Question

I am writing an encryption application that requires a 64 bit key. I am currently using the following code to automatically generate a key.

Function GenerateKey() As String
    ' Create an instance of a symmetric algorithm. The key and the IV are generated automatically.
    Dim desCrypto As DESCryptoServiceProvider = DESCryptoServiceProvider.Create()

    ' Use the automatically generated key for encryption. 
    Return ASCIIEncoding.ASCII.GetString(desCrypto.Key)

End Function

I am wanting the user to create their own key. Can I convert a user defined password (a string) into a 64 bit key that can be used?

Answer 1

The answer depends on how secure you want it to be, I’m no security expert so I wouldn’t give advice on it.

I did see this though: http://msdn.microsoft.com/en-us/library/system.security.cryptography.rfc2898derivebytes.aspx It can be used to derives bytes from a string key and salt in the way Jodrell eluded to, and would be far better than rolling yor own.

The other constructor that might be suited after that stage is detailed here: http://msdn.microsoft.com/en-us/library/51cy2e75.aspx

I’m sure if you searched for that on the web you could find examples of how to use it.