Winrar [95] the other path (Encryption Mechanism)
a good exercise in methodically cracking
student
Not Assigned
10 March 1998
by +Indian_Trail
Courtesy of Reverser's page of reverse engineering
 
fra_00xx
98xxxx
handle
1100
NA
PC
Well, when I receive this kind of essays I'm happy. They are one of the reasons I really enjoy keeping this site. Our reversers contributors are growing out of the childish 'I cracked program so and so" attitude and are tackling "higher" reversing tasks.
Here you have a (growing) strong cracker that -in my opinion correctly- tackles a pretty difficult subject methodically, and decides "mine de rien", NOT to include any crack or serial in his essay: "If someone helps me to pack my files 50% better than with winzip, he deserves some money or at least some respect".
Another very interesting aspect is the 'anthropomorphisation" of code snippets. I like a lot the Charlie and Tom approach chosen by +Indian_Trail, which gives 'life' to dull mathematical manipulations of bytes... as usual (and as +ORC wrote) giving "Names" is a very powerful weapon per se when reversing code.
I can only recommand this valid approach to anyone that has to reverse (and explain) snippets of code... that is, to anyone writing for the +HCU :-)
There is a crack, a crack in everything That's how the light gets in
Rating
( )Beginner (x)Intermediate ( )Advanced ( )Expert

Well Little-John gave us two path to wander on in his essay on Winrar 95 I've chosen the long way, studing the encryption mechanism in Winrar 95:
It's using base indexed relative adressing heavily inside tables, and shifting instructions as encryption mechanism. There is no echo of the correct serial number wich directs that the protectionists have learned something. The whole protection scheme is quite a mess, wich require alot of studing and experimenting
This is a good exercise in methodically mode of cracking procedure.


Winrar [95] the other path (Encryption Mechanism)
a good exercise in methodically cracking
Written by +Indian_Trail


Introduction

I read Little-John essay about Winrar[95]. It has two way of cracking paths, like all of these serial# protections, brute forcing them or crack the math behind the encryption. Little-John brute forced Winrar. I however became very curios on the encryption routines that Winrar use. In this essay I'll show you how Winrar's encryption works. Before we begin let me first tell you that there is no crack in this essay neither a serial number. This is because of three things