>>>The string will come from C++ application. Right now I want to simulate a test of such string.
>>
>>IIRC, a C++ string is a byte array. You could try:

string s = Convert.ToBase64String(cplusstring);

>
And if it works, how can I get back byte array from that?

Although it does not work, as I have it as a string and the ToBase64String accepts a byte array instead.