Force generation of Initialization Vector 32 bytes (16 characters) in length

Question

I want to generate an Initialization Vector (IV) for my AES encryption method. I have defined the key size as 256 (since I am using AES) so my IV needs to 32 bytes in length (256 / 8). I wish to store the IV as a string representation so using UTF-8, this would equate to a 16 character string.

Here is the code I am using to generate and return the IV ...

using (var aesProv = new AesCryptoServiceProvider())
{
  aesProv.GenerateIV();
  return System.Text.Encoding.Default.GetString(aesProv.IV);
}

How do I go about making sure that the IV is 16 characters in length? Can I count on a 16 character length being generated because I am using an AES library? AesCryptoServiceProvider

Answer 1

I wish to store the IV as a string representation so using UTF-8, this would equate to a 16 character string.

No. Just don't do this. Yes, you could interpret the 32 bytes as a UCS-2 sequence, but it's a really bad idea. This isn't naturally text - it's arbitrary binary data, basically. You could very easily end up with an invalid sequence of UTF-16 code units, due to surrogate pairs etc.

Assuming you want a string representation that you're likely to be able to transport safely etc, I'd suggest just using base64:

return Convert.ToBase64String(aesProv.IV);

Or you could use hex, of course. Both of these will be considerably longer than 16 characters of course, but that's the "price" of dealing with data appropriately.