diff --git a/CODEOWNERS b/CODEOWNERS
index 9ddbca5c71..3047072ea2 100644
--- a/CODEOWNERS
+++ b/CODEOWNERS
@@ -381,6 +381,7 @@ esphome/components/nextion/switch/* @senexcrenshaw
 esphome/components/nextion/text_sensor/* @senexcrenshaw
 esphome/components/nfc/* @jesserockz @kbx81
 esphome/components/noblex/* @AGalfra
+esphome/components/noise/* @esphome/core
 esphome/components/npi19/* @bakerkj
 esphome/components/nrf52/* @tomaszduda23
 esphome/components/number/* @esphome/core
diff --git a/esphome/components/api/__init__.py b/esphome/components/api/__init__.py
index 0dc4b905bf..53ad0fe5d7 100644
--- a/esphome/components/api/__init__.py
+++ b/esphome/components/api/__init__.py
@@ -1,4 +1,3 @@
-import base64
 import logging
 from typing import Any
 
@@ -6,6 +5,15 @@ from esphome import automation
 from esphome.automation import Condition
 import esphome.codegen as cg
 from esphome.components.logger import request_log_listener
+
+# ENCRYPTION_SCHEMA and validate_encryption_key are re-exported for external
+# components and downstream consumers that import them from api
+from esphome.components.noise import (  # noqa: F401
+    ENCRYPTION_SCHEMA,
+    decode_encryption_key,
+    encryption_schema,
+    validate_encryption_key,
+)
 from esphome.config_helpers import get_logger_level
 import esphome.config_validation as cv
 from esphome.const import (
@@ -38,6 +46,10 @@ from esphome.core import CORE, ID, CoroPriority, EsphomeError, coroutine_with_pr
 from esphome.cpp_generator import MockObj, TemplateArgsType
 from esphome.types import ConfigFragmentType, ConfigType
 
+# Compat alias: downstream consumers (e.g. device-builder) referenced the
+# schema by its old private name before it moved to the noise component
+_encryption_schema = encryption_schema
+
 _LOGGER = logging.getLogger(__name__)
 
 DOMAIN = "api"
@@ -46,9 +58,15 @@ CODEOWNERS = ["@esphome/core"]
 
 
 def AUTO_LOAD(config: ConfigType) -> list[str]:
-    """Conditionally auto-load json only when capture_response is used."""
+    """Conditionally auto-load noise (encryption) and json (capture_response)."""
     base = ["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:
+        base = base + ["noise"]
+
     # Check if any homeassistant.action/homeassistant.service has capture_response: true
     # This flag is set during config validation in _validate_response_config
     if not config or CORE.data.get(DOMAIN, {}).get(CONF_CAPTURE_RESPONSE, False):
@@ -130,20 +148,6 @@ def _register_provisioning_source(config: ConfigType) -> ConfigType:
     return config
 
 
-def validate_encryption_key(value: Any) -> str:
-    value = cv.string_strict(value)
-    try:
-        decoded = base64.b64decode(value, validate=True)
-    except ValueError as err:
-        raise cv.Invalid("Invalid key format, please check it's using base64") from err
-
-    if len(decoded) != 32:
-        raise cv.Invalid("Encryption key must be base64 and 32 bytes long")
-
-    # Return original data for roundtrip conversion
-    return value
-
-
 CONF_SUPPORTS_RESPONSE = "supports_response"
 
 # Enum values in api::enums namespace
@@ -250,18 +254,6 @@ ACTIONS_SCHEMA = automation.validate_automation(
     ),
 )
 
-ENCRYPTION_SCHEMA = cv.Schema(
-    {
-        cv.Optional(CONF_KEY): cv.sensitive(validate_encryption_key),
-    }
-)
-
-
-def _encryption_schema(config: ConfigType | None) -> ConfigType:
-    if config is None:
-        config = {}
-    return ENCRYPTION_SCHEMA(config)
-
 
 def _consume_api_sockets(config: ConfigType) -> ConfigType:
     """Register socket needs for API component."""
@@ -297,7 +289,7 @@ CONFIG_SCHEMA = cv.All(
                 CONF_SERVICES, group_of_exclusion=CONF_ACTIONS
             ): ACTIONS_SCHEMA,
             cv.Exclusive(CONF_ACTIONS, group_of_exclusion=CONF_ACTIONS): ACTIONS_SCHEMA,
-            cv.Optional(CONF_ENCRYPTION): _encryption_schema,
+            cv.Optional(CONF_ENCRYPTION): encryption_schema,
             cv.Optional(CONF_BATCH_DELAY, default="100ms"): cv.All(
                 cv.positive_time_period_milliseconds,
                 cv.Range(max=cv.TimePeriod(milliseconds=65535)),
@@ -484,7 +476,7 @@ async def to_code(config: ConfigType) -> None:
 
     if (encryption_config := config.get(CONF_ENCRYPTION, None)) is not None:
         if key := encryption_config.get(CONF_KEY):
-            decoded = base64.b64decode(key)
+            decoded = decode_encryption_key(key)
             cg.add(var.set_noise_psk(list(decoded)))
             cg.add_define("USE_API_NOISE_PSK_FROM_YAML")
         else:
@@ -498,10 +490,6 @@ async def to_code(config: ConfigType) -> None:
             # and plaintext disabled. Only a factory reset can remove it.
             cg.add_define("USE_API_PLAINTEXT")
         cg.add_define("USE_API_NOISE")
-        cg.add_library("esphome/noise-c", "0.1.21")
-        # Enable optimized memzero/memcmp in libsodium instead of volatile byte loops
-        cg.add_build_flag("-DHAVE_WEAK_SYMBOLS=1")
-        cg.add_build_flag("-DHAVE_INLINE_ASM=1")
     else:
         cg.add_define("USE_API_PLAINTEXT")
 
diff --git a/esphome/components/api/api_connection.cpp b/esphome/components/api/api_connection.cpp
index c1dded1271..91d13eed65 100644
--- a/esphome/components/api/api_connection.cpp
+++ b/esphome/components/api/api_connection.cpp
@@ -2130,7 +2130,7 @@ bool APIConnection::send_noise_encryption_set_key_response_(const NoiseEncryptio
   }
 #endif
 
-  psk_t psk{};
+  noise::psk_t psk{};
   if (msg.key_len == 0) {
     if (this->parent_->clear_noise_psk(true)) {
       resp.success = true;
@@ -2139,7 +2139,7 @@ bool APIConnection::send_noise_encryption_set_key_response_(const NoiseEncryptio
     }
   } else if (base64_decode(msg.key, msg.key_len, psk.data(), psk.size()) != psk.size()) {
     ESP_LOGW(TAG, "Invalid encryption key length");
-  } else if (APINoiseContext::is_all_zeros(psk)) {
+  } else if (noise::NoiseContext::is_all_zeros(psk)) {
     // Accepting the reserved provisioning PSK would report success without
     // enabling encryption (or silently clear an existing key)
     ESP_LOGW(TAG, "Rejecting all-zero encryption key");
diff --git a/esphome/components/api/api_frame_helper_noise.cpp b/esphome/components/api/api_frame_helper_noise.cpp
index 09e3ca2b9e..d7554e62c5 100644
--- a/esphome/components/api/api_frame_helper_noise.cpp
+++ b/esphome/components/api/api_frame_helper_noise.cpp
@@ -2,9 +2,9 @@
 #ifdef USE_API
 #ifdef USE_API_NOISE
 #include "api_connection.h"  // For ClientInfo struct
+#include "esphome/components/noise/noise.h"
 #include "esphome/core/application.h"
 #include "esphome/core/entity_base.h"
-#include "esphome/core/hal.h"
 #include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
 #include "proto.h"
@@ -17,6 +17,14 @@
 
 namespace esphome::api {
 
+using noise::noise_err_to_logstr;
+
+// api_frame_helper.h keeps its own MAX_HANDSHAKE_SIZE because that header is
+// also compiled in plaintext-only builds without the noise component; keep
+// the two definitions from drifting apart.
+static_assert(MAX_HANDSHAKE_SIZE == noise::MAX_HANDSHAKE_SIZE,
+              "api and noise component handshake size limits must match");
+
 static const char *const TAG = "api.noise";
 #ifdef USE_ESP8266
 static constexpr char PROLOGUE_INIT[] PROGMEM = "NoiseAPIInit";
@@ -51,45 +59,6 @@ static constexpr size_t API_MAX_LOG_BYTES = 168;
 #define LOG_PACKET_RECEIVED(buffer) ((void) 0)
 #endif
 
-/// Convert a noise error code to a readable error
-const LogString *noise_err_to_logstr(int err) {
-  if (err == NOISE_ERROR_NO_MEMORY)
-    return LOG_STR("NO_MEMORY");
-  if (err == NOISE_ERROR_UNKNOWN_ID)
-    return LOG_STR("UNKNOWN_ID");
-  if (err == NOISE_ERROR_UNKNOWN_NAME)
-    return LOG_STR("UNKNOWN_NAME");
-  if (err == NOISE_ERROR_MAC_FAILURE)
-    return LOG_STR("MAC_FAILURE");
-  if (err == NOISE_ERROR_NOT_APPLICABLE)
-    return LOG_STR("NOT_APPLICABLE");
-  if (err == NOISE_ERROR_SYSTEM)
-    return LOG_STR("SYSTEM");
-  if (err == NOISE_ERROR_REMOTE_KEY_REQUIRED)
-    return LOG_STR("REMOTE_KEY_REQUIRED");
-  if (err == NOISE_ERROR_LOCAL_KEY_REQUIRED)
-    return LOG_STR("LOCAL_KEY_REQUIRED");
-  if (err == NOISE_ERROR_PSK_REQUIRED)
-    return LOG_STR("PSK_REQUIRED");
-  if (err == NOISE_ERROR_INVALID_LENGTH)
-    return LOG_STR("INVALID_LENGTH");
-  if (err == NOISE_ERROR_INVALID_PARAM)
-    return LOG_STR("INVALID_PARAM");
-  if (err == NOISE_ERROR_INVALID_STATE)
-    return LOG_STR("INVALID_STATE");
-  if (err == NOISE_ERROR_INVALID_NONCE)
-    return LOG_STR("INVALID_NONCE");
-  if (err == NOISE_ERROR_INVALID_PRIVATE_KEY)
-    return LOG_STR("INVALID_PRIVATE_KEY");
-  if (err == NOISE_ERROR_INVALID_PUBLIC_KEY)
-    return LOG_STR("INVALID_PUBLIC_KEY");
-  if (err == NOISE_ERROR_INVALID_FORMAT)
-    return LOG_STR("INVALID_FORMAT");
-  if (err == NOISE_ERROR_INVALID_SIGNATURE)
-    return LOG_STR("INVALID_SIGNATURE");
-  return LOG_STR("UNKNOWN");
-}
-
 /// Initialize the frame helper, returns OK if successful.
 APIError APINoiseFrameHelper::init() {
   APIError err = init_common_();
@@ -194,9 +163,9 @@ APIError APINoiseFrameHelper::loop() {
  */
 APIError APINoiseFrameHelper::try_read_frame_() {
   // read header
-  if (rx_header_buf_len_ < 3) {
+  if (rx_header_buf_len_ < noise::FRAME_HEADER_SIZE) {
     // no header information yet
-    uint8_t to_read = 3 - rx_header_buf_len_;
+    uint8_t to_read = static_cast<uint8_t>(noise::FRAME_HEADER_SIZE) - rx_header_buf_len_;
     ssize_t received = this->socket_->read(&rx_header_buf_[rx_header_buf_len_], to_read);
     APIError err = handle_socket_read_result_(received);
     if (err != APIError::OK) {
@@ -208,7 +177,7 @@ APIError APINoiseFrameHelper::try_read_frame_() {
       return APIError::WOULD_BLOCK;
     }
 
-    if (rx_header_buf_[0] != 0x01) {
+    if (rx_header_buf_[0] != noise::FRAME_INDICATOR) {
       state_ = State::FAILED;
       HELPER_LOG("Bad indicator byte %u", rx_header_buf_[0]);
       return APIError::BAD_INDICATOR;
@@ -348,15 +317,15 @@ APIError APINoiseFrameHelper::state_action_server_hello_() {
   return APIError::OK;
 }
 APIError APINoiseFrameHelper::state_action_handshake_() {
-  int action = noise_handshakestate_get_action(this->handshake_);
-  if (action == NOISE_ACTION_READ_MESSAGE) {
+  noise::NoiseResponderHandshake::Action action = this->handshake_.action();
+  if (action == noise::NoiseResponderHandshake::Action::ACTION_READ) {
     return this->state_action_handshake_read_();
-  } else if (action == NOISE_ACTION_WRITE_MESSAGE) {
+  } else if (action == noise::NoiseResponderHandshake::Action::ACTION_WRITE) {
     return this->state_action_handshake_write_();
   }
   // bad state for action
   this->state_ = State::FAILED;
-  HELPER_LOG("Bad action for handshake: %d", action);
+  HELPER_LOG("Bad action for handshake: %d", (int) action);
   return APIError::HANDSHAKESTATE_BAD_STATE;
 }
 APIError APINoiseFrameHelper::state_action_handshake_read_() {
@@ -368,20 +337,16 @@ APIError APINoiseFrameHelper::state_action_handshake_read_() {
   if (this->rx_buf_.empty()) {
     this->send_explicit_handshake_reject_(LOG_STR("Empty handshake message"));
     return APIError::BAD_HANDSHAKE_ERROR_BYTE;
-  } else if (this->rx_buf_[0] != 0x00) {
+  } else if (this->rx_buf_[0] != noise::HANDSHAKE_STATUS_OK) {
     HELPER_LOG("Bad handshake error byte: %u", this->rx_buf_[0]);
     this->send_explicit_handshake_reject_(LOG_STR("Bad handshake error byte"));
     return APIError::BAD_HANDSHAKE_ERROR_BYTE;
   }
 
-  NoiseBuffer mbuf;
-  noise_buffer_init(mbuf);
-  noise_buffer_set_input(mbuf, this->rx_buf_.data() + 1, this->rx_buf_.size() - 1);
-  int err = noise_handshakestate_read_message(this->handshake_, &mbuf, nullptr);
+  int err = this->handshake_.read_message(this->rx_buf_.data() + 1, this->rx_buf_.size() - 1);
   if (err != 0) {
     // Special handling for MAC failure
-    this->send_explicit_handshake_reject_(err == NOISE_ERROR_MAC_FAILURE ? LOG_STR("Handshake MAC failure")
-                                                                         : LOG_STR("Handshake error"));
+    this->send_explicit_handshake_reject_(noise::reject_reason_for(err));
     return this->handle_noise_error_(err, LOG_STR("noise_handshakestate_read_message"),
                                      APIError::HANDSHAKESTATE_READ_FAILED);
   }
@@ -390,18 +355,16 @@ APIError APINoiseFrameHelper::state_action_handshake_read_() {
 }
 APIError APINoiseFrameHelper::state_action_handshake_write_() {
   uint8_t buffer[65];
-  NoiseBuffer mbuf;
-  noise_buffer_init(mbuf);
-  noise_buffer_set_output(mbuf, buffer + 1, sizeof(buffer) - 1);
+  size_t msg_len = 0;
 
-  int err = noise_handshakestate_write_message(this->handshake_, &mbuf, nullptr);
+  int err = this->handshake_.write_message(buffer + 1, sizeof(buffer) - 1, msg_len);
   APIError aerr = this->handle_noise_error_(err, LOG_STR("noise_handshakestate_write_message"),
                                             APIError::HANDSHAKESTATE_WRITE_FAILED);
   if (aerr != APIError::OK)
     return aerr;
-  buffer[0] = 0x00;  // success
+  buffer[0] = noise::HANDSHAKE_STATUS_OK;
 
-  aerr = this->write_frame_(buffer, mbuf.size + 1);
+  aerr = this->write_frame_(buffer, msg_len + 1);
   if (aerr != APIError::OK)
     return aerr;
   return this->check_handshake_finished_();
@@ -409,33 +372,22 @@ APIError APINoiseFrameHelper::state_action_handshake_write_() {
 void APINoiseFrameHelper::send_explicit_handshake_reject_(const LogString *reason) {
   // Max reject message: "Bad handshake packet len" (24) + 1 (failure byte) = 25 bytes
   uint8_t data[32];
-  data[0] = 0x01;  // failure
-
-#ifdef USE_STORE_LOG_STR_IN_FLASH
-  // On ESP8266 with flash strings, we need to use PROGMEM-aware functions
-  size_t reason_len = strlen_P(reinterpret_cast<PGM_P>(reason));
-  reason_len = std::min(reason_len, sizeof(data) - 1);
-  if (reason_len > 0) {
-    memcpy_P(data + 1, reinterpret_cast<PGM_P>(reason), reason_len);
-  }
-#else
-  // Normal memory access
-  const char *reason_str = LOG_STR_ARG(reason);
-  size_t reason_len = strlen(reason_str);
-  reason_len = std::min(reason_len, sizeof(data) - 1);
-  if (reason_len > 0) {
-    // NOLINTNEXTLINE(bugprone-not-null-terminated-result) - binary protocol, not a C string
-    std::memcpy(data + 1, reason_str, reason_len);
-  }
-#endif
-
-  size_t data_size = reason_len + 1;
+  static_assert(sizeof(data) >= noise::MAC_FAILURE_PAYLOAD_SIZE,
+                "reject buffer must fit the MAC failure wire contract");
+  size_t data_size = noise::format_reject_payload(data, sizeof(data), reason);
 
   // temporarily remove failed state
   auto orig_state = state_;
   state_ = State::EXPLICIT_REJECT;
-  write_frame_(data, data_size);
-  state_ = orig_state;
+  APIError aerr = write_frame_(data, data_size);
+  if (aerr != APIError::OK) {
+    // Best effort; the reject reason is a diagnosis aid, not a protocol step
+    ESP_LOGW(TAG, "Sending handshake reject failed: %d", (int) aerr);
+  }
+  if (state_ == State::EXPLICIT_REJECT) {
+    // write_frame_ may have moved the state to FAILED; keep that decision
+    state_ = orig_state;
+  }
 }
 APIError APINoiseFrameHelper::read_packet(ReadPacketBuffer *buffer) {
   APIError aerr = this->check_data_state_();
@@ -492,12 +444,10 @@ APIError APINoiseFrameHelper::read_packet(ReadPacketBuffer *buffer) {
 // Returns APIError::OK on success.
 APIError APINoiseFrameHelper::encrypt_noise_message_(uint8_t *buf_start, uint16_t payload_size, uint8_t message_type,
                                                      uint16_t &encrypted_len_out) {
-  // Write noise header
-  buf_start[0] = 0x01;  // indicator
-  // buf_start[1], buf_start[2] to be set after encryption
+  // The noise frame header is written after encryption, when the size is known
 
   // Write message header (to be encrypted)
-  constexpr uint8_t msg_offset = 3;
+  constexpr uint8_t msg_offset = noise::FRAME_HEADER_SIZE;
   buf_start[msg_offset] = static_cast<uint8_t>(message_type >> 8);      // type high byte
   buf_start[msg_offset + 1] = static_cast<uint8_t>(message_type);       // type low byte
   buf_start[msg_offset + 2] = static_cast<uint8_t>(payload_size >> 8);  // data_len high byte
@@ -515,11 +465,10 @@ APIError APINoiseFrameHelper::encrypt_noise_message_(uint8_t *buf_start, uint16_
   if (aerr != APIError::OK)
     return aerr;
 
-  // Fill in the encrypted size
-  buf_start[1] = static_cast<uint8_t>(mbuf.size >> 8);
-  buf_start[2] = static_cast<uint8_t>(mbuf.size);
+  // Fill in the frame header now that the encrypted size is known
+  noise::write_frame_header(buf_start, static_cast<uint16_t>(mbuf.size));
 
-  encrypted_len_out = static_cast<uint16_t>(3 + mbuf.size);  // indicator + size + encrypted data
+  encrypted_len_out = static_cast<uint16_t>(noise::FRAME_HEADER_SIZE + mbuf.size);
   return APIError::OK;
 }
 
@@ -568,21 +517,19 @@ APIError APINoiseFrameHelper::write_protobuf_messages(ProtoWriteBuffer buffer, s
 }
 
 APIError APINoiseFrameHelper::write_frame_(const uint8_t *data, uint16_t len) {
-  uint8_t header[3];
-  header[0] = 0x01;  // indicator
-  header[1] = (uint8_t) (len >> 8);
-  header[2] = (uint8_t) len;
+  uint8_t header[noise::FRAME_HEADER_SIZE];
+  noise::write_frame_header(header, len);
 
   if (len == 0) {
-    return this->write_raw_buf_(header, 3);
+    return this->write_raw_buf_(header, noise::FRAME_HEADER_SIZE);
   }
   struct iovec iov[2];
   iov[0].iov_base = header;
-  iov[0].iov_len = 3;
+  iov[0].iov_len = noise::FRAME_HEADER_SIZE;
   iov[1].iov_base = const_cast<uint8_t *>(data);
   iov[1].iov_len = len;
 
-  return this->write_raw_iov_(iov, 2, 3 + len);
+  return this->write_raw_iov_(iov, 2, noise::FRAME_HEADER_SIZE + len);
 }
 
 /** Initiate the data structures for the handshake.
@@ -590,45 +537,12 @@ APIError APINoiseFrameHelper::write_frame_(const uint8_t *data, uint16_t len) {
  * @return 0 on success, -1 on error (check errno)
  */
 APIError APINoiseFrameHelper::init_handshake_() {
-  int err;
-  // Noise_NNpsk0_25519_ChaChaPoly_SHA256, built on the stack:
-  // noise_handshakestate_new_by_id copies it, so a member would waste
-  // 104 bytes per connection, and a static const would sit in RAM on
-  // ESP8266 (.rodata is DRAM there).
-  const NoiseProtocolId nid = {
-      .prefix_id = NOISE_PREFIX_STANDARD,
-      .pattern_id = NOISE_PATTERN_NN,
-      .modifier_ids = {NOISE_MODIFIER_PSK0},
-      .dh_id = NOISE_DH_CURVE25519,
-      .cipher_id = NOISE_CIPHER_CHACHAPOLY,
-      .hash_id = NOISE_HASH_SHA256,
-      .hybrid_id = NOISE_DH_NONE,
-  };
-
-  err = noise_handshakestate_new_by_id(&handshake_, &nid, NOISE_ROLE_RESPONDER);
-  APIError aerr =
-      handle_noise_error_(err, LOG_STR("noise_handshakestate_new_by_id"), APIError::HANDSHAKESTATE_SETUP_FAILED);
+  int err = this->handshake_.init(this->ctx_.get_psk(), prologue_.data(), prologue_.size());
+  APIError aerr = handle_noise_error_(err, LOG_STR("noise_handshake_init"), APIError::HANDSHAKESTATE_SETUP_FAILED);
   if (aerr != APIError::OK)
     return aerr;
-
-  const auto &psk = this->ctx_.get_psk();
-  err = noise_handshakestate_set_pre_shared_key(handshake_, psk.data(), psk.size());
-  aerr = handle_noise_error_(err, LOG_STR("noise_handshakestate_set_pre_shared_key"),
-                             APIError::HANDSHAKESTATE_SETUP_FAILED);
-  if (aerr != APIError::OK)
-    return aerr;
-
-  err = noise_handshakestate_set_prologue(handshake_, prologue_.data(), prologue_.size());
-  aerr = handle_noise_error_(err, LOG_STR("noise_handshakestate_set_prologue"), APIError::HANDSHAKESTATE_SETUP_FAILED);
-  if (aerr != APIError::OK)
-    return aerr;
-  // set_prologue copies it into handshakestate, so we can get rid of it now
+  // init copies the prologue into the handshakestate, so we can get rid of it now
   prologue_.release();
-
-  err = noise_handshakestate_start(handshake_);
-  aerr = handle_noise_error_(err, LOG_STR("noise_handshakestate_start"), APIError::HANDSHAKESTATE_SETUP_FAILED);
-  if (aerr != APIError::OK)
-    return aerr;
   return APIError::OK;
 }
 
@@ -637,15 +551,17 @@ APIError APINoiseFrameHelper::check_handshake_finished_() {
   assert(state_ == State::HANDSHAKE);
 #endif
 
-  int action = noise_handshakestate_get_action(handshake_);
-  if (action == NOISE_ACTION_READ_MESSAGE || action == NOISE_ACTION_WRITE_MESSAGE)
+  noise::NoiseResponderHandshake::Action action = this->handshake_.action();
+  if (action == noise::NoiseResponderHandshake::Action::ACTION_READ ||
+      action == noise::NoiseResponderHandshake::Action::ACTION_WRITE)
     return APIError::OK;
-  if (action != NOISE_ACTION_SPLIT) {
+  if (action != noise::NoiseResponderHandshake::Action::ACTION_SPLIT) {
     state_ = State::FAILED;
-    HELPER_LOG("Bad action for handshake: %d", action);
+    HELPER_LOG("Bad action for handshake: %d", (int) action);
     return APIError::HANDSHAKESTATE_BAD_STATE;
   }
-  int err = noise_handshakestate_split(handshake_, &send_cipher_, &recv_cipher_);
+  // split() also frees the handshake state
+  int err = this->handshake_.split(send_cipher_, recv_cipher_);
   APIError aerr =
       handle_noise_error_(err, LOG_STR("noise_handshakestate_split"), APIError::HANDSHAKESTATE_SPLIT_FAILED);
   if (aerr != APIError::OK)
@@ -654,17 +570,11 @@ APIError APINoiseFrameHelper::check_handshake_finished_() {
   this->frame_footer_size_ = noise_cipherstate_get_mac_length(send_cipher_);
 
   HELPER_LOG("Handshake complete!");
-  noise_handshakestate_free(handshake_);
-  handshake_ = nullptr;
   state_ = State::DATA;
   return APIError::OK;
 }
 
 APINoiseFrameHelper::~APINoiseFrameHelper() {
-  if (handshake_ != nullptr) {
-    noise_handshakestate_free(handshake_);
-    handshake_ = nullptr;
-  }
   if (send_cipher_ != nullptr) {
     noise_cipherstate_free(send_cipher_);
     send_cipher_ = nullptr;
@@ -675,16 +585,6 @@ APINoiseFrameHelper::~APINoiseFrameHelper() {
   }
 }
 
-extern "C" {
-// declare how noise generates random bytes (here with a good HWRNG based on the RF system)
-void noise_rand_bytes(void *output, size_t len) {
-  if (!esphome::random_bytes(reinterpret_cast<uint8_t *>(output), len)) {
-    ESP_LOGE(TAG, "Acquiring random bytes failed; rebooting");
-    arch_restart();
-  }
-}
-}
-
 }  // namespace esphome::api
 #endif  // USE_API_NOISE
 #endif  // USE_API
diff --git a/esphome/components/api/api_frame_helper_noise.h b/esphome/components/api/api_frame_helper_noise.h
index 46bd366672..05060c77de 100644
--- a/esphome/components/api/api_frame_helper_noise.h
+++ b/esphome/components/api/api_frame_helper_noise.h
@@ -3,7 +3,7 @@
 #ifdef USE_API
 #ifdef USE_API_NOISE
 #include "noise/protocol.h"
-#include "api_noise_context.h"
+#include "esphome/components/noise/noise_handshake.h"
 
 namespace esphome::api {
 
@@ -14,9 +14,9 @@ class APINoiseFrameHelper final : public APIFrameHelper {
   // Pos 1-2: encrypted payload size (16-bit big-endian)
   // Pos 3-6: encrypted type (16-bit) + data_len (16-bit)
   // Pos 7+: actual payload data
-  static constexpr uint8_t HEADER_PADDING = 1 + 2 + 2 + 2;  // indicator + size + type + data_len
+  static constexpr uint8_t HEADER_PADDING = noise::FRAME_HEADER_SIZE + 2 + 2;  // frame header + type + data_len
 
-  APINoiseFrameHelper(std::unique_ptr<socket::Socket> socket, APINoiseContext &ctx)
+  APINoiseFrameHelper(std::unique_ptr<socket::Socket> socket, noise::NoiseContext &ctx)
       : APIFrameHelper(std::move(socket)), ctx_(ctx) {
     frame_header_padding_ = HEADER_PADDING;
   }
@@ -52,13 +52,13 @@ class APINoiseFrameHelper final : public APIFrameHelper {
   APIError handle_handshake_frame_error_(APIError aerr);
   APIError handle_noise_error_(int err, const LogString *func_name, APIError api_err);
 
-  // Pointers first (4 bytes each)
-  NoiseHandshakeState *handshake_{nullptr};
+  // Pointers first (4 bytes each; the handshake wrapper holds one pointer)
+  noise::NoiseResponderHandshake handshake_;
   NoiseCipherState *send_cipher_{nullptr};
   NoiseCipherState *recv_cipher_{nullptr};
 
   // Reference to noise context (4 bytes on 32-bit)
-  APINoiseContext &ctx_;
+  noise::NoiseContext &ctx_;
 
   // Buffer for noise handshake prologue (released after handshake)
   APIBuffer prologue_;
@@ -67,7 +67,7 @@ class APINoiseFrameHelper final : public APIFrameHelper {
   // Fixed-size header buffer for noise protocol:
   // 1 byte for indicator + 2 bytes for message size (16-bit value, not varint)
   // Note: Maximum message size is UINT16_MAX (65535), with a limit of 128 bytes during handshake phase
-  uint8_t rx_header_buf_[3];
+  uint8_t rx_header_buf_[noise::FRAME_HEADER_SIZE];
   uint8_t rx_header_buf_len_ = 0;
   // 4 bytes total, no padding
 };
diff --git a/esphome/components/api/api_noise_context.h b/esphome/components/api/api_noise_context.h
deleted file mode 100644
index 44484ffa2c..0000000000
--- a/esphome/components/api/api_noise_context.h
+++ /dev/null
@@ -1,37 +0,0 @@
-#pragma once
-#include <array>
-#include <cstdint>
-#include "esphome/core/defines.h"
-
-namespace esphome::api {
-
-#ifdef USE_API_NOISE
-using psk_t = std::array<uint8_t, 32>;
-
-class APINoiseContext {
- public:
-  // The all-zeros PSK is reserved: it marks the device as unprovisioned and
-  // doubles as the well-known provisioning PSK that unprovisioned devices
-  // accept for Noise handshakes (passive-sniffing protection only, no
-  // authentication). It is never a valid real key.
-  static bool is_all_zeros(const psk_t &psk) {
-    uint8_t acc = 0;
-    for (uint8_t b : psk) {
-      acc |= b;
-    }
-    return acc == 0;
-  }
-  void set_psk(psk_t psk) {
-    this->psk_ = psk;
-    this->has_psk_ = !is_all_zeros(psk);
-  }
-  const psk_t &get_psk() const { return this->psk_; }
-  bool has_psk() const { return this->has_psk_; }
-
- protected:
-  psk_t psk_{};
-  bool has_psk_{false};
-};
-#endif  // USE_API_NOISE
-
-}  // namespace esphome::api
diff --git a/esphome/components/api/api_server.cpp b/esphome/components/api/api_server.cpp
index 2d5f9e4155..751f2e4c3b 100644
--- a/esphome/components/api/api_server.cpp
+++ b/esphome/components/api/api_server.cpp
@@ -588,7 +588,7 @@ bool APIServer::load_and_apply_noise_psk_() {
   return true;
 }
 
-bool APIServer::save_noise_psk(psk_t psk, bool make_active) {
+bool APIServer::save_noise_psk(noise::psk_t psk, bool make_active) {
 #ifdef USE_API_NOISE_PSK_FROM_YAML
   // When PSK is set from YAML, this function should never be called
   // but if it is, reject the change
diff --git a/esphome/components/api/api_server.h b/esphome/components/api/api_server.h
index a58e42534b..072a583901 100644
--- a/esphome/components/api/api_server.h
+++ b/esphome/components/api/api_server.h
@@ -5,7 +5,10 @@
 #include "api_buffer.h"
 // Must precede clients_ so APIConnection is complete for default_delete (libc++).
 #include "api_connection.h"
-#include "api_noise_context.h"
+#ifdef USE_API_NOISE
+// Only present in the build when the noise component is loaded
+#include "esphome/components/noise/noise.h"
+#endif
 #include "api_pb2.h"
 #include "api_pb2_service.h"
 #include "esphome/components/socket/socket.h"
@@ -37,7 +40,7 @@ class UserServiceDescriptor;
 
 #ifdef USE_API_NOISE
 struct SavedNoisePsk {
-  psk_t psk;
+  noise::psk_t psk;
 } PACKED;  // NOLINT
 #endif
 
@@ -73,10 +76,10 @@ class APIServer final : public Component,
   APIBuffer &get_shared_buffer_ref() { return shared_write_buffer_; }
 
 #ifdef USE_API_NOISE
-  bool save_noise_psk(psk_t psk, bool make_active = true);
+  bool save_noise_psk(noise::psk_t psk, bool make_active = true);
   bool clear_noise_psk(bool make_active = true);
-  void set_noise_psk(psk_t psk) { this->noise_ctx_.set_psk(psk); }
-  APINoiseContext &get_noise_ctx() { return this->noise_ctx_; }
+  void set_noise_psk(noise::psk_t psk) { this->noise_ctx_.set_psk(psk); }
+  noise::NoiseContext &get_noise_ctx() { return this->noise_ctx_; }
 #endif  // USE_API_NOISE
 
   void handle_disconnect(APIConnection *conn);
@@ -354,7 +357,7 @@ class APIServer final : public Component,
 #endif
 
 #ifdef USE_API_NOISE
-  APINoiseContext noise_ctx_;
+  noise::NoiseContext noise_ctx_;
   ESPPreferenceObject noise_pref_;
 #endif  // USE_API_NOISE
 };
diff --git a/esphome/components/noise/__init__.py b/esphome/components/noise/__init__.py
new file mode 100644
index 0000000000..e5fcc94332
--- /dev/null
+++ b/esphome/components/noise/__init__.py
@@ -0,0 +1,69 @@
+import base64
+import binascii
+from typing import Any
+
+import esphome.codegen as cg
+import esphome.config_validation as cv
+from esphome.const import CONF_KEY
+from esphome.types import ConfigType
+
+CODEOWNERS = ["@esphome/core"]
+
+noise_ns = cg.esphome_ns.namespace("noise")
+
+CONFIG_SCHEMA = cv.Schema({})
+
+
+def validate_encryption_key(value: Any) -> str:
+    value = cv.string_strict(value)
+    try:
+        decoded = base64.b64decode(value, validate=True)
+    except ValueError as err:
+        raise cv.Invalid("Invalid key format, please check it's using base64") from err
+
+    if len(decoded) != 32:
+        raise cv.Invalid("Encryption key must be base64 and 32 bytes long")
+
+    # Return original data for roundtrip conversion
+    return value
+
+
+def decode_encryption_key(value: str) -> bytes:
+    """Decode a base64 encryption key to its 32 raw bytes.
+
+    a2b_base64 matches the decode the clients use (aioesphomeapi
+    decode_noise_psk), so both ends derive the same bytes. The length is
+    re-checked so a caller cannot turn an unvalidated short decode into a
+    zero-padded PSK.
+    """
+    try:
+        decoded = binascii.a2b_base64(value)
+    except ValueError as err:
+        raise cv.Invalid("Invalid key format, please check it's using base64") from err
+    if len(decoded) != 32:
+        raise cv.Invalid("Encryption key must be base64 and 32 bytes long")
+    return decoded
+
+
+ENCRYPTION_SCHEMA = cv.Schema(
+    {
+        cv.Optional(CONF_KEY): cv.sensitive(validate_encryption_key),
+    }
+)
+
+
+def encryption_schema(config: ConfigType | None) -> ConfigType:
+    # A bare `encryption:` block is valid; a missing key means the consumer
+    # falls back to its keyless behavior (api provisioning, ota inheriting
+    # the api key).
+    if config is None:
+        config = {}
+    return ENCRYPTION_SCHEMA(config)
+
+
+async def to_code(config: ConfigType) -> None:
+    cg.add_define("USE_NOISE")
+    cg.add_library("esphome/noise-c", "0.1.21")
+    # Enable optimized memzero/memcmp in libsodium instead of volatile byte loops
+    cg.add_build_flag("-DHAVE_WEAK_SYMBOLS=1")
+    cg.add_build_flag("-DHAVE_INLINE_ASM=1")
diff --git a/esphome/components/noise/noise.cpp b/esphome/components/noise/noise.cpp
new file mode 100644
index 0000000000..95fab322db
--- /dev/null
+++ b/esphome/components/noise/noise.cpp
@@ -0,0 +1,88 @@
+#include "noise.h"
+#ifdef USE_NOISE
+#include "esphome/core/log.h"
+
+#include <algorithm>
+#include <cstring>
+
+#include <noise/protocol.h>
+
+#ifdef USE_ESP8266
+#include <pgmspace.h>
+#endif
+
+namespace esphome::noise {
+
+static const char *const TAG = "noise";
+
+const LogString *noise_err_to_logstr(int err) {
+  if (err == NOISE_ERROR_NO_MEMORY)
+    return LOG_STR("NO_MEMORY");
+  if (err == NOISE_ERROR_UNKNOWN_ID)
+    return LOG_STR("UNKNOWN_ID");
+  if (err == NOISE_ERROR_UNKNOWN_NAME)
+    return LOG_STR("UNKNOWN_NAME");
+  if (err == NOISE_ERROR_MAC_FAILURE)
+    return LOG_STR("MAC_FAILURE");
+  if (err == NOISE_ERROR_NOT_APPLICABLE)
+    return LOG_STR("NOT_APPLICABLE");
+  if (err == NOISE_ERROR_SYSTEM)
+    return LOG_STR("SYSTEM");
+  if (err == NOISE_ERROR_REMOTE_KEY_REQUIRED)
+    return LOG_STR("REMOTE_KEY_REQUIRED");
+  if (err == NOISE_ERROR_LOCAL_KEY_REQUIRED)
+    return LOG_STR("LOCAL_KEY_REQUIRED");
+  if (err == NOISE_ERROR_PSK_REQUIRED)
+    return LOG_STR("PSK_REQUIRED");
+  if (err == NOISE_ERROR_INVALID_LENGTH)
+    return LOG_STR("INVALID_LENGTH");
+  if (err == NOISE_ERROR_INVALID_PARAM)
+    return LOG_STR("INVALID_PARAM");
+  if (err == NOISE_ERROR_INVALID_STATE)
+    return LOG_STR("INVALID_STATE");
+  if (err == NOISE_ERROR_INVALID_NONCE)
+    return LOG_STR("INVALID_NONCE");
+  if (err == NOISE_ERROR_INVALID_PRIVATE_KEY)
+    return LOG_STR("INVALID_PRIVATE_KEY");
+  if (err == NOISE_ERROR_INVALID_PUBLIC_KEY)
+    return LOG_STR("INVALID_PUBLIC_KEY");
+  if (err == NOISE_ERROR_INVALID_FORMAT)
+    return LOG_STR("INVALID_FORMAT");
+  if (err == NOISE_ERROR_INVALID_SIGNATURE)
+    return LOG_STR("INVALID_SIGNATURE");
+  return LOG_STR("UNKNOWN");
+}
+
+const LogString *reject_reason_for(int err) {
+  return err == NOISE_ERROR_MAC_FAILURE ? LOG_STR("Handshake MAC failure") : LOG_STR("Handshake error");
+}
+
+size_t format_reject_payload(uint8_t *buf, size_t capacity, const LogString *reason) {
+  if (capacity == 0) {
+    // A caller bug; the MAC_FAILURE_PAYLOAD_SIZE static_asserts at the call
+    // sites make this unreachable, kept as cheap memory safety
+    ESP_LOGVV(TAG, "Reject buffer has no capacity");
+    return 0;
+  }
+  buf[0] = HANDSHAKE_STATUS_REJECT;
+#ifdef USE_STORE_LOG_STR_IN_FLASH
+  // On ESP8266 with flash strings, we need to use PROGMEM-aware functions
+  size_t reason_len = strlen_P(reinterpret_cast<PGM_P>(reason));
+  reason_len = std::min(reason_len, capacity - 1);
+  if (reason_len > 0) {
+    memcpy_P(buf + 1, reinterpret_cast<PGM_P>(reason), reason_len);
+  }
+#else
+  const char *reason_str = LOG_STR_ARG(reason);
+  size_t reason_len = strlen(reason_str);
+  reason_len = std::min(reason_len, capacity - 1);
+  if (reason_len > 0) {
+    // NOLINTNEXTLINE(bugprone-not-null-terminated-result) - binary protocol, not a C string
+    std::memcpy(buf + 1, reason_str, reason_len);
+  }
+#endif
+  return reason_len + 1;
+}
+
+}  // namespace esphome::noise
+#endif  // USE_NOISE
diff --git a/esphome/components/noise/noise.h b/esphome/components/noise/noise.h
new file mode 100644
index 0000000000..f9da8d35b8
--- /dev/null
+++ b/esphome/components/noise/noise.h
@@ -0,0 +1,74 @@
+#pragma once
+#include "esphome/core/defines.h"
+#ifdef USE_NOISE
+#include <array>
+#include <cstddef>
+#include <cstdint>
+#include "esphome/core/log.h"
+
+namespace esphome::noise {
+
+using psk_t = std::array<uint8_t, 32>;
+
+class NoiseContext {
+ public:
+  // The all-zeros PSK is reserved: it marks the device as unprovisioned and
+  // doubles as the well-known provisioning PSK that unprovisioned devices
+  // accept for Noise handshakes (passive-sniffing protection only, no
+  // authentication). It is never a valid real key.
+  static bool is_all_zeros(const psk_t &psk) {
+    uint8_t acc = 0;
+    for (uint8_t b : psk) {
+      acc |= b;
+    }
+    return acc == 0;
+  }
+  void set_psk(psk_t psk) {
+    this->psk_ = psk;
+    this->has_psk_ = !is_all_zeros(psk);
+  }
+  const psk_t &get_psk() const { return this->psk_; }
+  bool has_psk() const { return this->has_psk_; }
+
+ protected:
+  psk_t psk_{};
+  bool has_psk_{false};
+};
+
+/// Convert a noise error code to a readable error
+const LogString *noise_err_to_logstr(int err);
+
+// Shared wire format for the noise transports (api and ota): every frame is
+// FRAME_INDICATOR, a 16-bit big-endian payload length, then the payload.
+// Handshake payloads start with a status byte; transport payloads end with
+// the ChaCha20-Poly1305 MAC.
+static constexpr uint8_t FRAME_INDICATOR = 0x01;
+static constexpr size_t FRAME_HEADER_SIZE = 3;
+static constexpr size_t MAC_SIZE = 16;
+static constexpr size_t MAX_HANDSHAKE_SIZE = 128;
+static constexpr uint8_t HANDSHAKE_STATUS_OK = 0x00;
+static constexpr uint8_t HANDSHAKE_STATUS_REJECT = 0x01;
+
+inline void write_frame_header(uint8_t *buf, uint16_t payload_len) {
+  buf[0] = FRAME_INDICATOR;
+  buf[1] = (uint8_t) (payload_len >> 8);
+  buf[2] = (uint8_t) payload_len;
+}
+
+/// Fill buf with a handshake reject payload (status byte plus the reason
+/// text, PROGMEM aware); returns the payload length. buf needs capacity for
+/// the status byte plus the truncated reason.
+size_t format_reject_payload(uint8_t *buf, size_t capacity, const LogString *reason);
+
+/// Reject reason for a failed handshake read. The MAC failure string is a
+/// wire contract: clients match it to report a wrong key.
+const LogString *reject_reason_for(int err);
+
+/// Payload size of the MAC failure reject, the one reason string that is a
+/// wire contract (sizeof's NUL stands in for the status byte). static_assert
+/// reject buffers against this so a wrong key report can never truncate;
+/// longer caller-supplied reasons are informational and sized by the caller.
+static constexpr size_t MAC_FAILURE_PAYLOAD_SIZE = sizeof("Handshake MAC failure");
+
+}  // namespace esphome::noise
+#endif  // USE_NOISE
diff --git a/esphome/components/noise/noise_handshake.cpp b/esphome/components/noise/noise_handshake.cpp
new file mode 100644
index 0000000000..6d426de012
--- /dev/null
+++ b/esphome/components/noise/noise_handshake.cpp
@@ -0,0 +1,139 @@
+#include "noise_handshake.h"
+#ifdef USE_NOISE
+#include "esphome/core/hal.h"
+#include "esphome/core/helpers.h"
+#include "esphome/core/log.h"
+
+namespace esphome::noise {
+
+static const char *const TAG = "noise";
+
+// Log the failing noise-c call at the same verbosity the api helper used
+// before this class existed; callers only see one collapsed error code.
+#define HANDSHAKE_STEP_LOG(func_name, err_code) \
+  ESP_LOGVV(TAG, "%s failed: %s", LOG_STR_ARG(LOG_STR(func_name)), LOG_STR_ARG(noise_err_to_logstr(err_code)))
+
+NoiseResponderHandshake::~NoiseResponderHandshake() {
+  if (this->handshake_ != nullptr) {
+    noise_handshakestate_free(this->handshake_);
+    this->handshake_ = nullptr;
+  }
+}
+
+int NoiseResponderHandshake::init(const psk_t &psk, const uint8_t *prologue, size_t prologue_len) {
+  if (this->handshake_ != nullptr) {
+    noise_handshakestate_free(this->handshake_);
+    this->handshake_ = nullptr;
+  }
+  // Noise_NNpsk0_25519_ChaChaPoly_SHA256, built on the stack:
+  // noise_handshakestate_new_by_id copies it, so a member would waste
+  // 104 bytes per connection, and a static const would sit in RAM on
+  // ESP8266 (.rodata is DRAM there).
+  const NoiseProtocolId nid = {
+      .prefix_id = NOISE_PREFIX_STANDARD,
+      .pattern_id = NOISE_PATTERN_NN,
+      .modifier_ids = {NOISE_MODIFIER_PSK0},
+      .dh_id = NOISE_DH_CURVE25519,
+      .cipher_id = NOISE_CIPHER_CHACHAPOLY,
+      .hash_id = NOISE_HASH_SHA256,
+      .hybrid_id = NOISE_DH_NONE,
+  };
+
+  int err = noise_handshakestate_new_by_id(&this->handshake_, &nid, NOISE_ROLE_RESPONDER);
+  if (err != 0) {
+    HANDSHAKE_STEP_LOG("noise_handshakestate_new_by_id", err);
+    return err;
+  }
+  err = noise_handshakestate_set_pre_shared_key(this->handshake_, psk.data(), psk.size());
+  if (err != 0) {
+    HANDSHAKE_STEP_LOG("noise_handshakestate_set_pre_shared_key", err);
+    return this->fail_init_(err);
+  }
+  err = noise_handshakestate_set_prologue(this->handshake_, prologue, prologue_len);
+  if (err != 0) {
+    HANDSHAKE_STEP_LOG("noise_handshakestate_set_prologue", err);
+    return this->fail_init_(err);
+  }
+  err = noise_handshakestate_start(this->handshake_);
+  if (err != 0) {
+    HANDSHAKE_STEP_LOG("noise_handshakestate_start", err);
+    return this->fail_init_(err);
+  }
+  return 0;
+}
+
+/// Release a half-initialized state so a failed init() leaves the object as
+/// if init() was never called.
+int NoiseResponderHandshake::fail_init_(int err) {
+  noise_handshakestate_free(this->handshake_);
+  this->handshake_ = nullptr;
+  return err;
+}
+
+NoiseResponderHandshake::Action NoiseResponderHandshake::action() const {
+  if (this->handshake_ == nullptr) {
+    // A caller bug: init() was never called, or split() already released the state
+    ESP_LOGVV(TAG, "action() on uninitialized or split handshake");
+    return Action::ACTION_FAILED;
+  }
+  int raw = noise_handshakestate_get_action(this->handshake_);
+  switch (raw) {
+    case NOISE_ACTION_READ_MESSAGE:
+      return Action::ACTION_READ;
+    case NOISE_ACTION_WRITE_MESSAGE:
+      return Action::ACTION_WRITE;
+    case NOISE_ACTION_SPLIT:
+      return Action::ACTION_SPLIT;
+    default:
+      // Preserve the raw code in debug logs; callers only see the collapsed enum
+      ESP_LOGVV(TAG, "Unexpected noise action %d", raw);
+      return Action::ACTION_FAILED;
+  }
+}
+
+int NoiseResponderHandshake::read_message(uint8_t *data, size_t len) {
+  NoiseBuffer mbuf;
+  noise_buffer_init(mbuf);
+  noise_buffer_set_input(mbuf, data, len);
+  return noise_handshakestate_read_message(this->handshake_, &mbuf, nullptr);
+}
+
+int NoiseResponderHandshake::write_message(uint8_t *out, size_t capacity, size_t &out_len) {
+  out_len = 0;
+  NoiseBuffer mbuf;
+  noise_buffer_init(mbuf);
+  noise_buffer_set_output(mbuf, out, capacity);
+  int err = noise_handshakestate_write_message(this->handshake_, &mbuf, nullptr);
+  if (err == 0)
+    out_len = mbuf.size;
+  return err;
+}
+
+int NoiseResponderHandshake::split(NoiseCipherState *&send_cipher, NoiseCipherState *&recv_cipher) {
+  // Defined error postcondition: noise-c leaves the out-params unwritten on
+  // its early error returns, so a caller passing uninitialized locals must
+  // never see garbage to free
+  send_cipher = nullptr;
+  recv_cipher = nullptr;
+  int err = noise_handshakestate_split(this->handshake_, &send_cipher, &recv_cipher);
+  if (err != 0)
+    return err;
+  noise_handshakestate_free(this->handshake_);
+  this->handshake_ = nullptr;
+  return 0;
+}
+
+extern "C" {
+// noise-c's only randomness source (the vendored library compiles no rand of
+// its own); HWRNG backed. Lives in this TU so every handshake consumer links
+// it and the definition can never be dropped from the archive.
+void noise_rand_bytes(void *output, size_t len) {
+  if (!esphome::random_bytes(reinterpret_cast<uint8_t *>(output), len)) {
+    ESP_LOGE(TAG, "Acquiring random bytes failed; rebooting");
+    arch_restart();
+  }
+}
+}
+
+}  // namespace esphome::noise
+#endif  // USE_NOISE
diff --git a/esphome/components/noise/noise_handshake.h b/esphome/components/noise/noise_handshake.h
new file mode 100644
index 0000000000..30596f35c2
--- /dev/null
+++ b/esphome/components/noise/noise_handshake.h
@@ -0,0 +1,63 @@
+#pragma once
+#include "esphome/core/defines.h"
+#ifdef USE_NOISE
+#include <cstddef>
+#include <cstdint>
+
+#include <noise/protocol.h>
+
+#include "noise.h"
+
+namespace esphome::noise {
+
+/** Sans-IO responder side of a Noise_NNpsk0_25519_ChaChaPoly_SHA256 handshake.
+ *
+ * Owns only the noise-c handshake state; the caller moves the raw handshake
+ * messages (no framing) over its own transport, driven by action():
+ * read_message() while READ, write_message() while WRITE, then split() to
+ * take ownership of the transport ciphers. All methods return a noise-c
+ * error code, 0 on success. Called outside their action() step (before
+ * init(), after split()) the message methods return a noise-c error rather
+ * than crashing; the library checks its state argument.
+ *
+ * Methods are deliberately small separate functions so callers on tight
+ * stacks (RP2040 core0 scratch bank) never pay for more than one branch;
+ * the curve25519 step alone needs ~2KB of stack.
+ */
+class NoiseResponderHandshake {
+ public:
+  // The ACTION_ prefix is macro-collision safety: SDK headers #define bare
+  // names like READ/WRITE, and macros expand even inside an enum class.
+  enum class Action : uint8_t { ACTION_READ, ACTION_WRITE, ACTION_SPLIT, ACTION_FAILED };
+
+  NoiseResponderHandshake() = default;
+  ~NoiseResponderHandshake();
+  // Owns a raw noise-c handshake state; copying would double free it
+  NoiseResponderHandshake(const NoiseResponderHandshake &) = delete;
+  NoiseResponderHandshake &operator=(const NoiseResponderHandshake &) = delete;
+
+  /// Create and start the handshake with the given PSK and prologue. A
+  /// repeated call frees the previous handshake state and starts over.
+  [[nodiscard]] int init(const psk_t &psk, const uint8_t *prologue, size_t prologue_len);
+  /// ACTION_FAILED is the catch-all: returned before init(), after split()
+  /// has released the state, and when noise-c reports a failed handshake.
+  [[nodiscard]] Action action() const;
+  /// Process one received handshake message. The buffer is consumed in
+  /// place: noise-c decrypts into it and zeroes it before returning.
+  [[nodiscard]] int read_message(uint8_t *data, size_t len);
+  /// Produce the next handshake message into out; out_len receives its size
+  /// and is zero on error.
+  [[nodiscard]] int write_message(uint8_t *out, size_t capacity, size_t &out_len);
+  /// Hand out the transport ciphers and free the handshake state. The caller
+  /// owns both cipher states and must free them with noise_cipherstate_free();
+  /// both are set to nullptr on error.
+  [[nodiscard]] int split(NoiseCipherState *&send_cipher, NoiseCipherState *&recv_cipher);
+
+ protected:
+  int fail_init_(int err);
+
+  NoiseHandshakeState *handshake_{nullptr};
+};
+
+}  // namespace esphome::noise
+#endif  // USE_NOISE
diff --git a/esphome/components/zephyr/library.py b/esphome/components/zephyr/library.py
index 0e6551ccf1..b339ae45b0 100644
--- a/esphome/components/zephyr/library.py
+++ b/esphome/components/zephyr/library.py
@@ -28,6 +28,7 @@ from esphome.platformio.library import (
     collect_filtered_files,
     convert_libraries,
     ensure_list,
+    lex_build_flags,
     split_list_by_condition,
 )
 
@@ -80,7 +81,11 @@ def generate_cmakelists_txt(component: ConvertedLibrary) -> str:
 
     build_include_dir = build.get("includeDir", DEFAULT_BUILD_INCLUDE_DIR)
     build_src_filter = ensure_list(build.get("srcFilter", DEFAULT_BUILD_SRC_FILTER))
-    build_flags = ensure_list(build.get("flags", DEFAULT_BUILD_FLAGS))
+    # The shared lexer re-glues spaced entries and drops bare/empty
+    # arguments, same as the espidf emitter
+    build_flags = lex_build_flags(
+        build.get("flags", DEFAULT_BUILD_FLAGS), component.name
+    )
 
     src_files = collect_filtered_files(
         read_path / Path(build_src_dir), build_src_filter
diff --git a/esphome/core/defines.h b/esphome/core/defines.h
index 20aca3776f..5f34437145 100644
--- a/esphome/core/defines.h
+++ b/esphome/core/defines.h
@@ -222,6 +222,7 @@
 #define API_MAX_SEND_QUEUE 8
 #define MAX_API_CONNECTIONS 6
 #define USE_MD5
+#define USE_NOISE
 #define USE_SHA256
 #ifndef USE_RP2  // no MQTT backend or esp_wireguard library on RP2
 #define USE_MQTT
diff --git a/esphome/espidf/component.py b/esphome/espidf/component.py
index 4655d1c54d..105413cf44 100644
--- a/esphome/espidf/component.py
+++ b/esphome/espidf/component.py
@@ -58,8 +58,10 @@ def generate_cmakelists_txt(component: IDFComponent) -> str:
     """
 
     def escape_entry(p: PathType) -> str:
-        # In CMakeLists.txt, backslashes need to be escaped
-        return f'"{str(p)}"'.replace("\\", "\\\\")
+        # In CMakeLists.txt, backslashes and embedded quotes need escaping
+        # (a quoted define value reaches here via the shlex round-trip)
+        escaped = str(p).replace("\\", "\\\\").replace('"', '\\"')
+        return f'"{escaped}"'
 
     def escape_path(p: PathType) -> str:
         # CMake uses forward slashes for paths on every platform and treats
diff --git a/esphome/platformio/extra_script.py b/esphome/platformio/extra_script.py
index e60a50d746..e04ccd1f55 100644
--- a/esphome/platformio/extra_script.py
+++ b/esphome/platformio/extra_script.py
@@ -33,7 +33,7 @@ def apply_extra_script(
     """Run a library's ``extraScript`` and fold its captured env vars into
     ``build.flags``; ``board_mcu`` is a callable so it resolves lazily."""
     extra_script = component.data.get("build", {}).get("extraScript")
-    if not extra_script:
+    if extra_script is None or extra_script == "":
         return
     if not isinstance(extra_script, str):
         # A list/dict value would raise an opaque TypeError on the join below
@@ -170,6 +170,15 @@ class _FakeSConsEnv:
             )
         return self._vars.get(key, default)
 
+    def __contains__(self, key: object) -> bool:
+        # Without this, "KEY" in env falls back to the legacy sequence
+        # protocol: __getitem__(0), (1), ... never raises, so it loops
+        # forever flooding the log
+        return key in self._vars
+
+    def __iter__(self):
+        return iter(self._vars)
+
     def __getitem__(self, key: str) -> str:
         # Scripts also read env["BOARD_MCU"]; an unmodelled subscript
         # degrades one branch instead of discarding the whole capture
diff --git a/esphome/platformio/library.py b/esphome/platformio/library.py
index bd16736dfb..853dae4d6c 100644
--- a/esphome/platformio/library.py
+++ b/esphome/platformio/library.py
@@ -687,15 +687,15 @@ def dependency_is_usable(
 
 
 def _valid_dependency_entry(entry: dict, manifest_name: str) -> bool:
-    """Whether a normalized entry carries a usable name (non-empty string)
-    and version (string, if present); invalid entries warn naming the
-    manifest."""
+    """Whether a normalized entry carries a usable name (non-empty string),
+    version (string, if present), and owner (string, if present); invalid
+    entries warn naming the manifest."""
     name = entry.get("name")
-    if (
-        isinstance(name, str)
-        and name
-        and ("version" not in entry or isinstance(entry["version"], str))
-    ):
+    owner = entry.get("owner")
+    name_ok = isinstance(name, str) and name
+    version_ok = "version" not in entry or isinstance(entry["version"], str)
+    owner_ok = owner is None or isinstance(owner, str)
+    if name_ok and version_ok and owner_ok:
         return True
     _LOGGER.warning(
         "Ignoring unrecognized dependency entry %r of %s", entry, manifest_name
@@ -714,7 +714,7 @@ def normalize_dependencies(
     so callers see a uniform list. ``manifest_name`` names the manifest in the
     warning for entries that cannot be normalized.
     """
-    if not dependencies:
+    if dependencies is None:
         return []
     if isinstance(dependencies, str):
         # A plain string is one or more comma-separated names; iterating it
@@ -1126,11 +1126,19 @@ def convert_libraries(
                     f"library.properties in {source_dir}"
                 )
 
-            if not isinstance(component.data, dict) or not isinstance(
-                component.data.get("build", {}), dict
-            ):
-                # A bare json.load imposes no shape; every backend dereferences
-                # data/build, so validate once here and name the library
+            # A bare json.load imposes no shape; every backend dereferences
+            # these fields, so validate once here and name the library
+            malformed = not isinstance(component.data, dict)
+            if not malformed:
+                build = component.data.get("build", {})
+                malformed = (
+                    not isinstance(build, dict)
+                    or not isinstance(component.data.get(ESPHOME_DATA_KEY, {}), dict)
+                    or not isinstance(build.get("srcDir", ""), str)
+                    or not isinstance(build.get("includeDir", ""), str)
+                    or not isinstance(build.get("srcFilter", ""), (str, list))
+                )
+            if malformed:
                 raise EsphomeError(f"Library {key} has a malformed manifest")
             warn_properties_depends(component.name, component.data)
 
@@ -1140,10 +1148,12 @@ def convert_libraries(
                 # An explicitly requested library fails fast; the routine
                 # cross-platform skip stays at debug, other causes warn
                 if key in top_level_keys:
-                    raise RuntimeError(
-                        f"Requested library {key} is not compatible with "
-                        f"{backend.framework}: {e}"
-                    ) from e
+                    reason = (
+                        f"is not compatible with {backend.framework}"
+                        if isinstance(e, IncompatiblePlatform)
+                        else "has a malformed manifest"
+                    )
+                    raise RuntimeError(f"Requested library {key} {reason}: {e}") from e
                 if isinstance(e, IncompatiblePlatform):
                     _LOGGER.debug("Skip incompatible dependency %s: %s", key, str(e))
                 else:
diff --git a/platformio.ini b/platformio.ini
index 4c372cc0bb..b2a36e687c 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -45,7 +45,7 @@ lib_deps_base =
 lib_deps =
     ${common.lib_deps_base}
     https://github.com/dudanov/MideaUART.git#eeea6c3e9b4474f067054592b435be1c4e466815 ; midea
-    esphome/noise-c@0.1.21                 ; api
+    esphome/noise-c@0.1.21                 ; noise (api, ota)
     improv/Improv@1.2.6                    ; improv_serial / esp32_improv
     kikuchan98/pngle@1.1.0                 ; online_image
     ; Using the repository directly, otherwise ESP-IDF can't use the library
@@ -244,7 +244,7 @@ lib_deps =
     ${common:idf-component-libs.lib_deps}
     ESP32Async/ESPAsyncWebServer@3.9.6    ; web_server_base
     droscy/esp_wireguard@0.4.5            ; wireguard
-    esphome/noise-c@0.1.21                ; api
+    esphome/noise-c@0.1.21                ; noise (api, ota)
     ESP32Async/AsyncTCP@3.4.5             ; async_tcp
     DNSServer                             ; captive_portal
     heman/AsyncMqttClient-esphome@2.0.0   ; mqtt
@@ -641,7 +641,7 @@ build_unflags =
 extends = common
 platform = platformio/native
 lib_deps =
-    esphome/noise-c@0.1.21  ; used by api
+    esphome/noise-c@0.1.21  ; used by noise (api, ota)
     lvgl/lvgl@9.5.0         ; lvgl
 build_flags =
     ${common.build_flags}
diff --git a/tests/benchmarks/components/api/__init__.py b/tests/benchmarks/components/api/__init__.py
index 0565bc5330..12c078911c 100644
--- a/tests/benchmarks/components/api/__init__.py
+++ b/tests/benchmarks/components/api/__init__.py
@@ -3,8 +3,9 @@ from tests.testing_helpers import ComponentManifestOverride
 
 
 def override_manifest(manifest: ComponentManifestOverride) -> None:
-    # api must run its to_code to define USE_API, USE_API_PLAINTEXT,
-    # and add the noise-c library dependency.
+    # api must run its to_code to define USE_API and USE_API_NOISE. The
+    # AUTO_LOADed noise component runs its own to_code via the override in
+    # tests/benchmarks/components/noise/__init__.py.
     manifest.enable_codegen()
 
     original_to_code = manifest.to_code
diff --git a/tests/benchmarks/components/noise/__init__.py b/tests/benchmarks/components/noise/__init__.py
new file mode 100644
index 0000000000..f430e9dd36
--- /dev/null
+++ b/tests/benchmarks/components/noise/__init__.py
@@ -0,0 +1,7 @@
+from tests.testing_helpers import ComponentManifestOverride
+
+
+def override_manifest(manifest: ComponentManifestOverride) -> None:
+    # to_code must run: it defines USE_NOISE and adds the noise-c library
+    # the api benchmark sources need.
+    manifest.enable_codegen()
diff --git a/tests/component_tests/noise/__init__.py b/tests/component_tests/noise/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/component_tests/noise/test_encryption_key.py b/tests/component_tests/noise/test_encryption_key.py
new file mode 100644
index 0000000000..62abae6487
--- /dev/null
+++ b/tests/component_tests/noise/test_encryption_key.py
@@ -0,0 +1,37 @@
+"""Tests for the shared noise encryption key helpers."""
+
+from __future__ import annotations
+
+import pytest
+
+from esphome import config_validation as cv
+from esphome.components.noise import decode_encryption_key, validate_encryption_key
+
+KEY = "AAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8="
+
+
+def test_validate_encryption_key_roundtrips() -> None:
+    assert validate_encryption_key(KEY) == KEY
+
+
+@pytest.mark.parametrize("value", ["not-base64!!!", "AAECAw=="])
+def test_validate_encryption_key_rejects_bad_input(value: str) -> None:
+    with pytest.raises(cv.Invalid):
+        validate_encryption_key(value)
+
+
+def test_decode_encryption_key_returns_32_bytes() -> None:
+    assert decode_encryption_key(KEY) == bytes(range(32))
+
+
+def test_decode_encryption_key_rejects_invalid_base64() -> None:
+    """The shared helper raises cv.Invalid, not binascii.Error."""
+    with pytest.raises(cv.Invalid, match="base64"):
+        decode_encryption_key("A")
+
+
+def test_decode_encryption_key_rejects_short_decode() -> None:
+    """a2b_base64 stops at embedded padding; a short decode must not become
+    a zero padded PSK on the device."""
+    with pytest.raises(cv.Invalid, match="32 bytes"):
+        decode_encryption_key("AAECAw==")
diff --git a/tests/components/noise/__init__.py b/tests/components/noise/__init__.py
new file mode 100644
index 0000000000..60a5740a83
--- /dev/null
+++ b/tests/components/noise/__init__.py
@@ -0,0 +1,7 @@
+from tests.testing_helpers import ComponentManifestOverride
+
+
+def override_manifest(manifest: ComponentManifestOverride) -> None:
+    # to_code must run: it defines USE_NOISE and adds the noise-c library
+    # the component sources under test need.
+    manifest.enable_codegen()
diff --git a/tests/components/noise/common.yaml b/tests/components/noise/common.yaml
new file mode 100644
index 0000000000..35253a35e6
--- /dev/null
+++ b/tests/components/noise/common.yaml
@@ -0,0 +1 @@
+noise:
diff --git a/tests/components/noise/test.esp32-idf.yaml b/tests/components/noise/test.esp32-idf.yaml
new file mode 100644
index 0000000000..550ffd1f88
--- /dev/null
+++ b/tests/components/noise/test.esp32-idf.yaml
@@ -0,0 +1,2 @@
+packages:
+  noise: !include common.yaml
diff --git a/tests/components/noise/test.esp8266-ard.yaml b/tests/components/noise/test.esp8266-ard.yaml
new file mode 100644
index 0000000000..550ffd1f88
--- /dev/null
+++ b/tests/components/noise/test.esp8266-ard.yaml
@@ -0,0 +1,2 @@
+packages:
+  noise: !include common.yaml
diff --git a/tests/components/noise/test.host.yaml b/tests/components/noise/test.host.yaml
new file mode 100644
index 0000000000..550ffd1f88
--- /dev/null
+++ b/tests/components/noise/test.host.yaml
@@ -0,0 +1,2 @@
+packages:
+  noise: !include common.yaml
diff --git a/tests/components/noise/test.rp2040-ard.yaml b/tests/components/noise/test.rp2040-ard.yaml
new file mode 100644
index 0000000000..550ffd1f88
--- /dev/null
+++ b/tests/components/noise/test.rp2040-ard.yaml
@@ -0,0 +1,2 @@
+packages:
+  noise: !include common.yaml
diff --git a/tests/components/noise/test_noise_handshake.cpp b/tests/components/noise/test_noise_handshake.cpp
new file mode 100644
index 0000000000..d879a26c43
--- /dev/null
+++ b/tests/components/noise/test_noise_handshake.cpp
@@ -0,0 +1,199 @@
+#include <gtest/gtest.h>
+
+#include <cstring>
+
+#include <noise/protocol.h>
+
+#include "esphome/components/noise/noise.h"
+#include "esphome/components/noise/noise_handshake.h"
+
+namespace esphome::noise::testing {
+
+using Action = NoiseResponderHandshake::Action;
+
+// A raw noise-c initiator driving the same Noise_NNpsk0_25519_ChaChaPoly_SHA256
+// pattern the responder class implements, so the tests exercise a real
+// two-message handshake rather than mirrored calls into the class under test.
+class Initiator {
+ public:
+  Initiator(const psk_t &psk, const uint8_t *prologue, size_t prologue_len) {
+    const NoiseProtocolId nid = {
+        .prefix_id = NOISE_PREFIX_STANDARD,
+        .pattern_id = NOISE_PATTERN_NN,
+        .modifier_ids = {NOISE_MODIFIER_PSK0},
+        .dh_id = NOISE_DH_CURVE25519,
+        .cipher_id = NOISE_CIPHER_CHACHAPOLY,
+        .hash_id = NOISE_HASH_SHA256,
+        .hybrid_id = NOISE_DH_NONE,
+    };
+    EXPECT_EQ(noise_handshakestate_new_by_id(&this->state_, &nid, NOISE_ROLE_INITIATOR), 0);
+    EXPECT_EQ(noise_handshakestate_set_pre_shared_key(this->state_, psk.data(), psk.size()), 0);
+    EXPECT_EQ(noise_handshakestate_set_prologue(this->state_, prologue, prologue_len), 0);
+    EXPECT_EQ(noise_handshakestate_start(this->state_), 0);
+  }
+  ~Initiator() {
+    if (this->state_ != nullptr)
+      noise_handshakestate_free(this->state_);
+    if (this->send_ != nullptr)
+      noise_cipherstate_free(this->send_);
+    if (this->recv_ != nullptr)
+      noise_cipherstate_free(this->recv_);
+  }
+  Initiator(const Initiator &) = delete;
+  Initiator &operator=(const Initiator &) = delete;
+
+  size_t write_message(uint8_t *out, size_t capacity) {
+    NoiseBuffer mbuf;
+    noise_buffer_init(mbuf);
+    noise_buffer_set_output(mbuf, out, capacity);
+    EXPECT_EQ(noise_handshakestate_write_message(this->state_, &mbuf, nullptr), 0);
+    return mbuf.size;
+  }
+
+  int read_message(uint8_t *data, size_t len) {
+    NoiseBuffer mbuf;
+    noise_buffer_init(mbuf);
+    noise_buffer_set_input(mbuf, data, len);
+    return noise_handshakestate_read_message(this->state_, &mbuf, nullptr);
+  }
+
+  void split() { EXPECT_EQ(noise_handshakestate_split(this->state_, &this->send_, &this->recv_), 0); }
+
+  NoiseCipherState *send_{nullptr};
+  NoiseCipherState *recv_{nullptr};
+
+ private:
+  NoiseHandshakeState *state_{nullptr};
+};
+
+static const uint8_t PROLOGUE[] = {'t', 'e', 's', 't', 'p', 'r', 'o', 'l', 'o', 'g', 'u', 'e'};
+
+static psk_t make_psk(uint8_t seed) {
+  psk_t psk;
+  for (size_t i = 0; i < psk.size(); i++) {
+    psk[i] = static_cast<uint8_t>(seed + i);
+  }
+  return psk;
+}
+
+TEST(NoiseResponderHandshakeTest, ActionFailedBeforeInit) {
+  NoiseResponderHandshake handshake;
+  EXPECT_EQ(handshake.action(), Action::ACTION_FAILED);
+}
+
+TEST(NoiseResponderHandshakeTest, MessageMethodsErrorBeforeInit) {
+  // The class doc promises a noise-c error, not a crash, when the message
+  // methods run outside their action() step; pin the library's null check
+  NoiseResponderHandshake handshake;
+  uint8_t buf[MAX_HANDSHAKE_SIZE] = {};
+  size_t out_len = 0;
+  EXPECT_NE(handshake.read_message(buf, sizeof(buf)), 0);
+  EXPECT_NE(handshake.write_message(buf, sizeof(buf), out_len), 0);
+  // Deliberately non-null: split() documents a nullptr postcondition on
+  // error, so a caller's uninitialized locals never hold garbage to free
+  auto *sentinel = reinterpret_cast<NoiseCipherState *>(0x1);
+  NoiseCipherState *send_cipher = sentinel;
+  NoiseCipherState *recv_cipher = sentinel;
+  EXPECT_NE(handshake.split(send_cipher, recv_cipher), 0);
+  EXPECT_EQ(send_cipher, nullptr);
+  EXPECT_EQ(recv_cipher, nullptr);
+}
+
+TEST(NoiseResponderHandshakeTest, FullHandshakeAndTransportRoundTrip) {
+  const psk_t psk = make_psk(7);
+  NoiseResponderHandshake responder;
+  ASSERT_EQ(responder.init(psk, PROLOGUE, sizeof(PROLOGUE)), 0);
+  EXPECT_EQ(responder.action(), Action::ACTION_READ);
+
+  Initiator initiator(psk, PROLOGUE, sizeof(PROLOGUE));
+  uint8_t msg[MAX_HANDSHAKE_SIZE];
+  size_t msg_len = initiator.write_message(msg, sizeof(msg));
+  ASSERT_GT(msg_len, 0u);
+
+  ASSERT_EQ(responder.read_message(msg, msg_len), 0);
+  ASSERT_EQ(responder.action(), Action::ACTION_WRITE);
+
+  size_t reply_len = 0;
+  ASSERT_EQ(responder.write_message(msg, sizeof(msg), reply_len), 0);
+  ASSERT_GT(reply_len, 0u);
+  ASSERT_EQ(responder.action(), Action::ACTION_SPLIT);
+
+  ASSERT_EQ(initiator.read_message(msg, reply_len), 0);
+  initiator.split();
+
+  NoiseCipherState *send_cipher = nullptr;
+  NoiseCipherState *recv_cipher = nullptr;
+  ASSERT_EQ(responder.split(send_cipher, recv_cipher), 0);
+  ASSERT_NE(send_cipher, nullptr);
+  ASSERT_NE(recv_cipher, nullptr);
+  // The handshake state is released by split(); the class reports FAILED after
+  EXPECT_EQ(responder.action(), Action::ACTION_FAILED);
+  EXPECT_EQ(static_cast<size_t>(noise_cipherstate_get_mac_length(send_cipher)), MAC_SIZE);
+
+  // Responder encrypts, initiator decrypts
+  uint8_t frame[64];
+  static constexpr char PLAINTEXT[] = "encrypted ota";
+  std::memcpy(frame, PLAINTEXT, sizeof(PLAINTEXT));
+  NoiseBuffer mbuf;
+  noise_buffer_init(mbuf);
+  noise_buffer_set_inout(mbuf, frame, sizeof(PLAINTEXT), sizeof(frame));
+  ASSERT_EQ(noise_cipherstate_encrypt(send_cipher, &mbuf), 0);
+  EXPECT_EQ(mbuf.size, sizeof(PLAINTEXT) + MAC_SIZE);
+
+  noise_buffer_set_inout(mbuf, frame, mbuf.size, sizeof(frame));
+  ASSERT_EQ(noise_cipherstate_decrypt(initiator.recv_, &mbuf), 0);
+  ASSERT_EQ(mbuf.size, sizeof(PLAINTEXT));
+  EXPECT_EQ(std::memcmp(frame, PLAINTEXT, sizeof(PLAINTEXT)), 0);
+
+  noise_cipherstate_free(send_cipher);
+  noise_cipherstate_free(recv_cipher);
+}
+
+TEST(NoiseResponderHandshakeTest, ReInitRestartsHandshake) {
+  // The documented retry shape: a repeated init() frees the previous state
+  // and starts over. The first message under the new key authenticating
+  // proves the restart took effect; the old state surviving would fail the
+  // MAC here.
+  NoiseResponderHandshake responder;
+  ASSERT_EQ(responder.init(make_psk(7), PROLOGUE, sizeof(PROLOGUE)), 0);
+  ASSERT_EQ(responder.init(make_psk(9), PROLOGUE, sizeof(PROLOGUE)), 0);
+  EXPECT_EQ(responder.action(), Action::ACTION_READ);
+
+  Initiator initiator(make_psk(9), PROLOGUE, sizeof(PROLOGUE));
+  uint8_t msg[MAX_HANDSHAKE_SIZE];
+  size_t msg_len = initiator.write_message(msg, sizeof(msg));
+  ASSERT_GT(msg_len, 0u);
+  EXPECT_EQ(responder.read_message(msg, msg_len), 0);
+}
+
+TEST(NoiseResponderHandshakeTest, WrongPskFailsWithMacFailure) {
+  NoiseResponderHandshake responder;
+  ASSERT_EQ(responder.init(make_psk(7), PROLOGUE, sizeof(PROLOGUE)), 0);
+
+  Initiator initiator(make_psk(200), PROLOGUE, sizeof(PROLOGUE));
+  uint8_t msg[MAX_HANDSHAKE_SIZE];
+  size_t msg_len = initiator.write_message(msg, sizeof(msg));
+  ASSERT_GT(msg_len, 0u);
+
+  int err = responder.read_message(msg, msg_len);
+  EXPECT_EQ(err, NOISE_ERROR_MAC_FAILURE);
+  EXPECT_EQ(responder.action(), Action::ACTION_FAILED);
+}
+
+TEST(NoiseResponderHandshakeTest, MismatchedPrologueFailsWithMacFailure) {
+  // The prologue binds the plaintext preamble for downgrade resistance; a
+  // tampered preamble must fail even with the right key.
+  const psk_t psk = make_psk(7);
+  NoiseResponderHandshake responder;
+  ASSERT_EQ(responder.init(psk, PROLOGUE, sizeof(PROLOGUE)), 0);
+
+  static const uint8_t TAMPERED[] = {'x'};
+  Initiator initiator(psk, TAMPERED, sizeof(TAMPERED));
+  uint8_t msg[MAX_HANDSHAKE_SIZE];
+  size_t msg_len = initiator.write_message(msg, sizeof(msg));
+  ASSERT_GT(msg_len, 0u);
+
+  EXPECT_EQ(responder.read_message(msg, msg_len), NOISE_ERROR_MAC_FAILURE);
+}
+
+}  // namespace esphome::noise::testing
diff --git a/tests/components/noise/test_noise_primitives.cpp b/tests/components/noise/test_noise_primitives.cpp
new file mode 100644
index 0000000000..018be9f717
--- /dev/null
+++ b/tests/components/noise/test_noise_primitives.cpp
@@ -0,0 +1,74 @@
+#include <gtest/gtest.h>
+
+#include <cstring>
+
+#include <noise/protocol.h>
+
+#include "esphome/components/noise/noise.h"
+
+namespace esphome::noise::testing {
+
+TEST(NoiseContextTest, AllZerosPskIsReserved) {
+  psk_t zeros{};
+  EXPECT_TRUE(NoiseContext::is_all_zeros(zeros));
+
+  psk_t psk{};
+  psk[31] = 1;
+  EXPECT_FALSE(NoiseContext::is_all_zeros(psk));
+
+  NoiseContext ctx;
+  EXPECT_FALSE(ctx.has_psk());
+  ctx.set_psk(zeros);
+  EXPECT_FALSE(ctx.has_psk());
+  ctx.set_psk(psk);
+  EXPECT_TRUE(ctx.has_psk());
+  EXPECT_EQ(ctx.get_psk(), psk);
+}
+
+TEST(WireFormatTest, FrameHeaderIsIndicatorPlusBigEndianLength) {
+  uint8_t header[FRAME_HEADER_SIZE];
+  write_frame_header(header, 0x1234);
+  EXPECT_EQ(header[0], FRAME_INDICATOR);
+  EXPECT_EQ(header[1], 0x12);
+  EXPECT_EQ(header[2], 0x34);
+}
+
+TEST(WireFormatTest, RejectPayloadCarriesStatusByteAndMacFailureContract) {
+  // The MAC failure string is a wire contract: clients match it to report a
+  // wrong key. Format the payload exactly the way the handshake read path does.
+  uint8_t buf[64];
+  size_t len = format_reject_payload(buf, sizeof(buf), reject_reason_for(NOISE_ERROR_MAC_FAILURE));
+  static constexpr char EXPECTED[] = "Handshake MAC failure";
+  ASSERT_EQ(len, 1 + strlen(EXPECTED));
+  EXPECT_EQ(buf[0], HANDSHAKE_STATUS_REJECT);
+  EXPECT_EQ(memcmp(buf + 1, EXPECTED, strlen(EXPECTED)), 0);
+  // The exported floor covers the full MAC failure payload exactly
+  EXPECT_EQ(MAC_FAILURE_PAYLOAD_SIZE, 1 + strlen(EXPECTED));
+
+  // Any other error maps to the generic reason
+  len = format_reject_payload(buf, sizeof(buf), reject_reason_for(NOISE_ERROR_INVALID_STATE));
+  static constexpr char GENERIC[] = "Handshake error";
+  ASSERT_EQ(len, 1 + strlen(GENERIC));
+  EXPECT_EQ(memcmp(buf + 1, GENERIC, strlen(GENERIC)), 0);
+}
+
+TEST(WireFormatTest, RejectPayloadTruncatesToCapacity) {
+  uint8_t buf[8];
+  size_t len = format_reject_payload(buf, sizeof(buf), reject_reason_for(NOISE_ERROR_MAC_FAILURE));
+  ASSERT_EQ(len, sizeof(buf));
+  EXPECT_EQ(buf[0], HANDSHAKE_STATUS_REJECT);
+  EXPECT_EQ(memcmp(buf + 1, "Handsha", 7), 0);
+
+  // A one-byte buffer still carries the status byte
+  uint8_t tiny[1];
+  len = format_reject_payload(tiny, sizeof(tiny), reject_reason_for(NOISE_ERROR_MAC_FAILURE));
+  ASSERT_EQ(len, 1u);
+  EXPECT_EQ(tiny[0], HANDSHAKE_STATUS_REJECT);
+
+  // A zero-capacity buffer yields no payload and stays untouched
+  uint8_t none[1] = {0xAA};
+  EXPECT_EQ(format_reject_payload(none, 0, reject_reason_for(NOISE_ERROR_MAC_FAILURE)), 0u);
+  EXPECT_EQ(none[0], 0xAA);
+}
+
+}  // namespace esphome::noise::testing
diff --git a/tests/unit_tests/test_espidf_component.py b/tests/unit_tests/test_espidf_component.py
index 957c98f8ad..a7d871b2f8 100644
--- a/tests/unit_tests/test_espidf_component.py
+++ b/tests/unit_tests/test_espidf_component.py
@@ -294,6 +294,19 @@ def test_generate_cmakelists_txt_multi_token_flag(tmp_component):
     assert '  "-include"\n  "cp_custom_alloc.h"\n' in content
 
 
+def test_generate_cmakelists_txt_escapes_embedded_quotes(tmp_component):
+    """A define value carrying a literal quote survives into CMake as an
+    escaped quote, not a prematurely-terminated string."""
+    src_dir = tmp_component.path / "src"
+    src_dir.mkdir()
+    (src_dir / "main.c").write_text("int main() {}")
+    # shlex keeps the backslash-escaped quotes as literal characters
+    tmp_component.data = {"build": {"flags": ['-DMSG=\\"hi\\"']}}
+
+    content = generate_cmakelists_txt(tmp_component)
+    assert '"-DMSG=\\"hi\\""' in content
+
+
 def test_generate_cmakelists_txt_extra_script_link_flags(tmp_component):
     """Captured extra-script LINKFLAGS come out as target_link_options, not
     compile options where they would be silently ineffective."""
diff --git a/tests/unit_tests/test_platformio_extra_script.py b/tests/unit_tests/test_platformio_extra_script.py
index 980ce29ccb..07f0e78500 100644
--- a/tests/unit_tests/test_platformio_extra_script.py
+++ b/tests/unit_tests/test_platformio_extra_script.py
@@ -461,6 +461,27 @@ def test_prepend_inserts_ahead_of_existing(method: str) -> None:
     assert env.result.libs == ["algobsec", "bsec", "m"]
 
 
+def test_env_membership_and_iteration(tmp_path) -> None:
+    """Membership tests and for-loops must use the mapping protocol; the
+    legacy sequence fallback through __getitem__ would loop forever."""
+    env = _FakeSConsEnv(
+        board_mcu="esp8266", pio_env="esphome_esp8266", pio_platform="espressif8266"
+    )
+    assert "BOARD_MCU" in env
+    assert "NOPE" not in env
+    assert sorted(env) == ["BOARD_MCU", "PIOENV", "PIOPLATFORM"]
+
+
+def test_apply_extra_script_non_string_falsey_raises(tmp_path) -> None:
+    """A falsey non-string extraScript (false, 0, []) is a malformed
+    manifest, not an absent script."""
+    c = IDFComponent("owner/name", "1.0", source=URLSource("http://dummy"))
+    c.path = tmp_path
+    c.data = {"build": {"extraScript": False}}
+    with pytest.raises(EsphomeError, match="must be a string"):
+        apply_extra_script(c, board_mcu=lambda: "esp8266", pio_platform="espressif8266")
+
+
 def test_env_get_unknown_key_warns_once(caplog) -> None:
     """A script branching on an unmodelled env var is diagnosable."""
     env = _FakeSConsEnv(
diff --git a/tests/unit_tests/test_platformio_library.py b/tests/unit_tests/test_platformio_library.py
index adfb30201a..d69f2b1200 100644
--- a/tests/unit_tests/test_platformio_library.py
+++ b/tests/unit_tests/test_platformio_library.py
@@ -800,10 +800,28 @@ def test_normalize_dependencies_forms(caplog) -> None:
     assert normalize_dependencies({"Foo": ["1.0", "2.0"]}, "libx") == []
     assert normalize_dependencies([{"name": "Foo", "version": 1}], "libx") == []
     assert caplog.text.count("unrecognized dependency entry") == 7
+    # A non-string owner would stringify into a malformed registry name
+    assert (
+        normalize_dependencies(
+            [{"name": "Foo", "owner": {"bad": 1}, "version": "1.0"}], "libx"
+        )
+        == []
+    )
+    # A falsey scalar (0, false) is malformed, not an empty list
+    assert normalize_dependencies(0, "libx") == []
+    assert "Ignoring unrecognized dependencies 0 of libx" in caplog.text
 
 
 @pytest.mark.parametrize(
-    "manifest", [["not", "a", "manifest"], {"name": "A", "build": "src"}]
+    "manifest",
+    [
+        ["not", "a", "manifest"],
+        {"name": "A", "build": "src"},
+        {"name": "A", "ESPHOME": "yes"},
+        {"name": "A", "build": {"srcDir": 123}},
+        {"name": "A", "build": {"includeDir": ["inc"]}},
+        {"name": "A", "build": {"srcFilter": {"+": "src"}}},
+    ],
 )
 def test_convert_libraries_malformed_manifest_raises(
     tmp_path, monkeypatch, manifest
diff --git a/tests/unit_tests/test_zephyr_library.py b/tests/unit_tests/test_zephyr_library.py
index b370fe0c47..0d899ec91d 100644
--- a/tests/unit_tests/test_zephyr_library.py
+++ b/tests/unit_tests/test_zephyr_library.py
@@ -66,6 +66,22 @@ def test_generate_cmakelists_txt_flags_and_includes(tmp_path):
     assert "-lm" in out
 
 
+def test_generate_cmakelists_txt_lexes_spaced_flags(tmp_path):
+    """A spaced -I entry routes to include dirs instead of landing verbatim
+    in compile options; same shared lexer as the espidf emitter."""
+    c = _make_component(tmp_path)
+    (tmp_path / "src").mkdir()
+    (tmp_path / "src" / "a.c").write_text("")
+    (tmp_path / "include").mkdir()
+    c.data = {"build": {"flags": "-I include -DBAR=1"}}
+
+    out = generate_cmakelists_txt(c)
+
+    assert str((tmp_path / "include").resolve()).replace("\\", "\\\\") in out
+    assert "-DBAR=1" in out
+    assert "-I include" not in out
+
+
 def test_generate_zephyr_modules_collects_all_dirs_and_writes(tmp_path, monkeypatch):
     # Two converted libraries: one top-level, one transitive dependency. The
     # converter calls backend.emit for both; generate_zephyr_modules must return