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DES Decryption tool

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

Axter

What is your OS, and what compiler are you using?

Axter

For Win32 programs, you can use the CryptoAPI functions.
Check out the following links:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/seccrypto/security/cryptacquirecontext.asp

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

Axter

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/

Axter

Here's another link with more CryptoAPI projects:
http://www.codeproject.com/system/#Cryptography

jkr

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")

awesomefennis

ASKER

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

Axter

>>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?

awesomefennis

ASKER

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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Axter

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awesomefennis

ASKER

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

Axter

Why the B grade?

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

awesomefennis

ASKER

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.

Axter

>>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:
https://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.