fix: properly decrypt legacy state blobs

packages/snaps-controllers/coverage.json

@@ -1,5 +1,5 @@
 {
-  "branches": 91.64,
+  "branches": 91.68,
   "functions": 96.77,
   "lines": 97.89,
   "statements": 97.57

packages/snaps-controllers/src/snaps/SnapController.test.tsx

@@ -78,6 +78,7 @@
   getSnapControllerOptions,
   getSnapControllerWithEES,
   getSnapControllerWithEESOptions,
+  LEGACY_ENCRYPTION_KEY_DERIVATION_OPTIONS,
   loopbackDetect,
   LoopbackLocation,
   MOCK_BLOCK_NUMBER,
@@ -1728,7 +1729,7 @@
   });
 
   // This isn't stable in CI unfortunately
   it.skip('throws if the Snap is terminated while executing', async () => {
     const { manifest, sourceCode, svgIcon } =
       await getMockSnapFilesWithUpdatedChecksum({
         sourceCode: `
@@ -8178,6 +8179,42 @@
       snapController.destroy();
     });
 
+    it('uses legacy decryption where needed', async () => {
+      const messenger = getSnapControllerMessenger();
+
+      const state = { foo: 'bar' };
+
+      const { data, iv, salt } = JSON.parse(
+        await encrypt(
+          ENCRYPTION_KEY,
+          state,
+          undefined,
+          undefined,
+          LEGACY_ENCRYPTION_KEY_DERIVATION_OPTIONS,
+        ),
+      );
+
+      const snapController = getSnapController(
+        getSnapControllerOptions({
+          messenger,
+          state: {
+            snaps: {
+              [MOCK_SNAP_ID]: getPersistedSnapObject(),
+            },
+            snapStates: {
+              [MOCK_SNAP_ID]: JSON.stringify({ data, iv, salt }),
+            },
+          },
+        }),
+      );
+
+      expect(
+        await messenger.call('SnapController:getSnapState', MOCK_SNAP_ID, true),
+      ).toStrictEqual(state);
+
+      snapController.destroy();
+    });
+
     it('throws an error if the state is corrupt', async () => {
       const messenger = getSnapControllerMessenger();
 

packages/snaps-controllers/src/snaps/SnapController.ts

@@ -1676,7 +1676,14 @@ export class SnapController extends BaseController<
         snapId,
         salt,
         useCache,
-        keyMetadata,
+        // When decrypting state we expect key metadata to be present.
+        // If it isn't present, we assume that the Snap state we are decrypting is old enough to use the legacy encryption params.
+        keyMetadata: keyMetadata ?? {
+          algorithm: 'PBKDF2',
+          params: {
+            iterations: 10_000,
+          },
+        },
       });
       const decryptedState = await this.#encryptor.decryptWithKey(key, parsed);
 

packages/snaps-controllers/src/test-utils/controller.ts

@@ -454,6 +454,13 @@ export const DEFAULT_ENCRYPTION_KEY_DERIVATION_OPTIONS = {
   },
 };
 
+export const LEGACY_ENCRYPTION_KEY_DERIVATION_OPTIONS = {
+  algorithm: 'PBKDF2' as const,
+  params: {
+    iterations: 10_000,
+  },
+};
+
 const getSnapControllerEncryptor = () => {
   return {
     encryptWithKey,