MAXREFDES143#: DeepCover Embedded Security in IoT Authenticated Sensing & Notification

Dependencies:   MaximInterface mbed

The MAXREFDES143# is an Internet of Things (IoT) embedded security reference design, built to protect an industrial sensing node by means of authentication and notification to a web server. The hardware includes a peripheral module representing a protected sensor node monitoring operating temperature and remaining life of a filter (simulated through ambient light sensing) and an mbed shield representing a controller node responsible for monitoring one or more sensor nodes. The design is hierarchical with each controller node communicating data from connected sensor nodes to a web server that maintains a centralized log and dispatches notifications as necessary. The mbed shield contains a Wi-Fi module, a DS2465 coprocessor with 1-Wire® master function, an LCD, LEDs, and pushbuttons. The protected sensor node contains a DS28E15 authenticator, a DS7505 temperature sensor, and a MAX44009 light sensor. The mbed shield communicates to a web server by the onboard Wi-Fi module and to the protected sensor node with I2C and 1-Wire. The MAXREFDES143# is equipped with a standard shield connector for immediate testing using an mbed board such as the MAX32600MBED#. The simplicity of this design enables rapid integration into any star-topology IoT network requiring the heightened security with low overhead provided by the SHA-256 symmetric-key algorithm.

More information about the MAXREFDES143# is available on the Maxim Integrated website.

WebServerInterface.cpp

Committer:
IanBenzMaxim
Date:
19 months ago
Revision:
35:3d414ba9ab6c
Parent:
32:0a09505a656d

File content as of revision 35:3d414ba9ab6c:

/*******************************************************************************
* Copyright (C) 2016 Maxim Integrated Products, Inc., All Rights Reserved.
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* OTHER DEALINGS IN THE SOFTWARE.
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* Products, Inc. Branding Policy.
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* The mere transfer of this software does not imply any licenses
* of trade secrets, proprietary technology, copyrights, patents,
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#include <vector>
#include <Serial.h>
#include <wait_api.h>
#include <MaximInterface/Devices/DS2465.hpp>
#include <MaximInterface/Utilities/HexConversions.hpp>
#include "WebServerInterface.hpp"
#include "ESP8266.hpp"
#include "SensorData.hpp"

using namespace MaximInterface;

const char WebServerInterface::wifiSsid[] = "WifiSsid";
const char WebServerInterface::wifiPassword[] = "WifiPassword";
const char WebServerInterface::serverAddress[] = "www.maxim-security.com";
const unsigned int WebServerInterface::serverPort = 80;
const char WebServerInterface::serverPostPath[] = "/maxrefdes143/post.php";
const char WebServerInterface::serverChallengePath[] =
    "/maxrefdes143/challenge.php";

// HTTP formatting constants
static const char keyValSeparator = '=';
static const char fieldSeparator = '&';
static const std::string newline = "\r\n";
static const char sessionIdKey[] = "SessionId";

// Authentication MAC constants
static const size_t challengeLen = 32;
static const uint8_t defaultPaddingByte = 0x00;

/// Select the Transport Secret for the web server in the Controller.
/// @returns True on success.
static bool setHttpPostSecret(DS2465 & macCoproc, const RomId & sessionId) {
  Sha256::SlaveSecretData data;
  data.fill(defaultPaddingByte);
  std::copy(sessionId.begin(), sessionId.end(), data.begin() + 64);
  return !macCoproc.computeSlaveSecret(data);
}

bool WebServerInterface::initialize() {
  esp8266.setPowered(true);
  esp8266.reset();
  bool result = (esp8266.performSelfTest() == ESP8266::AT_OK);
  if (result) {
    result = (esp8266.setCurrentWifiMode(ESP8266::softAP_station_mode) ==
              ESP8266::AT_OK);
  }
  if (result) {
    result = (esp8266.setMaxRFTXPower(10) == ESP8266::AT_OK);
  }
  if (result) {
    result = (esp8266.joinCurrentAccessPoint(wifiSsid, wifiPassword) ==
              ESP8266::AT_OK);
  }
  return result;
}

/// Format an HTTP GET request as a string for transmission.
/// @param host Web server address.
/// @param path Web server location to retrieve.
/// @param sessionId Session ID used to identify this controller.
/// @returns GET request string.
static std::string formatHttpGet(const std::string & host,
                                 const std::string & path,
                                 const std::string & sessionId) {
  std::ostringstream httpGetStream;
  httpGetStream << "GET " << path;
  if (sessionId.length() > 0)
    httpGetStream << '?' << sessionIdKey << keyValSeparator << sessionId;
  httpGetStream << " HTTP/1.1" << newline;
  httpGetStream << "Host: " << host << newline;
  httpGetStream << newline;
  return httpGetStream.str();
}

/// Computes a MAC using the Transport Secret to sign HTTP POST requests.
/// @param macCoproc
/// Coprocessor such as the DS2465 used to calculate the authentication MAC.
/// @param input Message array used for MAC calculation.
/// @param ilen Length of array input.
/// @param output Calculated MAC output.
static void calculateHttpPostMac(const DS2465 & macCoproc,
                                 const uint8_t * input, size_t ilen,
                                 Sha256::Hash & output) {
  const size_t blockSize = 32;
  output.fill(defaultPaddingByte); // Set initial hash value
  Sha256::AuthMacData macData;
  macData.fill(defaultPaddingByte);
  while (ilen > 0) {
    Sha256::AuthMacData::iterator macDataBegin =
        std::copy(output.begin(), output.end(), macData.begin());
    if (ilen >= blockSize) // Full block
    {
      std::copy(input, input + blockSize, macDataBegin);
      input += blockSize;
      ilen -= blockSize;
    } else // Partial block with padding
    {
      macDataBegin = std::copy(input, input + ilen, macDataBegin);
      std::fill(macDataBegin, macDataBegin + (blockSize - ilen),
                defaultPaddingByte);
      ilen = 0;
    }
    // Write data to coprocessor and hash block
    macCoproc.computeAuthMac(macData, output);
  }
}

/// Format an HTTP POST request as a string for transmission.
/// @param host Web server address.
/// @param path Web server location to receive POST.
/// @param sessionId Session ID used to identify this Controller.
/// @param macCoproc
/// Coprocessor such as the DS2465 used to calculate the authentication MAC.
/// @param event Event message type.
/// @param initialPostBody Message body as determined by the event message type.
/// @param challenge
/// Challenge previously received from web server for use in authentication MAC.
/// @returns POST request string.
static std::string formatHttpPost(const std::string & host,
                                  const std::string & path,
                                  const std::string & sessionId,
                                  const DS2465 & macCoproc, PostEvent event,
                                  const std::string & initialPostBody,
                                  const uint8_t (&challenge)[challengeLen]) {
  const size_t headerReserve = 115, bodyReserve = 200;

  std::string httpPost;
  httpPost.reserve(initialPostBody.length() + headerReserve + bodyReserve);

  // Add session ID to post body
  if (sessionId.length() > 0) {
    httpPost += sessionIdKey;
    httpPost += keyValSeparator;
    httpPost += sessionId;
  }

  // Add event to post body
  std::string eventString;
  switch (event) {
  case SensorDataEvent:
    eventString = "SensorData";
    break;

  case InvalidSensorEvent:
    eventString = "InvalidSensor";
    break;
  }
  if (eventString.length() > 0) {
    if (httpPost.length() > 0)
      httpPost += fieldSeparator;
    httpPost += "Event";
    httpPost += keyValSeparator;
    httpPost += eventString;
  }

  // Add initial post body
  if (initialPostBody.length() > 0) {
    if (httpPost.length() > 0)
      httpPost += fieldSeparator;
    httpPost += initialPostBody;
  }

  // Combine initial post body with initial secret and hash
  std::vector<uint8_t> hashInput;
  hashInput.reserve(challengeLen + httpPost.length());
  hashInput.assign(challenge, challenge + challengeLen);
  hashInput.insert(hashInput.end(), httpPost.begin(), httpPost.end());
  Sha256::Hash mac;
  calculateHttpPostMac(macCoproc, &hashInput[0], hashInput.size(), mac);

  char contentLen[5];
  snprintf(contentLen, sizeof(contentLen) / sizeof(contentLen[0]), "%u",
           (hashInput.size() - challengeLen) + (mac.size() * 2) +
               5 /* &MAC= */);

  // Construct full post request
  httpPost = "";
  httpPost += "POST ";
  httpPost += path;
  httpPost += " HTTP/1.1";
  httpPost += newline;
  httpPost += "Host: ";
  httpPost += host;
  httpPost += newline;
  httpPost += "Accept: */*";
  httpPost += newline;
  httpPost += "Content-Length: ";
  httpPost += contentLen;
  httpPost += newline;
  httpPost += "Content-Type: application/x-www-form-urlencoded";
  httpPost += newline;
  httpPost += newline;
  // Add post body
  httpPost.append(reinterpret_cast<char *>(&hashInput[challengeLen]),
                  hashInput.size() - challengeLen);
  // Convert hash to hex string and add to post body
  httpPost += fieldSeparator;
  httpPost += "MAC";
  httpPost += keyValSeparator;
  httpPost += byteArrayToHexString(mac.data(), mac.size());
  httpPost += newline;

  return httpPost;
}

bool WebServerInterface::authPostHttpEvent(DS2465 & macCoproc, PostEvent event,
                                           const std::string & postData,
                                           bool setSecret) {
  const std::string challengeSearch(newline + newline);
  bool result;
  uint8_t challenge[challengeLen];
  std::string response;

  std::memset(challenge, defaultPaddingByte, challengeLen);
  response.reserve(300);

  if (setSecret) {
    result = setHttpPostSecret(macCoproc, m_sessionId);
    if (!result)
      return result;
  }

  // Open connection
  esp8266.clearRecvData(); // Clear received data buffer
  result = (esp8266.openConnection(ESP8266::TCP, serverAddress, 80) ==
            ESP8266::AT_OK);
  if (result) {
    // Request challenge
    result =
        (esp8266.sendData(formatHttpGet(serverAddress, serverChallengePath,
                                        m_sessionIdString)) == ESP8266::AT_OK);
    if (result) {
      // Receive server response
      for (int i = 0; i < 10; i++) {
        while (esp8266.recvIpDataReadable()) {
          char read = esp8266.getcRecvIpData();
          if (response.length() < response.capacity()) {
            response += read;
          } else {
            // Wait for ESP8266 specified recovery time
            wait_ms(ESP8266::sendDataRecoveryTimeMs);
            goto close_get_connection;
          }
        }
        wait_ms(100);
      }
      // Close connection
    close_get_connection:
      esp8266.closeConnection();

      // Parse challenge from response
      size_t challengePos = response.find(challengeSearch);
      const size_t challengeStringLen = challengeLen * 2;
      if ((challengePos != std::string::npos) &&
          ((challengePos + challengeSearch.length() + challengeStringLen) <=
           response.length())) {
        challengePos += challengeSearch.length();
        const std::vector<uint_least8_t> parsedChallenge = hexStringToByteArray(
            response.substr(challengePos, challengeStringLen));
        std::copy(parsedChallenge.begin(), parsedChallenge.end(), challenge);
      }

      // Post sensor data
      result = (esp8266.openConnection(ESP8266::TCP, serverAddress,
                                       serverPort) == ESP8266::AT_OK);
      if (result) {
        result =
            (esp8266.sendData(formatHttpPost(
                 serverAddress, serverPostPath, m_sessionIdString, macCoproc,
                 event, postData, challenge)) == ESP8266::AT_OK);
        wait_ms(
            ESP8266::
                sendDataRecoveryTimeMs); // Wait for ESP8266 specified recovery time
      }
    }

    // Close connection
    esp8266.closeConnection();
  }

  return result;
}

std::string
WebServerInterface::formatSensorDataPostBody(const SensorData & sensorData) {
  // Create initial post body string from input data
  std::ostringstream postBodyStream;
  postBodyStream << "Temp" << keyValSeparator
                 << static_cast<int>(sensorData.temp);
  postBodyStream << fieldSeparator;
  postBodyStream << "FilterLife" << keyValSeparator
                 << static_cast<unsigned>(sensorData.filterLife);
  postBodyStream << fieldSeparator;
  postBodyStream << "TempAlarm" << keyValSeparator
                 << (sensorData.tempAlarm() ? "true" : "false");
  postBodyStream << fieldSeparator;
  postBodyStream << "FilterLifeAlarm" << keyValSeparator
                 << (sensorData.filterLifeAlarm() ? "true" : "false");
  return postBodyStream.str();
}

void WebServerInterface::setSessionId(const RomId & sessionId) {
  m_sessionIdString = byteArrayToHexString(sessionId.data(), sessionId.size());
  m_sessionId = sessionId;
}