diff --git a/oauth3.issuer.mock.js b/oauth3.issuer.mock.js
index 8208476..1358cd4 100644
--- a/oauth3.issuer.mock.js
+++ b/oauth3.issuer.mock.js
@@ -24,16 +24,109 @@
   };
 
   OAUTH3.crypto = {};
-  OAUTH3.crypto._generateKey = function () {
-    return window.crypto.subtle.generateKey({name: 'ECDSA', namedCurve: 'P-256'}, true, ['sign', 'verify'])
-    .catch(function (err) {
-      console.error('failed to generate ECDSA key', err);
-      return OAUTH3.PromiseA.reject(err);
+  OAUTH3.crypto.fingerprintJWK = function (jwk) {
+    var keys;
+    if (jwk.kty === 'EC') {
+      keys = ['crv', 'x', 'y'];
+    } else if (jwk.kty === 'RSA') {
+      keys = ['e', 'n'];
+    } else if (jwk.kty === 'oct') {
+      keys = ['k'];
+    } else {
+      return OAUTH3.PromiseA.reject(new Error('invalid JWK key type ' + jwk.kty));
+    }
+    keys.push('kty');
+    keys.sort();
+
+    var missing = keys.filter(function (name) { return !jwk.hasOwnProperty(name); });
+    if (missing.length > 0) {
+      return OAUTH3.PromiseA.reject(new Error('JWK of type '+jwk.kty+' missing fields ' + missing));
+    }
+
+    var jwkStr = '{' + keys.map(function (name) { return name+':'+jwk[name]; }).join(',') + '}';
+    return window.crypto.subtle.digest({name: 'SHA-256'}, OAUTH3.utils.binaryStringToBuffer(jwkStr))
+    .then(OAUTH3.utils.bufferToBinaryString).then(OAUTH3._base64.btoa);
+  };
+
+  OAUTH3.crypto._createKey = function (ppid) {
+    var ecdsaPromise, kekPromise;
+    var salt = window.crypto.getRandomValues(new Uint8Array(16));
+
+    ecdsaPromise = window.crypto.subtle.generateKey({name: 'ECDSA', namedCurve: 'P-256'}, true, ['sign', 'verify'])
+    .then(function (key) { return window.crypto.subtle.exportKey('jwk', key.privateKey); })
+    .then(function (jwk) {
+      return OAUTH3.crypto.fingerprintJWK(jwk).then(function (kid) {
+        delete jwk.ext;
+        delete jwk.key_ops;
+        jwk.alg = 'ES256';
+        jwk.kid = kid;
+        return OAUTH3.PromiseA.resolve(jwk);
+      });
+    });
+
+    kekPromise = window.crypto.subtle.importKey('raw', OAUTH3.utils.binaryStringToBuffer(ppid), {name: 'PBKDF2'}, false, ['deriveKey'])
+    .then(function (key) {
+      var opts = {name: 'PBKDF2', salt: salt, iterations: 8192, hash: {name: 'SHA-256'}};
+      return window.crypto.subtle.deriveKey(opts, key, {name: 'AES-GCM', length: 256}, false, ['encrypt']);
+    });
+
+    return OAUTH3.PromiseA.all([ecdsaPromise, kekPromise]).then(function (keys) {
+      var jwkBuf = OAUTH3.utils.binaryStringToBuffer(JSON.stringify(keys[0]));
+      var iv = window.crypto.getRandomValues(new Uint8Array(12));
+      return window.crypto.subtle.encrypt({name: 'AES-GCM', iv: iv}, keys[1], jwkBuf).then(function (encrypted) {
+        return {
+          kid:  keys[0].kid
+        , key:  OAUTH3._base64.btoa(OAUTH3.utils.bufferToBinaryString(encrypted))
+        , salt: OAUTH3._base64.btoa(OAUTH3.utils.bufferToBinaryString(salt))
+        , iv:   OAUTH3._base64.btoa(OAUTH3.utils.bufferToBinaryString(iv))
+        };
+      });
+    });
+  };
+
+  OAUTH3.crypto._decryptKey = function (ppid, storedObj) {
+    var salt   = OAUTH3.utils.binaryStringToBuffer(OAUTH3._base64.atob(storedObj.salt));
+    var encJwk = OAUTH3.utils.binaryStringToBuffer(OAUTH3._base64.atob(storedObj.key));
+    var iv     = OAUTH3.utils.binaryStringToBuffer(OAUTH3._base64.atob(storedObj.iv));
+
+    return window.crypto.subtle.importKey('raw', OAUTH3.utils.binaryStringToBuffer(ppid), {name: 'PBKDF2'}, false, ['deriveKey'])
+    .then(function (key) {
+      var opts = {name: 'PBKDF2', salt: salt, iterations: 8192, hash: {name: 'SHA-256'}};
+      return window.crypto.subtle.deriveKey(opts, key, {name: 'AES-GCM', length: 256}, false, ['decrypt']);
+    })
+    .then(function (key) {
+      return window.crypto.subtle.decrypt({name: 'AES-GCM', iv: iv}, key, encJwk);
+    })
+    .then(OAUTH3.utils.bufferToBinaryString)
+    .then(JSON.parse)
+    .then(function (jwk) {
+      return window.crypto.subtle.importKey('jwk', jwk, {name: 'ECDSA', namedCurve: jwk.crv}, false, ['sign']);
+    });
+  };
+
+  OAUTH3.crypto._getKey = function (ppid) {
+    return window.crypto.subtle.digest({name: 'SHA-256'}, OAUTH3.utils.binaryStringToBuffer(ppid))
+    .then(function (hash) {
+      var name = 'kek-' + OAUTH3._base64.btoa(OAUTH3.utils.bufferToBinaryString(hash));
+      var promise;
+
+      if (window.localStorage.getItem(name) === null) {
+        promise = OAUTH3.crypto._createKey(ppid).then(function (key) {
+          window.localStorage.setItem(name, JSON.stringify(key));
+          return OAUTH3.resolve(key);
+        });
+      } else {
+        promise = OAUTH3.PromiseA.resolve(JSON.parse(window.localStorage.getItem(name)));
+      }
+
+      return promise.then(function (storedObj) {
+        return OAUTH3.crypto._decryptKey(ppid, storedObj);
+      });
     });
   };
 
   OAUTH3.crypto._signPayload = function (payload) {
-    return OAUTH3.crypto._generateKey().then(function (key) {
+    return OAUTH3.crypto._getKey('some PPID').then(function (key) {
       var header = {type: 'jwt', alg: 'ES256'};
       var input = [
         OAUTH3._base64.encodeUrlSafe(JSON.stringify(header, null))
@@ -42,7 +135,7 @@
 
       return window.crypto.subtle.sign(
         {name: 'ECDSA', hash: {name: 'SHA-256'}}
-      , key.privateKey
+      , key
       , OAUTH3.utils.binaryStringToBuffer(input)
       ).then(function (signature) {
         var base64Sig = OAUTH3._base64.encodeUrlSafe(OAUTH3.utils.bufferToBinaryString(signature));