diff --git a/esphome/components/web_server_idf/web_server_idf.cpp b/esphome/components/web_server_idf/web_server_idf.cpp
index fdbd31a20e..9dd69bee41 100644
--- a/esphome/components/web_server_idf/web_server_idf.cpp
+++ b/esphome/components/web_server_idf/web_server_idf.cpp
@@ -354,7 +354,26 @@ bool AsyncWebServerRequest::authenticate(const char *username, const char *passw
   esp_crypto_base64_encode(reinterpret_cast<uint8_t *>(digest), max_digest_len, &out,
                            reinterpret_cast<const uint8_t *>(user_info), user_info_len);
 
-  return strcmp(digest, auth_str + auth_prefix_len) == 0;
+  // Constant-time comparison to avoid timing side channels.
+  // No early return on length mismatch — the length difference is folded
+  // into the accumulator so any mismatch is rejected.
+  const char *provided = auth_str + auth_prefix_len;
+  size_t digest_len = out;  // length from esp_crypto_base64_encode
+  // Derive provided_len from the already-sized std::string rather than
+  // rescanning with strlen (avoids attacker-controlled scan length).
+  size_t provided_len = auth.value().size() - auth_prefix_len;
+  // Use full-width XOR so any bit difference in the lengths is preserved
+  // (uint8_t truncation would miss differences in higher bytes, e.g.
+  // digest_len vs digest_len + 256).
+  volatile size_t result = digest_len ^ provided_len;
+  // Iterate over the expected digest length only — the full-width length
+  // XOR above already rejects any length mismatch, and bounding the loop
+  // prevents a long Authorization header from forcing extra work.
+  for (size_t i = 0; i < digest_len; i++) {
+    char provided_ch = (i < provided_len) ? provided[i] : 0;
+    result |= static_cast<uint8_t>(digest[i] ^ provided_ch);
+  }
+  return result == 0;
 }
 
 void AsyncWebServerRequest::requestAuthentication(const char *realm) const {
diff --git a/esphome/dashboard/settings.py b/esphome/dashboard/settings.py
index 6035b4a1d6..3b22180b1d 100644
--- a/esphome/dashboard/settings.py
+++ b/esphome/dashboard/settings.py
@@ -32,7 +32,7 @@ class DashboardSettings:
     def __init__(self) -> None:
         """Initialize the dashboard settings."""
         self.config_dir: Path = None
-        self.password_hash: str = ""
+        self.password_hash: bytes = b""
         self.username: str = ""
         self.using_password: bool = False
         self.on_ha_addon: bool = False
@@ -84,11 +84,14 @@ class DashboardSettings:
     def check_password(self, username: str, password: str) -> bool:
         if not self.using_auth:
             return True
-        if username != self.username:
-            return False
-
-        # Compare password in constant running time (to prevent timing attacks)
-        return hmac.compare_digest(self.password_hash, password_hash(password))
+        # Compare in constant running time (to prevent timing attacks)
+        username_matches = hmac.compare_digest(
+            username.encode("utf-8"), self.username.encode("utf-8")
+        )
+        password_matches = hmac.compare_digest(
+            self.password_hash, password_hash(password)
+        )
+        return username_matches and password_matches
 
     def rel_path(self, *args: Any) -> Path:
         """Return a path relative to the ESPHome config folder."""
diff --git a/esphome/dashboard/web_server.py b/esphome/dashboard/web_server.py
index da50279864..92cab929ef 100644
--- a/esphome/dashboard/web_server.py
+++ b/esphome/dashboard/web_server.py
@@ -120,8 +120,11 @@ def is_authenticated(handler: BaseHandler) -> bool:
         if auth_header := handler.request.headers.get("Authorization"):
             assert isinstance(auth_header, str)
             if auth_header.startswith("Basic "):
-                auth_decoded = base64.b64decode(auth_header[6:]).decode()
-                username, password = auth_decoded.split(":", 1)
+                try:
+                    auth_decoded = base64.b64decode(auth_header[6:]).decode()
+                    username, password = auth_decoded.split(":", 1)
+                except (binascii.Error, ValueError, UnicodeDecodeError):
+                    return False
                 return settings.check_password(username, password)
         return handler.get_secure_cookie(AUTH_COOKIE_NAME) == COOKIE_AUTHENTICATED_YES
 
@@ -1054,17 +1057,26 @@ class DownloadBinaryRequestHandler(BaseHandler):
         # fallback to type=, but prioritize file=
         file_name = self.get_argument("type", None)
         file_name = self.get_argument("file", file_name)
-        if file_name is None:
+        if file_name is None or not file_name.strip():
             self.send_error(400)
             return
-        file_name = file_name.replace("..", "").lstrip("/")
         # get requested download name, or build it based on filename
         download_name = self.get_argument(
             "download",
             f"{storage_json.name}-{file_name}",
         )
 
-        path = storage_json.firmware_bin_path.parent.joinpath(file_name)
+        if storage_json.firmware_bin_path is None:
+            self.send_error(404)
+            return
+
+        base_dir = storage_json.firmware_bin_path.parent.resolve()
+        path = base_dir.joinpath(file_name).resolve()
+        try:
+            path.relative_to(base_dir)
+        except ValueError:
+            self.send_error(403)
+            return
 
         if not path.is_file():
             args = ["esphome", "idedata", settings.rel_path(configuration)]
@@ -1078,7 +1090,7 @@ class DownloadBinaryRequestHandler(BaseHandler):
 
             found = False
             for image in idedata.extra_flash_images:
-                if image.path.endswith(file_name):
+                if image.path.as_posix().endswith(file_name):
                     path = image.path
                     download_name = file_name
                     found = True
diff --git a/esphome/espota2.py b/esphome/espota2.py
index 2d90251b38..c342eb4463 100644
--- a/esphome/espota2.py
+++ b/esphome/espota2.py
@@ -6,7 +6,7 @@ import hashlib
 import io
 import logging
 from pathlib import Path
-import random
+import secrets
 import socket
 import sys
 import time
@@ -300,8 +300,8 @@ def perform_ota(
         nonce = nonce_bytes.decode()
         _LOGGER.debug("Auth: %s Nonce is %s", hash_name, nonce)
 
-        # Generate cnonce
-        cnonce = hash_func(str(random.random()).encode()).hexdigest()
+        # Generate cnonce matching the hash algorithm's digest size
+        cnonce = secrets.token_hex(nonce_size // 2)
         _LOGGER.debug("Auth: %s CNonce is %s", hash_name, cnonce)
 
         send_check(sock, cnonce, "auth cnonce")
diff --git a/esphome/wizard.py b/esphome/wizard.py
index 4b74847996..f83342cc6a 100644
--- a/esphome/wizard.py
+++ b/esphome/wizard.py
@@ -1,6 +1,5 @@
 import base64
 from pathlib import Path
-import random
 import secrets
 import string
 from typing import Literal, NotRequired, TypedDict, Unpack
@@ -130,7 +129,7 @@ def wizard_file(**kwargs: Unpack[WizardFileKwargs]) -> str:
     if len(ap_name) > 32:
         ap_name = ap_name_base
     kwargs["fallback_name"] = ap_name
-    kwargs["fallback_psk"] = "".join(random.choice(letters) for _ in range(12))
+    kwargs["fallback_psk"] = "".join(secrets.choice(letters) for _ in range(12))
 
     base = BASE_CONFIG_FRIENDLY if kwargs.get("friendly_name") else BASE_CONFIG
 
diff --git a/tests/dashboard/test_settings.py b/tests/dashboard/test_settings.py
index 91a8ec70c3..55776ac7c4 100644
--- a/tests/dashboard/test_settings.py
+++ b/tests/dashboard/test_settings.py
@@ -1,4 +1,4 @@
-"""Tests for dashboard settings Path-related functionality."""
+"""Tests for DashboardSettings (path resolution and authentication)."""
 
 from __future__ import annotations
 
@@ -10,6 +10,7 @@ import pytest
 
 from esphome.core import CORE
 from esphome.dashboard.settings import DashboardSettings
+from esphome.dashboard.util.password import password_hash
 
 
 @pytest.fixture
@@ -221,3 +222,66 @@ def test_config_path_parent_resolves_to_config_dir(tmp_path: Path) -> None:
     # Verify that CORE.config_path itself uses the sentinel file
     assert CORE.config_path.name == "___DASHBOARD_SENTINEL___.yaml"
     assert not CORE.config_path.exists()  # Sentinel file doesn't actually exist
+
+
+@pytest.fixture
+def auth_settings(dashboard_settings: DashboardSettings) -> DashboardSettings:
+    """Create DashboardSettings with auth configured, based on dashboard_settings."""
+    dashboard_settings.username = "admin"
+    dashboard_settings.using_password = True
+    dashboard_settings.password_hash = password_hash("correctpassword")
+    return dashboard_settings
+
+
+def test_check_password_correct_credentials(auth_settings: DashboardSettings) -> None:
+    """Test check_password returns True for correct username and password."""
+    assert auth_settings.check_password("admin", "correctpassword") is True
+
+
+def test_check_password_wrong_password(auth_settings: DashboardSettings) -> None:
+    """Test check_password returns False for wrong password."""
+    assert auth_settings.check_password("admin", "wrongpassword") is False
+
+
+def test_check_password_wrong_username(auth_settings: DashboardSettings) -> None:
+    """Test check_password returns False for wrong username."""
+    assert auth_settings.check_password("notadmin", "correctpassword") is False
+
+
+def test_check_password_both_wrong(auth_settings: DashboardSettings) -> None:
+    """Test check_password returns False when both are wrong."""
+    assert auth_settings.check_password("notadmin", "wrongpassword") is False
+
+
+def test_check_password_no_auth(dashboard_settings: DashboardSettings) -> None:
+    """Test check_password returns True when auth is not configured."""
+    assert dashboard_settings.check_password("anyone", "anything") is True
+
+
+def test_check_password_non_ascii_username(
+    dashboard_settings: DashboardSettings,
+) -> None:
+    """Test check_password handles non-ASCII usernames without TypeError."""
+    dashboard_settings.username = "\u00e9l\u00e8ve"
+    dashboard_settings.using_password = True
+    dashboard_settings.password_hash = password_hash("pass")
+    assert dashboard_settings.check_password("\u00e9l\u00e8ve", "pass") is True
+    assert dashboard_settings.check_password("\u00e9l\u00e8ve", "wrong") is False
+    assert dashboard_settings.check_password("other", "pass") is False
+
+
+def test_check_password_ha_addon_no_password(
+    dashboard_settings: DashboardSettings,
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Test check_password doesn't crash in HA add-on mode without a password.
+
+    In HA add-on mode, using_ha_addon_auth can be True while using_password
+    is False, leaving password_hash as b"". This must not raise TypeError
+    in hmac.compare_digest.
+    """
+    monkeypatch.delenv("DISABLE_HA_AUTHENTICATION", raising=False)
+    dashboard_settings.on_ha_addon = True
+    dashboard_settings.using_password = False
+    # password_hash stays as default b""
+    assert dashboard_settings.check_password("anyone", "anything") is False
diff --git a/tests/dashboard/test_web_server.py b/tests/dashboard/test_web_server.py
index 7642876ee5..daff384515 100644
--- a/tests/dashboard/test_web_server.py
+++ b/tests/dashboard/test_web_server.py
@@ -2,12 +2,14 @@ from __future__ import annotations
 
 from argparse import Namespace
 import asyncio
+import base64
 from collections.abc import Generator
 from contextlib import asynccontextmanager
 import gzip
 import json
 import os
 from pathlib import Path
+import sys
 from unittest.mock import AsyncMock, MagicMock, Mock, patch
 
 import pytest
@@ -421,7 +423,7 @@ async def test_download_binary_handler_idedata_fallback(
 
     # Mock idedata response
     mock_image = Mock()
-    mock_image.path = str(bootloader_file)
+    mock_image.path = bootloader_file
     mock_idedata_instance = Mock()
     mock_idedata_instance.extra_flash_images = [mock_image]
     mock_idedata.return_value = mock_idedata_instance
@@ -528,14 +530,22 @@ async def test_download_binary_handler_subdirectory_file_url_encoded(
 @pytest.mark.asyncio
 @pytest.mark.usefixtures("mock_ext_storage_path")
 @pytest.mark.parametrize(
-    "attack_path",
+    ("attack_path", "expected_code"),
     [
-        pytest.param("../../../secrets.yaml", id="basic_traversal"),
-        pytest.param("..%2F..%2F..%2Fsecrets.yaml", id="url_encoded"),
-        pytest.param("zephyr/../../../secrets.yaml", id="traversal_with_prefix"),
-        pytest.param("/etc/passwd", id="absolute_path"),
-        pytest.param("//etc/passwd", id="double_slash_absolute"),
-        pytest.param("....//secrets.yaml", id="multiple_dots"),
+        pytest.param("../../../secrets.yaml", 403, id="basic_traversal"),
+        pytest.param("..%2F..%2F..%2Fsecrets.yaml", 403, id="url_encoded"),
+        pytest.param("zephyr/../../../secrets.yaml", 403, id="traversal_with_prefix"),
+        pytest.param("/etc/passwd", 403, id="absolute_path"),
+        pytest.param("//etc/passwd", 403, id="double_slash_absolute"),
+        pytest.param(
+            "....//secrets.yaml",
+            # On Windows, Path.resolve() treats "..." and "...." as parent
+            # traversal (like ".."), so the path escapes base_dir -> 403.
+            # On Unix, "...." is a literal directory name that stays inside
+            # base_dir but doesn't exist -> 404.
+            403 if sys.platform == "win32" else 404,
+            id="multiple_dots",
+        ),
     ],
 )
 async def test_download_binary_handler_path_traversal_protection(
@@ -543,11 +553,14 @@ async def test_download_binary_handler_path_traversal_protection(
     tmp_path: Path,
     mock_storage_json: MagicMock,
     attack_path: str,
+    expected_code: int,
 ) -> None:
     """Test that DownloadBinaryRequestHandler prevents path traversal attacks.
 
-    Verifies that attempts to use '..' in file paths are sanitized to prevent
-    accessing files outside the build directory. Tests multiple attack vectors.
+    Verifies that attempts to escape the build directory via '..' are rejected
+    using resolve()/relative_to() validation. Tests multiple attack vectors.
+    Real traversals that escape the base directory get 403. Paths like '....'
+    that resolve inside the base directory but don't exist get 404.
     """
     # Create build structure
     build_dir = get_build_path(tmp_path, "test")
@@ -565,14 +578,67 @@ async def test_download_binary_handler_path_traversal_protection(
     mock_storage.firmware_bin_path = firmware_file
     mock_storage_json.load.return_value = mock_storage
 
-    # Attempt path traversal attack - should be blocked
-    with pytest.raises(HTTPClientError) as exc_info:
+    # Mock async_run_system_command so paths that pass validation but don't exist
+    # return 404 deterministically without spawning a real subprocess.
+    with (
+        patch(
+            "esphome.dashboard.web_server.async_run_system_command",
+            new_callable=AsyncMock,
+            return_value=(2, "", ""),
+        ),
+        pytest.raises(HTTPClientError) as exc_info,
+    ):
         await dashboard.fetch(
             f"/download.bin?configuration=test.yaml&file={attack_path}",
             method="GET",
         )
-    # Should get 404 (file not found after sanitization) or 500 (idedata fails)
-    assert exc_info.value.code in (404, 500)
+    assert exc_info.value.code == expected_code
+
+
+@pytest.mark.asyncio
+@pytest.mark.usefixtures("mock_ext_storage_path")
+async def test_download_binary_handler_no_firmware_bin_path(
+    dashboard: DashboardTestHelper,
+    mock_storage_json: MagicMock,
+) -> None:
+    """Test that download returns 404 when firmware_bin_path is None.
+
+    This covers configs created by StorageJSON.from_wizard() where no
+    firmware has been compiled yet.
+    """
+    mock_storage = Mock()
+    mock_storage.name = "test_device"
+    mock_storage.firmware_bin_path = None
+    mock_storage_json.load.return_value = mock_storage
+
+    with pytest.raises(HTTPClientError) as exc_info:
+        await dashboard.fetch(
+            "/download.bin?configuration=test.yaml&file=firmware.bin",
+            method="GET",
+        )
+    assert exc_info.value.code == 404
+
+
+@pytest.mark.asyncio
+@pytest.mark.usefixtures("mock_ext_storage_path")
+@pytest.mark.parametrize("file_value", ["", "%20%20", "%20"])
+async def test_download_binary_handler_empty_file_name(
+    dashboard: DashboardTestHelper,
+    mock_storage_json: MagicMock,
+    file_value: str,
+) -> None:
+    """Test that download returns 400 for empty or whitespace-only file names."""
+    mock_storage = Mock()
+    mock_storage.name = "test_device"
+    mock_storage.firmware_bin_path = Path("/fake/firmware.bin")
+    mock_storage_json.load.return_value = mock_storage
+
+    with pytest.raises(HTTPClientError) as exc_info:
+        await dashboard.fetch(
+            f"/download.bin?configuration=test.yaml&file={file_value}",
+            method="GET",
+        )
+    assert exc_info.value.code == 400
 
 
 @pytest.mark.asyncio
@@ -1676,3 +1742,85 @@ def test_proc_on_exit_skips_when_already_closed() -> None:
 
     handler.write_message.assert_not_called()
     handler.close.assert_not_called()
+
+
+def _make_auth_handler(auth_header: str | None = None) -> Mock:
+    """Create a mock handler with the given Authorization header."""
+    handler = Mock()
+    handler.request = Mock()
+    if auth_header is not None:
+        handler.request.headers = {"Authorization": auth_header}
+    else:
+        handler.request.headers = {}
+    handler.get_secure_cookie = Mock(return_value=None)
+    return handler
+
+
+@pytest.fixture
+def mock_auth_settings(mock_dashboard_settings: MagicMock) -> MagicMock:
+    """Fixture to configure mock dashboard settings with auth enabled."""
+    mock_dashboard_settings.using_auth = True
+    mock_dashboard_settings.on_ha_addon = False
+    return mock_dashboard_settings
+
+
+@pytest.mark.usefixtures("mock_auth_settings")
+def test_is_authenticated_malformed_base64() -> None:
+    """Test that invalid base64 in Authorization header returns False."""
+    handler = _make_auth_handler("Basic !!!not-valid-base64!!!")
+    assert web_server.is_authenticated(handler) is False
+
+
+@pytest.mark.usefixtures("mock_auth_settings")
+def test_is_authenticated_bad_base64_padding() -> None:
+    """Test that incorrect base64 padding (binascii.Error) returns False."""
+    handler = _make_auth_handler("Basic abc")
+    assert web_server.is_authenticated(handler) is False
+
+
+@pytest.mark.usefixtures("mock_auth_settings")
+def test_is_authenticated_invalid_utf8() -> None:
+    """Test that base64 decoding to invalid UTF-8 returns False."""
+    # \xff\xfe is invalid UTF-8
+    bad_payload = base64.b64encode(b"\xff\xfe").decode("ascii")
+    handler = _make_auth_handler(f"Basic {bad_payload}")
+    assert web_server.is_authenticated(handler) is False
+
+
+@pytest.mark.usefixtures("mock_auth_settings")
+def test_is_authenticated_no_colon() -> None:
+    """Test that base64 payload without ':' separator returns False."""
+    no_colon = base64.b64encode(b"nocolonhere").decode("ascii")
+    handler = _make_auth_handler(f"Basic {no_colon}")
+    assert web_server.is_authenticated(handler) is False
+
+
+def test_is_authenticated_valid_credentials(
+    mock_auth_settings: MagicMock,
+) -> None:
+    """Test that valid Basic auth credentials are checked."""
+    creds = base64.b64encode(b"admin:secret").decode("ascii")
+    mock_auth_settings.check_password.return_value = True
+    handler = _make_auth_handler(f"Basic {creds}")
+    assert web_server.is_authenticated(handler) is True
+    mock_auth_settings.check_password.assert_called_once_with("admin", "secret")
+
+
+def test_is_authenticated_wrong_credentials(
+    mock_auth_settings: MagicMock,
+) -> None:
+    """Test that valid Basic auth with wrong credentials returns False."""
+    creds = base64.b64encode(b"admin:wrong").decode("ascii")
+    mock_auth_settings.check_password.return_value = False
+    handler = _make_auth_handler(f"Basic {creds}")
+    assert web_server.is_authenticated(handler) is False
+
+
+def test_is_authenticated_no_auth_configured(
+    mock_dashboard_settings: MagicMock,
+) -> None:
+    """Test that requests pass when auth is not configured."""
+    mock_dashboard_settings.using_auth = False
+    mock_dashboard_settings.on_ha_addon = False
+    handler = _make_auth_handler()
+    assert web_server.is_authenticated(handler) is True
diff --git a/tests/unit_tests/test_espota2.py b/tests/unit_tests/test_espota2.py
index 1885b769f1..20ba4b1f76 100644
--- a/tests/unit_tests/test_espota2.py
+++ b/tests/unit_tests/test_espota2.py
@@ -18,8 +18,8 @@ from esphome import espota2
 from esphome.core import EsphomeError
 
 # Test constants
-MOCK_RANDOM_VALUE = 0.123456
-MOCK_RANDOM_BYTES = b"0.123456"
+MOCK_MD5_CNONCE = "a" * 32  # Mock 32-char hex string from secrets.token_hex(16)
+MOCK_SHA256_CNONCE = "b" * 64  # Mock 64-char hex string from secrets.token_hex(32)
 MOCK_MD5_NONCE = b"12345678901234567890123456789012"  # 32 char nonce for MD5
 MOCK_SHA256_NONCE = b"1234567890123456789012345678901234567890123456789012345678901234"  # 64 char nonce for SHA256
 
@@ -55,10 +55,18 @@ def mock_time() -> Generator[None]:
 
 
 @pytest.fixture
-def mock_random() -> Generator[Mock]:
-    """Mock random for predictable test values."""
-    with patch("random.random", return_value=MOCK_RANDOM_VALUE) as mock_rand:
-        yield mock_rand
+def mock_token_hex() -> Generator[Mock]:
+    """Mock secrets.token_hex for predictable test values."""
+
+    def _token_hex(nbytes: int) -> str:
+        if nbytes == 16:
+            return MOCK_MD5_CNONCE
+        if nbytes == 32:
+            return MOCK_SHA256_CNONCE
+        raise ValueError(f"Unexpected nbytes for token_hex mock: {nbytes}")
+
+    with patch("esphome.espota2.secrets.token_hex", side_effect=_token_hex) as mock:
+        yield mock
 
 
 @pytest.fixture
@@ -236,7 +244,7 @@ def test_send_check_socket_error(mock_socket: Mock) -> None:
 
 @pytest.mark.usefixtures("mock_time")
 def test_perform_ota_successful_md5_auth(
-    mock_socket: Mock, mock_file: io.BytesIO, mock_random: Mock
+    mock_socket: Mock, mock_file: io.BytesIO, mock_token_hex: Mock
 ) -> None:
     """Test successful OTA with MD5 authentication."""
     # Setup socket responses for recv calls
@@ -272,8 +280,11 @@ def test_perform_ota_successful_md5_auth(
         )
     )
 
-    # Verify cnonce was sent (MD5 of random.random())
-    cnonce = hashlib.md5(MOCK_RANDOM_BYTES).hexdigest()
+    # Verify token_hex was called with MD5 digest size
+    mock_token_hex.assert_called_once_with(16)
+
+    # Verify cnonce was sent
+    cnonce = MOCK_MD5_CNONCE
     assert mock_socket.sendall.call_args_list[2] == call(cnonce.encode())
 
     # Verify auth result was computed correctly
@@ -366,7 +377,7 @@ def test_perform_ota_auth_without_password(mock_socket: Mock) -> None:
 
 @pytest.mark.usefixtures("mock_time")
 def test_perform_ota_md5_auth_wrong_password(
-    mock_socket: Mock, mock_file: io.BytesIO, mock_random: Mock
+    mock_socket: Mock, mock_file: io.BytesIO, mock_token_hex: Mock
 ) -> None:
     """Test OTA fails when MD5 authentication is rejected due to wrong password."""
     # Setup socket responses for recv calls
@@ -390,7 +401,7 @@ def test_perform_ota_md5_auth_wrong_password(
 
 @pytest.mark.usefixtures("mock_time")
 def test_perform_ota_sha256_auth_wrong_password(
-    mock_socket: Mock, mock_file: io.BytesIO, mock_random: Mock
+    mock_socket: Mock, mock_file: io.BytesIO, mock_token_hex: Mock
 ) -> None:
     """Test OTA fails when SHA256 authentication is rejected due to wrong password."""
     # Setup socket responses for recv calls
@@ -603,7 +614,7 @@ def test_progress_bar(capsys: CaptureFixture[str]) -> None:
 # Tests for SHA256 authentication
 @pytest.mark.usefixtures("mock_time")
 def test_perform_ota_successful_sha256_auth(
-    mock_socket: Mock, mock_file: io.BytesIO, mock_random: Mock
+    mock_socket: Mock, mock_file: io.BytesIO, mock_token_hex: Mock
 ) -> None:
     """Test successful OTA with SHA256 authentication."""
     # Setup socket responses for recv calls
@@ -639,8 +650,11 @@ def test_perform_ota_successful_sha256_auth(
         )
     )
 
-    # Verify cnonce was sent (SHA256 of random.random())
-    cnonce = hashlib.sha256(MOCK_RANDOM_BYTES).hexdigest()
+    # Verify token_hex was called with SHA256 digest size
+    mock_token_hex.assert_called_once_with(32)
+
+    # Verify cnonce was sent
+    cnonce = MOCK_SHA256_CNONCE
     assert mock_socket.sendall.call_args_list[2] == call(cnonce.encode())
 
     # Verify auth result was computed correctly with SHA256
@@ -654,7 +668,7 @@ def test_perform_ota_successful_sha256_auth(
 
 @pytest.mark.usefixtures("mock_time")
 def test_perform_ota_sha256_fallback_to_md5(
-    mock_socket: Mock, mock_file: io.BytesIO, mock_random: Mock
+    mock_socket: Mock, mock_file: io.BytesIO, mock_token_hex: Mock
 ) -> None:
     """Test SHA256-capable client falls back to MD5 for compatibility."""
     # This test verifies the temporary backward compatibility
@@ -692,7 +706,8 @@ def test_perform_ota_sha256_fallback_to_md5(
     )
 
     # But authentication was done with MD5
-    cnonce = hashlib.md5(MOCK_RANDOM_BYTES).hexdigest()
+    mock_token_hex.assert_called_once_with(16)
+    cnonce = MOCK_MD5_CNONCE
     expected_hash = hashlib.md5()
     expected_hash.update(b"testpass")
     expected_hash.update(MOCK_MD5_NONCE)
diff --git a/tests/unit_tests/test_wizard.py b/tests/unit_tests/test_wizard.py
index eb44c1c20f..0ce89230d8 100644
--- a/tests/unit_tests/test_wizard.py
+++ b/tests/unit_tests/test_wizard.py
@@ -2,7 +2,7 @@
 
 from pathlib import Path
 from typing import Any
-from unittest.mock import MagicMock
+from unittest.mock import MagicMock, patch
 
 import pytest
 from pytest import MonkeyPatch
@@ -632,3 +632,14 @@ def test_wizard_accepts_rpipico_board(tmp_path: Path, monkeypatch: MonkeyPatch):
     # rpipico doesn't support WiFi, so no api_encryption_key or ota_password
     assert "api_encryption_key" not in call_kwargs
     assert "ota_password" not in call_kwargs
+
+
+def test_fallback_psk_uses_secrets_choice(
+    default_config: dict[str, Any],
+) -> None:
+    """Test that fallback PSK is generated using secrets.choice."""
+    with patch("esphome.wizard.secrets.choice", return_value="X") as mock_choice:
+        config = wz.wizard_file(**default_config)
+
+    assert 'password: "XXXXXXXXXXXX"' in config
+    assert mock_choice.call_count == 12