diff --git a/lib/dingtalk/client.rb b/lib/dingtalk/client.rb
index 0964f03..c454a17 100644
--- a/lib/dingtalk/client.rb
+++ b/lib/dingtalk/client.rb
@@ -7,12 +7,17 @@ module Dingtalk
     end
 
     def decrypt(echo_str)
-      aes_key = Base64.decode64(Dingtalk.suite_aes_key + '=')
       content, status = Dingtalk::Prpcrypt.decrypt(aes_key, echo_str, Dingtalk.suite_key)
       # TODO check status
       JSON.parse(content)
     end
 
+    def signature(return_str)
+      encrypt = Dingtalk::Prpcrypt.encrypt(aes_key, return_str, Dingtalk.suite_key)
+      sort_params = [suite.suite_access_token, timestamp, nonce, encrypt].sort.join
+      Digest::SHA1.hexdigest(sort_params)
+    end
+
     def suite
       Api::Suite.new
     end
@@ -20,5 +25,18 @@ module Dingtalk
     def department
       Api::Department.new(@corp_id)
     end
+
+    private
+      def aes_key
+        Base64.decode64(Dingtalk.suite_aes_key + '=')
+      end
+
+      def timestamp
+        Time.now.to_i.to_s
+      end
+
+      def nonce
+        SecureRandom.hex
+      end
   end
 end
--
libgit2 0.21.0