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(requestJson: String, origin: String?, now: Long = System.currentTimeMillis()): PasskeyRegistrationResult? {35 val request = runCatching { json.parseToJsonElement(requestJson).jsonObject }.getOrNull() ?: return null36 val rp = request["rp"]?.jsonObject ?: return null37 val user = request["user"]?.jsonObject ?: return null38 val rpId = rp["id"]?.jsonPrimitive?.contentOrNull ?: return null39 val rpName = rp["name"]?.jsonPrimitive?.contentOrNull ?: rpId40 val userHandle = user["id"]?.jsonPrimitive?.contentOrNull ?: return null41 val userName = user["name"]?.jsonPrimitive?.contentOrNull ?: return null42 val userDisplayName = user["displayName"]?.jsonPrimitive?.contentOrNull ?: userName43 val challenge = request["challenge"]?.jsonPrimitive?.contentOrNull ?: return null44 val algorithm = pickAlgorithm(request["pubKeyCredParams"]) ?: return null4546 val keyMaterial = generateKeyMaterial(algorithm)47 val credentialId = ByteArray(32).also(random::nextBytes)48 val publicKeyCose = keyMaterial.publicKeyCose49 val authData = buildAttestationAuthData(rpId, credentialId, publicKeyCose)50 val attestationObject = Cbor.map(51 "fmt" to Cbor.text("none"),52 "attStmt" to Cbor.map(),53 "authData" to Cbor.bytes(authData),54 )55 val clientDataJson = clientDataJson("webauthn.create", challenge, origin ?: originFromRpId(rpId))56 val passkey = PasskeyData(57 credentialId = b64(credentialId),58 publicKeyCose = b64(publicKeyCose),59 privateKeyJwk = keyMaterial.privateKeyJwk,60 rpId = rpId,61 rpName = rpName,62 userHandle = userHandle,63 userName = userName,64 userDisplayName = userDisplayName,65 algorithm = algorithm,66 signCount = 0,67 aaguid = b64(ByteArray(16)),68 backupEligible = false,69 backupState = false,70 transports = listOf("internal"),71 createdAt = now,72 )73 val entry = VaultEntry(74 id = "",75 type = "login",76 title = rpName,77 username = userName,78 url = "https://$rpId",79 passkey = passkey,80 createdAt = 0,81 modifiedAt = 0,82 )83 val responseJson = json.encodeToString(84 JsonObject.serializer(),85 buildJsonObject {86 put("id", passkey.credentialId)87 put("rawId", passkey.credentialId)88 put("type", "public-key")89 put("response", buildJsonObject {90 put("clientDataJSON", b64(clientDataJson))91 put("authenticatorData", b64(authData))92 put("attestationObject", b64(attestationObject))93 put("transports", buildJsonArray { add(JsonPrimitive("internal")) })94 put("publicKey", b64(keyMaterial.publicKeySpki))95 put("publicKeyAlgorithm", algorithm)96 })97 put("authenticatorAttachment", "platform")98 put("clientExtensionResults", buildJsonObject {})99 },100 )101 return PasskeyRegistrationResult(entryDraft = entry, responseJson = responseJson)102 }103104 private data class KeyMaterial(105 val publicKeyCose: ByteArray,106 val publicKeySpki: ByteArray,107 val privateKeyJwk: String,108 )109110 private fun pickAlgorithm(value: kotlinx.serialization.json.JsonElement?): Int? {111 val params = runCatching { value?.jsonArray }.getOrNull() ?: return -7112 val offered = params.mapNotNull { item ->113 runCatching { item.jsonObject["alg"]?.jsonPrimitive?.intOrNull }.getOrNull()114 }.toSet()115 return when {116 -8 in offered -> -8117 -7 in offered -> -7118 else -> null119 }120 }121122 private fun generateKeyMaterial(algorithm: Int): KeyMaterial =123 if (algorithm == -8) generateEd25519KeyMaterial() else generateEs256KeyMaterial()124125 private fun generateEs256KeyMaterial(): KeyMaterial {126 val keyPair = KeyPairGenerator.getInstance("EC").apply {127 initialize(ECGenParameterSpec("secp256r1"))128 }.generateKeyPair()129 val privateKey = keyPair.private as ECPrivateKey130 val publicKey = keyPair.public as ECPublicKey131 val publicKeyCose = Cbor.map(132 1 to Cbor.uint(2),133 3 to Cbor.nint(-7),134 -1 to Cbor.uint(1),135 -2 to Cbor.bytes(publicKey.w.affineX.toFixed32()),136 -3 to Cbor.bytes(publicKey.w.affineY.toFixed32()),137 )138 return KeyMaterial(139 publicKeyCose = publicKeyCose,140 publicKeySpki = publicKey.encoded,141 privateKeyJwk = privateEs256Jwk(privateKey, publicKey),142 )143 }144145 private fun generateEd25519KeyMaterial(): KeyMaterial {146 val privateKey = Ed25519PrivateKeyParameters(random)147 val publicKey = privateKey.generatePublicKey().encoded148 val seed = privateKey.encoded149 val publicKeyCose = Cbor.map(150 1 to Cbor.uint(1),151 3 to Cbor.nint(-8),152 -1 to Cbor.uint(6),153 -2 to Cbor.bytes(publicKey),154 )155 val privateKeyJwk = json.encodeToString(156 JsonObject.serializer(),157 buildJsonObject {158 put("kty", "OKP")159 put("crv", "Ed25519")160 put("d", b64(seed))161 put("x", b64(publicKey))162 },163 )164 return KeyMaterial(165 publicKeyCose = publicKeyCose,166 publicKeySpki = ed25519Spki(publicKey),167 privateKeyJwk = privateKeyJwk,168 )169 }170171 private fun buildAttestationAuthData(rpId: String, credentialId: ByteArray, publicKeyCose: ByteArray): ByteArray {172 val base = ByteArray(37)173 java.security.MessageDigest.getInstance("SHA-256").digest(rpId.toByteArray(Charsets.UTF_8)).copyInto(base, 0)174 base[32] = 0x4d175 val length = byteArrayOf(((credentialId.size ushr 8) and 0xff).toByte(), (credentialId.size and 0xff).toByte())176 return base + ByteArray(16) + length + credentialId + publicKeyCose177 }178179 private fun clientDataJson(type: String, challenge: String, origin: String): ByteArray =180 json.encodeToString(181 JsonObject.serializer(),182 buildJsonObject {183 put("type", type)184 put("challenge", challenge)185 put("origin", origin)186 put("crossOrigin", JsonPrimitive(false))187 },188 ).toByteArray(Charsets.UTF_8)189190 private fun privateEs256Jwk(privateKey: ECPrivateKey, publicKey: ECPublicKey): String =191 json.encodeToString(192 JsonObject.serializer(),193 buildJsonObject {194 put("kty", "EC")195 put("crv", "P-256")196 put("d", b64(privateKey.s.toFixed32()))197 put("x", b64(publicKey.w.affineX.toFixed32()))198 put("y", b64(publicKey.w.affineY.toFixed32()))199 },200 )201202 private fun originFromRpId(rpId: String): String =203 if (rpId.equals("localhost", ignoreCase = true) || rpId == "127.0.0.1" || rpId == "[::1]") "http://$rpId" else "https://$rpId"204205 private fun b64(data: ByteArray): String = urlEncoder.encodeToString(data)206207 private fun ed25519Spki(publicKey: ByteArray): ByteArray =208 byteArrayOf(209 0x30, 0x2a, 0x30, 0x05, 0x06, 0x03, 0x2b, 0x65, 0x70, 0x03, 0x21, 0x00,210 ) + publicKey211}212213private object Cbor {214 fun uint(value: Int) = integer(value)215 fun nint(value: Int) = integer(value)216 fun bytes(value: ByteArray) = major(2, value.size) + value217 fun text(value: String): ByteArray {218 val bytes = value.toByteArray(Charsets.UTF_8)219 return major(3, bytes.size) + bytes220 }221 fun map(vararg entries: Pair<Any, ByteArray>): ByteArray {222 val body = entries.flatMap { (key, value) ->223 val encodedKey = when (key) {224 is Int -> integer(key)225 is String -> text(key)226 else -> error("unsupported cbor key")227 }228 listOf(encodedKey, value)229 }.fold(ByteArray(0)) { acc, bytes -> acc + bytes }230 return major(5, entries.size) + body231 }232 private fun integer(value: Int): ByteArray =233 if (value >= 0) major(0, value) else major(1, -1 - value)234 private fun major(type: Int, value: Int): ByteArray = when {235 value < 24 -> byteArrayOf(((type shl 5) or value).toByte())236 value < 0x100 -> byteArrayOf(((type shl 5) or 24).toByte(), value.toByte())237 value < 0x10000 -> byteArrayOf(((type shl 5) or 25).toByte(), (value ushr 8).toByte(), value.toByte())238 else -> error("cbor length too large")239 }240}241242private fun java.math.BigInteger.toFixed32(): ByteArray {243 val raw = toByteArray()244 val unsigned = if (raw.size > 1 && raw[0] == 0.toByte()) raw.copyOfRange(1, raw.size) else raw245 return ByteArray(32).also { unsigned.copyInto(it, 32 - unsigned.size) }246}