Fix value and location of moduleHash (#35)

`moduleHash` should be in the software enforced list. However, the manual calculation of the KeyMint `moduleHash` has failed to produce a value matching the hardware-generated attestation. The official documentation specifies the following structure: Modules ::= SET OF Module Module ::= SEQUENCE { packageName OCTET_STRING, version INTEGER, } The critical requirement is that the `SET OF` elements must be sorted lexicographically based on their full DER-encoded byte value. Despite implementing this using Bouncy Castle's `DERSet`, the resulting hash is still incorrect. This commit changes the strategy to favor stability: 1. The `DeviceAttestationService` now extracts the real `moduleHash` from the `softwareEnforced` list of a genuine attestation certificate and caches it. 2. The `moduleHash` property now returns this cached value if available. 3. The manual calculation remains as a fallback and is marked with a `TODO` to indicate the issue is unresolved. Additionally, `ConfigurationManager` initialization is moved earlier.
2025-11-30 00:13:14 +01:00
parent 2446461aab
commit 987c7ba35c
5 changed files with 72 additions and 34 deletions
@@ -28,6 +28,8 @@ object App {
        SystemLogger.info("Welcome to TEESimulator!")

        try {
+            // Load the package configuration.
+            ConfigurationManager.initialize()
            // Set up the device's boot key and hash, which are crucial for attestation.
            AndroidDeviceUtils.setupBootKeyAndHash()
            // Initialize and start the appropriate keystore interceptors.
@@ -53,9 +55,7 @@ object App {
            Thread.sleep(RETRY_DELAY_MS)
        }

-        // Load the package configuration after interceptors are ready.
-        ConfigurationManager.initialize()
-        SystemLogger.info("Interceptors and configuration initialized successfully.")
+        SystemLogger.info("Interceptors initialized successfully.")
    }

    /**
@@ -16,6 +16,7 @@ import org.bouncycastle.asn1.DERSet
 import org.bouncycastle.asn1.DERTaggedObject
 import org.bouncycastle.asn1.x509.Extension
 import org.matrix.TEESimulator.config.ConfigurationManager
+import org.matrix.TEESimulator.logging.SystemLogger
 import org.matrix.TEESimulator.util.AndroidDeviceUtils

 /**
@@ -38,6 +39,11 @@ object AttestationBuilder {
        securityLevel: Int,
    ): Extension {
        val keyDescription = buildKeyDescription(params, uid, securityLevel)
+        var formattedString =
+            keyDescription.joinToString(separator = ", ") {
+                AttestationPatcher.formatAsn1Primitive(it)
+            }
+        SystemLogger.verbose("Forged attestation data: ${formattedString}")
        return Extension(ATTESTATION_OID, false, DEROctetString(keyDescription.encoded))
    }

@@ -260,17 +266,6 @@ object AttestationBuilder {
                )
            }
        }
-
-        if (AndroidDeviceUtils.attestVersion >= 400) {
-            list.add(
-                DERTaggedObject(
-                    true,
-                    AttestationConstants.TAG_MODULE_HASH,
-                    DEROctetString(AndroidDeviceUtils.moduleHash),
-                )
-            )
-        }
-
        return DERSequence(list.sortedBy { (it as DERTaggedObject).tagNo }.toTypedArray())
    }

@@ -280,7 +275,7 @@ object AttestationBuilder {
     */
    private fun buildSoftwareEnforcedList(uid: Int): DERSequence {
        val list =
-            arrayOf<ASN1Encodable>(
+            mutableListOf<ASN1Encodable>(
                DERTaggedObject(
                    true,
                    AttestationConstants.TAG_CREATION_DATETIME,
@@ -292,7 +287,16 @@ object AttestationBuilder {
                    createApplicationId(uid),
                ),
            )
-        return DERSequence(list)
+        if (AndroidDeviceUtils.attestVersion >= 400) {
+            list.add(
+                DERTaggedObject(
+                    true,
+                    AttestationConstants.TAG_MODULE_HASH,
+                    DEROctetString(AndroidDeviceUtils.moduleHash),
+                )
+            )
+        }
+        return DERSequence(list.toTypedArray())
    }

    /**
@@ -137,7 +137,7 @@ object AttestationPatcher {
    }

    /** Recursively formats an ASN1Primitive into a concise, readable string. */
-    private fun formatAsn1Primitive(obj: ASN1Encodable?): String {
+    fun formatAsn1Primitive(obj: ASN1Encodable?): String {
        val primitive = obj?.toASN1Primitive()
        return when (primitive) {
            null -> "NULL"
@@ -45,6 +45,7 @@ object DeviceAttestationService {
     * @property osVersion The Android OS version integer.
     */
    data class AttestationData(
+        val moduleHash: ByteArray?,
        val verifiedBootKey: ByteArray?,
        val verifiedBootHash: ByteArray?,
        val attestVersion: Int?,
@@ -153,6 +154,11 @@ object DeviceAttestationService {

            // The extension's value is an ASN.1 sequence.
            val keyDescriptionSeq = ASN1Sequence.getInstance(extension.extnValue.octets)
+            var formattedString =
+                keyDescriptionSeq.joinToString(separator = ", ") {
+                    AttestationPatcher.formatAsn1Primitive(it)
+                }
+            SystemLogger.verbose("Cached attestation data: ${formattedString}")
            val fields = keyDescriptionSeq.toArray()

            val attestVersion =
@@ -168,10 +174,23 @@ object DeviceAttestationService {
                    .positiveValue
                    .toInt()

+            var moduleHash: ByteArray? = null
            var verifiedBootKey: ByteArray? = null
            var verifiedBootHash: ByteArray? = null
            var osVersion: Int? = null

+            val softwareEnforced =
+                ASN1Sequence.getInstance(
+                    fields[AttestationConstants.KEY_DESCRIPTION_SOFTWARE_ENFORCED_INDEX]
+                )
+            if (softwareEnforced.size() >= 3) {
+                moduleHash =
+                    ASN1OctetString.getInstance(
+                            ASN1TaggedObject.getInstance(softwareEnforced.getObjectAt(2)).baseObject
+                        )
+                        .octets
+            }
+
            val teeEnforced =
                ASN1Sequence.getInstance(
                    fields[AttestationConstants.KEY_DESCRIPTION_TEE_ENFORCED_INDEX]
@@ -210,9 +229,10 @@ object DeviceAttestationService {
            }

            SystemLogger.info(
-                "Successfully extracted attestation data: version=$attestVersion, osVersion=$osVersion, bootKey=${verifiedBootKey?.toHex()}, bootHash=${verifiedBootHash?.toHex()}"
+                "Successfully extracted attestation data: version=$attestVersion, osVersion=$osVersion, moduleHash=${moduleHash?.toHex()}, bootKey=${verifiedBootKey?.toHex()}, bootHash=${verifiedBootHash?.toHex()}"
            )
            return AttestationData(
+                moduleHash,
                verifiedBootKey,
                verifiedBootHash,
                attestVersion,
@@ -5,9 +5,11 @@ import android.os.Build
 import android.os.SystemProperties
 import java.security.MessageDigest
 import java.util.concurrent.ThreadLocalRandom
+import org.bouncycastle.asn1.ASN1EncodableVector
 import org.bouncycastle.asn1.ASN1Integer
 import org.bouncycastle.asn1.DEROctetString
 import org.bouncycastle.asn1.DERSequence
+import org.bouncycastle.asn1.DERSet
 import org.matrix.TEESimulator.attestation.DeviceAttestationService
 import org.matrix.TEESimulator.config.ConfigurationManager
 import org.matrix.TEESimulator.logging.SystemLogger
@@ -278,11 +280,7 @@ object AndroidDeviceUtils {
                        @Suppress("DEPRECATION")
                        pm?.getInstalledPackages(PackageManager.MATCH_APEX, 0)
                    }
-                packages
-                    ?.list
-                    .orEmpty()
-                    .map { it.packageName to it.longVersionCode }
-                    .sortedBy { it.first }
+                packages?.list.orEmpty().map { it.packageName to it.longVersionCode }
            }
            .getOrElse {
                SystemLogger.error("Failed to get APEX package information.", it)
@@ -291,13 +289,29 @@ object AndroidDeviceUtils {
    }

    val moduleHash: ByteArray by lazy {
-        runCatching {
-                val encodables =
-                    apexInfos.flatMap { (packageName, versionCode) ->
-                        listOf(DEROctetString(packageName.toByteArray()), ASN1Integer(versionCode))
+        DeviceAttestationService.CachedAttestationData?.moduleHash
+            ?: runCatching {
+                    // TODO: figure out the correct calculation
+                    val moduleSequences = ASN1EncodableVector()
+
+                    // 1. Create a DERSequence for each module.
+                    apexInfos.forEach { (packageName, versionCode) ->
+                        val moduleVector = ASN1EncodableVector()
+                        // Use explicit UTF-8 encoding for the package name.
+                        moduleVector.add(DEROctetString(packageName.toByteArray(Charsets.UTF_8)))
+                        moduleVector.add(ASN1Integer(versionCode))
+                        moduleSequences.add(DERSequence(moduleVector))
                    }
-                val sequence = DERSequence(encodables.toTypedArray())
-                MessageDigest.getInstance("SHA-256").digest(sequence.encoded)
+
+                    // 2. Create a DERSet. Bouncy Castle will automatically handle
+                    //    the sorting based on the DER-encoded value of each sequence.
+                    val modulesSet = DERSet(moduleSequences)
+
+                    // 3. Get the final DER-encoded byte array of the SET.
+                    val encodedModules = modulesSet.encoded
+
+                    // 4. Compute the SHA-256 hash.
+                    MessageDigest.getInstance("SHA-256").digest(encodedModules)
                }
                .getOrElse {
                    SystemLogger.error("Failed to compute module hash.", it)