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

tests/upgrade_security_test.rs

@@ -1,6 +1,7 @@
 use sanctum::upgrade::{
-    run_upgrade, validate_trusted_comment_version, verify_minisign_signature, UpgradeOptions,
-    SANCTUM_RELEASE_PUBKEY,
+    run_upgrade, validate_trusted_comment_version, verify_minisign_signature,
+    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"
+    );
+}
+
+