add: updated the loclass document

doc/loclass_notes.md

@@ -0,0 +1,22 @@
+# About LOCLASS attack
+
+This document is primarily intended for understanding `hf iclass loclass` and used files with it.
+
+LOCLASS aim is to recoved the used masterkey for that specific reader configued in Elite mode / High Security mode.
+
+LOCLASS, is a two part attack. First is the online part where you gather needed information from the reader by presenting a carefully selected CSN and save the responses to file.  For the first part you run `hf iclass sim 2` and take notice of the saved filename.
+
+The second part is offline,  where the information gathered from the first step is used in a series of DES operations to figure out the used 
+masterkey.  run `hf iclass loclass f abc.bin'
+
+If you don't have access to a iClass SE reader configured in Elite mode there is a test file which you can use.
+`hf iclass loclass f iclass_dump.bin` 
+
+
+# Unit testing
+In order to verify that loclass is actually working, there is a "unit" test mode.  run `hf iclass loclass t`.
+This test mode uses two files. 
+- iclass_dump.bin
+  this is a sample file from `hf iclass sim 2`, with complete keytable recovery, using 128 carefully selected CSN and the file contains the MAC results from reader. 
+- iclass_key.bin
+  this is file shall contain the legacy masterkey, AA1 key. loclass uses it to verify that permution / reversing / generation of key is correct.