feat: Migrate binary settings to json (#920)

## Summary

* This PR introduces a migration from binary file storage to JSON-based
storage for application settings, state, and various credential stores.
This improves readability, maintainability, and allows for easier manual
configuration editing.
* Benefits:
  - Settings files are now JSON and can be easily read/edited manually
  - Easier to inspect application state and settings during development
  - JSON structure is more flexible for future changes
* Drawback: around 15k of additional flash usage
* Compatibility: Seamless migration preserves existing user data

## Additional Context
1. New JSON I/O Infrastructure files:
- JsonSettingsIO: Core JSON serialization/deserialization logic using
ArduinoJson library
- ObfuscationUtils: XOR-based password obfuscation for sensitive data
2. Migrated Components (now use JSON storage with automatic binary
migration):
     - CrossPointSettings (settings.json): Main application settings
- CrossPointState (state.json): Application state (open book, sleep
mode, etc.)
- WifiCredentialStore (wifi.json): WiFi network credentials (Password
Obfuscation: Sensitive data like WiFi passwords, uses XOR encryption
with fixed keys. Note: This is obfuscation, not cryptographic security -
passwords can be recovered with the key)
- KOReaderCredentialStore (koreader.json): KOReader sync credentials
     - RecentBooksStore (recent.json): Recently opened books list
3. Migration Logic
     - Forward Compatibility: New installations use JSON format
- Backward Compatibility: Existing binary files are automatically
migrated to JSON on first load
- Backup Safety: Original binary files are renamed with .bak extension
after successful migration
- Fallback Handling: If JSON parsing fails, system falls back to binary
loading
4. Infrastructure Updates
     - HalStorage: Added rename() method for backup operations

---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _** YES**_

---------

Co-authored-by: Dave Allie <dave@daveallie.com>

lib/KOReaderSync/KOReaderCredentialStore.cpp

@@ -3,73 +3,81 @@
 #include <HalStorage.h>
 #include <Logging.h>
 #include <MD5Builder.h>
+#include <ObfuscationUtils.h>
 #include <Serialization.h>
 
+#include "../../src/JsonSettingsIO.h"
+
 // Initialize the static instance
 KOReaderCredentialStore KOReaderCredentialStore::instance;
 
 namespace {
-// File format version
+// File format version (for binary migration)
 constexpr uint8_t KOREADER_FILE_VERSION = 1;
 
-// KOReader credentials file path
-constexpr char KOREADER_FILE[] = "/.crosspoint/koreader.bin";
+// File paths
+constexpr char KOREADER_FILE_BIN[] = "/.crosspoint/koreader.bin";
+constexpr char KOREADER_FILE_JSON[] = "/.crosspoint/koreader.json";
+constexpr char KOREADER_FILE_BAK[] = "/.crosspoint/koreader.bin.bak";
 
 // Default sync server URL
 constexpr char DEFAULT_SERVER_URL[] = "https://sync.koreader.rocks:443";
 
-// Obfuscation key - "KOReader" in ASCII
-// This is NOT cryptographic security, just prevents casual file reading
-constexpr uint8_t OBFUSCATION_KEY[] = {0x4B, 0x4F, 0x52, 0x65, 0x61, 0x64, 0x65, 0x72};
-constexpr size_t KEY_LENGTH = sizeof(OBFUSCATION_KEY);
-}  // namespace
+// Legacy obfuscation key - "KOReader" in ASCII (only used for binary migration)
+constexpr uint8_t LEGACY_OBFUSCATION_KEY[] = {0x4B, 0x4F, 0x52, 0x65, 0x61, 0x64, 0x65, 0x72};
+constexpr size_t LEGACY_KEY_LENGTH = sizeof(LEGACY_OBFUSCATION_KEY);
 
-void KOReaderCredentialStore::obfuscate(std::string& data) const {
+void legacyDeobfuscate(std::string& data) {
   for (size_t i = 0; i < data.size(); i++) {
-    data[i] ^= OBFUSCATION_KEY[i % KEY_LENGTH];
+    data[i] ^= LEGACY_OBFUSCATION_KEY[i % LEGACY_KEY_LENGTH];
   }
 }
+}  // namespace
 
 bool KOReaderCredentialStore::saveToFile() const {
-  // Make sure the directory exists
   Storage.mkdir("/.crosspoint");
-
-  FsFile file;
-  if (!Storage.openFileForWrite("KRS", KOREADER_FILE, file)) {
-    return false;
-  }
-
-  // Write header
-  serialization::writePod(file, KOREADER_FILE_VERSION);
-
-  // Write username (plaintext - not particularly sensitive)
-  serialization::writeString(file, username);
-  LOG_DBG("KRS", "Saving username: %s", username.c_str());
-
-  // Write password (obfuscated)
-  std::string obfuscatedPwd = password;
-  obfuscate(obfuscatedPwd);
-  serialization::writeString(file, obfuscatedPwd);
-
-  // Write server URL
-  serialization::writeString(file, serverUrl);
-
-  // Write match method
-  serialization::writePod(file, static_cast<uint8_t>(matchMethod));
-
-  file.close();
-  LOG_DBG("KRS", "Saved KOReader credentials to file");
-  return true;
+  return JsonSettingsIO::saveKOReader(*this, KOREADER_FILE_JSON);
 }
 
 bool KOReaderCredentialStore::loadFromFile() {
+  // Try JSON first
+  if (Storage.exists(KOREADER_FILE_JSON)) {
+    String json = Storage.readFile(KOREADER_FILE_JSON);
+    if (!json.isEmpty()) {
+      bool resave = false;
+      bool result = JsonSettingsIO::loadKOReader(*this, json.c_str(), &resave);
+      if (result && resave) {
+        saveToFile();
+        LOG_DBG("KRS", "Resaved KOReader credentials to update format");
+      }
+      return result;
+    }
+  }
+
+  // Fall back to binary migration
+  if (Storage.exists(KOREADER_FILE_BIN)) {
+    if (loadFromBinaryFile()) {
+      if (saveToFile()) {
+        Storage.rename(KOREADER_FILE_BIN, KOREADER_FILE_BAK);
+        LOG_DBG("KRS", "Migrated koreader.bin to koreader.json");
+        return true;
+      } else {
+        LOG_ERR("KRS", "Failed to save KOReader credentials during migration");
+        return false;
+      }
+    }
+  }
+
+  LOG_DBG("KRS", "No credentials file found");
+  return false;
+}
+
+bool KOReaderCredentialStore::loadFromBinaryFile() {
   FsFile file;
-  if (!Storage.openFileForRead("KRS", KOREADER_FILE, file)) {
-    LOG_DBG("KRS", "No credentials file found");
+  if (!Storage.openFileForRead("KRS", KOREADER_FILE_BIN, file)) {
     return false;
   }
 
-  // Read and verify version
   uint8_t version;
   serialization::readPod(file, version);
   if (version != KOREADER_FILE_VERSION) {
@@ -78,29 +86,25 @@ bool KOReaderCredentialStore::loadFromFile() {
     return false;
   }
 
-  // Read username
   if (file.available()) {
     serialization::readString(file, username);
   } else {
     username.clear();
   }
 
-  // Read and deobfuscate password
   if (file.available()) {
     serialization::readString(file, password);
-    obfuscate(password);  // XOR is symmetric, so same function deobfuscates
+    legacyDeobfuscate(password);
   } else {
     password.clear();
   }
 
-  // Read server URL
   if (file.available()) {
     serialization::readString(file, serverUrl);
   } else {
     serverUrl.clear();
   }
 
-  // Read match method
   if (file.available()) {
     uint8_t method;
     serialization::readPod(file, method);
@@ -110,7 +114,7 @@ bool KOReaderCredentialStore::loadFromFile() {
   }
 
   file.close();
-  LOG_DBG("KRS", "Loaded KOReader credentials for user: %s", username.c_str());
+  LOG_DBG("KRS", "Loaded KOReader credentials from binary for user: %s", username.c_str());
   return true;
 }
 

lib/KOReaderSync/KOReaderCredentialStore.h

@@ -8,10 +8,17 @@ enum class DocumentMatchMethod : uint8_t {
   BINARY = 1,    // Match by partial MD5 of file content (more accurate, but files must be identical)
 };
 
+class KOReaderCredentialStore;
+namespace JsonSettingsIO {
+bool saveKOReader(const KOReaderCredentialStore& store, const char* path);
+bool loadKOReader(KOReaderCredentialStore& store, const char* json, bool* needsResave);
+}  // namespace JsonSettingsIO
+
 /**
  * Singleton class for storing KOReader sync credentials on the SD card.
- * Credentials are stored in /sd/.crosspoint/koreader.bin with basic
- * XOR obfuscation to prevent casual reading (not cryptographically secure).
+ * Passwords are XOR-obfuscated with the device's unique hardware MAC address
+ * and base64-encoded before writing to JSON (not cryptographically secure,
+ * but prevents casual reading and ties credentials to the specific device).
  */
 class KOReaderCredentialStore {
  private:
@@ -24,8 +31,10 @@ class KOReaderCredentialStore {
   // Private constructor for singleton
   KOReaderCredentialStore() = default;
 
-  // XOR obfuscation (symmetric - same for encode/decode)
-  void obfuscate(std::string& data) const;
+  bool loadFromBinaryFile();
+
+  friend bool JsonSettingsIO::saveKOReader(const KOReaderCredentialStore&, const char*);
+  friend bool JsonSettingsIO::loadKOReader(KOReaderCredentialStore&, const char*, bool*);
 
  public:
   // Delete copy constructor and assignment

lib/Serialization/ObfuscationUtils.cpp

@@ -0,0 +1,98 @@
+#include "ObfuscationUtils.h"
+
+#include <Logging.h>
+#include <base64.h>
+#include <esp_mac.h>
+#include <mbedtls/base64.h>
+
+#include <cstring>
+
+namespace obfuscation {
+
+namespace {
+constexpr size_t HW_KEY_LEN = 6;
+
+// Simple lazy init — no thread-safety concern on single-core ESP32-C3.
+const uint8_t* getHwKey() {
+  static uint8_t key[HW_KEY_LEN] = {};
+  static bool initialized = false;
+  if (!initialized) {
+    esp_efuse_mac_get_default(key);
+    initialized = true;
+  }
+  return key;
+}
+}  // namespace
+
+void xorTransform(std::string& data) {
+  const uint8_t* key = getHwKey();
+  for (size_t i = 0; i < data.size(); i++) {
+    data[i] ^= key[i % HW_KEY_LEN];
+  }
+}
+
+void xorTransform(std::string& data, const uint8_t* key, size_t keyLen) {
+  if (keyLen == 0 || key == nullptr) return;
+  for (size_t i = 0; i < data.size(); i++) {
+    data[i] ^= key[i % keyLen];
+  }
+}
+
+String obfuscateToBase64(const std::string& plaintext) {
+  if (plaintext.empty()) return "";
+  std::string temp = plaintext;
+  xorTransform(temp);
+  return base64::encode(reinterpret_cast<const uint8_t*>(temp.data()), temp.size());
+}
+
+std::string deobfuscateFromBase64(const char* encoded, bool* ok) {
+  if (encoded == nullptr || encoded[0] == '\0') {
+    if (ok) *ok = false;
+    return "";
+  }
+  if (ok) *ok = true;
+  size_t encodedLen = strlen(encoded);
+  // First call: get required output buffer size
+  size_t decodedLen = 0;
+  int ret = mbedtls_base64_decode(nullptr, 0, &decodedLen, reinterpret_cast<const unsigned char*>(encoded), encodedLen);
+  if (ret != 0 && ret != MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL) {
+    LOG_ERR("OBF", "Base64 decode size query failed (ret=%d)", ret);
+    if (ok) *ok = false;
+    return "";
+  }
+  std::string result(decodedLen, '\0');
+  ret = mbedtls_base64_decode(reinterpret_cast<unsigned char*>(&result[0]), decodedLen, &decodedLen,
+                              reinterpret_cast<const unsigned char*>(encoded), encodedLen);
+  if (ret != 0) {
+    LOG_ERR("OBF", "Base64 decode failed (ret=%d)", ret);
+    if (ok) *ok = false;
+    return "";
+  }
+  result.resize(decodedLen);
+  xorTransform(result);
+  return result;
+}
+
+void selfTest() {
+  const char* testInputs[] = {"", "hello", "WiFi P@ssw0rd!", "a"};
+  bool allPassed = true;
+  for (const char* input : testInputs) {
+    String encoded = obfuscateToBase64(std::string(input));
+    std::string decoded = deobfuscateFromBase64(encoded.c_str());
+    if (decoded != input) {
+      LOG_ERR("OBF", "FAIL: \"%s\" -> \"%s\" -> \"%s\"", input, encoded.c_str(), decoded.c_str());
+      allPassed = false;
+    }
+  }
+  // Verify obfuscated form differs from plaintext
+  String enc = obfuscateToBase64("test123");
+  if (enc == "test123") {
+    LOG_ERR("OBF", "FAIL: obfuscated output identical to plaintext");
+    allPassed = false;
+  }
+  if (allPassed) {
+    LOG_DBG("OBF", "Obfuscation self-test PASSED");
+  }
+}
+
+}  // namespace obfuscation

lib/Serialization/ObfuscationUtils.h

@@ -0,0 +1,35 @@
+#pragma once
+
+#include <Arduino.h>
+
+#include <cstddef>
+#include <cstdint>
+#include <string>
+
+/**
+ * Credential obfuscation utilities using the ESP32's unique hardware MAC address.
+ *
+ * XOR-based obfuscation with the 6-byte eFuse MAC as key. Not cryptographically
+ * secure, but prevents casual reading of credentials on the SD card and ties
+ * obfuscated data to the specific device (cannot be decoded on another chip or PC).
+ *
+ */
+namespace obfuscation {
+
+// XOR obfuscate/deobfuscate in-place using hardware MAC key (symmetric operation)
+void xorTransform(std::string& data);
+
+// Legacy overload for binary migration (uses the old per-store hardcoded keys)
+void xorTransform(std::string& data, const uint8_t* key, size_t keyLen);
+
+// Obfuscate a plaintext string: XOR with hardware key, then base64-encode for JSON storage
+String obfuscateToBase64(const std::string& plaintext);
+
+// Decode base64 and de-obfuscate back to plaintext.
+// Returns empty string on invalid base64 input; sets *ok to false if decode fails.
+std::string deobfuscateFromBase64(const char* encoded, bool* ok = nullptr);
+
+// Self-test: verifies round-trip obfuscation with hardware key. Logs PASS/FAIL.
+void selfTest();
+
+}  // namespace obfuscation

lib/hal/HalStorage.cpp

@@ -36,6 +36,8 @@ bool HalStorage::exists(const char* path) { return SDCard.exists(path); }
 
 bool HalStorage::remove(const char* path) { return SDCard.remove(path); }
 
+bool HalStorage::rename(const char* oldPath, const char* newPath) { return SDCard.rename(oldPath, newPath); }
+
 bool HalStorage::rmdir(const char* path) { return SDCard.rmdir(path); }
 
 bool HalStorage::openFileForRead(const char* moduleName, const char* path, FsFile& file) {

lib/hal/HalStorage.h

@@ -28,6 +28,7 @@ class HalStorage {
   bool mkdir(const char* path, const bool pFlag = true);
   bool exists(const char* path);
   bool remove(const char* path);
+  bool rename(const char* oldPath, const char* newPath);
   bool rmdir(const char* path);
 
   bool openFileForRead(const char* moduleName, const char* path, FsFile& file);

src/CrossPointSettings.cpp

@@ -1,6 +1,7 @@
 #include "CrossPointSettings.h"
 
 #include <HalStorage.h>
+#include <JsonSettingsIO.h>
 #include <Logging.h>
 #include <Serialization.h>
 
@@ -22,28 +23,9 @@ void readAndValidate(FsFile& file, uint8_t& member, const uint8_t maxValue) {
 
 namespace {
 constexpr uint8_t SETTINGS_FILE_VERSION = 1;
-// SETTINGS_COUNT is now calculated automatically in saveToFile
-constexpr char SETTINGS_FILE[] = "/.crosspoint/settings.bin";
-
-// Validate front button mapping to ensure each hardware button is unique.
-// If duplicates are detected, reset to the default physical order to prevent invalid mappings.
-void validateFrontButtonMapping(CrossPointSettings& settings) {
-  // Snapshot the logical->hardware mapping so we can compare for duplicates.
-  const uint8_t mapping[] = {settings.frontButtonBack, settings.frontButtonConfirm, settings.frontButtonLeft,
-                             settings.frontButtonRight};
-  for (size_t i = 0; i < 4; i++) {
-    for (size_t j = i + 1; j < 4; j++) {
-      if (mapping[i] == mapping[j]) {
-        // Duplicate detected: restore the default physical order (Back, Confirm, Left, Right).
-        settings.frontButtonBack = CrossPointSettings::FRONT_HW_BACK;
-        settings.frontButtonConfirm = CrossPointSettings::FRONT_HW_CONFIRM;
-        settings.frontButtonLeft = CrossPointSettings::FRONT_HW_LEFT;
-        settings.frontButtonRight = CrossPointSettings::FRONT_HW_RIGHT;
-        return;
-      }
-    }
-  }
-}
+constexpr char SETTINGS_FILE_BIN[] = "/.crosspoint/settings.bin";
+constexpr char SETTINGS_FILE_JSON[] = "/.crosspoint/settings.json";
+constexpr char SETTINGS_FILE_BAK[] = "/.crosspoint/settings.bin.bak";
 
 // Convert legacy front button layout into explicit logical->hardware mapping.
 void applyLegacyFrontButtonLayout(CrossPointSettings& settings) {
@@ -77,95 +59,65 @@ void applyLegacyFrontButtonLayout(CrossPointSettings& settings) {
 }
 }  // namespace
 
-class SettingsWriter {
- public:
-  bool is_counting = false;
-  uint8_t item_count = 0;
-  template <typename T>
-
-  void writeItem(FsFile& file, const T& value) {
-    if (is_counting) {
-      item_count++;
-    } else {
-      serialization::writePod(file, value);
+void CrossPointSettings::validateFrontButtonMapping(CrossPointSettings& settings) {
+  const uint8_t mapping[] = {settings.frontButtonBack, settings.frontButtonConfirm, settings.frontButtonLeft,
+                             settings.frontButtonRight};
+  for (size_t i = 0; i < 4; i++) {
+    for (size_t j = i + 1; j < 4; j++) {
+      if (mapping[i] == mapping[j]) {
+        settings.frontButtonBack = FRONT_HW_BACK;
+        settings.frontButtonConfirm = FRONT_HW_CONFIRM;
+        settings.frontButtonLeft = FRONT_HW_LEFT;
+        settings.frontButtonRight = FRONT_HW_RIGHT;
+        return;
+      }
     }
   }
-
-  void writeItemString(FsFile& file, const char* value) {
-    if (is_counting) {
-      item_count++;
-    } else {
-      serialization::writeString(file, std::string(value));
-    }
-  }
-};
-
-uint8_t CrossPointSettings::writeSettings(FsFile& file, bool count_only) const {
-  SettingsWriter writer;
-  writer.is_counting = count_only;
-
-  writer.writeItem(file, sleepScreen);
-  writer.writeItem(file, extraParagraphSpacing);
-  writer.writeItem(file, shortPwrBtn);
-  writer.writeItem(file, statusBar);
-  writer.writeItem(file, orientation);
-  writer.writeItem(file, frontButtonLayout);  // legacy
-  writer.writeItem(file, sideButtonLayout);
-  writer.writeItem(file, fontFamily);
-  writer.writeItem(file, fontSize);
-  writer.writeItem(file, lineSpacing);
-  writer.writeItem(file, paragraphAlignment);
-  writer.writeItem(file, sleepTimeout);
-  writer.writeItem(file, refreshFrequency);
-  writer.writeItem(file, screenMargin);
-  writer.writeItem(file, sleepScreenCoverMode);
-  writer.writeItemString(file, opdsServerUrl);
-  writer.writeItem(file, textAntiAliasing);
-  writer.writeItem(file, hideBatteryPercentage);
-  writer.writeItem(file, longPressChapterSkip);
-  writer.writeItem(file, hyphenationEnabled);
-  writer.writeItemString(file, opdsUsername);
-  writer.writeItemString(file, opdsPassword);
-  writer.writeItem(file, sleepScreenCoverFilter);
-  writer.writeItem(file, uiTheme);
-  writer.writeItem(file, frontButtonBack);
-  writer.writeItem(file, frontButtonConfirm);
-  writer.writeItem(file, frontButtonLeft);
-  writer.writeItem(file, frontButtonRight);
-  writer.writeItem(file, fadingFix);
-  writer.writeItem(file, embeddedStyle);
-  // New fields need to be added at end for backward compatibility
-
-  return writer.item_count;
 }
 
 bool CrossPointSettings::saveToFile() const {
-  // Make sure the directory exists
   Storage.mkdir("/.crosspoint");
-
-  FsFile outputFile;
-  if (!Storage.openFileForWrite("CPS", SETTINGS_FILE, outputFile)) {
-    return false;
-  }
-
-  // First pass: count the items
-  uint8_t item_count = writeSettings(outputFile, true);  // This will just count, not write
-
-  // Write header
-  serialization::writePod(outputFile, SETTINGS_FILE_VERSION);
-  serialization::writePod(outputFile, static_cast<uint8_t>(item_count));
-  // Second pass: actually write the settings
-  writeSettings(outputFile);  // This will write the actual data
-
-  outputFile.close();
-
-  LOG_DBG("CPS", "Settings saved to file");
-  return true;
+  return JsonSettingsIO::saveSettings(*this, SETTINGS_FILE_JSON);
 }
 
 bool CrossPointSettings::loadFromFile() {
+  // Try JSON first
+  if (Storage.exists(SETTINGS_FILE_JSON)) {
+    String json = Storage.readFile(SETTINGS_FILE_JSON);
+    if (!json.isEmpty()) {
+      bool resave = false;
+      bool result = JsonSettingsIO::loadSettings(*this, json.c_str(), &resave);
+      if (result && resave) {
+        if (saveToFile()) {
+          LOG_DBG("CPS", "Resaved settings to update format");
+        } else {
+          LOG_ERR("CPS", "Failed to resave settings after format update");
+        }
+      }
+      return result;
+    }
+  }
+
+  // Fall back to binary migration
+  if (Storage.exists(SETTINGS_FILE_BIN)) {
+    if (loadFromBinaryFile()) {
+      if (saveToFile()) {
+        Storage.rename(SETTINGS_FILE_BIN, SETTINGS_FILE_BAK);
+        LOG_DBG("CPS", "Migrated settings.bin to settings.json");
+        return true;
+      } else {
+        LOG_ERR("CPS", "Failed to save migrated settings to JSON");
+        return false;
+      }
+    }
+  }
+
+  return false;
+}
+
+bool CrossPointSettings::loadFromBinaryFile() {
   FsFile inputFile;
-  if (!Storage.openFileForRead("CPS", SETTINGS_FILE, inputFile)) {
+  if (!Storage.openFileForRead("CPS", SETTINGS_FILE_BIN, inputFile)) {
     return false;
   }
 
@@ -180,9 +132,7 @@ bool CrossPointSettings::loadFromFile() {
   uint8_t fileSettingsCount = 0;
   serialization::readPod(inputFile, fileSettingsCount);
 
-  // load settings that exist (support older files with fewer fields)
   uint8_t settingsRead = 0;
-  // Track whether remap fields were present in the settings file.
   bool frontButtonMappingRead = false;
   do {
     readAndValidate(inputFile, sleepScreen, SLEEP_SCREEN_MODE_COUNT);
@@ -195,7 +145,7 @@ bool CrossPointSettings::loadFromFile() {
     if (++settingsRead >= fileSettingsCount) break;
     readAndValidate(inputFile, orientation, ORIENTATION_COUNT);
     if (++settingsRead >= fileSettingsCount) break;
-    readAndValidate(inputFile, frontButtonLayout, FRONT_BUTTON_LAYOUT_COUNT);  // legacy
+    readAndValidate(inputFile, frontButtonLayout, FRONT_BUTTON_LAYOUT_COUNT);
     if (++settingsRead >= fileSettingsCount) break;
     readAndValidate(inputFile, sideButtonLayout, SIDE_BUTTON_LAYOUT_COUNT);
     if (++settingsRead >= fileSettingsCount) break;
@@ -261,17 +211,16 @@ bool CrossPointSettings::loadFromFile() {
     if (++settingsRead >= fileSettingsCount) break;
     serialization::readPod(inputFile, embeddedStyle);
     if (++settingsRead >= fileSettingsCount) break;
-    // New fields added at end for backward compatibility
   } while (false);
 
   if (frontButtonMappingRead) {
-    validateFrontButtonMapping(*this);
+    CrossPointSettings::validateFrontButtonMapping(*this);
   } else {
     applyLegacyFrontButtonLayout(*this);
   }
 
   inputFile.close();
-  LOG_DBG("CPS", "Settings loaded from file");
+  LOG_DBG("CPS", "Settings loaded from binary file");
   return true;
 }
 

src/CrossPointSettings.h

@@ -191,6 +191,12 @@ class CrossPointSettings {
   bool saveToFile() const;
   bool loadFromFile();
 
+  static void validateFrontButtonMapping(CrossPointSettings& settings);
+
+ private:
+  bool loadFromBinaryFile();
+
+ public:
   float getReaderLineCompression() const;
   unsigned long getSleepTimeoutMs() const;
   int getRefreshFrequency() const;

src/CrossPointState.cpp

@@ -1,34 +1,53 @@
 #include "CrossPointState.h"
 
 #include <HalStorage.h>
+#include <JsonSettingsIO.h>
 #include <Logging.h>
 #include <Serialization.h>
 
 namespace {
 constexpr uint8_t STATE_FILE_VERSION = 4;
-constexpr char STATE_FILE[] = "/.crosspoint/state.bin";
+constexpr char STATE_FILE_BIN[] = "/.crosspoint/state.bin";
+constexpr char STATE_FILE_JSON[] = "/.crosspoint/state.json";
+constexpr char STATE_FILE_BAK[] = "/.crosspoint/state.bin.bak";
 }  // namespace
 
 CrossPointState CrossPointState::instance;
 
 bool CrossPointState::saveToFile() const {
-  FsFile outputFile;
-  if (!Storage.openFileForWrite("CPS", STATE_FILE, outputFile)) {
-    return false;
-  }
-
-  serialization::writePod(outputFile, STATE_FILE_VERSION);
-  serialization::writeString(outputFile, openEpubPath);
-  serialization::writePod(outputFile, lastSleepImage);
-  serialization::writePod(outputFile, readerActivityLoadCount);
-  serialization::writePod(outputFile, lastSleepFromReader);
-  outputFile.close();
-  return true;
+  Storage.mkdir("/.crosspoint");
+  return JsonSettingsIO::saveState(*this, STATE_FILE_JSON);
 }
 
 bool CrossPointState::loadFromFile() {
+  // Try JSON first
+  if (Storage.exists(STATE_FILE_JSON)) {
+    String json = Storage.readFile(STATE_FILE_JSON);
+    if (!json.isEmpty()) {
+      return JsonSettingsIO::loadState(*this, json.c_str());
+    }
+  }
+
+  // Fall back to binary migration
+  if (Storage.exists(STATE_FILE_BIN)) {
+    if (loadFromBinaryFile()) {
+      if (saveToFile()) {
+        Storage.rename(STATE_FILE_BIN, STATE_FILE_BAK);
+        LOG_DBG("CPS", "Migrated state.bin to state.json");
+        return true;
+      } else {
+        LOG_ERR("CPS", "Failed to save state during migration");
+        return false;
+      }
+    }
+  }
+
+  return false;
+}
+
+bool CrossPointState::loadFromBinaryFile() {
   FsFile inputFile;
-  if (!Storage.openFileForRead("CPS", STATE_FILE, inputFile)) {
+  if (!Storage.openFileForRead("CPS", STATE_FILE_BIN, inputFile)) {
     return false;
   }
 

src/CrossPointState.h

@@ -19,6 +19,9 @@ class CrossPointState {
   bool saveToFile() const;
 
   bool loadFromFile();
+
+ private:
+  bool loadFromBinaryFile();
 };
 
 // Helper macro to access settings

src/JsonSettingsIO.cpp

@@ -0,0 +1,281 @@
+#include "JsonSettingsIO.h"
+
+#include <ArduinoJson.h>
+#include <HalStorage.h>
+#include <Logging.h>
+#include <ObfuscationUtils.h>
+
+#include <cstring>
+
+#include "CrossPointSettings.h"
+#include "CrossPointState.h"
+#include "KOReaderCredentialStore.h"
+#include "RecentBooksStore.h"
+#include "WifiCredentialStore.h"
+
+// ---- CrossPointState ----
+
+bool JsonSettingsIO::saveState(const CrossPointState& s, const char* path) {
+  JsonDocument doc;
+  doc["openEpubPath"] = s.openEpubPath;
+  doc["lastSleepImage"] = s.lastSleepImage;
+  doc["readerActivityLoadCount"] = s.readerActivityLoadCount;
+  doc["lastSleepFromReader"] = s.lastSleepFromReader;
+
+  String json;
+  serializeJson(doc, json);
+  return Storage.writeFile(path, json);
+}
+
+bool JsonSettingsIO::loadState(CrossPointState& s, const char* json) {
+  JsonDocument doc;
+  auto error = deserializeJson(doc, json);
+  if (error) {
+    LOG_ERR("CPS", "JSON parse error: %s", error.c_str());
+    return false;
+  }
+
+  s.openEpubPath = doc["openEpubPath"] | std::string("");
+  s.lastSleepImage = doc["lastSleepImage"] | (uint8_t)0;
+  s.readerActivityLoadCount = doc["readerActivityLoadCount"] | (uint8_t)0;
+  s.lastSleepFromReader = doc["lastSleepFromReader"] | false;
+  return true;
+}
+
+// ---- CrossPointSettings ----
+
+bool JsonSettingsIO::saveSettings(const CrossPointSettings& s, const char* path) {
+  JsonDocument doc;
+
+  doc["sleepScreen"] = s.sleepScreen;
+  doc["sleepScreenCoverMode"] = s.sleepScreenCoverMode;
+  doc["sleepScreenCoverFilter"] = s.sleepScreenCoverFilter;
+  doc["statusBar"] = s.statusBar;
+  doc["extraParagraphSpacing"] = s.extraParagraphSpacing;
+  doc["textAntiAliasing"] = s.textAntiAliasing;
+  doc["shortPwrBtn"] = s.shortPwrBtn;
+  doc["orientation"] = s.orientation;
+  doc["sideButtonLayout"] = s.sideButtonLayout;
+  doc["frontButtonBack"] = s.frontButtonBack;
+  doc["frontButtonConfirm"] = s.frontButtonConfirm;
+  doc["frontButtonLeft"] = s.frontButtonLeft;
+  doc["frontButtonRight"] = s.frontButtonRight;
+  doc["fontFamily"] = s.fontFamily;
+  doc["fontSize"] = s.fontSize;
+  doc["lineSpacing"] = s.lineSpacing;
+  doc["paragraphAlignment"] = s.paragraphAlignment;
+  doc["sleepTimeout"] = s.sleepTimeout;
+  doc["refreshFrequency"] = s.refreshFrequency;
+  doc["screenMargin"] = s.screenMargin;
+  doc["opdsServerUrl"] = s.opdsServerUrl;
+  doc["opdsUsername"] = s.opdsUsername;
+  doc["opdsPassword_obf"] = obfuscation::obfuscateToBase64(s.opdsPassword);
+  doc["hideBatteryPercentage"] = s.hideBatteryPercentage;
+  doc["longPressChapterSkip"] = s.longPressChapterSkip;
+  doc["hyphenationEnabled"] = s.hyphenationEnabled;
+  doc["uiTheme"] = s.uiTheme;
+  doc["fadingFix"] = s.fadingFix;
+  doc["embeddedStyle"] = s.embeddedStyle;
+
+  String json;
+  serializeJson(doc, json);
+  return Storage.writeFile(path, json);
+}
+
+bool JsonSettingsIO::loadSettings(CrossPointSettings& s, const char* json, bool* needsResave) {
+  if (needsResave) *needsResave = false;
+  JsonDocument doc;
+  auto error = deserializeJson(doc, json);
+  if (error) {
+    LOG_ERR("CPS", "JSON parse error: %s", error.c_str());
+    return false;
+  }
+
+  using S = CrossPointSettings;
+  auto clamp = [](uint8_t val, uint8_t maxVal, uint8_t def) -> uint8_t { return val < maxVal ? val : def; };
+
+  s.sleepScreen = clamp(doc["sleepScreen"] | (uint8_t)S::DARK, S::SLEEP_SCREEN_MODE_COUNT, S::DARK);
+  s.sleepScreenCoverMode =
+      clamp(doc["sleepScreenCoverMode"] | (uint8_t)S::FIT, S::SLEEP_SCREEN_COVER_MODE_COUNT, S::FIT);
+  s.sleepScreenCoverFilter =
+      clamp(doc["sleepScreenCoverFilter"] | (uint8_t)S::NO_FILTER, S::SLEEP_SCREEN_COVER_FILTER_COUNT, S::NO_FILTER);
+  s.statusBar = clamp(doc["statusBar"] | (uint8_t)S::FULL, S::STATUS_BAR_MODE_COUNT, S::FULL);
+  s.extraParagraphSpacing = doc["extraParagraphSpacing"] | (uint8_t)1;
+  s.textAntiAliasing = doc["textAntiAliasing"] | (uint8_t)1;
+  s.shortPwrBtn = clamp(doc["shortPwrBtn"] | (uint8_t)S::IGNORE, S::SHORT_PWRBTN_COUNT, S::IGNORE);
+  s.orientation = clamp(doc["orientation"] | (uint8_t)S::PORTRAIT, S::ORIENTATION_COUNT, S::PORTRAIT);
+  s.sideButtonLayout =
+      clamp(doc["sideButtonLayout"] | (uint8_t)S::PREV_NEXT, S::SIDE_BUTTON_LAYOUT_COUNT, S::PREV_NEXT);
+  s.frontButtonBack =
+      clamp(doc["frontButtonBack"] | (uint8_t)S::FRONT_HW_BACK, S::FRONT_BUTTON_HARDWARE_COUNT, S::FRONT_HW_BACK);
+  s.frontButtonConfirm = clamp(doc["frontButtonConfirm"] | (uint8_t)S::FRONT_HW_CONFIRM, S::FRONT_BUTTON_HARDWARE_COUNT,
+                               S::FRONT_HW_CONFIRM);
+  s.frontButtonLeft =
+      clamp(doc["frontButtonLeft"] | (uint8_t)S::FRONT_HW_LEFT, S::FRONT_BUTTON_HARDWARE_COUNT, S::FRONT_HW_LEFT);
+  s.frontButtonRight =
+      clamp(doc["frontButtonRight"] | (uint8_t)S::FRONT_HW_RIGHT, S::FRONT_BUTTON_HARDWARE_COUNT, S::FRONT_HW_RIGHT);
+  CrossPointSettings::validateFrontButtonMapping(s);
+  s.fontFamily = clamp(doc["fontFamily"] | (uint8_t)S::BOOKERLY, S::FONT_FAMILY_COUNT, S::BOOKERLY);
+  s.fontSize = clamp(doc["fontSize"] | (uint8_t)S::MEDIUM, S::FONT_SIZE_COUNT, S::MEDIUM);
+  s.lineSpacing = clamp(doc["lineSpacing"] | (uint8_t)S::NORMAL, S::LINE_COMPRESSION_COUNT, S::NORMAL);
+  s.paragraphAlignment =
+      clamp(doc["paragraphAlignment"] | (uint8_t)S::JUSTIFIED, S::PARAGRAPH_ALIGNMENT_COUNT, S::JUSTIFIED);
+  s.sleepTimeout = clamp(doc["sleepTimeout"] | (uint8_t)S::SLEEP_10_MIN, S::SLEEP_TIMEOUT_COUNT, S::SLEEP_10_MIN);
+  s.refreshFrequency =
+      clamp(doc["refreshFrequency"] | (uint8_t)S::REFRESH_15, S::REFRESH_FREQUENCY_COUNT, S::REFRESH_15);
+  s.screenMargin = doc["screenMargin"] | (uint8_t)5;
+  s.hideBatteryPercentage =
+      clamp(doc["hideBatteryPercentage"] | (uint8_t)S::HIDE_NEVER, S::HIDE_BATTERY_PERCENTAGE_COUNT, S::HIDE_NEVER);
+  s.longPressChapterSkip = doc["longPressChapterSkip"] | (uint8_t)1;
+  s.hyphenationEnabled = doc["hyphenationEnabled"] | (uint8_t)0;
+  s.uiTheme = doc["uiTheme"] | (uint8_t)S::LYRA;
+  s.fadingFix = doc["fadingFix"] | (uint8_t)0;
+  s.embeddedStyle = doc["embeddedStyle"] | (uint8_t)1;
+
+  const char* url = doc["opdsServerUrl"] | "";
+  strncpy(s.opdsServerUrl, url, sizeof(s.opdsServerUrl) - 1);
+  s.opdsServerUrl[sizeof(s.opdsServerUrl) - 1] = '\0';
+
+  const char* user = doc["opdsUsername"] | "";
+  strncpy(s.opdsUsername, user, sizeof(s.opdsUsername) - 1);
+  s.opdsUsername[sizeof(s.opdsUsername) - 1] = '\0';
+
+  bool passOk = false;
+  std::string pass = obfuscation::deobfuscateFromBase64(doc["opdsPassword_obf"] | "", &passOk);
+  if (!passOk || pass.empty()) {
+    pass = doc["opdsPassword"] | "";
+    if (!pass.empty() && needsResave) *needsResave = true;
+  }
+  strncpy(s.opdsPassword, pass.c_str(), sizeof(s.opdsPassword) - 1);
+  s.opdsPassword[sizeof(s.opdsPassword) - 1] = '\0';
+  LOG_DBG("CPS", "Settings loaded from file");
+  return true;
+}
+
+// ---- KOReaderCredentialStore ----
+
+bool JsonSettingsIO::saveKOReader(const KOReaderCredentialStore& store, const char* path) {
+  JsonDocument doc;
+  doc["username"] = store.getUsername();
+  doc["password_obf"] = obfuscation::obfuscateToBase64(store.getPassword());
+  doc["serverUrl"] = store.getServerUrl();
+  doc["matchMethod"] = static_cast<uint8_t>(store.getMatchMethod());
+
+  String json;
+  serializeJson(doc, json);
+  return Storage.writeFile(path, json);
+}
+
+bool JsonSettingsIO::loadKOReader(KOReaderCredentialStore& store, const char* json, bool* needsResave) {
+  if (needsResave) *needsResave = false;
+  JsonDocument doc;
+  auto error = deserializeJson(doc, json);
+  if (error) {
+    LOG_ERR("KRS", "JSON parse error: %s", error.c_str());
+    return false;
+  }
+
+  store.username = doc["username"] | std::string("");
+  bool ok = false;
+  store.password = obfuscation::deobfuscateFromBase64(doc["password_obf"] | "", &ok);
+  if (!ok || store.password.empty()) {
+    store.password = doc["password"] | std::string("");
+    if (!store.password.empty() && needsResave) *needsResave = true;
+  }
+  store.serverUrl = doc["serverUrl"] | std::string("");
+  uint8_t method = doc["matchMethod"] | (uint8_t)0;
+  store.matchMethod = static_cast<DocumentMatchMethod>(method);
+
+  LOG_DBG("KRS", "Loaded KOReader credentials for user: %s", store.username.c_str());
+  return true;
+}
+
+// ---- WifiCredentialStore ----
+
+bool JsonSettingsIO::saveWifi(const WifiCredentialStore& store, const char* path) {
+  JsonDocument doc;
+  doc["lastConnectedSsid"] = store.getLastConnectedSsid();
+
+  JsonArray arr = doc["credentials"].to<JsonArray>();
+  for (const auto& cred : store.getCredentials()) {
+    JsonObject obj = arr.add<JsonObject>();
+    obj["ssid"] = cred.ssid;
+    obj["password_obf"] = obfuscation::obfuscateToBase64(cred.password);
+  }
+
+  String json;
+  serializeJson(doc, json);
+  return Storage.writeFile(path, json);
+}
+
+bool JsonSettingsIO::loadWifi(WifiCredentialStore& store, const char* json, bool* needsResave) {
+  if (needsResave) *needsResave = false;
+  JsonDocument doc;
+  auto error = deserializeJson(doc, json);
+  if (error) {
+    LOG_ERR("WCS", "JSON parse error: %s", error.c_str());
+    return false;
+  }
+
+  store.lastConnectedSsid = doc["lastConnectedSsid"] | std::string("");
+
+  store.credentials.clear();
+  JsonArray arr = doc["credentials"].as<JsonArray>();
+  for (JsonObject obj : arr) {
+    if (store.credentials.size() >= store.MAX_NETWORKS) break;
+    WifiCredential cred;
+    cred.ssid = obj["ssid"] | std::string("");
+    bool ok = false;
+    cred.password = obfuscation::deobfuscateFromBase64(obj["password_obf"] | "", &ok);
+    if (!ok || cred.password.empty()) {
+      cred.password = obj["password"] | std::string("");
+      if (!cred.password.empty() && needsResave) *needsResave = true;
+    }
+    store.credentials.push_back(cred);
+  }
+
+  LOG_DBG("WCS", "Loaded %zu WiFi credentials from file", store.credentials.size());
+  return true;
+}
+
+// ---- RecentBooksStore ----
+
+bool JsonSettingsIO::saveRecentBooks(const RecentBooksStore& store, const char* path) {
+  JsonDocument doc;
+  JsonArray arr = doc["books"].to<JsonArray>();
+  for (const auto& book : store.getBooks()) {
+    JsonObject obj = arr.add<JsonObject>();
+    obj["path"] = book.path;
+    obj["title"] = book.title;
+    obj["author"] = book.author;
+    obj["coverBmpPath"] = book.coverBmpPath;
+  }
+
+  String json;
+  serializeJson(doc, json);
+  return Storage.writeFile(path, json);
+}
+
+bool JsonSettingsIO::loadRecentBooks(RecentBooksStore& store, const char* json) {
+  JsonDocument doc;
+  auto error = deserializeJson(doc, json);
+  if (error) {
+    LOG_ERR("RBS", "JSON parse error: %s", error.c_str());
+    return false;
+  }
+
+  store.recentBooks.clear();
+  JsonArray arr = doc["books"].as<JsonArray>();
+  for (JsonObject obj : arr) {
+    if (store.getCount() >= 10) break;
+    RecentBook book;
+    book.path = obj["path"] | std::string("");
+    book.title = obj["title"] | std::string("");
+    book.author = obj["author"] | std::string("");
+    book.coverBmpPath = obj["coverBmpPath"] | std::string("");
+    store.recentBooks.push_back(book);
+  }
+
+  LOG_DBG("RBS", "Recent books loaded from file (%d entries)", store.getCount());
+  return true;
+}

src/JsonSettingsIO.h

@@ -0,0 +1,31 @@
+#pragma once
+
+class CrossPointSettings;
+class CrossPointState;
+class WifiCredentialStore;
+class KOReaderCredentialStore;
+class RecentBooksStore;
+
+namespace JsonSettingsIO {
+
+// CrossPointSettings
+bool saveSettings(const CrossPointSettings& s, const char* path);
+bool loadSettings(CrossPointSettings& s, const char* json, bool* needsResave = nullptr);
+
+// CrossPointState
+bool saveState(const CrossPointState& s, const char* path);
+bool loadState(CrossPointState& s, const char* json);
+
+// WifiCredentialStore
+bool saveWifi(const WifiCredentialStore& store, const char* path);
+bool loadWifi(WifiCredentialStore& store, const char* json, bool* needsResave = nullptr);
+
+// KOReaderCredentialStore
+bool saveKOReader(const KOReaderCredentialStore& store, const char* path);
+bool loadKOReader(KOReaderCredentialStore& store, const char* json, bool* needsResave = nullptr);
+
+// RecentBooksStore
+bool saveRecentBooks(const RecentBooksStore& store, const char* path);
+bool loadRecentBooks(RecentBooksStore& store, const char* json);
+
+}  // namespace JsonSettingsIO

src/RecentBooksStore.cpp

@@ -2,6 +2,7 @@
 
 #include <Epub.h>
 #include <HalStorage.h>
+#include <JsonSettingsIO.h>
 #include <Logging.h>
 #include <Serialization.h>
 #include <Xtc.h>
@@ -12,7 +13,9 @@
 
 namespace {
 constexpr uint8_t RECENT_BOOKS_FILE_VERSION = 3;
-constexpr char RECENT_BOOKS_FILE[] = "/.crosspoint/recent.bin";
+constexpr char RECENT_BOOKS_FILE_BIN[] = "/.crosspoint/recent.bin";
+constexpr char RECENT_BOOKS_FILE_JSON[] = "/.crosspoint/recent.json";
+constexpr char RECENT_BOOKS_FILE_BAK[] = "/.crosspoint/recent.bin.bak";
 constexpr int MAX_RECENT_BOOKS = 10;
 }  // namespace
 
@@ -52,28 +55,8 @@ void RecentBooksStore::updateBook(const std::string& path, const std::string& ti
 }
 
 bool RecentBooksStore::saveToFile() const {
-  // Make sure the directory exists
   Storage.mkdir("/.crosspoint");
-
-  FsFile outputFile;
-  if (!Storage.openFileForWrite("RBS", RECENT_BOOKS_FILE, outputFile)) {
-    return false;
-  }
-
-  serialization::writePod(outputFile, RECENT_BOOKS_FILE_VERSION);
-  const uint8_t count = static_cast<uint8_t>(recentBooks.size());
-  serialization::writePod(outputFile, count);
-
-  for (const auto& book : recentBooks) {
-    serialization::writeString(outputFile, book.path);
-    serialization::writeString(outputFile, book.title);
-    serialization::writeString(outputFile, book.author);
-    serialization::writeString(outputFile, book.coverBmpPath);
-  }
-
-  outputFile.close();
-  LOG_DBG("RBS", "Recent books saved to file (%d entries)", count);
-  return true;
+  return JsonSettingsIO::saveRecentBooks(*this, RECENT_BOOKS_FILE_JSON);
 }
 
 RecentBook RecentBooksStore::getDataFromBook(std::string path) const {
@@ -107,8 +90,30 @@ RecentBook RecentBooksStore::getDataFromBook(std::string path) const {
 }
 
 bool RecentBooksStore::loadFromFile() {
+  // Try JSON first
+  if (Storage.exists(RECENT_BOOKS_FILE_JSON)) {
+    String json = Storage.readFile(RECENT_BOOKS_FILE_JSON);
+    if (!json.isEmpty()) {
+      return JsonSettingsIO::loadRecentBooks(*this, json.c_str());
+    }
+  }
+
+  // Fall back to binary migration
+  if (Storage.exists(RECENT_BOOKS_FILE_BIN)) {
+    if (loadFromBinaryFile()) {
+      saveToFile();
+      Storage.rename(RECENT_BOOKS_FILE_BIN, RECENT_BOOKS_FILE_BAK);
+      LOG_DBG("RBS", "Migrated recent.bin to recent.json");
+      return true;
+    }
+  }
+
+  return false;
+}
+
+bool RecentBooksStore::loadFromBinaryFile() {
   FsFile inputFile;
-  if (!Storage.openFileForRead("RBS", RECENT_BOOKS_FILE, inputFile)) {
+  if (!Storage.openFileForRead("RBS", RECENT_BOOKS_FILE_BIN, inputFile)) {
     return false;
   }
 
@@ -173,6 +178,6 @@ bool RecentBooksStore::loadFromFile() {
   }
 
   inputFile.close();
-  LOG_DBG("RBS", "Recent books loaded from file (%d entries)", recentBooks.size());
+  LOG_DBG("RBS", "Recent books loaded from binary file (%d entries)", static_cast<int>(recentBooks.size()));
   return true;
 }

src/RecentBooksStore.h

@@ -11,12 +11,19 @@ struct RecentBook {
   bool operator==(const RecentBook& other) const { return path == other.path; }
 };
 
+class RecentBooksStore;
+namespace JsonSettingsIO {
+bool loadRecentBooks(RecentBooksStore& store, const char* json);
+}  // namespace JsonSettingsIO
+
 class RecentBooksStore {
   // Static instance
   static RecentBooksStore instance;
 
   std::vector<RecentBook> recentBooks;
 
+  friend bool JsonSettingsIO::loadRecentBooks(RecentBooksStore&, const char*);
+
  public:
   ~RecentBooksStore() = default;
 
@@ -40,6 +47,9 @@ class RecentBooksStore {
 
   bool loadFromFile();
   RecentBook getDataFromBook(std::string path) const;
+
+ private:
+  bool loadFromBinaryFile();
 };
 
 // Helper macro to access recent books store

src/WifiCredentialStore.cpp

@@ -1,70 +1,77 @@
 #include "WifiCredentialStore.h"
 
 #include <HalStorage.h>
+#include <JsonSettingsIO.h>
 #include <Logging.h>
+#include <ObfuscationUtils.h>
 #include <Serialization.h>
 
 // Initialize the static instance
 WifiCredentialStore WifiCredentialStore::instance;
 
 namespace {
-// File format version
-constexpr uint8_t WIFI_FILE_VERSION = 2;  // Increased version
+// File format version (for binary migration)
+constexpr uint8_t WIFI_FILE_VERSION = 2;
 
-// WiFi credentials file path
-constexpr char WIFI_FILE[] = "/.crosspoint/wifi.bin";
+// File paths
+constexpr char WIFI_FILE_BIN[] = "/.crosspoint/wifi.bin";
+constexpr char WIFI_FILE_JSON[] = "/.crosspoint/wifi.json";
+constexpr char WIFI_FILE_BAK[] = "/.crosspoint/wifi.bin.bak";
 
-// Obfuscation key - "CrossPoint" in ASCII
-// This is NOT cryptographic security, just prevents casual file reading
-constexpr uint8_t OBFUSCATION_KEY[] = {0x43, 0x72, 0x6F, 0x73, 0x73, 0x50, 0x6F, 0x69, 0x6E, 0x74};
-constexpr size_t KEY_LENGTH = sizeof(OBFUSCATION_KEY);
-}  // namespace
+// Legacy obfuscation key - "CrossPoint" in ASCII (only used for binary migration)
+constexpr uint8_t LEGACY_OBFUSCATION_KEY[] = {0x43, 0x72, 0x6F, 0x73, 0x73, 0x50, 0x6F, 0x69, 0x6E, 0x74};
+constexpr size_t LEGACY_KEY_LENGTH = sizeof(LEGACY_OBFUSCATION_KEY);
 
-void WifiCredentialStore::obfuscate(std::string& data) const {
-  LOG_DBG("WCS", "Obfuscating/deobfuscating %zu bytes", data.size());
+void legacyDeobfuscate(std::string& data) {
   for (size_t i = 0; i < data.size(); i++) {
-    data[i] ^= OBFUSCATION_KEY[i % KEY_LENGTH];
+    data[i] ^= LEGACY_OBFUSCATION_KEY[i % LEGACY_KEY_LENGTH];
   }
 }
+}  // namespace
 
 bool WifiCredentialStore::saveToFile() const {
-  // Make sure the directory exists
   Storage.mkdir("/.crosspoint");
-
-  FsFile file;
-  if (!Storage.openFileForWrite("WCS", WIFI_FILE, file)) {
-    return false;
-  }
-
-  // Write header
-  serialization::writePod(file, WIFI_FILE_VERSION);
-  serialization::writeString(file, lastConnectedSsid);  // Save last connected SSID
-  serialization::writePod(file, static_cast<uint8_t>(credentials.size()));
-
-  // Write each credential
-  for (const auto& cred : credentials) {
-    // Write SSID (plaintext - not sensitive)
-    serialization::writeString(file, cred.ssid);
-    LOG_DBG("WCS", "Saving SSID: %s, password length: %zu", cred.ssid.c_str(), cred.password.size());
-
-    // Write password (obfuscated)
-    std::string obfuscatedPwd = cred.password;
-    obfuscate(obfuscatedPwd);
-    serialization::writeString(file, obfuscatedPwd);
-  }
-
-  file.close();
-  LOG_DBG("WCS", "Saved %zu WiFi credentials to file", credentials.size());
-  return true;
+  return JsonSettingsIO::saveWifi(*this, WIFI_FILE_JSON);
 }
 
 bool WifiCredentialStore::loadFromFile() {
+  // Try JSON first
+  if (Storage.exists(WIFI_FILE_JSON)) {
+    String json = Storage.readFile(WIFI_FILE_JSON);
+    if (!json.isEmpty()) {
+      bool resave = false;
+      bool result = JsonSettingsIO::loadWifi(*this, json.c_str(), &resave);
+      if (result && resave) {
+        LOG_DBG("WCS", "Resaving JSON with obfuscated passwords");
+        saveToFile();
+      }
+      return result;
+    }
+  }
+
+  // Fall back to binary migration
+  if (Storage.exists(WIFI_FILE_BIN)) {
+    if (loadFromBinaryFile()) {
+      if (saveToFile()) {
+        Storage.rename(WIFI_FILE_BIN, WIFI_FILE_BAK);
+        LOG_DBG("WCS", "Migrated wifi.bin to wifi.json");
+        return true;
+      } else {
+        LOG_ERR("WCS", "Failed to save wifi during migration");
+        return false;
+      }
+    }
+  }
+
+  return false;
+}
+
+bool WifiCredentialStore::loadFromBinaryFile() {
   FsFile file;
-  if (!Storage.openFileForRead("WCS", WIFI_FILE, file)) {
+  if (!Storage.openFileForRead("WCS", WIFI_FILE_BIN, file)) {
     return false;
   }
 
-  // Read and verify version
   uint8_t version;
   serialization::readPod(file, version);
   if (version > WIFI_FILE_VERSION) {
@@ -79,29 +86,20 @@ bool WifiCredentialStore::loadFromFile() {
     lastConnectedSsid.clear();
   }
 
-  // Read credential count
   uint8_t count;
   serialization::readPod(file, count);
 
-  // Read credentials
   credentials.clear();
   for (uint8_t i = 0; i < count && i < MAX_NETWORKS; i++) {
     WifiCredential cred;
-
-    // Read SSID
     serialization::readString(file, cred.ssid);
-
-    // Read and deobfuscate password
     serialization::readString(file, cred.password);
-    LOG_DBG("WCS", "Loaded SSID: %s, obfuscated password length: %zu", cred.ssid.c_str(), cred.password.size());
-    obfuscate(cred.password);  // XOR is symmetric, so same function deobfuscates
-    LOG_DBG("WCS", "After deobfuscation, password length: %zu", cred.password.size());
-
+    legacyDeobfuscate(cred.password);
     credentials.push_back(cred);
   }
 
   file.close();
-  LOG_DBG("WCS", "Loaded %zu WiFi credentials from file", credentials.size());
+  // LOG_DBG("WCS", "Loaded %zu WiFi credentials from binary file", credentials.size());
   return true;
 }
 

src/WifiCredentialStore.h

@@ -4,13 +4,20 @@
 
 struct WifiCredential {
   std::string ssid;
-  std::string password;  // Stored obfuscated in file
+  std::string password;  // Plaintext in memory; obfuscated with hardware key on disk
 };
 
+class WifiCredentialStore;
+namespace JsonSettingsIO {
+bool saveWifi(const WifiCredentialStore& store, const char* path);
+bool loadWifi(WifiCredentialStore& store, const char* json, bool* needsResave);
+}  // namespace JsonSettingsIO
+
 /**
  * Singleton class for storing WiFi credentials on the SD card.
- * Credentials are stored in /sd/.crosspoint/wifi.bin with basic
- * XOR obfuscation to prevent casual reading (not cryptographically secure).
+ * Passwords are XOR-obfuscated with the device's unique hardware MAC address
+ * and base64-encoded before writing to JSON (not cryptographically secure,
+ * but prevents casual reading and ties credentials to the specific device).
  */
 class WifiCredentialStore {
  private:
@@ -23,8 +30,10 @@ class WifiCredentialStore {
   // Private constructor for singleton
   WifiCredentialStore() = default;
 
-  // XOR obfuscation (symmetric - same for encode/decode)
-  void obfuscate(std::string& data) const;
+  bool loadFromBinaryFile();
+
+  friend bool JsonSettingsIO::saveWifi(const WifiCredentialStore&, const char*);
+  friend bool JsonSettingsIO::loadWifi(WifiCredentialStore&, const char*, bool*);
 
  public:
   // Delete copy constructor and assignment