From d9dfb49a239c221d7fc1bbfc1c252ff1e2729409 Mon Sep 17 00:00:00 2001
From: Peter Rounce <peter@rounce.me.uk>
Date: Tue, 28 Mar 2023 08:24:19 +0100
Subject: [PATCH] work in progress

---
 docs/CARD_PRIVACY.md | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/docs/CARD_PRIVACY.md b/docs/CARD_PRIVACY.md
index 06c19f2..b58acf3 100644
--- a/docs/CARD_PRIVACY.md
+++ b/docs/CARD_PRIVACY.md
@@ -2,6 +2,29 @@
 
 ## Brief
 
+The link that is programmed into the card and returned as the NDEF consists of three parts.
+1. The static part
+2. The encrypted part
+3. The authentication part
+
+```
+lnurlw://yourdomain.com/ln?p=012345&c=6789  example
+
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^      ^^^      static
+
+                             ^^^^^^         encrypted
+                             
+                                      ^^^^  authentication
+```
+
+Uses of the parts are as follows:
+
+| part | use |
+|------|-----|
+| static | specfying the protocol and service location as a URI |
+| encrypted | unique id and counter values encrypted by the card|
+| authentication | a value to authenticate that the entire URI is as generated by the card |
+
 ## NXP NTAG424DNA features
 
 ## Implementation