Question

I’m using dll for cryptography(des) which written by someone.Dll includes encrypt,decyrpt class,and that classes includes methods.Des required 8 bytes(64 bit) key.I describes a string for key.(a character is one byte).And then encoding bytes.

        string keyText= "abcdefghsdsdfsdfsdf";

        UTF8Encoding encoding = new UTF8Encoding();

        byte[] keyfile = new byte[8];
        keyfile = UTF8Encoding.UTF8.GetBytes(keyValue);

above way,even though i described size of byte array 8,size of byte array overflow,it s been length of string value.

Any suggestion.
Thanks.

Answer 1

To do it correctly, look at the PasswordDeriveBytes Class, and pick one of the overloaded methods.

Yes, you’ll have to pick a Salt but that can be a fixed value baked into your program. A Salt does not have to be kept secret.

And to answer the technical, not security related question:

    byte[] keyfile = new byte[8];
    keyfile = UTF8Encoding.UTF8.GetBytes(keyValue)

This code creates 2 arrays. The first one is 8 bytes but it is immediately discarded. GetBytes() creates a new one with a size it determines. You need to hash that array and then you can pick the first 8 of the hash, which is what PasswordDeriveBytes does for you.