PasskeyRegistration.kt

1package com.peachpasswords.passkeys23import com.peachpasswords.vault.PasskeyData4import com.peachpasswords.vault.VaultEntry5import java.security.KeyPairGenerator6import java.security.SecureRandom7import java.security.interfaces.ECPrivateKey8import java.security.interfaces.ECPublicKey9import java.security.spec.ECGenParameterSpec10import java.util.Base6411import org.bouncycastle.crypto.params.Ed25519PrivateKeyParameters12import kotlinx.serialization.json.Json13import kotlinx.serialization.json.JsonObject14import kotlinx.serialization.json.JsonPrimitive15import kotlinx.serialization.json.buildJsonArray16import kotlinx.serialization.json.buildJsonObject17import kotlinx.serialization.json.contentOrNull18import kotlinx.serialization.json.intOrNull19import kotlinx.serialization.json.jsonArray20import kotlinx.serialization.json.jsonObject21import kotlinx.serialization.json.jsonPrimitive22import kotlinx.serialization.json.put2324data class PasskeyRegistrationResult(25    val entryDraft: VaultEntry,26    val responseJson: String,27)2829object PasskeyRegistration {30    private val json = Json { ignoreUnknownKeys = true }31    private val random = SecureRandom()32    private val urlEncoder = Base64.getUrlEncoder().withoutPadding()3334    fun build(35        requestJson: String,36        origin: String?,37        now: Long = System.currentTimeMillis(),38        // Set to true only when a biometric / device-credential prompt has39        // actually succeeded for this registration. Defaults to false so40        // callers that bypass the prompt still produce a valid flag byte41        // (UV=0) rather than the old hard-coded UV=1 claim.42        userVerified: Boolean = false,43    ): PasskeyRegistrationResult? {44        val request = runCatching { json.parseToJsonElement(requestJson).jsonObject }.getOrNull() ?: return null45        val rp = request["rp"]?.jsonObject ?: return null46        val user = request["user"]?.jsonObject ?: return null47        val rpId = rp["id"]?.jsonPrimitive?.contentOrNull ?: return null48        val rpName = rp["name"]?.jsonPrimitive?.contentOrNull ?: rpId49        val userHandle = user["id"]?.jsonPrimitive?.contentOrNull ?: return null50        val userName = user["name"]?.jsonPrimitive?.contentOrNull ?: return null51        val userDisplayName = user["displayName"]?.jsonPrimitive?.contentOrNull ?: userName52        val challenge = request["challenge"]?.jsonPrimitive?.contentOrNull ?: return null53        val algorithm = pickAlgorithm(request["pubKeyCredParams"]) ?: return null5455        val keyMaterial = generateKeyMaterial(algorithm)56        val credentialId = ByteArray(32).also(random::nextBytes)57        val publicKeyCose = keyMaterial.publicKeyCose58        // Peach's vault always permits the credential's private key to leave the59        // device via PeachScript export or paired-device sync, so every freshly60        // registered passkey is by definition backup-eligible. backupState stays61        // false: at the moment of registration the credential has not yet been62        // mirrored anywhere — that fact is written here so the BE/BS bits in the63        // authenticator data never disagree with the persisted record.64        val backupEligible = true65        val backupState = false66        val authData = buildAttestationAuthData(rpId, credentialId, publicKeyCose, registrationFlags(userVerified))67        val attestationObject = Cbor.map(68            "fmt" to Cbor.text("none"),69            "attStmt" to Cbor.map(),70            "authData" to Cbor.bytes(authData),71        )72        val clientDataJson = clientDataJson("webauthn.create", challenge, origin ?: originFromRpId(rpId))73        val passkey = PasskeyData(74            credentialId = b64(credentialId),75            publicKeyCose = b64(publicKeyCose),76            privateKeyJwk = keyMaterial.privateKeyJwk,77            rpId = rpId,78            rpName = rpName,79            userHandle = userHandle,80            userName = userName,81            userDisplayName = userDisplayName,82            algorithm = algorithm,83            signCount = 0,84            aaguid = b64(ByteArray(16)),85            backupEligible = backupEligible,86            backupState = backupState,87            transports = listOf("internal"),88            createdAt = now,89        )90        val entry = VaultEntry(91            id = "",92            type = "login",93            title = rpName,94            username = userName,95            url = "https://$rpId",96            passkey = passkey,97            createdAt = 0,98            modifiedAt = 0,99        )100        val responseJson = json.encodeToString(101            JsonObject.serializer(),102            buildJsonObject {103                put("id", passkey.credentialId)104                put("rawId", passkey.credentialId)105                put("type", "public-key")106                put("response", buildJsonObject {107                    put("clientDataJSON", b64(clientDataJson))108                    put("authenticatorData", b64(authData))109                    put("attestationObject", b64(attestationObject))110                    put("transports", buildJsonArray { add(JsonPrimitive("internal")) })111                    put("publicKey", b64(keyMaterial.publicKeySpki))112                    put("publicKeyAlgorithm", algorithm)113                })114                put("authenticatorAttachment", "platform")115                put("clientExtensionResults", buildJsonObject {})116            },117        )118        return PasskeyRegistrationResult(entryDraft = entry, responseJson = responseJson)119    }120121    private data class KeyMaterial(122        val publicKeyCose: ByteArray,123        val publicKeySpki: ByteArray,124        val privateKeyJwk: String,125    )126127    private fun pickAlgorithm(value: kotlinx.serialization.json.JsonElement?): Int? {128        val params = runCatching { value?.jsonArray }.getOrNull() ?: return -7129        val offered = params.mapNotNull { item ->130            runCatching { item.jsonObject["alg"]?.jsonPrimitive?.intOrNull }.getOrNull()131        }.toSet()132        return when {133            -8 in offered -> -8134            -7 in offered -> -7135            else -> null136        }137    }138139    private fun generateKeyMaterial(algorithm: Int): KeyMaterial =140        if (algorithm == -8) generateEd25519KeyMaterial() else generateEs256KeyMaterial()141142    private fun generateEs256KeyMaterial(): KeyMaterial {143        val keyPair = KeyPairGenerator.getInstance("EC").apply {144            initialize(ECGenParameterSpec("secp256r1"))145        }.generateKeyPair()146        val privateKey = keyPair.private as ECPrivateKey147        val publicKey = keyPair.public as ECPublicKey148        val publicKeyCose = Cbor.map(149            1 to Cbor.uint(2),150            3 to Cbor.nint(-7),151            -1 to Cbor.uint(1),152            -2 to Cbor.bytes(publicKey.w.affineX.toFixed32()),153            -3 to Cbor.bytes(publicKey.w.affineY.toFixed32()),154        )155        return KeyMaterial(156            publicKeyCose = publicKeyCose,157            publicKeySpki = publicKey.encoded,158            privateKeyJwk = privateEs256Jwk(privateKey, publicKey),159        )160    }161162    private fun generateEd25519KeyMaterial(): KeyMaterial {163        val privateKey = Ed25519PrivateKeyParameters(random)164        val publicKey = privateKey.generatePublicKey().encoded165        val seed = privateKey.encoded166        val publicKeyCose = Cbor.map(167            1 to Cbor.uint(1),168            3 to Cbor.nint(-8),169            -1 to Cbor.uint(6),170            -2 to Cbor.bytes(publicKey),171        )172        val privateKeyJwk = json.encodeToString(173            JsonObject.serializer(),174            buildJsonObject {175                put("kty", "OKP")176                put("crv", "Ed25519")177                put("d", b64(seed))178                put("x", b64(publicKey))179            },180        )181        return KeyMaterial(182            publicKeyCose = publicKeyCose,183            publicKeySpki = ed25519Spki(publicKey),184            privateKeyJwk = privateKeyJwk,185        )186    }187188    private fun buildAttestationAuthData(rpId: String, credentialId: ByteArray, publicKeyCose: ByteArray, flags: Int): ByteArray {189        val base = ByteArray(37)190        java.security.MessageDigest.getInstance("SHA-256").digest(rpId.toByteArray(Charsets.UTF_8)).copyInto(base, 0)191        // UP=1 (implicit in the credential pick); BE set because Peach vaults192        // are exportable/syncable by construction; AT set because attested193        // credential data is always included at registration; UV reflects an194        // actual user-verification ceremony performed by the caller — never195        // assume it. H-07 fix: the flag byte used to hard-code UV=1 without196        // running any ceremony, which is precisely the misleading-claim bug.197        base[32] = flags.toByte()198        val length = byteArrayOf(((credentialId.size ushr 8) and 0xff).toByte(), (credentialId.size and 0xff).toByte())199        return base + ByteArray(16) + length + credentialId + publicKeyCose200    }201202    private const val FLAG_UP: Int = 0x01203    private const val FLAG_UV: Int = 0x04204    private const val FLAG_BE: Int = 0x08205    private const val FLAG_AT: Int = 0x40206207    // AT (0x40) is always included for registration because the response208    // carries attested credential data; BE (0x08) is set because Peach209    // vaults are exportable/syncable by construction; UP (0x01) is implicit210    // in the user picking a credential. UV (0x04) is set only when the211    // caller actually performed user verification.212    private fun registrationFlags(userVerified: Boolean): Int =213        FLAG_UP or FLAG_BE or FLAG_AT or (if (userVerified) FLAG_UV else 0)214215    private fun clientDataJson(type: String, challenge: String, origin: String): ByteArray =216        json.encodeToString(217            JsonObject.serializer(),218            buildJsonObject {219                put("type", type)220                put("challenge", challenge)221                put("origin", origin)222                put("crossOrigin", JsonPrimitive(false))223            },224        ).toByteArray(Charsets.UTF_8)225226    private fun privateEs256Jwk(privateKey: ECPrivateKey, publicKey: ECPublicKey): String =227        json.encodeToString(228            JsonObject.serializer(),229            buildJsonObject {230                put("kty", "EC")231                put("crv", "P-256")232                put("d", b64(privateKey.s.toFixed32()))233                put("x", b64(publicKey.w.affineX.toFixed32()))234                put("y", b64(publicKey.w.affineY.toFixed32()))235            },236        )237238    private fun originFromRpId(rpId: String): String =239        if (rpId.equals("localhost", ignoreCase = true) || rpId == "127.0.0.1" || rpId == "[::1]") "http://$rpId" else "https://$rpId"240241    private fun b64(data: ByteArray): String = urlEncoder.encodeToString(data)242243    private fun ed25519Spki(publicKey: ByteArray): ByteArray =244        byteArrayOf(245            0x30, 0x2a, 0x30, 0x05, 0x06, 0x03, 0x2b, 0x65, 0x70, 0x03, 0x21, 0x00,246        ) + publicKey247}248249private object Cbor {250    fun uint(value: Int) = integer(value)251    fun nint(value: Int) = integer(value)252    fun bytes(value: ByteArray) = major(2, value.size) + value253    fun text(value: String): ByteArray {254        val bytes = value.toByteArray(Charsets.UTF_8)255        return major(3, bytes.size) + bytes256    }257    fun map(vararg entries: Pair<Any, ByteArray>): ByteArray {258        val body = entries.flatMap { (key, value) ->259            val encodedKey = when (key) {260                is Int -> integer(key)261                is String -> text(key)262                else -> error("unsupported cbor key")263            }264            listOf(encodedKey, value)265        }.fold(ByteArray(0)) { acc, bytes -> acc + bytes }266        return major(5, entries.size) + body267    }268    private fun integer(value: Int): ByteArray =269        if (value >= 0) major(0, value) else major(1, -1 - value)270    private fun major(type: Int, value: Int): ByteArray = when {271        value < 24 -> byteArrayOf(((type shl 5) or value).toByte())272        value < 0x100 -> byteArrayOf(((type shl 5) or 24).toByte(), value.toByte())273        value < 0x10000 -> byteArrayOf(((type shl 5) or 25).toByte(), (value ushr 8).toByte(), value.toByte())274        else -> error("cbor length too large")275    }276}277278private fun java.math.BigInteger.toFixed32(): ByteArray {279    val raw = toByteArray()280    val unsigned = if (raw.size > 1 && raw[0] == 0.toByte()) raw.copyOfRange(1, raw.size) else raw281    return ByteArray(32).also { unsigned.copyInto(it, 32 - unsigned.size) }282}