From e83a4e141302edfb5e5746bcf070b061f28eca75 Mon Sep 17 00:00:00 2001
From: "nicolas.dorier" <nicolas.dorier@gmail.com>
Date: Tue, 24 Oct 2023 18:57:16 +0900
Subject: [PATCH] Update README

---
 README.md | 57 +++++++++++++++++++++++--------------------------------
 1 file changed, 24 insertions(+), 33 deletions(-)

diff --git a/README.md b/README.md
index b43d236..1d447de 100644
--- a/README.md
+++ b/README.md
@@ -63,34 +63,19 @@ using System;
 using System.Security;
 using System.Collections;
 
+// Set keys have you have setup the card
+var encryptionKey = AESKey.Default;
+var authenticationKey = AESKey.Default;
+
 using var ctx = await PCSCContext.WaitForCard();
 var ntag = ctx.CreateNTag424();
-// In prod: var issuerKey = IssuerKey.Random();
-var issuerKey = new IssuerKey("00000000000000000000000000000001".HexToBytes());
-// In prod: var cardKey = CardKey.Random();
-var cardKey = new CardKey("00000000000000000000000000000002".HexToBytes());
-
-// First time authenticate is with the default 00000000000000000000000000000000 key
-await ntag.AuthenticateEV2First(0, AESKey.Default);
-var uid = await ntag.GetCardUID();
-
-var keys = cardKey.DeriveBoltcardKeys(issuerKey, uid);
-await ntag.SetupBoltcard("lnurlw://blahblah.com", BoltcardKeys.Default, keys);
 
 var uri = await ntag.TryReadNDefURI();
-var piccData = issuerKey.TryDecrypt(uri);
-if (piccData is null)
-    throw new SecurityException("Impossible to decrypt with issuerKey");
+var piccData = PICCData.TryBoltcardDecryptCheck(encryptionKey, authenticationKey, uri);
+if (piccData == null)
+    throw new SecurityException("Impossible to decrypt or validate");
 
-// In production, you would fetch the card key from database
-// var cardKey = await GetCardKey(issuerKey.GetId(piccData.Uid));
-
-if (!cardKey.CheckSunMac(uri, piccData))
-    throw new SecurityException("Impossible to decrypt with issuerKey");
-
-await ntag.ResetCard(issuerKey, cardKey);
-// If this method didn't throw an exception, it has been successfully decrypted and authenticated.
-// You can reset the card with `await ntag.ResetCard(issuerKey, cardKey);`.
+// The LNUrlw service should also check `piccData.Counter` is always increasing between payments to avoid replay attacks.
 ```
 
 ### How to setup a bolt card
@@ -127,21 +112,26 @@ await ntag.SetupBoltcard(lnurlwService, BoltcardKeys.Default, keys);
 
 Here is an example of how to setup a card with deterministic keys, and decrypt the PICCData.
 ```csharp
+using System.Security;
+using BTCPayServer.NTag424;
+
 using var ctx = await PCSCContext.WaitForCard();
 var ntag = ctx.CreateNTag424();
-var issuerKey = new IssuerKey("00000000000000000000000000000001".HexToBytes());
+
+// In prod: var issuerKey = IssuerKey.Random();
+var issuerKey = new IssuerKey(new byte[16]);
+// In prod: var cardKey = CardKey.Random();
+var cardKey = new CardKey(new byte[16]);
 
 // First time authenticate is with the default 00.000 key
 await ntag.AuthenticateEV2First(0, AESKey.Default);
 var uid = await ntag.GetCardUID();
 
-//var nonce = IssuerKey.RandomNonce();
-var nonce = new byte[16]; // Please use IssuerKey.RandomNonce() in production
-
 // SaveNonce should be implemented by the server
-await SaveNonce(issuerKey.GetId(uid), nonce);
+await SaveCardKey(issuerKey.GetId(uid), cardKey);
 
-var keys = issuerKey.DeriveBoltcardKeys(uid, nonce);
+
+var keys = cardKey.DeriveBoltcardKeys(issuerKey, uid);
 await ntag.SetupBoltcard("lnurlw://blahblah.com", BoltcardKeys.Default, keys);
 
 var uri = await ntag.TryReadNDefURI();
@@ -149,14 +139,15 @@ var piccData = issuerKey.TryDecrypt(uri);
 if (piccData == null)
     throw new SecurityException("Impossible to decrypt with issuerKey");
 
-// In real life, you would fetch the nonce from database 
-// var nonce = await FetchNonce(issuerKey.GetId(piccData.Uid));
 
-if (!issuerKey.CheckSunMac(uri, piccData, nonce))
+// In production, you would fetch the card key from database
+// var cardKey = await GetCardKey(issuerKey.GetId(piccData.Uid));
+
+if (!cardKey.CheckSunMac(uri, piccData))
     throw new SecurityException("Impossible to check the SUN MAC");
 
 // If this method didn't throw an exception, it has been successfully decrypted and authenticated.
-// You can reset the card with `await ntag.ResetCard(issuerKey, nonce);`.
+// You can reset the card with `await ntag.ResetCard(issuerKey, cardKey);`.
 ```
 
 ## License