c# - Custom string to 128-bit string -

i trying force custom string length between 0 , 15 128-bit string, can use aescryptoserviceprovider key.

i have tried fiddling around multiple strategies, , have ended following:

        if (stringtoconvert.length > 16)         {             stringbuilder sb = new stringbuilder();             char[] cha = stringtoconvert.tochararray();             int chamaxlength = cha.length;              (int = 0; < 16; i++)             {                 if (i <= chamaxlength)                 {                     sb.append(cha[i]);                 }             }         } 

i need string 16 characters long (16*8 = 128).

i stuck it, , need helping hand go through obsticle.
apologize in advance if may seem simple.

example:
asd become
asdasdasdasdasda

stringbuilder b = new stringbuilder(); (int = 0; < 8; i++) {     b.append(stringtoconvert[i % stringtoconvert.length]); } stringtoconvert = b.tostring(); byte[] key = encoding.unicode.getbytes(stringtoconvert);//key size 16 bytes = 128 bits 

even better (without stringbuilder):

byte[] key = new byte[16]; (int = 0; < 16; i+=2) {     byte[] unicodebytes = bitconverter.getbytes(stringtoconvert[i % stringtoconvert.length]);     array.copy(unicodebytes, 0, key, i, 2); }