GSM48: Add a GSM48AuthRand class to parse the auth rand.

GSM48.st

@@ -248,6 +248,42 @@ Object subclass: GSM48RejectCause [
     ]
 ]
 
+Object subclass: GSM48AuthRand [
+    | rand |
+
+    <category: 'osmo-meesage'>
+    <comment: 'I represent the 10.5.3.1 Authentication parameter RAND'>
+
+    GSM48AuthRand class >> length: aByteArray [ ^ 16 ]
+    GSM48AuthRand class >> initWithData: aData [
+        ^ self new
+            rand: aData;
+            yourself.
+    ]
+
+    GSM48AuthRand class >> parseFrom: aByteArray [
+        ^ self new
+            rand: (aByteArray copyFrom: 1 to: 16);
+            yourself
+    ]
+
+    rand: aData [
+        aData size = 16
+            ifFalse: [
+                Error signal: 'Data needs to be 16 byte.'.
+            ].
+        rand := aData
+    ]
+
+    rand [
+        ^ rand
+    ]
+
+    writeOnDirect: aMsg [
+        aMsg putByteArray: rand.
+    ]
+]
+
 
 IEMessage subclass: GSM48MSG [
     <category: 'osmo-message'>