Generating a unique *and* random URL in C#

Question

My ultimate goal is to create a URL that is unique and cannot be guessed/predicted. The purpose of this URL is to allow users to perform operations like verifying their email ad

Answer 1

You can generate 128 bit, "random," unique numbers by running a counter through an AES counter keyed with a random key. As long as the same key is used this will never repeat any output.

static byte[] AESCounter(byte[] key, ulong counter) {
    byte[] InputBlock = new byte[16];
    InputBlock[0] = (byte)(counter & 0xffL);
    InputBlock[1] = (byte)((counter & 0xff00L) >> 8);
    InputBlock[2] = (byte)((counter & 0xff0000L) >> 16);
    InputBlock[3] = (byte)((counter & 0xff000000L) >> 24);
    InputBlock[4] = (byte)((counter & 0xff00000000L) >> 32);
    InputBlock[5] = (byte)((counter & 0xff0000000000L) >> 40);
    InputBlock[6] = (byte)((counter & 0xff000000000000L) >> 48);
    InputBlock[7] = (byte)((counter & 0xff00000000000000L) >> 54);
    using (AesCryptoServiceProvider AES = new AesCryptoServiceProvider())
    {
        AES.Key = key;
        AES.Mode = CipherMode.ECB;
        AES.Padding = PaddingMode.None;
        using (ICryptoTransform Encryptor = AES.CreateEncryptor())
        {
            return Encryptor.TransformFinalBlock(InputBlock, 0, 16);
        }
    }
}