DES Initialization Vector in C#

Question

I am trying to decrypt (using the DES algorithm) data that comes from a third party in C# code. There are plenty of examples here and elsewhere that have helped me out. The problem is that I don't know what to use for the 'initialization vector'.

The third party supplied a tool for use on the command line (DES.EXE, which I believe is an out-of-the-box build of the libdes library v4.01) which only requires that you supply an encryption key. So, I can decrypt fine with the tool. However, I would rather not spawn a process to run the tool from my code.

My question is how do I generate/find that initialization vector. I am 99.9% sure it can be done from looking at other posts but I can't figure it out. I talked to the third party and they said they do not support that approach. Any help would be greatly appreciated.

Answer 1

You probably don't have an initialization vector. Just pass in null an array of zero's for the initialization vector for CreateDecryptor:

byte[] iv = new byte[] {0, 0, 0, 0, 0, 0, 0, 0};
des.CreateDecryptor(key, iv);

Edit: I was wrong, it's an zero IV, not null.