dash ble tlk: start generating keys

omnipod-dash/src/main/java/info/nightscout/androidaps/plugins/pump/omnipod/dash/driver/comm/ltk/LTKExchanger.kt

@@ -1,21 +1,32 @@
 package info.nightscout.androidaps.plugins.pump.omnipod.dash.driver.comm.ltk
 
+import com.google.crypto.tink.mac.AesCmacKeyManager
+import com.google.crypto.tink.proto.AesCmac
 import com.google.crypto.tink.subtle.X25519
+
 import info.nightscout.androidaps.logging.AAPSLogger
 import info.nightscout.androidaps.logging.LTag
 import info.nightscout.androidaps.plugins.pump.omnipod.dash.driver.comm.Id
 import info.nightscout.androidaps.plugins.pump.omnipod.dash.driver.comm.OmnipodDashBleManagerImpl
+import info.nightscout.androidaps.plugins.pump.omnipod.dash.driver.comm.exceptions.MessageIOException
 import info.nightscout.androidaps.plugins.pump.omnipod.dash.driver.comm.message.MessageIO
 import info.nightscout.androidaps.plugins.pump.omnipod.dash.driver.comm.message.MessagePacket
 import info.nightscout.androidaps.plugins.pump.omnipod.dash.driver.comm.message.StringLengthPrefixEncoding
 import info.nightscout.androidaps.utils.extensions.hexStringToByteArray
 import info.nightscout.androidaps.utils.extensions.toHex
+import org.spongycastle.crypto.engines.AESEngine
 import java.security.SecureRandom
 
 internal class LTKExchanger(private val aapsLogger: AAPSLogger, private val msgIO: MessageIO) {
 
-    private val privateKey = X25519.generatePrivateKey()
+    private val pdmPrivate = X25519.generatePrivateKey()
-    private val nonce = ByteArray(16)
+    private val pdmPublic = X25519.publicFromPrivate(pdmPrivate)
+    private var podPublic = ByteArray(PUBLIC_KEY_SIZE)
+    private var podNonce = ByteArray(NONCE_SIZE)
+    private val pdmNonce = ByteArray(NONCE_SIZE)
+    private val confPdm = ByteArray(CONF_SIZE)
+    private val confPod = ByteArray(CONF_SIZE)
+
     private val controllerId = Id.fromInt(OmnipodDashBleManagerImpl.CONTROLLER_ID)
     val nodeId = controllerId.increment()
     private var seq: Byte = 1
@@ -24,7 +35,7 @@ internal class LTKExchanger(private val aapsLogger: AAPSLogger, private val msgI
 
     init {
         val random = SecureRandom()
-        random.nextBytes(nonce)
+        random.nextBytes(pdmNonce)
     }
 
     fun negotiateLTKAndNonce(): LTK? {
@@ -41,9 +52,9 @@ internal class LTKExchanger(private val aapsLogger: AAPSLogger, private val msgI
         val podSps1 = msgIO.receiveMessage()
         aapsLogger.info(LTag.PUMPBTCOMM, "Received message: %s", podSps1)
         processSps1FromPod(podSps1)
-
+        // now we have all the data to generate: confPod, confPdm, ltk and noncePrefix
+        generateKeys()
         seq++
-
         // send SPS2
         val sps2 = sps2()
         msgIO.sendMesssage(sps2.messagePacket)
@@ -52,6 +63,7 @@ internal class LTKExchanger(private val aapsLogger: AAPSLogger, private val msgI
         val podSps2 = msgIO.receiveMessage()
         validatePodSps2(podSps2)
 
+        seq++
         // send SP0GP0
         msgIO.sendMesssage(sp0gp0().messagePacket)
         // read P0
@@ -83,7 +95,7 @@ internal class LTKExchanger(private val aapsLogger: AAPSLogger, private val msgI
     }
 
     private fun sps1(): PairMessage {
-        val publicKey = X25519.publicFromPrivate(privateKey)
+        val publicKey = X25519.publicFromPrivate(pdmPrivate)
         val payload = StringLengthPrefixEncoding.formatKeys(
             arrayOf("SPS1="),
             arrayOf(publicKey + nonce),
@@ -98,7 +110,11 @@ internal class LTKExchanger(private val aapsLogger: AAPSLogger, private val msgI
 
     private fun processSps1FromPod(msg: MessagePacket) {
         aapsLogger.debug(LTag.PUMPBTCOMM, "Received SPS1 from pod: ${msg.payload.toHex()}")
-
+        if (msg.payload.size != 48) {
+            throw MessageIOException()
+        }
+        podPublic = msg.payload.copyOfRange(0, PUBLIC_KEY_SIZE)
+        podNonce = msg.payload.copyOfRange(PUBLIC_KEY_SIZE, PUBLIC_KEY_SIZE+ NONCE_SIZE)
     }
 
     private fun sps2(): PairMessage {
@@ -124,8 +140,23 @@ internal class LTKExchanger(private val aapsLogger: AAPSLogger, private val msgI
         TODO("implement")
 
     }
-    companion object {
 
+    fun generateKeys() {
+        val curveLTK = X25519.computeSharedSecret(pdmPrivate, podPublic)
+        aapsLogger.debug(LTag.PUMPBTCOMM, "LTK, donna key: ${curveLTK.toHex()}")
+        //first_key = data.pod_public[-4:] + data.pdm_public[-4:] + data.pod_nonce[-4:] + data.pdm_nonce[-4:]
+
+        val firstKey = podPublic.copyOfRange(podPublic.size-4, podPublic.size)
+            + pdmPublic.copyOfRange(pdmPublic.size-4, pdmPublic.size)
+            + podNonce.copyOfRange(podNonce.size-4, podNonce.size)
+            + pdmNonce.copyOfRange(pdmNonce.size-4, pdmNonce.size)
+        aapsLogger.debug(LTag.PUMPBTCOMM, "LTK, first key: ${firstKey.toHex()}")
+    }
+
+    companion object {
+        private val PUBLIC_KEY_SIZE = 32
+        private val NONCE_SIZE = 16
+        private val CONF_SIZE = 16
         private val GET_POD_STATUS_HEX_COMMAND = "ffc32dbd08030e0100008a" // TODO for now we are assuming this command is build out of constant parameters, use a proper command builder for that.
     }
 }