diff --git a/README.md b/README.md
index e69275f..2a0d8c7 100644
--- a/README.md
+++ b/README.md
@@ -104,6 +104,18 @@ const {blacklist} = require('@sapphirecode/auth-server-helper');
 blacklist.add_signature(token_id); // the token id is returned from any function that creates tokens
 ```
 
+### Exporting and importing public keys to validate tokens across server instances
+
+```js
+const {keystore} = require('@sapphirecode/auth-server-helper');
+
+const export = keystore.export_verification_data();
+
+// second instance
+
+keystore.import_verification_data(export);
+```
+
 ## License
 
 MIT © Timo Hocker <timo@scode.ovh>
diff --git a/lib/Authority.ts b/lib/Authority.ts
index 363c069..54c063b 100644
--- a/lib/Authority.ts
+++ b/lib/Authority.ts
@@ -49,7 +49,7 @@ class Authority {
       key,
       (info) => {
         try {
-          return keystore.get_key (info.iat / 1000);
+          return keystore.get_key (info.iat / 1000, info.iss);
         }
         catch {
           return '';
@@ -89,6 +89,7 @@ class Authority {
     const attributes = {
       id:          create_salt (),
       iat:         time,
+      iss:         keystore.instance_id,
       type,
       valid_for,
       next_module: options?.next_module
diff --git a/lib/KeyStore.ts b/lib/KeyStore.ts
index 147c42d..2032b94 100644
--- a/lib/KeyStore.ts
+++ b/lib/KeyStore.ts
@@ -5,9 +5,10 @@
  * Created by Timo Hocker <timo@scode.ovh>, December 2020
  */
 
-import { generate_keypair } from '@sapphirecode/crypto-helper';
+import { generate_keypair, random_hex } from '@sapphirecode/crypto-helper';
+import { to_b58 } from '@sapphirecode/encoding-helper';
 
-const renew_interval = 60;
+const renew_interval = 3600;
 
 interface Key {
   key: string;
@@ -21,11 +22,6 @@ interface KeyPair {
 
 type KeyStoreData = Record<string, KeyPair>;
 
-function get_index (iat: number): string {
-  return Math.floor (iat / renew_interval)
-    .toFixed (0);
-}
-
 async function create_key (valid_for: number) {
   const time = (new Date)
     .getTime ();
@@ -45,11 +41,22 @@ async function create_key (valid_for: number) {
 class KeyStore {
   private _keys: KeyStoreData = {};
   private _interval: NodeJS.Timeout;
+  private _instance: string;
+
+  public get instance_id (): string {
+    return this._instance;
+  }
 
   public constructor () {
     this._interval = setInterval (() => {
       this.garbage_collect ();
     }, renew_interval);
+    this._instance = to_b58 (random_hex (16), 'hex');
+  }
+
+  private get_index (iat: number, instance = this._instance): string {
+    return instance + Math.floor (iat / renew_interval)
+      .toFixed (0);
   }
 
   private garbage_collect (set: KeyStoreData = this._keys): void {
@@ -68,7 +75,11 @@ class KeyStore {
     }
   }
 
-  public async get_sign_key (iat: number, valid_for: number): Promise<string> {
+  public async get_sign_key (
+    iat: number,
+    valid_for: number,
+    instance?: string
+  ): Promise<string> {
     if (valid_for <= 0)
       throw new Error ('cannot create infinitely valid key');
 
@@ -76,7 +87,7 @@ class KeyStore {
       .getTime ())
       throw new Error ('cannot access already expired keys');
 
-    const index = get_index (iat);
+    const index = this.get_index (iat, instance);
 
     const valid_until = (new Date)
       .getTime () + (valid_for * 1000);
@@ -86,6 +97,9 @@ class KeyStore {
       if (key.public_key.valid_until < valid_until)
         key.public_key.valid_until = valid_until;
 
+      if (typeof key.private_key === 'undefined')
+        throw new Error ('cannot access already expired keys');
+
       return key.private_key?.key as string;
     }
 
@@ -93,8 +107,8 @@ class KeyStore {
     return this._keys[index].private_key?.key as string;
   }
 
-  public get_key (iat: number): string {
-    const index = get_index (iat);
+  public get_key (iat: number, instance?: string): string {
+    const index = this.get_index (iat, instance);
 
     if (typeof this._keys[index] === 'undefined')
       throw new Error ('key could not be found');
@@ -115,8 +129,12 @@ class KeyStore {
   public import_verification_data (data: KeyStoreData): void {
     const import_set = { ...data };
     this.garbage_collect (import_set);
-
-    // TODO: import
+    for (const key of Object.keys (import_set)) {
+      if (typeof this._keys[key] !== 'undefined')
+        throw new Error ('cannot import to the same instance');
+      this._keys[key] = import_set[key];
+    }
+    this.garbage_collect ();
   }
 }
 
diff --git a/test/Helper.ts b/test/Helper.ts
index f60bcf2..5237f8a 100644
--- a/test/Helper.ts
+++ b/test/Helper.ts
@@ -7,7 +7,6 @@
 
 /* eslint-disable no-console */
 import http from 'http';
-import { type } from 'os';
 import ks from '../lib/KeyStore';
 
 export class Response extends http.IncomingMessage {
@@ -64,7 +63,7 @@ export function clock_setup ():void {
   assert_keystore_state ();
 
   const date = (new Date);
-  date.setSeconds (2, 0);
+  date.setHours (0, 0, 2, 0);
   jasmine.clock ()
     .install ();
   jasmine.clock ()
diff --git a/test/spec/KeyStore.ts b/test/spec/KeyStore.ts
index 60759de..cbe4906 100644
--- a/test/spec/KeyStore.ts
+++ b/test/spec/KeyStore.ts
@@ -5,10 +5,10 @@
  * Created by Timo Hocker <timo@scode.ovh>, December 2020
  */
 
-import ks from '../../lib/KeyStore';
+import ks, { KeyStore } from '../../lib/KeyStore';
 import { clock_finalize, clock_setup } from '../Helper';
 
-const frame = 60;
+const frame = 3600;
 
 /* eslint-disable-next-line max-lines-per-function */
 describe ('key store', () => {
@@ -146,5 +146,40 @@ describe ('key store', () => {
       .toBeRejectedWithError ('cannot create infinitely valid key');
   });
 
-  // TODO: required use case: insert keys for verification of old tokens
+  it ('should export and import all keys', async () => {
+    const iat = (new Date)
+      .getTime () / 1000;
+
+    const sign = await ks.get_sign_key (iat, frame);
+    const ver = ks.get_key (iat);
+    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);
+
+    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);
+
+    const sign2 = await ks2.get_sign_key (iat, frame);
+    const ver2 = ks2.get_key (iat);
+    expect (sign).not.toEqual (sign2);
+    expect (ver).not.toEqual (ver2);
+    await expectAsync (ks2.get_sign_key (iat, 60, ks.instance_id))
+      .toBeRejectedWithError ('cannot access already expired keys');
+    expect (ks2.get_key (iat, ks.instance_id))
+      .toEqual (ver);
+  });
+
+  it ('should disallow importing to itself', () => {
+    const exp = ks.export_verification_data ();
+    expect (() => ks.import_verification_data (exp))
+      .toThrowError ('cannot import to the same instance');
+  });
 });