diff --git a/lib/KeyStore.ts b/lib/KeyStore.ts
index 2032b94..fa2a474 100644
--- a/lib/KeyStore.ts
+++ b/lib/KeyStore.ts
@@ -15,12 +15,17 @@ interface Key {
   valid_until: number;
 }
 
+interface LabelledKey extends Key {
+  index: string;
+}
+
 interface KeyPair {
   private_key?: Key;
   public_key: Key;
 }
 
 type KeyStoreData = Record<string, KeyPair>;
+type KeyStoreExport = LabelledKey[];
 
 async function create_key (valid_for: number) {
   const time = (new Date)
@@ -59,19 +64,19 @@ class KeyStore {
       .toFixed (0);
   }
 
-  private garbage_collect (set: KeyStoreData = this._keys): void {
+  private garbage_collect (): void {
     const time = (new Date)
       .getTime ();
-    const keys = Object.keys (set);
+    const keys = Object.keys (this._keys);
     for (const index of keys) {
-      const entry = set[index];
+      const entry = this._keys[index];
       if (typeof entry.private_key !== 'undefined'
         && entry.private_key.valid_until < time
       )
         delete entry.private_key;
 
       if (entry.public_key.valid_until < time)
-        delete set[index];
+        delete this._keys[index];
     }
   }
 
@@ -117,22 +122,25 @@ class KeyStore {
     return key.public_key.key;
   }
 
-  public export_verification_data (): KeyStoreData {
+  public export_verification_data (): KeyStoreExport {
     this.garbage_collect ();
-    const out: KeyStoreData = {};
+    const out: KeyStoreExport = [];
     for (const index of Object.keys (this._keys))
-      out[index] = { public_key: this._keys[index].public_key };
+      out.push ({ ...this._keys[index].public_key, index });
 
     return out;
   }
 
-  public import_verification_data (data: KeyStoreData): void {
-    const import_set = { ...data };
-    this.garbage_collect (import_set);
-    for (const key of Object.keys (import_set)) {
-      if (typeof this._keys[key] !== 'undefined')
+  public import_verification_data (data: KeyStoreExport): void {
+    for (const key of data) {
+      if (typeof this._keys[key.index] !== 'undefined')
         throw new Error ('cannot import to the same instance');
-      this._keys[key] = import_set[key];
+      this._keys[key.index] = {
+        public_key: {
+          key:         key.key,
+          valid_until: key.valid_until
+        }
+      };
     }
     this.garbage_collect ();
   }
@@ -140,4 +148,4 @@ class KeyStore {
 
 const ks: KeyStore = (new KeyStore);
 export default ks;
-export { KeyStore, KeyStoreData, Key, KeyPair };
+export { KeyStore, Key, LabelledKey, KeyStoreExport };
diff --git a/lib/index.ts b/lib/index.ts
index 2d1fa20..6dc6aa0 100644
--- a/lib/index.ts
+++ b/lib/index.ts
@@ -28,7 +28,10 @@ import create_gateway, {
   Gateway,
   AnyFunc
 } from './Gateway';
-import keystore, { KeyStore, KeyStoreData } from './KeyStore';
+import keystore, {
+  KeyStore, KeyStoreExport,
+  LabelledKey, Key
+} from './KeyStore';
 
 export {
   create_gateway,
@@ -54,5 +57,7 @@ export {
   Gateway,
   AnyFunc,
   KeyStore,
-  KeyStoreData
+  KeyStoreExport,
+  LabelledKey,
+  Key
 };
diff --git a/test/spec/KeyStore.ts b/test/spec/KeyStore.ts
index cbe4906..175b6f7 100644
--- a/test/spec/KeyStore.ts
+++ b/test/spec/KeyStore.ts
@@ -155,17 +155,14 @@ describe ('key store', () => {
     const exp = ks.export_verification_data ();
     // eslint-disable-next-line dot-notation
     expect (Object.keys (ks['_keys']))
-      .toEqual (Object.keys (exp));
-    expect (Object.keys (exp)
-      .filter ((v) => typeof exp[v].private_key !== 'undefined').length)
-      .toEqual (0);
+      .toEqual (exp.map ((v) => v.index));
 
     const ks2 = (new KeyStore);
     expect (ks2.instance_id).not.toEqual (ks.instance_id);
     ks2.import_verification_data (exp);
     // eslint-disable-next-line dot-notation
-    expect (ks2['_keys'])
-      .toEqual (exp);
+    expect (Object.keys (ks2['_keys']))
+      .toEqual (exp.map ((v) => v.index));
 
     const sign2 = await ks2.get_sign_key (iat, frame);
     const ver2 = ks2.get_key (iat);