Add function to generate device hash from QR code

Author: jdomnitz

HomeKitDotNet/QRParser.cs

@@ -1,12 +1,27 @@
-namespace HomeKitDotNet
+// HomeKitDotNet Copyright (C) 2024 
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or any later version.
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY, without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+// See the GNU Affero General Public License for more details.
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+using System.Security.Cryptography;
+using System.Text;
+
+namespace HomeKitDotNet
 {
     public class QRParser
     {
         public QRParser(string code)
         {
-            if (!code.StartsWith("X-HM://") || code.Length != 20)
+            if (!code.StartsWith("X-HM://") || code.Length < 20)
                 throw new ArgumentException("Invalid QR Code");
-            SetupCode = code.Substring(16);
+            SetupID = code.Substring(16, 4);
             code = code.Substring(7, 9);
             long lc = decode(code);
             Version = (byte)((lc >> 43) & 0xFF);
@@ -22,9 +37,19 @@ public QRParser(string code)
         public bool BTLE {  get; set; }
         public bool NFC { get; set; }
         public bool IP { get; set; }
-        public string SetupCode { get; set; }
+        public string SetupID { get; set; }
         public long SetupPin { get; set; }
 
+        public string ComputeHash(string deviceId)
+        {
+            byte[] devId = Encoding.UTF8.GetBytes(deviceId.ToUpper());
+            byte[] source = new byte[devId.Length + 4];
+            Encoding.UTF8.GetBytes(SetupID, 0, 4, source, 0);
+            Array.Copy(devId, 0, source, 4, devId.Length);
+            byte[] result = SHA512.HashData(source);
+            return Convert.ToHexString(result, 0, 4);
+        }
+
         private static long decode(string sIn)
         {
             const string map = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";