diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 12072072b9..34141b6723 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -268,6 +268,63 @@ jobs:
         shell: pwsh
         run: Get-ChildItem publish -Filter *.pdb -Recurse | Remove-Item
 
+      - name: Authenticode sign Windows executable
+        if: runner.os == 'Windows'
+        shell: pwsh
+        env:
+          WIN_SIGNING_CERT_BASE64: ${{ secrets.WIN_SIGNING_CERT_BASE64 }}
+          WIN_SIGNING_CERT_PASSWORD: ${{ secrets.WIN_SIGNING_CERT_PASSWORD }}
+        run: |
+          if ([string]::IsNullOrWhiteSpace($env:WIN_SIGNING_CERT_BASE64)) {
+            throw "WIN_SIGNING_CERT_BASE64 secret is required to Authenticode-sign Windows release binaries."
+          }
+          if ([string]::IsNullOrWhiteSpace($env:WIN_SIGNING_CERT_PASSWORD)) {
+            throw "WIN_SIGNING_CERT_PASSWORD secret is required to Authenticode-sign Windows release binaries."
+          }
+
+          $exe = Join-Path (Resolve-Path publish) "cdidx.exe"
+          if (-not (Test-Path -LiteralPath $exe)) {
+            throw "Published Windows executable was not found: $exe"
+          }
+
+          $pfxPath = Join-Path $env:RUNNER_TEMP "cdidx-signing.pfx"
+          [IO.File]::WriteAllBytes($pfxPath, [Convert]::FromBase64String($env:WIN_SIGNING_CERT_BASE64))
+
+          $password = ConvertTo-SecureString $env:WIN_SIGNING_CERT_PASSWORD -AsPlainText -Force
+          $cert = Import-PfxCertificate `
+            -FilePath $pfxPath `
+            -CertStoreLocation Cert:\CurrentUser\My `
+            -Password $password `
+            -Exportable:$false
+          try {
+            if (-not $cert.Thumbprint) {
+              throw "Imported signing certificate did not expose a thumbprint."
+            }
+
+            $signtool = Get-ChildItem "${env:ProgramFiles(x86)}\Windows Kits\10\bin" -Recurse -Filter signtool.exe |
+              Where-Object { $_.FullName -match '\\x64\\signtool\.exe$' } |
+              Sort-Object FullName -Descending |
+              Select-Object -First 1
+            if (-not $signtool) {
+              throw "signtool.exe was not found in the Windows Kits installation."
+            }
+
+            & $signtool.FullName sign /fd SHA256 /td SHA256 /tr http://timestamp.digicert.com /sha1 $cert.Thumbprint $exe
+            if ($LASTEXITCODE -ne 0) {
+              throw "signtool sign failed with exit code $LASTEXITCODE."
+            }
+
+            & $signtool.FullName verify /pa /v $exe
+            if ($LASTEXITCODE -ne 0) {
+              throw "signtool verify failed with exit code $LASTEXITCODE."
+            }
+          } finally {
+            if ($cert.Thumbprint) {
+              Remove-Item -LiteralPath "Cert:\CurrentUser\My\$($cert.Thumbprint)" -Force -ErrorAction SilentlyContinue
+            }
+            Remove-Item -LiteralPath $pfxPath -Force -ErrorAction SilentlyContinue
+          }
+
       - name: Add license and trademark notices to publish output (Linux/macOS)
         if: runner.os != 'Windows'
         run: cp LICENSE LICENSES/FSL-1.1-ALv2.txt LICENSES/Apache-2.0.txt COMMERCIAL_LICENSE.md INTEGRATION_POLICY.md TRADEMARKS.md publish/ && cp -R LICENSES publish/
diff --git a/README.md b/README.md
index ba52e204ff..54a5f1aa49 100644
--- a/README.md
+++ b/README.md
@@ -233,6 +233,14 @@ the per-platform `CodeIndex-<rid>.tar.gz` / `.zip` binaries:
 | `sha256sums.txt` | SHA-256 of every release asset (including the SBOM). `install.sh` uses it to verify the downloaded tarball before placing anything under `$HOME/.local/bin/`. |
 | `cdidx.sbom.cdx.json` | CycloneDX 1.x JSON Software Bill of Materials covering every NuGet dependency (including the bundled `SQLitePCLRaw` native asset) so compliance reviewers (SOC2, FedRAMP-style) and scanners (Snyk, Trivy, Grype) can audit transitive dependencies without re-deriving them from `.deps.json`. |
 
+Windows ZIP releases contain an Authenticode-signed `cdidx.exe`. After
+extracting the archive on Windows, verify the signature and timestamp before
+trusting the executable:
+
+```powershell
+Get-AuthenticodeSignature .\cdidx.exe | Format-List Status,SignerCertificate,TimeStamperCertificate
+```
+
 Quick check after downloading both files from the release page:
 
 ```bash
@@ -457,6 +465,14 @@ NuGet パッケージは .NET グローバルツールとして公開されて
 | `sha256sums.txt` | 各リリースアセット（SBOM を含む）の SHA-256。`install.sh` は `$HOME/.local/bin/` に何も書き込む前に tarball をこのファイルで検証します。 |
 | `cdidx.sbom.cdx.json` | CycloneDX 1.x JSON 形式の Software Bill of Materials。同梱の `SQLitePCLRaw` ネイティブアセットを含む全 NuGet 依存を列挙するため、SOC2 / FedRAMP 系のコンプライアンスレビューや Snyk / Trivy / Grype などのスキャナーが `.deps.json` から再構築せずに推移的依存を監査できます。 |
 
+Windows ZIP release に含まれる `cdidx.exe` は Authenticode 署名済みです。
+Windows で archive を展開したあと、実行ファイルを信頼する前に署名と
+timestamp を確認してください。
+
+```powershell
+Get-AuthenticodeSignature .\cdidx.exe | Format-List Status,SignerCertificate,TimeStamperCertificate
+```
+
 リリースページから両ファイルをダウンロードしたあとの簡易チェック例:
 
 ```bash
diff --git a/USER_GUIDE.md b/USER_GUIDE.md
index e486388045..7d072b16b1 100644
--- a/USER_GUIDE.md
+++ b/USER_GUIDE.md
@@ -450,6 +450,13 @@ sha256sum -c sha256sums.txt
 The GPG signature verifies the checksum manifest through the release signing
 key.
 
+Windows release ZIPs also contain an Authenticode-signed `cdidx.exe`. After
+extracting the archive, verify that Windows trusts the signature and timestamp:
+
+```powershell
+Get-AuthenticodeSignature .\cdidx.exe | Format-List Status,SignerCertificate,TimeStamperCertificate
+```
+
 Release workflows also emit GitHub build provenance attestations for the
 published archives, SBOM, checksum manifest, and checksum signature. Verify
 that an artifact was produced by this repository's GitHub Actions release
@@ -2437,6 +2444,39 @@ runtime の管理方法とネットワーク条件に合わせて install channe
 完全な比較、package maintainer guidance、winget / apt / rpm / Snap /
 Flatpak などの予定チャネルは [DISTRIBUTION.md](DISTRIBUTION.md) を参照してください。
 
+### リリースアセットの検証
+
+GitHub releases は、すべての archive と SBOM asset を対象にした
+`sha256sums.txt` と、detached GPG signature の `sha256sums.txt.asc` を
+公開します。download した release artifact を信頼する前に checksum manifest
+を検証してください。
+
+```bash
+gpg --verify sha256sums.txt.asc sha256sums.txt
+sha256sum -c sha256sums.txt
+```
+
+GPG signature は release signing key を通じて checksum manifest を検証します。
+
+Windows release ZIP にも Authenticode 署名済みの `cdidx.exe` が含まれます。
+archive を展開したあと、Windows が署名と timestamp を信頼していることを
+確認してください。
+
+```powershell
+Get-AuthenticodeSignature .\cdidx.exe | Format-List Status,SignerCertificate,TimeStamperCertificate
+```
+
+release workflow は、公開された archive、SBOM、checksum manifest、checksum
+signature に対する GitHub build provenance attestation も出力します。artifact が
+この repository の GitHub Actions release workflow で生成されたことを検証できます。
+
+```bash
+gh attestation verify CodeIndex-linux-x64.tar.gz -R Widthdom/CodeIndex
+```
+
+GitHub attestation は、その artifact が repository workflow identity により
+生成されたことを検証します。
+
 ### 方法A: ワンライナーインストール（.NET 不要）
 
 コンテナ、CI、Linux/macOS 環境で .NET SDK なしで使えます。
diff --git a/changelog.d/unreleased/1845.security.md b/changelog.d/unreleased/1845.security.md
new file mode 100644
index 0000000000..3291806223
--- /dev/null
+++ b/changelog.d/unreleased/1845.security.md
@@ -0,0 +1,17 @@
+---
+category: security
+issues:
+  - 1845
+affected:
+  - .github/workflows/release.yml
+  - README.md
+  - USER_GUIDE.md
+---
+
+## English
+
+- **Windows release binaries are Authenticode-signed (#1845)** — Windows release builds now import the release signing certificate from GitHub Actions secrets, sign `cdidx.exe`, and verify the signature before the ZIP artifact is uploaded.
+
+## 日本語
+
+- **Windows release binary を Authenticode 署名するようになりました (#1845)** — Windows release build は GitHub Actions secrets から release signing certificate を import し、`cdidx.exe` に署名してから、ZIP artifact の upload 前に署名検証を行います。