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 kotlinx.serialization.json.Json12import kotlinx.serialization.json.JsonArray13import 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 if (!offersEs256(request["pubKeyCredParams"])) return null4546 val keyPair = KeyPairGenerator.getInstance("EC").apply {47 initialize(ECGenParameterSpec("secp256r1"))48 }.generateKeyPair()49 val privateKey = keyPair.private as ECPrivateKey50 val publicKey = keyPair.public as ECPublicKey51 val credentialId = ByteArray(32).also(random::nextBytes)52 val publicKeyCose = Cbor.map(53 1 to Cbor.uint(2),54 3 to Cbor.nint(-7),55 -1 to Cbor.uint(1),56 -2 to Cbor.bytes(publicKey.w.affineX.toFixed32()),57 -3 to Cbor.bytes(publicKey.w.affineY.toFixed32()),58 )59 val authData = buildAttestationAuthData(rpId, credentialId, publicKeyCose)60 val attestationObject = Cbor.map(61 "fmt" to Cbor.text("none"),62 "attStmt" to Cbor.map(),63 "authData" to Cbor.bytes(authData),64 )65 val clientDataJson = clientDataJson("webauthn.create", challenge, origin ?: originFromRpId(rpId))66 val passkey = PasskeyData(67 credentialId = b64(credentialId),68 publicKeyCose = b64(publicKeyCose),69 privateKeyJwk = privateJwk(privateKey, publicKey),70 rpId = rpId,71 rpName = rpName,72 userHandle = userHandle,73 userName = userName,74 userDisplayName = userDisplayName,75 algorithm = -7,76 signCount = 0,77 aaguid = b64(ByteArray(16)),78 backupEligible = false,79 backupState = false,80 transports = listOf("internal"),81 createdAt = now,82 )83 val entry = VaultEntry(84 id = "",85 type = "login",86 title = rpName,87 username = userName,88 url = "https://$rpId",89 passkey = passkey,90 createdAt = 0,91 modifiedAt = 0,92 )93 val responseJson = json.encodeToString(94 JsonObject.serializer(),95 buildJsonObject {96 put("id", passkey.credentialId)97 put("rawId", passkey.credentialId)98 put("type", "public-key")99 put("response", buildJsonObject {100 put("clientDataJSON", b64(clientDataJson))101 put("authenticatorData", b64(authData))102 put("attestationObject", b64(attestationObject))103 put("transports", buildJsonArray { add(JsonPrimitive("internal")) })104 put("publicKey", b64(publicKey.encoded))105 put("publicKeyAlgorithm", -7)106 })107 put("authenticatorAttachment", "platform")108 put("clientExtensionResults", buildJsonObject {})109 },110 )111 return PasskeyRegistrationResult(entryDraft = entry, responseJson = responseJson)112 }113114 private fun offersEs256(value: kotlinx.serialization.json.JsonElement?): Boolean {115 val params = runCatching { value?.jsonArray }.getOrNull() ?: return true116 return params.any { item ->117 runCatching { item.jsonObject["alg"]?.jsonPrimitive?.intOrNull == -7 }.getOrDefault(false)118 }119 }120121 private fun buildAttestationAuthData(rpId: String, credentialId: ByteArray, publicKeyCose: ByteArray): ByteArray {122 val base = ByteArray(37)123 java.security.MessageDigest.getInstance("SHA-256").digest(rpId.toByteArray(Charsets.UTF_8)).copyInto(base, 0)124 base[32] = 0x4d125 val length = byteArrayOf(((credentialId.size ushr 8) and 0xff).toByte(), (credentialId.size and 0xff).toByte())126 return base + ByteArray(16) + length + credentialId + publicKeyCose127 }128129 private fun clientDataJson(type: String, challenge: String, origin: String): ByteArray =130 json.encodeToString(131 JsonObject.serializer(),132 buildJsonObject {133 put("type", type)134 put("challenge", challenge)135 put("origin", origin)136 put("crossOrigin", JsonPrimitive(false))137 },138 ).toByteArray(Charsets.UTF_8)139140 private fun privateJwk(privateKey: ECPrivateKey, publicKey: ECPublicKey): String =141 json.encodeToString(142 JsonObject.serializer(),143 buildJsonObject {144 put("kty", "EC")145 put("crv", "P-256")146 put("d", b64(privateKey.s.toFixed32()))147 put("x", b64(publicKey.w.affineX.toFixed32()))148 put("y", b64(publicKey.w.affineY.toFixed32()))149 },150 )151152 private fun originFromRpId(rpId: String): String =153 if (rpId.equals("localhost", ignoreCase = true) || rpId == "127.0.0.1" || rpId == "[::1]") "http://$rpId" else "https://$rpId"154155 private fun b64(data: ByteArray): String = urlEncoder.encodeToString(data)156}157158private object Cbor {159 fun uint(value: Int) = integer(value)160 fun nint(value: Int) = integer(value)161 fun bytes(value: ByteArray) = major(2, value.size) + value162 fun text(value: String): ByteArray {163 val bytes = value.toByteArray(Charsets.UTF_8)164 return major(3, bytes.size) + bytes165 }166 fun map(vararg entries: Pair<Any, ByteArray>): ByteArray {167 val body = entries.flatMap { (key, value) ->168 val encodedKey = when (key) {169 is Int -> integer(key)170 is String -> text(key)171 else -> error("unsupported cbor key")172 }173 listOf(encodedKey, value)174 }.fold(ByteArray(0)) { acc, bytes -> acc + bytes }175 return major(5, entries.size) + body176 }177 private fun integer(value: Int): ByteArray =178 if (value >= 0) major(0, value) else major(1, -1 - value)179 private fun major(type: Int, value: Int): ByteArray = when {180 value < 24 -> byteArrayOf(((type shl 5) or value).toByte())181 value < 0x100 -> byteArrayOf(((type shl 5) or 24).toByte(), value.toByte())182 value < 0x10000 -> byteArrayOf(((type shl 5) or 25).toByte(), (value ushr 8).toByte(), value.toByte())183 else -> error("cbor length too large")184 }185}186187private fun java.math.BigInteger.toFixed32(): ByteArray {188 val raw = toByteArray()189 val unsigned = if (raw.size > 1 && raw[0] == 0.toByte()) raw.copyOfRange(1, raw.size) else raw190 return ByteArray(32).also { unsigned.copyInto(it, 32 - unsigned.size) }191}