Crypto questions (Looking for professional advices =]))

The fear of every surveillance society: citizens protecting their own privacy with strong cryptography

Crypto questions (Looking for professional advices =]))

Post by jameslui on Wed Mar 31, 2010 9:23 pm
([msg=37548]see Crypto questions (Looking for professional advices =]))[/msg])

Hi all, I am recently working on a reverse engineering project and encountering a decryption problem, I am here looking for some suggestions or ideas from all the professional people here like you, so here is the scenario:

1) We have a system which can be accessed by a mobile client (Java) or a windows app (C++, or VB, I m not sure) which like the following:
Code: Select all
Mobile Client -----\
                   |----- Web application
Windows App -------/

2) So, what actually the system is doing? Actually both mobile and winapp clients retrieve information from the web application, I've successfully cracked the encryption which is used to encrypt the information passing to the web application on mobile client (It's using blowfish and a random generated key which will be attached to the request that is sending to the web application ;) ).

3) Now, what I am trying to do is to crack the windows app. It downloads information from the web application (same as the mobile client), and save it in a encrypted file. And this encrypted file is what I'm trying to decrypt.
The sample of the file is like the following:
Code: Select all
1F D3 6B C7 5D 2D 63 0F 8D 9E 6A 8F 6E 80 89 23 4D DC .................................................................... [and more]

Ya, the encrypted file can be decrypted by the winapp and displaying the plain-text which is the information I'm looking for, is there any way I could decompile this winapp and try to figure out how it's doing the decryption ? I'm familar with Java but not windows application. Please let me know if you need more information and I appreciate so much for your time to read this long thread :D :D :D
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