Add noise encryption to the esphome OTA platform

2026-08-31 01:56:01 +00:00 · 2026-08-26 19:48:47 -05:00
parent 39177402dd
commit f0255a8a4f
14 changed files with 651 additions and 32 deletions
@@ -23,7 +23,8 @@ For this repository there are two trusted inputs by design:
 1. **The configuration.** Anyone who can supply or edit a YAML config is trusted
   (see below).
 2. **Authenticated peers of a running device** — clients holding the device's
-   API encryption key / password, OTA password, or web server credentials.
+   API/OTA encryption key, API password, OTA password, or web server
+   credentials.

 The security boundary is therefore **unauthenticated network traffic vs. those
 trusted inputs.** A bug that lets an unauthenticated attacker cross it is a
@@ -76,8 +77,8 @@ These *are* security bugs in this repo, and we want to hear about them privately
  captive portal, etc.) **without** valid credentials.
 - Authentication or encryption bypass on the device — reaching API calls, OTA
  updates, or the web server without the configured key/password.
- Flaws that weaken the device's API encryption (Noise), OTA, or web server auth
-  below their documented guarantees.
+- Flaws that weaken the device's API or OTA encryption (Noise), OTA auth, or
+  web server auth below their documented guarantees.

 ## The web server is an open HTTP API by design

@@ -121,6 +122,37 @@ and any memory-safety or protocol bug in the server reachable without credential
 This section documents the current design and scope; it is not a judgment that the
 design is optimal or that it will not change.

+## OTA update encryption
+
+The `esphome` OTA platform optionally encrypts updates with the same Noise
+`NNpsk0` pattern the native API uses; one key protects the device. With an
+`encryption:` block configured the guarantees are: the firmware image is
+confidential in transit, the uploader is authenticated by the pre-shared key,
+and the plaintext negotiation preceding the handshake is bound into the
+handshake prologue, so stripping or tampering with it fails the first MAC.
+Both ends fail closed with no override: a device built with a key refuses
+plaintext uploads, and the CLI refuses to send plaintext when a key is
+configured.
+
+Defeating any of that without the key is in scope: a keyed device accepting a
+plaintext or downgraded upload, getting past the MAC, or recovering image
+contents from captured traffic.
+
+The following are **not** vulnerabilities, by design:
+
+- Plaintext OTA on a device with no `encryption:` block. That is the
+  documented default, authenticated (if at all) by the OTA password.
+- The enablement window: turning encryption on takes one last upload of the
+  encryption-enabled firmware over the existing plaintext channel, with the
+  pre-existing plaintext exposure.
+- The web OTA `/update` endpoint alongside encryption. The `web_server`
+  component keeps it always reachable, and `captive_portal:` auto-loads it
+  for the fallback AP window; validation warns about both combinations, and
+  the operator keeps the recovery path.
+- CLI retry behavior on transport or MAC failures; every attempt renegotiates
+  a fresh handshake with fresh ephemerals, so retrying does not weaken
+  authentication.
+
 ## Explicitly out of scope

 - Local attackers who already have shell access on the host that runs `esphome`.
@@ -1,12 +1,20 @@
 import logging

 import esphome.codegen as cg
+from esphome.components.noise import (
+    decode_encryption_key,
+    encryption_schema,
+    is_reserved_key,
+)
 from esphome.components.ota import BASE_OTA_SCHEMA, OTAComponent, ota_to_code
 from esphome.config_helpers import merge_config
 import esphome.config_validation as cv
 from esphome.const import (
+    CONF_API,
+    CONF_ENCRYPTION,
    CONF_ESPHOME,
    CONF_ID,
+    CONF_KEY,
    CONF_NUM_ATTEMPTS,
    CONF_OTA,
    CONF_PASSWORD,
@@ -15,6 +23,7 @@ from esphome.const import (
    CONF_REBOOT_TIMEOUT,
    CONF_SAFE_MODE,
    CONF_VERSION,
+    CONF_WEB_SERVER,
 )
 from esphome.core import CORE, coroutine_with_priority
 from esphome.coroutine import CoroPriority
@@ -22,6 +31,7 @@ import esphome.final_validate as fv
 from esphome.types import ConfigType

 CONF_ALLOW_PARTITION_ACCESS = "allow_partition_access"
+CONF_CAPTIVE_PORTAL = "captive_portal"

 _LOGGER = logging.getLogger(__name__)

@@ -30,7 +40,15 @@ CODEOWNERS = ["@esphome/core"]
 DEPENDENCIES = ["network"]


-AUTO_LOAD = ["sha256", "socket"]
+def AUTO_LOAD(config: ConfigType) -> list[str]:
+    """Auto-load noise only when encryption is configured."""
+    base = ["sha256", "socket"]
+    # A falsy config is a tooling probe for the maximal set (None from
+    # dependency resolution, {} from the components-graph platform probe);
+    # a validated config always carries defaults, never empty
+    if not config or CONF_ENCRYPTION in config:
+        return base + ["noise"]
+    return base


 esphome = cg.esphome_ns.namespace("esphome")
@@ -67,11 +85,24 @@ def ota_esphome_final_validate(config: ConfigType) -> None:
                    CONF_PASSWORD in merged_ota_esphome_configs_by_port[conf_port]
                    and CONF_PASSWORD in ota_conf
                    and merged_ota_esphome_configs_by_port[conf_port][CONF_PASSWORD]
-                    != ota_conf.get(CONF_PASSWORD)
+                    != ota_conf[CONF_PASSWORD]
                ):
                    raise cv.Invalid(
                        f"Found multiple configurations but {CONF_PASSWORD} is inconsistent"
                    )
+                # Encryption blocks conflict only when both pin a key; a bare
+                # `encryption:` (a package/device split) is compatible with a
+                # keyed one, and merge_config yields the keyed result
+                merged_key = (
+                    merged_ota_esphome_configs_by_port[conf_port]
+                    .get(CONF_ENCRYPTION, {})
+                    .get(CONF_KEY)
+                )
+                other_key = ota_conf.get(CONF_ENCRYPTION, {}).get(CONF_KEY)
+                if merged_key and other_key and merged_key != other_key:
+                    raise cv.Invalid(
+                        f"Found multiple configurations but {CONF_ENCRYPTION} is inconsistent"
+                    )

                ports_with_merged_configs.append(conf_port)
                merged_ota_esphome_configs_by_port[conf_port] = merge_config(
@@ -94,6 +125,20 @@ def ota_esphome_final_validate(config: ConfigType) -> None:

    new_ota_conf.extend(merged_ota_esphome_configs_by_port.values())

+    api_conf = full_conf.get(CONF_API) or {}
+    for ota_conf in merged_ota_esphome_configs_by_port.values():
+        # Merging same-port blocks can combine a password from one block with
+        # encryption from another; re-check the exclusion on the merged result.
+        _validate_no_password_with_encryption(ota_conf)
+        if (encryption_conf := ota_conf.get(CONF_ENCRYPTION)) is not None:
+            _resolve_encryption_key(encryption_conf, api_conf)
+    if any(
+        conf.get(CONF_PLATFORM) == CONF_WEB_SERVER for conf in full_ota_conf
+    ) and any(
+        CONF_ENCRYPTION in conf for conf in merged_ota_esphome_configs_by_port.values()
+    ):
+        _warn_web_server_ota(full_conf)
+
    full_conf[CONF_OTA] = new_ota_conf
    fv.full_config.set(full_conf)

@@ -107,6 +152,73 @@ def ota_esphome_final_validate(config: ConfigType) -> None:
        )


+def _warn_web_server_ota(full_conf: ConfigType) -> None:
+    """The web_server ota platform accepts the same image over plaintext HTTP
+    with basic auth, bypassing the encryption; warn rather than fail so the
+    operator keeps the recovery path."""
+    if CONF_CAPTIVE_PORTAL in full_conf and CONF_WEB_SERVER not in full_conf:
+        # The captive_portal auto-load: the endpoint only exists while the
+        # fallback AP is active
+        _LOGGER.warning(
+            "OTA encryption does not cover the %s OTA platform (auto-loaded "
+            "by captive_portal); the plaintext /update endpoint stays "
+            "reachable while the fallback AP is active",
+            CONF_WEB_SERVER,
+        )
+    else:
+        _LOGGER.warning(
+            "OTA encryption does not cover the %s OTA platform; its "
+            "plaintext /update endpoint accepts the same image",
+            CONF_WEB_SERVER,
+        )
+
+
+def _resolve_encryption_key(encryption_conf: ConfigType, api_conf: ConfigType) -> None:
+    """Resolve the one encryption key per device into the ota block.
+
+    An explicit ota key must match the api key, a bare block inherits it,
+    a runtime provisioned api key cannot be inherited, and the all-zeros
+    provisioning sentinel is rejected (the device treats it as no key).
+    """
+    api_key = api_conf.get(CONF_ENCRYPTION, {}).get(CONF_KEY)
+    if ota_key := encryption_conf.get(CONF_KEY):
+        if api_key and ota_key != api_key:
+            raise cv.Invalid(
+                f"'{CONF_OTA}' {CONF_ENCRYPTION} {CONF_KEY} must match the "
+                f"'{CONF_API}' {CONF_ENCRYPTION} {CONF_KEY}; omit the "
+                f"'{CONF_OTA}' {CONF_KEY} to use the '{CONF_API}' one"
+            )
+    elif not api_key:
+        if CONF_ENCRYPTION in api_conf:
+            raise cv.Invalid(
+                f"the '{CONF_API}' {CONF_ENCRYPTION} {CONF_KEY} is provisioned at "
+                f"runtime and cannot be inherited at build time; set an explicit "
+                f"'{CONF_OTA}' {CONF_ENCRYPTION} {CONF_KEY}"
+            )
+        raise cv.Invalid(
+            f"'{CONF_OTA}' {CONF_ENCRYPTION} has no {CONF_KEY} and there is no "
+            f"'{CONF_API}' {CONF_ENCRYPTION} {CONF_KEY} to inherit; set one of them"
+        )
+    else:
+        encryption_conf[CONF_KEY] = api_key
+    if is_reserved_key(encryption_conf[CONF_KEY]):
+        raise cv.Invalid(
+            f"The all-zeros {CONF_KEY} is reserved and provides no protection; "
+            f"generate a real key with: openssl rand -base64 32"
+        )
+
+
+# Also called on merged same-port configs in final validate, where schemas
+# do not run
+def _validate_no_password_with_encryption(config: ConfigType) -> ConfigType:
+    if CONF_PASSWORD in config and CONF_ENCRYPTION in config:
+        raise cv.Invalid(
+            f"'{CONF_PASSWORD}' cannot be combined with '{CONF_ENCRYPTION}'; the "
+            f"encryption key already authenticates the uploader, remove '{CONF_PASSWORD}'"
+        )
+    return config
+
+
 def _consume_ota_sockets(config: ConfigType) -> ConfigType:
    """Register socket needs for OTA component."""
    from esphome.components import socket
@@ -134,6 +246,7 @@ CONFIG_SCHEMA = cv.All(
            ): cv.port,
            cv.Optional(CONF_ALLOW_PARTITION_ACCESS, default=False): cv.boolean,
            cv.Optional(CONF_PASSWORD): cv.sensitive(),
+            cv.Optional(CONF_ENCRYPTION): encryption_schema,
            cv.Optional(CONF_NUM_ATTEMPTS): cv.invalid(
                f"'{CONF_SAFE_MODE}' (and its related configuration variables) has moved from 'ota' to its own component. See https://esphome.io/components/safe_mode"
            ),
@@ -147,12 +260,24 @@ CONFIG_SCHEMA = cv.All(
    )
    .extend(BASE_OTA_SCHEMA)
    .extend(cv.COMPONENT_SCHEMA),
+    _validate_no_password_with_encryption,
    _consume_ota_sockets,
 )

 FINAL_VALIDATE_SCHEMA = ota_esphome_final_validate


+def FILTER_SOURCE_FILES() -> list[str]:
+    """Filter out the noise transport when no ota entry configures encryption."""
+    for ota_conf in CORE.config.get(CONF_OTA, []):
+        if (
+            ota_conf.get(CONF_PLATFORM) == CONF_ESPHOME
+            and ota_conf.get(CONF_ENCRYPTION) is not None
+        ):
+            return []
+    return ["ota_esphome_noise.cpp"]
+
+
@coroutine_with_priority(CoroPriority.OTA_UPDATES)
 async def to_code(config: ConfigType) -> None:
    var = cg.new_Pvariable(config[CONF_ID])
@@ -171,6 +296,12 @@ async def to_code(config: ConfigType) -> None:
    if config.get(CONF_ALLOW_PARTITION_ACCESS):
        cg.add_define("USE_OTA_PARTITIONS")

+    if (encryption_conf := config.get(CONF_ENCRYPTION)) is not None:
+        # A missing key was resolved from the api component in final validate.
+        key = encryption_conf[CONF_KEY]
+        cg.add_define("USE_OTA_ENCRYPTION")
+        cg.add(var.set_noise_psk(list(decode_encryption_key(key))))
+
    # Build flag so lwip_fast_select.c (a .c file that can't include defines.h) sees it.
    cg.add_build_flag("-DUSE_OTA_PLATFORM_ESPHOME")

@@ -27,7 +27,6 @@ namespace esphome {

 static const char *const TAG = "esphome.ota";
 static constexpr uint16_t OTA_BLOCK_SIZE = 8192;
-static constexpr size_t OTA_BUFFER_SIZE = 1024;                  // buffer size for OTA data transfer
 static constexpr uint32_t OTA_SOCKET_TIMEOUT_HANDSHAKE = 20000;  // milliseconds for initial handshake
 static constexpr uint32_t OTA_SOCKET_TIMEOUT_DATA = 90000;       // milliseconds for data transfer

@@ -105,6 +104,11 @@ void ESPHomeOTAComponent::dump_config() {
    ESP_LOGCONFIG(TAG, "  Password configured");
  }
 #endif
+#ifdef USE_OTA_ENCRYPTION
+  if (this->noise_ctx_.has_psk()) {
+    ESP_LOGCONFIG(TAG, "  Encryption configured");
+  }
+#endif
 #ifdef USE_OTA_PARTITIONS
  ESP_LOGCONFIG(TAG,
                "  Partition access allowed\n"
@@ -148,8 +152,10 @@ void ESPHomeOTAComponent::loop() {
 static constexpr uint8_t CLIENT_FEATURE_SUPPORTS_COMPRESSION = 0x01;
 static constexpr uint8_t CLIENT_FEATURE_SUPPORTS_SHA256_AUTH = 0x02;
 static constexpr uint8_t CLIENT_FEATURE_SUPPORTS_EXTENDED_PROTOCOL = 0x04;
+static constexpr uint8_t CLIENT_FEATURE_SUPPORTS_NOISE = 0x08;
 static constexpr uint8_t SERVER_FEATURE_SUPPORTS_COMPRESSION = 0x01;
 static constexpr uint8_t SERVER_FEATURE_SUPPORTS_PARTITION_ACCESS = 0x02;
+static constexpr uint8_t SERVER_FEATURE_SUPPORTS_NOISE = 0x04;

 void ESPHomeOTAComponent::handle_handshake_() {
  /// Handle the OTA handshake and authentication.
@@ -201,8 +207,7 @@ void ESPHomeOTAComponent::handle_handshake_() {
      }

      // Validate magic bytes
-      static const uint8_t MAGIC_BYTES[5] = {0x6C, 0x26, 0xF7, 0x5C, 0x45};
-      if (memcmp(this->handshake_buf_, MAGIC_BYTES, 5) != 0) {
+      if (memcmp(this->handshake_buf_, MAGIC_BYTES, sizeof(MAGIC_BYTES)) != 0) {
        ESP_LOGW(TAG, "Magic bytes mismatch! 0x%02X-0x%02X-0x%02X-0x%02X-0x%02X", this->handshake_buf_[0],
                 this->handshake_buf_[1], this->handshake_buf_[2], this->handshake_buf_[3], this->handshake_buf_[4]);
        this->send_error_and_cleanup_(ota::OTA_RESPONSE_ERROR_MAGIC);
@@ -234,6 +239,19 @@ void ESPHomeOTAComponent::handle_handshake_() {
      }
      this->ota_features_ = this->handshake_buf_[0];
      ESP_LOGV(TAG, "Features: 0x%02X", this->ota_features_);
+
+#ifdef USE_OTA_ENCRYPTION
+      // Fail closed: with a PSK configured the client must negotiate encryption
+      // (which requires the extended protocol); refuse plaintext uploads.
+      static constexpr uint8_t NOISE_REQUIRED_FEATURES =
+          CLIENT_FEATURE_SUPPORTS_NOISE | CLIENT_FEATURE_SUPPORTS_EXTENDED_PROTOCOL;
+      if (this->noise_ctx_.has_psk() && (this->ota_features_ & NOISE_REQUIRED_FEATURES) != NOISE_REQUIRED_FEATURES) {
+        ESP_LOGW(TAG, "Client does not support encryption");
+        this->send_error_and_cleanup_(ota::OTA_RESPONSE_ERROR_ENCRYPTION_REQUIRED);
+        return;
+      }
+#endif
+
      this->transition_ota_state_(OTAState::FEATURE_ACK);

      const bool supports_compression =
@@ -249,6 +267,11 @@ void ESPHomeOTAComponent::handle_handshake_() {
        this->handshake_buf_[1] = (supports_compression ? SERVER_FEATURE_SUPPORTS_COMPRESSION : 0);
 #ifdef USE_OTA_PARTITIONS
        this->handshake_buf_[1] |= SERVER_FEATURE_SUPPORTS_PARTITION_ACCESS;
+#endif
+#ifdef USE_OTA_ENCRYPTION
+        if (this->noise_ctx_.has_psk()) {
+          this->handshake_buf_[1] |= SERVER_FEATURE_SUPPORTS_NOISE;
+        }
 #endif
      } else {
        this->handshake_buf_[0] =
@@ -264,6 +287,20 @@ void ESPHomeOTAComponent::handle_handshake_() {
      if (!this->try_write_(ack_size, LOG_STR("ack feature"))) {
        return;
      }
+#ifdef USE_OTA_ENCRYPTION
+      // With a PSK configured the rest of the session runs inside the noise
+      // transport; the client sends the first handshake frame next, so there
+      // is nothing to do until data arrives.
+      if (this->noise_ctx_.has_psk()) {
+        // handshake_buf_ still holds the feature ack composed above; a
+        // would-block re-entry lands here without rebuilding it
+        if (!this->noise_start_session_(this->handshake_buf_[1])) {
+          return;
+        }
+        this->transition_ota_state_(OTAState::NOISE_HANDSHAKE);
+        return;
+      }
+#endif
 #ifdef USE_OTA_PASSWORD
      // If password is set, move to auth phase
      if (!this->password_.empty()) {
@@ -301,6 +338,16 @@ void ESPHomeOTAComponent::handle_handshake_() {
      this->handle_data_();
      return;

+#ifdef USE_OTA_ENCRYPTION
+    case OTAState::NOISE_HANDSHAKE:
+      if (!this->handle_noise_handshake_()) {
+        return;
+      }
+      this->transition_ota_state_(OTAState::DATA);
+      this->handle_data_();
+      return;
+#endif
+
    default:
      break;
  }
@@ -339,6 +386,8 @@ void ESPHomeOTAComponent::handle_data_() {
  ///   Raw TCP (8266, RP2040):  setblocking is no-op; SO_RCVTIMEO uses
  ///                            wakeable_delay() in read();
  ///                            write() always returns immediately
+  // Backend calls overwrite this with OK; reset to UNKNOWN before any
+  // goto error that follows a successful begin()/write()
  ota::OTAResponseTypes error_code = ota::OTA_RESPONSE_ERROR_UNKNOWN;
  size_t total = 0;
  uint32_t last_progress = 0;
@@ -360,11 +409,11 @@ void ESPHomeOTAComponent::handle_data_() {
  this->client_->setblocking(true);

  // Acknowledge auth OK - 1 byte
-  this->write_byte_(ota::OTA_RESPONSE_AUTH_OK);
+  this->data_write_byte_(ota::OTA_RESPONSE_AUTH_OK);

  if (this->extended_proto_) {
    // Read ota type, 1 byte
-    if (!this->readall_(buf, 1)) {
+    if (!this->data_readall_(buf, 1)) {
      this->log_read_error_(LOG_STR("OTA type"));
      goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
    }
@@ -373,7 +422,7 @@ void ESPHomeOTAComponent::handle_data_() {
  ESP_LOGV(TAG, "OTA type is 0x%02x", ota_type);

  // Read size, 4 bytes MSB first
-  if (!this->readall_(buf, 4)) {
+  if (!this->data_readall_(buf, 4)) {
    this->log_read_error_(LOG_STR("size"));
    goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
  }
@@ -404,11 +453,12 @@ void ESPHomeOTAComponent::handle_data_() {
    goto error;  // NOLINT(cppcoreguidelines-avoid-goto)

  // Acknowledge prepare OK - 1 byte
-  this->write_byte_(ota::OTA_RESPONSE_UPDATE_PREPARE_OK);
+  this->data_write_byte_(ota::OTA_RESPONSE_UPDATE_PREPARE_OK);

  // Read binary MD5, 32 bytes
-  if (!this->readall_(buf, 32)) {
+  if (!this->data_readall_(buf, 32)) {
    this->log_read_error_(LOG_STR("MD5 checksum"));
+    error_code = ota::OTA_RESPONSE_ERROR_UNKNOWN;
    goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
  }
  sbuf[32] = '\0';
@@ -416,7 +466,7 @@ void ESPHomeOTAComponent::handle_data_() {
  this->backend_->set_update_md5(sbuf);

  // Acknowledge MD5 OK - 1 byte
-  this->write_byte_(ota::OTA_RESPONSE_BIN_MD5_OK);
+  this->data_write_byte_(ota::OTA_RESPONSE_BIN_MD5_OK);

  // Track when we last received data so a silently-vanished peer (no FIN/RST
  // delivered, e.g. uploader killed mid-transfer or NAT/router dropped state)
@@ -432,19 +482,35 @@ void ESPHomeOTAComponent::handle_data_() {
    }
    size_t remaining = ota_size - total;
    size_t requested = remaining < OTA_BUFFER_SIZE ? remaining : OTA_BUFFER_SIZE;
-    ssize_t read = this->client_->read(buf, requested);
-    if (read == -1) {
-      const int err = errno;
-      if (this->would_block_(err)) {
-        // read() already waited up to SO_RCVTIMEO for data, just feed WDT
-        App.feed_wdt();
-        continue;
+    ssize_t read;
+#ifdef USE_OTA_ENCRYPTION
+    if (this->noise_ != nullptr) {
+      // One frame per call; noise_read_data_ waits internally (readall_), so
+      // there is no would-block retry here and failures are already logged.
+      read = this->noise_read_data_(buf, requested);
+      if (read <= 0) {
+        error_code = ota::OTA_RESPONSE_ERROR_UNKNOWN;
+        goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
+      }
+    } else
+#endif
+    {
+      read = this->client_->read(buf, requested);
+      if (read == -1) {
+        const int err = errno;
+        if (this->would_block_(err)) {
+          // read() already waited up to SO_RCVTIMEO for data, just feed WDT
+          App.feed_wdt();
+          continue;
+        }
+        ESP_LOGW(TAG, "Read err %d", err);
+        error_code = ota::OTA_RESPONSE_ERROR_UNKNOWN;
+        goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
+      } else if (read == 0) {
+        ESP_LOGW(TAG, "Remote closed");
+        error_code = ota::OTA_RESPONSE_ERROR_UNKNOWN;
+        goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
      }
-      ESP_LOGW(TAG, "Read err %d", err);
-      goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
-    } else if (read == 0) {
-      ESP_LOGW(TAG, "Remote closed");
-      goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
    }

    last_data_ms = millis();
@@ -456,7 +522,7 @@ void ESPHomeOTAComponent::handle_data_() {
    total += read;
 #if USE_OTA_VERSION == 2
    while (size_acknowledged + OTA_BLOCK_SIZE <= total || (total == ota_size && size_acknowledged < ota_size)) {
-      this->write_byte_(ota::OTA_RESPONSE_CHUNK_OK);
+      this->data_write_byte_(ota::OTA_RESPONSE_CHUNK_OK);
      size_acknowledged += OTA_BLOCK_SIZE;
    }
 #endif
@@ -475,7 +541,7 @@ void ESPHomeOTAComponent::handle_data_() {
  }

  // Acknowledge receive OK - 1 byte
-  this->write_byte_(ota::OTA_RESPONSE_RECEIVE_OK);
+  this->data_write_byte_(ota::OTA_RESPONSE_RECEIVE_OK);

  error_code = this->backend_->end();
  if (error_code != ota::OTA_RESPONSE_OK) {
@@ -484,10 +550,10 @@ void ESPHomeOTAComponent::handle_data_() {
  }

  // Acknowledge Update end OK - 1 byte
-  this->write_byte_(ota::OTA_RESPONSE_UPDATE_END_OK);
+  this->data_write_byte_(ota::OTA_RESPONSE_UPDATE_END_OK);

  // Read ACK
-  if (!this->readall_(buf, 1) || buf[0] != ota::OTA_RESPONSE_OK) {
+  if (!this->data_readall_(buf, 1) || buf[0] != ota::OTA_RESPONSE_OK) {
    this->log_read_error_(LOG_STR("ack"));
    // do not go to error, this is not fatal
  }
@@ -510,7 +576,7 @@ void ESPHomeOTAComponent::handle_data_() {
  App.safe_reboot();

 error:
-  this->write_byte_(static_cast<uint8_t>(error_code));
+  this->data_write_byte_(static_cast<uint8_t>(error_code));

  // Abort backend before cleanup - cleanup_connection_() destroys the backend.
  // Always call abort() unconditionally: backends register external partitions before
@@ -677,6 +743,9 @@ void ESPHomeOTAComponent::cleanup_connection_() {
  this->backend_ = nullptr;
 #ifdef USE_OTA_PASSWORD
  this->cleanup_auth_();
+#endif
+#ifdef USE_OTA_ENCRYPTION
+  this->noise_ = nullptr;
 #endif
  // Intentionally no disable_loop() — letting loop() run one more iteration catches
  // any connection that queued on the listener mid-session (otherwise the wake flag,
@@ -4,6 +4,9 @@
 #ifdef USE_OTA
 #include "esphome/components/ota/ota_backend_factory.h"
 #include "esphome/components/socket/socket.h"
+#ifdef USE_OTA_ENCRYPTION
+#include "esphome/components/noise/noise_handshake.h"
+#endif
 #include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
 #include "esphome/core/preferences.h"
@@ -24,7 +27,10 @@ class ESPHomeOTAComponent final : public ota::OTAComponent {
    AUTH_SEND,  // Sending authentication request
    AUTH_READ,  // Reading authentication data
 #endif          // USE_OTA_PASSWORD
-    DATA,       // BLOCKING! Processing OTA data (update, etc.)
+#ifdef USE_OTA_ENCRYPTION
+    NOISE_HANDSHAKE,  // Exchanging Noise handshake frames
+#endif
+    DATA,  // BLOCKING! Processing OTA data (update, etc.)
  };
 #ifdef USE_OTA_PASSWORD
  void set_auth_password(const std::string &password) { password_ = password; }
@@ -38,6 +44,10 @@ class ESPHomeOTAComponent final : public ota::OTAComponent {
  }
 #endif  // USE_OTA_PASSWORD

+#ifdef USE_OTA_ENCRYPTION
+  void set_noise_psk(noise::psk_t psk) { this->noise_ctx_.set_psk(psk); }
+#endif
+
  /// Manually set the port OTA should listen on
  void set_port(uint16_t port) { this->port_ = port; }

@@ -63,6 +73,48 @@ class ESPHomeOTAComponent final : public ota::OTAComponent {
  bool writeall_(const uint8_t *buf, size_t len);
  inline bool write_byte_(uint8_t byte) { return this->writeall_(&byte, 1); }

+#ifdef USE_OTA_ENCRYPTION
+  // Heap-allocated only while an encrypted OTA session is active.
+  struct NoiseSession {
+    ~NoiseSession();
+    noise::NoiseResponderHandshake handshake;
+    NoiseCipherState *send_cipher{nullptr};
+    NoiseCipherState *recv_cipher{nullptr};
+    uint16_t frame_len{0};  // total frame size once the header is parsed, 0 until then
+    uint16_t frame_pos{0};  // bytes read or written so far
+    bool writing{false};    // a produced handshake frame is still being flushed
+    uint8_t frame_buf[noise::FRAME_HEADER_SIZE + 1 + noise::MAX_HANDSHAKE_SIZE];
+  };
+  bool noise_start_session_(uint8_t server_feature_flags);
+  bool handle_noise_handshake_();
+  bool noise_try_read_frame_();
+  bool noise_try_write_frame_();
+  void noise_send_reject_(const LogString *reason);
+  ssize_t noise_decrypt_(uint8_t *buf, size_t len);
+  ssize_t noise_read_frame_blocking_(uint8_t *buf, size_t min_ciphertext, size_t max_ciphertext);
+  bool noise_readall_(uint8_t *buf, size_t len);
+  ssize_t noise_read_data_(uint8_t *buf, size_t capacity);
+  bool noise_write_byte_(uint8_t byte);
+#endif  // USE_OTA_ENCRYPTION
+
+  // Data-phase I/O dispatch: through the noise transport when a session is
+  // active, straight to the socket otherwise.
+  inline bool data_write_byte_(uint8_t byte) {
+#ifdef USE_OTA_ENCRYPTION
+    if (this->noise_ != nullptr)
+      return this->noise_write_byte_(byte);
+#endif
+    return this->write_byte_(byte);
+  }
+  // When encrypted, buf must have room for len + noise::MAC_SIZE bytes.
+  inline bool data_readall_(uint8_t *buf, size_t len) {
+#ifdef USE_OTA_ENCRYPTION
+    if (this->noise_ != nullptr)
+      return this->noise_readall_(buf, len);
+#endif
+    return this->readall_(buf, len);
+  }
+
  bool try_read_(size_t to_read, const LogString *desc);
  bool try_write_(size_t to_write, const LogString *desc);

@@ -91,6 +143,10 @@ class ESPHomeOTAComponent final : public ota::OTAComponent {
  std::string password_;
  std::unique_ptr<uint8_t[]> auth_buf_;
 #endif  // USE_OTA_PASSWORD
+#ifdef USE_OTA_ENCRYPTION
+  noise::NoiseContext noise_ctx_;
+  std::unique_ptr<NoiseSession> noise_;
+#endif  // USE_OTA_ENCRYPTION

  socket::ListenSocket *server_{nullptr};
  std::unique_ptr<socket::Socket> client_;
@@ -98,6 +154,18 @@ class ESPHomeOTAComponent final : public ota::OTAComponent {

  uint32_t client_connect_time_{0};
  static constexpr size_t HANDSHAKE_BUF_SIZE = 5;
+  // Buffer size for OTA data transfer. The upload client derives its maximum
+  // encrypted frame plaintext from this (espota2.NOISE_MAX_PLAINTEXT is this
+  // minus the 16-byte MAC); both must change together.
+  static constexpr size_t OTA_BUFFER_SIZE = 1040;
+#ifdef USE_OTA_ENCRYPTION
+  // espota2.NOISE_MAX_PLAINTEXT; shrinking the buffer would reject every
+  // frame a current CLI sends
+  static constexpr size_t NOISE_CLIENT_MAX_PLAINTEXT = 1024;
+  static_assert(OTA_BUFFER_SIZE >= NOISE_CLIENT_MAX_PLAINTEXT + noise::MAC_SIZE,
+                "OTA_BUFFER_SIZE must fit a full encrypted data frame");
+#endif
+  static constexpr uint8_t MAGIC_BYTES[5] = {0x6C, 0x26, 0xF7, 0x5C, 0x45};
 #ifdef USE_OTA_PARTITIONS
  uint32_t running_app_offset_{0};
  size_t running_app_size_{0};
@@ -0,0 +1,279 @@
+#include "ota_esphome.h"
+#ifdef USE_OTA
+#ifdef USE_OTA_ENCRYPTION
+#include "esphome/components/noise/noise.h"
+#include "esphome/components/ota/ota_backend.h"
+#include "esphome/core/log.h"
+
+#include <cstring>
+#include <new>
+
+#ifdef USE_ESP8266
+#include <pgmspace.h>
+#endif
+
+namespace esphome {
+
+static const char *const TAG = "esphome.ota";
+
+#ifdef USE_ESP8266
+static constexpr char OTA_NOISE_PROLOGUE_INIT[] PROGMEM = "NoiseOTAInit";
+#else
+static constexpr char OTA_NOISE_PROLOGUE_INIT[] = "NoiseOTAInit";
+#endif
+static constexpr size_t OTA_NOISE_PROLOGUE_INIT_LEN = sizeof(OTA_NOISE_PROLOGUE_INIT) - 1;
+
+ESPHomeOTAComponent::NoiseSession::~NoiseSession() {
+  if (this->send_cipher != nullptr) {
+    noise_cipherstate_free(this->send_cipher);
+  }
+  if (this->recv_cipher != nullptr) {
+    noise_cipherstate_free(this->recv_cipher);
+  }
+}
+
+/** Allocate the session and start the responder handshake.
+ *
+ * The prologue binds the whole plaintext preamble, so any tampering with the
+ * negotiation (a stripped feature flag, a changed version) breaks the first
+ * handshake MAC on either side:
+ *   "NoiseOTAInit" | magic(5) | OK,version | client_features | FEATURE_FLAGS,server_flags
+ */
+bool ESPHomeOTAComponent::noise_start_session_(uint8_t server_feature_flags) {
+  // NOLINTNEXTLINE(clang-analyzer-cplusplus.NewDeleteLeaks)
+  this->noise_ = std::unique_ptr<NoiseSession>(new (std::nothrow) NoiseSession());
+  if (this->noise_ == nullptr) {
+    ESP_LOGW(TAG, "Session allocation failed");
+    this->cleanup_connection_();
+    return false;
+  }
+
+  static constexpr size_t PROLOGUE_ACK_LEN = 2;  // OTA_RESPONSE_OK + version
+  static constexpr size_t PROLOGUE_CLIENT_FEATURES_LEN = 1;
+  static constexpr size_t PROLOGUE_FEATURE_ACK_LEN = 2;  // OTA_RESPONSE_FEATURE_FLAGS + server flags
+  uint8_t prologue[OTA_NOISE_PROLOGUE_INIT_LEN + sizeof(MAGIC_BYTES) + PROLOGUE_ACK_LEN + PROLOGUE_CLIENT_FEATURES_LEN +
+                   PROLOGUE_FEATURE_ACK_LEN];
+#ifdef USE_ESP8266
+  memcpy_P(prologue, OTA_NOISE_PROLOGUE_INIT, OTA_NOISE_PROLOGUE_INIT_LEN);
+#else
+  std::memcpy(prologue, OTA_NOISE_PROLOGUE_INIT, OTA_NOISE_PROLOGUE_INIT_LEN);
+#endif
+  uint8_t *p = prologue + OTA_NOISE_PROLOGUE_INIT_LEN;
+  // Magic bytes, already validated in MAGIC_READ
+  std::memcpy(p, MAGIC_BYTES, sizeof(MAGIC_BYTES));
+  p += sizeof(MAGIC_BYTES);
+  // Our magic ack
+  *p++ = ota::OTA_RESPONSE_OK;
+  *p++ = USE_OTA_VERSION;
+  // The feature byte the client sent
+  *p++ = this->ota_features_;
+  // The feature ack we sent (noise requires the extended protocol)
+  *p++ = ota::OTA_RESPONSE_FEATURE_FLAGS;
+  *p++ = server_feature_flags;
+
+  int err = this->noise_->handshake.init(this->noise_ctx_.get_psk(), prologue, sizeof(prologue));
+  if (err != 0) {
+    ESP_LOGW(TAG, "Handshake init: %s", LOG_STR_ARG(noise::noise_err_to_logstr(err)));
+    this->cleanup_connection_();
+    return false;
+  }
+  return true;
+}
+
+/** Drive the non-blocking handshake from loop(); returns true once the
+ * transport ciphers are ready. A would-block returns false and the next
+ * loop() resumes from the NoiseSession cursors; on failure the connection
+ * is cleaned up.
+ */
+bool ESPHomeOTAComponent::handle_noise_handshake_() {
+  NoiseSession &s = *this->noise_;
+  while (true) {
+    if (s.writing) {
+      if (!this->noise_try_write_frame_()) {
+        return false;  // would block, or errored and cleaned up
+      }
+      s.writing = false;
+      s.frame_pos = 0;
+      s.frame_len = 0;
+    }
+    switch (s.handshake.action()) {
+      case noise::NoiseResponderHandshake::Action::ACTION_READ: {
+        if (!this->noise_try_read_frame_()) {
+          return false;
+        }
+        const uint16_t payload_len = s.frame_len - noise::FRAME_HEADER_SIZE;
+        s.frame_pos = 0;
+        s.frame_len = 0;
+        if (s.frame_buf[noise::FRAME_HEADER_SIZE] != noise::HANDSHAKE_STATUS_OK) {
+          ESP_LOGW(TAG, "Bad handshake error byte: %u", s.frame_buf[noise::FRAME_HEADER_SIZE]);
+          this->cleanup_connection_();
+          return false;
+        }
+        int err = s.handshake.read_message(s.frame_buf + noise::FRAME_HEADER_SIZE + 1, payload_len - 1);
+        if (err != 0) {
+          ESP_LOGW(TAG, "Handshake read: %s", LOG_STR_ARG(noise::noise_err_to_logstr(err)));
+          this->noise_send_reject_(noise::reject_reason_for(err));
+          this->cleanup_connection_();
+          return false;
+        }
+        break;
+      }
+      case noise::NoiseResponderHandshake::Action::ACTION_WRITE: {
+        size_t msg_len = 0;
+        int err =
+            s.handshake.write_message(s.frame_buf + noise::FRAME_HEADER_SIZE + 1, noise::MAX_HANDSHAKE_SIZE, msg_len);
+        if (err != 0) {
+          ESP_LOGW(TAG, "Handshake write: %s", LOG_STR_ARG(noise::noise_err_to_logstr(err)));
+          this->cleanup_connection_();
+          return false;
+        }
+        const uint16_t payload_len = msg_len + 1;
+        noise::write_frame_header(s.frame_buf, payload_len);
+        s.frame_buf[noise::FRAME_HEADER_SIZE] = noise::HANDSHAKE_STATUS_OK;
+        s.frame_len = noise::FRAME_HEADER_SIZE + payload_len;
+        s.frame_pos = 0;
+        s.writing = true;
+        break;
+      }
+      case noise::NoiseResponderHandshake::Action::ACTION_SPLIT: {
+        int err = s.handshake.split(s.send_cipher, s.recv_cipher);
+        if (err != 0) {
+          ESP_LOGW(TAG, "Handshake split: %s", LOG_STR_ARG(noise::noise_err_to_logstr(err)));
+          this->cleanup_connection_();
+          return false;
+        }
+        ESP_LOGD(TAG, "Noise handshake complete");
+        return true;
+      }
+      default: {
+        ESP_LOGW(TAG, "Bad handshake state");
+        this->cleanup_connection_();
+        return false;
+      }
+    }
+  }
+}
+
+/// Non-blocking read of one handshake frame into the session buffer.
+bool ESPHomeOTAComponent::noise_try_read_frame_() {
+  NoiseSession &s = *this->noise_;
+  while (s.frame_pos < noise::FRAME_HEADER_SIZE) {
+    ssize_t read = this->client_->read(s.frame_buf + s.frame_pos, noise::FRAME_HEADER_SIZE - s.frame_pos);
+    if (!this->handle_read_error_(read, LOG_STR("read noise header"))) {
+      return false;
+    }
+    s.frame_pos += read;
+  }
+  if (s.frame_len == 0) {
+    const uint16_t payload_len = encode_uint16(s.frame_buf[1], s.frame_buf[2]);
+    if (s.frame_buf[0] != noise::FRAME_INDICATOR || payload_len < 1 || payload_len > 1 + noise::MAX_HANDSHAKE_SIZE) {
+      ESP_LOGW(TAG, "Bad handshake frame: 0x%02X, %u bytes", s.frame_buf[0], payload_len);
+      this->cleanup_connection_();
+      return false;
+    }
+    s.frame_len = noise::FRAME_HEADER_SIZE + payload_len;
+  }
+  while (s.frame_pos < s.frame_len) {
+    ssize_t read = this->client_->read(s.frame_buf + s.frame_pos, s.frame_len - s.frame_pos);
+    if (!this->handle_read_error_(read, LOG_STR("read noise frame"))) {
+      return false;
+    }
+    s.frame_pos += read;
+  }
+  return true;
+}
+
+/// Non-blocking write of the pending session-buffer frame.
+bool ESPHomeOTAComponent::noise_try_write_frame_() {
+  NoiseSession &s = *this->noise_;
+  while (s.frame_pos < s.frame_len) {
+    ssize_t written = this->client_->write(s.frame_buf + s.frame_pos, s.frame_len - s.frame_pos);
+    if (!this->handle_write_error_(written, LOG_STR("write noise frame"))) {
+      return false;
+    }
+    s.frame_pos += written;
+  }
+  return true;
+}
+
+/// Best-effort explicit reject frame so the client can log a readable reason.
+void ESPHomeOTAComponent::noise_send_reject_(const LogString *reason) {
+  // Every reason here comes from noise::reject_reason_for(), so the exported
+  // floor is the exact capacity needed
+  uint8_t data[noise::FRAME_HEADER_SIZE + noise::MAC_FAILURE_PAYLOAD_SIZE];
+  const size_t payload_len =
+      noise::format_reject_payload(data + noise::FRAME_HEADER_SIZE, sizeof(data) - noise::FRAME_HEADER_SIZE, reason);
+  noise::write_frame_header(data, payload_len);
+  this->client_->write(data, noise::FRAME_HEADER_SIZE + payload_len);  // Best effort, non-blocking
+}
+
+/// Decrypt a ciphertext in place; returns the plaintext size or -1.
+ssize_t ESPHomeOTAComponent::noise_decrypt_(uint8_t *buf, size_t len) {
+  NoiseBuffer mbuf;
+  noise_buffer_init(mbuf);
+  noise_buffer_set_inout(mbuf, buf, len, len);
+  int err = noise_cipherstate_decrypt(this->noise_->recv_cipher, &mbuf);
+  if (err != 0) {
+    ESP_LOGW(TAG, "Decrypt: %s", LOG_STR_ARG(noise::noise_err_to_logstr(err)));
+    return -1;
+  }
+  return mbuf.size;
+}
+
+/** Blocking read of one frame whose ciphertext size must be within the given
+ * bounds, decrypted in place; returns the plaintext size, or -1 on error.
+ * buf needs max_ciphertext capacity.
+ */
+ssize_t ESPHomeOTAComponent::noise_read_frame_blocking_(uint8_t *buf, size_t min_ciphertext, size_t max_ciphertext) {
+  uint8_t header[noise::FRAME_HEADER_SIZE];
+  if (!this->readall_(header, sizeof(header))) {
+    return -1;
+  }
+  const size_t ciphertext_len = encode_uint16(header[1], header[2]);
+  if (header[0] != noise::FRAME_INDICATOR || ciphertext_len < min_ciphertext || ciphertext_len > max_ciphertext) {
+    ESP_LOGW(TAG, "Bad frame: 0x%02X, %zu bytes", header[0], ciphertext_len);
+    return -1;
+  }
+  if (!this->readall_(buf, ciphertext_len)) {
+    return -1;
+  }
+  return this->noise_decrypt_(buf, ciphertext_len);
+}
+
+/** Blocking read of one frame whose plaintext must be exactly len bytes
+ * (control units are one unit per frame). buf needs len + noise::MAC_SIZE
+ * capacity; the plaintext lands at buf[0..len).
+ */
+bool ESPHomeOTAComponent::noise_readall_(uint8_t *buf, size_t len) {
+  return this->noise_read_frame_blocking_(buf, len + noise::MAC_SIZE, len + noise::MAC_SIZE) == (ssize_t) len;
+}
+
+/** Blocking read of one data-phase frame, decrypted in place; returns the
+ * plaintext size, or -1 on error. buf is the OTA_BUFFER_SIZE data buffer.
+ * The ciphertext must fit that buffer and its plaintext must fit what the
+ * caller accepts (the remaining image bytes).
+ */
+ssize_t ESPHomeOTAComponent::noise_read_data_(uint8_t *buf, size_t capacity) {
+  const size_t max_ciphertext = std::min(capacity + noise::MAC_SIZE, OTA_BUFFER_SIZE);
+  return this->noise_read_frame_blocking_(buf, noise::MAC_SIZE + 1, max_ciphertext);
+}
+
+/// Blocking write of one response byte as an encrypted frame.
+bool ESPHomeOTAComponent::noise_write_byte_(uint8_t byte) {
+  uint8_t frame[noise::FRAME_HEADER_SIZE + 1 + noise::MAC_SIZE];
+  frame[noise::FRAME_HEADER_SIZE] = byte;
+  NoiseBuffer mbuf;
+  noise_buffer_init(mbuf);
+  noise_buffer_set_inout(mbuf, frame + noise::FRAME_HEADER_SIZE, 1, 1 + noise::MAC_SIZE);
+  int err = noise_cipherstate_encrypt(this->noise_->send_cipher, &mbuf);
+  if (err != 0) {
+    ESP_LOGW(TAG, "Encrypt: %s", LOG_STR_ARG(noise::noise_err_to_logstr(err)));
+    return false;
+  }
+  noise::write_frame_header(frame, mbuf.size);
+  return this->writeall_(frame, noise::FRAME_HEADER_SIZE + mbuf.size);
+}
+
+}  // namespace esphome
+#endif  // USE_OTA_ENCRYPTION
+#endif  // USE_OTA
@@ -45,6 +45,15 @@ def decode_encryption_key(value: str) -> bytes:
    return decoded


+def is_reserved_key(value: str) -> bool:
+    """Whether the key is the reserved all-zeros provisioning sentinel.
+
+    The device treats it as no key configured, so consumers that require a
+    real key must reject it.
+    """
+    return not any(decode_encryption_key(value))
+
+
 ENCRYPTION_SCHEMA = cv.Schema(
    {
        cv.Optional(CONF_KEY): cv.sensitive(validate_encryption_key),
@@ -49,6 +49,7 @@ enum OTAResponseTypes {
  OTA_RESPONSE_ERROR_BOOTLOADER_VERIFY = 0x91,
  OTA_RESPONSE_ERROR_BOOTLOADER_UPDATE = 0x92,
  OTA_RESPONSE_ERROR_VERSION_DOWNGRADE = 0x93,
+  OTA_RESPONSE_ERROR_ENCRYPTION_REQUIRED = 0x94,
  OTA_RESPONSE_ERROR_UNKNOWN = 0xFF,
 };

@@ -237,6 +237,7 @@
 #define USE_RUNTIME_IMAGE_JPEG
 #define USE_RUNTIME_STATS
 #define USE_OTA
+#define USE_OTA_ENCRYPTION
 #define USE_OTA_PASSWORD
 #define USE_OTA_VERSION 2
 #define USE_TIME_TIMEZONE
@@ -0,0 +1,9 @@
+wifi:
+  ssid: MySSID
+  password: password1
+
+ota:
+  - platform: esphome
+    port: 3288
+    encryption:
+      key: "AAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8="
@@ -0,0 +1,12 @@
+wifi:
+  ssid: MySSID
+  password: password1
+
+api:
+  encryption:
+    key: "AAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8="
+
+ota:
+  - platform: esphome
+    port: 3289
+    encryption:
@@ -0,0 +1,2 @@
+packages:
+  ota: !include encryption.yaml
@@ -0,0 +1,2 @@
+packages:
+  ota: !include encryption.yaml
@@ -0,0 +1,2 @@
+packages:
+  ota: !include encryption.yaml
@@ -0,0 +1,2 @@
+packages:
+  ota: !include encryption_inherit.yaml