I am trying to force a custom string with a length between 0 and 15 to a 128-bit string, so I can use it as a `AesCryptoServiceProvider` key.

I have tried fiddling around with multiple strategies, and have ended up with the following: 

```
        if (stringToConvert.Length > 16)
        {
            StringBuilder sB = new StringBuilder();
            char[] chA = stringToConvert.ToCharArray();
            int chAMaxLength = chA.Length;

            for (int i = 0; i < 16; i++)
            {
                if (i <= chAMaxLength)
                {
                    sB.Append(chA[i]);
                }
            }
        }

```

I need a string exactly 16 characters long (16\*8 = 128).

I am now stuck with it, and just need a helping hand to go through this obsticle.  

I apologize in advance if this may seem simple.

Example:  

`asd` would become  

`asdasdasdasdasda`