public void StoreKey(string bucket, string handle, CryptoKey key)
        {
            var keyRow = new SymmetricCryptoKey { Bucket = bucket, Handle = handle, Secret = key.Key, ExpiresUtc = key.ExpiresUtc, };

            this.db.SymmetricCryptoKeys.Add(keyRow);
            this.db.SaveChanges();
        }