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DES Decryption tool

Posted on 2005-02-28
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Last Modified: 2008-01-09
Hello

I need to find (or write) a tool that decrypts DES encrypted image files.

As an input it will take the encrypted DES file, and the key (which will be supplied by the user). It should then be possible to decrypt the file using the standard implementation of DES.

I have programmed in C++ a while ago, but I am a bit rusty. Can anyone help me with where I should start if I needed to program this in C++? I don't want to be reproducing code if this has been done before.

Any help or indicators would be really appreciated.

Fennis
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Question by:awesomefennis
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13 Comments
 
LVL 30

Expert Comment

by:Axter
ID: 13420839
What is your OS, and what compiler are you using?
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LVL 30

Expert Comment

by:Axter
ID: 13421049
FYI:
For single DES, look for the keyword CALG_DES.

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/seccrypto/security/cryptexportkey.asp

Check out the following link for projects and wrapper classes using CryptoAPI:
http://www.codeguru.com/Cpp/misc/misc/cryptoapi/
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LVL 30

Expert Comment

by:Axter
ID: 13421083
Here's another link with more CryptoAPI projects:
http://www.codeproject.com/system/#Cryptography
0
 
LVL 86

Expert Comment

by:jkr
ID: 13421150
Regardless of the platform you're using, I'd suggest taking a look at http://www.eskimo.com/~weidai/cryptlib.html ("Crypto++® Library 5.2.1")
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Author Comment

by:awesomefennis
ID: 13422941
The OS is windows.

I will be trying (and I meqan trying as my C++ is not great) to write this tool using Microsoft Visual Studio C++.

If you have any tips on how I should go about this. I have never used MS VS, and it has been a while since I have used C++ regardless.

Thanks,

Fennis
0
 
LVL 30

Expert Comment

by:Axter
ID: 13422973
>>If you have any tips on how I should go about this. I have never used MS VS, and it has been a while since I have used C++ regardless.

What version of VC++ do you have?
What compiler have you used before?
0
 
LVL 1

Author Comment

by:awesomefennis
ID: 13423188
I will be using Visual C++ 2005 express (http://lab.msdn.microsoft.com/express/)

I can't even remember (i'm ashamed to say) what compiler I used before...it was few years back in university!!!

Any help would be really appreciated.

Or if you can just let me know what I should be doing when I start VC++.
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LVL 30

Accepted Solution

by:
Axter earned 300 total points
ID: 13423222
From the discription you gave in your question, it sounds like all you need is a console application.

I recommend you make a console application with MFC support.
0
 
LVL 1

Author Comment

by:awesomefennis
ID: 13423320
I am sure the C++ will come back to me, I'm just a little worried having never used VC++


I presume it should be straight forward, as all it has to do is take a file and a key which both will be user supplied, and then run the DES
decryption algorithm on the file using the key
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LVL 30

Expert Comment

by:Axter
ID: 13476394
Why the B grade?

I think for a 100 point question, I gave you an A grade answer.
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LVL 1

Author Comment

by:awesomefennis
ID: 13484536
Axter,

sorry, i didnt realise that "B" was bad or anything. i thought A was to be used for exceptional answers, which your answer did help me, but i didnt class it as exceptional, but if i am misreading what A,B,C means let me know how I can change it and I will.

I don't want to down play peoples help here, as I do appreciate it.
0
 
LVL 30

Expert Comment

by:Axter
ID: 13485121
>>i thought A was to be used for exceptional answers

The grade value has more to do with the completeness of the answer.
Most questioners post an A grade, unless they're not satisfied with the answer, and they've given the expert a chance to give a more satisfactory answer.
For more info, see following EE grading guide lines:
http://www.experts-exchange.com/help.jsp#hi73

>>but if i am misreading what A,B,C means let me know how I can change it and I will.

Don't worry about change it.  Most members (including myself) make this mistake when first joining.
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