Restrict RAND to producing 63 random bits

[Robert Moskowitz <rgm@xxxxxxxxxxxxxxx>]

Given that the serialNumber encoding adds a 0x00 in front if the first 
bit of the serialNumber is a '1', how can I use the RAND function to 
limit itself to 63 bits rather than an 8-byte via:

openssl rand -hex 8 > serial

Other than pumping the output into a script that forces the high-order 
bit to zero.

thanks