05/18 Enhanced codes and functionalities 3

app/routes/auth.py

@@ -922,8 +922,11 @@ def recovery_items():
     the client must derive it by decrypting the recovery blob with the recovery
     code. This ensures only the holder of the recovery code can compute the proof.
 
-    The challenge row is NOT consumed here — it is consumed by the final
-    POST /recover call so that endpoint can also validate the proof.
+    Replay prevention: the challenge is consumed (deleted) on success, then
+    immediately re-issued with the same expected_proof but a new nonce and a
+    fresh TTL.  This means each call to /recovery/items rotates the challenge,
+    so a captured X-Recovery-Proof header cannot be replayed by a third party.
+    POST /recover will consume the rotated challenge on final commit.
     Items are returned as encrypted ciphertext blobs only.
     """
     from app.models.recovery_challenge import RecoveryChallenge
@@ -938,11 +941,9 @@ def recovery_items():
     if not user or not user.recovery_enc_salt:
         return jsonify({'error': 'No recovery data found'}), 404
 
-    # Validate against the DB-stored challenge without consuming it —
-    # POST /recover will consume it atomically on commit.
-    challenge = RecoveryChallenge.query.filter_by(user_id=user.id).first()
-    from datetime import datetime, timezone
-    if not challenge or challenge.expires_at < datetime.now(timezone.utc).replace(tzinfo=None):
+    # Consume the current challenge atomically.
+    challenge = RecoveryChallenge.consume(user.id)
+    if not challenge:
         return jsonify({'error': 'No active recovery challenge. Call /recovery/data first.'}), 400
 
     if not verify_recovery_proof(challenge.expected_proof, client_proof):
@@ -957,6 +958,17 @@ def recovery_items():
         db.session.commit()
         return jsonify({'error': 'Invalid recovery proof'}), 401
 
+    # Re-issue a fresh challenge with the same expected_proof but a new nonce
+    # and TTL. POST /recover will consume this rotated challenge on final commit.
+    # The client continues to send the same proof value — no client change needed.
+    new_nonce = generate_recovery_nonce()
+    RecoveryChallenge.create(
+        user_id=user.id,
+        nonce=new_nonce,
+        expected_proof=challenge.expected_proof,  # same proof, new nonce
+    )
+    db.session.commit()
+
     from app.models.vault_item import VaultItem
     items = VaultItem.query.filter_by(user_id=user.id).all()
     return jsonify({