From a7f93de3ad62914d74bc172290934d60aa01dbe1 Mon Sep 17 00:00:00 2001
From: Kevin Hester <kevinh@geeksville.com>
Date: Sat, 2 Jan 2021 18:20:51 +0800
Subject: [PATCH] add a software based cross platform AES-CTR implementation

---
 platformio.ini                              |  3 +
 src/portduino/CrossPlatformCryptoEngine.cpp | 82 +++++++++++++++++++++
 src/portduino/PortduinoGlue.cpp             |  3 -
 3 files changed, 85 insertions(+), 3 deletions(-)
 create mode 100644 src/portduino/CrossPlatformCryptoEngine.cpp

diff --git a/platformio.ini b/platformio.ini
index aa8e3eb8..977d2cd5 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -314,6 +314,9 @@ src_filter = ${env.src_filter} -<esp32/> -<nimble/> -<nrf52/> -<meshwifi/>
 build_flags = ${arduino_base.build_flags} -O0
 framework = arduino
 board = linux_x86_64
+lib_deps =
+  ${arduino_base.lib_deps}
+  rweather/Crypto
 
 ; The GenieBlocks LORA prototype board
 [env:genieblocks_lora]
diff --git a/src/portduino/CrossPlatformCryptoEngine.cpp b/src/portduino/CrossPlatformCryptoEngine.cpp
new file mode 100644
index 00000000..b9e818c0
--- /dev/null
+++ b/src/portduino/CrossPlatformCryptoEngine.cpp
@@ -0,0 +1,82 @@
+#include "AES.h"
+#include "CTR.h"
+#include "CryptoEngine.h"
+#include "configuration.h"
+
+/** A platform independent AES engine implemented using Tiny-AES
+ */
+class CrossPlatformCryptoEngine : public CryptoEngine
+{
+
+    CTRCommon *ctr = NULL;
+
+    /// How many bytes in our key
+    uint8_t keySize = 0;
+
+  public:
+    CrossPlatformCryptoEngine() {}
+
+    ~CrossPlatformCryptoEngine() {}
+
+    /**
+     * Set the key used for encrypt, decrypt.
+     *
+     * As a special case: If all bytes are zero, we assume _no encryption_ and send all data in cleartext.
+     *
+     * @param numBytes must be 16 (AES128), 32 (AES256) or 0 (no crypt)
+     * @param bytes a _static_ buffer that will remain valid for the life of this crypto instance (i.e. this class will cache the
+     * provided pointer)
+     */
+    virtual void setKey(size_t numBytes, uint8_t *bytes)
+    {
+        keySize = numBytes;
+        DEBUG_MSG("Installing AES%d key!\n", numBytes * 8);
+        if (ctr) {
+            delete ctr;
+            ctr = NULL;
+        }
+        if (numBytes != 0) {
+            if (numBytes == 16)
+                ctr = new CTR<AES128>();
+            else
+                ctr = new CTR<AES256>();
+
+            ctr->setKey(bytes, numBytes);
+        }
+    }
+
+    /**
+     * Encrypt a packet
+     *
+     * @param bytes is updated in place
+     */
+    virtual void encrypt(uint32_t fromNode, uint64_t packetNum, size_t numBytes, uint8_t *bytes)
+    {
+        if (keySize != 0) {
+            uint8_t stream_block[16];
+            static uint8_t scratch[MAX_BLOCKSIZE];
+            size_t nc_off = 0;
+
+            // DEBUG_MSG("ESP32 encrypt!\n");
+            initNonce(fromNode, packetNum);
+            assert(numBytes <= MAX_BLOCKSIZE);
+            memcpy(scratch, bytes, numBytes);
+            memset(scratch + numBytes, 0,
+                   sizeof(scratch) - numBytes); // Fill rest of buffer with zero (in case cypher looks at it)
+
+            ctr->setIV(nonce, sizeof(nonce));
+            ctr->setCounterSize(4);
+            ctr->encrypt(bytes, scratch, numBytes);
+        }
+    }
+
+    virtual void decrypt(uint32_t fromNode, uint64_t packetNum, size_t numBytes, uint8_t *bytes)
+    {
+        // For CTR, the implementation is the same
+        encrypt(fromNode, packetNum, numBytes, bytes);
+    }
+
+  private:
+};
+
+CryptoEngine *crypto = new CrossPlatformCryptoEngine();
diff --git a/src/portduino/PortduinoGlue.cpp b/src/portduino/PortduinoGlue.cpp
index 6af00666..2d5f0a36 100644
--- a/src/portduino/PortduinoGlue.cpp
+++ b/src/portduino/PortduinoGlue.cpp
@@ -35,9 +35,6 @@ void cpuDeepSleep(uint64_t msecs) {
     notImplemented("cpuDeepSleep");
 }
 
-// FIXME - implement real crypto for linux
-CryptoEngine *crypto = new CryptoEngine();
-
 void updateBatteryLevel(uint8_t level) NOT_IMPLEMENTED("updateBatteryLevel");
 
 /** Dear pinetab hardware geeks!