fix(upgrade): U-03 — configure secondary backup release public key

src/upgrade.rs

@@ -20,6 +20,8 @@ pub const OFFICIAL_UPGRADE_URL: &str = "https://gitea.pansi.eu";
 pub const CHECKSUM_ASSET_NAME: &str = "SHA256SUMS.txt";
 pub const CHECKSUM_SIG_ASSET_NAME: &str = "SHA256SUMS.txt.minisig";
 pub const SANCTUM_RELEASE_PUBKEY: &str = "RWSsVphPgr8157M9rTPkWDw3c0qIjc7xi28Gmw+cIWbMipOy4L6ToJEU";
+pub const SANCTUM_RELEASE_PUBKEY_BACKUP: &str =
+    "RWQEeUSLlX2p4EPUPN1GjeUv34qA0p2B6wJYzcou5oOwAkkw0f+r9FmZ";
 
 /// Repräsentiert ein Asset in einem Gitea-Release
 #[derive(Debug, Deserialize, Clone)]
@@ -122,6 +124,28 @@ pub fn validate_trusted_comment_version(
     Ok(())
 }
 
+/// Überprüft eine Minisign-Signatur für ein Release-Manifest.
+///
+/// Prüft primär gegen `SANCTUM_RELEASE_PUBKEY`. Falls diese Verifikation fehlschlägt,
+/// wird transparent gegen den sekundären Backup-Schlüssel `SANCTUM_RELEASE_PUBKEY_BACKUP`
+/// geprüft (U-03), um unterbrechungsfreie Schlüsselrotationen zu ermöglichen.
+pub fn verify_release_manifest_signature(data: &[u8], sig_str: &str) -> Result<String> {
+    match verify_minisign_signature(data, sig_str, SANCTUM_RELEASE_PUBKEY) {
+        Ok(comment) => Ok(comment),
+        Err(primary_err) => {
+            match verify_minisign_signature(data, sig_str, SANCTUM_RELEASE_PUBKEY_BACKUP) {
+                Ok(comment) => {
+                    tracing::info!(
+                        "Minisign-Signatur erfolgreich mit sekundärem Backup-Schlüssel verifiziert."
+                    );
+                    Ok(comment)
+                }
+                Err(_) => Err(primary_err),
+            }
+        }
+    }
+}
+
 /// Erkannter Paketmanager
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum PackageManager {
@@ -545,7 +569,7 @@ pub fn run_upgrade(options: &UpgradeOptions) -> Result<()> {
         "  {} Verifiziere Minisign-Signatur gegen eingebetteten Herstellerschlüssel ...",
         ui::dim("[-]")
     );
-    let trusted_comment = verify_minisign_signature(sums_content.as_bytes(), &sig_content, SANCTUM_RELEASE_PUBKEY)
+    let trusted_comment = verify_release_manifest_signature(sums_content.as_bytes(), &sig_content)
         .context("Minisign-Signaturprüfung für Prüfsummendatei FEHLGESCHLAGEN! Release ist nicht vertrauenswürdig.")?;
     validate_trusted_comment_version(&trusted_comment, remote_tag)?;
     println!(

tests/upgrade_security_test.rs

@@ -1,6 +1,7 @@
 use sanctum::upgrade::{
-    run_upgrade, validate_trusted_comment_version, verify_minisign_signature, UpgradeOptions,
+    run_upgrade, validate_trusted_comment_version, verify_minisign_signature,
-    SANCTUM_RELEASE_PUBKEY,
+    verify_release_manifest_signature, UpgradeOptions, SANCTUM_RELEASE_PUBKEY,
+    SANCTUM_RELEASE_PUBKEY_BACKUP,
 };
 
 #[test]
@@ -144,3 +145,54 @@ fn test_u02_reject_mismatched_release_tag_replay() {
     assert!(res2.is_err());
 }
 
+#[test]
+fn test_u03_verify_signature_with_backup_key_fallback() {
+    let payload = b"Hello Sanctum Release 0.8.0 Backup Key Testing\n";
+    let backup_sig = "\
+untrusted comment: signature from minisign secret key\n\
+RUQEeUSLlX2p4HrXDO2TYykyNK0C41Vdrq6MIts14mQgNDClGC2RkBV3jHRbP7IclWv+h/IuzvyYi9yz8/RqfhpDVwhqtvC02gk=\n\
+trusted comment: version:0.8.0\n\
+zjZAS4uy1PH+0S9KQ0EU435lpBczU3lULyS5SkWf093iCEBc1ULiscwE5gWkEkex3ecPdRugopT+fKaZBQQnBg==\n";
+
+    // 1. Direct verification against primary key MUST fail (key rotation scenario)
+    let prim_res = verify_minisign_signature(payload, backup_sig, SANCTUM_RELEASE_PUBKEY);
+    assert!(
+        prim_res.is_err(),
+        "Backup-Signatur darf nicht gegen den Primärschlüssel verifizieren"
+    );
+
+    // 2. Direct verification against backup key MUST succeed
+    let back_res = verify_minisign_signature(payload, backup_sig, SANCTUM_RELEASE_PUBKEY_BACKUP);
+    assert!(
+        back_res.is_ok(),
+        "Backup-Signatur muss gegen SANCTUM_RELEASE_PUBKEY_BACKUP gültig sein: {:?}",
+        back_res.err()
+    );
+
+    // 3. Fallback verification via verify_release_manifest_signature MUST succeed transparently
+    let fallback_res = verify_release_manifest_signature(payload, backup_sig);
+    assert!(
+        fallback_res.is_ok(),
+        "verify_release_manifest_signature muss via Backup-Schlüssel erfolgreich sein"
+    );
+    assert_eq!(fallback_res.unwrap(), "version:0.8.0");
+}
+
+#[test]
+fn test_u03_verify_signature_rejects_untrusted_third_party_key() {
+    let fake_sig = "\
+untrusted comment: signature from minisign secret key\n\
+RUQEeUSLlX2p4HrXDO2TYykyNK0C41Vdrq6MIts14mQgNDClGC2RkBV3jHRbP7IclWv+h/IuzvyYi9yz8/RqfhpDVwhqtvC02gk=\n\
+trusted comment: version:0.8.0\n\
+zjZAS4uy1PH+0S9KQ0EU435lpBczU3lULyS5SkWf093iCEBc1ULiscwE5gWkEkex3ecPdRugopT+fKaZBQQnBg==\n";
+
+    // Tampered payload with neither primary nor backup key matching
+    let tampered = b"Tampered data not signed by either key";
+    let res = verify_release_manifest_signature(tampered, fake_sig);
+    assert!(
+        res.is_err(),
+        "Weder Primär- noch Backup-Schlüssel dürfen manipulierte Nutzdaten akzeptieren"
+    );
+}
+
+