dash encryption: add encryption and decryption for messsages

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

@@ -0,0 +1,63 @@
+package info.nightscout.androidaps.plugins.pump.omnipod.dash.driver.comm.endecrypt
+
+import info.nightscout.androidaps.logging.AAPSLogger
+import info.nightscout.androidaps.logging.LTag
+import info.nightscout.androidaps.plugins.pump.omnipod.dash.driver.comm.message.MessagePacket
+import info.nightscout.androidaps.utils.extensions.toHex
+import org.spongycastle.crypto.engines.AESEngine
+import org.spongycastle.crypto.modes.CCMBlockCipher
+import org.spongycastle.crypto.params.AEADParameters
+import org.spongycastle.crypto.params.KeyParameter
+
+class EnDecrypt(private val aapsLogger: AAPSLogger, private val nonce: Nonce, private val ck: ByteArray) {
+
+    val engine = AESEngine()
+    val cipher = CCMBlockCipher(engine)
+
+    fun decrypt(msg: MessagePacket): MessagePacket {
+        val payload = msg.payload
+        val header = msg.asByteArray().copyOfRange(0, 16)
+
+        val n = nonce.increment()
+        aapsLogger.debug(LTag.PUMPBTCOMM, "Decrypt header ${header.toHex()} payload: ${payload.toHex()}")
+        aapsLogger.debug(LTag.PUMPBTCOMM, "Decrypt NONCE ${n.toHex()}")
+        cipher.init(
+            false, AEADParameters(
+            KeyParameter(ck),
+            MAC_SIZE * 8, // in bits
+            n,
+            header
+        )
+        )
+        val decryptedPayload = ByteArray(payload.size - MAC_SIZE)
+        cipher.processPacket(payload, 0, payload.size, decryptedPayload, 0)
+        return msg.copy(payload = decryptedPayload)
+    }
+
+    fun encrypt(headerMessage: MessagePacket): MessagePacket {
+        val payload = headerMessage.payload
+        val header = headerMessage.asByteArray(true).copyOfRange(0, 16)
+
+        val n = nonce.increment()
+        aapsLogger.debug(LTag.PUMPBTCOMM, "Encrypt header ${header.toHex()} payload: ${payload.toHex()}")
+        aapsLogger.debug(LTag.PUMPBTCOMM, "Encrypt NONCE ${n.toHex()}")
+        val encryptedPayload = ByteArray(payload.size + MAC_SIZE)
+
+        cipher.init(
+            true, AEADParameters(
+            KeyParameter(ck),
+            MAC_SIZE * 8, // in bits
+            n,
+            header
+        )
+        )
+        cipher.processPacket(payload, 0, payload.size, encryptedPayload, 0)
+
+        return headerMessage.copy(payload = encryptedPayload)
+    }
+
+    companion object {
+
+        private val MAC_SIZE = 8
+    }
+}

omnipod-dash/src/test/java/info/nightscout/androidaps/plugins/pump/omnipod/dash/driver/comm/endecrypt/EnDecryptTest.kt

@@ -0,0 +1,59 @@
+package info.nightscout.androidaps.plugins.pump.omnipod.dash.driver.comm.endecrypt
+
+import info.nightscout.androidaps.logging.AAPSLoggerTest
+import info.nightscout.androidaps.plugins.pump.omnipod.dash.driver.comm.message.MessagePacket
+import info.nightscout.androidaps.utils.extensions.toHex
+import org.junit.Assert
+import org.junit.Test
+import org.spongycastle.util.encoders.Hex
+
+class EnDecryptTest {
+
+    @Test
+    fun decrypt() {
+        val aapsLogger = AAPSLoggerTest()
+        val enDecrypt = EnDecrypt(
+            aapsLogger,
+            Nonce(
+                Hex.decode("dda23c090a0a0a0a"),
+                Hex.decode("0000000001")
+            ),
+            Hex.decode("ba1283744b6de9fab6d9b77d95a71d6e"),
+        )
+        val encryptedMessage = Hex.decode(
+            "54571101070003400242000002420001" +
+                "e09158bcb0285a81bf30635f3a17ee73f0afbb3286bc524a8a66" +
+                "fb1bc5b001e56543"
+        )
+        val decrypted = Hex.decode("53302e303d000effffffff00060704ffffffff82b22c47302e30")
+        val msg = MessagePacket.parse(encryptedMessage)
+        val decryptedMsg = enDecrypt.decrypt(msg)
+
+        Assert.assertEquals(decrypted.toHex(), decryptedMsg.payload.toHex())
+    }
+
+    @Test
+    fun encrypt() {
+        val aapsLogger = AAPSLoggerTest()
+        val enDecrypt = EnDecrypt(
+            aapsLogger,
+            Nonce(
+                Hex.decode("dda23c090a0a0a0a"),
+                Hex.decode("0000000001")
+            ),
+            Hex.decode("ba1283744b6de9fab6d9b77d95a71d6e"),
+        )
+        val encryptedMessage = Hex.decode(
+            "54571101070003400242000002420001" +
+                "e09158bcb0285a81bf30635f3a17ee73f0afbb3286bc524a8a66" +
+                "fb1bc5b001e56543"
+        )
+        val command = Hex.decode("53302e303d000effffffff00060704ffffffff82b22c47302e30")
+        val msg = MessagePacket.parse(encryptedMessage).copy(payload = command) // copy for the headers
+
+        val encrypted = enDecrypt.encrypt(msg)
+
+        Assert.assertEquals(encryptedMessage.toHex(), encrypted.asByteArray().toHex())
+
+    }
+}