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Securing files using Cryptography

.Net framework provides the cryptography function. You have to specify a password & a salt and your program has the capability to either encrypt or decrypt the file. You can select any encryption mechanism. In my example I've used Rijndael algorithm. If you use the built-in security in power point it will prompt you for the password. But the suggested encryption ruins the power point structure so it will not prompt for a password instead PowerPoint will fail to open the file. So the PowerPoint hacking/bruteforce tools cannot break this. The standard encryption algorithms I've used are considered as safe and practically unbreakable. Even you can have more complicated versions. As an example you can first encrypt the file using a one algorithm, password, salt and re-encrypt using a different algorithm, password and salt. This will make the file more secured. Demo is at: https://www.dropbox.com/s/gquzd9s47hy0z7u/Demo.zip Let me know your thoughts on this solution.

Inscrição nº 7 do Concurso para                                                 secure my presentations
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  • chathusrilanka
    chathusrilanka
    • 10 anos atrás

    Answering to your newly added queries.

    The step 1 and 2 are totally independent. You can encrypt, terminate and then execute the program and terminate. In other words you can have a different program to encrypt (may be in your build system) and only embed the decryption part to your release binary.

    To be in safe side we can add a hash checking mechanism such as MD5 verification. When encrypting the file you can save the MD5 hash with your program and then compare the hash after the decryption. By this test you know that the original file is back there after decryption. If the Hashes does not match we can instruct the program to perform the encryption again.

    • 10 anos atrás
    1. chathusrilanka
      chathusrilanka
      • 10 anos atrás

      It is for binding the object in the class module with the Application object. I cannot provide a deeper insight on this since I am not familiar with VBA. :(

      • 10 anos atrás
    2. amrosamaeg
      Proprietário do Concurso
      • 10 anos atrás

      no problem, add me to skype amrosama_eg

      • 10 anos atrás
  • chathusrilanka
    chathusrilanka
    • 10 anos atrás

    And always there would be a trade-off between performance and the security. But the .NET framework is optimized to do this in effective manner. If you still want the numbers I can add some timers to my code and send another demo version so you can play with different files and see the execution time. Is that OK with you?

    • 10 anos atrás
    1. amrosamaeg
      Proprietário do Concurso
      • 10 anos atrás

      No thank you, I just need to test your solution/code in my exe and see how it will work

      • 10 anos atrás
    2. chathusrilanka
      chathusrilanka
      • 10 anos atrás

      https://www.dropbox.com/sh/l9b1viiwysmwwg0/2chtKpS8xi This is the source code. You can play around with that :)

      • 10 anos atrás
  • chathusrilanka
    chathusrilanka
    • 10 anos atrás

    Let me know you want further clarifications :)

    • 10 anos atrás
    1. amrosamaeg
      Proprietário do Concurso
      • 10 anos atrás

      Please send me text file (or paste full code for 2 methods) contains the 2 methods, so I can integrate with my code and see how this will work for my application, thank you

      • 10 anos atrás
    2. chathusrilanka
      chathusrilanka
      • 10 anos atrás

      https://www.dropbox.com/sh/l9b1viiwysmwwg0/2chtKpS8xi

      This is the link for complete source.

      • 10 anos atrás
  • chathusrilanka
    chathusrilanka
    • 10 anos atrás

    I have a question to contest owner.

    Does the client simply use power point to open the file or does your program contains a PowerPoint viewer?

    If the client is going to open the file manually then anyway there should be a power point friendly file so the client can always copy the file after the decryption.

    You can avoid this problem if you have a viewer embedded with your software.

    1. Software reads the encrypted file from file system and decrypts the file as a Memory mapped file
    2. The viewer opens the memory mapped file.

    This will ensure the security of your power point file because there is no decrypted physical file.

    • 10 anos atrás

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