diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
new file mode 100644
index 0000000000..d9275dc521
--- /dev/null
+++ b/.github/CODEOWNERS
@@ -0,0 +1,5 @@
+# Release-critical paths require review from the repository owner.
+/.github/workflows/ @Widthdom
+/install.sh @Widthdom
+/src/CodeIndex/CodeIndex.csproj @Widthdom
+/nuget.config @Widthdom
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 22c9962ad1..12072072b9 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -18,6 +18,8 @@ on:
 
 permissions:
   contents: write
+  id-token: write
+  attestations: write
 
 jobs:
   release:
@@ -388,6 +390,52 @@ jobs:
           cd release-files
           sha256sum * > sha256sums.txt
 
+      - name: Import release GPG key
+        env:
+          RELEASE_GPG_PRIVATE_KEY: ${{ secrets.RELEASE_GPG_PRIVATE_KEY }}
+          RELEASE_GPG_PASSPHRASE: ${{ secrets.RELEASE_GPG_PASSPHRASE }}
+        run: |
+          set -euo pipefail
+          if [ -z "${RELEASE_GPG_PRIVATE_KEY}" ]; then
+            echo "RELEASE_GPG_PRIVATE_KEY secret is required to sign sha256sums.txt." >&2
+            exit 1
+          fi
+
+          mkdir -p ~/.gnupg
+          chmod 700 ~/.gnupg
+          printf '%s' "${RELEASE_GPG_PRIVATE_KEY}" | gpg --batch --import
+          if [ -n "${RELEASE_GPG_PASSPHRASE}" ]; then
+            printf '%s' "${RELEASE_GPG_PASSPHRASE}" > ~/.gnupg/release-passphrase
+            chmod 600 ~/.gnupg/release-passphrase
+          fi
+
+      - name: Sign release checksum manifest
+        env:
+          RELEASE_GPG_KEY_ID: ${{ secrets.RELEASE_GPG_KEY_ID }}
+          RELEASE_GPG_PASSPHRASE: ${{ secrets.RELEASE_GPG_PASSPHRASE }}
+        run: |
+          set -euo pipefail
+          sign_args=(--batch --yes --armor --detach-sign)
+          if [ -n "${RELEASE_GPG_KEY_ID}" ]; then
+            sign_args+=(--local-user "${RELEASE_GPG_KEY_ID}")
+          fi
+          if [ -n "${RELEASE_GPG_PASSPHRASE}" ]; then
+            sign_args+=(--pinentry-mode loopback --passphrase-file ~/.gnupg/release-passphrase)
+          fi
+
+          gpg "${sign_args[@]}" --output release-files/sha256sums.txt.asc release-files/sha256sums.txt
+          test -s release-files/sha256sums.txt.asc
+
+      - name: Attest release artifacts
+        uses: actions/attest-build-provenance@v2
+        with:
+          subject-path: |
+            release-files/*.tar.gz
+            release-files/*.zip
+            release-files/*.cdx.json
+            release-files/sha256sums.txt
+            release-files/sha256sums.txt.asc
+
       - name: Write release install notes
         run: |
           cat > release-install-notes.md <<'EOF'
@@ -472,7 +520,7 @@ jobs:
           # リリースが "Failed to download sha256sums.txt ... HTTP 404" で
           # 失敗した。verify step が取得する全 asset をポーリングし、伝播の
           # 遅い asset があってもリリースを失敗させず待ち切る。
-          VERIFY_ASSET_NAMES: CodeIndex-linux-x64.tar.gz sha256sums.txt
+          VERIFY_ASSET_NAMES: CodeIndex-linux-x64.tar.gz sha256sums.txt sha256sums.txt.asc
         run: |
           set -euo pipefail
           mapfile -t expected_assets < <(cd release-files && printf '%s\n' *)
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index d705095cfc..9802724505 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -62,6 +62,20 @@ Keep changes focused and follow the existing style of the files you touch:
   contracts change;
 - add or update tests when behavior changes.
 
+## Release-Critical Paths
+
+Changes to release-critical files require CODEOWNERS review once branch
+protection is configured to require it:
+
+- `.github/workflows/`
+- `install.sh`
+- `src/CodeIndex/CodeIndex.csproj`
+- `nuget.config`
+
+When adding a new file that can affect release artifact contents, signing,
+publishing, installer behavior, or package restore trust, add it to
+`.github/CODEOWNERS` in the same change.
+
 Before opening a pull request, run the checks that match the change. For code
 changes, the default full validation is:
 
diff --git a/USER_GUIDE.md b/USER_GUIDE.md
index 24b1a62d65..6a60f225fc 100644
--- a/USER_GUIDE.md
+++ b/USER_GUIDE.md
@@ -436,6 +436,32 @@ Choose the install channel based on runtime ownership and network shape:
 For a full comparison, package maintainer guidance, and planned channels such
 as winget, apt, rpm, Snap, and Flatpak, see [DISTRIBUTION.md](DISTRIBUTION.md).
 
+### Release artifact verification
+
+GitHub releases publish `sha256sums.txt` for every archive and SBOM asset,
+plus a detached GPG signature at `sha256sums.txt.asc`. Verify the checksum
+manifest before trusting downloaded release artifacts:
+
+```bash
+gpg --verify sha256sums.txt.asc sha256sums.txt
+sha256sum -c sha256sums.txt
+```
+
+The GPG signature verifies the checksum manifest through the release signing
+key.
+
+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
+workflow:
+
+```bash
+gh attestation verify CodeIndex-linux-x64.tar.gz -R Widthdom/CodeIndex
+```
+
+The GitHub attestation verifies that the artifact was generated by the
+repository workflow identity.
+
 ### Option A: One-liner install (no .NET required)
 
 Works in containers, CI, and any Linux/macOS environment — no .NET SDK needed.
diff --git a/changelog.d/unreleased/1674.security.md b/changelog.d/unreleased/1674.security.md
new file mode 100644
index 0000000000..534e749cf9
--- /dev/null
+++ b/changelog.d/unreleased/1674.security.md
@@ -0,0 +1,16 @@
+---
+category: security
+issues:
+  - 1674
+affected:
+  - .github/workflows/release.yml
+  - USER_GUIDE.md
+---
+
+## English
+
+- **Release artifacts now receive GitHub provenance attestations (#1674)** - release archives, SBOMs, checksum manifests, and checksum signatures now get GitHub build provenance attestations so users can verify they came from the repository release workflow.
+
+## 日本語
+
+- **リリース成果物に GitHub provenance attestation を付与するようになりました (#1674)** - リリースアーカイブ、SBOM、チェックサム manifest、チェックサム署名に GitHub build provenance attestation を付与し、リポジトリの release workflow 由来であることを検証できるようにしました。
diff --git a/changelog.d/unreleased/1677.security.md b/changelog.d/unreleased/1677.security.md
new file mode 100644
index 0000000000..1552fa2426
--- /dev/null
+++ b/changelog.d/unreleased/1677.security.md
@@ -0,0 +1,16 @@
+---
+category: security
+issues:
+  - 1677
+affected:
+  - .github/CODEOWNERS
+  - CONTRIBUTING.md
+---
+
+## English
+
+- **Release-critical paths now have CODEOWNERS coverage (#1677)** - workflow, installer, package project, and NuGet configuration changes now route through repository-owner review once branch protection requires CODEOWNERS approval.
+
+## 日本語
+
+- **リリース重要パスを CODEOWNERS でカバーしました (#1677)** - workflow、installer、package project、NuGet 設定の変更が、branch protection で CODEOWNERS 承認を必須化したときに repository owner review へ回るようになりました。
diff --git a/changelog.d/unreleased/1847.security.md b/changelog.d/unreleased/1847.security.md
new file mode 100644
index 0000000000..805eaf3b16
--- /dev/null
+++ b/changelog.d/unreleased/1847.security.md
@@ -0,0 +1,16 @@
+---
+category: security
+issues:
+  - 1847
+affected:
+  - .github/workflows/release.yml
+  - USER_GUIDE.md
+---
+
+## English
+
+- **Release checksum manifests are now GPG-signed (#1847)** - the release workflow now publishes `sha256sums.txt.asc` alongside `sha256sums.txt` and documents manual verification before trusting downloaded assets.
+
+## 日本語
+
+- **リリース checksum manifest を GPG 署名するようになりました (#1847)** - release workflow が `sha256sums.txt` と一緒に `sha256sums.txt.asc` を公開し、ダウンロードした成果物を信頼する前の手動検証手順を文書化しました。