1.1.0: refactor API

a-sit-plus · Sep 12, 2023 · f6d3d99 · f6d3d99
1 parent 4ef1723
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -60,3 +60,7 @@ attestation on Android, please re-read the readme!
 - Kotlin 1.9.10!
 - Bouncy Castle 1.76
 - Android-Attestation 1.0.0
+
+### 1.1.0
+- remove `verifyAttestation`
+- introduce `verifyKeyAttestation` taking an encoded public key as a byte array
diff --git a/README.md b/README.md
@@ -163,7 +163,7 @@ no real use case for such a configuration-
 1. The general workflow this library caters to assumes a back-end service, sending an attestation challenge to the mobile app. This challenge needs to be kept for future reference
 2. The app is assumed to generate a key pair with attestation (passing the received challenge the platforms' respective crypto APIs)
 3. The app responds with a platform-dependent attestation proof and the public key just created.
-4. On the back-end, a single call to `service.verifyKeyAttestation()` (or `service.verifyAttestation()`) is sufficient to remotely verify
+4. On the back-end, a single call to `service.verifyKeyAttestation()`  is sufficient to remotely verify
    whether the key is indeed stored in HW (and whether the app can be trusted). This call requires the challenge from step 1.
 
 Various flavours of this attestation call from step 4 exist, some of which are platform-dependent

diff --git a/attestation-service/build.gradle.kts b/attestation-service/build.gradle.kts
@@ -11,7 +11,7 @@ plugins {
 }
 
 group = "at.asitplus"
-version = "1.0.0"
+version = "1.1.0"
 
 sourceSets.test {
     kotlin {

diff --git a/attestation-service/src/main/kotlin/AttestationService.kt b/attestation-service/src/main/kotlin/AttestationService.kt
@@ -87,47 +87,21 @@ data class IOSAttestationConfiguration @JvmOverloads constructor(
 
 }
 
-interface AttestationService {
+abstract class AttestationService {
 
-    /**
-     * Convenience method to verifies both Android Key Attestation or Apple App Attestation
-     * structures of the client (in [attestationProof]) if the device can be verified and [challenge] matches
-     * the attestation challenge. On Android, this is simply the certificate chain from the attestation certificate
-     * (i.e. the certificate corresponding to the key to be attested) up to one of the [Google hardware attestation root
-       certificates](https://developer.android.com/training/articles/security-key-attestation#root_certificate).
-     * on iOS this contains at least the [AppAttest attestation statement](https://developer.apple.com/documentation/devicecheck/validating_apps_that_connect_to_your_server#3576643).
-     * Calls [verifyAttestationAndroid] or [verifyAttestationApple] depending on the kind of attestation proof prpvoded.
-     *
-     * For iOS clients it is optionally possible to pass [clientData]. In this case [attestationProof] must also
-     * contain an [assertion](https://developer.apple.com/documentation/devicecheck/validating_apps_that_connect_to_your_server#3576644)
-     * at index `1`, which, by default, is verified to match [clientData].
-     * The signature counter in the attestation must be `0` and the signature counter in the assertion must be `1`.
-     *
-     * Passing a public key created in the same app on the iDevice's secure hardware as [clientData] effectively
-     * emulates Android's key attestation: Attesting such a secondary key through an assertion, proves that
-     * it was also created within the same app, on the same device, resulting in an attested key, which can then be used
-     * for general-purpose crypto. **BEWARE if you pass the public key on iOS to be signed as is. iOS uses the ANSI X9.63
-     * format represent public keys, so conversion is needed**
-     *
-     * @see verifyAttestationApple
-     * @see verifyAttestationAndroid
-     *
-     * @return [AttestationResult] indicating whether Android or iOS was successfully attested,
-     * [AttestationResult.Error] in case attestation failed
-     */
-    fun verifyAttestation(
+
+    internal abstract fun verifyAttestation(
         attestationProof: List<ByteArray>,
         challenge: ByteArray,
         clientData: ByteArray? = null
     ): AttestationResult
 
 
     /**
-     * Verifies key attestation for both Android and Apple devices.
-     *
+     * Verifies key attestation for both Android and Apple devices.     *
      *
      * Succeeds if attestation data structures of the client (in [attestationProof]) can be verified and [expectedChallenge] matches
-     * the attestation challenge. For Android clients, this function Makes sure that [keyToBeAttested] matches the key contained in the attestation certificate.
+     * the attestation challenge. For Android clients, this function makes sure that [keyToBeAttested] matches the key contained in the attestation certificate.
      * For iOS this key needs to be specified explicitly anyhow to emulate key attestation
      *
      * @param attestationProof On Android, this is simply the certificate chain from the attestation certificate
@@ -185,13 +159,22 @@ interface AttestationService {
             is AttestationResult.IOS -> KeyAttestation(keyToBeAttested, firstTry)
         }
 
+    /** Same as [verifyKeyAttestation], but taking an encoded (either ANSI X9.63 or DER) publix key as a byte array
+     * @see verifyKeyAttestation
+     */
+    fun verifyKeyAttestation(
+        attestationProof: List<ByteArray>,
+        challenge: ByteArray,
+        encodedPublicKey: ByteArray
+    ): KeyAttestation<PublicKey> =
+        verifyKeyAttestation(attestationProof, challenge, encodedPublicKey.parseToPublicKey())
 
     /**
      * Groups ios-specific API to reduce toplevel clutter.
      *
      * Exposes iOS-specific functionality in a more expressive, and less confusing manner
      */
-    val ios: IOS
+    abstract val ios: IOS
 
     interface IOS {
         /**
@@ -225,7 +208,7 @@ interface AttestationService {
         ): AttestationResult
     }
 
-    val android: Android
+    abstract val android: Android
 
     interface Android {
         /**
@@ -300,7 +283,14 @@ sealed class AttestationResult {
                 "Verified(keyMaster security level: ${attestationRecord.keymasterSecurityLevel.name}, " +
                         "attestation security level: ${attestationRecord.attestationSecurityLevel.name}, " +
                         "${attestationRecord.attestedKey.algorithm} public key: ${attestationRecord.attestedKey.encoded.encodeBase64()}" + attestationRecord.softwareEnforced.attestationApplicationId.getOrNull()
-                    ?.let { app -> ", packageInfos: ${app.packageInfos.joinToString(prefix = "[", postfix = "]") { info -> "${info.packageName}:${info.version}" }}" }
+                    ?.let { app ->
+                        ", packageInfos: ${
+                            app.packageInfos.joinToString(
+                                prefix = "[",
+                                postfix = "]"
+                            ) { info -> "${info.packageName}:${info.version}" }
+                        }"
+                    }
         }
     }
 
@@ -370,7 +360,7 @@ data class KeyAttestation<T : PublicKey> internal constructor(
  * Do not use in production!
  */
 
-object NoopAttestationService : AttestationService {
+object NoopAttestationService : AttestationService() {
 
     private val log = LoggerFactory.getLogger(this.javaClass)
     override fun verifyAttestation(
@@ -381,8 +371,8 @@ object NoopAttestationService : AttestationService {
         if (attestationProof.size > 2) AttestationResult.Android.NOOP(attestationProof)
         else AttestationResult.IOS.NOOP(clientData)
 
-    override val ios: AttestationService.IOS
-        get() = object : AttestationService.IOS {
+    override val ios: IOS
+        get() = object : IOS {
             override fun verifyAppAttestation(attestationObject: ByteArray, challenge: ByteArray) =
                 verifyAttestation(listOf(attestationObject), challenge, clientData = null)
 
@@ -395,7 +385,7 @@ object NoopAttestationService : AttestationService {
             ) = verifyAttestation(listOf(attestationObject, assertionFromDevice), challenge, referenceClientData)
 
         }
-    override val android: AttestationService.Android
+    override val android: Android
         get() = TODO("Not yet implemented")
 }
 
@@ -416,7 +406,7 @@ class DefaultAttestationService(
     private val iosAttestationConfiguration: IOSAttestationConfiguration,
     private val clock: Clock = Clock.System,
     private val verificationTimeOffset: Duration = Duration.ZERO
-) : AttestationService {
+) : AttestationService() {
 
     /**
      * Java-friendly constructor with `java.time` types
@@ -487,7 +477,7 @@ class DefaultAttestationService(
             )
         }
 
-    override val ios = object : AttestationService.IOS {
+    override val ios = object : IOS {
         override fun verifyAppAttestation(attestationObject: ByteArray, challenge: ByteArray) =
             verifyAttestationApple(attestationObject, challenge, assertionData = null, counter = 0L)
 
@@ -505,7 +495,7 @@ class DefaultAttestationService(
         )
     }
 
-    override val android = object : AttestationService.Android {
+    override val android = object : Android {
         override fun verifyKeyAttestation(
             attestationCerts: List<X509Certificate>,
             expectedChallenge: ByteArray

diff --git a/attestation-service/src/main/kotlin/Extensions.kt b/attestation-service/src/main/kotlin/Extensions.kt
@@ -3,15 +3,25 @@ package at.asitplus.attestation
 import kotlinx.datetime.Clock
 import kotlinx.datetime.toJavaInstant
 import kotlinx.datetime.toKotlinInstant
+import org.bouncycastle.jce.ECNamedCurveTable
+import org.bouncycastle.jce.provider.JCEECPublicKey
 import org.bouncycastle.util.encoders.Base64
+import java.math.BigInteger
+import java.security.KeyFactory
+import java.security.PublicKey
 import java.security.cert.CertificateFactory
 import java.security.cert.X509Certificate
 import java.security.interfaces.ECPublicKey
+import java.security.spec.InvalidKeySpecException
+import java.security.spec.X509EncodedKeySpec
 import java.time.Instant
 import java.time.ZoneId
 import java.util.*
 
 
+private val ecKeyFactory = KeyFactory.getInstance("EC")
+private val rsaKeyFactory = KeyFactory.getInstance("RSA")
+
 //copied from AppAttest Library
 private val certificateFactory = CertificateFactory.getInstance("X.509")
 fun ByteArray.parseToCertificate(): X509Certificate? = kotlin.runCatching {
@@ -54,6 +64,21 @@ fun ECPublicKey.toAnsi() = let {
     byteArrayOf(0x04) + xFromBc + yFromBc
 }
 
+fun ByteArray.parseToPublicKey(): PublicKey =
+    try {
+        (if (size < 1024) ecKeyFactory else rsaKeyFactory).generatePublic(X509EncodedKeySpec(this))
+    } catch (e: Throwable) {
+        if (first() != 0x04.toByte()) throw InvalidKeySpecException("Encoded public key does not start with 0x04")
+
+        val parameterSpec = ECNamedCurveTable.getParameterSpec("P-256")
+        val ecPoint = parameterSpec.curve.createPoint(
+            BigInteger(1, sliceArray(1..<33)),
+            BigInteger(1, takeLast(32).toByteArray())
+        )
+        val ecPublicKeySpec = org.bouncycastle.jce.spec.ECPublicKeySpec(ecPoint, parameterSpec)
+        JCEECPublicKey("EC", ecPublicKeySpec)
+    }
+
 /**
  * Drops or adds zero bytes at the start until the [size] is reached
  */

diff --git a/attestation-service/src/test/java/JavaInteropTest.java b/attestation-service/src/test/java/JavaInteropTest.java
@@ -98,28 +98,6 @@ public static void testAttestationCallsJavaFriendliness() throws NoSuchAlgorithm
                         "14.1"),
                 Duration.ZERO);
 
-        AttestationResult result = service.verifyAttestation(Collections.emptyList(), new byte[]{}, null);
-
-
-        if (result instanceof AttestationResult.Android) {
-            ((AttestationResult.Android) result).getAttestationCertificate();
-            ((AttestationResult.Android) result).getAttestationRecord();
-        }
-
-        if (result instanceof AttestationResult.IOS) {
-            ((AttestationResult.IOS) result).getClientData();
-        }
-
-        if (result instanceof AttestationResult.Error) {
-            Throwable cause = ((AttestationResult.Error) result).getCause();
-            String explanation = ((AttestationResult.Error) result).getExplanation();
-            Assertions.assertEquals("Attestation proof is empty", explanation);
-            Assertions.assertNull(cause);
-        }
-
-        Assertions.assertTrue(result instanceof AttestationResult.Error);
-
-
         KeyAttestation<ECPublicKey> keyAttestationResult = service.verifyKeyAttestation(Collections.emptyList(),
                 new byte[]{0, 2, 3, 2, 2}, (ECPublicKey) KeyPairGenerator.getInstance("EC").
                         generateKeyPair().getPublic());