added check to see if browser is gcm compliant

frontend/src/utils.js

@@ -32,8 +32,42 @@ function notify(str) {
   }
 }
 
+function gcmCompliant() {
+  try {
+    return window.crypto.subtle.generateKey(
+      {
+        name: 'AES-GCM',
+        length: 128
+      },
+      true,
+      ['encrypt', 'decrypt']
+    ).then(key => {
+      return window.crypto.subtle.encrypt(
+        {
+          name: 'AES-GCM',
+          iv: window.crypto.getRandomValues(new Uint8Array(12)),
+          additionalData: window.crypto.getRandomValues(new Uint8Array(6))
+        },
+        key,
+        new ArrayBuffer(8)
+      )
+      .then(() => {
+        return Promise.resolve()
+      })
+      .catch(err => {
+        return Promise.reject()
+      })
+    }).catch(err => {
+      return Promise.reject();
+    })
+  } catch(err) {
+    return Promise.reject();
+  }
+}
+
 module.exports = {
   arrayToHex,
   hexToArray,
-  notify
+  notify,
+  gcmCompliant
 };