fix(ota): Use secure password hashing algorithm

Author: lucasssvaz

libraries/ArduinoOTA/examples/BasicOTA/BasicOTA.ino

@@ -19,6 +19,7 @@
 
 const char *ssid = "..........";
 const char *password = "..........";
+uint32_t last_ota_time = 0;
 
 void setup() {
   Serial.begin(115200);
@@ -40,9 +41,13 @@ void setup() {
   // No authentication by default
   // ArduinoOTA.setPassword("admin");
 
-  // Password can be set with it's md5 value as well
-  // MD5(admin) = 21232f297a57a5a743894a0e4a801fc3
-  // ArduinoOTA.setPasswordHash("21232f297a57a5a743894a0e4a801fc3");
+  // Password can be set with plain text (will be hashed internally)
+  // The authentication uses PBKDF2-HMAC-SHA256 with 10,000 iterations
+  // ArduinoOTA.setPassword("admin");
+
+  // Or set password with pre-hashed value (SHA256 hash of "admin")
+  // SHA256(admin) = 8c6976e5b5410415bde908bd4dee15dfb167a9c873fc4bb8a81f6f2ab448a918
+  // ArduinoOTA.setPasswordHash("8c6976e5b5410415bde908bd4dee15dfb167a9c873fc4bb8a81f6f2ab448a918");
 
   ArduinoOTA
     .onStart([]() {
@@ -60,7 +65,10 @@ void setup() {
       Serial.println("\nEnd");
     })
     .onProgress([](unsigned int progress, unsigned int total) {
-      Serial.printf("Progress: %u%%\r", (progress / (total / 100)));
+      if (millis() - last_ota_time > 500) {
+        Serial.printf("Progress: %u%%\n", (progress / (total / 100)));
+        last_ota_time = millis();
+      }
     })
     .onError([](ota_error_t error) {
       Serial.printf("Error[%u]: ", error);

libraries/ArduinoOTA/src/ArduinoOTA.cpp

@@ -19,7 +19,8 @@
 #include "ArduinoOTA.h"
 #include "NetworkClient.h"
 #include "ESPmDNS.h"
-#include "MD5Builder.h"
+#include "SHA256Builder.h"
+#include "PBKDF2_HMACBuilder.h"
 #include "Update.h"
 
 // #define OTA_DEBUG Serial
@@ -72,18 +73,20 @@ String ArduinoOTAClass::getHostname() {
 
 ArduinoOTAClass &ArduinoOTAClass::setPassword(const char *password) {
   if (_state == OTA_IDLE && password) {
-    MD5Builder passmd5;
-    passmd5.begin();
-    passmd5.add(password);
-    passmd5.calculate();
+    // Hash the password with SHA256 for storage (not plain text)
+    SHA256Builder pass_hash;
+    pass_hash.begin();
+    pass_hash.add(password);
+    pass_hash.calculate();
     _password.clear();
-    _password = passmd5.toString();
+    _password = pass_hash.toString();
   }
   return *this;
 }
 
 ArduinoOTAClass &ArduinoOTAClass::setPasswordHash(const char *password) {
   if (_state == OTA_IDLE && password) {
+    // Store the pre-hashed password directly
     _password.clear();
     _password = password;
   }
@@ -188,17 +191,18 @@ void ArduinoOTAClass::_onRx() {
     _udp_ota.read();
     _md5 = readStringUntil('\n');
     _md5.trim();
-    if (_md5.length() != 32) {
+    if (_md5.length() != 32) {  // MD5 produces 32 character hex string for firmware integrity
       log_e("bad md5 length");
       return;
     }
 
     if (_password.length()) {
-      MD5Builder nonce_md5;
-      nonce_md5.begin();
-      nonce_md5.add(String(micros()));
-      nonce_md5.calculate();
-      _nonce = nonce_md5.toString();
+      // Generate a random challenge (nonce)
+      SHA256Builder nonce_sha256;
+      nonce_sha256.begin();
+      nonce_sha256.add(String(micros()) + String(random(1000000)));
+      nonce_sha256.calculate();
+      _nonce = nonce_sha256.toString();
 
       _udp_ota.beginPacket(_udp_ota.remoteIP(), _udp_ota.remotePort());
       _udp_ota.printf("AUTH %s", _nonce.c_str());
@@ -222,20 +226,37 @@ void ArduinoOTAClass::_onRx() {
     _udp_ota.read();
     String cnonce = readStringUntil(' ');
     String response = readStringUntil('\n');
-    if (cnonce.length() != 32 || response.length() != 32) {
+    if (cnonce.length() != 64 || response.length() != 64) {  // SHA256 produces 64 character hex string
       log_e("auth param fail");
       _state = OTA_IDLE;
       return;
     }
 
-    String challenge = _password + ":" + String(_nonce) + ":" + cnonce;
-    MD5Builder _challengemd5;
-    _challengemd5.begin();
-    _challengemd5.add(challenge);
-    _challengemd5.calculate();
-    String result = _challengemd5.toString();
-
-    if (result.equals(response)) {
+    // Verify the challenge/response using PBKDF2-HMAC-SHA256
+    // The client should derive a key using PBKDF2-HMAC-SHA256 with:
+    // - password: the OTA password (or its hash if using setPasswordHash)
+    // - salt: nonce + cnonce
+    // - iterations: 10000 (or configurable)
+    // Then hash the challenge with the derived key
+
+    String salt = _nonce + ":" + cnonce;
+    SHA256Builder sha256;
+    // Use the stored password hash for PBKDF2 derivation
+    PBKDF2_HMACBuilder pbkdf2(&sha256, _password, salt, 10000);
+
+    pbkdf2.begin();
+    pbkdf2.calculate();
+    String derived_key = pbkdf2.toString();
+
+    // Create challenge: derived_key + nonce + cnonce
+    String challenge = derived_key + ":" + _nonce + ":" + cnonce;
+    SHA256Builder challenge_sha256;
+    challenge_sha256.begin();
+    challenge_sha256.add(challenge);
+    challenge_sha256.calculate();
+    String expected_response = challenge_sha256.toString();
+
+    if (expected_response.equals(response)) {
       _udp_ota.beginPacket(_udp_ota.remoteIP(), _udp_ota.remotePort());
       _udp_ota.print("OK");
       _udp_ota.endPacket();
@@ -266,7 +287,8 @@ void ArduinoOTAClass::_runUpdate() {
     _state = OTA_IDLE;
     return;
   }
-  Update.setMD5(_md5.c_str());
+
+  Update.setMD5(_md5.c_str());  // Note: Update library still uses MD5 for firmware integrity, this is separate from authentication
 
   if (_start_callback) {
     _start_callback();

libraries/ArduinoOTA/src/ArduinoOTA.h

@@ -54,7 +54,7 @@ class ArduinoOTAClass {
   //Sets the password that will be required for OTA. Default NULL
   ArduinoOTAClass &setPassword(const char *password);
 
-  //Sets the password as above but in the form MD5(password). Default NULL
+  //Sets the password as above but in the form SHA256(password). Default NULL
   ArduinoOTAClass &setPasswordHash(const char *password);
 
   //Sets the partition label to write to when updating SPIFFS. Default NULL

tools/espota.py

@@ -54,7 +54,6 @@
 # Constants
 PROGRESS_BAR_LENGTH = 60
 
-
 # update_progress(): Displays or updates a console progress bar
 def update_progress(progress):
     if PROGRESS:
@@ -119,7 +118,7 @@ def serve(remote_addr, local_addr, remote_port, local_port, password, filename,
             return 1
         sock2.settimeout(TIMEOUT)
         try:
-            data = sock2.recv(37).decode()
+            data = sock2.recv(69).decode()  # "AUTH " + 64-char SHA3-256 nonce
             break
         except:  # noqa: E722
             sys.stderr.write(".")
@@ -133,18 +132,32 @@ def serve(remote_addr, local_addr, remote_port, local_port, password, filename,
     if data != "OK":
         if data.startswith("AUTH"):
             nonce = data.split()[1]
+
+            # Generate client nonce (cnonce)
             cnonce_text = "%s%u%s%s" % (filename, content_size, file_md5, remote_addr)
-            cnonce = hashlib.md5(cnonce_text.encode()).hexdigest()
-            passmd5 = hashlib.md5(password.encode()).hexdigest()
-            result_text = "%s:%s:%s" % (passmd5, nonce, cnonce)
-            result = hashlib.md5(result_text.encode()).hexdigest()
+            cnonce = hashlib.sha256(cnonce_text.encode()).hexdigest()
+
+            # PBKDF2-HMAC-SHA256 challenge/response protocol
+            # The ESP32 stores the password as SHA256 hash, so we need to hash the password first
+            # 1. Hash the password with SHA256 (to match ESP32 storage)
+            password_hash = hashlib.sha256(password.encode()).hexdigest()
+
+            # 2. Derive key using PBKDF2-HMAC-SHA256 with the password hash
+            salt = nonce + ":" + cnonce
+            derived_key = hashlib.pbkdf2_hmac('sha256', password_hash.encode(), salt.encode(), 10000)
+            derived_key_hex = derived_key.hex()
+
+            # 3. Create challenge response
+            challenge = derived_key_hex + ":" + nonce + ":" + cnonce
+            response = hashlib.sha256(challenge.encode()).hexdigest()
+
             sys.stderr.write("Authenticating...")
             sys.stderr.flush()
-            message = "%d %s %s\n" % (AUTH, cnonce, result)
+            message = "%d %s %s\n" % (AUTH, cnonce, response)
             sock2.sendto(message.encode(), remote_address)
             sock2.settimeout(10)
             try:
-                data = sock2.recv(32).decode()
+                data = sock2.recv(64).decode()  # SHA256 produces 64 character response
             except:  # noqa: E722
                 sys.stderr.write("FAIL\n")
                 logging.error("No Answer to our Authentication")