Add in-memory secret encryption

src/password_manager/manager.py

@@ -40,6 +40,7 @@ from utils.password_prompt import (
     prompt_existing_password,
     confirm_action,
 )
+from utils.memory_protection import InMemorySecret
 from constants import MIN_HEALTHY_RELAYS
 
 from constants import (
@@ -93,7 +94,7 @@ class PasswordManager:
         self.backup_manager: Optional[BackupManager] = None
         self.vault: Optional[Vault] = None
         self.fingerprint_manager: Optional[FingerprintManager] = None
-        self.parent_seed: Optional[str] = None
+        self._parent_seed_secret: Optional[InMemorySecret] = None
         self.bip85: Optional[BIP85] = None
         self.nostr_client: Optional[NostrClient] = None
         self.config_manager: Optional[ConfigManager] = None
@@ -114,6 +115,22 @@ class PasswordManager:
         # Set the current fingerprint directory
         self.fingerprint_dir = self.fingerprint_manager.get_current_fingerprint_dir()
 
+    @property
+    def parent_seed(self) -> Optional[str]:
+        """Return the decrypted parent seed if set."""
+        if self._parent_seed_secret is None:
+            return None
+        return self._parent_seed_secret.get_str()
+
+    @parent_seed.setter
+    def parent_seed(self, value: Optional[str]) -> None:
+        if value is None:
+            if self._parent_seed_secret:
+                self._parent_seed_secret.wipe()
+            self._parent_seed_secret = None
+        else:
+            self._parent_seed_secret = InMemorySecret(value.encode("utf-8"))
+
     def update_activity(self) -> None:
         """Record the current time as the last user activity."""
         self.last_activity = time.time()

src/utils/__init__.py

@@ -24,6 +24,7 @@ try:
     )
     from .password_prompt import prompt_for_password
     from .input_utils import timed_input
+    from .memory_protection import InMemorySecret
 
     if logger.isEnabledFor(logging.DEBUG):
         logger.info("Modules imported successfully.")
@@ -47,4 +48,5 @@ __all__ = [
     "shared_lock",
     "prompt_for_password",
     "timed_input",
+    "InMemorySecret",
 ]

src/utils/memory_protection.py

@@ -0,0 +1,31 @@
+from __future__ import annotations
+
+import os
+from cryptography.hazmat.primitives.ciphers.aead import AESGCM
+
+
+class InMemorySecret:
+    """Store sensitive data encrypted in RAM using AES-GCM."""
+
+    def __init__(self, data: bytes) -> None:
+        if not isinstance(data, (bytes, bytearray)):
+            raise TypeError("data must be bytes")
+        self._key = AESGCM.generate_key(bit_length=128)
+        self._nonce = os.urandom(12)
+        self._cipher = AESGCM(self._key)
+        self._encrypted = self._cipher.encrypt(self._nonce, bytes(data), None)
+
+    def get_bytes(self) -> bytes:
+        """Decrypt and return the plaintext bytes."""
+        return self._cipher.decrypt(self._nonce, self._encrypted, None)
+
+    def wipe(self) -> None:
+        """Zero out internal data."""
+        self._key = None
+        self._nonce = None
+        self._cipher = None
+        self._encrypted = None
+
+    def get_str(self) -> str:
+        """Return the decrypted plaintext as a UTF-8 string."""
+        return self.get_bytes().decode("utf-8")