AppCompatActivity() {
val authData = AuthenticatorData.parse(makeCredResult.authData)
val credentialId = authData?.attestedCredentialData?.credentialId ?: ByteArray(0)
// Check if credProps extension was requested
val extensions = requestJson.optJSONObject("extensions")
val credPropsRequested = extensions?.optBoolean("credProps", false) ?: false
// Determine if credential is actually discoverable
// If we requested rk AND the authenticator supports it AND succeeded, it's discoverable
val supportsResidentKey = deviceInfo?.options?.get("rk") ?: true
val isDiscoverable = residentKey.requiresResidentKey() && supportsResidentKey
// Check if hmac-secret was confirmed in the authenticator's authData extensions
val hmacSecretEnabled = if (prfRequested && authenticatorSupportsHmacSecret) {
// If the authenticator supports hmac-secret and we requested it,
// check if the authData extensions confirm it
val extData = authData?.extensions
extData?.bool("hmac-secret") ?: true // null means it was accepted without explicit confirmation
} else false
// Build response JSON
val responseJson = JSONObject().apply {
put("id", Base64.encodeToString(credentialId, Base64.URL_SAFE or Base64.NO_PADDING or Base64.NO_WRAP))
@@ -928,6 +947,11 @@ class CredentialProviderActivity : AppCompatActivity() {
put("rk", isDiscoverable)
})
}
if (prfRequested) {
put("prf", JSONObject().apply {
put("enabled", hmacSecretEnabled)
})
}
})
}
@@ -959,6 +983,77 @@ class CredentialProviderActivity : AppCompatActivity() {
}
}
// Parse PRF extension
val extensions = requestJson.optJSONObject("extensions")
val prfExtension = extensions?.optJSONObject("prf")
val prfEval = prfExtension?.optJSONObject("eval")
val authenticatorSupportsHmacSecret = deviceInfo?.extensions?.contains("hmac-secret") == true
val prfRequested = prfEval != null && authenticatorSupportsHmacSecret
// Prepare hmac-secret extension for getAssertion if PRF is requested
var hmacSecretExtensions: CborRaw? = null
var prfHasTwoSalts = false
var effectiveProtocol = pinProtocol
if (prfRequested) {
val protocol = pinProtocol ?: this.pinProtocol
?: throw Exception("PIN protocol not available for PRF")
// Ensure key agreement is initialized (needed for hmac-secret even without PIN)
if (!protocol.isInitialized) {
val initialized = withContext(Dispatchers.IO) { protocol.initialize() }
if (!initialized) {
throw Exception("Failed to initialize key agreement for PRF")
}
}
effectiveProtocol = protocol
// Extract and convert PRF salts to hmac-secret salts
// PRF salt → hmac-secret salt: SHA-256("WebAuthn PRF" || 0x00 || salt)
val sha256 = MessageDigest.getInstance("SHA-256")
val prfPrefix = "WebAuthn PRF".toByteArray(Charsets.UTF_8)
val firstSaltRaw = Base64.decode(
prfEval!!.getString("first"),
Base64.URL_SAFE or Base64.NO_PADDING or Base64.NO_WRAP
)
sha256.reset()
sha256.update(prfPrefix)
sha256.update(0x00.toByte())
val salt1 = sha256.digest(firstSaltRaw)
var salt2: ByteArray? = null
if (prfEval.has("second")) {
val secondSaltRaw = Base64.decode(
prfEval.getString("second"),
Base64.URL_SAFE or Base64.NO_PADDING or Base64.NO_WRAP
)
sha256.reset()
sha256.update(prfPrefix)
sha256.update(0x00.toByte())
salt2 = sha256.digest(secondSaltRaw)
prfHasTwoSalts = true
}
// Build hmac-secret extension input
val hmacInput = protocol.buildHmacSecretInput(salt1, salt2)
?: throw Exception("Failed to build hmac-secret input")
// Build the CBOR extensions map: {"hmac-secret": {1: coseKey, 2: saltEnc, 3: saltAuth}}
val coseKey = protocol.encodePlatformCoseKeyBytes()
?: throw Exception("Failed to encode platform key")
hmacSecretExtensions = cbor {
map {
"hmac-secret" to map {
1 to coseKey
2 to bytes(hmacInput.saltEnc)
3 to bytes(hmacInput.saltAuth)
}
}
}.let { CborRaw(it.toList()) }
}
// Build clientDataJSON with proper origin
val origin = computeOrigin()
val clientData = providedClientDataHash.let { hash ->
@@ -977,8 +1072,8 @@ class CredentialProviderActivity : AppCompatActivity() {
// Compute pinUvAuthParam if needed
var pinUvAuthParam: ByteArray? = null
if (pinProtocol != null) {
pinUvAuthParam = pinProtocol.computeAuthParam(clientData.hash)
if (effectiveProtocol != null && effectiveProtocol.hasPinToken()) {
pinUvAuthParam = effectiveProtocol.computeAuthParam(clientData.hash)
}
// Build and send command
@@ -987,8 +1082,9 @@ class CredentialProviderActivity : AppCompatActivity() {
clientDataHash = clientData.hash,
allowList = if (allowList.isNotEmpty()) allowList else null,
requireUserVerification = false, // UV is provided by pinUvAuthParam
extensions = hmacSecretExtensions,
pinUvAuthParam = pinUvAuthParam,
pinUvAuthProtocol = if (pinProtocol != null) 1 else null
pinUvAuthProtocol = if (effectiveProtocol != null && effectiveProtocol.hasPinToken()) 1 else null
)
runOnUiThread {
@@ -1028,6 +1124,31 @@ class CredentialProviderActivity : AppCompatActivity() {
val credentialId = selectedAssertion.credential?.id
?: if (allowList.isNotEmpty()) allowList[0] else ByteArray(0)
// Parse PRF results from authenticator data extensions
var prfResults: JSONObject? = null
if (prfRequested && effectiveProtocol != null) {
val authData = AuthenticatorData.parse(selectedAssertion.authData)
val hmacSecretOutput = authData?.extensions?.bytes("hmac-secret")
if (hmacSecretOutput != null) {
val decrypted = effectiveProtocol.decryptHmacSecretOutput(hmacSecretOutput)
if (decrypted != null) {
prfResults = JSONObject().apply {
val first = decrypted.sliceArray(0 until 32)
put("first", Base64.encodeToString(
first, Base64.URL_SAFE or Base64.NO_PADDING or Base64.NO_WRAP
))
if (prfHasTwoSalts && decrypted.size >= 64) {
val second = decrypted.sliceArray(32 until 64)
put("second", Base64.encodeToString(
second, Base64.URL_SAFE or Base64.NO_PADDING or Base64.NO_WRAP
))
}
}
}
}
}
// Build response JSON
val responseJson = JSONObject().apply {
put("id", Base64.encodeToString(credentialId, Base64.URL_SAFE or Base64.NO_PADDING or Base64.NO_WRAP))
@@ -1056,7 +1177,13 @@ class CredentialProviderActivity : AppCompatActivity() {
))
}
})
put("clientExtensionResults", JSONObject())
put("clientExtensionResults", JSONObject().apply {
if (prfResults != null) {
put("prf", JSONObject().apply {
put("results", prfResults)
})
}
})
}
returnGetResult(responseJson.toString())
app/src/main/java/pl/lebihan/authnkey/FidoCommands.kt
+14
View File
@@ -15,6 +15,7 @@ object FidoCommands {
excludeList: List<ByteArray>? = null,
requireResidentKey: Boolean = true,
requireUserVerification: Boolean = true,
extensions: Map<String, Any>? = null,
pinUvAuthParam: ByteArray? = null,
pinUvAuthProtocol: Int? = null
): ByteArray {
@@ -53,6 +54,14 @@ object FidoCommands {
}
}
if (extensions != null && extensions.isNotEmpty()) {
6 to map {
for ((key, value) in extensions) {
key to value
}
}
}
7 to map { "rk" to requireResidentKey }
if (pinUvAuthParam != null) {
@@ -73,6 +82,7 @@ object FidoCommands {
clientDataHash: ByteArray,
allowList: List<ByteArray>? = null,
requireUserVerification: Boolean = true,
extensions: CborRaw? = null,
pinUvAuthParam: ByteArray? = null,
pinUvAuthProtocol: Int? = null
): ByteArray {
@@ -92,6 +102,10 @@ object FidoCommands {
}
}
if (extensions != null) {
4 to extensions
}
5 to map { "up" to true }
if (pinUvAuthParam != null) {
app/src/main/java/pl/lebihan/authnkey/PinProtocol.kt
+66
View File
@@ -318,6 +318,9 @@ class PinProtocol(private val transport: FidoTransport) {
fun hasPinToken(): Boolean = pinToken != null
val isInitialized: Boolean
get() = sharedSecret != null && platformPublicKey != null
fun computeAuthParam(message: ByteArray): ByteArray? {
val token = pinToken ?: return null
@@ -331,6 +334,46 @@ class PinProtocol(private val transport: FidoTransport) {
}
}
/**
* Build the hmac-secret extension input for getAssertion.
*
* @param salt1 First 32-byte salt (required)
* @param salt2 Second 32-byte salt (optional)
* @return Encrypted salts and authentication tag, or null if not initialized
*/
fun buildHmacSecretInput(salt1: ByteArray, salt2: ByteArray? = null): HmacSecretInput? {
val secret = sharedSecret ?: return null
val salts = if (salt2 != null) salt1 + salt2 else salt1
val saltEnc = aesEncrypt(secret, salts)
val mac = Mac.getInstance("HmacSHA256")
mac.init(SecretKeySpec(secret, "HmacSHA256"))
val saltAuth = mac.doFinal(saltEnc).copyOf(16)
return HmacSecretInput(saltEnc, saltAuth)
}
/**
* Decrypt the hmac-secret output from the authenticator.
*
* @param encrypted The encrypted output bytes from the authenticator's authData extensions
* @return Decrypted output (32 bytes for one salt, 64 for two)
*/
fun decryptHmacSecretOutput(encrypted: ByteArray): ByteArray? {
val secret = sharedSecret ?: return null
return try {
aesDecrypt(secret, encrypted)
} catch (e: Exception) {
null
}
}
data class HmacSecretInput(
val saltEnc: ByteArray,
val saltAuth: ByteArray
)
private fun buildGetKeyAgreementCommand(): ByteArray {
return byteArrayOf(CTAP.CMD_CLIENT_PIN.toByte()) + cbor {
map {
@@ -340,6 +383,29 @@ class PinProtocol(private val transport: FidoTransport) {
}
}
/**
* Encode an EC public key as a COSE_Key map using the CBOR builder.
* Exposed for use by hmac-secret extension building.
*/
fun encodePlatformCoseKeyBytes(): CborRaw? {
val pubKey = platformPublicKey ?: return null
val point = pubKey.w
val x = bigIntegerToBytes(point.affineX, 32)
val y = bigIntegerToBytes(point.affineY, 32)
val bytes = cbor {
map {
1 to 2
3 to -25
-1 to 1
-2 to bytes(x)
-3 to bytes(y)
}
}
// The cbor {} block wraps it in a map header, which is already what we need
return CborRaw(bytes.toList())
}
private fun buildGetPinTokenCommand(platformKey: ECPublicKey, encryptedPinHash: ByteArray): ByteArray {
return byteArrayOf(CTAP.CMD_CLIENT_PIN.toByte()) + cbor {
map {