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Code Issues Projects Releases Wiki Activity

Verifiy signature of received keyfiles

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Christian Grigis 2021-02-09 15:49:21 +01:00 committed by Marvin W
parent 925ce2ddd9
commit 3885ed6ef8
1 changed files with 87 additions and 0 deletions
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87
play-services-nearby-core/src/main/kotlin/org/microg/gms/nearby/exposurenotification/ExposureNotificationServiceImpl.kt
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@ -11,6 +11,7 @@ import android.bluetooth.BluetoothAdapter
import android.content.*
import android.location.LocationManager
import android.os.*
import android.util.Base64
import android.util.Log
import androidx.core.location.LocationManagerCompat
import androidx.lifecycle.Lifecycle
@ -26,12 +27,17 @@ import org.json.JSONArray
import org.json.JSONObject
import org.microg.gms.common.PackageUtils
import org.microg.gms.nearby.exposurenotification.Constants.*
import org.microg.gms.nearby.exposurenotification.proto.TEKSignatureList
import org.microg.gms.nearby.exposurenotification.proto.TemporaryExposureKeyExport
import org.microg.gms.nearby.exposurenotification.proto.TemporaryExposureKeyProto
import org.microg.gms.utils.warnOnTransactionIssues
import java.io.File
import java.io.InputStream
import java.security.KeyFactory
import java.security.MessageDigest
import java.security.Signature
import java.security.spec.X509EncodedKeySpec
import java.util.zip.ZipEntry
import java.util.zip.ZipFile
import kotlin.math.max
import kotlin.math.roundToInt
@ -39,6 +45,25 @@ import kotlin.random.Random
class ExposureNotificationServiceImpl(private val context: Context, private val lifecycle: Lifecycle, private val packageName: String) : INearbyExposureNotificationService.Stub(), LifecycleOwner {
// Table of back-end public keys, used to verify the signature of the diagnosed TEKs.
// The table is indexed by package names.
private val backendPubKeyForPackage = mapOf<String, String>(
Pair("ch.admin.bag.dp3t.dev",
"MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEsFcEnOPY4AOAKkpv9HSdW2BrhUCWwL15Hpqu5zHaWy1Wno2KR8G6dYJ8QO0uZu1M6j8z6NGXFVZcpw7tYeXAqQ=="),
Pair("ch.admin.bag.dp3t.test",
"MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEsFcEnOPY4AOAKkpv9HSdW2BrhUCWwL15Hpqu5zHaWy1Wno2KR8G6dYJ8QO0uZu1M6j8z6NGXFVZcpw7tYeXAqQ=="),
Pair("ch.admin.bag.dp3t.abnahme",
"MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEsFcEnOPY4AOAKkpv9HSdW2BrhUCWwL15Hpqu5zHaWy1Wno2KR8G6dYJ8QO0uZu1M6j8z6NGXFVZcpw7tYeXAqQ=="),
Pair("ch.admin.bag.dp3t",
"MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEK2k9nZ8guo7JP2ELPQXnUkqDyjjJmYmpt9Zy0HPsiGXCdI3SFmLr204KNzkuITppNV5P7+bXRxiiY04NMrEITg=="),
)
// Table of supported signature algorithms for the diagnosed TEKs.
// The table is indexed by ASN.1 OIDs as specified in https://tools.ietf.org/html/rfc5758#section-3.2
private val sigAlgoForOid = mapOf<String, Signature>(
Pair("1.2.840.10045.4.3.2", Signature.getInstance("SHA256withECDSA")),
Pair("1.2.840.10045.4.3.4", Signature.getInstance("SHA512withECDSA")),
)
private fun LifecycleCoroutineScope.launchSafely(block: suspend CoroutineScope.() -> Unit): Job = launchWhenStarted { try { block() } catch (e: Exception) { Log.w(TAG, "Error in coroutine", e) } }
override fun getLifecycle(): Lifecycle = lifecycle
@ -333,6 +358,10 @@ class ExposureNotificationServiceImpl(private val context: Context, private val
var newKeys = if (params.keys != null) database.finishSingleMatching(tid) else 0
for ((cacheFile, hash) in todoKeyFiles) {
withContext(Dispatchers.IO) {
if (!verifyKeyFile(cacheFile)) {
// FIXME: do something, perhaps reject according to some user setting
Log.w(TAG, "Using non-verified key file")
}
try {
ZipFile(cacheFile).use { zip ->
for (entry in zip.entries()) {
@ -404,6 +433,64 @@ class ExposureNotificationServiceImpl(private val context: Context, private val
}
}
private fun verifyKeyFile(file: File): Boolean {
try {
val publicKeyData = backendPubKeyForPackage.get(packageName) ?: throw Exception("Public key for ${packageName} is not available")
val publicKeyBytes: ByteArray = Base64.decode(publicKeyData, Base64.DEFAULT)
val publicKey = KeyFactory.getInstance("EC").generatePublic(X509EncodedKeySpec(publicKeyBytes))
ZipFile(file).use { zip ->
var dataEntry: ZipEntry? = null
var sigEntry: ZipEntry? = null
for (entry in zip.entries()) {
when (entry.name) {
"export.bin" -> dataEntry = entry
"export.sig" -> sigEntry = entry
else -> throw Exception("Unexpected entry in zip archive: ${entry.name}")
}
}
when {
dataEntry == null -> throw Exception("Zip archive does not contain 'export.bin'")
sigEntry == null -> throw Exception("Zip archive does not contain 'export.sin'")
}
val sigStream = zip.getInputStream(sigEntry)
val sigList = TEKSignatureList.ADAPTER.decode(sigStream)
for (sig in sigList.signatures) {
Log.d(TAG, "Verifying signature ${sig.batch_num}/${sig.batch_size}")
val sigInfo = sig.signature_info ?: throw Exception("Signature information is missing")
Log.d(TAG, "Signature info: algo=${sigInfo.signature_algorithm} key={id=${sigInfo.verification_key_id}, version=${sigInfo.verification_key_version}}")
val signature = sig.signature?.toByteArray() ?: throw Exception("Signature contents is missing")
val sigVerifier = sigAlgoForOid.get(sigInfo.signature_algorithm) ?: throw Exception("Signature algorithm not supported: ${sigInfo.signature_algorithm}")
sigVerifier.initVerify(publicKey)
val stream = zip.getInputStream(dataEntry)
val buf = ByteArray(1024)
var nbRead = 0
while (nbRead != -1) {
nbRead = stream.read(buf)
if (nbRead > 0) {
sigVerifier.update(buf, 0, nbRead)
}
}
if (!sigVerifier.verify(signature)) {
throw Exception("Signature does not verify")
}
}
}
} catch (e: Exception) {
Log.w(TAG, "Key file verification failed: " + e.message)
return false
}
Log.i(TAG, "Key file verification successful")
return true
}
override fun getExposureSummary(params: GetExposureSummaryParams) {
lifecycleScope.launchSafely {
val response = buildExposureSummary(params.token)