fix(secret-scan): exempt SSH known_hosts entries from leaked-key detection

PR #331 introduced github.com host fingerprints pinned in
.gitlab-ci.yml's mirror-to-github before_script. The scanner flagged
them as embedded secrets and blocked CI:

  BLOCKED: Embedded secrets/tokens found in:
    .gitlab-ci.yml
      133: github.com ssh-ed25519 AAAA...
      135: github.com ssh-rsa AAAA...

These are PUBLIC host keys — the whole point of pinning known_hosts is
to publish the fingerprint widely so a MITM is detectable. They are
documented at https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/githubs-ssh-key-fingerprints
and committing them is the correct, secure practice.

Fix: add a KNOWN_HOSTS_LINE regex to the content-scan block that
recognizes `<host-or-ip> [salt] <algo> AAAA...` shape lines (the
exact format used in ~/.ssh/known_hosts) and filters them out before
flagging the file. Bare `ssh-rsa AAAA...` lines without a host prefix
are still caught — only the host-key shape is exempt.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitlab-ci.yml

@@ -20,10 +20,15 @@
 # Auth notes:
 #   - The image build/push uses $CI_JOB_TOKEN, which GitLab provides
 #     automatically. No credentials need to be configured.
-#   - The reverse mirror requires a GitHub personal access token stored
+#   - The reverse mirror authenticates to GitHub via a per-repo SSH
-#     as the GitLab CI/CD variable GITHUB_MIRROR_TOKEN (Protected + Masked).
+#     deploy key. The private half is stored as the File-type GitLab
-#     Scope: public_repo (or repo for private). If the variable isn't
+#     CI/CD variable GITHUB_MIRROR_SSH_KEY (Protected). The matching
-#     set the mirror job is skipped — image builds still run.
+#     public key is added to github.com/BigBodyCobain/Shadowbroker/
+#     settings/keys with write access. This is a tighter-scoped
+#     replacement for a personal access token: it can ONLY push to
+#     Shadowbroker, never expires, and rotating it is a one-click
+#     delete on GitHub's deploy-keys page. If the variable isn't set,
+#     the mirror job is skipped — image builds still run.
 
 stages:
   - build
@@ -101,18 +106,35 @@ build-frontend:
         - .gitlab-ci.yml
 
 # ── Reverse mirror to GitHub ─────────────────────────────────────────────
-# Pushes refs/heads/main to github.com/BigBodyCobain/Shadowbroker.
+# Pushes refs/heads/main to github.com/BigBodyCobain/Shadowbroker via SSH
-# Fast-forward-only — if GitLab main and GitHub main have diverged, this
+# using a per-repo deploy key. Fast-forward-only by default — if GitLab
-# fails loudly rather than silently overwriting either side.
+# main and GitHub main have diverged, the push fails loudly rather than
+# silently overwriting either side.
 #
-# Only runs if GITHUB_MIRROR_TOKEN is set as a CI/CD variable. See the
+# Only runs if GITHUB_MIRROR_SSH_KEY is set as a File-type CI/CD variable.
-# header comment of this file for setup instructions.
+# See the header comment of this file for setup instructions.
 mirror-to-github:
   stage: mirror
   image: alpine:3.20
   needs: []
   before_script:
     - apk add --no-cache git openssh-client ca-certificates
+    - mkdir -p ~/.ssh
+    - chmod 700 ~/.ssh
+    # Install the deploy key. File-type CI variable exposes the path; copy
+    # to ~/.ssh/id_ed25519 with restrictive perms so ssh accepts it.
+    - cp "$GITHUB_MIRROR_SSH_KEY" ~/.ssh/id_ed25519
+    - chmod 600 ~/.ssh/id_ed25519
+    # Pin github.com's current host keys so we never trust a man-in-the-
+    # middle. Sourced from https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/githubs-ssh-key-fingerprints
+    # (rotated 2023-03-24 after the previous RSA key leak).
+    - |
+      cat > ~/.ssh/known_hosts <<'EOF'
+      github.com ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIOMqqnkVzrm0SdG6UOoqKLsabgH5C9okWi0dh2l9GKJl
+      github.com ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBEmKSENjQEezOmxkZMy7opKgwFB9nkt5YRrYMjNuG5N87uRgg6CLrbo5wAdT/y6v0mKV0U2w0WZ2YB/++Tpockg=
+      github.com ssh-rsa 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
+      EOF
+    - chmod 644 ~/.ssh/known_hosts
   script:
     - git config --global user.email "ci-mirror@gitlab.com"
     - git config --global user.name "GitLab CI Mirror"
@@ -123,7 +145,7 @@ mirror-to-github:
     - cd repo
     - >
       git push
-      "https://x-access-token:${GITHUB_MIRROR_TOKEN}@github.com/BigBodyCobain/Shadowbroker.git"
+      "git@github.com:BigBodyCobain/Shadowbroker.git"
       "${CI_COMMIT_SHA}:refs/heads/main"
   rules:
-    - if: $CI_COMMIT_BRANCH == "main" && $GITHUB_MIRROR_TOKEN
+    - if: $CI_COMMIT_BRANCH == "main" && $GITHUB_MIRROR_SSH_KEY

backend/scripts/scan-secrets.sh

@@ -92,18 +92,37 @@ SECRET_REGEX+='pypi-[0-9a-zA-Z-]{50,}'                        # PyPI token
 TEXT_FILES=$(grep -ivE '\.(png|jpg|jpeg|gif|ico|svg|woff2?|ttf|eot|pbf|zip|tar|gz|db|sqlite|xlsx|pdf|mp[34]|wav|ogg|webm|webp|avif)$' "$FILELIST" | grep -v 'scan-secrets\.sh$' || true)
 
 if [[ -n "$TEXT_FILES" ]]; then
+    # Known-public exclusions: lines matching `<host-or-ip> ssh-<algo> <key>`
+    # are SSH known_hosts entries — the host's PUBLIC fingerprint, which is
+    # by definition safe to commit (the whole point of pinning known_hosts
+    # is to publish the fingerprint widely so MITM is detectable). Filter
+    # these out before flagging the file.
+    KNOWN_HOSTS_LINE='^[[:space:]]*[a-zA-Z0-9._:,*-]+([[:space:]]+[a-zA-Z0-9._:,*-]+)?[[:space:]]+(ssh-rsa|ssh-ed25519|ssh-dss|ecdsa-sha2-nistp256|ecdsa-sha2-nistp384|ecdsa-sha2-nistp521)[[:space:]]+AAAA'
+
     # Use grep with file list, skip missing/binary, limit output
     CONTENT_HITS=$(echo "$TEXT_FILES" | xargs grep -lE "$SECRET_REGEX" 2>/dev/null || true)
     if [[ -n "$CONTENT_HITS" ]]; then
-        echo -e "\n${RED}BLOCKED: Embedded secrets/tokens found in:${NC}"
+        REAL_HITS=""
-        echo "$CONTENT_HITS" | while read -r f; do
+        REAL_REPORT=""
-            echo -e "  ${RED}$f${NC}"
+        while IFS= read -r f; do
-            # Show first matching line for context
+            [[ -z "$f" ]] && continue
-            grep -nE "$SECRET_REGEX" "$f" 2>/dev/null | head -2 | while read -r line; do
+            # Re-grep this file, but filter out known_hosts-style lines.
-                echo -e "    ${YELLOW}$line${NC}"
+            FILE_HITS=$(grep -nE "$SECRET_REGEX" "$f" 2>/dev/null | grep -vE "$KNOWN_HOSTS_LINE" || true)
-            done
+            if [[ -n "$FILE_HITS" ]]; then
-        done
+                REAL_HITS+="$f"$'\n'
-        FOUND=1
+                REAL_REPORT+="  ${RED}$f${NC}"$'\n'
+                # Show first 2 matching lines for context
+                while IFS= read -r line; do
+                    [[ -z "$line" ]] && continue
+                    REAL_REPORT+="    ${YELLOW}$line${NC}"$'\n'
+                done < <(echo "$FILE_HITS" | head -2)
+            fi
+        done <<< "$CONTENT_HITS"
+        if [[ -n "$REAL_HITS" ]]; then
+            echo -e "\n${RED}BLOCKED: Embedded secrets/tokens found in:${NC}"
+            echo -en "$REAL_REPORT"
+            FOUND=1
+        fi
     fi
 fi