From ed5b6fb1f52c57213d7410c5c0a2dc05f77ef87a Mon Sep 17 00:00:00 2001
From: Andreas Fitzek <andreas.fitzek@gmail.com>
Date: Fri, 17 Jul 2015 21:32:41 +0200
Subject: [PATCH] description of additionalData for AES-GCM

added description for additionalData for AES-GCM
---
 README.md | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 654c29a..ec3cff1 100644
--- a/README.md
+++ b/README.md
@@ -978,8 +978,15 @@ window.crypto.subtle.encrypt(
         //Always generate a new iv every time your encrypt!
         iv: window.crypto.getRandomValues(new Uint8Array(16)),
 
-        //Additional authentication data (unsure what proper use for this is)
+        //Additional authenticated data: 
+        //AES-GCM protects the confidentiality and the integrity. The additionalData is not 
+        //encrypted but the integrity is stil protected.
+        //Decryption will only succeed if the additionalData is the same during 
+        //decryption and encryption. 
+        //This is an optional property.
         additionalData: window.crypto.getRandomValues(new Uint8Array(256)),
+        
+        //Length of the authentication tag
         tagLength: 128,
         };
     },