Renew challenge on expiry

include/controller.h

@@ -3,25 +3,34 @@
 #include "server.h"
 #include "servo.h"
 #include "message.h"
-#include "storage.h"
-#include "fresh.h"
 #include <ESPAsyncWebServer.h>
 
-struct WifiConfiguration {
+struct EthernetConfiguration {
 
-    // The WiFi network to connect to
+    // The MAC address of the ethernet connection
-    const char* ssid;
+    uint8_t macAddress[6];
 
-    // The WiFi password to connect to the above network
+    // The master-in slave-out pin of the SPI connection for the Ethernet module
-    const char* password;
+    int8_t spiPinMiso;
 
-    // The name of the device on the network
+    // The master-out slave-in pin of the SPI connection for the Ethernet module
-    const char* networkName;
+    int8_t spiPinMosi;
 
-    // The interval to reconnect to WiFi if the connection is broken
+    // The slave clock pin of the SPI connection for the Ethernet module
-    uint32_t reconnectInterval;
+    int8_t spiPinSclk;
+
+    // The slave-select pin of the SPI connection for the Ethernet module
+    int8_t spiPinSS;
+
+    unsigned long dhcpLeaseTimeoutMs;
+    unsigned long dhcpLeaseResponseTimeoutMs;
+
+    // The static IP address to assign if DHCP fails
+    uint8_t manualIp[4];
+
+    // The IP address of the DNS server, if DHCP fails
+    uint8_t manualDnsAddress[4];
 
-    uint32_t periodicReconnectInterval;
 };
 
 struct KeyConfiguration {
@@ -29,55 +38,133 @@ struct KeyConfiguration {
     const uint8_t* remoteKey;
 
     const uint8_t* localKey;
+
+    uint32_t challengeExpiryMs;
 };
 
 class SesameController: public ServerConnectionCallbacks {
 
 public:
-    SesameController(uint16_t localWebServerPort, uint8_t remoteDeviceCount);
+    SesameController(uint16_t localWebServerPort);
 
-    void configure(ServoConfiguration servoConfig, ServerConfiguration serverConfig, TimeConfiguration timeConfig, WifiConfiguration wifiConfig, KeyConfiguration keyConfig);
+    void configure(ServoConfiguration servoConfig, ServerConfiguration serverConfig, EthernetConfiguration ethernetConfig, KeyConfiguration keyConfig);
 
     void loop(uint32_t millis);
 
 private:
 
+    uint32_t currentTime = 0;
+
     ServerConnection server;
     ServoController servo;
     AsyncWebServer localWebServer;
-    TimeCheck timeCheck;
-    Storage storage;
 
-    WifiConfiguration wifiConfig;
+    EthernetConfiguration ethernetConfig;
+    bool ethernetIsConfigured = false;
+
     KeyConfiguration keyConfig;
 
     bool isReconnecting = false;
 
-    // The buffer to hold a received message while it is read
+    // Buffer to get local message
-    uint8_t receivedMessageBuffer[AUTHENTICATED_MESSAGE_SIZE];
+    SignedMessage receivedLocalMessage;
 
-    // The buffer to hold a response while it is sent
+    uint32_t currentClientChallenge;
-    uint8_t responseBuffer[AUTHENTICATED_MESSAGE_SIZE+1];
+    uint32_t currentChallengeExpiry = 0;
-    SesameEvent* responseStatus;
+    uint32_t currentServerChallenge;
-    AuthenticatedMessage* responseMessage;
-    uint16_t responseSize = 0;
 
-    void ensureWiFiConnection(uint32_t time);
+    SignedMessage outgoingMessage;
-    void ensureWebSocketConnection();
+    
+    bool hasCurrentChallenge() {
+        return currentChallengeExpiry > currentTime;
+    }
+
+    void clearCurrentChallenge() {
+        currentClientChallenge = 0;
+        currentServerChallenge = 0;
+        currentChallengeExpiry = 0;
+    }
+
+    // MARK: Local client callbacks
 
     void handleLocalMessage(AsyncWebServerRequest *request);
-    // Based on https://stackoverflow.com/a/23898449/266720
+    
-    bool convertHexMessageToBinary(const char* str);
+    // MARK: Socket Callbacks
+
+    /**
+     * @brief Callback to send an error back to the server via the web socket.
+     * 
+     * This function is called when the socket get's an error.
+     * 
+     * @param event The error to report back
+     */
+    void sendServerError(MessageResult event);
 
     void handleServerMessage(uint8_t* payload, size_t length);
-    void sendServerError(SesameEvent event);
 
-    void processMessage(AuthenticatedMessage* message);
+    // MARK: Message processing
-    SesameEvent verifyAndProcessReceivedMessage(AuthenticatedMessage* message);
 
-    void prepareResponseBuffer(SesameEvent event, uint8_t deviceId = 0);
+    /**
+     * @brief Process a received message (local or socket).
+     * 
+     * @param message The message to process.
+     * 
+     * Note: Prepares the response in the outgoing message buffer.
+     */
+    void processMessage(SignedMessage* message);
+
+    /**
+     * @brief Checks that the message is valid and prepares a challenge.
+     * 
+     * This function is also called when a challenge response arrives too late.
+     * 
+     * @param message The message to respond to
+     * 
+     * Note: Prepares the response in the outgoing message buffer.
+     */
+    void checkAndPrepareChallenge(Message* message);
+
+    /**
+     * @brief Prepare a server challenge for a local or socket message.
+     * 
+     * @param message The message to respond to
+     * 
+     * Note: Prepares the response in the outgoing message buffer.
+     */
+    void prepareChallenge(Message* message);
+
+    /**
+     * @brief Complete an unlock request for a local or socket message.
+     * 
+     * @param message The message to respond to
+     * 
+     * Note: Prepares the response in the outgoing message buffer.
+     */
+    void completeUnlockRequest(Message* message);
+
+    // MARK: Responses
+
+    /**
+     * @brief Prepare the outgoing message buffer for both socket and local responses.
+     * 
+     * @param event The resulting state to transmit
+     * @param message An optional message to echo
+     */
+    void prepareResponseBuffer(MessageResult event, Message* message = NULL);
+
+    /**
+     * @brief Send the prepared outgoing message to a locally connected client
+     * 
+     * @param request The original request of the client
+     */
     void sendPreparedLocalResponse(AsyncWebServerRequest *request);
-    void sendPreparedServerResponse();
 
-    void periodicallyReconnectWifiAndSocket(uint32_t millis);
+    /**
+     * @brief Send the prepared outgoing message to the server
+     */
+    void sendPreparedResponseToServer();
+
+    // MARK: Helper
+
+     bool convertHexMessageToBinary(const char* str);
 };

include/crypto.h

@@ -3,6 +3,15 @@
 #include "message.h"
 #include <stddef.h>
 
+void enableCrypto();
+
+/**
+ * @brief Create a random server challenge.
+ * 
+ * @return uint32_t 
+ */
+uint32_t randomChallenge();
+
 /**
  * @brief Create a message authentication code (MAC) for some data.
  * 
@@ -10,11 +19,10 @@
  * @param dataLength The number of bytes to authenticate
  * @param mac The output to store the MAC (must be at least 32 bytes)
  * @param key The secret key used for authentication
- * @param keyLength The length of the secret key
  * @return true The MAC was successfully written
  * @return false The MAC could not be created
  */
-bool authenticateData(const uint8_t* data, size_t dataLength, uint8_t* mac, const uint8_t* key, size_t keyLength);
+bool authenticateData(const uint8_t* data, size_t dataLength, uint8_t* mac, const uint8_t* key);
 
 /**
  * @brief Calculate a MAC for message content.
@@ -22,22 +30,20 @@ bool authenticateData(const uint8_t* data, size_t dataLength, uint8_t* mac, cons
  * @param message The message for which to calculate the MAC.
  * @param mac The output where the computed MAC is stored
  * @param key The secret key used for authentication
- * @param keyLength The length of the secret key
  * @return true The MAC was successfully computed
  * @return false The MAC could not be created
  */
-bool authenticateMessage(Message* message, uint8_t* mac, const uint8_t* key, size_t keyLength);
+bool authenticateMessage(Message* message, uint8_t* mac, const uint8_t* key);
 
 /**
  * @brief Create a message authentication code (MAC) for a message.
  * 
  * @param message The message to authenticate
  * @param key The secret key used for authentication
- * @param keyLength The length of the secret key
  * @return true The MAC was successfully added to the message
  * @return false The MAC could not be created
  */
-bool authenticateMessage(AuthenticatedMessage* message, const uint8_t* key, size_t keyLength);
+bool authenticateMessage(SignedMessage* message, const uint8_t* key);
 
 /**
  * @brief Check if a received unlock message is authentic
@@ -48,8 +54,7 @@ bool authenticateMessage(AuthenticatedMessage* message, const uint8_t* key, size
  * 
  * @param message The message to authenticate
  * @param key The secret key used for authentication
- * @param keyLength The length of the key in bytes
  * @return true The message is authentic
  * @return false The message is invalid, or the MAC could not be calculated
  */
-bool isAuthenticMessage(AuthenticatedMessage* message, const uint8_t* key, size_t keyLength);
+bool isAuthenticMessage(SignedMessage* message, const uint8_t* key);

include/fresh.h

@@ -1,80 +0,0 @@
-#pragma once
-
-#include <stdint.h>
-
-struct TimeConfiguration {
-
-    /**
-     * @brief The timezone offset in seconds
-     */
-    int32_t offsetToGMT;
-
-    /**
-     * @brief The daylight savings offset in seconds
-     */
-    int32_t offsetDaylightSavings;
-
-    /**
-     * @brief The url of the NTP server
-     */
-    const char* ntpServerUrl;
-
-    /**
-     * @brief The allowed discrepancy between the time of a received message
-     * and the device time (in seconds)
-     * 
-     * A stricter (lower) value better prevents against replay attacks,
-     * but may lead to issues when dealing with slow networks and other
-     * routing delays.
-     */
-    uint32_t allowedTimeOffset;
-};
-
-class TimeCheck {
-
-public:
-
-    /**
-     * @brief Create a time checker instance
-     */
-    TimeCheck();
-
-    /**
-     * @brief Set the configuration
-     */
-    void configure(TimeConfiguration configuration);
-
-    /**
-     * @brief Configure the NTP server to get the current time
-     */
-    void startNTP();
-
-    /**
-     * @brief Print the current time to the serial output
-     * 
-     * The time must be initialized by calling `configureNTP()` before use.
-     */
-    void printLocalTime();
-
-    /** 
-     * Gets the current epoch time
-     */
-    uint32_t getEpochTime();
-
-    /**
-     * @brief Check wether the time of a message is within the allowed bounds regarding freshness.
-     * 
-     * The timestamp is used to ensure 'freshness' of the messages,
-     * i.e. that they are not unreasonably delayed or captured and
-     * later replayed by an attacker.
-     * 
-     * @param messageTime The timestamp of the message (seconds since epoch) 
-     * @return true The time is within the acceptable offset of the local time
-     * @return false The message time is invalid
-     */
-    bool isMessageTimeAcceptable(uint32_t messageTime);
-
-private:
-
-    TimeConfiguration config;
-};

include/message.h

@@ -14,58 +14,96 @@
 
 #pragma pack(push, 1)
 
+typedef enum {
+
+    /// @brief The initial message from remote to device to request a challenge.
+    initial = 0,
+
+    /// @brief The second message in an unlock with the challenge from the device to the remote
+    challenge = 1,
+
+    /// @brief The third message with the signed challenge from the remote to the device
+    request = 2,
+
+    /// @brief The final message with the unlock result from the device to the remote
+    response = 3,
+
+} MessageType;
+
+enum class MessageResult: uint8_t {
+
+    /// @brief The message was accepted.
+    MessageAccepted = 0,
+    
+    /// @brief The web socket received text while waiting for binary data.
+    TextReceived = 1,
+
+    /// @brief An unexpected socket event occured while performing the exchange.
+    UnexpectedSocketEvent = 2,
+
+    /// @brief The received message size is invalid.
+    InvalidMessageSize = 3,
+
+    /// @brief The message signature was incorrect.
+    MessageAuthenticationFailed = 4,
+
+    /// @brief The server challenge of the message did not match previous messages
+    ServerChallengeMismatch = 5,
+
+    /// @brief The client challenge of the message did not match previous messages
+    ClientChallengeInvalid = 6,
+
+    /// @brief An unexpected or unsupported message type was received
+    InvalidMessageType = 7,
+
+    /// @brief A message is already being processed
+    TooManyRequests = 8,
+
+    /// @brief The received message result was invalid
+    InvalidMessageResult = 9,
+
+    /// @brief An invalid Url parameter was set sending a message to the device over a local connection
+    InvalidUrlParameter = 10,
+
+};
+
 /**
- * @brief The content of an unlock message.
+ * @brief A generic message to exchange during challenge-response authentication.
- * 
- * The content is necessary to ensure freshness of the message
- * by requiring a recent time and a monotonously increasing counter.
- * This prevents messages from being delayed or being blocked and
- * replayed later.
  */
 typedef struct {
 
-    /** 
+    /// @brief The type of message being sent.
-     * The timestamp of message creation
+    MessageType messageType;
-     * 
-     * The timestamp is encoded as the epoch time, i.e. seconds since 1970 (GMT).
-     * 
-     * The timestamp is used to ensure 'freshness' of the messages,
-     * i.e. that they are not unreasonably delayed or captured and
-     * later replayed by an attacker.
-     */
-    uint32_t time;
-
-    /** 
-     * The counter of unlock messages
-     * 
-     * This counter must always increase with each message from the remote
-     * in order for the messages to be deemed valid. Transfering the counters
-     * back and forth also gives information about lost messages and potential
-     * attacks. Both the remote and the device keep a record of at least the
-     * last used counter.
-     */
-    uint32_t id;
 
     /**
-     * @brief The id of the device sending the message
+     * @brief The random nonce created by the remote
+     * 
+     * This nonce is a random number created by the remote, different for each unlock request.
+     * It is set for all message types.
      */
-    uint8_t device;
+    uint32_t clientChallenge;
+
+    /**
+     * @brief A random number to sign by the remote
+     * 
+     * This nonce is set by the server after receiving an initial message.
+     * It is set for the message types `challenge`, `request`, and `response`.
+     */
+    uint32_t serverChallenge;
+
+    /**
+     * @brief The response status for the previous message.
+     * 
+     * It is set only for messages from the server, e.g. the `challenge` and `response` message types.
+     * Must be set to `MessageAccepted` for other messages.
+     */
+    MessageResult result;
 
 } Message;
 
-constexpr size_t messageCounterSize = sizeof(uint32_t);
-
 /**
- * @brief An authenticated message by the mobile device to command unlocking.
+ * @brief The signed version of a message.
  * 
- * The message is protected by a message authentication code (MAC) based on
- * a symmetric key shared by the device and the remote. This code ensures
- * that the contents of the request were not altered. The message further
- * contains a timestamp to ensure that the message is recent, and not replayed
- * by an attacker. An additional counter is also included for this purpose,
- * which must continously increase for a message to be valid. This increases
- * security a bit, since the timestamp validation must be tolerant to some 
- * inaccuracy due to mismatching clocks.
  */
 typedef struct {
 
@@ -77,38 +115,18 @@ typedef struct {
      */
     uint8_t mac[SHA256_MAC_SIZE];
 
-    /**
+    /// @brief The message
-     * @brief The message content.
-     * 
-     * The content is necessary to ensure freshness of the message
-     * by requiring a recent time and a monotonously increasing counter.
-     * This prevents messages from being delayed or being blocked and
-     * replayed later.
-     */
     Message message;
 
-} AuthenticatedMessage;
+} SignedMessage;
+
+constexpr size_t messageCounterSize = sizeof(uint32_t);
+
 #pragma pack(pop)
 
 constexpr int MESSAGE_CONTENT_SIZE = sizeof(Message);
 
-constexpr int AUTHENTICATED_MESSAGE_SIZE = sizeof(AuthenticatedMessage);
+constexpr int SIGNED_MESSAGE_SIZE = sizeof(SignedMessage);
-
-/**
- * An event signaled from the device
- */
-enum class SesameEvent {
-    TextReceived = 1,
-    UnexpectedSocketEvent = 2,
-    InvalidMessageSize = 3,
-    MessageAuthenticationFailed = 4,
-    MessageTimeMismatch = 5,
-    MessageCounterInvalid = 6,
-    MessageAccepted = 7,
-    MessageDeviceInvalid = 8,
-    InvalidUrlParameter = 20, 
-    InvalidResponseAuthentication = 21,
-};
 
 /**
  * @brief A callback for messages received over the socket
@@ -121,5 +139,5 @@ typedef void (*MessageCallback)(uint8_t* payload, size_t length);
 /**
  * @brief A callback for socket errors
  */
-typedef void (*ErrorCallback)(SesameEvent event);
+typedef void (*ErrorCallback)(MessageResult event);
 

include/server.h

@@ -2,8 +2,6 @@
 
 #include "message.h"
 #include "crypto.h"
-#include <WiFiMulti.h>
-#include <WiFiClientSecure.h>
 #include <WebSocketsClient.h>
 
 struct ServerConfiguration {
@@ -30,13 +28,17 @@ struct ServerConfiguration {
     
     uint32_t reconnectTime;
 
+    uint32_t socketHeartbeatIntervalMs;
+    uint32_t socketHeartbeatTimeoutMs;
+    uint8_t socketHeartbeatFailureReconnectCount;
+
 };
 
 class ServerConnectionCallbacks {
 
 public:
 
-    virtual void sendServerError(SesameEvent event) = 0;
+    virtual void sendServerError(MessageResult event) = 0;
     virtual void handleServerMessage(uint8_t* payload, size_t length) = 0;
 };
 
@@ -53,11 +55,13 @@ public:
      */
     void configure(ServerConfiguration configuration, ServerConnectionCallbacks* callbacks);
 
-    void connect();
+    /**
-
+     * @brief Call this function regularly to handle socket operations.
-    void disconnect();
+     * 
-
+     * Connecting and disconnecting is done automatically.
-    void loop();
+     * 
+     */
+    void loop(uint32_t millis);
 
     /**
      * @brief Send a response message over the socket
@@ -67,11 +71,26 @@ public:
      */
     void sendResponse(uint8_t* buffer, uint16_t length);
 
-    bool isSocketConnected() {
+private:
+
+    uint32_t currentTime;
+
+    bool socketIsConnected() {
         return webSocket.isConnected();
     }
 
-private:
+    void connect();
+
+    void disconnect();
+
+    bool shouldReconnect = true;
+    bool isConnecting = false;
+    uint32_t connectionTimeout = 0;
+    uint32_t nextReconnectAttemptMs = 0;
+
+    void didDisconnect();
+    void didConnect();
+
 
     ServerConfiguration configuration;
 

include/storage.h

@@ -1,83 +0,0 @@
-#pragma once
-
-#include <stdint.h>
-
-class Storage {
-
-public:
-
-    Storage(uint8_t remoteDeviceCount) : remoteDeviceCount(remoteDeviceCount) { };
-
-    /**
-     * @brief Initialize the use of the message counter API
-     * 
-     * The message counter is stored in EEPROM, which must be initialized before use.
-     * 
-     * @note The ESP32 does not have a true EEPROM, 
-     * which is emulated using a section of the flash memory.
-     */
-    void configure();
-
-    /**
-     * @brief Check if a device ID is allowed
-     * 
-     * @param deviceId The ID to check
-     * @return true The id is valid
-     * @return false The id is invalid
-     */
-    bool isDeviceIdValid(uint8_t deviceId);
-
-    /**
-     * @brief Check if a received counter is valid
-     * 
-     * The counter is valid if it is larger than the previous counter
-     * (larger or equal to the next expected counter).
-     * 
-     * @param counter The counter to check
-     * @return true The counter is valid
-     * @return false The counter belongs to an old message
-     */
-    bool isMessageCounterValid(uint32_t counter, uint8_t deviceId);
-
-    /**
-     * @brief Mark a counter of a message as used.
-     * 
-     * The counter value is stored in EEPROM to persist across restarts.
-     * 
-     * All messages with counters lower than the given one will become invalid.
-     * 
-     * @param counter The counter used in the last message.
-     */
-    void didUseMessageCounter(uint32_t counter, uint8_t deviceId);
-
-    /**
-     * @brief Get the expected count for the next message.
-     * 
-     * The counter is stored in EEPROM to persist across restarts
-     * 
-     * @return The next counter to use by the remote 
-     */
-    uint32_t getNextMessageCounter(uint8_t deviceId);
-
-    /**
-     * @brief Print info about the current message counter to the serial output
-     * 
-     */
-    void printMessageCounters();
-
-    /**
-     * @brief Reset the message counter.
-     * 
-     * @warning The counter should never be reset in production environments,
-     * and only together with a new secret key. Otherwise old messages may be
-     * used for replay attacks.
-     * 
-     */
-    void resetMessageCounters();
-
-private:
-
-    uint8_t remoteDeviceCount;
-
-    void setMessageCounter(uint32_t counter, uint8_t deviceId);
-};

platformio.ini

@@ -13,7 +13,11 @@ platform = espressif32
 board = az-delivery-devkit-v4
 framework = arduino
 lib_deps = 
-	links2004/WebSockets@^2.3.7
+	; links2004/WebSockets@^2.4.0
 	madhephaestus/ESP32Servo@^1.1.0
 	ottowinter/ESPAsyncWebServer-esphome@^3.0.0
+	arduino-libraries/Ethernet@^2.0.2
+	https://github.com/christophhagen/arduinoWebSockets#master
+	
 monitor_speed = 115200
+build_flags= -D WEBSOCKETS_NETWORK_TYPE=NETWORK_W5100

src/controller.cpp

@@ -2,23 +2,48 @@
 #include "crypto.h"
 #include "config.h"
 
-#include <WiFi.h>
+#include <SPI.h>
+#include <Ethernet.h>
+
+SesameController::SesameController(uint16_t localWebServerPort) : localWebServer(localWebServerPort) {
 
-SesameController::SesameController(uint16_t localWebServerPort, uint8_t remoteDeviceCount) : 
-    storage(remoteDeviceCount), localWebServer(localWebServerPort) {
-    
-    // Set up response buffer
-    responseStatus = (SesameEvent*) responseBuffer;
-    responseMessage = (AuthenticatedMessage*) (responseBuffer + 1);
 }
 
-void SesameController::configure(ServoConfiguration servoConfig, ServerConfiguration serverConfig, TimeConfiguration timeConfig, WifiConfiguration wifiConfig, KeyConfiguration keyConfig) {
+void SesameController::configure(ServoConfiguration servoConfig, ServerConfiguration serverConfig, EthernetConfiguration ethernetConfig, KeyConfiguration keyConfig) {
-    this->wifiConfig = wifiConfig;
+    this->ethernetConfig = ethernetConfig;
     this->keyConfig = keyConfig;
 
-    // Prepare EEPROM for reading and writing
+    // Ensure source of random numbers without WiFi and Bluetooth
-    storage.configure();
+    enableCrypto();
-    Serial.println("[INFO] Storage configured");
+
+    // Initialize SPI interface to Ethernet module
+    SPI.begin(ethernetConfig.spiPinSclk, ethernetConfig.spiPinMiso, ethernetConfig.spiPinMosi, ethernetConfig.spiPinSS); //SCLK, MISO, MOSI, SS
+    pinMode(ethernetConfig.spiPinSS, OUTPUT);
+
+    Ethernet.init(ethernetConfig.spiPinSS);
+
+    if (Ethernet.begin(ethernetConfig.macAddress, ethernetConfig.dhcpLeaseTimeoutMs, ethernetConfig.dhcpLeaseResponseTimeoutMs) == 1) {
+        Serial.print("[INFO] DHCP assigned IP ");
+        Serial.println(Ethernet.localIP());
+        ethernetIsConfigured = true;
+    } else {
+        // Check for Ethernet hardware present
+        if (Ethernet.hardwareStatus() == EthernetNoHardware) {
+            Serial.println("[ERROR] Ethernet shield not found.");
+        } else if (Ethernet.linkStatus() == LinkOFF) {
+            Serial.println("[ERROR] Ethernet cable is not connected.");
+        } else if (Ethernet.linkStatus() == Unknown) {
+            Serial.println("[ERROR] Ethernet cable status unknown.");
+        } else if (Ethernet.linkStatus() == LinkON) {
+            Serial.println("[INFO] Ethernet cable is connected.");
+        
+            // Try to configure using IP address instead of DHCP
+            Ethernet.begin(ethernetConfig.macAddress, ethernetConfig.manualIp, ethernetConfig.manualDnsAddress);
+            Serial.print("[WARNING] DHCP failed, using self-assigned IP ");
+            Serial.println(Ethernet.localIP());
+            ethernetIsConfigured = true;
+        }
+    }
     
     servo.configure(servoConfig);
     Serial.println("[INFO] Servo configured");
@@ -26,9 +51,6 @@ void SesameController::configure(ServoConfiguration servoConfig, ServerConfigura
     // Direct messages and errors over the websocket to the controller
     server.configure(serverConfig, this);
     Serial.println("[INFO] Server connection configured");
-
-    timeCheck.configure(timeConfig);
-
     
     // Direct messages from the local web server to the controller
     localWebServer.on("/message", HTTP_POST, [this] (AsyncWebServerRequest *request) { 
@@ -37,18 +59,12 @@ void SesameController::configure(ServoConfiguration servoConfig, ServerConfigura
     });
 
     Serial.println("[INFO] Local web server configured");
-
-    //storage.resetMessageCounters();
-    storage.printMessageCounters();
 }
 
 void SesameController::loop(uint32_t millis) {
-    server.loop();
+    currentTime = millis;
+    server.loop(millis);
     servo.loop(millis);
-
-    periodicallyReconnectWifiAndSocket(millis);
-    ensureWiFiConnection(millis);
-    ensureWebSocketConnection();
 }
 
 // MARK: Local
@@ -56,141 +72,154 @@ void SesameController::loop(uint32_t millis) {
 void SesameController::handleLocalMessage(AsyncWebServerRequest *request) {
     if (!request->hasParam(messageUrlParameter)) {
         Serial.println("Missing url parameter");
-        prepareResponseBuffer(SesameEvent::InvalidUrlParameter);
+        prepareResponseBuffer(MessageResult::InvalidUrlParameter);
         return;
     }
     String encoded = request->getParam(messageUrlParameter)->value();
     if (!convertHexMessageToBinary(encoded.c_str())) {
         Serial.println("Invalid hex encoding");
-        prepareResponseBuffer(SesameEvent::InvalidMessageSize);
+        prepareResponseBuffer(MessageResult::InvalidMessageSize);
         return;
     }
-    processMessage((AuthenticatedMessage*) receivedMessageBuffer);
+    processMessage(&receivedLocalMessage);
 }
 
 void SesameController::sendPreparedLocalResponse(AsyncWebServerRequest *request) {
-    request->send_P(200, "application/octet-stream", responseBuffer, responseSize);
+    request->send_P(200, "application/octet-stream", (uint8_t*) &outgoingMessage, SIGNED_MESSAGE_SIZE);
-    Serial.printf("[INFO] Local response %u (%u bytes)\n", responseBuffer[0], responseSize);
+    Serial.printf("[INFO] Local response %u\n", outgoingMessage.message.messageType);
 }
 
 // MARK: Server
 
-void SesameController::sendServerError(SesameEvent event) {
+void SesameController::sendServerError(MessageResult result) {
-    prepareResponseBuffer(event);
+    prepareResponseBuffer(result); // No message to echo
-    sendPreparedServerResponse();
+    sendPreparedResponseToServer();
 }
 
 void SesameController::handleServerMessage(uint8_t* payload, size_t length) {
-    if (length != AUTHENTICATED_MESSAGE_SIZE) {
+    if (length != SIGNED_MESSAGE_SIZE) {
-        prepareResponseBuffer(SesameEvent::InvalidMessageSize);
+        // No message saved to discard, don't accidentally delete for other operation
+        sendServerError(MessageResult::InvalidMessageSize);
         return;
     }
-    
+    processMessage((SignedMessage*) payload);
-    processMessage((AuthenticatedMessage*) payload);
+    sendPreparedResponseToServer();
-    sendPreparedServerResponse();
 }
 
-void SesameController::sendPreparedServerResponse() {
+void SesameController::sendPreparedResponseToServer() {
-    server.sendResponse(responseBuffer, responseSize);
+    server.sendResponse((uint8_t*) &outgoingMessage, SIGNED_MESSAGE_SIZE);
-    Serial.printf("[INFO] Server response %u (%u bytes)\n", responseBuffer[0], responseSize);
+    Serial.printf("[INFO] Server response %u\n", outgoingMessage.message.messageType);
 }
 
 // MARK: Message handling
 
-void SesameController::processMessage(AuthenticatedMessage* message) {
+void SesameController::processMessage(SignedMessage* message) {
-    SesameEvent event = verifyAndProcessReceivedMessage(message);
+    // Result must be empty
-    prepareResponseBuffer(event, message->message.device);
+    if (message->message.result != MessageResult::MessageAccepted) {
+        prepareResponseBuffer(MessageResult::InvalidMessageResult);
+        return;
+    }
+    if (!isAuthenticMessage(message, keyConfig.remoteKey)) {
+        prepareResponseBuffer(MessageResult::MessageAuthenticationFailed);
+        return;
+    }
+    switch (message->message.messageType) {
+    case MessageType::initial:
+        checkAndPrepareChallenge(&message->message);
+        return;
+    case MessageType::request:
+        completeUnlockRequest(&message->message);
+        return;
+    default:
+        prepareResponseBuffer(MessageResult::InvalidMessageType);
+        return;
+    }
 }
 
-/**
+void SesameController::checkAndPrepareChallenge(Message* message) {
- * Process a received message.
+    // Server challenge must be empty
- *
+    if (message->serverChallenge != 0) {
- * Checks whether the received data is a valid,
+        prepareResponseBuffer(MessageResult::ClientChallengeInvalid);
- * and then signals that the motor should move.
+        return;
- *
- * @param message The message received from the remote
- * @return The response to signal to the server.
- */
-SesameEvent SesameController::verifyAndProcessReceivedMessage(AuthenticatedMessage* message) {
-    if (!isAuthenticMessage(message, keyConfig.remoteKey, keySize)) {
-        return SesameEvent::MessageAuthenticationFailed;
     }
-    if (!storage.isDeviceIdValid(message->message.device)) {
+    prepareChallenge(message);
-        return SesameEvent::MessageDeviceInvalid;
+}
-    }
+
-    if (!storage.isMessageCounterValid(message->message.id, message->message.device)) {
+void SesameController::prepareChallenge(Message* message) {
-        return SesameEvent::MessageCounterInvalid;
+    if (hasCurrentChallenge()) {
-    }
+        Serial.println("[INFO] Overwriting old challenge");
-    if (!timeCheck.isMessageTimeAcceptable(message->message.time)) {
-        return SesameEvent::MessageTimeMismatch;
     }
 
-    storage.didUseMessageCounter(message->message.id, message->message.device);
+    // Set challenge and respond
+    currentClientChallenge = message->clientChallenge;
+    currentServerChallenge = randomChallenge();
+    currentChallengeExpiry = currentTime + keyConfig.challengeExpiryMs;
+
+    prepareResponseBuffer(MessageResult::MessageAccepted, message);
+}
+
+void SesameController::completeUnlockRequest(Message* message) {
+    // Client and server challenge must match
+    if (message->clientChallenge != currentClientChallenge) {
+        prepareResponseBuffer(MessageResult::ClientChallengeInvalid, message);
+        return;
+    }
+    if (message->serverChallenge != currentServerChallenge) {
+        prepareResponseBuffer(MessageResult::ServerChallengeMismatch, message);
+        return;
+    }
+    if (!hasCurrentChallenge()) {
+        // Directly send new challenge on expiry, since rest of message is valid
+        // This allows the remote to directly try again without requesting a new challenge.
+        // Security note: The client nonce is reused in this case, but an attacker would still 
+        // not be able to create a valid unlock request due to the new server nonce.
+        prepareChallenge(message);
+        return;
+    }
+
+    clearCurrentChallenge();
+    
     // Move servo
     servo.pressButton();
-    Serial.printf("[Info] Accepted message %d\n", message->message.id);
+    prepareResponseBuffer(MessageResult::MessageAccepted, message);
-    return SesameEvent::MessageAccepted;
+    Serial.println("[INFO] Accepted message");
 }
 
-bool allowMessageResponse(SesameEvent event) {
+void SesameController::prepareResponseBuffer(MessageResult result, Message* message) {
-    switch (event) {
+    outgoingMessage.message.result = result;
-    case SesameEvent::MessageTimeMismatch:
+    if (message != NULL) {
-    case SesameEvent::MessageCounterInvalid:
+        outgoingMessage.message.clientChallenge = message->clientChallenge;
-    case SesameEvent::MessageAccepted:
+        outgoingMessage.message.serverChallenge = message->serverChallenge;
-    case SesameEvent::MessageDeviceInvalid:
+        // All outgoing messages are responses, except if an initial message is accepted
-        return true;
+        if (message->messageType == MessageType::initial && result == MessageResult::MessageAccepted) {
-    default:
+            outgoingMessage.message.messageType = MessageType::challenge;
-        return false;
+        } else {
+            outgoingMessage.message.messageType = MessageType::response;
+        }
+    } else {
+        outgoingMessage.message.clientChallenge = message->clientChallenge;
+        outgoingMessage.message.serverChallenge = message->serverChallenge;
+        outgoingMessage.message.messageType = MessageType::response;
     }
-}
 
-void SesameController::prepareResponseBuffer(SesameEvent event, uint8_t deviceId) {
+    if (!authenticateMessage(&outgoingMessage, keyConfig.localKey)) {
-    *responseStatus = event;
+        Serial.println("[ERROR] Failed to sign message");
-    responseSize = 1;
-    if (!allowMessageResponse(event)) {
-        return;
-    }
-    responseMessage->message.time = timeCheck.getEpochTime();
-    responseMessage->message.id = storage.getNextMessageCounter(deviceId);
-    responseMessage->message.device = deviceId;
-
-    if (!authenticateMessage(responseMessage, keyConfig.localKey, keySize)) {
-        *responseStatus = SesameEvent::InvalidResponseAuthentication;
-        return;
-    }
-    responseSize += AUTHENTICATED_MESSAGE_SIZE;
-}
-
-// MARK: Reconnecting
-
-void SesameController::ensureWiFiConnection(uint32_t millis) {
-    static uint32_t nextWifiReconnect = 0;
-    // Reconnect to WiFi
-    if(millis > nextWifiReconnect && WiFi.status() != WL_CONNECTED) {
-        Serial.println("[INFO] Reconnecting WiFi...");
-        WiFi.setHostname(wifiConfig.networkName);
-        WiFi.begin(wifiConfig.ssid, wifiConfig.password);
-        isReconnecting = true;
-        nextWifiReconnect = millis + wifiConfig.reconnectInterval;
-    }
-}
-
-void SesameController::ensureWebSocketConnection() {
-    if (isReconnecting && WiFi.status() == WL_CONNECTED) {
-        isReconnecting = false;
-        Serial.print("WiFi IP address: ");
-        Serial.println(WiFi.localIP());
-        server.connect();
-        timeCheck.startNTP();
-        timeCheck.printLocalTime();
-        localWebServer.begin();
     }
 }
 
 // MARK: Helper
 
-// Based on https://stackoverflow.com/a/23898449/266720
+/**
+ * @brief 
+ * 
+ * Based on https://stackoverflow.com/a/23898449/266720
+ * 
+ * @param str 
+ * @return true 
+ * @return false 
+ */
 bool SesameController::convertHexMessageToBinary(const char* str) {
+    uint8_t* buffer = (uint8_t*) &receivedLocalMessage;
     // TODO: Fail if invalid hex values are used
     uint8_t  idx0, idx1;
 
@@ -203,7 +232,7 @@ bool SesameController::convertHexMessageToBinary(const char* str) {
     };
 
     size_t len = strlen(str);
-    if (len != AUTHENTICATED_MESSAGE_SIZE * 2) {
+    if (len != SIGNED_MESSAGE_SIZE * 2) {
         // Require exact message size
         return false;
     }
@@ -211,17 +240,7 @@ bool SesameController::convertHexMessageToBinary(const char* str) {
     for (size_t pos = 0; pos < len; pos += 2) {
         idx0 = ((uint8_t)str[pos+0] & 0x1F) ^ 0x10;
         idx1 = ((uint8_t)str[pos+1] & 0x1F) ^ 0x10;
-        receivedMessageBuffer[pos/2] = (uint8_t)(hashmap[idx0] << 4) | hashmap[idx1];
+        buffer[pos/2] = (uint8_t)(hashmap[idx0] << 4) | hashmap[idx1];
     };
     return true;
-}
-
-void SesameController::periodicallyReconnectWifiAndSocket(uint32_t millis) {
-    static uint32_t nextWifiReconnect = wifiConfig.periodicReconnectInterval;
-    if (millis > nextWifiReconnect) {
-        nextWifiReconnect += wifiConfig.periodicReconnectInterval;
-
-        server.disconnect();
-        WiFi.disconnect();
-    }
 }

src/crypto.cpp

@@ -1,8 +1,19 @@
 #include "crypto.h"
+#include "config.h"
 #include <string.h>
 #include <mbedtls/md.h>
+#include <esp_random.h>
+#include <bootloader_random.h>
 
-bool authenticateData(const uint8_t* data, size_t dataLength, uint8_t* mac, const uint8_t* key, size_t keyLength) {
+void enableCrypto() {
+    bootloader_random_enable();
+}
+
+uint32_t randomChallenge() {
+    return esp_random();
+}
+
+bool authenticateData(const uint8_t* data, size_t dataLength, uint8_t* mac, const uint8_t* key) {
     mbedtls_md_context_t ctx;
     mbedtls_md_type_t md_type = MBEDTLS_MD_SHA256;
     int result;
@@ -12,7 +23,7 @@ bool authenticateData(const uint8_t* data, size_t dataLength, uint8_t* mac, cons
     if (result) {
         return false;
     }
-    result = mbedtls_md_hmac_starts(&ctx, key, keyLength);
+    result = mbedtls_md_hmac_starts(&ctx, key, keySize);
     if (result) {
         return false;
     }
@@ -28,17 +39,17 @@ bool authenticateData(const uint8_t* data, size_t dataLength, uint8_t* mac, cons
     return true;
 }
 
-bool authenticateMessage(Message* message, uint8_t* mac, const uint8_t* key, size_t keyLength) {
+bool authenticateMessage(Message* message, uint8_t* mac, const uint8_t* key) {
-    return authenticateData((const uint8_t*) message, MESSAGE_CONTENT_SIZE, mac, key, keyLength);
+    return authenticateData((const uint8_t*) message, MESSAGE_CONTENT_SIZE, mac, key);
 }
 
-bool authenticateMessage(AuthenticatedMessage* message, const uint8_t* key, size_t keyLength) {
+bool authenticateMessage(SignedMessage* message, const uint8_t* key) {
-    return authenticateMessage(&message->message, message->mac, key, keyLength);
+    return authenticateMessage(&message->message, message->mac, key);
 }
 
-bool isAuthenticMessage(AuthenticatedMessage* message, const uint8_t* key, size_t keyLength) {
+bool isAuthenticMessage(SignedMessage* message, const uint8_t* key) {
     uint8_t mac[SHA256_MAC_SIZE];
-    if (!authenticateMessage(&message->message, mac, key, keyLength)) {
+    if (!authenticateMessage(&message->message, mac, key)) {
         return false;
     }
     return memcmp(mac, message->mac, SHA256_MAC_SIZE) == 0;

src/fresh.cpp

@@ -1,49 +0,0 @@
-#include "fresh.h"
-
-#include <Arduino.h> // configTime()
-#include <time.h>
-
-TimeCheck::TimeCheck() { }
-
-void TimeCheck::configure(TimeConfiguration configuration) {
-    config = configuration;
-}
-
-void TimeCheck::startNTP() {
-    configTime(config.offsetToGMT, config.offsetDaylightSavings, config.ntpServerUrl);
-}
-
-void TimeCheck::printLocalTime() {
-    struct tm timeinfo;
-    if (getLocalTime(&timeinfo)) {
-        Serial.println(&timeinfo, "[INFO] Time is %A, %d. %B %Y %H:%M:%S");
-    } else {
-        Serial.println("[WARN] No local time available");
-    }
-}
-
-uint32_t TimeCheck::getEpochTime() {
-    time_t now;
-    struct tm timeinfo;
-    if (!getLocalTime(&timeinfo)) {
-        Serial.println("[WARN] Failed to obtain local time");
-        return(0);
-    }
-    time(&now);
-    return now;
-}
-
-bool TimeCheck::isMessageTimeAcceptable(uint32_t t) {
-    uint32_t localTime = getEpochTime();
-    if (localTime == 0) {
-        Serial.println("No epoch time available");
-        return false;
-    }
-    if (t > localTime + config.allowedTimeOffset) {
-        return false;
-    }
-    if (t < localTime - config.allowedTimeOffset) {
-        return false;
-    }
-    return true;
-}

src/main.cpp

@@ -4,6 +4,15 @@
  *
  * The code for a simple door unlock mechanism where a servo pushes on an existing
  * physical button.
+ * 
+ * On compile error:
+ * 
+ * In <Server.h>
+ * 
+ * change:
+ *      virtual void begin(uint16_t port=0) =0;
+ * to:
+ *      virtual void begin() =0;
  */
 #include <Arduino.h>
 
@@ -13,7 +22,7 @@
 #include "controller.h"
 #include "config.h"
 
-SesameController controller(localPort, remoteDeviceCount);
+SesameController controller(localPort);
 
 void setup() {
     Serial.begin(serialBaudRate);
@@ -35,29 +44,30 @@ void setup() {
         .path = serverPath,
         .key = serverAccessKey,
         .reconnectTime = 5000,
+        .socketHeartbeatIntervalMs = socketHeartbeatIntervalMs,
+        .socketHeartbeatTimeoutMs = socketHeartbeatTimeoutMs,
+        .socketHeartbeatFailureReconnectCount = socketHeartbeatFailureReconnectCount,
     };
 
-    TimeConfiguration timeConfig {
+    EthernetConfiguration ethernetConfig {
-        .offsetToGMT = timeOffsetToGMT,
+        .macAddress = ethernetMacAddress,
-        .offsetDaylightSavings = timeOffsetDaylightSavings,
+        .spiPinMiso = spiPinMiso,
-        .ntpServerUrl = ntpServerUrl,
+        .spiPinMosi = spiPinMosi,
-        .allowedTimeOffset = 60,
+        .spiPinSclk = spiPinSclk,
-    };
+        .spiPinSS = spiPinSS,
-
+        .dhcpLeaseTimeoutMs = dhcpLeaseTimeoutMs,
-    WifiConfiguration wifiConfig {
+        .dhcpLeaseResponseTimeoutMs = dhcpLeaseResponseTimeoutMs,
-        .ssid = wifiSSID,
+        .manualIp = manualIpAddress,
-        .password = wifiPassword,
+        .manualDnsAddress = manualDnsServerAddress,
-        .networkName = networkName,
-        .reconnectInterval = wifiReconnectInterval,
-        .periodicReconnectInterval = wifiPeriodicReconnectInterval,
     };
 
     KeyConfiguration keyConfig {
         .remoteKey = remoteKey,
         .localKey = localKey,
+        .challengeExpiryMs = challengeExpiryMs,
     };
 
-    controller.configure(servoConfig, serverConfig, timeConfig, wifiConfig, keyConfig);
+    controller.configure(servoConfig, serverConfig, ethernetConfig, keyConfig);
 }
 
 void loop() {

src/server.cpp

@@ -20,7 +20,11 @@ void ServerConnection::connect() {
         return;
     }
 
-    webSocket.beginSSL(configuration.url, configuration.port, configuration.path);
+    isConnecting = true;
+    Serial.printf("[INFO] Connecting to %s:%d%s\n", configuration.url, configuration.port, configuration.path);
+    connectionTimeout = currentTime + configuration.socketHeartbeatIntervalMs;
+    webSocket.begin(configuration.url, configuration.port, configuration.path);
+    webSocket.setAuthorization(configuration.key);
 
     std::function<void(WStype_t, uint8_t *, size_t)> f = [this](WStype_t type, uint8_t *payload, size_t length) {
         this->webSocketEventHandler(type, payload, length);
@@ -29,26 +33,50 @@ void ServerConnection::connect() {
     webSocket.setReconnectInterval(configuration.reconnectTime);
 }
 
+void ServerConnection::didDisconnect() {
+    if (shouldReconnect || isConnecting) {
+        return; // Disconnect already registered. 
+    }
+    Serial.println("[INFO] Socket disconnected");
+    nextReconnectAttemptMs = currentTime + configuration.socketHeartbeatIntervalMs;
+    shouldReconnect = true;
+}
+
+void ServerConnection::didConnect() {
+    isConnecting = false;
+    Serial.println("[INFO] Socket connected");
+    webSocket.enableHeartbeat(configuration.socketHeartbeatIntervalMs, configuration.socketHeartbeatTimeoutMs, configuration.socketHeartbeatFailureReconnectCount);
+}
+
 void ServerConnection::disconnect() {
     webSocket.disconnect();
 }
 
-void ServerConnection::loop() {
+void ServerConnection::loop(uint32_t millis) {
+    currentTime = millis;
     webSocket.loop();
+    if (shouldReconnect && !isConnecting) {
+        shouldReconnect = false;
+        connect();
+    }
+    if (isConnecting && millis > connectionTimeout) {
+        Serial.println("[INFO] Failed to connect");
+        disconnect();
+        shouldReconnect = true;
+        isConnecting = false;
+    }
 }
 
 void ServerConnection::webSocketEventHandler(WStype_t type, uint8_t * payload, size_t length) {
 switch(type) {
     case WStype_DISCONNECTED:
-        Serial.println("[INFO] Socket disconnected.");
+        didDisconnect();
         break;
     case WStype_CONNECTED:
-        webSocket.sendTXT(configuration.key);
+        didConnect();
-        Serial.printf("[INFO] Socket connected to url: %s\n", payload);
-        webSocket.enableHeartbeat(pingInterval, pongTimeout, disconnectTimeoutCount);
         break;
     case WStype_TEXT:
-        controller->sendServerError(SesameEvent::TextReceived);
+        controller->sendServerError(MessageResult::TextReceived);
         break;
     case WStype_BIN:
         controller->handleServerMessage(payload, length);
@@ -56,16 +84,20 @@ switch(type) {
     case WStype_PONG:
         break;
     case WStype_PING:
+        break;
     case WStype_ERROR:
     case WStype_FRAGMENT_TEXT_START:
     case WStype_FRAGMENT_BIN_START:
     case WStype_FRAGMENT:
     case WStype_FRAGMENT_FIN:
-        controller->sendServerError(SesameEvent::UnexpectedSocketEvent);
+    Serial.printf("[WARN] Unexpected socket event %d\n", type);
+        controller->sendServerError(MessageResult::UnexpectedSocketEvent);
         break;
     }
 }
 
 void ServerConnection::sendResponse(uint8_t* buffer, uint16_t length) {
-    webSocket.sendBIN(buffer, length);
+    if (socketIsConnected()) {
+        webSocket.sendBIN(buffer, length);
+    }
 }

src/storage.cpp

@@ -1,53 +0,0 @@
-#include "storage.h"
-#include "message.h"
-#include <EEPROM.h>
-
-void Storage::configure() {
-    EEPROM.begin(messageCounterSize * remoteDeviceCount);
-}
-
-bool Storage::isDeviceIdValid(uint8_t deviceId) {
-    return deviceId < remoteDeviceCount;
-}
-
-bool Storage::isMessageCounterValid(uint32_t counter, uint8_t deviceId) {
-    return counter >= getNextMessageCounter(deviceId);
-}
-
-void Storage::didUseMessageCounter(uint32_t counter, uint8_t deviceId) {
-    // Store the next counter, so that resetting starts at 0
-    setMessageCounter(counter+1, deviceId);
-}
-
-void Storage::setMessageCounter(uint32_t counter, uint8_t deviceId) {
-    int offset = deviceId * messageCounterSize;
-    EEPROM.write(offset + 0, (counter >> 24) & 0xFF);
-    EEPROM.write(offset + 1, (counter >> 16) & 0xFF);
-    EEPROM.write(offset + 2, (counter >>  8) & 0xFF);
-    EEPROM.write(offset + 3,  counter        & 0xFF);
-    EEPROM.commit();
-}
-
-uint32_t Storage::getNextMessageCounter(uint8_t deviceId) {
-    int offset = deviceId * messageCounterSize;
-    uint32_t counter = (uint32_t) EEPROM.read(offset + 0) << 24;
-    counter         += (uint32_t) EEPROM.read(offset + 1) << 16;
-    counter         += (uint32_t) EEPROM.read(offset + 2) << 8;
-    counter         += (uint32_t) EEPROM.read(offset + 3);
-    return counter;
-}
-
-void Storage::printMessageCounters() {
-    Serial.print("[INFO] Next message numbers:");
-    for (uint8_t i = 0; i < remoteDeviceCount; i += 1) {
-        Serial.printf(" %u", getNextMessageCounter(i));
-    }
-    Serial.println("");
-}
-
-void Storage::resetMessageCounters() {
-    for (uint8_t i = 0; i < remoteDeviceCount; i += 1) {
-        setMessageCounter(0, i);
-    }
-    Serial.println("[WARN] Message counters reset");
-}