Using RSACryptoServiceProvider in C# to encrypt/decrypt an excel file?

Question

How can I use private/public keys for encryption/decryption of an an excel file in C#.NET?

The article RSA Encryption in C# describes a way of doing this encryption, but this example only works for encrypting/decrypting text, not for an excel file.

How can I encrypt / decrypt an excel file (using asymmetric RSA encryption)?

I reworded your question a bit, as far as I understood it. Please check that it still says what you wanted to say - if not, feel free to revert my edit. — Paŭlo Ebermann, Aug 12 '11 at 18:47
How doesn't this way work for an excel file? Do you get any error message, or is your decrypted file simply garbage? How big are the text and excel files you did use? — Paŭlo Ebermann, Aug 12 '11 at 18:48
When I encrypt excel file , encrypted but can't decrypt and can't see data properly. — RedsDevils, Aug 15 '11 at 11:56
I suppose the length of your files is the reason. How long are they? (The link in poupou's answer shows how to do it right.) — Paŭlo Ebermann, Aug 15 '11 at 12:01
It's Symmetric, I want Asymmetric with public key & private key. — RedsDevils, Aug 17 '11 at 04:32

score 2 · Accepted Answer · answered Aug 12 '11 at 13:12

2

The link you provide is not the way you should use RSA to encrypt data (such as a file). I have an old (but still up to date) blog entry on the subject:

http://pages.infinit.net/ctech/20031101-0151.html

answered Aug 12 '11 at 13:12

poupou

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Could you add the essence from your blog article ("combine RSA with a symmetric encryption") to your answer? This way it stays useful even if your blog dissappears. – Paŭlo Ebermann Aug 12 '11 at 18:50
That page was made in 2003 (way before stackoverflow ;-) because I could not bear to repeat its content everytime the question was asked (mostly in newsgroup at the time). It's well linked-in and archived at http://web.archive.org/web/20031204135734/http://pages.infinit.net/ctech/20031101-0151.html – poupou Aug 14 '11 at 16:51

score 0 · Answer 2 · answered Aug 12 '11 at 11:33

One way...

In the EncryptData method of that article it accepts a string to be encrypted which it then converts to bytes before encrypting it. To get the bytes from a file, you can use a FileStream.

Simply change the method so that the parameter is a filepath instead of text data, and use the filestream to Read/Write bytes as required. Likewise for the DecryptData method.

Using RSACryptoServiceProvider in C# to encrypt/decrypt an excel file?

2 Answers2