Introduce DeviceAttestationSoftware. (#1663)

Right now our DeviceCheck machinery only works on real iOS devices
(excluding the iOS simulator) and Android devices (real or emulator)
and we need them to work for the web (for the web version of Multipaz
Wallet) and it would also be nice if they worked for the iOS
simulator.

As such, introduce `DeviceAttestationSoftware` which can be generated
in any environment which lacks hardware-backed attestation. This is
inherently insecure but the backend has access to the attestation so
it can provide a subset of functionality to e.g. web clients. For
example, for Multipaz Wallet we can allow access to shared state
(bound to e.g. a Google account) for web clients but refuse access to
e.g. key attestation services.

Also introduce the notion of a "proof of secret" embedded in this new
attestation. This is inhererently insecure (an attacker can exfiltrate
this client-side secret from the binary or app process) and HW-backed
attestation should be preferred but in an environment without
HW-backed attestation this adds a little bit of security.

Change DeviceCheck for JVM so it uses `DeviceAttestationSoftware` and
also DeviceCheck for iOS when running on the iOS simulator. This way
it's actually possible to develop Multipaz Wallet using the iOS
simulator when using its dev backend configured to accept software
attestations.

Add a new screen to Compose TestApp to easily test both device
attestations and assertions, both strict and non-strict.

This also uncovered a bug in `ClientRegistrationImpl` where we would
always generate empty challenges. Fix this.

Test: Unit tests for DeviceAttestationSoftware.
Test: Manually tested on Android and iOS.

Signed-off-by: David Zeuthen <zeuthen@google.com>

Author: davidz25

multipaz-compose/build.gradle.kts

@@ -78,7 +78,8 @@ kotlin {
         it.binaries.all {
             linkerOpts(
                 "-L/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/${platform}/",
-                "-Wl,-rpath,/usr/lib/swift"
+                "-Wl,-rpath,/usr/lib/swift",
+                "-lsqlite3"
             )
         }
     }

multipaz-csa/src/main/java/org/multipaz/securearea/cloud/CloudSecureAreaServer.kt

@@ -176,13 +176,15 @@ class CloudSecureAreaServer(
             request1.deviceAttestation.validate(
                 DeviceAttestationValidationData(
                     attestationChallenge = state.attestationChallenge!!,
+                    softwareAccepted = false,
+                    softwareSecrets = emptySet(),
                     iosReleaseBuild = iosReleaseBuild,
                     iosAppIdentifiers = iosAppIdentifiers.toSet(),
                     androidGmsAttestation = androidGmsAttestation,
                     androidVerifiedBootGreen = androidVerifiedBootGreen,
                     androidAppSignatureCertificateDigests = androidAppSignatureCertificateDigests.toSet(),
                     androidAppPackageNames = androidAppPackageNames.toSet(),
-                    androidRequiredKeyMintSecurityLevel = androidKeystoreSecurityLevel
+                    androidRequiredKeyMintSecurityLevel = androidKeystoreSecurityLevel,
                 )
             )
         } catch (e: Exception) {

multipaz-dcapi/build.gradle.kts

@@ -60,7 +60,8 @@ kotlin {
         it.binaries.all {
             linkerOpts(
                 "-L/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/${platform}/",
-                "-Wl,-rpath,/usr/lib/swift"
+                "-Wl,-rpath,/usr/lib/swift",
+                "-lsqlite3"
             )
         }
     }

multipaz-doctypes/build.gradle.kts

@@ -52,7 +52,8 @@ kotlin {
         it.binaries.all {
             linkerOpts(
                 "-L/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/${platform}/",
-                "-Wl,-rpath,/usr/lib/swift"
+                "-Wl,-rpath,/usr/lib/swift",
+                "-lsqlite3"
             )
         }
     }

multipaz-longfellow/build.gradle.kts

@@ -82,6 +82,7 @@ kotlin {
             linkerOpts(
                 "-L$rootDir/multipaz-longfellow/src/iosMain/nativeLibs/$zkLibExt/lib",
                 "-Wl,-rpath,/usr/lib/swift",
+                "-lsqlite3",
                 "-lmdoc_static"
             )
         }

multipaz-swiftui/build.gradle.kts

@@ -52,7 +52,8 @@ kotlin {
         it.binaries.all {
             linkerOpts(
                 "-L/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/${platform}/",
-                "-Wl,-rpath,/usr/lib/swift"
+                "-Wl,-rpath,/usr/lib/swift",
+                "-lsqlite3"
             )
         }
     }

multipaz/build.gradle.kts

@@ -96,7 +96,8 @@ kotlin {
                         "-L/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/${platform}/",
                         "-L$rootDir/multipaz/SwiftBridge/build/Release-${platform}/",
                         "-lSwiftBridge",
-                        "-Wl,-rpath,/usr/lib/swift"
+                        "-Wl,-rpath,/usr/lib/swift",
+                        "-lsqlite3"
                     )
                 }
             }

multipaz/src/androidMain/kotlin/org/multipaz/device/DeviceCheck.android.kt

@@ -1,25 +1,34 @@
 package org.multipaz.device
 
+import kotlinx.io.bytestring.ByteString
+import kotlinx.io.bytestring.isEmpty
 import org.multipaz.securearea.AndroidKeystoreCreateKeySettings
-import org.multipaz.crypto.Algorithm
 import org.multipaz.securearea.SecureArea
-import kotlinx.io.bytestring.ByteString
+import org.multipaz.util.Logger
 
 /**
  * Generates statements validating device/app/OS integrity. Details of these
  * statements are inherently platform-specific.
  */
 actual object DeviceCheck {
+    private const val TAG = "DeviceCheck"
+
     actual suspend fun generateAttestation(
         secureArea: SecureArea,
-        challenge: ByteString
+        challenge: ByteString,
+        secret: String?
     ): DeviceAttestationResult {
+        if (challenge.isEmpty()) {
+            Logger.w(TAG, "Generating an attestation with an empty challenge is not secure")
+        }
         val keySettings = AndroidKeystoreCreateKeySettings.Builder(challenge)
             .build()
         val keyInfo = secureArea.createKey(null, keySettings)
         return DeviceAttestationResult(
             deviceAttestationId = keyInfo.alias,
-            deviceAttestation = DeviceAttestationAndroid(keyInfo.attestation.certChain!!)
+            deviceAttestation = DeviceAttestationAndroid(
+                certificateChain = keyInfo.attestation.certChain!!,
+            )
         )
     }
 

multipaz/src/commonMain/kotlin/org/multipaz/device/DeviceAttestation.kt

@@ -5,10 +5,14 @@ import kotlin.time.Clock
 import kotlin.time.Instant
 
 /**
- * A platform-issued statement vouching for the integrity of the wallet app.
+ * A platform-issued statement vouching for the integrity of an application.
  *
  * Validity checks are cross-platform, as we need to be able to run them on the server
  * (e.g. one does not have to be on iOS to validate [DeviceAttestationIos]).
+ *
+ * For platforms without dedicated support, [DeviceAttestationSoftware] exists
+ * which relies on the ability of the application to prove that it possesses
+ * a secret.
  */
 @CborSerializable
 sealed class DeviceAttestation {

multipaz/src/commonMain/kotlin/org/multipaz/device/DeviceAttestationAndroid.kt

@@ -4,18 +4,20 @@ import kotlinx.coroutines.CancellationException
 import org.multipaz.crypto.Algorithm
 import org.multipaz.crypto.Crypto
 import org.multipaz.crypto.EcSignature
+import org.multipaz.crypto.SignatureVerificationException
 import org.multipaz.crypto.X509CertChain
 import org.multipaz.util.validateAndroidKeyAttestation
-import org.multipaz.crypto.SignatureVerificationException
 import kotlin.time.Instant
 
 /**
  * On Android we create a private key in secure area and use its key attestation as the
  * device attestation.
+ *
+ * @property certificateChain the certificate chain.
  */
 data class DeviceAttestationAndroid(
     val certificateChain: X509CertChain
-) : DeviceAttestation() {
+): DeviceAttestation() {
     override suspend fun validate(
         validationData: DeviceAttestationValidationData,
         validateAt: Instant